CYP3A4 activity of paclitaxel and vinorelbine in microemulsions

Purpose: To determine the CYP3A4 enzyme activity of two anticancer agents, paclitaxel (PAC), vinorelbine (VIN) and two microemulsions.

Methods: The effect of PAC, VIN and two microemulsions on CYP3A4 enzyme activity was measured using a cytochrome P450 luminescent assay (P450-Glo^TM Assay). PAC and VIN were dissolved in CE (1:1 (w/w) cremophor EL: ethanol) and water respectively, and diluted with water to obtain concentrations from 100 μM to 10 pM. Test compounds were mixed with CYP3A4 enzyme and the luciferin derivative of the CYP3A4 substrate in 96 well plates, and incubated for 10 minutes at room temperature. NADPH solutions were added to initiate the enzyme reaction. After 10 minutes of incubation, luminescence detection reagents were added luminescence measured after 20 minutes using a SpectraMax M5 plate reader. The half maximal inhibitory concentration (IC₅₀) of PAC, VIN, and the microemulsions without drug was determined.

Results: Table 1. The half maximal inhibitory concentration (IC₅₀) of test compounds

Test compound	IC50
PAC in CE	63 nM
VIN	4.7 μM
ME1*	2.0 x 10-5***
ME2**	2.7 x 10-6***
CE	7.2 x 10-5***

^* ME1 (1:1:1 (w/w) span 80-LQ: propylene glycol: capmul) ^** ME2 (2:1 (w/w) brij 010-SS: propylene glycol)

^*** Dilution factor at which luminescence was 50% of maximum values

Conclusion: PAC in CE had a lower apparent IC₅₀ value compared to VIN against the CYP3A4 enzyme. ME1 and ME2 had inhibitory effects on CYP3A4 at compatible or more dilute conditions than CE. Both PAC in CE and CE had similar inhibitory patterns at corresponding dilutions (data not shown), which suggests the inhibitory effect of PAC in CE was attributed to the inhibitory effect of CE rather than PAC.