The HIV protease inhibitors nelfinavir and saquinavir, but not a variety of HIV reverse transcriptase inhibitors, adversely affect human proteasome function

BACKGROUND

In HIV-infected patients some clinical and immunological benefits of antiretroviral therapy, which frequently include a combination of HIV protease inhibitors (PIs) and reverse transcriptase inhibitors (RTIs), cannot be solely explained by the drugs' action on viral enzymes. Proteasomes constitute the central protease of the ubiquitin ATP-dependent pathway involved in many cellular processes, as well as in HIV maturation and aggressiveness.

OBJECTIVE

To explore whether the PIs nelfinavir and saquinavir and the RTIs abacavir, nevirapine, delavirdine, stavudine and didanosine affect proteasome function in vitro and in vivo.

METHODS

Peptidase activity of purified human 26S and 20S proteasomes was assayed with and without the drugs at different concentrations. Intracellular proteasome proteolytic activity was evaluated by searching for ubiquitin-tagged proteins in HL60 cells incubated with and without the drugs.

RESULTS

At therapeutic dosages, nelfinavir and saquinavir inhibited proteasome peptidase activity and caused intracellular accumulation of polyubiquitinated proteins, a hallmark of proteasome proteolytic inhibition in vivo; the RTIs failed to evoke either effect.

CONCLUSION

Proteasomes are targeted by the two PIs but not the RTIs. Therefore, in HIV-infected patients the beneficial effect of a therapy including one of the two PIs should partly rely on inhibition of host proteasome function.

Altered adipokine response in murine 3T3-F442A adipocytes treated with protease inhibitors and nucleoside reverse transcriptase inhibitors

BACKGROUND

Abnormal levels of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and adiponectin have been observed in HIV patients with lipodystrophy. However, because these patients have long drug and disease histories, it is unclear which drugs are responsible for these abnormalities. We have therefore investigated the effects of individual antiretrovirals on adipokine expression and adipogenesis using a murine cell line in vitro.

METHODS

Differentiating murine 3T3-F442A adipocytes were incubated with 20 microM nucleoside reverse transcriptase inhibitors (NRTIs) zidovudine or stavudine, or protease inhibitors (PIs) indinavir, ritonavir, saquinavir or nelfinavir, in the presence and absence of rosiglitazone (10 microM). Adipogenesis was assessed using glycerol-3-phosphate dehydrogenase activity, while expression of TNF-alpha, IL-6 and adiponectin at protein and mRNA levels was assessed by ELISA and quantitative real-time PCR, respectively.

RESULTS

Nelfinavir, ritonavir and saquinavir inhibited adipogenesis and up-regulated the expression of TNF-alpha and IL-6, but this effect was not seen with indinavir, zidovudine and stavudine. Adiponectin expression was significantly reduced in both NRTI- and PI-treated cells, although the most profound reductions were found with ritonavir and saquinavir. Co-incubation with rosiglitazone led to a partial attenuation of the change in TNF-alpha, IL-6 and adiponectin secretion.

CONCLUSIONS

Our data suggest that the PIs nelfinavir, ritonavir and saquinavir have potent effects in inhibiting adipocyte differentiation whilst up-regulating TNF-alpha and IL-6 mRNA levels and decreasing adiponectin levels. These changes were partially attenuated by rosiglitazone. Taken together, the data show that antiretrovirals have complex effects on adipocyte function, which may be mediated by an altered adipokine response.

Potential for interactions between caspofungin and nelfinavir or rifampin

The potential for interactions between caspofungin and nelfinavir or rifampin was evaluated in two parallel-panel studies. In study A, healthy subjects received a 14-day course of caspofungin alone (50 mg administered intravenously [IV] once daily) (n = 10) or with nelfinavir (1,250 mg administered orally twice daily) (n = 9) or rifampin (600 mg administered orally once daily) (n = 10). In study B, 14 subjects received a 28-day course of rifampin (600 mg administered orally once daily), with caspofungin (50 mg administered IV once daily) coadministered on the last 14 days, and 12 subjects received a 14-day course of caspofungin alone (50 mg administered IV once daily). The coadministration/administration alone geometric mean ratio for the caspofungin area under the time-concentration profile calculated for the 24-h period following dosing [AUC(0-24)] was as follows (values in parentheses are 90% confidence intervals [CIs]): 1.08 (0.93-1.26) for nelfinavir, 1.12 (0.97-1.30) for rifampin (study A), and 1.01 (0.91-1.11) for rifampin (study B). The shape of the caspofungin plasma profile was altered by rifampin, resulting in a 14 to 31% reduction in the trough concentration at 24 h after dosing (C(24h)), consistent with a net induction effect at steady state. Both the AUC and the C(24h) were elevated in the initial days of rifampin coadministration in study A (61 and 170% elevations, respectively, on day 1) but not in study B, consistent with transient net inhibition prior to full induction. The coadministration/administration alone geometric mean ratio for the rifampin AUC(0-24) on day 14 was 1.07 (90% CI, 0.83-1.38). Nelfinavir does not meaningfully alter caspofungin pharmacokinetics. Rifampin both inhibits and induces caspofungin disposition, resulting in a reduced C(24h) at steady state. An increase in the caspofungin dose to 70 mg, administered daily, should be considered when the drug is coadministered with rifampin.

Long-term effects of HIV-1 protease inhibitors on insulin secretion and insulin signaling in INS-1 beta cells

The mechanism by which chronic treatment with HIV (human immunodeficiency virus)-1 protease inhibitors leads to a deterioration of glucose metabolism appears to involve insulin resistance, and may also involve impaired insulin secretion. Here we investigated the long-term effects of HIV-1 protease inhibitors on glucose-stimulated insulin secretion from beta cells and explored whether altered insulin secretion might be related to altered insulin signaling. INS-1 cells were incubated for 48 h with different concentrations of amprenavir, indinavir, nelfinavir, ritonavir or saquinavir, stimulated with 20 mM d-glucose, and insulin determined in the supernatant. To evaluate insulin signaling, cells were stimulated with 100 nM insulin for 2 min, and insulin-receptor substrate (IRS)-1, -2 and Akt phosphorylation determined. Incubation for 48 h with ritonavir, nelfinavir and saquinavir resulted in impaired glucose-induced insulin secretion at 2.5, 5 and 5 microM respectively, whereas amprenavir or indinavir had no effects even at 20 and 100 microM respectively. The impaired insulin secretion by ritonavir, nelfinavir and saquinavir was associated with decreased insulin-stimulated IRS-2 phosphorylation, and, for nelfinavir and saquinavir, with decreased insulin-stimulated IRS-1 and Thr308-Akt phosphorylation. No such effects on signaling were observed with amprenavir or indinavir. In conclusion, certain HIV-1 protease inhibitors, such as ritonavir, nelfinavir and saquinavir, not only induce peripheral insulin resistance, but also impair glucose-stimulated insulin secretion from beta cells. With respect to the long-term effect on beta-cell function there appear to be differences between the protease inhibitors that may be clinically relevant. Finally, these effects on insulin secretion after a 48 h incubation with protease inhibitor were associated with a reduction of the insulin-stimulated phosphorylation of insulin signaling parameters, particularly IRS-2, suggesting that protease inhibitor-induced alterations in the insulin signaling pathway may contribute to the impaired beta-cell function.

Nelfinavir Induces Necrosis of 3T3F44-2A Adipocytes by Oxidative Stress

Protease inhibitor treatment strongly diminishes mortality in HIV-infected patients. This treatment has also been associated with lipodystrophy and has been shown to alter adipocyte differentiation. The protease inhibitor nelfinavir has been indirectly implicated in the appearance and development of lipodystrophic syndrome, as well as in adipocyte cell death. The aim of this study was to evaluate the effects of nelfinavir on the 3T3-F442A adipocyte cell line. Nelfinavir (30 microM) induced cell death of 3T3-F442A adipocytes by a necrotic process that was not mediated by TNF-alpha. Treatment of cells with this protease inhibitor led to a significant increase in expression of the heme oxygenase-1 gene that could be reduced by 100 microM of the antioxidant ascorbate. Moreover, ascorbate had a protective effect on nelfinavir-induced necrosis, decreasing the percentage of necrotic cells by 70%. Our results show that nelfinavir induces necrosis of adipocytes mediated by a cellular increase of reactive oxygen species. This deleterious effect could be counterbalanced by ascorbate.

[Development of microchips for the detection of mutations of HIV-1 variability to protease inhibitors and the usage results]

An original biochip was constructed for the detection of 34 mutations of HIV-1 resistance to protease. A technology was worked out, which is based on the hybridization of a fluorescence-labeled amplified fragment of the pol gene of the HIV-1 provirus DNA with a set of specific oligonucleotides immobilized in 3-D hydrogel pads of the biological microchip. The biochip was used to analyze 115 samples of the subtype-1 provirus HIV-1 DNA isolated from untreated IDUs and their sexual partners in 15 regions of former USSR countries. Substitution of Val/IIe in position 77 of protease (V771) is known as secondary mutation of resistance to Nelfinavir detected in 55 (47.8%) of 115 HIV-1 variations. Its first appearance was registered in a patient with HIV in April 1997 in Tver, where its carrying variant caused an HIV outbreak. It is demonstrated that the V771-substitution variant, that dominates in Moscow, caused outbreaks in Irkutsk and Yekaterinburg and spread into separate districts of Perm and Perm Region. At the same time, no V771 HIV-1 was detected in any of the HIV studied cases diagnosed before 1998 in Moldova, Ukraine and Rostov Region.

Alternative, age- and viral load-related routes of nelfinavir resistance in human immunodeficiency virus type 1-infected children receiving highly active antiretroviral therapy

To assess prevalence of nelfinavir resistance mutations in children receiving highly active antiretroviral therapy, sequencing of protease gene from plasma of 53 human immunodeficiency virus-infected children was performed. The prevalence of L90M was similar to that of D30N. There was a significant correlation with a higher viral load and lower age and the occurrence of L90M. These findings suggest differential molecular age- and viral load-related routes for nelfinavir resistance.

Impact of nelfinavir resistance mutations on in vitro phenotype, fitness, and replication capacity of human immunodeficiency virus type 1 with subtype B and C proteases

Human immunodeficiency virus type 1 subtype B and C proteases were manipulated to contain 90M, 88D, or 89L, and their in vitro biological properties were studied. We showed that D30N has significantly more impact in subtype C than in subtype B counterparts, accounting for the reported low prevalence of this mutation in patients failing nelfinavir-based regimens.

Peptidomimetic inhibitors of HIV protease

There are currently (July, 2002) six protease inhibitors approved for the treatment of HIV infection, each of which can be classified as peptidomimetic in structure. These agents, when used in combination with other antiretroviral agents, produce a sustained decrease in viral load, often to levels below the limits of quantifiable detection, and a significant reconstitution of the immune system. Therapeutic regimens containing one or more HIV protease inhibitors thus provide a highly effective method for disease management. The important role of protease inhibitors in HIV therapy, combined with numerous challenges remaining in HIV treatment, have resulted in a continued effort both to optimize regimens using the existing agents and to identify new protease inhibitors that may provide unique properties. This review will provide an overview of the discovery and clinical trials of the currently approved HIV protease inhibitors, followed by an examination of important aspects of therapy, such as pharmacokinetic enhancement, resistance and side effects. A description of new peptidomimetic compounds currently being investigated in the clinic and in preclinical discovery will follow.

[Impairment of IRS-2 signaling in rat insulinoma INS-1 cells by nelfinavir]

OBJECTIVE

To investigate whether HIV-1 protease inhibitor nelfinavir alters the insulin stimulated phosphorylation of insulin signaling parameters in rat insulinoma INS-1 cells.

METHODS

INS-1 cells were incubated with nelfinavir for 48 h and stimulated with 100 nmol/L insulin for 2 min. Immunoprecipitation and Western blot analysis of the insulin stimulated insulin receptor substrate (IRS)-1,-2 and Akt-Thr(308) phosphorylation were performed on cell lysates. Cytotoxic effects of nelfinavir were measured by cell count with trypan blue and MTT reduction test.

RESULT

Nelfinavir decreased insulin stimulated phosphorylation of IRS-2 and Akt-Thr(308) in a dose-dependent manner; for 10 micromol/L of nelfinavir, the decrease was 52% and 55%, respectively.

CONCLUSION

Treatment with nelfinavir might impair IRS-2-mediated signaling in pancreatic beta cells.

HIV protease inhibitor nelfinavir inhibits replication of SARS-associated coronavirus

A novel coronavirus has been identified as an etiological agent of severe acute respiratory syndrome (SARS). To rapidly identify anti-SARS drugs available for clinical use, we screened a set of compounds that included antiviral drugs already in wide use. Here we report that the HIV-1 protease inhibitor, nelfinavir, strongly inhibited replication of the SARS coronavirus (SARS-CoV). Nelfinavir inhibited the cytopathic effect induced by SARS-CoV infection. Expression of viral antigens was much lower in infected cells treated with nelfinavir than in untreated infected cells. Quantitative RT-PCR analysis showed that nelfinavir could decrease the production of virions from Vero cells. Experiments with various timings of drug addition revealed that nelfinavir exerted its effect not at the entry step, but at the post-entry step of SARS-CoV infection. Our results suggest that nelfinavir should be examined clinically for the treatment of SARS and has potential as a good lead compound for designing anti-SARS drugs.

Baseline HIV‐1 RNA Level and CD4 Cell Count Predict Time to Loss of Virologic Response to Nelfinavir, but Not Lopinavir/Ritonavir, in Antiretroviral Therapy–Naive Patients

Baseline CD4 cell counts and human immunodeficiency virus (HIV)-1 RNA levels have been shown to predict immunologic and virologic responses in HIV-infected patients receiving antiretroviral therapy. In our randomized, double-blind, comparative trial, 653 antiretroviral therapy-naive patients received lopinavir/ritonavir or nelfinavir, plus stavudine and lamivudine, for up to 96 weeks. The risk of loss of virologic response was significantly higher for nelfinavir-treated patients than for lopinavir/ritonavir-treated patients (Cox model hazard ratio, 2.2; 95% confidence interval, 1.7-3.0; P<.001). For nelfinavir-treated patients, but not for lopinavir/ritonavir-treated patients, higher baseline HIV-1 RNA levels and lower baseline CD4 cell counts were associated with a higher risk of loss of virologic response.

Mutation D30N is not preferentially selected by human immunodeficiency virus type 1 subtype C in the development of resistance to nelfinavir

Differences in baseline polymorphisms between subtypes may result in development of diverse mutational pathways during antiretroviral treatment. We compared drug resistance in patients with human immunodeficiency virus subtype C (referred to herein as "subtype-C-infected patients") versus subtype-B-infected patients following protease inhibitor (PI) therapy. Genotype, phenotype, and replication capacity (Phenosense; Virologic) were determined. We evaluated 159 subtype-C- and 65 subtype-B-infected patients failing first PI treatment. Following nelfinavir treatment, the unique nelfinavir mutation D30N was substantially less frequent in C (7%) than in B (23%; P = 0.03) while L90M was similar (P < 0.5). Significant differences were found in the rates of M36I (98 and 36%), L63P (35 and 59%), A71V (3 and 32%), V77I (0 and 36%), and I93L (91 and 32%) (0.0001 < P < 0.05) in C and B, respectively. Other mutations were L10I/V, K20R, M46I, V82A/I, I84V, N88D, and N88S. Subtype C samples with mutation D30N showed a 50% inhibitory concentration (IC(50)) change in susceptibility to nelfinavir only. Other mutations increased IC(50) correlates to all PIs. Following accumulation of mutations, replication capacity of the C virus was reduced from 43% +/- 22% to 22% +/- 15% (P = 0.04). We confirmed the selective nature of the D30N mutation in C, and the broader cross-resistance of other common protease inhibitor mutations. The rates at which these mutational pathways develop differ in C and subtype-B-infected patients failing therapy, possibly due to the differential impact of baseline polymorphisms. Because mutation D30N is not preferentially selected in nelfinavir-treated subtype-C-infected patients, as it is in those infected with subtype B, the consideration of using this drug initially to preserve future protease inhibitor options is less relevant for subtype-C-infected patients.

Direct interference of HIV protease inhibitors with pancreatic �-cell function

The aim of the present study was to evaluate whether HIV protease inhibitors directly interfere with stimulus-secretion coupling in pancreatic beta-cells. Insulin secretion was determined by a radioimmunoassay (RIA), cytosolic free Ca2+ concentration ([Ca2+]c) with the fluorescence dye fura-2 and whole-cell membrane currents with the patch-clamp technique. Glucose-induced insulin secretion was inhibited in a concentration-dependent manner by ritonavir and nelfinavir but not by indinavir. Ritonavir and nelfinavir lowered [Ca2+]c in the presence of a stimulatory glucose concentration whereas indinavir again had no effect. Ritonavir and nelfinavir completely inhibited the effect of tolbutamide, which normally increases [Ca2+]c by blocking KATP channels. This observation points to an action of both drugs on KATP channels or a step distal to these channels in stimulus-secretion coupling. Ritonavir was used to further evaluate the direct effects of HIV protease inhibitors on beta-cell ion channel currents. Unexpectedly, ritonavir inhibited neither the whole-cell KATP current nor the whole-cell L-type Ca2+ current. Tolbutamide almost completely suppressed the KATP current in the presence of ritonavir excluding that ritonavir alters the tolbutamide sensitivity of the KATP channel. Ritonavir increased the length and decreased the frequency of glucose-induced action potentials. This effect can be attributed to inhibition of voltage-dependent K+ currents. Intracellular stores seem not to be involved in the ritonavir-induced lowering of [Ca2+]c. In conclusion, different HIV protease inhibitors surprisingly reveal distinct effects on insulin secretion. Ritonavir inhibits insulin secretion by lowering [Ca2+]c but this effect is evidently independent of the opening of KATP channels or the closure of voltage-dependent Ca2+ channels, which are commonly considered to play a key role in stimulus-secretion coupling.

Persistence of mutations during replication of an HIV library containing combinations of selected protease mutations

It has been known that, in some cases, accumulation of specific mutations in HIV-1 protease leads to multi-protease inhibitor (PI) resistance. We examined the persistence of mutations detected in HIV-1 clinical isolates cross-resistant to the current PIs using an HIV-1 protease restricted library (HXB2 protease in an HIV-1(NL4-3) background) in the absence of protease inhibitors. The virus library contained combinations of 0-11 amino acid substitutions (4,096 possible combinations) in the protease-encoding region. We examined the frequency of each amino acid substitution in the library using a T cell line, MT-2. The frequency of the amino acid substitutions V82T/I and L90M decreased rapidly with a short half life (t(1/2) < 10 days). However, the mutations M36I, M46I and I84V were relatively persistent: t(1/2) = 34.2, 28.1 and 30.6 days, respectively. Other amino acid substitutions, i.e., L10I, I54V, L63P, A71V and V82A, were well retained (t(1/2) > 36 days). By contrast, the half lives (t(1/2)) of the D30N and N88D mutations associated with nelfinavir (NFV) resistance were only 7.2 and 1.8 days, respectively. These results indicate that this type of the HIV-1 protease restricted library is useful to evaluate the persistence of PI resistance-associated mutations in the absence of drug selective pressure.

Sex‐Based Differences in Saquinavir Pharmacology and Virologic Response in AIDS Clinical Trials Group Study 359

AIDS Clinical Trials Group study 359 was a controlled study of saquinavir with either ritonavir or nelfinavir, together with delavirdine, adefovir, or both, in indinavir-experienced persons. Saquinavir was common in all study arms, and the study investigated relationships among characteristics of patients, saquinavir area under the curve (AUC) and trough concentrations (C(min)), and virologic response. Concentrations of saquinavir were higher when it was combined with ritonavir than when it was combined with nelfinavir and were lower with adefovir-containing regimens. Females had higher AUC and C(min) values than did males. Higher saquinavir AUC and C(min) values were associated with a greater likelihood of human immunodeficiency virus (HIV) RNA levels </=500 copies/mL (P=.008) and were better predictors of response than was the saquinavir inhibitory quotient. Males had a lower probability of having HIV RNA levels </=500 copies/mL at week 16 than did females (28% vs. 42%; adjusted odds ratio, 0.43). In this study, a greater proportion of females had HIV RNA levels </=500 copies/mL than did males, which can be attributed to higher concentrations of saquinavir in females than in males.

HIV protease inhibitors are inhibitors but not substrates of the human breast cancer resistance protein (BCRP/ABCG2)

Breast cancer resistance protein (BCRP) is a recently discovered ATP-binding cassette drug transporter. Hence, the full spectrum of therapeutic agents that interact with BCRP remains to be elucidated. Because human immunodeficiency virus protease inhibitors (HPIs) are well known P-glycoprotein (P-gp) substrates, and there is an overlap in substrate specificity between P-gp and BCRP, this study was performed to investigate whether HPIs are substrates and/or inhibitors of BCRP. First, the effect of HPIs on BCRP efflux activity in human embryonic kidney (HEK) cells stably expressing wild-type BCRP (482R) and its two mutants (482T and 482G) was studied by measuring intracellular mitoxantrone fluorescence using flow cytometry. We found that ritonavir, saquinavir, and nelfinavir were effective inhibitors of wild-type BCRP (482R) with IC50 values of 19.5 +/- 0.8 microM, 19.5 +/- 7.6 microM, and 12.5 +/- 4.1 microM, respectively. Ritonavir, saquinavir, and nelfinavir inhibited 482T and 482G with IC50 values that were approximately 2 times greater than that for 482R. Indinavir and amprenavir had no significant inhibition on BCRP activity. Direct efflux of radiolabeled HPIs in HEK cells was measured to determine whether the HPIs are substrates of BCRP. None of the HPIs were found to be transported by BCRP. Together, ritonavir, saquinavir, nelfinavir, indinavir, and amprenavir are not substrates for BCRP. However, ritonavir, saquinavir, and nelfinavir are effective inhibitors of the transporter. These results suggest that BCRP may play an important role in drug-drug interactions involving coadministration of the HPIs with drugs that are substrates of the transporter.

Differential effect of HIV protease inhibitors on adipogenesis: intracellular ritonavir is not sufficient to inhibit differentiation

OBJECTIVES

Lipodystrophy is a major side effect of HIV protease inhibitor (PI) antiretroviral therapy. It has been shown that protease inhibitors interfere in vitro with adipocyte differentiation. However, there is no evidence that PIs accumulate into preadipocytes and adipocytes and that intra-cellular accumulation is sufficient to alter differentiation. We assessed the effect of six different PIs on the differentiation of cells from four clonal lines. We also studied the capacity of ritonavir to accumulate both into drug-sensitive and drug-resistant cultured adipocytes.

METHODS

Adipocyte differentiation of mouse 3T3-F442A, 3T3-L1 and Ob1771 cells as well as embryonic stem cells were investigated at pharmacological concentrations of indinavir, saquinavir, ritonavir, amprenavir, nelfinavir and lopinavir. We used a sensitive ELISA to determine intracellular concentration of ritonavir from 3T3-L1 and Ob1771 preadipocytes.

RESULTS

Nelfinavir and lopinavir inhibited adipocyte differentiation whereas amprenavir was ineffective. Indinavir, saquinavir and ritonavir inhibited differentiation of 3T3-L1 and 3T3-F442A cells but did not alter differentiation of either Ob1771 or embryonic stem cells. We showed that ritonavir accumulated in preadipocytes and fully differentiated 3T3-L1 adipocytes as a function of its extracellular concentration. Although Ob1771 cells were resistant and 3T3-L1 cells were sensitive to ritonavir, the drug accumulated to similar levels in both cases.

CONCLUSIONS

Protease inhibitors inhibit adipocyte differentiation depending on the cell model used. We showed for the first time that ritonavir accumulates into preadipocytes and adipocytes, suggesting a direct effect on intracellular targets. However, intracellular accumulation was clearly not sufficient as Ob1771 cells remained resistant to the inhibitory effect of ritonavir.

Prodrugs of HIV protease inhibitors—saquinavir, indinavir and nelfinavir—derived from diglycerides or amino acids: synthesis, stability and anti-HIV activity

With the aim of improving the pharmacological properties of current protease inhibitors (PIs), the synthesis of various acyl and carbamate amino acid- or diglyceride-containing prodrugs derived from saquinavir, indinavir and nelfinavir, their in vitro stability with respect to hydrolysis and their anti-HIV activity in CEM-SS and MT4 cells have been investigated. l-Leucine (Leu) and l-phenylalanine (Phe) were connected through their carboxyl to the PIs while l-tyrosine (Tyr) was conjugated through its aromatic hydroxyl via various spacer units. Hydrolysis of the prodrug with liberation of the active free drug was crucial for antiviral activity. The Leu- and Phe-PI prodrugs released the active free drug very rapidly (half-lives of hydrolysis in buffer at 37 degree C of 3-4 h). The Tyr-PI conjugates with a -C(O)(CH(2))(4)- linker exhibited half-lives in the 40-70 h range and antiviral activities in the 21-325 nM range (from 2 to 22 nM for the free PIs). The chemically very stable carbamate "peptidomimetic" Tyr-PI prodrugs (no hydrolysis detected after 7 days in buffer) displayed a very low anti-HIV activity or were even inactive (EC(50) from 2300 nM to >10 microM). A very low antiviral activity was measured for the diglyceride-substituted saquinavir and for all of the disubstituted indinavir and nelfinavir prodrugs. All these prodrugs probably released the active parent PI too slowly under the antiviral assay conditions. These results combined with those from transepithelial transport studies (Rouquayrol et al., Pharm. Res., 2002, 19, 1704-1712) indicate that conjugation of amino acids (through their carboxyl) to the PIs constitutes a most appealing alternative which could improve the intestinal absorption of the PIs and reduce their recognition by efflux carriers.

HIV envelope gp120-mediated regulation of osteoclastogenesis via receptor activator of nuclear factor kappa B ligand (RANKL) secretion and its modulation by certain HIV protease inhibitors through interferon-gamma/RANKL cross-talk

Accelerated bone resorption leading to osteopenia and osteoporosis has been noted in human immunodeficiency virus (HIV) seropositive, treatment-naive patients, but it may be greatly increased in incidence in those receiving highly active anti-retroviral therapies that incorporate certain protease inhibitors (PI). The pathophysiology of these processes is unclear. We have documented the induction of the primary cytokine responsible for osteoclast differentiation and bone resorption, the receptor activator of nuclear factor kappa B ligand (RANKL), in T cells exposed to soluble HIV-1 envelope glycoprotein gp120. Using a murine osteoclast precursor cell line as well as primary human osteoclast precursors, we demonstrate that pharmacologic levels of two PIs that are linked clinically to osteopenia, ritonavir and saquinavir, abrogate a physiological block to RANKL activity, interferon-gamma-mediated degradation of the RANKL signaling adapter protein, TRAF6 (tumor necrosis factor receptor-associated protein 6) in proteasomes. In contrast, indinavir and nelfinavir, PIs that may promote or stabilize bone formation in vivo, had no impact on this system. These findings offer a molecular basis for the acceleration of bone resorption by certain PIs and provide the first example of clinically useful drugs that can interfere with the cross-talk between RANKL and interferon-gamma via the proteasome. They also suggest a novel therapeutic approach to HIV osteopenia through modulation of these two molecules.

Some HIV protease inhibitors alter lamin A/C maturation and stability, SREBP-1 nuclear localization and adipocyte differentiation

OBJECTIVES

To study whether HIV protease inhibitors could induce nuclear lamina alterations in adipocytes as observed in a genetic form of lipodystrophy due to lamin A/C mutation.

DESIGN

We have previously observed that indinavir (IDV) impairs adipocyte differentiation and sterol regulatory element-binding protein-1 (SREBP-1) nuclear localization in 3T3-F442A adipocytes. We compared here the effects of IDV with that produced by two other PIs, nelfinavir (NFV) and amprenavir (APV) on adipose conversion, cellular localization of SREBP-1, nuclear morphology, and maturation and stability of the lamina network.

RESULTS

IDV and NFV, but not APV, altered adipose cell differentiation, as shown by lipid staining and protein expression of SREBP-1, CAAAT/enhancer binding protein (C/EBP)alpha and fatty acid synthase (FAS). In IDV-treated cells, 50-60 % of the nuclei could not accumulate SREBP-1. Twenty percent of these SREBP-negative nuclei were grossly dysmorphic, with blebs and prominent herniations, and showed an altered distribution of lamin A/C and lamin B. In IDV-treated cells, nuclear fragilization was shown by the abnormal extractibility of lamina proteins and SREBP-1, and the accumulation of prelamin A. NFV similarly altered lamin A/C maturation whereas APV was almost ineffective.

CONCLUSIONS

We show in an adipose cell line that IDV and NFV induced alterations at the nuclear level by promoting defects in lamin A/C maturation, organization and stability. We suggest that these lamina network alterations might be responsible for SREBP-1 nuclear mislocalization therefore resulting in altered adipocyte differentiation.

Modulation of the LDL receptor and LRP levels by HIV protease inhibitors

Inhibitors of the human immunodeficiency virus (HIV)-1 protease have proven to be effective antiretroviral drugs. However, patients receiving these drugs develop serious metabolic abnormalities, including hypercholesterolemia. The objective of the present study was to identify mechanisms by which HIV protease inhibitors increase plasma cholesterol levels. We hypothesized that HIV protease inhibitors may affect gene regulation of certain LDL receptor (LDLR) family members, thereby altering the catabolism of cholesterol-containing lipoproteins. In this present study we investigated the effect of several HIV protease inhibitors (ABT-378, Amprenavir, Indinavir, Nelfinavir, Ritonavir, and Saquinavir) on mRNA, protein, and functional levels of LDLR family members. Our results demonstrate that one of these drugs, Nelfinavir, significantly decreases LDLR and LDLR-related protein (LRP) mRNA and protein levels, resulting in the reduced functional activity of these two receptors. Nelfinavir exerts its effect by reducing levels of active SREBP1 in the nucleus. The finding that Nelfinavir reduces the levels of two key receptors (LRP and LDLR) involved in lipoprotein catabolism and maintenance of vessel wall integrity identifies a mechanism that causes hypercholesterolemia complications in HIV patients treated with this drug and raises concerns about the atherogenic nature of Nelfinavir.

Parameters driving the selection of nelfinavir-resistant human immunodeficiency virus type 1 variants

We investigated the parameters driving nelfinavir resistance, along the D30N and L90M evolutionary pathways. The advantage of the D30N mutant was mostly due to its resistance level, while the L90M mutation allowed preservation of infectivity coupled with minimal resistance. Emergence of secondary mutations further increased the selective advantage of viruses harboring D30N.

Short-term effects of cannabinoids in patients with HIV-1 infection: a randomized, placebo-controlled clinical trial

BACKGROUND

Cannabinoid use could potentially alter HIV RNA levels by two mechanisms: immune modulation or cannabinoid-protease inhibitor interactions (because both share cytochrome P-450 metabolic pathways).

OBJECTIVE

To determine the short-term effects of smoked marijuana on the viral load in HIV-infected patients.

DESIGN

Randomized, placebo-controlled, 21-day intervention trial.

SETTING

The inpatient General Clinical Research Center at the San Francisco General Hospital, San Francisco, California.

PARTICIPANTS

67 patients with HIV-1 infection.

INTERVENTION

Participants were randomly assigned to a 3.95%-tetrahydrocannabinol marijuana cigarette, a 2.5-mg dronabinol (delta-9-tetrahydrocannabinol) capsule, or a placebo capsule three times daily before meals.

MEASUREMENTS

HIV RNA levels, CD4+ and CD8+ cell subsets, and pharmacokinetic analyses of the protease inhibitors.

RESULTS

62 study participants were eligible for the primary end point (marijuana group, 20 patients; dronabinol group, 22 patients; and placebo group, 20 patients). Baseline HIV RNA level was less than 50 copies/mL for 36 participants (58%), and the median CD4+ cell count was 340 x 109 cells/L. When adjusted for baseline variables, the estimated average effect versus placebo on change in log10 viral load from baseline to day 21 was -0.07 (95% CI, -0.30 to 0.13) for marijuana and -0.04 (CI, -0.20 to 0.14) for dronabinol. The adjusted average changes in viral load in marijuana and dronabinol relative to placebo were -15% (CI, -50% to 34%) and -8% (CI, -37% to 37%), respectively. Neither CD4+ nor CD8+ cell counts appeared to be adversely affected by the cannabinoids.

CONCLUSIONS

Smoked and oral cannabinoids did not seem to be unsafe in people with HIV infection with respect to HIV RNA levels, CD4+ and CD8+ cell counts, or protease inhibitor levels over a 21-day treatment.

The effects of protease inhibitors and nonnucleoside reverse transcriptase inhibitors on p-glycoprotein expression in peripheral blood mononuclear cells in vitro

Several antiretroviral compounds have been shown to be substrates for the efflux protein P-glycoprotein (P-gp) although few studies have investigated the effects of drug on expression of this protein. Here, an in vitro system has been adopted to investigate the effects of protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) on P-gp expression in peripheral blood mononuclear cells (PBMCs). PBMCs isolated from healthy volunteers were incubated with 10 or 100 microM PI (saquinavir, ritonavir, lopinavir, indinavir, nelfinavir, amprenavir) or 10 microM NNRTI (efavirenz, nevirapine) for 72 hours. Surface P-gp expression was measured by flow cytometry and compared with vehicle-incubated controls. Toxicity was assessed by MTT assay and the effects of each compound were compared between individuals with differing genotypes at position 3435 of exon 26 of MDR1, which was assigned by restriction fragment length polymorphism. Significant increases in median P-gp expression were observed following incubation with 10 microM nelfinavir (10.2 versus 6.7% P-gp-positive cells) and efavirenz (10.0 versus 6.7% P-gp-positive cells). No significant differences in induction were observed between genotypes (CC, CT, TT). Following incubation with 100 microM PI, significant upregulation of P-gp occurred except with amprenavir. However, nelfinavir, ritonavir, and lopinavir caused marked toxicity, indicating that at higher concentrations, the increase in P-gp may be at least partially related to a stress response. These results indicate the potential of some PIs and NNRTIs to induce P-gp expression in PBMCs in vitro.

Primary nelfinavir (NFV)-associated resistance mutations during a follow-up period of 108 weeks in protease inhibitor naïve patients treated with NFV-containing regimens in an HIV clinic cohort

BACKGROUND

Nelfinavir (NFV) is a widely prescribed HIV-1 specific protease inhibitor (PI). However, there are only a few reports that have described the long-term effects of NFV-containing regimens, especially with regard to the emergence of drug resistance in inner-city clinics.

OBJECTIVES

The aim of this study was to investigate the clinical and virologic responses to treatment with NFV-containing regimens for up to 108 weeks and determine the timing and rate of emergence of primary NFV-resistance associated mutations in daily clinical practice.

STUDY DESIGN

A cohort study in an inner-city clinic. Our study included 51 consecutive patients who were PI-nai;ve and commenced therapy in February 1997 through April 1999.

RESULTS AND CONCLUSIONS

The proportions of patients who continued the same therapeutic regimen and showed virologic success (viral load <400 copies/ml) up to 108 weeks were 78 and 63%, respectively, based on intent-to-treat analysis. Among patients with a viral load persistently >400 copies/ml at week 12 (n=30), 11 developed primary NFV-resistance associated mutations by 108 weeks (stratified log-rank test; P<0.05). The Cox proportional hazard model showed that prior use of reverse transcriptase inhibitors (n=22) (relative hazard (RH); 2.10, 95% CI; 0.67-6.62), prior AIDS diagnosis (n=6) (RH; 1.70, 95% CI; 0.37-7.77), CD4 < 200/microl at baseline (n=19) (RH; 2.48, 95% CI; 0.78-7.81) and viral load >30,000 copies/ml at baseline (n=21) (RH; 2.10, 95% CI; 0.67-6.62) were not independent predictors of the NFV-resistance, although some tendency was noted. In total, 77% of the patients continued NFV-containing treatment without the NFV-resistance for 108 weeks. The viral load at week 12 could be used as a predictor of treatment success in our cohort study.

pol gene sequence variation in Swedish HIV-2 patients failing antiretroviral therapy

There is limited knowledge about how to treat and interpret results from genotypic resistance assays in HIV-2 infection. Here, genetic variation in HIV-2 pol gene was studied in 20 of 23 known HIV-2 cases in Sweden. Five patients with signs of virological treatment failure were longitudinally studied. Clinical, virological and immunological data were collected and the protease (PR) and first half of the reverse transcriptase (RT) was amplified and directly sequenced from plasma samples. Moderate to extensive genetic evolution was observed in four of the five patients who failed treatment. Some mutations occurred at positions known to confer resistance in HIV-1, but many occurred at other positions in PR and RT. All patients had been treated with zidovudine alone or in combination with other antiretroviral drugs, but none displayed a mutation at position 215, which is the primary zidovudine resistance site in HIV-1. Instead, a E219D mutation evolved in virus from two patients and a Q151M mutation evolved in two other patients. A M184V mutation indicative of lamivudine resistance was detected in three patients. The virus of one patient who had been treated with ritonavir, nelfinavir, and lopinavir successively acquired nine unusual mutations in the protease gene, most of which are not considered primary or secondary resistance mutations in HIV-1. Our data indicate that the evolutionary pathways that lead to antiretroviral resistance in HIV-2 and HIV-1 exhibit both similarities and differences. Genotypic HIV-2 resistance assays cannot be interpreted using algorithms developed for HIV-1, instead new algorithms specific for HIV-2 have to be developed.

HIV protease inhibitors acutely impair glucose-stimulated insulin release

HIV protease inhibitors (PIs) acutely and reversibly inhibit the insulin-responsive glucose transporter Glut 4, leading to peripheral insulin resistance and impaired glucose tolerance. Minimal modeling analysis of glucose tolerance tests on PI-treated patients has revealed an impaired insulin secretory response, suggesting additional pancreatic beta-cell dysfunction. To determine whether beta-cell function is acutely affected by PIs, we assayed glucose-stimulated insulin secretion in rodent islets and the insulinoma cell line MIN6. Insulin release from MIN6 cells and rodent islets was significantly inhibited by the PI indinavir with IC(50) values of 1.1 and 2.1 micro mol/l, respectively. The uptake of 2-deoxyglucose in MIN6 cells was similarly inhibited (IC(50) of 2.0 micro mol/l), whereas glucokinase activity was unaffected at drug levels as high as 1 mmol/l. Glucose utilization was also impaired at comparable drug levels. Insulin secretogogues acting downstream of glucose transport mostly reversed the indinavir-mediated inhibition of insulin release in MIN6 cells. Intravenous infusion of indinavir during hyperglycemic clamps on rats significantly suppressed the first-phase insulin response. These data suggest that therapeutic levels of PIs are sufficient to impair glucose sensing by beta-cells. Thus, together with peripheral insulin resistance, beta-cell dysfunction likely contributes to altered glucose homeostasis associated with highly active antiretroviral therapy.

Factors associated with accelerated atherosclerosis in HIV-1-infected persons treated with protease inhibitors

Recent evidence suggests that as a group protease inhibitors (PIs) may accelerate certain factors associated with atherosclerosis. The objective of this study was to evaluate the effect of individual PIs (indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir) on certain factors associated with atherosclerosis. Persons who took saquinavir and/or ritonavir were compared with those on other PIs. Between May 2000 and July 2001, the lipid profiles, C-reactive protein (CRP) levels, coronary artery calcium (CAC) scores, and blood cell morphologic parameters were measured in 98 black adult participants aged 25 to 45 years with HIV-1 infection in Baltimore, Maryland. Among these 98, there were 55 (56.1%) taking PIs. Students' t-test and chi2 test were used to detect the between-group differences. Study participants in both the PI and non-PI groups were similar in age, sex, body mass index, blood pressure, red and white blood cell counts, time since HIV diagnosis, and duration on anti-retroviral therapy. Compared with those who took non-PI regimens, those who took indinavir, nelfinavir, or saquinavir had significantly higher levels of mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH). Those taking any PI had significantly higher total cholesterol and low-density lipoprotein. Those taking nelfinavir, ritonavir, or saquinavir were more likely to have a higher CAC score (>5) than those on non-PI regimens. There were no differences in the lipid profiles, MCV, MCH, CRP, and CAC between those taking saquinavir and/or ritonavir and those taking other PIs. Overall, the changes noted might lead to anticipation of clinical changes linked to accelerated atherosclerosis in patients on PIs.

Treatment with indinavir, efavirenz, and adefovir after failure of nelfinavir therapy

A prospective, open-label study was conducted to assess the response to indinavir, efavirenz, and adefovir in human immunodeficiency virus (HIV)-infected patients experiencing viral rebound while receiving therapy with nelfinavir-containing regimens, to determine whether the protease genotype influenced the outcome of the salvage regimen. Genotyping from 29 nelfinavir failures revealed D30N in 17 (59%) and L90M in 11 (38%) cases. Suppression to <400 viral RNA copies/mL was achieved at week 48 in 56% of patients with the D30N virus versus 18% of patients with the L90M virus.

HIV-protease inhibitors impair vitamin D bioactivation to 1,25-dihydroxyvitamin D

BACKGROUND

A high prevalence of bone demineralization occurs in people living with HIV/AIDS. The contribution of HIV itself and its treatment is still unclear. Protease inhibitors (PIs) are potent inhibitors of the cytochrome p450 enzyme system. Three cytochrome p450 mixed function oxygenases control serum levels of 1,25-dihydroxyvitamin D (1,25(OH) D ), which is responsible for vitamin D actions in target tissues including bone. The 25- and 1alpha-hydroxylases regulate 1,25(OH) D synthesis and 24-hydroxylase 1,25(OH) D catabolism.

OBJECTIVE

To assess whether HIV-protease inhibitors (ritonavir, indinavir, nelfinavir) impair the activity of the main enzymes involved in 1,25(OH) D homeostasis.

DESIGN AND METHODS

Studies were conducted in the human hepatocyte (H3B)- and monocyte (THP-1) cell lines, expressing 25-hydroxylase and 1alpha-hydroxylase, respectively. The 24-hydroxylase expression was induced in macrophages by exposure to 1,25(OH) D. Conversion rates of vitamin D to 25-hydroxyvitamin D [25(OH)D ]; 25(OH)D to 1,25(OH) D or 24,25(OH) D, and 1,25(OH) D degradation were quantified in untreated and HIV-PI-treated cells after C -cartridge extraction and high-performance liquid chromatography purification of 25(OH)D - 24,25(OH) D - and 1,25(OH) D fractions.

RESULTS

The PIs impair hepatocyte 25(OH)D - and macrophage 1,25(OH) D synthesis in a reversible, dose-dependent manner. Furthermore, PIs inhibit 1,25(OH) D -degradation in macrophages with lower potency than that elicited on 1alpha-hydroxylase. Thus, reduced macrophage 1,25(OH) D production is the net effect of PIs action.

CONCLUSIONS

In intact cells, HIV-PIs markedly suppress the activities of 25- and 1alpha-hydroxylase, which are critical in 1,25(OH) D synthesis, while exerting mild inhibition of 24-hydroxylase, responsible for 1,25(OH) D catabolism. If PIs elicit a similar potency in inhibiting these critical steps for 1,25(OH) D homeostasis, defective 1,25(OH) D production could contribute to the bone demineralization in HIV patients.

Inhibition of TNF-alpha mediated cell death by HIV-1 specific protease inhibitors

HIV-1 protease inhibitors have contributed significantly to the reduction in morbidity and mortality associated with HIV-1 disease. Some of their clinical benefit may be attributed to inhibition of non-viral pathogen proteases and mammalian proteases involved in apoptosis. Our objective was to investigate the effect of HIV-1 protease inhibitors on two different mechanisms of apoptosis in cells not exposed to HIV-1. Modulation of apoptosis induced in U937 or Jurkat cells by CD95 (Fas-ligand) or TNF-alpha was measured using flow cytometry using the 7-AAD and annexin/propidium iodide methods. - HIV-1 protease inhibitors reduced TNF-alpha mediated cell death in a dose-dependent manner, with a maximum inhibition ranging between 38% and 60% observed for 100 microM indinavir. Saquinavir and ritonavir, but not nelfinavir also inhibited TNF-alpha induced cell death. Nevirapine (an HIV-1 reverse transcriptase inhibitor) showed no effect. The TNF-alpha activity was also inhibited by the caspase inhibitors Z-VAD-fmk at concentrations of 10 microM or less, and by DEVD-cmk. In contrast, HIV-1 protease inhibitors did not affect CD95 induced apoptosis in Jurkat cells at any of the concentrations tested. Our findings indicate that HIV-1 protease inhibitors may act on mammalian proteases involved in the regulation of apoptosis; whether this is relevant in the clinical setting remains to be established. Identification of the pathways involved may lead to a better understanding of the clinical impact of this drug class and their role in HAART associated toxicities.

Agent and cell-type specificity in the induction of insulin resistance by HIV protease inhibitors

OBJECTIVE

To test agent and cell-type specificity in insulin resistance induced by prolonged exposure to HIV protease inhibitors (HPI), and to assess its relation to the direct, short-term inhibition of insulin-stimulated glucose uptake.

METHODS

Following prolonged (18 h) and short (5-10 min) exposure to HPI, insulin-stimulated glucose transport, protein kinase B (PKB) phosphorylation, and GLUT4 translocation were evaluated in 3T3-L1 adipocytes, fibroblasts, L6 myotubes, and L6 cells overexpressing a myc tag on the first exofacial loop of GLUT4 or GLUT1.

RESULTS

Prolonged exposure of 3T3-L1 adipocytes to nelfinavir, but not to indinavir or saquinavir, resulted in increased basal lipolysis but decreased insulin-stimulated glucose transport and PKB phosphorylation. In addition, impaired insulin-stimulated glucose uptake and PKB phosphorylation were also observed in the skeletal muscle cell line L6, and in 3T3-L1 fibroblasts. Interestingly, this coincided with increased basal glucose uptake as well as with elevated total-membrane glucose transporter GLUT1 protein content. In contrast to these unique effects of nelfinavir, the mere presence of any of the agents in the 5 min transport assay inhibited insulin-stimulated glucose-uptake activity. This appeared to be caused by direct and specific interaction of the drugs with GLUT4 fully assembled at the plasma membrane, since insulin-stimulated cell-surface exposure of an exofacial myc epitope on GLUT4 was normal.

CONCLUSIONS

Independent mechanisms for HPI-induced insulin resistance exist: prolonged exposure to nelfinavir interferes with insulin signaling and alters cellular metabolism of adipocytes and muscle cells, whereas a direct inhibitory effect on insulin-stimulated glucose uptake may occurs through specific interaction of HPI with GLUT4.

Isolation and molecular characterization of a nelfinavir (NFV)-resistant human immunodeficiency virus type 1 that exhibits NFV-dependent enhancement of replication

During the use of a phenotypic anti-human immunodeficiency virus type 1 (HIV-1) drug resistance assay in a large set of clinical virus isolates, we found a unique variant (CL-4) that exhibited a high level of nelfinavir (NFV) resistance and rather enhanced replication under subinhibitory concentrations of NFV (0.001 to 0.1 micro M). Comparison of gag-pol sequences of the CL-4 variant and its predecessor virus isolates showed a stepwise accumulation of a total of 19 amino acid substitutions in protease (PR) and Gag p17 during 32-month NFV-containing antiretroviral therapy, while other Gag regions including the cleavage sites of the p55 precursor remained highly conserved. To understand the relationship between the genetic and phenotypic changes in CL-4, we constructed chimeric viruses using pNL4-3, replacing the PR, p24PR, or p17PR gene segment of CL-4 or its predecessor. A series of tissue culture infections with the chimeras in the absence or presence of increasing concentrations of NFV demonstrated that only the p17PR segment of CL-4 could confer the NFV-dependent replication enhancement phenotype on NL4-3. Our data suggest a novel adaptation mechanism of HIV-1 to NFV, in which coevolution of Gag and PR genes generates a variant that replicates more efficiently in the cellular environment in the presence of NFV than without the drug.

Effects of nelfinavir and its M8 metabolite on lymphocyte P-glycoprotein activity during antiretroviral therapy

The efflux pump P-glycoprotein decreases drug penetration into cells and tissues. To determine whether nelfinavir or its metabolites inhibit P-glycoprotein in lymphocytes from a healthy volunteer, whole blood cells from human immunodeficiency virus-negative donors were incubated either in human plasma to which nelfinavir or its M8 metabolite were added ex vivo or in plasma from human immunodeficiency virus-positive patients receiving nelfinavir. The 50% P-glycoprotein inhibitory concentrations of purified nelfinavir and M8 were 10.9 micromol/L and 29.5 micromol/L, respectively, for CD4(+) T cells and 19.3 micromol/L and >48 micromol/L, respectively, for CD8(+) T cells. Significant inhibitory activity was present in plasma from 27 of 46 patients (59%) receiving nelfinavir. Plasma nelfinavir concentrations correlated with percent inhibition on CD4(+) (rho = 0.85, P <.0001) and CD8(+) (rho = 0.83, P <.0001) T cells. The M8 concentrations correlated weakly with both inhibition and nelfinavir concentrations. On the basis of our findings in lymphocytes from a healthy volunteer exposed to plasma from human immunodeficiency virus-positive patients, we believe it is likely that CD4(+) and CD8(+) lymphocytes in patients receiving nelfinavir as therapy for human immunodeficiency virus may have P-glycoprotein inhibited by plasma concentrations of nelfinavir.

Rapid phenotypic assay for human immunodeficiency virus type 1 protease using in vitro translation

A rapid in vitro phenotyping method for human immunodeficiency virus type 1 (HIV-1) protease was developed. In this system, both HIV-1 protease and substrates are prepared using a rabbit reticulocyte based coupled in vitro transcription/translation system. The activity of protease is evaluated by the amount of cleaved substrate measured by ELISA. In this system, wild-type protease derived from strain HXB2 was specifically inhibited in a dose-dependent manner by the protease inhibitors, indinavir and nelfinavir. Three drug-resistant proteases carrying a single mutation, D30N, L90M, and V82F, were analyzed in the absence of the inhibitors. Reflecting their impaired fitness, they exhibited decreased protease activity compared with the wild type. The apparent protease activity was greater for a Gag-Pol substrate encompassing the Gag-protease-reverse transcriptase junctions than for a substrate only covering the Gag region. Using the Gag-Pol substrate as the target, the indinavir-resistant mutant V82F was evaluated further. V82F showed 9-fold resistance to its cognitive protease inhibitor, indinavir; however, it manifested only moderate (2-fold) resistance to a non-cognitive inhibitor, nelfinavir. This simple and rapid method may be useful for phenotyping of drug-resistant HIV-1 protease as well as for screening new inhibitors of HIV-1 protease.

[HIV genotypic mutation selectively induced by the protease inhibitor nelfinavir at codon 30. Case series and consequences for antiretroviral management]

In a survey of 247 HIV-infected patients which received at least six months of combined antiretroviral therapy including the protease inhibitor nelfinavir during the last two years (2000-2001), the specific primary genotypic mutation D30N (with or without the minor mutation N88D), was detected in only four of the 149 (2.7%) subjects who received genotypization after virological failure. Three of these cases of primary nelfinavir resistance occurred among the 84 patients who were protease inhibitor- and/or non-nucleoside reverse transcriptase inhibitor-na ve, while the last episode was registered in a female patient treated since five years, who received an indinavir-based therapy of nearly 12-month duration (interrupted because of untoward kidney effects). During the subsequent follow-up, the substitution of nelfinavir had a favourable laboratory and clinical outcome in all reported patients who continued a different highly active anti-HIV treatment, while a significantly less positive virological and immunological response was seen in all the remaining subjects, and especially in those who experienced virological failure after undergoing at least two prior changes of combined antiretroviral therapy, and were borne by a broad spectrum of protease gene mutations (save those regarding codons 30 and 88). Due to its exclusive resistance pattern, nelfinavir may represent a favorable first-line choice among protease inhibitor-based regimens, since it may spare further treatment options even in the same pharmacological class. In fact, cross-resistance with other protease inhibitors may be limited also in patients experiencing prior long-term antiretroviral therapy, from second-line to rescue regimens, provided that they were pre-treated with drugs other than nelfinavir.

Nelfinavir-resistant, amprenavir-hypersusceptible strains of human immunodeficiency virus type 1 carrying an N88S mutation in protease have reduced infectivity, reduced replication capacity, and reduced fitness and process the Gag polyprotein precursor aberrantly

The evolution of human immunodeficiency virus type 1 (HIV-1) strains with reduced susceptibility to protease inhibitors (PIs) is a major cause of PI treatment failure. A subset of subjects failing a therapy regimen containing the PI nelfinavir developed mutations at position 88 in the protease region. The N88S mutation occurring in some of these subjects induces amprenavir hypersusceptibility and a reduction of fitness and replication capacity. Here we demonstrate that substitutions L63P and V77I in protease, in combination, partially compensate for the loss of fitness, loss of replication capacity, loss of specific infectivity, and aberrant Gag processing induced by the N88S mutation. In addition, these mutations partially ablate amprenavir hypersusceptibility. Addition of mutation M46L to a strain harboring mutations L63P, V77I, and N88S resulted in a reduction of fitness and infectivity without changing Gag-processing efficiency, while amprenavir hypersusceptibility was further diminished. The ratio of reverse transcriptase activity to p24 protein was reduced in this strain compared to that in the other variants, suggesting that the M46L effect on fitness occurred through a mechanism different from a Gag-processing defect. We utilized these mutant strains to undertake a systematic comparison of indirect, single, cycle-based measures of fitness with direct, replication-based fitness assays and demonstrated that both yield consistent results. However, we observed that the magnitude of the fitness loss for one of the mutants varied depending on the assay used.

Modulation of human immunodeficiency virus (HIV)-specific immune response by using efavirenz, nelfinavir, and stavudine in a rescue therapy regimen for HIV-infected, drug-experienced patients

Analysis of the virologic and immunomodulatory effects of an association of efavirenz (EFV), nelfinavir (NFV), and stavudine (d4T) was performed in 18 human immunodeficiency virus (HIV)-infected and highly active antiretroviral therapy (HAART)-experienced patients who failed multiple therapeutic protocols. Patients (<500 CD4(+) cells/ micro l; >10,000 HIV copies/ml) were nonnucleoside reverse transcriptase inhibitor (NNRTI)-naive and were treated for 10 months with EFV (600 mg/day) in association with NFV (750 mg three times daily) and d4T (30 or 40 mg twice daily). Measurement of HIV peptide- and mitogen-stimulated production of interleukin-2 (IL-2), gamma interferon (IFN-gamma), IL-4, and IL-10 as well as quantitation of mRNA for the same cytokines in unstimulated peripheral blood mononuclear cells were performed at baseline and 2 weeks (t1), 2 months (t2), and 10 months (t3) into therapy. The results showed that HIV-specific (but not mitogen-stimulated) IL-2 and IFN-gamma production was augmented and IL-10 production was reduced in patients who received EFV, NFV, and d4T. Therapy was also associated with a reduction in HIV RNA in plasma and an increase in CD4(+) cell count. These changes occurred in the first year of therapy (t2 and t3) and were confirmed by quantitation of cytokine-specific mRNA. Therapy with EFV, NFV, and d4T increases HIV-specific type 1 cytokine production as well as CD4 counts and reduces plasma viremia. This therapeutic regimen may be considered for use in cases of advanced HIV infection.

Effect of coadministration of nelfinavir, indinavir, and saquinavir on the pharmacokinetics of amprenavir

OBJECTIVE

Pharmacokinetic interactions are expected when human immunodeficiency virus (HIV) protease inhibitors are coadministered because many are both substrates for and inhibitors of CYP3A4. The goal of this model-based pharmacokinetic analysis was to describe the differences observed in amprenavir pharmacokinetics among treatment arms in the Adult AIDS Clinical Trial Group (AACTG) study protocol 398 and to propose mechanisms to account for them.

METHODS

One hundred seventy-six HIV-positive subjects receiving 1200 mg amprenavir twice daily as part of AACTG protocol 398 were included in the pharmacokinetic study. All patients also received background medications efavirenz, adefovir dipivoxil, and abacavir and, depending on the study arm, placebo or one of the following protease inhibitors: nelfinavir, indinavir, or saquinavir. A population pharmacokinetic model was fitted to a total of 565 amprenavir concentration measurements. The blood samples for concentration measurements were drawn at week 2 (12-hour pharmacokinetic study, approximately 7 samples per study; 46 patients) and at week 24 (6-hour pharmacokinetic study, approximately 5 samples per study; 10 patients). In addition, samples were collected at 1 or more follow-up visits (population pharmacokinetic study, 1 to 3 occasions per patient; 150 patients).

RESULTS AND CONCLUSION

Amprenavir intrinsic clearance was significantly reduced relative to placebo by nelfinavir (-41%) and indinavir (-54%) but not by saquinavir. The absolute magnitude of amprenavir intrinsic clearance suggests that CYP3A4 inhibition by nelfinavir and indinavir is balanced by enzymatic induction in the presence of the background drug(s), most likely efavirenz. Amprenavir intrinsic clearance apparently increases by more than 30% between weeks 2 and 24, possibly because of the time course of CYP3A4 induction.

Amplification of the effects of drug resistance mutations by background polymorphisms in HIV-1 protease from African subtypes

The vast majority of HIV-1 infections worldwide are caused by the C and A viral subtypes rather than the B subtype prevalent in the United States and Western Europe. Genomic differences between subtypes give rise to sequence variations in the encoded proteins, including those identified as targets for antiretroviral therapies. In the case of the HIV-1 protease, we reported earlier [Velazquez-Campoy et al. (2001) Proc. Natl. Acad. Sci. U.S.A. 98, 6062-6067] that proteases from the C and A subtypes exhibit a higher biochemical fitness in the presence of widely prescribed protease inhibitors. In this paper we present a complete thermodynamic dissection of the differences between proteases from different subtypes and the effects of the V82F/I84V drug-resistant mutation within the framework of the B, C, and A subtypes. These studies involved four inhibitors in clinical use (indinavir, saquinavir, ritonavir, and nelfinavir) and a second-generation protease inhibitor (KNI-764). Naturally occurring amino acid polymorphisms found in proteases from the C and A subtypes lower the binding affinities of existing clinical inhibitors by factors ranging between 2 and 7.5 which by themselves are not enough to cause drug resistance. The preexisting lower affinity in the C and A subtypes, however, significantly amplifies the effects of the drug-resistant mutation. Relative to the wild-type B subtype protease, the V82F/I84V drug-resistant mutation within the C and A subtypes lowers the binding affinity of inhibitors by factors ranging between 40 and 3000. When the enzyme kinetic properties (k(cat) and K(m)) are included in the analysis, the biochemical fitness of the C and A subtype drug-resistant mutants can be up to 1000-fold higher than that of the wild-type B subtype protease in the presence of the studied inhibitors. From a thermodynamic standpoint, the combined effects of the drug-resistant mutations and the natural amino acid polymorphisms on the Gibbs energy are additive and involve significant alterations in the enthalpy and entropy changes associated with inhibitor binding. At the biochemical level, the combined effects of naturally existing polymorphisms and drug-resistant mutations might have important consequences on the long-term viability of current HIV-1 protease inhibitors.

Select HIV protease inhibitors alter bone and fat metabolism ex vivo

Human immunodeficiency virus (HIV) therapies have been associated with alterations in fat metabolism and bone mineral density. This study examined the effects of HIV protease inhibitors (PIs) on bone resorption, bone formation, and adipocyte differentiation using ex vivo cultured osteoclasts, osteoblasts, and adipocytes, respectively. Osteoclast activity, measured using a rat neonatal calvaria assay, increased in the presence of nelfinavir (NFV; 47.2%, p = 0.001), indinavir (34.6%, p = 0.001), saquinavir (24.3%, p = 0.001), or ritonavir (18%, p < 0.01). In contrast, lopinavir (LPV) and amprenavir did not increase osteoclast activity. In human mesenchymal stem cells (hMSCs), the PIs LPV and NFV decreased osteoblast alkaline phosphatase enzyme activity and gene expression significantly (p < 0.05). LPV and NFV diminished calcium deposition and osteoprotegrin expression (p < 0.05), whereas the other PIs investigated did not. Adipogenesis of hMSCs was strongly inhibited by saquinavir and NFV (>50%, p < 0.001) and moderately inhibited by ritonavir and LPV (>40%, p < 0.01). Expression of diacylglycerol transferase, a marker of adipocyte differentiation, decreased in hMSCs treated with NFV. Amprenavir and indinavir did not affect adipogenesis or lipolysis. These results suggest that bone and fat formation in hMSCs of bone marrow may be coordinately down-regulated by some but not all PIs.

Plasma drug levels, genotypic resistance, and virological response to a nelfinavir plus saquinavir-containing regimen

OBJECTIVE

To determine the importance of resistance and drug levels in the response to a dual-protease inhibitor (PI) combination.

METHODS

Prospective study of 62 HIV-positive patients who switched to a salvage regimen including nelfinavir plus saquinavir. Virological response was defined as a decrease in viraemia > 0.5 log10 after 24 weeks. Optimal PI levels were defined as those above the protein binding-corrected 95% inhibitory concentration (IC95), as estimated in the presence of 50% human serum.

RESULTS

Baseline median HIV load was 4.78 log10 copies/ml. The median number of mutations in the protease gene was nine (range, 2-25), predominantly at residues 82 (52%), and 90 (40%). After 24 weeks, 45% of patients had responded and 19% were < 50 copies/ml. A higher number of mutations in the protease gene (12 versus 8;P = 0.001), and the L90M mutation (36% versus 67%; P = 0.001) were associated with treatment failure. Trough levels of nelfinavir and saquinavir were two- and fivefold, respectively, greater than those reached when used as the only PI (2480 and 260 ng/ml, respectively), and they were above the estimated protein-corrected IC95 in 96% and 32% of cases. Thus, the Cmin : IC95 ratio ranged from 0.1 to 10 for nelfinavir and from 0.12 to 3.24 for saquinavir. Suboptimal PI levels were associated with a poorer response, but there was no correlation between optimal drug levels and a better response.

CONCLUSION

Genotypic resistance predicts the virological response to a nelfinavir-saquinavir salvage regimen. Our data suggest that higher than optimal drug levels could be necessary to control the replication of many PI-resistant viruses.

CYP3A4-mediated hepatic metabolism of the HIV-1 protease inhibitor saquinavir in vitro

1. The aim was to identify the major metabolites of saquinavir (SQV) from human hepatic microsomal incubations and the CYP isoform(s) responsible. 2. Ten fractions containing various metabolites were separated by isocratic reversed-phase HPLC and characterized by HPLC, mass spectrometry and NMR. 3. Metabolites were either mono- or di-hydroxylated derivatives of SQV. Fast-atom bombardment and electrospray MS showed that hydroxylation was predominantly situated on the decahydroisoquinoline ring. A major metabolite (M4) was rigorously identified as 6-equatorial-hydroxy SQV. 4. Metabolism of saquinavir to all metabolites was inhibited by the CYP3A4-selective inhibitor ketoconazole (IC50 = 0.55 +/- 0.12 microM). Other isoform-selective inhibitors were non-inhibitory. The protease inhibitors ritonavir, indinavir and nelfinavir potently inhibited SQV metabolism in hepatic microsomes with IC50 = 0.025 +/- 0.004, 0.82 +/- 0.26 and 0. 58 +/- 0.14 microM, respectively. 5. Saquinavir metabolism correlated with immunochemically determined CYP3A4 levels and testosterone 6beta-hydroxylation, but it failed to correlate with either immunochemically determined CYPIA2 levels or marker activities for CYP1A2, 2C9 or 2E1. 6. Heterologously expressed CYP3A4 metabolized saquinavir with a similar metabolic profile to that of human liver microsomes. 7. Km, and Vmax for total SQV metabolism were 0.61 +/- 0.19 microM and 1.82 +/- 1.13 nmol mg(-1) min(-1), respectively. 8. The extensive involvement of hepatic CYP3A4 in the metabolism of saquinavir predicts high intrinsic clearance of saquinavir. Inhibitors of CYP3A4 such as other protease inhibitors will substantially increase the bioavailability of saquinavir.

Synthesis and anti-HIV activity of glucose-containing prodrugs derived from saquinavir, indinavir and nelfinavir

With the aim at improving the transport of the current HIV protease inhibitors across the intestinal and blood brain barriers and their penetration into the central nervous system, the synthesis of various acyl and carbamatoyl glucose-containing prodrugs derived from saquinavir, indinavir and nelfinavir, their in vitro stability with respect to hydrolysis, and their anti-HIV activity have been investigated. D-Glucose, which is actively transported across these barriers, was connected through its 3-hydroxyl to these antiproteases via a linker. The liberation of the active free drug during the incubation time of the prodrugs with the cells was found to be crucial for HIV inhibition. The labile ester linking of the glucose-containing moiety to the peptidomimetic hydroxyl of saquinavir or to the indinavir C-8 hydroxyl, which is not part of the transition state isostere, is not an obstacle for anti-HIV activity. This is not the case for its stable carbamate linking to the peptidomimetic hydroxyl of saquinavir, indinavir and nelfinavir. The chemical stability with respect to hydrolysis of some of the saquinavir and indinavir prodrugs reported here, the liberation rate of the active free drug and the HIV inhibitory potency are acceptable for an in vivo use of these prodrugs. These glucose-linked ester and carbamate prodrugs display a promising therapeutic potential provided that their bioavailability, penetration into the HIV sanctuaries, and/or the liberation of the active free drug from the carbamate prodrugs are improved. Furthermore, no cytotoxicity was detected for the prodrugs for concentrations as high as 10 or even 100 microM, thus indicating an encouraging therapeutic index.

Antiapoptotic mechanism of HIV protease inhibitors: preventing mitochondrial transmembrane potential loss

Treatment of cells with the HIV drugs ritonavir, saquinavir, or nelfinavir (Nfv) inhibits apoptosis induced by a variety of stimuli. Because these drugs are protease inhibitors, they have been postulated to inhibit apoptosis by blocking caspase activity. This study shows that Nfv has no effect on caspase activity or on the transcription or synthesis of a variety of apoptosis regulatory molecules. Instead, Nfv inhibits mitochondrial transmembrane potential loss (Delta psi(m)) and the subsequent release of apoptotic mediators. Consequently, the antiapoptotic effects of Nfv are restricted to apoptotic pathways that involve Delta psi(m). (Blood. 2001;98:1078-1085)