Effect of FK866, NAMPT inhibitor, on small cell lung cancer cell lines

Background: Nicotinamide phosphoribosyl transferase (NAMPT) is the rate-limiting enzyme in the primary salvage pathway for nicotinamide adenine dinucleotide (NAD) synthesis. FK866 is a potent and specific small molecule inhibitor of NAMPT. The objective of this study was to validate the effect of NAD depletion on proliferation, and elucidate mechanism of cell death in small cell lung cancer (SCLC) cell lines. Methods: SCLC chemotherapy-sensitive lines (NCI-H209, NCI-H69, NCI-H446, & DMS79) and a resistant cell line (H69AR) were treated with increasing concentrations of FK866. CellTiter-Glo Luminescent Assay was used to measure ATP to assess cell viability, and the lethal dose 50 (LD50) was determined. A non-SCLC cell line (A549) was treated as a comparator. Treated cell lines were assessed for expression of NAMPT, Bcl-2, PARP and caspase-3 cleavage using Western blot. Chemo-sensitization potential by FK866 to doxorubicin and cisplatin was also evaluated. Results: Cell death measured at 72 hours occurred at very low FK866 concentrations (LD50 range = 0.38-7.2 nM) in both chemotherapy-sensitive and-resistant SCLC cell lines compared to the non-SCLC line (LD50= 100 nM). FK866 did not demonstrate synergy with doxorubicin or cisplatin in SCLC. At 24 hours, evidence of increased apoptosis was not observed as measured by Bcl-2 expression and caspase-3 cleavage, suggesting an alternate mechanism of cell death. Further work to establish mechanism is ongoing. Conclusions: This study confirms that SCLC cell lines are very sensitive to NAMPT inhibition by FK866 in vitro. Phase I clinical trials with FK866 suggest this is a well-tolerated drug. FK866 and related compounds may represent a novel treatment approach for SCLC, especially chemotherapy-resistant disease where active agents are desperately needed.