P-Glycoprotein and transporter MRP1 reduce HIV protease inhibitor uptake in CD4 cells: potential for accelerated viral drug resistance?

Intracellular Indinavir Pharmacokinetics in HIV-Infected Patients: Comparison with Plasma Pharmacokinetics

Objective

To determine intracellular concentrations of indinavir (IDV) and investigate the relationship between plasma and intracellular IDV pharmacokinetics in HIV-infected patients.

Methods

A pharmacokinetic study of 10 patients receiving IDV plus dual nucleoside analogue therapy. Peripheral blood mononuclear cells were isolated by density gradient centrifugation and cell counts estimated. IDV was extracted from cells in the presence of 60% methanol and evaporated to dryness. Both plasma and intracellular IDV samples were assayed by high performance liquid chromatography linked to mass spectrometry. Data were subjected to non-compartmental pharmacokinetic analysis.

Results

The mean intracellular IDV area under the curve over 8 h (AUC0-8) was lower than the plasma AUC0-8 (7574 ±1003 vs 25060 ±4171 ng/ml/h; P<0.004). However, both the elimination half-life (t1/2) and the mean residence time (MRT) of IDV intracellularly were prolonged compared with plasma (t1/2: 2.0 ±0.3 vs 1.2 ±0.09 h; MRT: 3.6 ±0.6 vs 2.1 ±0.1 h; P<0.05). All patients were responsive to therapy at the time of the study, as assessed by HIV plasma RNA levels. Individual plasma versus intracellular time course results suggest that, due to the prolonged intracellular half-life, some patients may achieve acceptable intracellular IDV concentrations despite sub-therapeutic plasma levels. Similarly, potentially inadequate intracellular concentrations may occur despite therapeutic plasma concentrations.

Conclusions

There is no significant intracellular accumulation of IDV within the lymphocytes of HIV-1-infected patients relative to plasma. However, intracellular concentrations are compatible with reported IDV-free drug concentrations in plasma. The intracellular elimination half-life and mean residence time of IDV are significantly prolonged compared with plasma. This may in part explain why certain patients maintain adequate viral suppression despite sub-therapeutic plasma IDV levels.

Influence of polymorphisms within the CX3CR1 and MDR-1 genes on initial antiretroviral therapy response

OBJECTIVE

Single nucleotide polymorphisms (SNP) in the genes encoding the human CX3CR1 chemokine receptor and the P-glycoprotein multidrug transporter have been associated with accelerated disease progression in untreated individuals and implicated in therapeutic response, respectively. This retrospective study assessed the influence of SNP in the CX3CR1 and MDR-1 genes on initial virological and immunological response in 461 HIV-infected, antiretroviral-naive individuals initiating antiretroviral therapy in British Columbia, Canada.

METHODS

CX3CR1 and MDR-1 SNP were determined by PCR amplification of human DNA from plasma, followed by DNA sequencing. Time to virological success [time to HIV plasma viral load (pVL) < or = 500 copies/ml], virological failure (subsequent time to the second of two consecutive pVL > or = 500) and immunological failure (time to the second consecutive CD4 cell count below baseline) were analyzed by Kaplan-Meier methods.

RESULTS

Frequencies of CX3CR1 amino acid haplotypes were 249V 280T (0.75), 249I 280M (0.15), and 249I 280T (0.1). Frequencies of MDR-1 nucleotide polymorphisms were 3435C (0.47) and 3435T (0.53). There was no effect detected for SNP in CX3CR1 or MDR-1 on time to virological success, nor of CX3CR1 and MDR-1 SNP on time to virological and immunological failure, respectively ( P > 0.1). There was a trend to earlier virological failure in the MDR-1 3435C/C genotype group ( P = 0.07), and a statistically significant trend to earlier immunological failure in individuals with the CX3CR1 249I polymorphism ( P = 0.02). These remained significant after correcting for baseline age, sex, pVL, CD4 cell count, type of therapy, and adherence ( P < or = 0.05).

CONCLUSION

Polymorphisms in MDR-1 and CX3CR1 may be associated with accelerated virological and immunological therapy failure, respectively.

Multidrug resistance protein 2 (MRP2) transports HIV protease inhibitors, and transport can be enhanced by other drugs

BACKGROUND

Various drug transporters of the ATP-binding cassette (ABC) family restrict the oral bioavailability and cellular, brain, testis, cerebrospinal fluid and fetal penetration of substrate drugs. MDRI P-glycoprotein (P-gp) has been demonstrated to transport most HIV protease inhibitors (HPI) and to reduce their oral bioavailability and lymphocyte, brain, testis and fetal penetration, possibly resulting in major limiting effects on the therapeutic efficacy of these drugs.

OBJECTIVES

To investigate whether the ABC transporters MRP1, MRP2, MRP3, MRP5 and breast cancer resistance protein 1 (Bcrp1) are efficient transporters of the HPI saquinavir, ritonavir and indinavir.

METHODS

Polarized epithelial non-human (canine) cell lines transduced with human or murine complementary DNA (cDNA) for each of the transporters were used to study transepithelial transport of the HPI.

RESULTS

MRP2 efficiently transported saquinavir, ritonavir and indinavir and this transport could be enhanced by probenecid. Sulfinpyrazone was also able to enhance MRP2-mediated saquinavir transport. In contrast, MRP1, MRP3, MRP5, or Bcrp1 did not efficiently transport the HPI tested.

CONCLUSIONS

Human MRP2 actively transports several HPI and could, based on its known and assumed tissue distribution, therefore reduce HPI oral bioavailability. It may also limit brain and fetal penetration of these drugs and increase their hepatobiliary, intestinal and renal clearance. MRP2 function and enhancement of its activity could adversely affect the therapeutic efficacy, including the pharmacological sanctuary penetration, of HPI. In vivo inhibition of MRP2 function might, therefore, improve HIV/AIDS therapy.

Direct evidence that saquinavir is transported by multidrug resistance-associated protein (MRP1) and canalicular multispecific organic anion transporter (MRP2)

To determine if saquinavir mesylate (saquinavir) is a substrate of human multidrug resistance-associated protein 1 (hMRP1 [ABCC1]) or hMRP2 (cMOAT, or ABCC2), MDCKII cells that overexpress either hMRP1 (MDCKII-MRP1) or hMRP2 (MDCKII-MRP2) were used to investigate saquinavir's cytotoxicity and transport in comparison with those of control MDCKII wild-type (MDCKII/wt) cells. Cytotoxicity was assessed with the mitochondrial marker MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium], and saquinavir transport was measured directly through the cell monolayers. GF120918 (an inhibitor of P glycoprotein, but not of the MRP family) and MK-571 (an MRP family inhibitor) were used to delineate the specific contributions of these transporters to saquinavir cytotoxicity and transport. In the presence of GF120918 and increasing saquinavir concentrations, the MDCKII-MRP1 (50% lethal dose [LD(50)] = 10.5 micro M) and MDCKII-MRP2 (LD(50) = 27.1 micro M) cell lines exhibited statistically greater viability than the MDCKII/wt cells (LD(50) = 7.8 micro M). Saquinavir efflux was directional, not saturable, and was inhibited by MK-571 (35 and 75 micro M) in all cell lines. The ratios of saquinavir (3 micro M) basolateral to apical permeability (i.e., efflux ratios) for the MDCKII/wt, MDCKII-MRP1, and MDCKII-MRP2 cell monolayers were 2.6, 1.8, and 6.8, respectively. The MDCKII-MRP1 cells have a significantly reduced saquinavir efflux ratio relative to MDCKII/wt cells, due to basolaterally directed transport by hMRP1 competing with endogenous, apically directed canine MRP2. The MDCKII-MRP2 cells have a significantly increased saquinavir efflux ratio relative to MDCKII/wt cells, due to the additive effects of the apically directed transport by hMRP2 and endogenous MRP2. Collectively, the cytotoxicity and transport results provide direct evidence that saquinavir is transported by MRP1 and MRP2.

Intracellular concentration of protease inhibitors in HIV-1-infected patients: correlation with MDR-1 gene expression and low dose of ritonavir

BACKGROUND

Protease inhibitors (PIs) are substrates for the P-glycoprotein (P-gp/170) encoded by the multi-drug resistance gene (MDR-1). HIV infection is associated with increased expression of P-gp. The role of MDR gene overexpression in clinical pharmacokinetics is not known.

METHOD

We determined by HPLC, at trough and peak levels, the current PI concentrations in plasma (P) and in peripheral blood mononuclear cells (PBMCs) (intracellular concentration [IC]) from 49 HIV-infected patients receiving different treatment combinations: nelfinavir ([NFV] n = 12); indinavir ([IDV] n = 10); amprenavir ([APV] n = 5); ritonavir (RTV) 100 bid/IDV 800 mg bid (n = 6); RTV 400 bid/IDV 400 mg bid (n = 3); RTV 100 bid/saquinavir (SQV) 600 mg tid (n = 9); APV 600 bid/RTV 100 mg bid (n = 4). We determined the mean ratio of intracellular/plasma PI concentration for each treatment group. The MDR-1 gene expression was determined by a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). HIV viral load was simultaneously measured.

RESULTS

49 patients (mean age 41 +/- 8.7 years; mean CD4 cell count 418 [57-972]; mean HIV RNA 2.1 +/- 0.8 log(10)) were included in the study. Patients who overexpressed the MDR-1 gene had significantly lower trough intracellular PI levels (p =.02) or lower intracellular accumulation of PI (p =.042). Patients treated with low-dose RTV in combined regimens with detectable RTV intracellular concentration showed lack of MDR-1 gene expression (p =.01). Patients with HIV RNA < 40 copies/mL had significantly higher RTV intracellular accumulation (p =.029).

CONCLUSION

In HIV-infected patients, IC of PI is inversely correlated with MDR-1 gene overexpression. Undetectable viral load was associated with the use of low-dose RTV, probably linked to better intracellular accumulation of the drug. Nevertheless, further investigation is needed to confirm these results.

Intracellular accumulation of human immunodeficiency virus protease inhibitors

Intracellular accumulation of the protease inhibitors (PIs) saquinavir (SQV), ritonavir (RTV), and indinavir (IDV) was determined in 50 human immunodeficiency virus-positive patients. Following extraction, PIs were quantified by mass spectrometry. Paired plasma and intracellular samples were collected over a full dosing interval from patients (13 on SQV, 6 on RTV, 8 on IDV, 16 on SQV plus RTV, 7 on IDV plus RTV) with a plasma viral load of <400 copies/ml. Data were expressed as intracellular/plasma drug concentration ratios. A hierarchy of intracellular accumulation was demonstrated by the following medians: 9.45 for SQV > 1.00 for RTV > 0.51 for IDV. Coadministration of RTV did not boost ratios of SQV or IDV within the cell or in plasma, although absolute plasma and intracellular SQV concentrations were increased by RTV. Seven individuals receiving SQV in hard-gel capsule form (median, 32 months) had higher intracellular/plasma drug ratios than all other patients receiving SQV (median, 17.62 versus 4.83; P = 0.04), despite consistently low plasma SQV concentrations. How this occurs may provide insight into the mechanisms that limit adequate drug penetration into sanctuary sites.

No association between GB virus-C viremia and virological or immunological failure after starting initial antiretroviral therapy

INTRODUCTION

Co-infection with GBV-C ('Hepatitis G' virus) appears to be associated with slower disease progression in HIV-infected, untreated individuals. We wished to determine whether detection of GBV-C RNA was associated with differential response to HIV therapy in a population-based cohort of 461 individuals initiating antiretroviral therapy between June 1996 and August 1998, in British Columbia, Canada.

METHODS

The presence of GBV-C RNA in plasma was identified by nested RT-PCR, using detection of HIV RNA as a positive control. Time to virological success [achieving HIV plasma viral load (pVL) < or = 500 copies/ml], virological failure (subsequent confirmed pVL > 500 copies/ml) and immunological failure (confirmed CD4 cell count below baseline) were assessed by Kaplan-Meier methods and Cox proportional hazard regression.

RESULTS

Of the 441 individuals for whom results were available, 90 (20.4%) had detectable plasma GBV-C RNA. GBV-C RNA was significantly associated with a lower HIV pVL at baseline (P = 0.004). In univariate and multivariate Cox models, GBV-C RNA positive and negative individuals did not differ with respect to time to virological success [risk ratio (RR), 0.98; 95% confidence interval (CI), 0.75-1.27], time to virological failure (RR, 1.10; 95% CI, 0.74-1.65), or time to immunological failure (RR, 1.09; 95% CI, 0.73-1.63). There was no correlation between detection of GBV-C RNA and mutations in the human chemokine receptors CCR5 and CX CR1, or HIV viral tropism as predicted by the HIV envelope sequence (P > 0.1).

CONCLUSION

GBV-C viremia is relatively common in individuals seeking treatment for HIV infection; however, it does not appear to have any effect on initial antiretroviral therapy response.

The protease inhibitor ritonavir inhibits the functional activity of the multidrug resistance related-protein 1 (MRP-1)

BACKGROUND

Efflux pumps situated on the plasma membrane, such as P-glycoprotein (Pgp) and the multidrug resistance related-protein 1 (MRP-1), have been shown to extrude HIV protease inhibitors from the cell. MRP-1 is present on many barrier sites throughout the body, such as the blood-brain and blood-testis interfaces and could reduce the concentration of protease inhibitors in these sanctuary sites for HIV-1 replication. Factors that modulate efflux pump function in vivo are poorly defined.

OBJECTIVE

To analyze the inhibitory potential of the anti-retroviral drugs indinavir, amprenavir, ritonavir, lamivudine or zidovudine to modulate MRP-1 function.

METHODS

Effect of anti-HIV drugs on the efflux pump activity of MRP-1 was evaluated in the presence of increasing concentrations of human plasma, using UMCC-1/VP cells which stably over-express MRP-1. MRP-1 activity was abrogated by probenecid. The potential of blocking MRP-1 function for an extended (3 day) time period, was also examined in MRP-1 over-expressing cells cultured with either probenecid or the anti-retroviral drugs and a cytotoxic compound (etoposide) that is transported by MRP-1.

RESULTS

Ritonavir inhibited the functional activity of MRP-1 similarly to probenecid, as demonstrated by re-sensitization of MRP-1 over-expressing cells to cytotoxic effects of etoposide. Inhibition by ritonavir was inversely related to the concentration of human plasma added to the cells (r2 = 0.89). Other anti-HIV drugs didn't affect the MRP-1 mediated efflux of etoposide.

CONCLUSIONS

These data may be exploitable to further improve sanctuary site concentrations of anti-HIV or anti-cancer drugs by using ritonavir as a lead compound to develop more potent MRP-1 inhibitors.

Nelfinavir, a protease inhibitor, increases sirolimus levels in a liver transplantation patient: a case report

With the increasing success of liver transplantation and the proven effectiveness of highly active retroviral therapy in HIV-positive patients, liver transplantation has been performed successfully in selected HIV-positive recipients with CD4 and an HIV viral load response to highly active antiretroviral therapy. In these patients, an interaction between a protease inhibitor (nelfinavir) and tacrolimus has been shown. The effect of nelfinavir on the pharmacokinetics of sirolimus, a newer immunosuppressive drug, is currently not known. The goal of the present case report is to document the interaction between sirolimus and nelfinavir in a liver transplantation patient. A 40-year-old woman who was HIV positive underwent a cadaveric liver transplantation for acute fulminant liver failure secondary to nevirapine (a nonnucleoside reverse transcriptase inhibitor). Postoperatively, she was treated with tacrolimus and steroids. She experienced steroid-resistant rejection and was started on sirolimus on the 17th postoperative day. Kinetic parameters were determined after a 2-mg oral dose of sirolimus and 250 mg of nelfinavir by collecting multiple peripheral venous blood samples before and after sirolimus administration. The kinetic parameters were compared with parameters from three liver transplantation patients on sirolimus who were not on nelfinavir. After normalizing the kinetic parameters to sirolimus dose of 1 mg/d, 0-hour and 24-hour trough sirolimus concentrations were nine-fold and five-fold higher for the patient who was on nelfinavir, compared with those who were not on nelfinavir. The maximum concentration was 3.2 times higher, the area under the concentration curve was 1.6 times higher, and the terminal disposition half-life was prolonged by 60%. The time to reach the peak concentration was 1 hour in all patients. Increase in trough concentration, peak concentration area under the curve concentration, and prolongation of half-life of sirolimus has been shown in a patient who was on a low dose (one fifth the recommended dose) of nelfinavir.

Human immunodeficiency virus infection unresponsive to highly active antiretroviral therapy: denial of poor medication adherence or recalcitrant infection?

Poor clinical and virologic response to combination antiretroviral therapy for human immunodeficiency virus (HIV) infection may stem from a variety of factors including poor medication adherence, development of drug-resistant HIV strains, drug interactions, efflux pumps, and unfavorable pharmacokinetics. Diagnosing nonadherence to medication is particularly challenging. We present a case of lack of response to antiretroviral therapy in a patient who denied problems with medication adherence. The patient underwent a variety of objective examinations, all of which suggested poor medication adherence was responsible for his nonresponse to antiretrovirals. An approach to evaluating patients for causes of poor response to antiretroviral therapy and nonadherence and implications for clinical practice are discussed.

In vitro antiviral interaction of lopinavir with other protease inhibitors

The in vitro inhibition of wild-type human immunodeficiency virus (HIV) by combinations of lopinavir and six other protease inhibitors over a range of two-drug combination ratios was evaluated. Combinations of lopinavir with indinavir, nelfinavir, amprenavir, tipranavir, and BMS-232632 generally displayed an additive relationship. In contrast, a consistent, statistically significant synergistic inhibition of HIV type 1 replication with combinations of lopinavir and saquinavir was observed. Analysis of the combination indices indicated that lopinavir with saquinavir was synergistic over the entire range of drug combination ratios tested and at all levels of inhibition in excess of 40%. Cellular toxicity was not observed at the highest drug concentrations tested. These results suggest that administration of combinations of the appropriate dose of lopinavir with other protease inhibitors in vivo may result in enhanced antiviral activity with no associated increase in cellular cytotoxicity. More importantly, the observed in vitro synergy between lopinavir and saquinavir provides a theoretical basis for the clinical exploration of a novel regimen of lopinavir-ritonavir and saquinavir.

Intracellular pharmacology of nucleoside analogues and protease inhibitors: role of transporter molecules

Antiretroviral agents target HIV replication within infected cells. It is therefore important to focus on the pharmacology of these drugs at their site of action rather than just in plasma. Activation of nucleoside analogues to a triphosphate is essential for antiretroviral activity. Following activation, by intracellular kinases, drug triphosphates compete with endogenous triphosphates for HIV reverse transcriptase. Methodologies to measure triphosphates in peripheral blood mononuclear cells from HIV patients have been described. This has allowed investigation of once-daily dosing regimens, drug interactions, modulation of intracellular activation and the bypassing of initial phosphorylation steps. Drug accumulation within a cell is a balance between influx and efflux. There is a growing body of evidence indicating that transport proteins are vitally important in regulating intracellular concentrations of antiretroviral drugs. Allelic variants, inhibition (or induction) are all potentially critical determinants of active drug present in the cell. It is hoped that understanding the intracellular pharmacology will improve long-term therapy and reduce the likelihood of cellular resistance in therapeutic failure.