As in Humans, Pregnancy Increases the Clearance of the Protease Inhibitor Nelfinavir in the Nonhuman Primate Macaca nemestrina

Protease inhibitors (PIs) are a class of antiretroviral agents that inhibit protease activity of HIV, thus preventing the postintegration step in HIV replication. For the treatment of the HIV-infected pregnant women and to prevent mother-to-infant HIV transmission, current antiretroviral guidelines recommend triple combination highly active antiretroviral therapy (Centers for Disease Control and Prevention, 1998). Because of its safety, tolerability, and potency, nelfinavir (NFV), together with nucleoside/non-nucleoside reverse transcriptase inhibitors, is the recommended treatment for pregnant women infected with HIV (Mofenson, 2003; Thorne and Newell, 2004). HIV PIs, among several other classes of drugs, have altered pharmacokinetics during pregnancy (Anderson 2005). Several studies have shown that given the standard dosing regimen, pregnant women achieve lower PI plasma concentrations than nonpregnant women. For example, we have observed that the exposure of antepartum women to indinavir is 68% lower than during the postpartum period (Unadkat et al., 2007). In addition, pregnant women taking saquinavir have approximately 77% lower exposure [area under the curve (AUC)] to the drug than nonpregnant women (Acosta et al., 2001). Likewise, the antepartum exposure to NFV is ∼25% lower in pregnant versus postpartum women (Angel et al., 2001; Nellen et al., 2004; van Heeswijk et al., 2004). Likewise, steady-state plasma concentrations and exposure to ritonavir are ∼40% lower in pregnant versus postpartum women (Acosta et al., 2004). These low plasma concentrations of PIs are of significant clinical concern because they are strongly associated with increased risk of virological failure and may result in transmission of resistant virus to the offspring (Angel et al., 2001; Burger et al., 2003). Because NFV and other protease inhibitors are cleared predominantly by CYP3A metabolism and the drug efflux transporter P-glycoprotein (P-gp) (Kim et al., 1998; Unadkat and Wang, 2000; Zhang et al., 2001), we have speculated that this decreased exposure to PIs during pregnancy is due to increased CYP3A or P-gp activity or both. To test this hypothesis, we replicated this phenomenon in the pregnant mouse. We found that this decreased exposure to PI during pregnancy could be attributed to a significant decrease in the bioavailability of NFV (Mathias et al., 2006). In addition, we found that the hepatic expression and activity of Cyp3a enzymes are significantly higher in pregnant mice than that in nonpregnant mice, whereas hepatic and intestinal P-glycoprotein expression are unaffected (Mathias et al., 2006; Zhang et al., 2008). However, determining the mechanistic basis for this change is difficult because there are at least six Cyp3a isoforms and two P-gp isoforms present in the mouse, and these isoforms have been shown to be differentially regulated (Anakk et al., 2004; Zhang et al., 2008). In addition, specific antibody or purified protein of each of these P450 isoforms are not available. To determine whether the phenomenon of decreased exposure to PIs during pregnancy could be replicated in an alternative animal model that is genetically and physiologically closer to humans, we studied the pregnant nonhuman primate, Macaca nemestrina. To be specific, we used NFV as a model PI to determine whether 1) pregnancy-related changes in exposure to oral NFV, observed in pregnant women, could be replicated in the macaque; 2) the systemic clearance and bioavailability of NFV are altered during pregnancy; and 3) pregnancy accelerates in vitro metabolism of NFV in hepatic and proximal small intestine S-9 fractions.