Search

Pancreatic cancer (PC) is one of the most lethal human malignancies and a major health problem. Patients diagnosed with PC and treated with conventional approaches have an overall 5-year survival rate of less than 5%. Novel strategies are needed to treat this disease. Herein, we propose a combinatorial strategy that targets two unrelated metabolic enzymes overexpressed in PC cells: NAD(P)H:quinone oxidoreductase-1 (NQO1) and nicotinamide phosphoribosyl transferase (NAMPT) using β-lapachone (BL) and APO866, respectively. We show that BL tremendously enhances the antitumor activity of APO866 on various PC cell lines without affecting normal cells, in a PARP-1 dependent manner. The chemopotentiation of APO866 with BL was characterized by the following: (i) nicotinamide adenine dinucleotide (NAD) depletion; (ii) catalase (CAT) degradation; (iii) excessive H 2 O 2 production; (iv) dramatic drop of mitochondrial membrane potential (MMP); and finally (v) autophagic-associated cell death. H 2 O 2 production, loss of MMP and cell death (but not NAD depletion) were abrogated by exogenous supplementation with CAT or pharmacological or genetic inhibition of PARP-1. Our data demonstrates that the combination of a non-lethal dose of BL and low dose of APO866 optimizes significantly cell death on various PC lines over both compounds given separately and open new and promising combination in PC therapy.

APO866 is an inhibitor of nicotinamide adenine dinucleotide (NAD) biosynthesis that exhibits potent anti-lymphoma activity. Rituximab (RTX), an anti-CD20 antibody, kills lymphoma cells by direct apoptosis and antibody- and complement-dependent cell-mediated cytotoxicities, and has clinical efficacy in non-Hodgkin cell lymphomas. In the present study, we evaluated whether RTX could potentiate APO866-induced human B-lymphoma cell death and shed light on death-mediated mechanisms associated with this drug combination. We found that RTX significantly increases APO866-induced death in lymphoma cells from patients and lines. Mechanisms include enhancement of autophagy-mediated cell death, activation of caspase 3 and exacerbation of mitochondrial depolarization, but not increase of reactive oxygen species (ROS) production, when compared with those induced by each drug alone. In vivo, combined administration of APO866 with RTX in a laboratory model of human aggressive lymphoma significantly decreased tumor burden and prolonged survival over single-agent treatment. Our study demonstrates that the combination of RTX and APO866 optimizes B-cell lymphoma apoptosis and therapeutic efficacy over both compounds administered separately.

APO866, an inhibitor of NAD biosynthesis, exhibits potent antitumor properties in various malignancies. Recently, it has been shown that APO866 induces apoptosis and autophagy in human hematological cancer cells, but the role of autophagy in APO866-induced cell death remains unclear. Here, we report studies on the molecular mechanisms underlying APO866-induced cell death with emphasis on autophagy. Treatment of leukemia and lymphoma cells with APO866 induced both autophagy, as evidenced by an increase in autophagosome formation and in SQSTM1/p62 degradation, but also increased caspase activation as revealed by CASP3/caspase 3 cleavage. As an underlying mechanism, APO866-mediated autophagy was found to deplete CAT/catalase, a reactive oxygen species (ROS) scavenger, thus promoting ROS production and cell death. Inhibition of autophagy by ATG5 or ATG7 silencing prevented CAT degradation, ROS production, caspase activation, and APO866-induced cell death. Finally, supplementation with exogenous CAT also abolished APO866 cytotoxic activity. Altogether, our results indicated that autophagy is essential for APO866 cytotoxic activity on cells from hematological malignancies and also indicate an autophagy-dependent CAT degradation, a novel mechanism for APO866-mediated cell killing. Autophagy-modulating approaches could be a new way to enhance the antitumor activity of APO866 and related agents.