Disruption of GPSM1/CSF1 signaling reprograms tumor-associated macrophages to overcome anti-PD-1 resistance in colorectal cancer.

Background: Immune checkpoint blockade (ICB) therapies, particularly anti-PD-1, benefit only a limited subset of colorectal cancer (CRC) patients. G-protein signaling modulator 1 (GPSM1) is implicated in immunity and oncology, yet its role in regulating the CRC tumor microenvironment (TME) and contributing to anti-PD-1 resistance remains poorly understood.

Methods: We employed single-cell RNA sequencing and multiplex immunofluorescence on tumor samples from anti-PD-1-resistant CRC patients to evaluate GPSM1 expression and its impact on macrophage polarization. An orthotopic CRC xenograft model in C57BL/6 mice was used to assess the role of GPSM1 in vivo. An in vitro co-culture system, alongside mass cytometry and flow cytometry, explored GPSM1's biological functions within the TME. We further used ChIP-PCR, mass spectrometry, and co-immunoprecipitation to elucidate the mechanisms regulating GPSM1 activity.

Results: GPSM1 expression was significantly elevated in anti-PD-1-resistant CRC tissues. Enhanced GPSM1 levels promoted anti-PD-1 resistance by driving macrophage polarization toward an immunosuppressive M2 phenotype, facilitating their infiltration into the TME. We identified the deubiquitinase USP9X as a key factor preventing GPSM1 degradation through K63-polyubiquitination. This stabilization of GPSM1 led to MEIS3 nuclear translocation, activating macrophage colony-stimulating factor expression. Importantly, ruxolitinib emerged as a promising GPSM1-targeting candidate, demonstrating improved efficacy in combination with anti-PD-1 therapy in both microsatellite instability-high and microsatellite stable CRC models.

Conclusions: Our findings highlight the pivotal role of GPSM1-driven M2 macrophage infiltration in mediating anti-PD-1 resistance in CRC. Targeting GPSM1 offers a novel therapeutic strategy to enhance ICB efficacy, potentially broadening the patient population that may benefit from these therapies.