Perspectives on the clinical development of immunotherapy in prostate cancer

MSH2-deficient prostate tumours have a distinct immune response and clinical outcome compared to MSH2-deficient colorectal or endometrial cancer

BACKGROUND

Recent publications have shown patients with defects in the DNA mismatch repair (MMR) pathway driven by either MSH2 or MSH6 loss experience a significant increase in the incidence of prostate cancer. Moreover, this increased incidence of prostate cancer is accompanied by rapid disease progression and poor clinical outcomes.

METHODS AND RESULTS

We show that androgen-receptor activation, a key driver of prostate carcinogenesis, can disrupt the MSH2 gene in prostate cancer. We screened tumours from two cohorts (recurrent/non-recurrent) of prostate cancer patients to confirm the loss of MSH2 protein expression and identified decreased MSH2 expression in recurrent cases. Stratifying the independent TCGA prostate cancer cohort for MSH2/6 expression revealed that patients with lower levels of MSH2/6 had significant worse outcomes, in contrast, endometrial and colorectal cancer patients with lower MSH2/6 levels. MMRd endometrial and colorectal tumours showed the expected increase in mutational burden, microsatellite instability and enhanced immune cell mobilisation but this was not evident in prostate tumours.

CONCLUSIONS

We have shown that loss or reduced levels of MSH2/MSH6 protein in prostate cancer is associated with poor outcome. However, our data indicate that this is not associated with a statistically significant increase in mutational burden, microsatellite instability or immune cell mobilisation in a cohort of primary prostate cancers.

Quo Vadis Advanced Prostate Cancer Therapy? Novel Treatment Perspectives and Possible Future Directions

Prostate cancer is a very common disease, which is, unfortunately, often the cause of many male deaths. This is underlined by the fact that the early stages of prostate cancer are often asymptomatic. Therefore, the disease is usually detected and diagnosed at late advanced or even metastasized stages, which are already difficult to treat. Hence, it is important to pursue research and development not only in terms of novel diagnostic methods but also of therapeutic ones, as well as to increase the effectiveness of the treatment by combinational medicinal approach. Therefore, in this review article, we focus on recent approaches and novel potential tools for the treatment of advanced prostate cancer; these include not only androgen deprivation therapy, antiandrogen therapy, photodynamic therapy, photothermal therapy, immunotherapy, multimodal therapy, but also poly(ADP-ribose) polymerase, Akt and cyclin-dependent kinase inhibitors.

Robust antigen-specific CD8 T cell tolerance to a model prostate cancer neoantigen

Immunotherapy has shown limited success in prostate cancer; this may be partially explained by its immunosuppressive tumor microenvironment (TME). Although androgen-deprivation therapy (ADT), the most common treatment for prostate cancer, initially promotes a robust T cell infiltrate, T cell responses are later attenuated. Based on the castration-sensitive Myc-CaP model, we developed an antigen-specific system to study CD8 T cell tolerance to prostate tumors. This model is unique in that CD8 T cells recognize a bona-fide tumor antigen (Her-2/neu), rather than an overexpressed xenogenic antigen like chicken ovalbumin or influenza hemagglutinin. Using this novel model, we demonstrate robust tolerance that is not alleviated by TLR agonists or ADT. This model may serve as a novel and useful tool to further interrogate methods by which to augment anti-tumor cancer immune responses to prostate cancer.

Significance

Prostate cancer is a leading cause of cancer-related death in men worldwide, with an estimated 33,000 deaths projected in the U.S. in 2020. Although primary (localized) tumors can be cured by surgery or radiation, approximately 40% of patients eventually develop recurrent disease. While initially responsive to androgen-deprivation, many patients with recurrent prostate cancer eventually progress to a more advanced disease state known as metastatic castration-resistant prostate cancer (mCRPC); this is the lethal phenotype. These studies describe a novel androgen-responsive murine cell line that expresses a bona-fide tumor antigen (Her-2/neu). Pre-clinical work with this model shows robust and antigen-specific CD8 T cell tolerance, providing a novel preclinical model to study CD8 T cell tolerance to prostate tumors.

Targeting prostate cancer stem-like cells by an immunotherapeutic platform based on immunogenic peptide-sensitized dendritic cells-cytokine-induced killer cells

Background

Autologous cellular immunotherapy or immune enhancement therapy has demonstrated some promising benefits for prostate cancer. T cell-based immunotherapy or sipuleucel-T therapy has yielded certain beneficial responses and a slight improvement on the overall survival of patients with metastatic castration-resistant prostate cancer (mCRPC) as shown in some clinical trials, suggesting that prostate cancer is immunoresponsive.

Methods

In this study, we developed an adaptive cytokine-induced killer cell (CIK)-based immunotherapeutic application targeting the prostate cancer stem-like cells (PCSCs). In this therapeutic platform, dendritic cells (DC) were isolated from the peripheral blood mononuclear cells (PBMCs) and preloaded or sensitized with immunogenic peptides derived from two PCSC-associated cell membrane molecules, CD44 and EpCAM, followed by co-culture with the expanded peripheral blood lymphocyte (PBL)-derived CIK cells. The in vitro cytotoxic activity of DC-activated CIK cells against PCSCs was determined by CCK8 and TUNEL assays, and the in vivo anti-tumor effect of DC-activated CIK cells on prostate cancer xenograft tumors was evaluated in subcutaneous and orthotopic xenograft models.

Results

Our results showed that the peptide-sensitized DC-CIK cell preparation manifested significant in vitro cytotoxic activity against the PCSC-enriched prostatospheroids and also in vivo anti-tumor effect against prostate cancer xenografts derived from the PCSC-enriched prostatospheroids.

Conclusions

Together, our established immunogenic peptide-sensitized DC-CIK-based cell preparation platform manifests its potential immunotherapeutic application in targeting the PCSCs and also prostate cancer.

Molecular Underpinnings Governing Genetic Complexity of ETS-Fusion-Negative Prostate Cancer

Inter- and intra-patient molecular heterogeneity of primary and metastatic prostate cancer (PCa) confers variable clinical outcome and poses a formidable challenge in disease management. High-throughput integrative genomics and functional approaches have untangled the complexity involved in this disease and revealed a spectrum of diverse aberrations prevalent in various molecular subtypes, including ETS fusion negative. Emerging evidence indicates that SPINK1 upregulation, mutations in epigenetic regulators or chromatin modifiers, and SPOP are associated with the ETS-fusion negative subtype. Additionally, patients with defects in a DNA-repair pathway respond to poly-(ADP-ribose)-polymerase (PARP) inhibition therapies. Furthermore, a new class of immunogenic subtype defined by CDK12 biallelic loss has also been identified in ETS-fusion-negative cases. This review focuses on the emerging molecular underpinnings driving key oncogenic aberrations and advancements in therapeutic strategies of this disease.

The Novel Combination of Nitroxoline and PD-1 Blockade, Exerts a Potent Antitumor Effect in a Mouse Model of Prostate Cancer

Programmed cell death protein 1 (PD-1) blockade is a promising therapeutic strategy against prostate cancer. Nitroxoline has been found to have effective anticancer properties in several cancer types. We investigated the efficacy of a combination therapy involving nitroxoline and PD-1 blockade in a prostate cancer mouse model. In our in vitro analysis, we found that nitroxoline inhibited the viability and proliferation of the mouse prostate cancer cell line RM9-Luc-PSA. Additionally, nitroxoline downregulated the expressions of phospho-PI3 kinase, phospho-Akt (Thr308), phospho-Akt (Ser473), phospho-GSK-3β, Bcl-2, and Bcl-xL. Nitroxoline also downregulated programmed death-ligand 1 (PD-L1) expression levels in prostate cancer cell line and tumor tissue. In our murine prostate cancer orthotopic model, nitroxoline plus PD-1 blockade synergistically suppressed tumor growth when compared with nitroxoline or PD-1 blockade alone, leading to reductions in tumor weight, bioluminescence tumor signals, and serum prostate-specific antigen levels. Furthermore, fluorescence-activated cell sorting analysis showed that the combination strategy significantly enhanced antitumor immunity by increasing CD44⁺CD62L⁺CD8⁺ memory T cell numbers and reducing myeloid-derived suppressor cell numbers in peripheral blood. In conclusion, our findings suggest that nitroxoline plus PD-1 blockade may be a promising treatment strategy in patients with prostate cancer.

CD1d highly expressed on DCs reduces lung tumor burden by enhancing antitumor immunity

Dendritic cells (DCs), as professional antigen-presenting cells are essential for the initial activation of adaptive antitumor immunity. CD1d is considered to present phospholipid and glycosphingolipid antigens to NKT cells. However, it is currently unknown whether CD1d expression on DCs is capable of enhancing antitumor immunity, particularly T-cell related immunity. We observed that CD1d was predominantly expressed on DCs in 3LL tumor-bearing mice, whilst a deficiency of CD1d promoted tumor growth. Notably, CD1d expression on DCs was not only required for presenting antigen to NKT cells, but also markedly promoted CD4⁺T and CD8⁺T cell activation, particularly cytotoxic T cells. All the T cells (NKT, CD4⁺T and CD8⁺T cells) upregulated CD69, CD107a and IFN-γ after the adoptive transfer of CD1d-positive DCs (CD1d⁺DCs) and tumor growth was suppressed. With regard to the mechanism, we revealed that CD1d⁺DCs were concomitant with a higher expression of costimulatory molecules (CD40, CD80 and CD86) and MHCI/II, which are essential for DCs to present antigens to T cells. Consistently, CD1d⁺DCs displayed stronger activation-associated-ERK1/2 and NF-κB signals; whereas JAK2-STAT3/6 signaling was required for maintaining a high level of CD1d on DCs. In lung cancer patients, the antitumor activities of all the T cells were enhanced with the increase of CD1d⁺DCs. Analysis of TCGA data revealed that high levels of CD1d indicated better outcomes for patients. Collectively, CD1d enhanced DC-based antitumor immunity, not only by targeting NKT, but also by activating CD4⁺T and CD8⁺T cells. CD1d⁺DCs may be superior to the bulk population of DCs in cancer immunotherapy.

Targeting androgen receptor-independent pathways in therapy-resistant prostate cancer

Since androgen receptor (AR) signaling is critically required for the development of prostate cancer (PCa), targeting AR axis has been the standard treatment of choice for advanced and metastatic PCa. Unfortunately, although the tumor initially responds to the therapy, treatment resistance eventually develops and the disease will progress. It is therefore imperative to identify the mechanisms of therapeutic resistance and novel molecular targets that are independent of AR signaling. Recent advances in pathology, molecular biology, genetics and genomics research have revealed novel AR-independent pathways that contribute to PCa carcinogenesis and progression. They include neuroendocrine differentiation, cell metabolism, DNA damage repair pathways and immune-mediated mechanisms. The development of novel agents targeting the non-AR mechanisms holds great promise to treat PCa that does not respond to AR-targeted therapies.

Pembrolizumab: patient selection or immune intensification?

Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1) or programmed cell death 1 ligand 1 (PD-L1) have had limited clinical impact in prostate cancer. To find a niche for immune checkpoint inhibition in this disease, future strategies might require improved biomarker-based patient selection or combination strategies to enhance in vivo immune activity.