Simultaneous quantification of atorvastatin, erlotinib and OSI-420 in rat serum and liver microsomes using a novel liquid chromatography-mass spectrometry method

Erlotinib is an epidermal growth factor receptor tyrosine kinase inhibitor used in the treatment of cancer. Atorvastatin is a statin commonly applied to treat hypercholesterolemia. In humans, both compounds are metabolized by CYP3A4 and are transported by OATP2B1, ABCB1 and ABCG2. We aimed to generate and validate a bioanalytical method for simultaneous determination of atorvastatin, erlotinib and its major metabolite OSI-420 applicable to biological samples. Quantification of erlotinib, OSI-420, and atorvastatin was achieved with an Agilent high-performance liquid chromatography system 1100/1200 coupled to a triple quadrupole G6410B. The method involved separation over the column Kinetex C8 (100 ×3 mm, 2.6 µm) using 2 mM ammonium acetate (pH 4.0) and acetonitrile as eluent. The method was assessed for selectivity, accuracy, recovery, matrix effect, and stability over a range from 1 to 4,000 ng/mL according to the respective guidelines. We applied the bioanalytical method to quantify the formation of OSI-420 in liver microsomes isolated from male and female Wistar rats. The optimized experiment revealed slower formation in microsomes of female compared to male rats, in which we observed lower amounts of CYP3A1 by Western blot analysis. Moreover, the presence of atorvastatin inhibited the CYP3A-mediated metabolism of erlotinib. Serum obtained from a drug-drug interaction study performed in male rats was also analyzed using the validated method. Non-compartmental pharmacokinetic analysis revealed a lower clearance of erlotinib when atorvastatin was co-administered. However, for atorvastatin we observed a lower systemic exposure in presence of erlotinib. In summary, we report a method to detect OSI-420, erlotinib and atorvastatin applicable to samples from ex vivo and in vivo studies.