Abstract C71: Preclinical evaluation of high-dose APO866, a Nampt inhibitor, with nicotinic acid rescue

Abstract

Abstract Leucovorin (folinic acid) rescue is clinically used to protect normal tissues fom methotrexate induced toxicity establishing the concept of rescue in high-dose anti-cancer therapy. Nicotinamide phosphoribosyltransferase (Nampt), a homodimeric enzyme, is the rate-limiting step in the resynthesis of nicotinamide adenine dinucleotide (NAD) from nicotinamide. Inhibition of Nampt results in depletion of cellular NAD and ATP in cancer cells leading to cell death. Cancer cells require more energy than somatic cells due to increased proliferation and activity, and many tumors also display increased activity of sirtuins and poly (ADP ribose) polymerises (PARPs) and this is the basis for the therapeutic potential of Nampt inhibitors in cancer. APO866 is an inhibitor of Nampt with a broad anti-tumor activity in cell lines. APO866 is currently in several phase II clinical trials in oncology. Here we present a preclinical study of increasing the therapeutic potential of APO866 more than 3-fold in a subset of tumor cell line xenografts through administration of nicotinic acid. Nicotinic acid can be used by cells to synthesize NAD in a Nampt-independent pathway. We find that oral administration of 50 mg/kg nicotinic acid (a fifth of the typical pharmacological dose in humans) protects mice from death or severe toxicity from a dose of 60 mg/kg APO866, where the maximally tolerated dose is normally 15 mg/kg. In a broad panel of cancer cell lines we find that 50 % (including ML-2 cells) are rescued from cell death by the addition of nicotinic acid to the media whereas the cytotoxicity of APO866 remains unchanged in the remaining 50 % (including A-2780 cells). We compared the in vivo effect of standard dose 15 mg/kg APO866 treatment with the combination of 50 mg/kg nicotinic acid and 60 mg/kg APO866 in mouse xenografts of ML-2 and A2780 tumor cells. We find that where standard treatment in A2780 xenografts results in an increase of lifespan (ILS) of 50 %, the combination treatment with a higher dose of APO866 yields an ILS of 180%. Conversely, in mouse xenografts of ML-2 the combination of nicotinic acid and high dose APO866 results in a poorer survival than standard dose treatment with 15 mg/kg APO866. The first step in NAD synthesis from nicotinic acid is catalysed by nicotinic acid phosphoribosyltransferase (NAPRT). We find that the mRNA expression of NAPRT is low in tumor cell lines not rescued fromAPO866 induced cell death by nicotinic acid whereas cell lines protected fromAPO866 display a high expression of NAPRT. Thus, ML-2 cells have 24-fold higher expression compared with A2780 and a similar difference is seen in samples from the xenograft tumors. In conclusion we find that since the adverse reactions of APO866 are linked to the mechanism of action it is well suited for combinatorial treatment. Furthermore, we conclude that combination of high doses of APO866 with rescue by moderate doses of nicotinic acid may increase the therapeutic potential in a subset of cancers with low expression of NAPRT. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C71.