Traditional cancer treatments may lose efficacy following the emergence of novel mutations or the development of chemoradiotherapy resistance. Late diagnosis, high-cost of treatment, and the requirement of highly efficient infrastructure to dispense cancer therapies hinder the availability of adequate treatment in low-income and resource-limited settings. Repositioning approved drugs as cancer therapeutics may reduce the cost and timeline for novel drug development and expedite the availability of newer, efficacious options for patients in need. Nelfinavir is a human immunodeficiency virus (HIV) protease inhibitor that has been approved and is extensively used as an anti-infective agent to treat acquired immunodeficiency syndrome (AIDS). Yet nelfinavir has also shown anti-cancer effects in in vitro and in vivo studies. The anti-cancer mechanism of nelfinavir includes modulation of different cellular conditions, such as unfolded protein response, cell cycle, apoptosis, autophagy, the proteasome pathway, oxidative stress, the tumor microenvironment, and multidrug efflux pumps. Multiple clinical trials indicated tolerable and reversible toxicities during nelfinavir treatment in cancer patients, either as a monotherapy or in combination with chemo- or radiotherapy. Since orally available nelfinavir has been a safe drug of choice for both adult and pediatric HIV-infected patients for over two decades, exploiting its anti-cancer off-target effects will enable fast-tracking this newer option into the existing repertoire of cancer chemotherapeutics.

High-grade serous ovarian cancer (HGSOC) is a significant cause of mortality among women worldwide. Traditional treatment consists of platinum-based therapy; however, rapid development of platinum resistance contributes to lower life expectancy, warranting newer therapies to supplement the current platinum-based protocol. Repurposing market-available drugs as cancer therapeutics is a cost- and time-effective way to avail new therapies to drug-resistant patients. The anti-HIV agent nelfinavir (NFV) has shown promising toxicity against various cancers; however, its role against HGSOC is unknown. Here, we studied the effect of NFV against HGSOC cells obtained from patients along disease progression and carrying different sensitivities to platinum. NFV triggered, independently of platinum sensitivity, a dose-dependent reduction in the HGSOC cell number and viability, and a parallel increase in hypo-diploid DNA content. Moreover, a dose-dependent reduction in clonogenic survival of cells escaping the acute toxicity was indicative of long-term residual damage. In addition, dose- and time-dependent phosphorylation of H2AX indicated NFV-mediated DNA damage, which was associated with decreased survival and proliferation signals driven by the AKT and ERK pathways. NFV also mediated a dose-dependent increase in endoplasmic reticulum stress-related molecules associated with long-term inhibition of protein synthesis and concurrent cell death; such events were accompanied by a proapoptotic environment, signaled by increased phospho-eIF2α, ATF4, and CHOP, increased Bax/Bcl-2 ratio, and cleaved executer caspase-7. Finally, we show that NFV potentiates the short-term cell cycle arrest and long-term toxicity caused by the proteasome inhibitor bortezomib. Overall, our in vitro study demonstrates that NFV can therapeutically target HGSOC cells of differential platinum sensitivities via several mechanisms, suggesting its prospective repurposing benefit considering its good safety profile.

High-grade serous ovarian cancer (HGSOC) is a significant cause of mortality among women worldwide. Traditional treatment consists of platinum-based therapy; however, rapid development of platinum resistance contributes to lower life expectancy, warranting newer therapies to supplement the current platinum-based protocol. Repurposing market-available drugs as cancer therapeutics is a cost- and time-effective way to avail new therapies to drug-resistant patients. The anti-HIV agent nelfinavir (NFV) has shown promising toxicity against various cancers; however, its role against HGSOC is unknown. Here, we studied the effect of NFV against HGSOC cells obtained from patients along disease progression and carrying different sensitivities to platinum. NFV triggered, independently of platinum sensitivity, a dose-dependent reduction of HGSOC cell number and viability, and a parallel increase in hypo-diploid DNA content. Moreover, a dose-dependent reduction of clonogenic survival of cells escaping the acute toxicity was indicative of long-term residual damage. In addition, dose- and time-dependent phosphorylation of gama-H2AX indicated NFV-mediated DNA damage, which was associated with decreased proliferation signals driven by the AKT and ERK pathways. NFV also mediated a dose-dependent increase in endoplasmic reticulum stress-related molecules associated with long-term inhibition of protein synthesis and concurrent cell death; such events were accompanied by a proapoptotic environment, signaled by increased phospho-eIF2-alpha, ATF4, and CHOP, increased Bax/Bcl-2 ratio, and cleaved executer caspase-7. Finally, we show that NFV potentiates the short-term cell cycle arrest and long-term toxicity caused by the proteasome inhibitor bortezomib. Overall, our in vitro study demonstrates that NFV can therapeutically target HGSOC cells of differential platinum sensitivities via several mechanisms, suggesting its prospective repurposing benefit considering its good safety profile.

Epithelial ovarian cancer (EOC) is a fatal disease due to late diagnosis and lack of effective long-term treatment(s). Since the introduction of debulking surgery and platinum (Pt)-taxane (Tx) therapy over 30 yrs. ago, there has been no significant breakthrough impacting the overall survival of these patients. Though over 70% of diagnosed women respond to front-line standard of care with remission, the disease hides as microscopic (minimal residual) within the abdominal cavity for about 18-24 months (mo.), recurring thereafter with a phenotype usually not responsive to current chemotherapeutic agents. As patients are left without treatment between remission and recurrence, our research initiative is to develop a consolidation therapy for chronic use after standard of care. In this work we explored whether such consolidation therapy could be developed from two simultaneous strategies: proteasome inhibition and aggravation of the stress of the endoplasmic reticulum (ER). The rationale for this combination therapy is that malignant cells are more susceptible to the toxicity of proteasome inhibition and operate with increased expression of ER stress-related proteins—coined as unfolded protein response (UPR) addiction—allowing cancer cells to survive in a hostile environment of reduced nutrients, acidosis, energy deficiency, and low oxygen tension (hypoxia). We hypothesized that simultaneous ER stress aggravation and blockage of the proteolytic capacity of the proteasome should cause sufficient ER stress to tilt cells to a death fate. We report that antiprogestin/antiglucocorticoid mifepristone (MF) as well as HIV protease inhibitor nelfinavir (NFV) enhanced the stress of the ER in EOC cells of high-grade serous origin (HGSOC), which is the most aggressive subtype of EOC, represents the majority of cases of EOC, and causes 2/3 of all deaths from this disease. We demonstrated, in HGSOC cells, that both MF and NFV cause cell cycle arrest associated with increased expression of cyclin dependent kinase inhibitor p27kip1, while triggering the UPR in a dose-dependent manner assessed by increased subrogate ER stress biomarkers GRP78, ATF4, and CHOP. We also discovered that blocking the ubiquitin proteasome system (UPS) using cytostatic concentrations of the proteasome inhibitor bortezomib (BZ) causes accumulation of poly-ubiquitinated proteins and further activation of the UPR. More importantly, when we combined BZ with either MF or NFV, we observed a potentiation of the action of BZ leading to EOC lethality. These results suggest that targeting the ER stress-associated protein quality control machinery with either an antiprogestin/antiglucocorticoid agent or an HIV protease inhibitor may provide an alternative chronic treatment approach against HGSOC after standard of care. In addition, the data provide the rationale for rapid repurposing to treating HGSOC, of three drugs clinically approved for other uses, as their systemic toxicities have already been assessed. Citation Format: Mahbuba Subeha, Lei Zhang, Alicia Goyeneche, Carlos Telleria. THE ANTIPROGESTIN/ANTIGLUCOCORTICOID MIFEPRISTONE AND THE HIV PROTEASE INHIBITOR NELFINAVIR CAUSE ENDOPLASMIC RETICULUM STRESS AND POTENTIATE THE TOXICITY OF PROTEASOME INHIBITION IN HIGH-GRADE SEROUS EPITHELIAL OVARIAN CANCER CELLS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-111.

High-grade serous ovarian cancer (HGSOC) is a significant cause of mortality among women worldwide. Traditional treatment consists of platinum-based therapy; however, the rapid development of platinum resistance contributes to lower life expectancy, warranting newer therapies to supplement the current platinum-based protocol. Repurposing market-available drugs as cancer therapeutics is a cost- and time-effective way to avail new therapies to drug-resistant patients. The anti-HIV agent nelfinavir (NFV) has shown promising toxicity against various cancers; however, its role against HGSOC is unknown. Here, we studied the effect of NFV against HGSOC cells obtained from patients along disease progression and carrying different sensitivities to platinum. NFV triggered, independently of platinum sensitivity, a dose-dependent reduction of HGSOC cell number and viability, and a parallel increase in hypo-diploid DNA content. Moreover, a dose-dependent reduction of clonogenic survival of cells escaping the acute toxicity was indicative of long-term residual damage. Western blot analysis of underlying molecular mechanisms revealed activation by NFV of the three signaling arms of the unfolded protein response (UPR): PERK, IRE1alpha and ATF6 - in a similar manner to the classical endoplasmic reticulum (ER) stressor tunicamycin. NFV-mediated modulation of the UPR was accompanied by the inhibition of global protein synthesis as analyzed through a non-radioactive method by labelling the nascent polypeptides with puromycin. NFV maintained a proapoptotic environment through the UPR, evidenced by a dose- and time-dependent enhanced expression of ATF4, CHOP, increased Bax/Bcl2 ratio, and cleavage of executioner caspase-7. Enhanced gamma-H2AX suggested NFV-mediated induction of DNA damage, which was associated with decreased proliferation signals driven by the AKT and ERK pathways. NFV increased the level of autophagosome-associated protein LC3II in HGSOC cells of varying platinum sensitivities; however, the autophagic flux was not increased during co-treatment with NFV and the lysosomal inhibitor bafilomycin A1, suggesting a likely impairment of the lysosomes by NFV impeding autophagosome clearance. Finally, we show that NFV potentiates the short-term cell cycle arrest and long-term toxicity caused by the proteasome inhibitor bortezomib. Overall, our in vitro study demonstrates that NFV can therapeutically target HGSOC cells of differential platinum sensitivities via several mechanisms, suggesting its prospective repurposing benefit considering its good safety profile. Citation Format: Mahbuba R. Subeha, Alicia A. Goyeneche, Prisca Bustamante, Michael A. Lisio, Julia V. Burnier, Carlos M. Telleria. Nelfinavir induced-cytotoxicity towards high-grade serous ovarian cancer cells involves induction of the unfolded protein response, modulation of protein synthesis, DNA damage, lysosomal impairment, and potentiation of toxicity caused by proteasome inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1839.