Resistance to chemotherapy is a major challenge in the treatment of advanced melanoma. Targeting the innate immune response to improve chemotherapy efficacy is a promising yet understudied area. We identified Pros1 as an innate immune checkpoint utilized by tumors to suppress the macrophage pro-inflammatory response. Secreted Pros1 prevents macrophage response to tumor damage-associated molecular patterns (DAMPs) released during chemotherapy. However, the effect of Pros1 on other immune system cells and the molecular mechanism that triggers its expression remain unclear.
To determine how Pros1 affects chemotherapy efficacy and immune activation, we generated a melanoma cell line (B16F10) lacking Pros1 using CRISPR-Cas9 and tested it in a syngeneic murine preclinical model. Immune infiltration was assessed by single-cell RNA-seq in end-stage tumors.
Mice bearing Pros1-deficient tumors showed a 63±10% (mean ± SEM) decrease in tumor growth after cisplatin treatment and a 5-fold increase in immune infiltration when compared to wild type. B cells were the most enriched group in Pros1-deficient tumors, with increased communication with T cells. Using bulk RNA-seq, we determined that Ifnγ stimulates Pros1 expression in melanoma cells as well as other immune suppressors, including Ido1, Pd-l1 and Tgfb1. Ifnγ-dependent Pros1 expression was conserved among several cancer cell types, including melanoma, lung, breast, and pancreatic cancer, suggesting its role as a global immune suppressor. By using siRNA, we determined that Ifngr1/Ifngr2 and Stat1 are key modulators of Ifnγ-dependent Pros1 expression, but not Stat3.
We identified a novel mechanism through which cancer cells promote Pros1 expression in response to chemotherapy. A better understanding of the mechanisms that regulate Pros1 expression may allow us to increase the efficacy of conventional therapies in melanoma patients.
NIH grant R01CA262241
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Nestor Prieto-Dominguez, Oluwaseyi Omodiminiyi, Eric Ubil· Journal of Immunology· 0 citations
Despite advancements in immunotherapy, more than half of melanoma patients will either not respond or will later relapse after treatment with immune checkpoint blockade (ICB). For later-stage patients, chemotherapy is an essential treatment modality, but tumor intrinsic cell survival mechanisms and an immunosuppressive tumor microenvironment often limit efficacy. We recently discovered that by upregulating the secretion of Pros1, tumor cells limit the response of macrophages to chemotherapy released tumor Damage Associated Molecular Patterns (DAMPs). By pharmacologically inhibiting Ptp1b, a signaling intermediary downstream of the Mer receptor, macrophage responsiveness to DAMPs can be restored. This is associated with increased macrophage M1 polarization and immune infiltration, as well as a 40-80% decrease in tumor volume in multiple preclinical models.
We hypothesize that because Ptp1b inhibition prevents tumor suppression of DAMP responsiveness, combining Ptp1b inhibition may improve the efficacy of multiple chemotherapies, particularly those that promote necrotic and immunogenic cell death. To test this, macrophages were co-cultured with murine melanoma cells (B16F10) and cisplatin, doxorubicin, or dacarbazine in the presence or absence of Ptp1b inhibitor via transwell assay, after determining the relative amounts of apoptosis/necrosis produced by each chemotherapy.
Preliminary results indicate that Ptp1b inhibition significantly increases macrophage pro-inflammatory gene expression by 7.5-fold in a setting of chemotherapy-induced tumor DAMP release. This indicates that inhibiting Ptp1b could synergistically improve chemotherapy effectiveness.
As Ptp1b inhibitors have a reasonable safety profile based on multiple clinical trials, combining Ptp1b inhibiting drugs with chemotherapy may be a novel way to restore the innate immune response during treatment while also improving patient outcomes.
NCI- RO1 CA262241(Ubil)
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Oluwaseyi Omodiminiyi, Nestor Prieto-Dominguez, Eric Ubil· Journal of Immunology· 0 citations
