Abstract 5468: SAR650984, a humanized anti-CD38 antibody potently modulates intracellular and extracellular nucleotide levels of cancer cells
Authors: Zhang Bailin , Yang Guang , Dai Shujia , He Tim , Simard Daniel , Song Zhili , Licht Stuart , Adrian Francisco , Cheng Hong , Cai Ti 
Published: May 2015

Abstract
CD38 is a type II transmembrane glycoprotein with both ectozyme activity and receptor function that has been implicated in cancer cell adhesion, signal transduction and calcium signaling. CD38 is highly expressed at the surface of many hematological cancer cells. SAR650984 is a humanized IgG1 antibody targeting CD38 in early clinical development to treat patients with CD38+ hematological malignancies. Several potential mechanisms of action of SAR650984 have been identified including antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and direct apoptosis induction (ASH 2008 Abstract #2756). In addition, SAR650984 displays potent inhibition of recombinant CD38 ADP-ribosyl cyclase activity in a biochemical assay (AACR 2013, Abstract #4735).
To further explore the impact of anti-CD38 antibodies on CD38 ecto-enzymatic activities in cancer cells, we have developed a robust LC-MS-based cellular CD38 enzymatic assay that monitors the depletion of CD38 substrates nicotinamide adenosine dinucleotide (NAD) or nicotinamide mononucleotide (NMN), and the production of cyclic adenosine diphosphoribose (cADPR) and adenosine diphosphoribose (ADPR) from CD38 cyclase and CD38 NAD glycohydrolyase activities, respectively. Preliminary results demonstrate that in response to the treatment of SAR650984, CD38 cyclase activity in multiple myeloma and lymphoma cancer cells was significantly inhibited by more than 90% as shown by a rapid and dose-dependent decrease in the rate of both substrate NAD/NMN depletion as well as extracellular cADPR production. Interestingly, a significant reduction of intracellular cADPR (over 60%) was also observed after SAR650984 treatment. On the other hand, extracellular ADPR level was only moderately affected by SAR650984 treatment with a reduction about 20% which could be hypothetically attributed to the relatively different potency of SAR650984 toward CD38 cyclase and hydrolase activity, or to its potential binding preference to different CD38 oligomers.
Emerging data suggest that nucleotides such as NAD and cADPR are important regulators of cell growth, survival and homeostasis. The altered levels of intracellular and extracellular nucleotides resulting from CD38 inhibition by SAR65084 in tumor microenvironment therefore could contribute to the anti-tumor efficacy of the antibody in addition to the previously identified mechanisms. Collectively, these results provide new insights toward understanding the multiple antitumor mechanisms of SAR650984. Additional studies to further understand these observations are currently ongoing.
Citation Format: Bailin Zhang, Guang Yang, Shujia Dai, Tim He, Daniel Simard, Zhili Song, Stuart Licht, Francisco Adrian, Hong Cheng, Ti Cai. SAR650984, a humanized anti-CD38 antibody potently modulates intracellular and extracellular nucleotide levels of cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5468. doi:10.1158/1538-7445.AM2014-5468