In breast cancer, progression from localized stage I to distant metastatic stage IV disease is associated with a reduction of 5-year survival from nearly 100% to 23.2%. Expression of the calcium-activated protease isoforms calpain-1 and calpain-2 has been correlated with cell migration and invasion in vitro, metastatic potential in preclinical mouse models of cancer, and breast cancer prognosis in patients. It is unclear which of these two calpain isoforms is responsible for the apparent metastatic potential of cancer cells. Here, we demonstrate that while individual CRISPR-Cas9 knockouts of either CAPN1 or CAPN2 genes (encoding the catalytic subunits of calpain-1 and -2, respectively) reduce in vitro migration and marginally suppress in vivo metastasis, genetic disruption of both calpain-1 and calpain-2 through knockout of the CAPNS1 gene (encoding the common regulatory subunit of calpain-1 and -2) diminishes metastasis by 83.4 ± 13.6% in a mouse xenograft model of human triple-negative breast cancer. The effect of calpain-1/2 deficiency was replicated in vitro with a modified cell-permeable calpastatin (CAST)-based peptide inhibitor (cell migration reduced to 53.5 ± 11.0% of vehicle control). However, this peptide inhibitor was not effective in vivo at reducing metastasis under the conditions used (vehicle vs. CAST, 1.12 ± 1.35 lung metastases per mm² vs. 0.34 ± 0.20 metastases per mm²), likely due to rapid clearance, as indicated by the short serum half-life. This work demonstrates that calpain-1/2 disruption effectively abrogates metastasis and provides rationale for development of effective calpain inhibitors.

Homeostatic immunoregulatory mechanisms that prevent adverse effects of immune overaction can serve as barriers to successful anticancer immunity, representing attractive targets to improve cancer immunotherapy. Here, we demonstrated the role of the nonreceptor tyrosine kinase Fes, abundantly expressed in immune cells, as an innate intracellular immune checkpoint. Host Fes deficiency delayed tumor onset in a gene dose-dependent manner and improved tumor control, survival, doxorubicin efficacy, and sensitized tumors to anti–PD-1 therapy in murine triple-negative breast cancer and melanoma models. These effects were associated with a shift to an antitumorigenic immune microenvironment. Fes-deficient macrophages displayed increased Toll-like receptor signaling, proinflammatory cytokine production, and antigen presentation to and activation of T cells, leading to increased cancer cell killing in vitro and tumor control in vivo. This study highlights Fes as an innate immune checkpoint with potential as a therapeutic target and a predictive biomarker to guide immune checkpoint inhibitor treatment. Significance: Fes activity modulates the inflammatory cytokine presentation and T-cell priming capabilities of macrophages, supporting the potential of Fes as a target for developing therapeutic and biomarker strategies to improve cancer immunotherapy.

Immune profiling antibody panels

Fes-deficiency improves T cell priming capabilities of BMDMs at a range of SIINFEKL concentrations in a Signal 2-independent mechanism.

Fes-deficiency increases sensitivity to LPS stimulation.

PD-1 therapy delays tumor growth rates only in Fes-/- mice.