A review of strategies to overcome immune resistance in the treatment of advanced prostate cancer

Immunotherapy has become integral in cancer therapeutics over the past two decades and is now part of standard-of-care treatment in multiple cancer types. While various biomarkers and pathway alterations such as dMMR, CDK12, and AR-V7 have been identified in advanced prostate cancer to predict immunotherapy responsiveness, the vast majority of prostate cancer remain intrinsically immune-resistant, as evidenced by low response rates to anti-PD(L)1 monotherapy. Since regulatory approval of the vaccine therapy sipuleucel-T in the biomarker-unselected population, there has not been much success with immunotherapy treatment in advanced prostate cancer. Researchers have looked at various strategies to overcome immune resistance, including the identification of more biomarkers and the combination of immunotherapy with existing effective prostate cancer treatments. On the horizon, novel drugs using bispecific T-cell engager (BiTE) and chimeric antigen receptors (CAR) technology are being explored and have shown promising early efficacy in this disease. Here we discuss the features of the tumour microenvironment that predispose to immune resistance and rational strategies to enhance antitumour responsiveness in advanced prostate cancer.

Targeting the Interplay of Independent Cellular Pathways and Immunity: A Challenge in Cancer Immunotherapy

Immunotherapy is a cancer treatment that exploits the capacity of the body's immune system to prevent, control, and remove cancer. Immunotherapy has revolutionized cancer treatment and significantly improved patient outcomes for several tumor types. However, most patients have not benefited from such therapies yet. Within the field of cancer immunotherapy, an expansion of the combination strategy that targets independent cellular pathways that can work synergistically is predicted. Here, we review some consequences of tumor cell death and increased immune system engagement in the modulation of oxidative stress and ubiquitin ligase pathways. We also indicate combinations of cancer immunotherapies and immunomodulatory targets. Additionally, we discuss imaging techniques, which are crucial for monitoring tumor responses during treatment and the immunotherapy side effects. Finally, the major outstanding questions are also presented, and directions for future research are described.

Immunotherapy in Advanced Prostate Cancer: Current Knowledge and Future Directions

The advent of immunotherapy has revolutionized cancer treatment. Unfortunately, this has not been the case for metastatic castration-resistant prostate cancer (mCRPC), likely due to the heterogeneous and immune-suppressive microenvironment present in prostate cancer. The identification of molecular biomarkers that could predict response to immunotherapy represents one of the current challenges in this clinical scenario. The management of advanced castration-resistant prostate cancer is rapidly evolving and immunotherapy treatments, mostly consisting of immune checkpoint inhibitors combinations, BiTE® (bispecific T-cell engager) immune therapies, and chimeric antigen receptors (CAR) are in development with promising results. This review analyses the current evidence of immunotherapy treatments for mCRPC, evaluating past failures and promising approaches and discussing the directions for future research.

Evolving Role of Immunotherapy in Metastatic Castration Refractory Prostate Cancer

Immunotherapies have shown remarkable success in the treatment of multiple cancer types; however, despite encouraging preclinical activity, registration trials of immunotherapy in prostate cancer have largely been unsuccessful. Sipuleucel-T remains the only approved immunotherapy for the treatment of asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer based on modest improvement in overall survival. This immune evasion in the case of prostate cancer has been attributed to tumor-intrinsic factors, an immunosuppressive tumor microenvironment, and host factors, which ultimately make it an inert 'cold' tumor. Recently, multiple approaches have been investigated to turn prostate cancer into a 'hot' tumor. Antibodies directed against programmed cell death protein 1 have a tumor agnostic approval for a small minority of patients with microsatellite instability-high or mismatch repair-deficient metastatic prostate cancer. Herein, we present an overview of the current immunotherapy landscape in metastatic castration-resistant prostate cancer with a focus on immune checkpoint inhibitors. We describe the results of clinical trials of immune checkpoint inhibitors in patients with metastatic castration-resistant prostate cancer; either as single agents or in combination with other checkpoint inhibitors, poly (ADP-ribose) polymerase (PARP) inhibitors, tyrosine kinase inhibitors, novel hormonal therapies, chemotherapies, and radioligands. Finally, we review upcoming immunotherapies, including novel monoclonal antibodies, chimeric-antigen receptor (CAR) T cells, Bi-Specific T cell Engagers (BiTEs), therapies targeting the adenosine pathway, and other miscellaneous agents.