Background:

GMX1778 (CHS828) is a potent and specific inhibitor of nicotinamide phosphoribosyltransferase (NAMPT) with a Kd value of 120 nM [1].

NAMPT is an NAD+ biosynthesis enzyme. NAD+ is a cofactor of enzymatic redox reactions that are involved in cellular metabolism, including ATP production. NAD+ is also important in many cellular pathways responsible for gene regulation, calcium homeostasis, genomic integrity, longevity and apoptosis. Cancer cells are significantly dependent on NAD+ for supporting high levels of ATP production for rapid cell proliferation [1].

Treatment with 30 nM GMX1778 for 6 h, extracts of IM-9 cells showed decreased NAD+ and NM levels, compared to cytosolic extracts of untreated cells. These levels continued to decrease throughout the rest of the time course experiment. The most profoundly changed was the metabolite NAD+ level. Between the 6- and 20-h time points, the decline of NAD+ occurred [1].

The NAD+ salvage pathway produces NAD+ using either nicotinic acid (niacin) (NA) or nicotinamide (niacinamide) (NM) as a substrate. NAPRT1 is short for NA phosphoribosyltransferase 1. On xenograft tumors derived from NAPRT1-proficient (HCT-116) and NAPRT1-deficient (HT1080) cell lines in mice, a 24-h iv infusion of GMX1777 at 150 mg/kg or 650 mg/kg produced antitumor activity. A 4-h iv infusion of NA at 120 mg/kg did not adversely affect the antitumor activity of GMX1777 in the NAPRT1-deficient xenograft, but abolished the antitumor activity of GMX1777 against the NAPRT1-proficient HCT-116 cell line [1].

Reference:
[1].  Watson M, Roulston A, Bélec L, et al. The small molecule GMX1778 is a potent inhibitor of NAD+ biosynthesis: strategy for enhanced therapy in nicotinic acid phosphoribosyltransferase 1-deficient tumors. Molecular and cellular biology, 2009, 29(21): 5872-5888.