Drug transporter gene expression in human colorectal tissue and cell lines: modulation with antiretrovirals for microbicide optimization

Objectives: The objectives of this study were to comprehensively assess mRNA expression of 84 drug transporters in human colorectal biopsies and six representative cell lines, and to investigate the alteration of drug transporter gene expression after exposure to three candidate microbicidal antiretroviral (ARV) drugs (tenofovir, darunavir and dapivirine) in the colorectal epithelium. The outcome of the objectives informs development of optimal ARV-based microbicidal formulations for prevention of HIV-1 infection. Methods: Drug transporter mRNA expression was quantified from colorectal biopsies and cell lines by quantita- tive real-time PCR. Relative mRNA expression was quantified in Caco-2 cells and colorectal explants after induc- tion with ARVs. Data were analysed using Pearson’s product moment correlation (r), hierarchical clustering and principal component analysis (PCA). Results: Expression of 58 of the 84 transporters was documented in colorectal biopsies, with genes for CNT2, P-glycoprotein (P-gp) and MRP3 showing the highest expression. No difference was noted between individual subjects when analysed by age, gender or anatomical site (rectum or recto-sigmoid) (r ¼ 0.95 – 0.99). High expres- sion of P-gp and CNT2 proteins was confirmed by immunohistochemical staining. Similarity between colorectal tissue and cell-line drug transporter gene expression was variable (r ¼ 0.64 – 0.84). PCA showed distinct clustering of human colorectal biopsy samples, with the Caco-2 cells defined as the best surrogate system. Induction of Caco-2 cell lines with ARV drugs suggests that darunavir-based microbicides incorporating tenofovir may result in drug– drug interactions likely to affect distribution of individual drugs to sub-epithelial target cells. Conclusions: These findings will help optimize complex formulations of rectal microbicides to realize their full potential as an effective approach for pre-exposure prophylaxis against HIV-1 infection