Abstract B172: RP10107, a novel and potent glutaminase inhibitor, potentiates taxol activity in breast cancer cell lines
Authors: Penmetsa Kumar V. , Eleswarapu Satyanarayana , Dinavahi Saketh Sriram , Viswanadha Srikant , Vakkalanka Swaroop 
Published: May 2016

Abstract
Background: Breast cancer is the leading cause of cancer-related death among women worldwide. While early detection techniques, adjuvant therapy, and hormone replacement therapy, have led to a substantial decrease in mortality rates, breast cancer, especially triple negative breast cancer (TNBC) remains an important unmet clinical challenge. Although, Taxol, a mitotic inhibitor, is widely used in conjunction with other chemotherapeutic drugs for both early and late stage breast cancer, it is fraught with adverse effects. With cancer cell metabolism emerging as a critical regulator of tumor progression, combining Taxol with an inhibitor of the metabolic machinery represents a potential therapeutic strategy to prevent breast cancer progression. RP10107 is a novel, potent, and selective glutaminase (GLS-1) inhibitor that demonstrated high potency against mouse (IC50 = 21.2 nM), rat (IC50 = 18.2 nM) and human (IC50 = 26.4 nM) enzymes with selectivity over GLS-2 (&gt;380-fold). The objective of this study was to evaluate the effect of a combination of Taxol and RP10107 in breast cancer cell lines.
Methods: Half-maximal growth inhibition of MDA-MB-231 (TNBC), MCF-7 (ER+, PR+), and ZR 75.1 (ER+) cells was assessed using the colorimetric MTT reagent following incubation with Taxol or in combination with 30 nM RP10107 for 72 h. Additionally, synergism between Taxol and RP10107 was determined using different concentrations of the compounds in a 5 × 5 grid. Synergism, additivity, or antagonism was calculated based on the BLISS score. Apoptosis was determined by Annexin V/7AAD staining using a MUSE® Annexin V and dead cell assay kit (Millipore).
Results: Taxol inhibited growth of MDA-MB-231, MCF-7, and ZR 75.1 cells with GI50 of 48.9, 2.9, and 1.6 nM, respectively. Although the shift in GI50 upon addition of 30 nM RP10107 in MCF-7 and ZR 75.1 was modest, a &gt;480-fold reduction was observed in the TNBC cell line, MDA-MB-231 (GI50 = 0.9 nM). Similarly, while synergism (BLISS score &gt;10) between Taxol and RP10107 was noticed in all the cell lines tested, effect was most pronounced in MDA-MB-231 cells with &gt;70% growth inhibition seen upon combining of 3 nM Taxol with 10 nM RP10107. Additionally, incubation with the combination (1 nM Taxol + 1 nM RP10107) for 72 h increased the percent of apoptotic cells in MDA-MB-231 cells (35%) compared to the individual agents.
Conclusions: Addition of RP10107, a potent and selective GLS-1 inhibitor, potentiated Taxol activity in breast cancer cells with remarkable synergy evident in the TNBC cell line, MDA-MB-231. Findings provide a rationale for use of the combination in future clinical trials involving hard-to-treat TNBC patients thereby providing a safer and much effective option compared to currently available therapy.
Citation Format: Kumar V. Penmetsa, Satyanarayana Eleswarapu, Saketh Sriram Dinavahi, Srikant Viswanadha, Swaroop Vakkalanka. RP10107, a novel and potent glutaminase inhibitor, potentiates taxol activity in breast cancer cell lines. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B172.