Short Communication: Expression of Transporters and Metabolizing Enzymes in the Female Lower Genital Tract: Implications for Microbicide Research

Abstract

Topical vaginal microbicides have been considered a promising option for preventing the male-to-female sexual transmission of HIV; however, clinical trials to date have not clearly demonstrated robust and reproducible effectiveness results. While multiple approaches may help enhance product effectiveness observed in clinical trials, increasing the drug exposure in lower genital tract tissues is a compelling option, given the difficulty in achieving sufficient drug exposure and positive correlation between tissue exposure and microbicide efficacy. Since many microbicide drug candidates are substrates of transporters and/or metabolizing enzymes, there is emerging interest in improving microbicide exposure and efficacy through local modulation of transporters and enzymes in the female lower genital tract. However, no systematic information on transporter/enzyme expression is available for ectocervical and vaginal tissues of premenopausal women, the genital sites most relevant to microbicide drug delivery. The current study utilized reverse transcriptase polymerase chain reaction (RT-PCR) to examine the mRNA expression profile of 22 transporters and 19 metabolizing enzymes in premenopausal normal human ectocervix and vagina. Efflux and uptake transporters important for antiretroviral drugs, such as P-gp, BCRP, OCT2, and ENT1, were found to be moderately or highly expressed in the lower genital tract as compared to liver. Among the metabolizing enzymes examined, most CYP isoforms were not detected while a number of UGTs such as UGT1A1 were highly expressed. Moderate to high expression of select transporters and enzymes was also observed in mouse cervix and vagina. The implications of this information on microbicide research is also discussed, including microbicide pharmacokinetics, the utilization of the mouse model in microbicide screening, as well as the in vivo functional studies of cervicovaginal transporters and enzymes.

Expression and Localization of P-Glycoprotein, Multidrug Resistance Protein 4, and Breast Cancer Resistance Protein in the Female Lower Genital Tract of Human and Pigtailed Macaque

“…Our previous study has examined the mRNA expression of transporters and enzymes in the human lower genital tract (ectocervix and vagina) using conventional RT-PCR. 16 Although a number of efflux transporters (P-gp, BCRP, MRP4, MRP5, and MRP7) were found to be expressed at moderate to high levels compared to liver, only a limited number of uptake transporters, such as OCT2 and ENT1 was found to be positively expressed in both the epithelium and stroma of the ectocervix and vagina. 16 OAT1 and OAT3, the major uptake transporters for tenofovir, were not detectable by RT-PCR in these tissues.…”

“…16 Although a number of efflux transporters (P-gp, BCRP, MRP4, MRP5, and MRP7) were found to be expressed at moderate to high levels compared to liver, only a limited number of uptake transporters, such as OCT2 and ENT1 was found to be positively expressed in both the epithelium and stroma of the ectocervix and vagina. 16 OAT1 and OAT3, the major uptake transporters for tenofovir, were not detectable by RT-PCR in these tissues. 16 The majority of CYP isoforms, such as CYP3A4, were not detectable or were expressed at much lower levels compared to the liver.…”

“…[30][31][32][33][34][35] With respect to the transporters in the human female genital tract, we validated the findings on cervical tissue P-gp and BCRP, which were previously reported by other researchers and our group. 16,35,36 Furthermore, we extended the characterization of these two transporters to the human vagina. To our knowledge, this study is the first to characterize MRP4 protein localization in the human lower genital tract.…”

“…[25][26][27] There has been an urgent need to identify critical determinants of cervicovaginal tissue drug PK/PD to optimize PrEP strategies. 6,16,37 Efflux transporters and uptake transporters have been reported to pump out or influx many antiretroviral drugs. 9,38,39 In addition, cytochrome P450 (CYP) metabolizing enzymes play a role in the metabolic activation or inactivation of these drugs.…”

“…9,[11][12][13][14][15] We have previously examined the mRNA expression of antiretroviral-related efflux and uptake transporters in human cervicovaginal tissue by using conventional reverse transcriptase polymerase chain reaction (RT-PCR) and found that a number of ABC transporters were highly expressed. 16 Among those highly expressed, P-glycoprotein (P-gp), multidrug resistance-associated protein 4 (MRP4), and breast cancer resistance protein (BCRP) are most relevant to antiretroviral drugs. Their substrates span all classes of antiretroviral drugs used in AIDS treatment and/or microbicide development, such as the entry inhibitor maraviroc, most protease inhibitors, the reverse transcriptase inhibitors tenofovir and zidovudine, and the integrase inhibitor raltegravir.…”