Abstract 279: Unraveling biological differences of high grade serous ovarian cancer subtypes by metabolomics

Abstract Epithelial ovarian cancer (EOC) accounts for ∼90% of ovarian cancers and continues to be a deadly disease. High grade serous ovarian cancer (HGSOC) is the most common subtype of EOC. PARP inhibitors (PARPis) are important drugs for treating recurrent ovarian cancer post-platinum-based chemotherapy and recently this has been applied to first-line maintenance treatment after chemotherapy. Meta-analysis suggested that PARPis are most effective for patients with Brca mutations. Studies also suggested better efficacy of PARPis in HGSOC patients with Brca2 mutations than patients with Brca1 mutations. However, only ∼15-20% of HGSOC tumors carry germline Brca1 or Brca2 mutations and somatic mutations are found in ∼8% of cases. In addition, the increasing use of PARPis for treating HGSOC has raised concerns about PARPi resistance in clinical practice. Clearly, there is an urgent need to identify new metabolic vulnerabilities in HGSOC in general, and in Brca1/Brca2 mutant subtypes in particular, that can be targeted alone, or in combination with existing medications including PARPis. The ID8 HGSOC model is the most widely used transplantable mouse syngeneic model of ovarian cancer. ID8 variants including single (Trp53-/-) or double (Trp53-/-/Brca1-/- or Trp53-/-/Brca2-/-) gene deletions recapulate characteristics of human HGSOC subtypes including the expected patterns of sensitivity to cisplatin and PARPis (i.e., olaparib). Our previous studies showed that in primary patient specimens [including normal ovary (n=8) and HGSOC (n=40)], transcripts for one-carbon (C1) genes in mitochondria (SLC25A32, SHMT2, MTHFD2, MTHFD1L) and in cytosol (GARFTase, AICARFTase) increased significantly over normal ovaries. We performed untargeted metabolomics studies (∼2000 metabolites) with the aforementioned ID8 sublines. The results showed significant quantitative differences between wild-type ID8 and ID8/Trp53-/-, ID8/Trp53-/-/Brca1-/- or ID8/Trp53-/-/Brca2-/- cells, as well as between ID8/Trp53-/-/Brca1-/- and ID8/Trp53-/-/Brca2-/- cells, involving C1 metabolism including metabolites of glycine, serine, threonine, cysteine, methionine, pyrimidines and purines. Targeted metabolomics and flux analysis with [13C (U)]serine and LC-MS/MS revealed enhanced mitochondrial C1 flux in the ID8 variants, reflected in levels of total serine and serine isotopomers (ID8 > ID8/Trp53-/- = ID8/Trp53-/-/Brca1-/- > ID8/Trp53-/-/Brca2-/-). C1 flux from [13C (U)]serine in the cytosol was also significantly elevated in ID8 variants, reflected in a dramatic decrease of glycinamide ribonucleotide (GAR) (M+0, M+2) in de novo purine biosynthesis compared to wild-type ID8 cells. Collectively, our results suggest that C1 metabolism in both the mitochondria and cytosol is a bona fide metabolic vulnerability in HGSOC that can be therapeutically exploited. Citation Format: Zhanjun Hou, Madelyn Brzezinski, Carrie O’Connor, Xun Bao, Ayesha B. Alvero, Radhika Gogoi, Ramandeep Rattan, Gil Mor, Jing Li, Aleem Gangjee, Larry H. Matherly. Unraveling biological differences of high grade serous ovarian cancer subtypes by metabolomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 279.