Metastatic Castration-Resistant Prostate Cancer, Immune Checkpoint Inhibitors, and Beyond

T-Cell redirecting bispecific antibodies: a review of a novel class of immuno-oncology for advanced prostate cancer

Novel T-cell immunotherapies such as bispecific T-cell engagers (BiTEs) are emerging as promising therapeutic strategies for prostate cancer. BiTEs are engineered bispecific antibodies containing two distinct binding domains that allow for concurrent binding to tumor-associated antigens (TAAs) as well as immune effector cells, thus promoting an immune response against cancer cells. Prostate cancer is rich in tumor associated antigens such as, but not limited to, PSMA, PSCA, hK2, and STEAP1 and there is strong biologic rationale for employment of T-cell redirecting BiTEs within the prostate cancer disease space. Early generation BiTE constructs employed in clinical study have demonstrated meaningful antitumor activity, but challenges related to drug delivery, immunogenicity, and treatment-associated adverse effects limited their success. The ongoing development of novel BiTE constructs continues to address these barriers and to yield promising results in terms of efficacy and safety. This review will highlight some of most recent developments of BiTE therapies for patients with advanced prostate cancer and the evolving data surrounding BiTE constructs undergoing clinical evaluation.

A landscape of checkpoint blockade resistance in cancer: underlying mechanisms and current strategies to overcome resistance

The discovery of immune checkpoints and the development of immune checkpoint inhibitors (ICI) have achieved a durable response in advanced-stage cancer patients. However, there is still a high proportion of patients who do not benefit from ICI therapy due to a lack of response when first treated (primary resistance) or detection of disease progression months after objective response is observed (acquired resistance). Here, we review the current FDA-approved ICI for the treatment of certain solid malignancies, evaluate the contrasting responses to checkpoint blockade in different cancer types, explore the known mechanisms associated with checkpoint blockade resistance (CBR), and assess current strategies in the field that seek to overcome these mechanisms. In order to improve current therapies and develop new ones, the immunotherapy field still has an unmet need in identifying other molecules that act as immune checkpoints, and uncovering other mechanisms that promote CBR.

The recovery from taxane mediated apoptosis in PC-3 castration-resistant metastatic prostate cancer cells

Here, we revealed the reversibility of cabazitaxel (CBZ)-induced apoptosis in PC-3 castration resistant metastatic prostate cancer cells (mCRPC) through the hallmarks of apoptosis. The recovery of PC-3 cells from apoptosis upon removal of CBZ at different recovery periods was evaluated by Annexin V, DNA damage, oxidative damage, mitochondrial membrane depolarization, and caspase activation. Our results showed that the administration of CBZ caused apoptosis for 72 h in PC-3 cells. However, recovered cells exhibited decreased nuclear damage, plasma membrane disruption, ROS level, release cytochrome c level and caspase-3 activation with upregulation of Bcl-2 expression upon removal of especially 1 nM CBZ for 24 h recovery period in PC-3 cells. Our study indicates that CBZ treated PC-3 cells can recover after apoptotic cell death. However, advanced molecular analysis should elucidate the relationship between the molecular mechanisms of recovery and taxane response or resistance in PC-3 mCRPC cells.

Circulating Tumor DNA in Genitourinary Cancers: Detection, Prognostics, and Therapeutic Implications

CtDNA is emerging as a non-invasive clinical detection method for several cancers, including genitourinary (GU) cancers such as prostate cancer, bladder cancer, and renal cell carcinoma (RCC). CtDNA assays have shown promise in early detection of GU cancers, providing prognostic information, assessing real-time treatment response, and detecting residual disease and relapse. The ease of obtaining a "liquid biopsy" from blood or urine in GU cancers enhances its potential to be used as a biomarker. Interrogating these "liquid biopsies" for ctDNA can then be used to detect common cancer mutations, novel genomic alterations, or epigenetic modifications. CtDNA has undergone investigation in numerous clinical trials, which could address clinical needs in GU cancers, for instance, earlier detection in RCC, therapeutic response prediction in castration-resistant prostate cancer, and monitoring for recurrence in bladder cancers. The utilization of liquid biopsy for ctDNA analysis provides a promising method of advancing precision medicine within the field of GU cancers.

Germline and somatic mutations in prostate cancer: Implications for treatment

Genetic testing is an integral part of the workup of metastatic prostate cancer, in part, because the results can have a profound impact on the subsequent management of this disease. There are now several Food & Drug Administration (FDA) approved therapeutics available for patients with prostate cancer and certain genetic abnormalities - most notably, mutations in DNA damage repair (DDR) pathways such mismatch repair (MMR) and homologous recombination repair (HRR). In this review of the current literature, we discuss the indications for somatic and germline testing, the genetic changes of particular clinical relevance, the associated therapeutic options, and the clinical data supporting their use. We also highlight select trials-in-progress and future directions for the field.

Molecular Mechanisms of Prostate Cancer Development in the Precision Medicine Era: A Comprehensive Review

The progression of prostate cancer (PCa) relies on the activation of the androgen receptor (AR) by androgens. Despite efforts to block this pathway through androgen deprivation therapy, resistance can occur through several mechanisms, including the abnormal activation of AR, resulting in castration-resistant PCa following the introduction of treatment. Mutations, amplifications, and splicing variants in AR-related genes have garnered attention in this regard. Furthermore, recent large-scale next-generation sequencing analysis has revealed the critical roles of AR and AR-related genes, as well as the DNA repair, PI3K, and cell cycle pathways, in the onset and progression of PCa. Moreover, research on epigenomics and microRNA has increasingly become popular; however, it has not translated into the development of effective therapeutic strategies. Additionally, treatments targeting homologous recombination repair mutations and the PI3K/Akt pathway have been developed and are increasingly accessible, and multiple clinical trials have investigated the efficacy of immune checkpoint inhibitors. In this comprehensive review, we outline the status of PCa research in genomics and briefly explore potential future developments in the field of epigenetic modifications and microRNAs.

Pembrolizumab for metastatic castration-resistant prostate cancer: trials and tribulations

INTRODUCTION

Immunotherapies have revolutionized the management of various malignancies but have only recently been evaluated systematically in prostate cancer. Pembrolizumab, a programmed-death 1 (PD-1) blocking antibody, has been utilized in a small subset of prostate cancer patients with mismatch repair deficiency/microsatellite instability, but has now been assessed in broader populations of metastatic prostate cancer patients.

AREAS COVERED

The results of four pembrolizumab-based phase III clinical trials for metastatic castration-resistant prostate cancer (mCRPC) and metastatic hormone-sensitive prostate cancer (mHSPC) patients, including KEYNOTE-641, KEYNOTE-921, KEYNOTE-991, and KEYLYNK-010 are summarized. Programmed death-ligand 1 (PD-L1) expression, the efficacy of pembrolizumab in prostate cancer patients with certain molecular defects, and emerging pembrolizumab-based therapeutic combinations are also reviewed.

EXPERT OPINION

Pembrolizumab has not benefitted unselected metastatic prostate cancer patients when combined with chemotherapy, next-generation hormonal agents (NHA), or poly(ADP-ribose) polymerase inhibitors (PARPi). PD-L1 positivity does not predict the response to pembrolizumab in this disease. A small number of responding patients can likely be explained by rare genetic and molecular defects, and more innovative combination strategies are needed to improve outcomes in prostate cancer patients who are not sensitive to pembrolizumab. Emphasis should be placed on developing additional or alternative immuno-oncology approaches beyond classical immune checkpoint inhibition.

The Prognostic Significance of Selected HLA Alleles on Prostate Cancer Outcome

Recently, we have shown that HLA-A*02:01 and HLA-A*24:02 in de novo metastatic prostate cancer (MPCa) have an important role in disease progression. Since de novo MPCa represents a small group among patients diagnosed with prostate cancer (PCa), it was obvious to try to extend the validity of our results to larger cohorts of PCa patients. Herein, we analyzed patients irrespective of their disease status at diagnosis to include, besides patients with MPCa, those with localized PCa (LPCa). Our goal was to specify the prognostic value of HLA-A*02:01 and HLA-A*24:02 for overall survival (OS) prospectively and for early biochemical recurrence (BCR) and castrate resistance (CR) as additional clinical endpoints in a prospective/retrospective manner, to improve clinical decisions for patients covering all stages of PCa. On univariate analysis, HLA-A alleles were significantly associated as prognostic biomarkers with early BCR (p = 0.028; HR = 1.822), OS (p = 0.013; HR = 1.547) and showed a trend for CR (p = 0.150; HR = 1.239). On multivariate analysis, HLA-A alleles proved to be independent prognosticators for early BCR (p = 0.017; HR = 2.008), CR (p = 0.005; HR = 1.615), and OS (p = 0.002; HR = 2.063). Kaplan-Meier analyses revealed that patients belonging to the HLA-A*02:01+HLA-A*24:02- group progressed much faster to BCR and CR and had also shorter OS compared to HLA-A*24:02+ patients. Patients being HLA-A*02:01-HLA-A*24:02- exhibited varying clinical outcomes, pointing to the presence of additional HLA-A alleles with potential prognostic value. Our data underline the HLA-A alleles as valuable prognostic biomarkers for PCa that may assist with the appropriate treatment and follow-up schedule based on the risk for disease progression to avoid over-diagnosis and over-treatment.

Novel therapies for metastatic prostate cancer

INTRODUCTION

Patients with metastatic prostate cancer, especially in the castrate-resistant setting, have a poor prognosis. Many agents have been approved for metastatic prostate cancer, such as androgen receptor pathway inhibitors, taxane-based chemotherapy, radiopharmaceuticals, and immunotherapy. However, prostate cancer remains the leading cause of cancer deaths in nonsmoking men. Fortunately, many more novel agents are under investigation.

AREAS COVERED

We provide an overview of the broad group of novel therapies for metastatic prostate cancer, with an emphasis on active and recruiting clinical trials that have been recently published and/or presented at national or international meetings.

EXPERT OPINION

The future for patients with metastatic prostate cancer is promising, with further development of novel therapies such as radiopharmaceuticals. Based on a growing understanding of prostate cancer biology, novel agents are being designed to overcome resistance to approved therapies. There are many trials using novel agents either as monotherapy or in combination with already approved agents with potential to further improve outcomes for men with advanced prostate cancer.