Goran Micevic

Chronic stimulation of CD8⁺ T cells within the tumor microenvironment (TME) induces a hypofunctional state characterized by diminished cytotoxicity and functionally impaired anti-tumor function, known as exhaustion. Exhaustion is associated with epigenetic changes that remain relatively stable despite interventions like immune checkpoint inhibition (ICI). Although epigenetic changes are potentially reversible, reports of therapeutic strategies to effectively restore function in exhausted CD8⁺ T cells remain limited. Here, we report DNA methyltransferase 1 (DNMT1) inhibition (DNMT1i) in counteracting CD8 ⁺ T cell dysfunction during the anti-tumor response. We show that DNMT1i synergizes with ICI to rescue the tumor cell killing activity of chronically stimulated CD8⁺ T cells in a melanoma model. DNMT1i mitigates transcriptional features of exhaustion while inducing a divergent effector program. DNMT1i attenuates the global increase in chromatin accessibility associated with exhaustion and enables epigenetic remodeling of the exhausted chromatin landscape upon restimulation. Finally, DNMT1i enhances the effector function of melanoma patient-derived tumor infiltrating lymphocytes after prolonged ex vivo expansion. These studies establish DNMT1 targeting as a promising strategy to counteract CD8⁺ T cell exhaustion and potentiate ICI efficacy.

DepMap HMGCR gene expression and gene effect scores for 1,078 cancer cell lines

Differential expression of SKO vs YRG cells ± IFNAR blockade by RNAseq.

Mevalonate pathway activity distinguishes treatment response in melanoma tumor cells.

Summary of exonic mutations in YRG cells compared with YMG and WT C57BL6/J cells.

Statins have been reported to exert anticancer activity, varying with cancer type and specific statins. These findings suggest that more mechanistic insights into the anticancer effects of statins are needed. In this study, we interrogated the ability of statins to induce cell death and ferroptosis in melanoma and colorectal cancer. First, we showed that statins induce cell death in patient-derived melanoma cell lines and that lower expression of mevalonate pathway genes correlates with increased CD8+ T-cell infiltration and improved overall survival in patients with melanoma. We found that lipophilic statins induce cell death with features of ferroptosis. Transcriptional data also revealed system-level changes to a variety of ferroptosis-related pathways. We found that mevalonate rescued statin-induced cell death. Mechanistically, mevalonate-derived isopentyl pyrophosphate is necessary for isopentylation of tRNA [Ser]Sec, which is required for efficient synthesis of the selenoprotein ferroptosis suppressor GPX4. Given the emerging role for ferroptosis in antitumor immunity, we tested lipophilic statins, including simvastatin, alone and in combination with α-PD1 in vivo and found that simvastatin and α-PD1 promoted tumor clearance and extended survival in 20% to 60% of mice alone but in nearly 100% of mice when administered together. Simvastatin also depleted GPX4 in vivo. These results highlight the therapeutic potential of statin use in combination with immunotherapies.

Differential expression of SKO vs YRG cells, by RNAseq.

Figure S2: CRISPR screen guide distributions, related to Figure 1

Statins suppress GPX4 expression and mevalonate rescues statin-induced cell death