Summary Targeting sirtuins for cancer treatment has been a topic of debate due to conflicting reports and lack of potent and specific inhibitors. We have developed a thiomyristoyl lysine compound, TM, as a potent SIRT2-specific inhibitor with broad anticancer effect in various human cancer cells and mouse models of breast cancer. Mechanistically, SIRT2 inhibition promotes c-Myc ubiquitination and degradation. The anticancer effect of TM correlates with its ability to decrease c-Myc level. TM had limited effects on non-cancerous cells and tumor-free mice, suggesting that cancer cells have an increased dependency on SIRT2 that can be exploited for therapeutic benefit. Our studies demonstrate that SIRT2-selective inhibitors are promising anticancer agents and may represent a general strategy to target certain c-Myc-driven cancers.

Highlights d SIRT3 is highly expressed and linked to unfavorable outcome in DLBCL d SIRT3 is required for anaplerotic metabolism in DLBCL by enhancing GDH activity d Loss of Sirt3 impairs lymphomagenesis and prolongs survival of VavP-Bcl2 mice d Selective inhibition of SIRT3 by YC8-02 kills DLBCLs in vitro and in vivo

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Two mechanism-based activity probes, adopting a cassette-like design, for protein tyrosine phosphatases (PTPs) were synthesized. Both probes carry a phosphate group that serves as the recognition head for the target PTPs but differ in their reporter groups; probe LCL-1 uses a dansyl fluorophore, while LCL-2 has a biotin reporter group. LCL-1 and LCL-2 are specifically activated by phosphatase, leading to its covalent labeling, as exemplified with PTP-1B. However, they show no activation with other classes of hydrolases, including trypsin and beta-galactosidase. LCL-1 and LCL-2 thus represent the first example of class-selective probes for phosphatases.

SIRT5 is a member of the sirtuin family of NAD +-dependent protein lysine deacylases implicated in a variety of physiological processes. SIRT5 removes negatively charged malonyl, succinyl, and glutaryl groups from lysine residues and thereby regulates multiple enzymes involved in cellular metabolism and other biological processes. SIRT5 is overexpressed in human breast cancers and other malignancies, but little is known about the therapeutic potential of SIRT5 inhibition for treating cancer. Here we report that genetic SIRT5 disruption in breast cancer cell lines and mouse models caused increased succinylation of IDH2 and other metabolic enzymes, increased oxidative stress, and impaired transformation and tumorigenesis. We, therefore, developed potent, selective, and cell-permeable small-molecule SIRT5 inhibitors. SIRT5 inhibition suppressed the transformed properties of cultured breast cancer cells and significantly reduced mammary tumor growth in vivo, in both genetically engineered and xenotransplant mouse models. Considering that Sirt5 knockout mice are generally normal, with only mild phenotypes observed, these data establish SIRT5 as a promising target for treating breast cancer. The new SIRT5 inhibitors provide useful probes for future investigations of SIRT5 and an avenue for targeting SIRT5 as a therapeutic strategy.