Clements, A. N. | bioRxiv Science

bioRxiv2024

Inhibition of PIM kinase in tumor associated macrophages suppresses inflammasome 1 activation and sensitizes prostate cancer to immunotherapy

Immunotherapy has changed the treatment paradigm for many types of cancer, but immune checkpoint inhibitors (ICIs) have not shown benefit in prostate cancer (PCa). Chronic inflammation contributes to the immunosuppressive prostate tumor microenvironment (TME) and is associated with poor response to ICIs. The primary source of inflammatory cytokine production is the inflammasome. Here, we identify PIM kinases as important regulators of inflammasome activation in tumor associated macrophages (TAMs). Analysis of clinical data from a cohort of treatment naive, hormone responsive PCa patients revealed that tumors from patients with high PIM1/2/3 display an immunosuppressive TME characterized by high inflammation (IL-1{beta} and TNF) and a high density of repressive immune cells, most notably TAMs. Strikingly, macrophage-specific knockout of PIM reduced tumor growth in syngeneic models of prostate cancer. Transcriptional analyses indicate that eliminating PIM from macrophages enhanced the adaptive immune response and increased cytotoxic immune cells. Combined treatment with PIM inhibitors and ICIs synergistically reduced tumor growth. Immune profiling revealed that PIM inhibitors sensitized PCa tumors to ICIs by increasing tumor suppressive TAMs and increasing the activation of cytotoxic T cells. Collectively, our data implicate macrophage PIM as a driver of inflammation that limits the potency of ICIs and provides preclinical evidence that PIM inhibitors are an effective strategy to improve the efficacy of immunotherapy in prostate cancer.

cancer biology↗

bioRxiv2021

Direct phosphorylation and stabilization of HIF-1α by PIM1 kinase drives angiogenesis in solid tumors

Angiogenesis is essential for sustained growth of solid tumors. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of angiogenesis and constitutive activation of HIF-1 is frequently observed in human cancers. Thus, understanding mechanisms governing the activation of HIF-1 is critical for successful therapeutic targeting of tumor angiogenesis. Herein, we establish a new regulatory mechanism responsible for the constitutive activation of HIF-1 in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1 at threonine 455, a previously uncharacterized site within its oxygen-dependent degradation domain. This phosphorylation event disrupts the ability of prolyl hydroxylases (PHDs) to bind and hydroxylate HIF-1, interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Overexpression of PIM1 is sufficient to stabilize HIF-1 in normoxia and stimulate angiogenesis in a HIF-1-dependent manner in vivo. CRISPR mutants of HIF-1 (Thr455D) showed increased tumor growth, proliferation and angiogenesis. Moreover, T455D xenograft tumors were refractory to the anti-angiogenic and cytotoxic effects of PIM inhibitors. These data identify a new signaling axis responsible for hypoxia-independent activation of HIF-1 and expand our understanding of the tumorigenic role of PIM1 in solid tumors.

cancer biology↗