This work is supported by Canadian Institutes of Health Research, operating grants MOP-42546 and MOP-119514.

1. Preparation of Amino Acid Solutions
<ol>
	<li>Prepare and label two 50 mL conical centrifuge tubes for each amino acid (one each for both &#34;low&#34; and &#34;high&#34; concentrations).</li>
	<li>Prepare a large 2 L flask containing purified water (18.2 M&#937;&#183;cm at 25 &#176;C).</li>
	<li>Calculate the amount of each amino acid (in grams) to reach the desired concentrations, and weigh the appropriate amount of amino acid into their respective 50 mL centrifuge tubes using a spatula. 
	NOTE: For the &#34;High&#34; concentration of the two negatively charged amino acids, PBS is used instead of water. We could not increase their concentrations due to their low water solubility, and using PBS instead of water helps to maintain the low pH. Furthermore, the concentration calculations were obtained using a final volume of 40 mL for each amino acid solution. All amino acid concentrations are outlined in Table 3. Be sure to rinse the spatula in between amino acids to avoid contamination. We recommend a water rinse, followed by wiping with 70% ethanol.</li>
	<li>Add 40 mL of purified water (or PBS) into each 50 mL tube using a serological pipette. Cap tubes and vortex or shake vigorously until dissolved. Water bath sonication (room temperature, 130 W, 40 kHz) can also be used to assist in the solubility process. 
	NOTE: The following amino acid solutions are sensitive to light and should be covered with aluminum foil: tryptophan, phenylalanine, and tyrosine (which consist of aromatic ring-like structures) and cysteine (reactive -SH group).</li>
</ol>
2. Preparation of SAP-AA Solutions
<ol>
	<li>Prepare 20 mL scintillation vials for the self-assembling peptides. For a given self-assembling peptide, prepare one vial per prepared amino acid solution (each combination will be made in a separate vial).</li>
	<li>Using a high-performance analytical balance (with a readability down to 0.1 mg or less), weigh approximately 1 &#177; 0.2 mg of peptide into the bottom of each vial. Cap after weighing and record the exact weight of the peptide on the cap.</li>
	<li>Pipette the appropriate volume of amino acid solution (prepared in Section 1) into each vial containing peptide, in order to reach the desired concentration of self-assembling peptide (0.1 mg/mL for long peptides with a length of 16 amino acids, or 0.2 mg/mL for shorter peptides with a length of 8 amino acids).</li>
	<li>Sonicate for 10 min in a water bath sonicator (130 W, 40 kHz) at room temperature, ensuring the solutions within vials are completely immersed in the water bath.</li>
</ol>
3. Preparation of Drug-DMSO or Drug-Ethanol Stock Solutions
<ol>
	<li>Combine 1 mg of drug (in this case, curcumin) with 100% DMSO, and another 1 mg with 100% ethanol to create two stock solutions. 
	NOTE: We added 200 &#181;L of DMSO and 400 &#181;L ethanol to make DMSO-curcumin and ethanol-curcumin stocks that were 5 mg/mL and 2.5 mg/mL, respectively, due to varying solubility in each solvent; however, it is important to note that the concentration of stock should be adjusted depending on the hydrophobic drug of interest. Factors such as drug solubility and effective biological concentration are important in determining this value. Also, keep in mind that the stock will be diluted 100-fold and 50-fold in DMSO and ethanol formulations, respectively, when combined with SAP-AA solutions (see Section 4). It may be preferred to prepare a larger volume of stock depending on the number of formulations required &#8211; in this case, more than 1 mg of drug would be used. The stock can be stored at -20 &#176;C; thaw on ice and vortex before use.</li>
	<li>Vortex vials for 15 s to completely dissolve the drug.</li>
</ol>
4. Preparation of Drug Formulations
<ol>
	<li>Prepare clear, 1.5 mL microcentrifuge tubes for each formulation. Be sure to label tubes with the intended self-assembling peptide, amino acid (and concentration), and co-solvent.</li>
	<li>Add 10 &#181;L of Drug-DMSO stock, or 20 &#181;L Drug-Ethanol stock to appropriate microcentrifuge tubes.</li>
	<li>Add 990 &#181;L of SAP-AA acid solutions to the appropriate labeled microcentrifuge tubes containing Drug-DMSO stock, and 980 &#181;L to those containing Drug-Ethanol stock. This produces 1 mL drug formulations with 1% DMSO or 2% ethanol. 
	NOTE: The final concentration of all curcumin formulations was 0.5 mg/mL according to the protocol. Again, this will vary when using other hydrophobic compounds and/or beginning with a different stock concentration (see step 3.1)</li>
	<li>Vortex vigorously for 30 s and allow formulations to rest for 30 min.</li>
</ol>
5. Solubility Testing
<ol>
	<li>After rest period, vortex vigorously once again for 30 s.</li>
	<li>Centrifuge the formulations at 14,220 x g for 1 min.</li>
	<li>Analyze the bottom of the microcentrifuge tubes for precipitation (by visualization).</li>
</ol>

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I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembling+peptide+scaffolds+for+regenerative+medicine.">Self-assembling peptide scaffolds for regenerative medicine.</a> Chem. Commun. 48 (1), 26-33 (2012).</li><li>Tatman, P. D., Muhonen, E. G., Wickers, S. T., Gee, A. O., Kim, E., Kim, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembling+peptides+for+stem+cell+and+tissue+engineering.">Self-assembling peptides for stem cell and tissue engineering.</a> Biomater. Sci. 4 (4), 543-554 (2016).</li><li>Keyes-Baig, C., Duhamel, J., Fung, S. -. 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The authors have nothing to disclose.

In the formulation procedure, there are various critical steps and points to consider in troubleshooting. First, as we are working with various components and concentrations, multiple vortex steps throughout the protocol ensure that all concentrations are uniform and correct. Some of the high-concentration, hydrophobic amino acid solutions may still not be completely dissolved after vortexing, and in this case, they can be shaken vigorously by hand to assist in the process. Likewise, it is essential that SAP-AA solutions undergo the sonication step outlined in step 2.4 as SAPs naturally tend to aggregate, and sonication will assist in fragmenting SAP clusters, thus resulting in a more uniform solution. Second, for a given hydrophobic drug, the stock and final concentrations within SAP-AA formulations should depend on the effective concentration of that compound in biological settings. The protocol should be modified accordingly to reflect this active concentration. Furthermore, drug loading capacity is also an important factor to consider; it is likely that each drug will have a unique loading capacity using this strategy, and that each SAP-AA combination may support a different amount of drug based on compatibility. This demonstrates the importance of screening to find the optimal SAP-AA combination for a given compound.
There are a number of advantages to using our technique over others; more specifically, there is great significance over the conventional method of using SAPs alone for encapsulation and potential delivery of a compound. As mentioned previously, amino acids are already clinically-accepted and adding these solutions to SAP formulations increases osmolarity to decrease hemolytic activity, such that intravenous injections in clinical scenarios are possible. We have also found that they greatly increase hydrophobic compound solubility in cases where SAPs alone are insufficient for solubility17,18. The multiple different combinations of SAPs and amino acids involved allows for expansion into a high-throughput method to screen for hydrophobic drug solubility. Solubility data can be analyzed in detail to reveal trends; we have found that sorting results by formulation component (SAP or amino acid) shows a pattern likely to be unique for each hydrophobic drug. As an example, positively charged amino acids improve solubility of curcumin (Figure 1), whereas our previous studies showed that negatively charged amino acids were better for PP218. These trends can help determine the suitability of specific components for dissolving drugs with similar chemical structure. Furthermore, the simplicity of our solubility screen is both an advantage and a limitation; although it is easy to perform, there are more technical and accurate ways to experimentally assess the solubility of a compound within solution (e.g., spectroscopy or chromatographic methods). However, the screening strategy outlined in this protocol allows for the quick and efficient selection of SAP-AA combinations which result in the highest drug solubility, and accordingly, the highest potential biological activity for further analysis. As there are numerous formulations of differing combinations of self-assembling peptide, amino acid, amino acid concentration, and co-solvent, (480 total in our previous manuscript18), this is a necessary step for narrowing down to find optimal components for a given drug. After finding soluble drug formulations, they can be assessed for solubility by more technical methods and should be further validated in functional assays, which assess biological activity and safety. These functional assays should be tailored to the intended use of the formulated drug, as outlined in our manuscript optimizing PP2 formulations18. Expanding our platform on other hydrophobic compounds will reveal additional trends and mechanisms for enhancing solubility, and assist in engineering new SAPs for clinical formulation of specific hydrophobic compounds.
The future of our method lies in the potential pipeline for drug deliver, as well as its ability to be automated. There are many steps that involve weighing powders and dispensing liquids, which are the major time-limiting factors in the formulation process. Although it may seem like a lengthy procedure to perform in laboratory settings, these steps can easily performed using robotic devices. Likewise, the method has great potential to be scaled up into commercial production with the use of automated scales and dispensers in order to simultaneously test the solubility of many hydrophobic drugs. This would greatly speed up the formulation and screening processes, while increasing accuracy and reducing human error. Thus, our drug formulation method consisting of SAP-AA combinations is a generalized platform for solubility and delivery of hydrophobic compounds, and would greatly benefit from high-throughput technologies.

SAPs are a class of biomaterials that have been studied extensively as 3D scaffolds in regenerative medicine1,2,3,4. More recently however, they have been exploited as vehicles for delivery of therapeutics due to their unique biological properties5,6,7,8. SAPs naturally assemble into stable nanostructures9, thus providing a means of drug encapsulation and protection. SAPs are amphipathic, comprised of a specific pattern of hydrophobic and hydrophilic amino acid repeats, driving their self-assembly9,10 and allowing them to serve as a medium between hydrophobic and hydrophilic environments. Consequently, for the clinical delivery of hydrophobic drugs &#8211; which have extremely low bioavailability and absorption in the body due to lack of solubility in aqueous environments11,12&#160; &#8211; SAPs are promising as a delivery vehicle. Furthermore, their sequence pattern also implies that SAPs can be rationally designed and engineered to maximize compatibility with any given drug or compound (i.e., based on functional groups) and further assist solubility.
SAPs have been applied as effective drug delivery vehicles in many in vitro and in vivo settings13,14,15,16. They have also shown great safety and biocompatibility. However, due to low osmolarity of SAP-drug preparations, they cannot be used for intravenous injections as in clinical settings13. Considering this restraint, we have recently developed a strategy which combines SAPs with amino acid solutions in order to reduce the use of toxic co-solvents and increase the formulation osmolarity, and therefore, clinical relevance. We chose to use amino acids as they are the building blocks of SAPs, are already clinically-accepted, and in combination with SAPs, they increase hydrophobic drug solubility while reducing the amount of SAP required17,18.
We have scrutinized SAP-AA combinations as a generalized platform for hydrophobic drug solubility and subsequent delivery by creating a multi-step screening pipeline and applying it to the Src inhibitor, PP2, as a model hydrophobic compound. In this process, we examined the effect of changing components of the formulation &#8211; ultimately testing 6 different SAPs, all 20 amino acids at 2 different concentrations (low and high; low based on concentrations in existing clinical applications, and high concentrations were 2x, 3x, or 5x the clinical concentration based on the maximum solubility of each amino acid in water), and 2 different co-solvents &#8211; and selected combinations that solubilized PP2 for further analysis. This drug formulation proved to be effective as a drug delivery vehicle in cell culture, as well as in vivo models using both intratracheal and intravenous administrations. Likewise, our work touched on the versatility of SAP-AA combinations in solubilizing multiple, structurally-different hydrophobic compounds in aqueous environments; specifically, the drugs rottlerin and curcumin18. This manuscript outlines the SAP-AA formulation method and analysis of curcumin solubility as an example of the primary step in our screening pipeline. This protocol provides a simple, reproducible way to screen for the optimal SAP-AA combinations, which dissolve any given hydrophobic compound.

<table style="border-collapse:collapse;width:1034pt" width="1379">
	<tbody>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">EAK16-I</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20" style="width:510pt" width="680">Sequence: AEAKAEAKAEAKAEAK, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">EAK16-II</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20">Sequence: AEAEAKAKAEAEAKAK, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">EAK16-IV</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20">Sequence: AEAEAEAEAKAKAKAK, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">EFK8-II</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20">Sequence: FEFEFKFK, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">A6KE</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20">Sequence: AAAAAAKE, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">P6KE</td>
			<td class="xl17" style="width:106pt" width="141">CanPeptide Inc.</td>
			<td class="xl17" style="width:101pt" width="135">Custom peptide</td>
			<td class="xl20">Sequence: PPPPPPPKE, N-terminus acetylation and C-terminus amidation, &#62;95% pure by HPLC</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Alanine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">A7469-100G</td>
			<td class="xl20">L-Alanine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Isoleucine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">I7403-100G</td>
			<td class="xl20">L-Isoleucine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Leucine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">L8912-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Leucine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Methionine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">M5308-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Methionine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Proline</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">P5607-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Proline</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Valine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">V0513-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Valine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Phenylalanine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">P5482-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Phenylalanine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Tryptophan</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">T8941-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Tryptophan</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Tyrosine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">T8566-100G</td>
			<td class="xl20">L-Tyrosine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Glycine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">G8790-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Glycine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Asparagine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">A4159-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Asparagine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Glutamine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">G8540-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Glutamine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Serine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">A7219-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Serine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Threonine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">T8441-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Threonine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Histidine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">H6034-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Histidine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Lysine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl17" style="width:101pt" width="135">L5501-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Lysine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Arginine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">A8094-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Arginine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Aspartic Acid</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">A7219-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Aspartic Acid</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Glutamic Acid</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">G8415-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Glutamic Acid</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Cysteine</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">C7352-100G</td>
			<td class="xl17" style="width:510pt" width="680">L-Cysteine</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Dimethyl Sulfoxide</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">D4540-500ML</td>
			<td class="xl22">DMSO</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl17" height="21" style="width:317pt;height:15.75pt" width="423">Ethanol</td>
			<td class="xl17" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl25">277649-100ML</td>
			<td class="xl22">Anhydrous</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl22" height="21" style="height:15.75pt">Curcumin</td>
			<td class="xl21" style="width:106pt" width="141">Sigma-Aldrich</td>
			<td class="xl22">08511-10MG</td>
			<td class="xl22">Hydrophobic drug, curcumin</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl22" height="21" style="height:15.75pt">Rottlerin</td>
			<td class="xl21" style="width:106pt" width="141">EMD Millipore</td>
			<td class="xl22">557370-10MG</td>
			<td class="xl22">Hydrophobic drug, rottlerin</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl21" height="21" style="width:317pt;height:15.75pt" width="423">PP2</td>
			<td class="xl21" style="width:106pt" width="141">Enzo&#160;</td>
			<td class="xl22">BML-EI297-0001</td>
			<td class="xl21" style="width:510pt" width="680">Hydrophobic drug, PP2</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl21" height="21" style="width:317pt;height:15.75pt" width="423">Scintillation Vials</td>
			<td class="xl21" style="width:106pt" width="141">VWR</td>
			<td class="xl21" style="width:101pt" width="135">2650-66022-081</td>
			<td class="xl22">Borosilicate Glass, with Screw Cap, 20 mL. Vials for weighing peptide.</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl21" height="21" style="width:317pt;height:15.75pt" width="423">Falcon 50 mL Conical Centrifugation Tubes</td>
			<td class="xl21" style="width:106pt" width="141">VWR</td>
			<td class="xl23" style="width:101pt" width="135">352070</td>
			<td class="xl22">Polypropylene, Sterile, 50 mL. For amino acid solutions.</td>
		</tr>
	</tbody>
</table>

solubility of hydrophobic compounds in aqueous solution using combinations of self-assembling peptide and amino acid

Self-assembling peptides (SAPs) are promising vehicles for the delivery of hydrophobic therapeutics for clinical applications; their amphipathic properties allow them to dissolve hydrophobic compounds in the aqueous environment of the human body. However, self-assembling peptide solutions have poor blood compatibility (e.g., low osmolarity), hindering their clinical application through intravenous administrations. We have recently developed a generalized platform for hydrophobic drug delivery, which combines SAPs with amino acid solutions (SAP-AA) to enhance drug solubility and increase formulation osmolarity to reach the requirements for clinical uses. This formulation strategy was thoroughly tested in the context of three structurally different hydrophobic compounds &#8211; PP2, rottlerin, and curcumin &#8211; in order to demonstrate its versatility. Furthermore, we examined effects of changing formulation components by analyzing 6 different SAPs, 20 naturally existing amino acids at low and high concentrations, and two different co-solvents dimethyl sulfoxide (DMSO) and ethanol. Our strategy proved to be effective in optimizing components for a given hydrophobic drug, and therapeutic function of the formulated inhibitor, PP2, was observed both in vitro and in vivo. This manuscript outlines our generalized formulation method using SAP-AA combinations for hydrophobic compounds, and analysis of solubility as a first step towards potential use of these formulations in more functional studies. We include representative solubility results for formulation of the hydrophobic compound, curcumin, and discuss how our methodology serves as a platform for future biological studies and disease models.

For the hydrophobic drug, curcumin, we produced formulations using all 20 naturally existing amino acids at low concentrations, in combination with only one SAP, EAK16-II, as a proof-of-principle. We also tested formulations using both DMSO and ethanol as co-solvents. In total, this produced 40 curcumin formulations, each containing different components. It is important to note that, in our previous studies using the Src inhibitor, PP2, we included more options for SAP (total of 6) and amino acid concentration (clinical, as well as a higher concentration), which produced a total of 480 different formulations. Trends from this work were taken into account when selecting EAK16-II as the SAP for this study. Concentrations of various components are included in Table 1, Table 2, and Table 3 as a reference. All hydrophobic drug formulations are screened for drug solubility by visualization, and considered soluble if the solution is completely clear of any precipitate after centrifugation (Figure 1). If the drug precipitates to the bottom of the tube, this is considered non-soluble and does not go through further testing. Furthermore, solubility is tested in triplicate and by two different individuals; if these results are not reproducible, formulations are also not considered to be truly soluble.
Out of the 40 formulations tested in this study, 7 formulations successfully dissolved curcumin (Table 4). Grouping formulations by components identified two major trends: ethanol seems to be a better co-solvent for dissolving curcumin, and positively charged amino acids lysine (K) and arginine (R) also seem to be optimal components for dissolving curcumin (Table 4). It is interesting to note the color change for formulations containing R and K, which reveal curcumin is dissolved in the alkaline condition (Figure 1). It is helpful to group formulations by properties of the various components to make such observations.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56158/56158fig1.jpg" /> 
Figure 1: Example of precipitation analysis. For these curcumin formulations containing the peptide EAK16-II, ethanol, and charged amino acids, precipitate can be seen clearly in the microcentrifuge tubes after centrifugation. Formulations containing lysine (K), arginine (R) or aspartic acid (D) dissolve curcumin (no precipitate), whereas those containing histidine (H) or glutamic acid (E) do not (precipitate, circled in red). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56158/56158fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td>Drug</td>
			<td>Formulation Concentration (mg/mL)</td>
		</tr>
		<tr>
			<td>PP2</td>
			<td>0.05</td>
		</tr>
		<tr>
			<td>Curcumin</td>
			<td>0.05</td>
		</tr>
		<tr>
			<td>Rottlerin</td>
			<td>0.02</td>
		</tr>
	</tbody>
</table>
Table 1:&#160;Concentration of drugs used in formulations. Drug formulation concentrations differ as each have a different bioactive concentration, and also different loading capacities.
<table fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td>Self-Assembling Peptide</td>
			<td>Properties</td>
			<td>Formulation Concentration (mg/mL)</td>
		</tr>
		<tr>
			<td>EAK16-I</td>
			<td>EAK family, long</td>
			<td>0.1</td>
		</tr>
		<tr>
			<td>EAK16-II</td>
			<td>EAK family, long</td>
			<td>0.1</td>
		</tr>
		<tr>
			<td>EAK16-IV</td>
			<td>EAK family, long</td>
			<td>0.1</td>
		</tr>
		<tr>
			<td>EFK8-II</td>
			<td>Modified EAK, short</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td>A6KE</td>
			<td>Surfactant-like, short</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td>P6KE</td>
			<td>Surfactant-like, short</td>
			<td>0.2</td>
		</tr>
	</tbody>
</table>
Table 2: Concentration of self-assembling peptides used in formulations. With the addition of amino acids, only small concentrations of self-assembling peptide are required (0.1-0.2 mg/mL). Shorter peptides are double the concentration compared to longer peptides as they have half the sequence length (8 amino acids versus 16 amino acids).
<img alt="Table 3" src="/files/ftp_upload/56158/56158table3.jpg" /> 
Table 3: Concentration of amino acid solutions used in formulations. Low concentrations of amino acids were chosen based on the existing clinical applications of each. High concentrations are 2x, 3x, or 5x the clinical concentration and within the maximum solubility of each amino acid in water. This figure has been modified from Pacheco et al.18
<img alt="Table 4" src="/files/ftp_upload/56158/56158table4.jpg" /> 
Table 4: Representative solubility results for curcumin. A summary of the SAP-AA combinations which effectively dissolved curcumin after screening for solubility. This figure has been modified from Pacheco et al.18

Watch this Scientific Journal Video about Solubility of Hydrophobic Compounds in Aqueous Solution Using Combinations of Self-assembling Peptide and Amino Acid at JoVE.com

Solubility of Hydrophobic Compounds in Aqueous Solution Using Combinations of Self-assembling Peptide and Amino Acid

This protocol describes a clinically-applicable means of dissolving hydrophobic compounds in an aqueous environment using combinations of self-assembling peptide and amino acid solutions. Our method resolves a major limitation of hydrophobic therapeutics, which lack safe, efficient means of solubility and delivery methods into clinical settings.

Self-assembling peptides (SAPs) are promising vehicles for the delivery of hydrophobic therapeutics for clinical applications; their amphipathic ...

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16.6K Views.  University Health Network. This protocol describes a clinically-applicable means of dissolving hydrophobic compounds in an aqueous environment using combinations of self-assembling peptide and amino acid solutions. Our method resolves a major limitation of hydrophobic therapeutics, which lack safe, efficient means of solubility and delivery methods into clinical settings.

Video: Solubility of Hydrophobic Compounds in Aqueous Solution Using Combinations of Self-assembling Peptide and Amino Acid

Assessment of Gastric Emptying in Non-obese Diabetic Mice Using a [13C]-octanoic Acid Breath Test

Gastric emptying studies in mice have been limited by the inability to follow gastric emptying changes in the same animal since the most commonly used techniques require killing of the animals and postmortem recovery of the meal1,2. This approach prevents longitudinal studies to determine changes in gastric emptying with age and progression of disease. The commonly used [13C]-octanoic acid breath test for humans3 has been modified for use in mice4-6 and rats7 and we previously showed that this test is reliable and responsive to changes in gastric emptying in response to drugs and during diabetic disease progression8. In this video presentation the principle and practical implementation of this modified test is explained. As in the previous study, NOD LtJ mice are used, a model of type 1 diabetes9. A proportion of these mice develop the symptoms of gastroparesis, a complication of diabetes characterized by delayed gastric emptying without mechanical obstruction of the stomach10.
This paper demonstrates how to train the mice for testing, how to prepare the test meal and obtain 4 hr gastric emptying data and how to analyze the obtained data. The carbon isotope analyzer used in the present study is suitable for the automatic sampling of the air samples from up to 12 mice at the same time. This technique allows the longitudinal follow-up of gastric emptying from larger groups of mice with diabetes or other long-standing diseases.

Assessment of Gastric Emptying in Non-obese Diabetic Mice Using a [13C]-octanoic Acid Breath Test

Determination of gastric emptying with a non-invasive [13C]-octanoic acid breath test for tracking gastroparesis in female NOD LtJ mice.

Gastric emptying studies in mice have been limited by the inability to follow gastric emptying changes in the same animal since the most commonly used ...

Synergetic Use of Neural Precursor Cells and Self-assembling Peptides in Experimental Cervical Spinal Cord Injury

Spinal cord injuries (SCI) cause serious neurological impairment and psychological, economic, and social consequences for patients and their families. Clinically, more than 50% of SCI affect the cervical spine1. As a consequence of the primary injury, a cascade of secondary mechanisms including inflammation, apoptosis, and demyelination occur finally leading to tissue scarring and development of intramedullary cavities2,3. Both represent physical and chemical barriers to cell transplantation, integration, and regeneration. Therefore, shaping the inhibitory environment and bridging cavities to create a supportive milieu for cell transplantation and regeneration is a promising therapeutic target4. Here, a contusion/compression model of cervical SCI using an aneurysm clip is described. This model is more clinically relevant than other experimental models, since complete transection or ruptures of the cord are rare. Also in comparison to the weight drop model, which in particular damage the dorsum columns, circumferential compression of the spinal cord appears advantageous. Clip closing force and duration can be adjusted to achieve different injury severity. A ring spring facilitates precise calibration and constancy of clip force. Under physiological conditions, synthetic self-assembling peptides (SAP) self-assemble into nanofibers and thus, are appealing for application in SCI5. They can be injected directly into the lesion minimizing damage to the cord. SAPs are biocompatible structures erecting scaffolds to bridge intramedullary cavities and thus, equip the damaged cord for regenerative treatments. K2(QL)6K2 (QL6) is a novel SAP introduced by Dong et al.6 In comparison to other peptides, QL6 self-assembles into &#946;-sheets at neutral pH6.14 days after SCI, after the acute stage, SAPs are injected into the center of the lesion and neural precursor cells (NPC) are injected into adjacent dorsal columns. In order to support cell survival, transplantation is combined with continuous subdural administration of growth factors by osmotic micro pumps for 7 days.

Treating cervical spinal cord injury with both self-assembling peptides (SAP) and neural precursor cells (NPC), together with growth factors, is a promising approach to promote regeneration and recovery. A contusion/compression aneurysm clip rat model of cervical SCI and combined treatment involving SAP injection and NPC transplantation is established.

Spinal cord injuries (SCI) cause serious neurological impairment and psychological, economic, and social consequences for patients and their families. ...

Using Multi-fluorinated Bile Acids and In Vivo Magnetic Resonance Imaging to Measure Bile Acid Transport

Along with their traditional role as detergents that facilitate fat absorption, emerging literature indicates that bile acids are potent signaling molecules that affect multiple organs; they modulate gut motility and hormone production, and alter vascular tone, glucose metabolism, lipid metabolism, and energy utilization. Changes in fecal bile acids may alter the gut microbiome and promote colon pathology including cholerrheic diarrhea and colon cancer. Key regulators of fecal bile acid composition are the small intestinal Apical Sodium-dependent Bile Acid Transporter (ASBT) and fibroblast growth factor-19 (FGF19). Reduced expression and function of ASBT decreases intestinal bile acid up-take. Moreover, in vitro data suggest that some FDA-approved drugs inhibit ASBT function. Deficient FGF19 release increases hepatic bile acid synthesis and release into the intestines to levels that overwhelm ASBT. Either ASBT dysfunction or FGF19 deficiency increases fecal bile acids and may cause chronic diarrhea and promote colon neoplasia. Regrettably, tools to measure bile acid malabsorption and the actions of drugs on bile acid transport in vivo are limited. To understand the complex actions of bile acids, techniques are required that permit simultaneous monitoring of bile acids in the gut and metabolic tissues. This led us to conceive an innovative method to measure bile acid transport in live animals using a combination of proton (1H) and fluorine (19F) magnetic resonance imaging (MRI). Novel tracers for fluorine (19F)-based live animal MRI were created and tested, both in vitro and in vivo. Strengths of this approach include the lack of exposure to ionizing radiation and translational potential for clinical research and practice.

Using Multi-fluorinated Bile Acids and In Vivo Magnetic Resonance Imaging to Measure Bile Acid Transport

Tools to diagnose bile acid malabsorption and measure bile acid transport in vivo are limited. An innovative approach in live animals is described that utilizes combined proton (1H) plus fluorine (19F) magnetic resonance imaging; this novel methodology has translational potential to screen for bile acid malabsorption in clinical practice.

Along with their traditional role as detergents that facilitate fat absorption, emerging literature indicates that bile acids are potent signaling ...

Estimation of Nephron Number in Whole Kidney using the Acid Maceration Method

Nephron endowment refers to the total number of nephrons an individual is born with, as nephrogenesis in humans is completed by 36 weeks of gestation and no new nephrons are formed post-birth. Nephron number refers to the total number of nephrons measured at any point in time post-birth. Both genetic and environmental factors influence both nephron endowment and number. Understanding how specific genes or factors influence the process of nephrogenesis and nephron loss or demise is important as individuals with lower nephron endowment or number are thought to be at a higher risk of developing renal or cardiovascular disease. Understanding how environmental exposures over the course of a person's lifetime affects nephron number will also be vital in determining future disease risk. Thus, the ability to assess whole kidney nephron number quickly and reliably is a basic experimental requirement to better understand mechanisms that contribute to or promote nephrogenesis or nephron loss. Here, we describe the acid maceration method for the estimation of whole kidney nephron number based on the procedure described by Damadian, Shawayri, and Bricker, with slight modifications. The acid maceration method provides fast and reliable estimates of nephron number (as assessed by counting glomeruli) that are within 5% of those determined using more advanced, albeit expensive, methods such as magnetic resonance imaging. Moreover, the acid maceration method is an excellent high-throughput method to assess nephron number in large numbers of samples or experimental conditions.

Estimates of whole kidney nephron number are important clinically and experimentally, as there is an inverse association between nephron number and an enhanced risk of renal and cardiovascular disease.Herein, the use of the acid maceration method, which provides fast and reliable estimates of whole kidney nephron number, is demonstrated.

Nephron endowment refers to the total number of nephrons an individual is born with, as nephrogenesis in humans is completed by 36 weeks of gestation and ...

Rapid Evaluation of Toxicity of Chemical Compounds Using Zebrafish Embryos

The zebrafish is a widely used vertebrate model organism for the disease and phenotype-based drug discovery. The zebrafish generates many offspring, has transparent embryos and rapid external development. Zebrafish embryos can, therefore, also be used for the rapid evaluation of toxicity of the drugs that are precious and available in small quantities. In the present article, a method for the efficient screening of the toxicity of chemical compounds using 1-5-day post fertilization embryos is described. The embryos are monitored by stereomicroscope to investigate the phenotypic defects caused by the exposure to different concentrations of compounds. Half-maximal lethal concentrations (LC50) of the compounds are also determined. The present study required 3-6 mg of an inhibitor compound, and the whole experiment takes about 8-10 h to be completed by an individual in a laboratory having basic facilities. The current protocol is suitable for testing any compound to identify intolerable toxic or off-target effects of the compound in the early phase of drug discovery and to detect subtle toxic effects that may be missed in the cell culture or other animal models. The method reduces procedural delays and costs of drug development.

Zebrafish embryos are used for evaluating the toxicity of chemical compounds. They develop externally and are sensitive to chemicals, allowing detection of subtle phenotypic changes. The experiment only requires a small amount of compound, which is directly added to the plate containing embryos, making the testing system efficient and cost-effective.

The zebrafish is a widely used vertebrate model organism for the disease and phenotype-based drug discovery. The zebrafish generates many offspring, has ...

Using a Chemical Biopsy for Graft Quality Assessment

Kidney transplantation is a life-saving treatment for a large number of people with end-stage renal dysfunction worldwide. The procedure is associated with an increased survival rate and greater quality of patient&#8217;s life when compared to conventional dialysis. Regrettably, transplantology suffers from a lack of reliable methods for organ quality assessment. Standard diagnostic techniques are limited to macroscopic appearance inspection or invasive tissue biopsy, which do not provide comprehensive information about the graft. The proposed protocol aims to introduce solid phase microextraction (SPME) as an ideal analytical method for comprehensive metabolomics and lipidomic analysis of all low molecular compounds present in kidneys allocated for transplantation. The small size of the SPME probe enables performance of a chemical biopsy, which enables extraction of metabolites directly from the organ without any tissue collection. The minimum invasiveness of the method permits execution of multiple analyses over time: directly after organ harvesting, during its preservation, and immediately after revascularization at the recipient&#8217;s body. It is hypothesized that the combination of this novel sampling method with a high-resolution mass spectrometer will allow for discrimination of a set of characteristic compounds that could serve as biological markers of graft quality and indicators of possible development of organ dysfunction.

The protocol presents utilization of the chemical biopsy approach followed by comprehensive metabolomic and lipidomic analysis for quality assessment of kidney grafts allocated for transplantation.

Kidney transplantation is a life-saving treatment for a large number of people with end-stage renal dysfunction worldwide. The procedure is associated ...

On-Site Sampling and Extraction of Brain Tumors for Metabolomics and Lipidomics Analysis

Despite the variety of tools available for cancer diagnosis and classification, methods that enable fast and simple characterization of tumors are still in need. In recent years, mass spectrometry has become a method of choice for untargeted profiling of discriminatory compound as potential biomarkers of a disease. Biofluids are generally considered as preferable matrices given their accessibility and easier sample processing while direct tissue profiling provides more selective information about a given cancer. Preparation of tissues for the analysis via traditional methods is much more complex and time-consuming, and, therefore, not suitable for fast on-site analysis. The current work presents a protocol combining sample preparation and extraction of small molecules on-site, immediately after tumor resection. The sampling device, which is of the size of an acupuncture needle, can be inserted directly into the tissue and then transported to the nearby laboratory for instrumental analysis. The results of metabolomics and lipidomics analyses demonstrate the capability of the approach for the establishment of phenotypes of tumors related to the histological origin of the tumor, malignancy, and genetic mutations, as well as for the selection of discriminating compounds or potential biomarkers. The non-destructive nature of the technique permits subsequent performance of routinely used tests e.g., histological tests, on the same samples used for SPME analysis, thus enabling attainment of more comprehensive information to support personalized diagnostics.

The manuscript presents on-site sampling of human brain tumors with solid phase microextraction followed by their biochemical profiling towards the discovery of biomarkers.

Despite the variety of tools available for cancer diagnosis and classification, methods that enable fast and simple characterization of tumors are still ...

Preparation of Naringenin Solution for In Vivo Application

The preparation of a compound (phytochemical) solution is an overlooked but critical step prior to its application in studies such as drug screening. The complete solubilization of the compound is necessary for its safe use and relatively stable results. Here, a protocol for preparing naringenin solution and its intraperitoneal administration in a high-fat diet and streptozotocin (STZ)-induced diabetic model is demonstrated as an example. A small amount of naringenin (3.52-6.69 mg) was used to test its solubilization in solvents, including ethanol, dimethylsulfoxide (DMSO), and DMSO plus Tween 80 reconstituted in physiological saline (PS), respectively. Complete solubilization of the compound is determined by observing the color of the solution, the presence of precipitates after centrifugation (2000 x g for 30 s), or allowing the solution to stand for 2 h at room temperature (RT). After obtaining a stable compound/phytochemical solution, the final concentration/amount of the compound required for in vivo studies can be prepared in a solvent-only (no PS) stock solution, and then diluted/mixed with PS as desired. The antidiabetic osteoporotic effects of naringenin in mice (intraperitoneal administration at 20 mg/kg b.w., 2 mg/mL) were assessed by measuring blood glucose, bone mass (micro-CT), and bone resorption rate (TRAP staining and ELISA). Researchers looking for detailed organic/phytochemical solution preparations will benefit from this technique.

Preparation of Naringenin Solution for In Vivo Application

Here, the protocol presents the preparation of naringenin solution for in vivo intraperitoneal administration. Naringenin is fully dissolved in a mixture of dimethylsulfoxide, Tween 80, and saline. The antidiabetic osteoporotic effects of naringenin were assessed by blood glucose testing, tartrate-resistant acid phosphatase staining, and enzyme-linked immunosorbent assay.

The preparation of a compound (phytochemical) solution is an overlooked but critical step prior to its application in studies such as drug screening. The ...

Evaluation of Amino Acid Consumption in Cultured Bone Cells and Isolated Bone Shafts

Bone development and homeostasis is dependent upon the differentiation and activity of bone forming osteoblasts. Osteoblast differentiation is sequentially characterized by proliferation followed by protein synthesis and ultimately bone matrix secretion. Proliferation and protein synthesis require a constant supply of amino acids. Despite this, very little is known about amino acid consumption in osteoblasts. Here we describe a very sensitive protocol that is designed to measure amino acid consumption using radiolabeled amino acids. This method is optimized to quantify changes in amino acid uptake that are associated with osteoblast proliferation or differentiation, drug or growth factor treatments, or various genetic manipulations. Importantly, this method can be used interchangeably to quantify amino acid consumption in cultured cell lines or primary cells in vitro or in isolated bone shafts ex vivo. Finally, our method can be easily adapted to measure the transport of any of the amino acids as well as glucose and other radiolabeled nutrients.

This protocol presents a radiolabeled amino acid uptake assay, which is useful for evaluating amino acid consumption either in primary cells or in isolated bones.

Bone development and homeostasis is dependent upon the differentiation and activity of bone forming osteoblasts. Osteoblast differentiation is ...

Visualizing and Quantifying Pharmaceutical Compounds within Skin using Coherent Raman Scattering Imaging

Cutaneous pharmacokinetics (cPK) after topical formulation application has been a research area of particular interest for regulatory and drug development scientists to mechanistically understand topical bioavailability (BA). Semi-invasive techniques, such as tape-stripping, dermal microdialysis, or dermal open-flow microperfusion, all quantify macroscale cPK. While these techniques have provided vast cPK knowledge, the community lacks a mechanistic understanding of active pharmaceutical ingredient (API) penetration and permeation at the cellular level. 
One noninvasive approach to address microscale cPK is coherent Raman scattering imaging (CRI), which selectively targets intrinsic molecular vibrations without the need for extrinsic labels or chemical modification. CRI has two main methods-coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS)-that enable sensitive and selective quantification of APIs or inactive ingredients. CARS is typically utilized to derive structural skin information or visualize chemical contrast. In contrast, the SRS signal, which is linear with molecular concentration, is used to quantify APIs or inactive ingredients within skin stratifications. 
Although mouse tissue has commonly been utilized for cPK with CRI, topical BA and bioequivalence (BE) must ultimately be assessed in human tissue before regulatory approval. This paper presents a methodology to prepare and image ex vivo skin to be used in quantitative pharmacokinetic CRI studies in the evaluation of topical BA and BE. This methodology enables reliable and reproducible API quantification within human and mouse skin over time. The concentrations within lipid-rich and lipid-poor compartments, as well as total API concentration over time are quantified; these are utilized for estimates of micro- and macroscale BA and, potentially, BE.

A coherent Raman scattering imaging methodology to visualize and quantify pharmaceutical compounds within the skin is described. This paper describes skin tissue preparation (human and mouse) and topical formulation application, image acquisition to quantify spatiotemporal concentration profiles, and preliminary pharmacokinetic analysis to assess topical drug delivery.

Cutaneous pharmacokinetics (cPK) after topical formulation application has been a research area of particular interest for regulatory and drug development ...