Oct-1 DNA binding activity unresponsive to retinoblastoma protein expression prevents MHC class II induction in a non-small cell lung carcinoma cell line

BET Inhibition Sensitizes Immunologically Cold Rb-Deficient Prostate Cancer to Immune Checkpoint Blockade

Non-T-cell-inflamed immunologically "cold" tumor microenvironments (TME) are associated with poor responsiveness to immune checkpoint blockade (ICB) and can be sculpted by tumor cell genomics. Here, we evaluated how retinoblastoma (Rb) tumor-suppressor loss-of-function (LOF), one of the most frequent alterations in human cancer and associated with lineage plasticity, poor prognosis, and therapeutic outcomes, alters the TME, and whether therapeutic strategies targeting the molecular consequences of Rb loss enhance ICB efficacy. We performed bioinformatics analysis to elucidate the impact of endogenous Rb LOF on the immune TME in human primary and metastatic tumors. Next, we used isogenic murine models of Rb-deficient prostate cancer for in vitro and in vivo mechanistic studies to examine how Rb loss and bromodomain and extraterminal (BET) domain inhibition (BETi) reprograms the immune landscape, and evaluated in vivo therapeutic efficacy of BETi, singly and in combination with ICB and androgen deprivation therapy. Rb loss was enriched in non-T-cell-inflamed tumors, and Rb-deficient murine tumors demonstrated decreased immune infiltration in vivo. The BETi JQ1 increased immune infiltration into the TME through enhanced tumor cell STING/NF-κB activation and type I IFN signaling within tumor cells, resulting in differential macrophage and T-cell-mediated tumor growth inhibition and sensitization of Rb-deficient prostate cancer to ICB. BETi can reprogram the immunologically cold Rb-deficient TME via STING/NF-κB/IFN signaling to sensitize Rb-deficient prostate cancer to ICB. These data provide the mechanistic rationale to test combinations of BETi and ICB in clinical trials of Rb-deficient prostate cancer.

The RB tumor suppressor at the intersection of proliferation and immunity: relevance to disease immune evasion and immunotherapy

The retinoblastoma tumor suppressor (RB) was the first identified tumor suppressor based on germline predisposition to the pediatric eye tumor. Since these early studies, it has become apparent that the functional inactivation of RB is a common event in nearly all human malignancy. A great deal of research has gone into understanding how the loss of RB promotes tumor etiology and progression. Since malignant tumors are characterized by aberrant cell division, much of this research has focused upon the ability of RB to regulate the cell cycle by repression of proliferation-related genes. However, it is progressively understood that RB is an important mediator of multiple functions. One area that is gaining progressive interest is the emerging role for RB in regulating diverse features of immune function. These findings suggest that RB is more than simply a regulator of cellular proliferation; it is at the crossroads of proliferation and the immune response. Here we review the data related to the functional roles of RB on the immune system, relevance to immune evasion, and potential significance to the response to immune-therapy.

Rescue of major histocompatibility-DR surface expression in retinoblastoma-defective, non-small cell lung carcinoma cells by the MS-275 histone deacetylase inhibitor

Major histocompatibility (MHC) class II expression is ordinarily inducible by interferon-gamma (IFN-gamma), but the induction is repressed in retinoblastoma protein (Rb)-defective cells. The repression can be rescued by histone deacetylase (HDAC) inhibitor treatment, but this has never been shown for an HDAC inhibitor that is suitable for clinical trials and eventual patient therapy. Here we demonstrate that the HDAC inhibitor, MS-275, can rescue the IFN-gamma inducibility of human leukocyte antigen (HLA)-DR in non-small cell lung cancer cells. This HDAC inhibitor is currently being tested in phase I/II clinical trials for non-small cell lung cancer. We further verified that the MS-275 effect is related to an HDAC tethered to the HLA-DRA promoter by the transcription factor, YY1. HDAC inhibitors that can be used to treat patients may augment the expression of tumor cell MHC class II, and the results suggest an opportunity to determine the immunological consequences of HDAC inhibitor treatment in tumor therapy.