Use of HIV protease inhibitors to block Kaposi's sarcoma and tumour growth

HIV protease inhibitors are antiretroviral drugs that block the enzyme required for production of infectious viral particles. Although these agents have been designed to selectively bind to the catalytic site of HIV protease, evidence indicates that other cellular and microbial enzymes and pathways are also affected. It has been reported that patients treated with highly active anti-retroviral therapy (HAART) containing a protease inhibitor may be at reduced risk of Kaposi's sarcoma (KS) and some types of non-Hodgkin lymphomas; some disease regressions have also been described. Here we review recent data showing that several widely used protease inhibitors, including indinavir, saquinavir, ritonavir, and nelfinavir, can affect important cellular and tissue processes such as angiogenesis, tumour growth and invasion, inflammation, antigen processing and presentation, cell survival, and tissue remodelling. Most of these non-HIV-related effects of protease inhibitors are due to inhibition of cell invasion and matrix metalloprotease activity, or modulation of the cell proteasome and NFkappaB. These elements are required for development of most tumours. Thus, by direct and indirect activities, protease inhibitors can simultaneously block several pathways involved in tumour growth, invasion, and metastasis. These findings indicate that protease inhibitors can be exploited for the therapy of KS and other tumours that occur in both HIV-infected and non-infected individuals. A multicentre phase II clinical trial with indinavir in non-HIV-associated KS is about to start in Italy.     

Remission from Kaposi's sarcoma on HAART is associated with suppression of HIV replication and is independent of protease inhibitor therapy

Highly active antiretroviral therapy (HAART) reduces the incidence and improves the prognosis of Kaposi's sarcoma (KS). This study was designed to identify factors associated with KS clinical responses in HIV-infected patients during HAART. We reviewed the files of 138 HIV-1-infected patients with KS. Epidemiologic and HIV-related clinical and biological parameters were recorded at KS diagnosis (baseline) and every 6 months thereafter. In a subset of 73 antiretroviral-naive patients, we compared the clinical outcome of KS according to the use or nonuse of protease inhibitors (PI). After 6 months of follow-up, KS remission was more frequent in patients who were naive of HAART and who were at ACTG stage S0 at baseline (P = 0.03 and 0.02). Undetectable HIV viral load was strongly associated with KS remission (P< or = 0.004 at all time points), while CD4 cell count was not. Among the 73 antiretroviral-naive patients at baseline, and who were studied for 24 months, KS outcome did not differ between patients who were prescribed PI-containing and PI-sparing regimens. Intercurrent multicentric Castleman's disease was associated with poor outcome after 60 months of follow-up (P< or = 0.0001). Fourteen deaths occurred after a median follow-up of 37.5 months, eight of which were KS related. Suppression of HIV replication appears to be crucial to control KS. Non-PI-based regimens were equivalent to PI-based regimens as regards the clinical and virological outcome of antiretroviral-naive HIV-infected patients with KS.     

AIDS and cancer in the era of highly active antiretroviral therapy (HAART)

Combination therapy with protease inhibitors and nucleoside analogues dramatically suppresses plasma HIV-1 RNA and delays progression to AIDS, but the impact on HIV-associated malignancy remains to be established. Observational and time–trend data indicate that the incidence of Kaposi's sarcoma (KS) and primary brain lymphoma have decreased, but suggest that current therapies have not had a proportionate effect on systemic non-Hodgkin's lymphomas (NHL). As opportunistic infection and mortality are yielding to advances in antiretroviral therapy, lymphoma may increase in importance as a cause of AIDS-related morbidity and mortality. Further improvements in the long-term consequences of HIV infection will depend on better prevention and treatment of this serious malignant complication.     

Impact of HAART on the clinical management of AIDS-related cancers

The development of HIV-related disease has changed dramatically since the introduction of highly active antiretroviral therapy (HAART) into clinical practice. Since the use of protease inhibitors became widespread, a 30–50% reduction in Kaposi's sarcoma (KS) has been observed. The results of recent studies indicate that HAART may be a useful alternative both to immune response modifiers during less aggressive stages of KS disease and to systemic cytotoxic drugs in the long-term maintenance therapy of advanced KS. The impact of HAART regimens on the incidence of systemic lymphoma (NHL-HIV) remains unclear, but it can be hypothesised that patients treated with HAART may survive longer with continued B cell stimulation and dysregulation resulting in an increased incidence of lymphoma over time. The impact of HAART on survival in patients affected by NHL-HIV has recently been evaluated and a positive correlation between HAART and outcome in these patients has been found. The spectrum of cancers in patients with HIV infection may develop further since these patients survive longer with HAART and with a better control of opportunistic infections. With the increasing use of HAART, the dilemma is whether to institute or continue protease inhibitors use during chemotherapy. Based on the advances in our understanding of HIV-related disease and the availability of new antiretroviral therapies, the choice for anti-HIV agents in patients receiving chemotherapy is important.     

Antitumor effect of the human immunodeficiency virus protease inhibitor ritonavir: induction of tumor-cell apoptosis associated with perturbation of proteasomal proteolysis

Ritonavir is an HIV protease inhibitor used in the therapy of HIV infection. Ritonavir has also been shown to inhibit the chymotrypsin-like activity of isolated 20S proteasomes. Here, we demonstrate that ritonavir, like classical proteasome inhibitors, has antitumoral activities. In vitro, ritonavir strongly reduced the rate of proliferation of several tumor cell lines and induced their apoptosis. Nontransformed cell lines and terminally differentiated bone-marrow macrophages were comparatively resistant to the apoptosis-inducing effect. In vivo, ritonavir, administered p.o. for a week at doses of 6-8.8 mg/mouse/day, caused significant growth inhibition (76-79% after 7 days of treatment) of established EL4-T cell thymomas growing s.c. in syngeneic C57BL/6 mice. Unexpectedly, we found that ritonavir activates the chymotrypsin-like activity of isolated 26S proteasomes, in strong contrast to its effect on isolated 20S proteasomes. The net effect of low micromolar concentrations of ritonavir on the chymotrypsin-like activity in cells and cell lysates was a weak inhibition, consistent with marginal alterations of polyubiquitinated proteins, marginal alterations in acid-soluble proteolytic peptide levels, and a small accumulation of the tumor suppressor protein p53, in cells treated with ritonavir. In contrast, we found a relatively strong accumulation of the cyclin-dependent kinase inhibitor p21(WAF-1), a sign of deregulation of cell-cycle progression typical for apoptosis induction in transformed cells by classical proteasome inhibitors. We demonstrate that p21 accumulation in the presence of ritonavir is attributable to the inhibition of proteolytic degradation. Accumulation of p21 most likely reflects a selective inhibition of proteasomes, in line with the atypical degradation of p21, which does not require ubiquitination. These findings suggest that selective perturbation of proteasomal protein degradation may play a role in the antitumoral activities of ritonavir.     

A new synthetic protein, TAT-RH, inhibits tumor growth through the regulation of NFκB activity

Background

Ovarian cancer is the leading cause of mortality from gynecological malignancies, often undetectable in early stages. The difficulty of detecting the disease in its early stages and the propensity of ovarian cancer cells to develop resistance to known chemotherapeutic treatments dramatically decreases the 5-year survival rate. Chemotherapy with paclitaxel after surgery increases median survival only by 2 to 3 years in stage IV disease highlights the need for more effective drugs. The human immunodeficiency virus (HIV) infection is characterized by increased risk of several solid tumors due to its inherent nature of weakening of immune system. Recent observations point to a lower incidence of some cancers in patients treated with protease inhibitor (PI) cocktail treatment known as HAART (Highly Active Anti-Retroviral Therapy).

Results

Here we show that ritonavir, a HIV protease inhibitor effectively induced cell cycle arrest and apoptosis in ovarian cell lines MDH-2774 and SKOV-3 in a dose dependent manner. Over a 3 day period with 20 μM ritonavir resulted in the cell death of over 60% for MDAH-2774 compared with 55% in case of SKOV-3 cell line. Ritonavir caused G1 cell cycle arrest of the ovarian cancer cells, mediated by down modulating levels of RB phosphorylation and depleting the G1 cyclins, cyclin-dependent kinase and increasing their inhibitors as determined by gene profile analysis. Interestingly, the treatment of ritonavir decreased the amount of phosphorylated AKT in a dose-dependent manner. Furthermore, inhibition of AKT by specific siRNA synergistically increased the efficacy of the ritonavir-induced apoptosis. These results indicate that the addition of the AKT inhibitor may increase the therapeutic efficacy of ritonavir.

Conclusion

Our results demonstrate a potential use of ritonavir for ovarian cancer with additive effects in conjunction with conventional chemotherapeutic regimens. Since ritonavir is clinically approved for human use for HIV, drug repositioning for ovarian cancer could accelerate the process of traditional drug development. This would reduce risks, limit the costs and decrease the time needed to bring the drug from bench to bedside.     

Clinical Overview: Issues in Kaposi's Sarcoma Therapeutics

Four questions are posed that are critical to the developmentof improved therapeutic and prophylactic strategies for Kaposi'ssarcoma (KS). 1) Can we predict who will develop KS? Accurateidentification of high-risk factors for KS development is essentialfor the development of KS prophylaxis trials. 2) Can developinginsights into KS pathogenesis be translated into improved therapeuticand/or new prophylactic strategies for patients at high risk?Several approaches are being developed that target new bloodvessel development, inflammatory cytokines, and the virusesthat are implicated in KS pathogenesis. 3) How does the improvedprognosis for human immunodeficiency virus (HIV)-infected patientsaffect KS treatment strategy? Improved anti-HIV therapy hasimplications for the timing of KS therapy, the choice of therapeutic approaches,and the potential for adverse drug interactions. 4) How canwe best evaluate benefits from KS treatment? More rigorous,standardized criteria are in development and will be essentialnot only for accurate documentation of objective tumor regression,but also for assessment of tumor-associated symptom relief ina quantitative, function-oriented way.     

New therapies for the treatment of AIDS-related Kaposi sarcoma

Kaposi sarcoma (KS) is the most common tumor arising in HIV-infected patients and is an AIDS-defining illness by the Centers for Disease Control guidelines. The clinical course of AIDS-related KS is highly variable, ranging from minimal stable disease to explosive growth. Recent advances in the elucidation of the pathogenesis of KS are uncovering many potential targets for KS therapies. Such targets include the processes of angiogenesis and cellular differentiation, sex hormones, and the KS herpesvirus/human herpesvirus-8. With the increasing recognition that effective antiretroviral regimens are associated with both a decreased proportion of new AIDS-defining KS cases and a regression in the size of existing KS lesions, most, if not all, KS patients should be advised to take antiretroviral drugs that will maximally decrease HIV-1 viral load. Five agents are currently approved by the Food and Drug Administration for the treatment of KS: alitretinoin gel for topical administration; and liposomal daunorubicin, liposomal doxorubicin, paclitaxel, and interferon-alpha for systemic administration. Many more agents, particularly angiogenesis inhibitors, are in early clinical development. The potential interaction between anti-KS agents and antiretroviral agents needs to be kept in mind. Virtually all patients with KS can derive benefit from the many approved and investigational agents developed through years of collaborative translational and clinical research.     

Immune reconstitution inflammatory syndrome associated with Kaposi's sarcoma.

PURPOSE: A proportion of patients with HIV infection who subsequently receive highly active antiretroviral therapy (HAART) exhibit a deterioration in their clinical status, despite control of virologic and immunologic parameters. This clinical response, known as the immune reconstitution inflammatory syndrome (IRIS), occurs secondary to an immune response against previously diagnosed pathogens. PATIENTS AND METHODS: From our cohort of 5,832 patients treated in the HAART era, we identified 150 therapy-naive patients with a first presentation of Kaposi's sarcoma (KS). Their clinicopathologic features and progress were recorded prospectively. RESULTS: After commencing HAART, ten patients (6.6%) developed progressive KS, which we identify as IRIS-associated KS. In a comparison of these individuals with those whose KS did not progress, we found that IRIS-KS occurred in patients with higher CD4 counts (P = .03), KS-associated edema (P = .01), and therapy with both protease inhibitors and non-nucleosides together (P = .03). Time to treatment failure was similar for both groups, although the CD4 count declined more rapidly at first, in those patients with IRIS-associated KS. Despite this initial decline, in our clinical experience HAART could be successfully continued in those with IRIS-associated KS. CONCLUSION: We have identified IRIS-KS in a cohort of HIV patients with KS who start HAART.     

Vinorelbine is an effective and safe drug for AIDS-related Kaposi's sarcoma: results of a phase II study.

PURPOSE: To assess the safety and efficacy of vinorelbine in patients with AIDS-related Kaposi's sarcoma (KS). PATIENTS AND METHODS: From December 1994 to May 1997, within the Italian Cooperative Group on AIDS and Tumors, we enrolled 36 patients with AIDS-related KS who experienced disease progression after one or more regimens of systemic chemotherapy. Patients were treated with vinorelbine 30 mg/m(2) every 2 weeks by intravenous bolus. RESULTS: Of 35 assessable patients, three (9%) had a clinical complete response and 12 (34%) had a partial remission, for an overall objective response rate of 43% (95% confidence interval, 26% to 61%). For the 15 patients with objective responses, the median duration of response from the beginning of therapy until the development of progression was 176 days, whereas the median progression-free survival and the median survival durations for 35 assessable patients were 151 days and 216 days, respectively. Vinorelbine also induced responses in patients who had become resistant to regimens that included other vinca alkaloids. Overall, vinorelbine was well tolerated. Toxicity, including neurologic toxicity, was mild and reversible. Neutropenia was the most frequent dose-limiting toxicity. CONCLUSION: Vinorelbine is safe and effective in the treatment of patients with advanced KS who have been previously treated with one or more chemotherapy regimens.     

Management of AIDS-related Kaposi's sarcoma: advances in target discovery and treatment

Kaposi's sarcoma is the most common tumor arising in HIV-infected patients and is an AIDS-defining illness by the Centers for Disease Control guidelines. Recent advances in the elucidation of the pathogenesis of KS are uncovering potential targets for KS therapies. Such targets include the processes of angiogenesis and cellular differentiation and the Kaposi's sarcoma herpesvirus/human herpesvirus-8. With the increasing recognition that effective antiretroviral regimens are associated with both a decreased proportion of new AIDS-defining Kaposi's sarcoma cases and a regression in the size of existing Kaposi's sarcoma lesions, most, if not all, Kaposi's sarcoma patients should be advised to take antiretroviral drugs that will maximally decrease HIV-1 viral load. Five agents are currently approved by the US FDA for the treatment of Kaposi's sarcoma; alitretinoin gel for topical administration; and liposomal daunorubicin, liposomal doxorubicin, paclitaxel and interferon-alpha for systemic administration. Many more agents, particularly angiogenesis inhibitors and other pathogenesis-targeted therapies are in early clinical development. Over the next 5 years, we may see even more of these pathogenesis-targeted therapies in trials and just as important we may identify, develop and validate clinically practical tools for assessing the biological effects of these therapies. The next 5 years may also bring a better understanding of the pharmacokinetic interactions among the many agents in the Kaposi's sarcoma and AIDS armamentariums.     

Therapy insight: AIDS-related malignancies--the influence of antiviral therapy on pathogenesis and management

Patients with HIV infection are at an increased risk of a number of malignancies, including Kaposi's sarcoma (KS) and certain B-cell lymphomas. Most of these tumors are caused by oncogenic DNA viruses, including KS-associated herpesvirus and Epstein-Barr virus. HIV contributes to the development of these tumors through several mechanisms, including immunodeficiency, immunodysregulation, and the effects of HIV proteins such as Tat. The development of highly active antiretroviral therapy (HAART) has reduced the incidence of many HIV-associated tumors and has generally improved their responsiveness to therapy. However, the number of people living with AIDS is increasing, and it is possible that the number of AIDS-associated malignancies will rise and the pattern of tumors will change as more people live longer with HIV infection. The goal of KS therapy is long-term tumor control with minimal toxicity. HAART is an important component of this therapy, and some patients do not require other KS-specific therapies. By contrast, the goal of AIDS-related lymphoma therapy in most cases is the attainment of a complete response with curative intent, and the benefits of administering HAART during therapy must be weighed against possible disadvantages. The past decade has seen substantial improvements in the treatment of AIDS-related lymphoma, which is attributed partially to a shift in tumor type and more effective regimens. There is currently an interest in developing new therapies for HIV-associated malignancies, based on viral, vascular or other pathogenesis-based targets.     

HIV protease inhibitors differentially inhibit adhesion of Candida albicans to acrylic surfaces

Highly active antiretroviral therapy (HAART), using HIV protease inhibitors, is commonly used in the management of HIV infection. HIV protease inhibitors also have a direct effect on a key virulence factor of Candida albicans, its secreted aspartyl proteinase (Sap). Although protease inhibitors can attenuate Candida adhesion to human epithelial cells, their effects on adhesion to acrylic substances, which is a common component of oral appliances, is unknown. This study investigated whether protease inhibitors affect C. albicans adhesion to acrylic substances. C. albicans suspensions were pretreated with different concentrations of saquinavir, ritonavir or indinavir for 1 h and allowed to adhere on acrylic strips, which had been pretreated with pooled human saliva for 30 min, for another hour in the presence of each drug. The test groups showed a significantly lower degree of adhesion than the controls. Adhesion was reduced by 50% at drug concentrations of 100, 100 and 20 μmol l^?1 for saquinavir, ritonavir and indinavir respectively. In conclusion, protease inhibitors attenuated C. albicans adhesion to an acrylic surface in vitro in a dose‐dependent manner, and different protease inhibitors exhibited different degrees of inhibition.     

Multicenter trial of low-dose paclitaxel in patients with advanced AIDS-related Kaposi sarcoma

BACKGROUND: Treatment options are limited for patients with advanced acquired immunodeficiency syndrome (AIDS)-related Kaposi sarcoma (AIDS-KS) whose disease has progressed after receiving therapy with liposomal anthracyclines or combination chemotherapy with doxorubicin (Adriamycin), bleomycin, and vincristine (ABV). This study was performed to assess the safety and efficacy of a novel dose and schedule of paclitaxel in patients with AIDS-KS who failed to respond to previous systemic chemotherapy. METHODS: This was an open-label, multicenter Phase II study. Eligible patients had advanced AIDS-KS consisting of at least 25 mucocutaneous lesions, visceral disease, or lymphedema, and had failed to respond to at least one previous systemic chemotherapy regimen. Patients were treated with paclitaxel at a dose of 100 mg/m(2) given intravenously over 3 hours, every 2 weeks. Primary efficacy end points were tumor response, time to progression, time to treatment failure, and survival. Quality of life and adverse events were evaluated using the Symptom Distress Scale (SDS) and the World Health Organization Toxicity Criteria, respectively. RESULTS: One hundred and seven male patients with advanced AIDS-KS were enrolled from nine participating sites. The median entry CD4+ lymphocyte count was 41/mm(3) (range 0-1139). Previous treatment regimens included ABV in 52, liposomal daunorubicin in 49, and liposomal doxorubicin in 40 patients. Forty-one patients (38%) received two or more previous chemotherapy regimens. Protease inhibitor use during the study was reported by 82 (77%) patients overall; 47 patients (44%) were receiving a protease inhibitor before study entry. Complete or partial response was documented in 60 patients (56%). The median duration of response was 8.9 months. Major response rate was similar when comparing patients not on a protease inhibitor at the time of response (59%) with patients on a protease inhibitor at time of response (54%). However, protease inhibitor use had a significant impact on survival (P = 0.04). Grade 4 neutropenia was reported in 35% of patients; other life-threatening side effects were uncommon. Significant improvements were seen in the total quality of life scores measured by the SDS, including significant improvement in KS-related symptoms such as facial disease, tumor-associated edema, and pulmonary involvement. CONCLUSION: Paclitaxel given every 2 weeks induces major tumor regression in the majority of patients with advanced KS who failed to respond to previous systemic chemotherapy. Paclitaxel is associated with significant improvement in quality of life with acceptable toxicity and should be considered as an effective treatment option for patients with advanced KS.     

Ritonavir inhibits intratumoral docetaxel metabolism and enhances docetaxel antitumor activity in an immunocompetent mouse breast cancer model

Docetaxel (Taxotere^®) is currently used intravenously as an anticancer agent and is primarily metabolized by Cytochrome P450 3A (CYP3A). The HIV protease inhibitor ritonavir, a strong CYP3A4 inhibitor, decreased first‐pass metabolism of orally administered docetaxel. Anticancer effects of ritonavir itself have also been described. We here aimed to test whether ritonavir co‐administration could decrease intratumoral metabolism of intravenously administered docetaxel and thus increase the antitumor activity of docetaxel in an orthotopic, immunocompetent mouse model for breast cancer. Spontaneously arising K14cre;Brca1^F/F;p53^F/F mouse mammary tumors were orthotopically implanted in syngeneic mice lacking Cyp3a (Cyp3a^?/?) to limit ritonavir effects on systemic docetaxel clearance. Over 3 weeks, docetaxel (20 mg/kg) was administered intravenously once weekly, with or without ritonavir (12.5 mg/kg) administered orally for 5 days per week. Untreated mice were used as control for tumor growth. Ritonavir treatment alone did not significantly affect the median time of survival (14 vs. 10 days). Median time of survival in docetaxel‐treated mice was 54 days. Ritonavir co‐treatment significantly increased this to 66 days, and substantially reduced relative average tumor size, without altering tumor histology. Concentrations of the major docetaxel metabolite M2 in tumor tissue were reduced by ritonavir co‐administration, whereas tumor RNA expression of Cyp3a was unaltered. In this breast cancer model, we observed no direct antitumor effect of ritonavir alone, but we found enhanced efficacy of docetaxel treatment when combined with ritonavir. Our data, therefore, suggest that decreased docetaxel metabolism inside the tumor as a result of Cyp3a inhibition contributes to increased antitumor activity.     

Management of AIDS-related Kaposi’s sarcoma: advances in target discovery and treatment

Kaposi’s sarcoma is the most common tumor arising in HIV-infected patients and is an AIDS-defining illness by the Centers for Disease Control guidelines. Recent advances in the elucidation of the pathogenesis of KS are uncovering potential targets for KS therapies. Such targets include the processes of angiogenesis and cellular differentiation and the Kaposi’s sarcoma herpesvirus/human herpesvirus-8. With the increasing recognition that effective antiretroviral regimens are associated with both a decreased proportion of new AIDS-defining Kaposi’s sarcoma cases and a regression in the size of existing Kaposi’s sarcoma lesions, most, if not all, Kaposi’s sarcoma patients should be advised to take antiretroviral drugs that will maximally decrease HIV-1 viral load. Five agents are currently approved by the US FDA for the treatment of Kaposi’s sarcoma; alitretinoin gel for topical administration; and liposomal daunorubicin, liposomal doxorubicin, paclitaxel and interferon-α for systemic administration. Many more agents, particularly angiogenesis inhibitors and other pathogenesis-targeted therapies are in early clinical development. Over the next 5 years, we may see even more of these pathogenesis-targeted therapies in trials and just as important we may identify, develop and validate clinically practical tools for assessing the biological effects of these therapies. The next 5 years may also bring a better understanding of the pharmacokinetic interactions among the many agents in the Kaposi’s sarcoma and AIDS armamentariums.