Expression of six drug transporters in vaginal, cervical, and colorectal tissues: Implications for drug disposition in HIV prevention

Abstract

Effective antiretroviral (ARV)-based HIV prevention strategies require optimizing drug exposure in mucosal tissues; yet factors influencing mucosal tissue disposition remain unknown. We hypothesized drug transporter expression in vaginal, cervical, and colorectal tissues is a contributing factor and selected 3 efflux (ABCB1/MDR1, ABCC2/MRP2, ABCC4/MRP4) and 3 uptake (SLC22A6/OAT1, SLC22A8/OAT3, SLCO1B1/OATP1B1) transporters to further investigate based on their affinity for 2 ARVs central to prevention (tenofovir, maraviroc). Tissue was collected from 98 donors. mRNA and protein expression were quantified using qPCR and immunohistochemistry (IHC). Hundred percent of tissues expressed efflux transporter mRNA. IHC localized them to the epithelium and/or submucosa. Multivariable analysis adjusted for age, smoking, and co-medications revealed significant (P < 0.05) differences in efflux transporter mRNA between tissue types (vaginal ABCB1 3.9-fold > colorectal; vaginal ABCC2 2.9-fold > colorectal; colorectal ABCC4 2.0-fold > cervical). In contrast, uptake transporter mRNA was expressed in <25% of tissues. OAT1 protein was detected in 0% of female genital tissues and in 100% of colorectal tissues, but only in rare epithelial cells. These data support clinical findings of higher maraviroc and tenofovir concentrations in rectal tissue compared to vaginal or cervical tissue after oral dosing. Quantifying mucosal transporter expression and localization can facilitate ARV selection to target these tissues.

Keywords: HIV; antiretrovirals; mucosal; pharmacokinetics; prevention; transporters.

Figure 1

mRNA expression of three ABC transporters in vaginal, cervical, and colorectal tissues. mRNA was detected by qRT-PCR and levels were normalized to ACTB Ct values using the 2^-ΔCt method. Box plots represent the 50^th percentile (line), 25^th and 75^th percentile (box), 10^th and 90^th percentile (error bars), and outliers (circles). Tissues were compared using an exact Kruskal Wallis test and pairwise comparisons were made using the Dunn's method * p<0.05

Figure 2

Immunohistochemical staining of vaginal, cervical, and colorectal tissues. Black arrows identify expression efflux transporters expressed in the epithelial layers. Submucosal lymphocytes and/or monocytes are highlighted by the yellow arrows. The red arrow identifies a rare positive columnar epithelial cell. Images of OAT1 expression in vaginal and cervical tissue, and MDR1 in vaginal tissue were taken at an original objective magnification of 20x, and all others at an original magnification of 60x.

Figure 3

Hypothesized influence of drug transporters on drug exposure in colorectal and vaginal tissues. The differential expression between colorectal and vaginal epithelial tissues for each transporter relevant to a specific substrate's drug distribution is summarized. A) Tenofovir is a substrate for MRP2, MRP4, and OAT1 B) Maraviroc is an MDR1 substrate. The black circles represent the respective drug molecules. The relative in vivo tissue exposures observed (colorectal:vaginal) following oral doses is summarized in the boxes to the left of the schematic.