Abstract B011: GPT2 as a novel driver of platinum-resistant ovarian cancer
Authors: Ponton-Almodovar Adriana L. , Bernard Jamie , Horibata Sachi 
Published: March 2024

Abstract
The majority of ovarian cancer patients experience tumor recurrence and chemoresistance to platinum-based drugs, i.e., cisplatin and carboplatin, leading to significant morbidity and mortality. Metabolic adaptations are often a hallmark feature of chemoresistance; however, how metabolic reprogramming drives drug resistance in ovarian cancer is unknown. The purpose of this study is to determine metabolic changes that promote chemoresistance and exploit these targets for treatment. For this study, we utilized a novel model of platinum-induced resistance in treatment-naïve 1A9 ovarian cancer cells. Specifically, platinum-sensitive 1A9 cells acquired resistance to a high concentration of cisplatin after increased exposure over time; after a year of treatment, the cisplatin was removed, and the platinum-resistant cells became re-sensitized. Transcriptomic analysis of resistant/re-sensitized 1A9 cells revealed that glutamate-pyruvate transaminase (GPT) is upregulated in platinum-resistant 1A9 cells and downregulated in re-sensitized cells, suggesting that glutamine metabolism is associated with resistance. GPT is downstream of the glutaminolysis pathway and catalyzes the reversible transamination of glutamate and pyruvate to α-ketoglutarate and alanine. The enzyme contributes to anapleurosis by directly fueling the TCA cycle to produce energy. RNA-seq transcriptomic analysis of GPT modulation was validated in 1A9 and OVCAR8 (high-grade serous carcinoma) using qRT-PCR and Western Blotting. Chemoresistance in both cell models was associated with the overexpression of two GPT isoforms - GPT1 and GPT2. We hypothesized that GPT2, the mitochondrial isoform, is required for survival in presence of cisplatin and promotes chemoresistance. To evaluate if GPT2 is necessary to drive chemoresistance, we utilize CRISPR-Cas9 gene editing system to knockdown GPT2 in platinum-resistant OVCAR8 cells. The knockdown of GPT2 in platinum-resistant, GPT2high cells resulted in the re-sensitization to cisplatin, suggesting GPT2 may be necessary for survival in the context of chemotherapy. To pharmacologically target this pathway, chemoresistant, GPT2high cells were treated with BPTES (bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl) ethyl sulfide), a glutaminase inhibitor that reduces intracellular glutamine. The 50% inhibitory concentration (IC50) of BPTES in chemoresistant, GPT2high cells was lower than that of chemosensitive, GPT2low cells, demonstrating a greater efficacy of this treatment in resistant cells. Furthermore, altering the microenvironment by depriving glutamine or culturing with adipose tissue-conditioned medium modulated GPT2 expression. These studies suggest that (1) glutaminolysis is necessary for survival of platinum-resistant ovarian cancer cells, (2) GPT2 is modulated by nutrients in the microenvironment, and (3) GPT2 expression is a biomarker of chemoresistance.
Citation Format: Adriana L. Ponton-Almodovar, Jamie Bernard, Sachi Horibata. GPT2 as a novel driver of platinum-resistant ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B011.