Abstract 1985: Ablation of adenylosuccinate lyase retarded the cell proliferation and induces mitochondrial dysfunction in endocrine therapy resistant breast cancer cells

Abstract Approximately 75% of breast tumors express estrogen receptors (ER+); recurrent ER+ breast cancer is generally incurable. Endocrine therapy (ET) is the mainstay of treatment for ER+ breast cancer and works by targeting either ER activity (Tamoxifen or Fulvestrant) or availability of its ligand estrogen (Letrozole, Exemestane). Unfortunately, endocrine therapies are limited by the emergence of resistance; resistance to endocrine therapies (ET) remains a significant clinical challenge. We have explored the role of adenylosuccinate lyase (ADSL), an enzyme of the de-novo purine biosynthesis pathway, in ET-resistant breast cancer cells. Protein expression of ADSL was significantly higher in two different ET-resistant cells (LCC9 and T47D-4HT) when compared with their respective parental ET-sensitive cells (MCF-7 and T47D). siRNA mediated ablation of ADSL in LCC9 and T47D-4HT cells blocked cell proliferation and both colony and spheroid formation. Depletion of ADSL in LCC9 cells obstructed cell cycle progression from G1 to S phase and elevated the protein expression of cyclin D1/D3, CDK2/4, and cyclin E. In T47D-4HT cells, ADSL depletion led to an accumulation of cells in S-phase with reduced protein expression of cyclin D1. Notably, ADSL ablation in LCC9 cells lead to DNA replication stress, resulting in activation (phosphorylation) of ataxia-telangiectasia-mutated-and-Rad3-related kinase (ATR) and its key downstream effector checkpoint kinase 1 (Chk1), which further limited the phosphatase activity of cdc25A leading to deactivation (phosphorylation) of Cyclin-Dependent Kinase 2 (CDK2). ADSL knockdown reduced the mitochondrial membrane potential and impaired the oxygen consumption (OCR) and extracellular acidification (ECAR) rates in both LCC9 and T47D-4HT cells. Of note, addition of AICAR to ADSL-depleted LCC9 cells significantly increased cell proliferation, colony formation, and restored mitochondrial membrane potential. RNA sequencing data revealed the effect of ADSL depletion on enrichment of different pathways in LCC9 and TH47D-4HT cells. Importantly, p53 signaling was significantly enriched in LCC9 cells but not in T47D-4HT cells after ADSL knockdown (T47D cells have a mutated p53 gene). ER+ breast cancer patients treated with ET showed high ADSL expression that is associated with poor recurrence-free survival. In summary, our findings indicate that ADSL-mediated de novo purine synthesis is crucial for cell proliferation. Therefore, targeting ADSL may be a novel therapeutic approach for ER, ET-resistant breast cancer. Citation Format: ANIL KUMAR Yadav, Lu Jin, Robert Clarke, Surojeet Sengupta. Ablation of adenylosuccinate lyase retarded the cell proliferation and induces mitochondrial dysfunction in endocrine therapy resistant breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1985.