Abstract 550: Targeting heat shock factor 1 in pancreatic ductal adenocarcinoma autophagy and iron-sulfur cluster protein stability.

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) cells exhibit elevated copper levels, an essential cofactor for cellular function, to support pancreatic tumor growth. Recent studies show that high levels of copper disrupt mitochondrial function by downregulating iron-sulfur (Fe-S) cluster proteins, leading to proteotoxic stress response and cell death; however, the detailed mechanism remains unclear. Heat shock factor 1 (HSF1), a key regulator of the proteotoxic stress response, is highly expressed in PDAC and supports protein stability, mitochondrial function, and tumor progression. This suggests HSF1 may help PDAC cells resist copper-induced cytotoxicity. The copper treatment also induces autophagy, yet whether copper-induced autophagy is regulated by HSF1 is not fully understood. Objective: The objective of this study is to study the role of HSF1 in copper-mediated loss of mitochondrial Fe-S cluster proteins and autophagy in PDAC cells. Methods and Results: In PDAC cell lines MIA PaCa-2 and PANC-1, treatment with copper ionophore elesclomol-copper (ES-Cu) led to reduced protein levels of mitochondrial Fe-S cluster proteins, including aconitase 2 (ACO2), ferredoxin 1 (FDX1), and lipoic acid synthase (LIAS), but not mRNA expression. Notably, HSF1 overexpression rescued the ES-Cu-decreased protein levels of ACO2, FDX1, and LIAS. Pharmacological inhibition of HSF1 led to increased lipidation of the autophagy marker microtubule-associated protein 1A/1B-light chain 3 (LC3). To investigate the mechanism of ES-Cu-mediated decrease of Fe-S cluster proteins, we pre-treated MIA PaCa-2 cells with hydroxychloroquine (CQ) along with ES-Cu. CQ did not rescue the ES-Cu-mediated decrease in Fe-S cluster proteins, suggesting that the degradation of Fe-S cluster proteins is not mediated by autophagy in copper-mediated cytotoxicity. Interestingly, inhibition of the mitochondrial-specific protease reversed the decrease in Fe-S cluster proteins under ES-Cu stress. Further, HSF1 inhibition with a small-molecule inhibitor significantly enhanced ES-Cu-reduced cell viability in PDAC cells. Conclusion: Our findings suggest that HSF1 protects PDAC cells from mitochondrial toxicity by maintaining the stability of Fe-S proteins under copper stress. Targeting HSF1 in combination with copper-based therapies may enhance treatment efficacy by disrupting mitochondrial stress adaptation in PDAC. Citation Format: Rejina Shrestha, Shruti Ghai, Hannah Nam, Kuo-Hui Su. Targeting heat shock factor 1 in pancreatic ductal adenocarcinoma autophagy and iron-sulfur cluster protein stability abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 550.