Breast cancer remains one of the most diagnosed cancers among women worldwide, with triple-negative breast cancer (TNBC) being the most aggressive form and having the fewest treatment options. To develop more effective treatment for patients with TNBC, much work is needed to understand the mechanisms that drive this disease. Sirtuin 5 (SIRT5), a mitochondrial lysine deacylase, regulates various metabolic pathways, including the TCA cycle, glutamine metabolism, and redox homeostasis. Unlike other members of the Sirtuin family, SIRT5 uniquely removes negatively charged short-chain acyl groups, such as succinyl and malonyl, from target proteins, making it an exciting candidate for identifying novel cellular mechanisms. SIRT5 is upregulated in tumors from TNBC patients and has recently been identified as a new druggable target in cancer cells, with preclinical studies showing reduced tumor progression. However, the regulatory roles of SIRT5 in the tumor microenvironment (TME) remain unexplored. The TME has been receiving more attention in the development of new therapeutic mechanisms, and understanding whether and how SIRT5 in the TME contributes to TNBC progression could inspire novel therapeutic strategies.

Here, I describe a tumor-extrinsic role for SIRT5 in breast cancer progression, specifically in the regulation of endothelial cell (EC) metabolism and tumor vasculature function. Inhibition of SIRT5 in human ECs in vitro led to increased mitochondrial ROS (mtROS) and a deficiency in angiogenic function, and treatment with an mtROS scavenger rescued these phenotypes. In a 3-dimensional microfluidic culture model, SIRT5-inhibited ECs failed to maintain a cohesive blood vessel structure and initiate angiogenesis normally, further highlighting the importance of SIRT5 in vasculature homeostasis and angiogenesis. This SIRT5-dependent endothelial fitness was then validated in various cancer mouse models, in which endothelial SIRT5 inhibition led to reduced and dysfunctional tumor vasculature.

Broader systemic requirements for SIRT5 and its potential for synergistic therapeutic interventions were also explored. The tumor-suppressive effect of SIRT5 deficiency persisted independently of mature adaptive immune populations (T and B cells), suggesting the immunological roles of SIRT5 lie more in the innate immune system. I also characterized the requirement for SIRT5 in maintaining mitochondrial homeostasis within malignant cells, noting that, while it is essential for respiration, its role in supporting glycolytic flux varies. To exploit these metabolic vulnerabilities, I demonstrated that pharmacological inhibition of SIRT5 with the small-molecule inhibitor DK1-04e synergistically potentiated the anti-tumor effects of Artesunate, an FDA-approved ROS-inducing agent. This combination achieved robust efficacy at reduced drug dosages, suggesting that DK1-04e pharmacologically lowers the lethal oxidative threshold while artesunate induces ROS in both malignant and endothelial cells.