OR05-02 Silencing Of Adenylosuccinate Lyase Impairs Growth And Perturbs Mitochondrial Function Of Endocrine Therapy Resistant Breast Cancer Cells

Abstract Disclosure: A.K. Yadav: None. L. Jin: None. R. Clarke: None. S. Sengupta: None. The estrogen receptor positive (ER+) subtype comprises of ∼80% of all breast cancers and is the major contributor to cancer related deaths in women. While ER+ breast cancers respond to treatment with endocrine therapies (ET) such as tamoxifen, Fulvestrant and aromatase inhibitors, a major limitation is emergence of resistance to ET resulting from adaptive pathways that promote relapse and disease progression. Hence, there is an urgent need for identification and validation of new molecular targets for potential therapeutic treatment of ET resistant-ER+ breast cancer. Here, we have determined the role of adenylosuccinate lyase (ADSL), a crucial enzyme involved in the de novo purine synthesis pathway, as a potential molecular target for ER+ breast cancer cells. ADSL enzyme catalyzes two non-sequential steps in de-novo purine synthesis pathway that produces aminoimidazole carboxamide ribonucleotide (AICAR) and adenosine monophosphate (AMP); fumarate is generated as a byproduct. We observed higher protein expression of ADSL in LCC9 (endocrine therapy crossresistant cells) when compared with LCC1 or MCF-7 (antiestrogen sensitive) cells. Additionally, T47D-4HT cells (also endocrine therapy resistant) also expressed modestly higher ADSL protein level in comparison to its parental endocrine therapy sensitive T47D-A18 cells. Notably, siRNA-mediated knockdown of ADSL in both LCC9 and T47D-4HT cells leads to strong inhibition of cell proliferation, long-term colony, and spheroid formation. Furthermore, ADSL depletion in LCC9 increased the accumulation of cells in G0/G1 phase along with elevated protein expression of cyclin D1. In T47D-4HT cells, ADSL knockdown caused cells to accumulate in S-phase, with a reduction of total cyclin D1 protein levels. Further investigation revealed that ADSL knockdown decreased ATP levels and mitochondrial membrane potential in both LCC9 and T47D-4HT cells and significantly reduced the basal oxygen consumption rate (OCR) and maximal respiration capacity. Notably, addition of AICAR (100 µM) to ADSL deficient LCC9 cells partially rescued cell proliferation, colony formation, and restored the mitochondrial membrane potential. In clinical datasets higher expression of ADSL transcripts correlates with poor relapse free survival in ER+ breast cancer patients treated with endocrine therapies. Overall, our results indicate that ADSL-mediated de novo purine synthesis plays an important role in growth and proliferation of endocrine therapy resistant ER+ breast cancer cells through mitochondrial function. Therefore, targeting ADSL is a novel potential therapeutic approach for ER+ endocrine resistance breast cancer. Presentation: Thursday, June 15, 2023