Preclinical Efficacy of an Antibody-Drug Conjugate Targeting Mesothelin Correlates with Quantitative 89Zr-ImmunoPET.

Antibody-drug conjugates (ADC) use monoclonal antibodies (mAb) as vehicles to deliver potent cytotoxic drugs selectively to tumor cells expressing the target. Molecular imaging with zirconium-89 (89Zr)-labeled mAbs recapitulates similar targeting biology and might help predict the efficacy of these ADCs. An anti-mesothelin antibody (AMA, MMOT0530A) was used to make comparisons between its efficacy as an ADC and its tumor uptake as measured by 89Zr immunoPET imaging. Mesothelin-targeted tumor growth inhibition by monomethyl auristatin E (MMAE), ADC AMA-MMAE (DMOT4039A), was measured in mice bearing xenografts of ovarian cancer OVCAR-3×2.1, pancreatic cancers Capan-2, HPAC, AsPC-1, and HPAF-II, or mesothelioma MSTO-211H. Ex vivo analysis of mesothelin expression was performed using immunohistochemistry. AMA-MMAE showed the greatest growth inhibition in OVCAR-3×2.1, Capan-2, and HPAC tumors, which showed target-specific tumor uptake of 89Zr-AMA. The less responsive xenografts (AsPC-1, HPAF-II, and MSTO-211H) did not show 89Zr-AMA uptake despite confirmed mesothelin expression. ImmunoPET can demonstrate the necessary delivery, binding, and internalization of an ADC antibody in vivo and this correlates with the efficacy of mesothelin-targeted ADC in tumors vulnerable to the cytotoxic drug delivered. Mol Cancer Ther; 16(1); 134-42. ©2016 AACR.

Supplementation of nicotinic acid with NAMPT inhibitors results in loss of in vivo efficacy in NAPRT1-deficient tumor models.

Nicotinamide adenine dinucleotide (NAD) is a metabolite essential for cell survival and generated de novo from tryptophan or recycled from nicotinamide (NAM) through the nicotinamide phosphoribosyltransferase (NAMPT)-dependent salvage pathway. Alternatively, nicotinic acid (NA) is metabolized to NAD through the nicotinic acid phosphoribosyltransferase domain containing 1 (NAPRT1)-dependent salvage pathway. Tumor cells are more reliant on the NAMPT salvage pathway making this enzyme an attractive therapeutic target. Moreover, the therapeutic index of NAMPT inhibitors may be increased by in NAPRT-deficient tumors by NA supplementation as normal tissues may regenerate NAD through NAPRT1. To confirm the latter, we tested novel NAMPT inhibitors, GNE-617 and GNE-618, in cell culture- and patient-derived tumor models. While NA did not protect NAPRT1-deficient tumor cell lines from NAMPT inhibition in vitro, it rescued efficacy of GNE-617 and GNE-618 in cell culture- and patient-derived tumor xenografts in vivo. NA co-treatment increased NAD and NAM levels in NAPRT1-deficient tumors to levels that sustained growth in vivo. Furthermore, NAM co-administration with GNE-617 led to increased tumor NAD levels and rescued in vivo efficacy as well. Importantly, tumor xenografts remained NAPRT1-deficient in the presence of NA, indicating that the NAPRT1-dependent pathway is not reactivated. Protection of NAPRT1-deficient tumors in vivo may be due to increased circulating levels of metabolites generated by mouse liver, in response to NA or through competitive reactivation of NAMPT by NAM. Our results have important implications for the development of NAMPT inhibitors when considering NA co-treatment as a rescue strategy.