Self-microemulsion Delivery System Study Of Antitumor Drug Candidate Mitoxantole

Mitothiorole, a new chemical entity with independent intellectual properties, has been shown by previous studies to possess wide anti-tumor spectrum via oral administration. However, its poor physicochemical properties, especially its water insolubility, hindered the conduction of its pharmacological and toxicological studies. The main aims of this research were to study the physicochemical properties and the intestinal absorption mechanisms of mitothiorole, and to investigate the factors that affect the absorption of mitothiorole in order to design a novel oral delivery system for mitothiorole. Self-microemulsifying drug delivery systems (SMEDDS) of mitothiorole were developed. The uptake and transport behavior of mitothiorole SMEDDS in Caco-2 cells was observed. The studies on pharmacokinetics and pharmacodynamics of mitothiorole SMEDDSs were also determined.First, the physicochemical properties of mitothiorole were characterized using reverse-phase HPLC method. Mitothiorole showed extremely low solubility in water. The Caco-2 cell model was used to study the uptake and transport behavior of mitothiorole. The results indicted that the uptake of mitothiorole is more likely via carrier mediated active transport, because the uptake of mitothiorole was time correlated and became saturated in 30 minutes. Besides, it was observed that medium pH also affected the uptake of mitothiorole. The P-gp inhibitors, cyclosporine A and verapamil, didn't show significant impact on the uptake of mitothiorole(P>0.05). The Papps of mitothiorole was less than 10-7cm/sec, which might contribute to the poor absorption of mitothiorole.In preformulation study, the equilibrium solubility of mitothiorole in different kinds of oil, surfactants and co-surfactants was determined and pseudo-ternary phase diagrams were constructed to evaluate the formula factors that influenced the preparation of self-microemulsion. An optimized formulation consisted of MCT as oil phase, Cremopher El and Labrasol as co-surfactants was selected. Independent formulation variables like the mass ratio of Cremophor EL to Labrasol (Km) and the proportion of oil phase (oil%) were optimized with a two-factor-five-level Central Composite Experimental Design combined with Response Surface Methodology, using particle size, zeta potential and solubility as response variables. The optimized formula of mitothiorole SMEDDs was quickly and conveniently obtained as follow: MCT:Cremopher EL:Labrasol=11:59:30.The pharmacokinetic parameters of mitothiorole SMEDDS and mitothiorole suspension were investigated after oral administration to rats at a single dose of 20mg/kg, compared to those of mitothiorole injection (using Transcutol P as solvent). The results were as follows:The Cmax was (13.55±5.82), (3.27±1.11) and (60.83±11.93)?g/ml, respectively; AUC was (229.47±100.77), (52.59±23.57) and (1247.34±223.67) hr·?g/ml, respectively. The relative bioavailability of mitothiorole SMEDDS to suspension was 436.34%, and its absolute bioavailability was 18.40%.Drug sensitivity screening studies were conducted on various tumor cell lines, among which, human lung cancer cells, H460, and human glioma cells, U87, manifested more sensitive to mitothiorole. H460 transplant tumor and U87 in situ brain tumor models were established in nude mice and the pharmacodynamic studies were carried out. In H460 transplant tumor models, tumor inhibition rate of mitothiorole SMEDDS was 56.2%, compared to the saline group (negative control), which was significantly better than that of mitothiorole suspension (36.86%, P<0.05) and CTX injection (positive control, P<0.05). The pharmacodynamic studies of different dosage forms of mitothiorole and TMZ in U87 brain tumor models were also investigated. After treatment with mitothiorole SMEDDS, the median survival time of the mice was significantly prolonged compared to that of the suspension (P<0.05) and very close to that of TMZ (P>0.05). The results indicated that SMEDDS could significantly enhance the antitumor effect of mitothiorole by increasing the dissolution and oral absorption of mitothiorole.In conclusion, the physicochemical properties of mitothiorole were characterized. The intestinal absorption mechanism of mitothiorole was investigated using Caco-2 models. Accordingly, mitothiorole SMEDDS was designed and the formulation was optimized. The results of pharmacokinetic and pharmacodynamic studies indicated that SMEDDS could enhance the antitumor effect of mitothiorole through increasing its dissolution and absorption in GI tract, which proved mitothiorole as a potential antitumor drug candidate for development.