A long-acting injectable form of rilpivirine (RPV) is being evaluated in clinical trials for HIV prevention. Preclinical testing was done to define pharmacokinetic (PK) and pharmacodynamic (PD) activity of RPV in ectocervical and colonic tissues treated in vitro and to help inform PK data obtained from clinical trials.
In vitro 99% effective dose (ED99) and cytotoxic dose (CD99) of RPV against HIV-1BaL was defined using a TZM-bl assay. RPV was evaluated for potency using polarized ectocervical and colonic explant tissues. Ten-fold dilutions of RPV, starting at 100 µM, were applied either to the apical tissue surface with HIV or in the basolateral medium, 24 hours prior to HIV being applied to the apical tissue surface. Supernatants were collected over the culture period and assessed for HIV replication using a p24 ELISA. RPV was quantified in mucosal tissue using a validated liquid chromatography-mass spectrometry assay. PK/PD correlations were determined using GraphPad Prism. Non-linear Emax model with variable slope was used to evaluate concentration-response relationships using SigmaPlot.
TZM-bl assay results showed RPV has an ED99 of 8.27 nM and a CD99 of 492 nM against HIV-1BaL. When applied to the apical surface at the same time as HIV-1BaL, 100 µM of RPV added to the cultures was needed to fully inhibit HIV infection in ectocervical tissue, while 10 µM was needed to inhibit HIV infection in colonic tissue. RPV added to the basolateral medium was more effective with 10 µM and 1 µM protecting ectocervical and colonic tissues, respectively. Improved activity was likely due to a longer pre-incubation with basolateral drug. To better estimate the amount needed for protection, RPV was quantified from ectocervical and colonic explant tissues treated basolaterally and significant inverse linear correlations (P < 0.001) with culture p24 were obtained. An Emax model showed RPV concentrations of >273 nM in ectocervical and >27.3 nM in colonic tissues were associated with HIV inhibition.
Our data show that RPV can suppress HIV infection in mucosal tissue, but higher levels of RPV are needed in female genital tissue than gastrointestinal tissue for protection. Based on our findings, rectal tissue RPV concentrations reached in clinical trials appears to be sufficient to block HIV infection, but at least 2-fold more drug is needed in female genital tissue to demonstrate similar inhibition. These data suggest targeted use of RPV for HIV prevention may be warranted