Stimulation of antitumor immunity by FoxP3-targeting PROTAC.

CD4 + regulatory T cells (Tregs) play a central role in regulating and suppressing anti-tumor immune responses. FoxP3 is a transcription factor and master regulator of the Treg lineage. We developed and characterized a proteolysis targeting chimeric (PROTAC) drug that targets FoxP3 (PF). PF was created by linking the FoxP3 binding peptide P60 to pomalidomide, a ligand for E3 ligase. Ternary complex formation between PF, FoxP3, and cereblon (component of an E3 ligase) was confirmed using surface plasmon resonance assay (cooperativity factor of 2.27). PF decreased mouse and human FoxP3 expression in vitro in a proteasome-dependent manner. In mice, PF decreased FoxP3 in both the spleen and peripheral lymphocytes. PF-treated lymphocytes (human or mice) were better at stimulating CD8 + lymphocyte proliferation and activation. PF treatment decreased RENCA tumor growth in mice. PF enhanced antitumor immunity associated with αPD1 or mTOR inhibitor (mTORi). Lymphocytes from mice treated with PF and mTORi showed reduced metastatic tumor growth in untreated mice, providing further evidence for an adaptive immune response as the mechanism of action. We showed that PF binds FoxP3 and decreases FoxP3 expression in Tregs, reducing Treg function and generating antitumor immunity.

PAK4 inhibition improves PD1 blockade immunotherapy in prostate cancer by increasing immune infiltration.

Antitumor immunity requires lymphocytes to localize to the tumor. Prostate cancers (PCs) are immunologically cold and tend to lack T-cell infiltration. Most advanced PCs are insensitive to PD1 blockade therapies. Using syngeneic RM1 prostate tumors, p21-activated kinase-4 (PAK4) knockdown (KD) and pharmacological inhibition was assessed in C57BL/6J mice treated with PD1 antibodies (αPD1). RNASeq was used to characterize the immune response in the tumor. Immunohistochemistry, flow cytometry, and in vivo blocking studies confirmed the role of cell surface proteins in the generation of immune responses. In The Cancer Genome Atlas, PAK4 expression was inversely correlated with immune cell infiltration. PAK4 expression was controlled by the androgen receptor and its pioneering factor, FOXA1. PAK4 KD increased CD8+ T-cell infiltration and expression of IFNγ response genes. PAK4 KD also upregulated angiogenesis and endothelial cell adhesion molecules in the tumor microenvironment, contributing to CD8+ lymphocyte recruitment. Pharmacological inhibition of PAK4 made PC more responsive to immunotherapy with αPD1. A decrease in PAK4 activity increases immune activation and vascularity, which increases CD8+ lymphocyte infiltration into the tumor. Therefore, targeting PAK4 may improve the response of human PC to immunotherapy.

Hypoxia-inducible factor pathway genes predict survival in metastatic clear cell renal cell carcinoma.

PURPOSE: Hypoxia inducible factor (HIF) pathway alterations drive progression of clear cell renal cell carcinoma (ccRCC). We aim to evaluate genes within the canonical and non-canonical HIF pathways as predictors of survival in metastatic ccRCC. MATERIALS AND METHODS: Gene expression was determined from 324 archival pretreatment nephrectomy specimens from CALGB90206, a phase III trial of patients treated with interferon alpha (INF-α) vs. INF-α plus bevacizumab. TaqMan RT-qPCR was performed using RNA from tumors macrodissected based on review by genitourinary pathology. RESULTS: A total of 35 HIF-related genes were assessed by Cox regression analysis. After adjusting for sex and Memorial Sloan Kettering Cancer Center risk score (MSKCC-RS), 11 genes predicted OS: HIF2A (HR 1.059, P = 0.012), EGLN3 (HR 1.089, P = 0.012), VEGFC (HR 0.904, P = 0.039), VEGFD (HR 1.085, P = 0.016), FLT4 (HR 1.093, P = 0.038), CCND1 (HR 1.077, P = 0.026), TGFA (HR 1.127, P = 0.003), EGFR (HR 1.151, P = 0.028), VHL (HR 0.764, P = 0.002), HSP90AA1 (HR 0.845, P = 0.002), and PTEN (HR 1.163, P = 0.050); 7 genes predicted PFS: HIF2A (HR 1.060, P = 0.011), CCND1 (HR 1.082, P = 0.016), TGFA (HR 1.096, P = 0.026), EP300 (HR 1.171, P = 0.031), VHL (HR 0.775, P = 0.007), HSP90AA1 (HR 0.871, P = 0.015), and TP53 (HR 1.119, P = 0.050). Most of these genes validated as significant predictors of survival in the external, TCGA dataset. In multivariate analysis of all externally validated genes, VEGFC (HR 0.906, P = 0.043), TGFA (HR 1.122, P = 0.003), CITED2 (HR 1.113, P = 0.035) and EP300 (HR 1.136, P = 0.049) predicted OS; and HIF2A (HR 1.049, P = 0.036) and EP300 (HR 1.199, P = 0.010) predicted PFS. EGLN3 (HR 1.156, P = 0.045) and BNIP3 (HR 1.254, P = 0.049) significantly interacted with treatment status and predicted PFS in patients treated with IFN-α and IFN-α+bevacizumab, respectively. CONCLUSIONS: We identified specific gene isoforms in both the canonical and non-canonical HIF pathways associated with metastatic RCC survival. EGLN3 and BNIP3 showed significant interaction with treatment arm and may be predictive of treatment response. We have identified genes for future prospective investigation as predictive biomarkers and novel drug targets.

Cholesterol-Lowering Intervention Decreases mTOR Complex 2 Signaling and Enhances Antitumor Immunity.

PURPOSE: There is a need for strategies to prevent prostate cancer. Cholesterol-lowering interventions are employed widely and safely to reduce risk of cardiovascular disease and has been proposed for chemoprevention. Using preclinical models and a window-of-opportunity clinical trial, we describe an adaptive antitumor immunity resulting from cholesterol lowering. EXPERIMENTAL DESIGN: Statins do not reliably lower serum cholesterol in mice. Therefore, oral ezetimibe was administered to mice to lower serum cholesterol to clinically relevant levels and evaluated the final adaptive immune response. T-lymphocytes-specific mTORC2 knockout mice were used to evaluate mTOR signaling and antitumor immunity. Pretreatment and posttreatment prostate tumors and lymphocytes were examined from a window-of-opportunity clinical trial where men with prostate cancer were treated with 2 to 6 weeks of aggressive cholesterol-lowering intervention prior to radical prostatectomy. RESULTS: Mice treated with oral ezetimibe exhibited enhanced antitumor immunity against syngeneic cancers in a CD8+ lymphocyte-dependent manner, produced immunity that was transferrable through lymphocytes, and had enhanced central CD8+ T-cell memory. In mice and in patients undergoing prostatectomy, lowering serum cholesterol inhibited mTORC2 signaling in lymphocytes and increased infiltration of CD8+ lymphocytes into prostate tumors. T-lymphocyte-specific mTORC2 knockout mice demonstrated enhanced CD8+ lymphocyte function and antitumor capacity. In patients, cholesterol-lowering intervention prior to prostatectomy decreased the proliferation of normal prostate and low-grade adenocarcinomas. CONCLUSIONS: Lowering serum cholesterol decreased signaling through mTORC2 and enhanced antitumor CD8+ T-cell memory. We provide a rationale for large-scale clinical testing of cholesterol lowering strategies for prostate cancer chemoprevention.

Syngeneic murine model for prostate cancer using RM1 cells transfected with gp100.

BACKGROUND: Prostate cancer (PC) is the most commonly diagnosed solid tumor in men. A major challenge in PC immunotherapy is the lack of an animal model that resembles human adenocarcinoma and allows for manipulation or monitoring of the immune response. Mouse models are needed for preclinical testing of new immunotherapies, whether used alone or in combination with established drugs, and to develop companion biomarkers that can be validated in clinical trials. METHODS: To develop a syngeneic prostate adenocarcinoma model with a well-defined tumor antigen, murine RM1 PC cells were transfected with the endogenous mouse melanoma protein, gp100 (RM1-gp100). Gp100 was attractive because it is a self-protein and it instantly allowed us to use the large trove of immune research tools developed for melanoma research. A dendritic cell (DC) vaccine was used as model immunotherapy to demonstrate that adoptive immunotherapy against gp100 decreases the growth of RM1-gp100 but not RM1. RESULTS: Expressing gp100 did not change the growth of RM1 cell in vitro or in vivo. The DCs pulsed with RM1-gp100 could be used to stimulate Pmel-1 lymphocyte proliferation and activation. Pmel-1 lymphocytes could be adoptively transferred into C57Bl/6 mice that were treated with DCs pulsed with RM1-gp100. The resulting Pmel-1 lymphocytes were monitored to assess the primary cellular immune response and memory response. CONCLUSION: We describe a murine model for prostate adenocarcinoma with a well-characterized antigen that can be used in an immunologically intact mice to monitor the temporal CD8+ lymphocyte-mediated antitumor immunity.