Preformulation studies on trametinib and panobinostat for a prospective topical combination product for the treatment of melanoma

Abstract

Specific Aims: Specific Aim #1: Evaluate the stability of both pharmacologic agents in the varying conditions (pH and temperature). Our working hypothesis #1 is that both agents will degrade readily at an elevated temperature (65°C) and pH (>7).

Specific Aim #2: Determine the solubility profiles of both pharmacologic agents in varying conditions (pH and solvent). Our working hypothesis #2 is that solubility of panobinostat and trametinib will be greatest at a pH <7, as well as in a polyethylene glycol (PEG) solvent.

Methods: Data for quantity, solubility, and stability will be recorded for trametinib and panobinostat. 1. Standards: Stock solutions of both compounds will be repeatedly diluted into 5 concentrations in varying solvents until a quantifiable, distinct peak is present on the HPLC around 6-8 minutes. 2. Solubility: In order to test the solubility of both compounds, 1-2 mg of each drug will be put into varying solvents and buffers. If the drug is visibly in solution, 1-2 mg more of drug will be added at a time until a limit of solubility is determined. a. Trametinib: The solubility as a function of pH will be conducted at four pH values between 3.0 and 9.0, as well as with various solvents (ACN, EtOH, PEG400, and PG). Each sample will be saturated with raw drug and allowed to agitate for at least 30 min. Samples will then be visually inspected to ensure that solid drug is still in excess, then will be filtered through an RC filter. The filtrate will be diluted appropriately with distilled water and analyzed using the HPLC assay. b. Panobinostat: The solubility as a function of pH will be conducted at ten pH values between 4.0 and 10.0, as well as with various solvents (10% ACN, 10% DMSO, 10% PEG, and 100% PEG). Each sample will be saturated with raw drug and allowed to agitate for at least 30 min. Samples will then be visually inspected to ensure that solid drug is still in excess, then will be filtered through an RC filter. The filtrate will be diluted appropriately with distilled water and analyzed using the HPLC assay.

3. Stability: The stability of both agents will be tested in various conditions including temperature, pH, and solvents. Stability results will be obtained until peaks varied from that of the original determined during respective standards. a. Trametinib: The influence of pH will be studied with a citrate buffer (pH 2.0), and a borate buffer (pH 9.0). The pH will be adjusted with distilled water. b. Panobinostat: The influence of pH on the stability will be studied with a citrate buffer (pH 4.0 and 5.1), a phosphate buffer (pH 6.0, 7.0, 7.4, and 8.0), and a borate buffer (pH 9 and 10). The pH will be adjusted with NaOH or concentrated HCl. The influence of solvents will be studied with 10% ACN, 10% DMSO, 10% PEG, and 100% PEG.

Main Results: 1. Panobinostat: a. Solubility – Increased solubility around pH < 6.5, and > 8.5. Intrinsic solubility seems to be around 7.4 to 7.8. Solubility in 100% PEG appears to be roughly 2750 ug/mL, while in 10% showed moderate solubility (~140 ug/mL). b. Stability – 1st order degradation is noted, with higher rates with an increase in pH for the most part. The most distinguished degradation is seen at pH 7 for this experiment. Higher temperatures (65 C) yielded faster degradation. With respect to both experimented temperatures (48 C and 65 C), pH 4 and 5.1 appeared to be most stable (see attached graphs). Stability in PEG complex was poor. c. Dermabase: Drug crystals present in both phases: Not in solution. 2. Trametinib: a. Solubility – @63 C: Not soluble in MeOH, low solubility in EtOH and PG, pH 3 solubility > 2 mg/mL, ~1.93 mg/mL in PEG, 0.73 mg/mL in ACN. Limit of quantification > 40 nanograms. b. Stability – Relatively stable in light, degrades fast a pH 9, slow at pH 2. New peak present at pH 2, degradation around 11%. c. Dermabase: Drug crystals present in both phases: Not in solution. Conclusion: 1. The two medications in combination were incompatible in solution in Dermabase. 2. Additional research will need to be completed in efforts to get these two medications to go into a solution. 3. However, time, money, and the unfortunate death of the preceptor terminated further research for this project.