Investigation on permeation of CPT-11 acid versus lactone and optimization of transmucosal delivery of CPT-11

摘要

CPT-11 is a water soluble camptothecin derivative with broad spectrum of antitumor activities. The therapeutic use of CPT-11 is limited due to its dose limiting toxicity of severe grade 3-4 diarrhea. CPT-11 in the body is converted to its active form SN-38 by the action of carboxylesterases enzyme. Intravenous route of CPT-11 administration at its MTD leads to higher levels of SN-38 in the body which causes diarrhea. Oral administration can be used to lower the dosage of CPT-11. However oral leads to lower bioavailability due to first pass metabolism. An alternative route of delivery which would has the advantages of intravenous and oral but has side-effects of neither is critical.;This research intends to prove that transmucosal (buccal) is a preferred alternative to conventional routes of CPT-11 delivery. The specific aims of this dissertation were: 1) To understand the fundamental physicochemical properties of CPT-11, 2) To establish and validate parameters for in vitro permeation of CPT-11 across porcine buccal mucosa, 3) To characterize the fundamental transport properties of CPT-11 across the buccal mucosa, 4) To study the effect of penetration enhancers on CPT-11 permeability and transport across the buccal membrane and 5) To evaluate the feasibility for buccal delivery of CPT-11 in vivo in rabbits.;CPT-11 was analyzed in mobile phase and rabbit plasma by a validated HPLC method. In order to optimize delivery and to enhance its efficacy, a detailed physicochemical characterization of CPT-11 was carried out. Molecular and system properties were determined by partition and solubility studies using UV spectroscopy and HPLC. Also solid state characterization of CPT-11 was carried out using DSC, XRD and FTIR. Spectral scans of various pH solutions of CPT-11 revealed that the pKa of quinoline moiety was 1.09.Equilibrium hydrolysis revealed that only 13% CPT-11-lactone is present at physiological pH. Distribution coefficient increases with increase in pH, with log D of 0.72 at pH 7.4. Equilibrium solubility decreases from pH 4 -- 9.The hydrolysis of CPT-11-lactone to carboxylate at pH 7.4 follows a pseudo first order kinetics.;To characterize the nature of permeation of CPT-11, in-vitro transmucosal studies were designed to evaluate the feasibility and this included the release of drug at different pH, donor concentration or using multitude of penetration enhancers. Porcine buccal mucosa was used for all of these studies. The pH studies showed that it had no effect on the permeability coefficient of CPT-11 in the range of pH 4.0 to pH 9.0. This indicates the CPT-Ms predominately transported through the paracellular route. Concentration dependency study demonstrated that the steady state flux increased linearly with increasing the donor concentration (0.5 -- 15 mg/ml) at pH 4 and (0.5 -- 10 mg/ml) at pH 6.8. Steady state flux plotted against donor concentration was linear indicating that CPT-11 permeated passively through the buccal mucosa.;Evaluating the permeation of the two form of CPT-11 through the buccal mucosa revealed that the lactone form had two fold higher permeability in comparison to the carboxylate form. This showed that the active form of the drug was delivered through the buccal mucosa. Out of the 16 transcellular and paracellular enhancers studied at donor pH of 4.0, the ones with a significant impact were 1% Transcutol, 20% PEG, 20% PG, 1 mM Sodium deoxycholate, 2% Tween 80 and combination of 10% ethanol and 30% PG. Enhancers were also studied for their penetration effects at donor pH of 9.0, but none showed any significant change.;The in-vivo studies conducted on rabbits showed that the maximum plasma concentration at 10 mg/kg IV infusion reached a maximum of 10 mg/mi. and dropped to 0.75 mg/ml in 8 h. Mean values of systemic clearance was 1086.15mlfh while t 1/2 was 2.77h and distribution volume at steady state was 3481.25 ml. These studies showed that rabbit is a better model for predicting clearance of CPT-11 for humans compared to dogs and other rodents. This aspect of the investigation could not demonstrate systemic delivery of CPT-11 in rabbits. However, the observed GI toxicity in rabbits that received CPT-11 suggests potential metabolic conversion of CPT-11 in the buccal membrane.