O2190: Use of NAMPT inhibitor ATN-940 in an orthotopic rhabdomyosarcoma mouse model

Background: Little improvement has been observed in rhabdomyosarcoma (RMS) outcomes over the last two decades, highlighting the need for novel therapies. Due to the metabolic shift described by the Warburg effect, cancer cells have an increased requirement for nicotinamide adenine dinucleotide (NAD+). Depletion of NAD+ via inhibition of nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme in NAD+ production has been proposed as a therapeutic intervention – however, clinical translation has been limited by thrombocytopenia and retinal toxicity. Previous studies have proposed that this toxicity could be limited through supplementation with nicotinic acid (NA), which restores NAD+ via a nicotinate phosphoribosyltransferase (NAPRT) dependent pathway. Because NAPRT is expressed in normal tissue but frequently absent in RMS, this mechanism might be exploited to “rescue” non-tumor tissue (e.g. bone marrow and retina) from the off-target side effects of NAPRT inhibition.

Methods: ATN-940, a NAMPT inhibitor from Alphina Therapeutics, was used to treat orthotopic mouse models bearing wild-type NAPRT-negative (RH41 WT) or NAPRT overexpressing (RH 41 OE) tumors. Mice were randomized into 3 treatment groups: ATN 940 alone (3mg/kg BID), ATN 940 + NA (3mg/kg + 25 mg/kg BID), or control (3% DMSO + 20% captisol). Tumor volume curves were analyzed using either one-way ANOVA or unpaired t-tests. Kaplan-Meier curves were analyzed using log rank testing. Mouse weights were analyzed using either one-way ANOVA or unpaired t-tests. Mice were sacrificed if tumors reached greater than 2000 mm3 or weight was reduced by greater than 20%.

Results: In the NAPRT-negative RH41 WT group, both ATN-940 and the combination of ATN-940 and NA exhibited significant anti-tumor effects compared to controls (Figure 1). In the NAPRT-positive RH 41 OE mice, only ATN alone exhibited an anti-tumor effect – the addition of NA allowed regeneration of NAD+ and was able to bypass the effect of NAMPT inhibition (Figure 1). This pattern affected not only tumor growth but also overall survival – NAMPT inhibition in mice with NAPRT-negative tumors was associated with prolonged survival independent of NA supplementation, whereas mice with NAPRT overexpressing tumors responded to ATN-940 alone, but rapidly met study end points if NAMPT inhibition was bypassed by supplementation with NA (Figure 2). Mouse weights were not significantly different across groups.

Conclusion: ATN-940 is effective in rhabdomyosarcoma. Selectively targeting NAPRT-negative tumors allows for retention of anti-tumor effect even with co-administration of nicotinic acid while tissues that are NAPRT-positive appear to be resistant to ATN-940 if supplemented with NA. This suggests that a NAMPT inhibitor plus NA could be used to treat NAPRT-negative RMS while mitigating dose-related toxicities in non-tumor tissue.