Update on prostate cancer vaccines

Therapeutic metastatic prostate cancer vaccines: lessons learnt from urologic oncology

INTRODUCTION

Therapeutic cancer vaccines have been recognized as a promising treatment option in clinical oncology for nearly three decades. However, despite many efforts, only one cancer vaccine - sipuleucel-T, activating the anti-PAP (prostatic acid phosphatase) immune response, has obtained Food and Drug Administration (FDA) approval.

MATERIAL AND METHODS

This review describes the most advanced research on the use of therapeutic cancer vaccines in the treatment of prostate cancer.

RESULTS

In addition to sipuleucel-T, which was approved in urologic oncology in 2010, four cancer vaccines were and have been tested in phase III clinical trials in patients with metastatic castration resistant prostate cancer (mCRPC): GVAX (prostate cancer variant) containing irradiated prostate cancer cell, PPV peptide vaccine, PCVAC/PCa dendritic cell-based vaccine and PROSTVAC anti PSA (prostate-specific antigen) vaccine. This review compares the most promising and best-studied cancer vaccines: sipuleucel-T and PROSTVAC. Currently, both vaccines have been tested in combination with other therapeutic approaches, including check point inhibitors.

CONCLUSIONS

It seems possible that the efficacy of sipuleucel-T and PROSTVAC could be increased in combination therapy with other medications.

Standing Variations Modeling Captures Inter-Individual Heterogeneity in a Deterministic Model of Prostate Cancer Response to Combination Therapy

Sipuleucel-T (Provenge) is the first live cell vaccine approved for advanced, hormonally refractive prostate cancer. However, survival benefit is modest and the optimal combination or schedule of sipuleucel-T with androgen depletion remains unknown. We employ a nonlinear dynamical systems approach to modeling the response of hormonally refractive prostate cancer to sipuleucel-T. Our mechanistic model incorporates the immune response to the cancer elicited by vaccination, and the effect of androgen depletion therapy. Because only a fraction of patients benefit from sipuleucel-T treatment, inter-individual heterogeneity is clearly crucial. Therefore, we introduce our novel approach, Standing Variations Modeling, which exploits inestimability of model parameters to capture heterogeneity in a deterministic model. We use data from mouse xenograft experiments to infer distributions on parameters critical to tumor growth and to the resultant immune response. Sampling model parameters from these distributions allows us to represent heterogeneity, both at the level of the tumor cells and the individual (mouse) being treated. Our model simulations explain the limited success of sipuleucel-T observed in practice, and predict an optimal combination regime that maximizes predicted efficacy. This approach will generalize to a range of emerging cancer immunotherapies.

Dendritic cell vaccine immunotherapy; the beginning of the end of cancer and COVID-19. A hypothesis

Immunotherapy is the newest approach to combat cancer. It can be achieved using several strategies, among which is the dendritic cell (DC) vaccine therapy. Several clinical trials are ongoing using DC vaccine therapy either as a sole agent or in combination with other interventions to tackle different types of cancer. Immunotherapy can offer a potential treatment to coronavirus disease 2019 (COVID-19) the worst pandemic facing this generation, a disease with deleterious effects on the health and economic systems worldwide. We hypothesize that DC vaccine therapy may provide a potential treatment strategy to help combat COVID-19. Cancer patients are at the top of the vulnerable population owing to their immune-compromised status. In this review, we discuss DC vaccine therapy in the light of the body's immunity, cancer, and newly emerging infections such as COVID-19 in hopes of better-customized treatment options for patients with multiple comorbidities.

Surface engineering tumor cells with adjuvant-loaded particles for use as cancer vaccines

Cell surface engineering is an expanding field and whilst extensive research has been performed decorating cell surfaces with biomolecules, the engineering of cell surfaces with particles has been a largely unexploited area. This study reports on the assembly of cell-particle hybrids where irradiated tumor cells were surface engineered with adjuvant-loaded, biodegradable, biocompatible, polymeric particles, with the aim of generating a construct capable of functioning as a therapeutic cancer vaccine. Successfully assembled cell-particle hybrids presented here comprised either melanoma cells or prostate cancer cells stably adorned with Toll-like receptor-9 ligand-loaded particles using streptavidin-biotin cross-linking. Both cell-particle assemblies were tested in vivo for their potential as therapeutic cancer vaccines yielding promising therapeutic results for the prostate cancer model. The ramifications of results obtained for both tumor models are openly discussed.

Advances on immunotherapy in genitourinary and renal cell carcinoma

Genitourinary (GU) cancers are a group of epithelial malignancies associated with the organs involved in the excretion of urine. Renal cell, urothelial, and prostatic carcinoma are the overwhelming subtypes diagnosed by oncologists. Each of these was traditionally treated surgically when local and non-invasive. When these carcinomas spread, invade, or metastasize, surgical control lacks in efficacy. Chemotherapeutic regimens have been implemented for decades and have increased overall survival but many patients progress. Molecular targeting through tyrosine kinase inhibition of the vascular endothelial growth factor (VEGF) has emerged as a frontline therapy in kidney cancer with more durable responses. More recently, immunotherapy has begun to find efficacy in many other solid tumors including melanoma and non-small cell lung cancer. The inherent genetic instability of this group of cancers makes them ideal solid tumors for immune modulation. Vaccines manufactured to initiate T-Cell regulation through neoplastic-antigen presentation are available for prostate cancer and are currently on trial in renal cell carcinoma (RCC). Programmed death-1 (PD-1) and its ligand (PD-L1) are intricate members of cellular immunity against neoplastic cells. In an activated, unbound state, these molecules permit T-cell activation and cytotoxic killing of cancer cells. However, when they are linked, cellular immunity is attenuated and local cancer cells are permitted the opportunity to proliferate and invade. A novel class of monoclonal antibodies have been developed which stop PD-1 linkage and thus uncouple the 'stop' signal of these neoplastic regulatory cells. The increased overall and progression free survival have made them attractive options alone as well as in combination with anti-VEGF inhibitors for patients. Although more tolerable than chemotherapy, immunotherapeutics have adverse potential toxicities. Overall, the use of immunomodulatory medications have opened a new paradigm in the anti-neoplastic regimen of GU cancers and further developments will determine the appropriate patient to treat for optimum tumor burden eradication.

Prophylactic Dendritic Cell-Based Vaccines Efficiently Inhibit Metastases in Murine Metastatic Melanoma

Recent data on the application of dendritic cells (DCs) as anti-tumor vaccines has shown their great potential in therapy and prophylaxis of cancer. Here we report on a comparison of two treatment schemes with DCs that display the models of prophylactic and therapeutic vaccination using three different experimental tumor models: namely, Krebs-2 adenocarcinoma (primary tumor), melanoma (B16, metastatic tumor without a primary node) and Lewis lung carcinoma (LLC, metastatic tumor with a primary node). Dendritic cells generated from bone marrow-derived DC precursors and loaded with lysate of tumor cells or transfected with the complexes of total tumor RNA with cationic liposomes were used for vaccination. Lipofectamine 2000 and liposomes consisting of helper lipid DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) and cationic lipid 2D3 (1,26-Bis(1,2-de-O-tetradecyl-rac-glycerol)-7,11,16,20-tetraazahexacosan tetrahydrocloride) were used for RNA transfection. It was shown that DCs loaded with tumor lysate were ineffective in contrast to tumor-derived RNA. Therapeutic vaccination with DCs loaded by lipoplexes RNA/Lipofectamine 2000 was the most efficient for treatment of non-metastatic Krebs-2, where a 1.9-fold tumor growth retardation was observed. Single prophylactic vaccination with DCs loaded by lipoplexes RNA/2D3 was the most efficient to treat highly aggressive metastatic tumors LLC and B16, where 4.7- and 10-fold suppression of the number of lung metastases was observed, respectively. Antimetastatic effect of single prophylactic DC vaccination in metastatic melanoma model was accompanied by the reductions in the levels of Th2-specific cytokines however the change of the levels of Th1/Th2/Th17 master regulators was not found. Failure of double prophylactic vaccination is explained by Th17-response polarization associated with autoimmune and pro-inflammatory reactions. In the case of therapeutic DC vaccine the polarization of Th1-response was found nevertheless the antimetastatic effect was less effective in comparison with prophylactic DC vaccine.

Mechanistic target of rapamycin inhibition extends cellular lifespan in dendritic cells by preserving mitochondrial function

TLR-mediated activation of dendritic cells (DCs) is associated with a metabolic transition in which mitochondrial oxidative phosphorylation is inhibited by endogenously synthesized NO and the cells become committed to glucose and aerobic glycolysis for survival. We show that inhibition of mechanistic target of rapamycin (mTOR) extends the lifespan of TLR-activated DCs by inhibiting the induction of NO production, thereby allowing the cells to continue to use their mitochondria to generate ATP, and allowing them the flexibility to use fatty acids or glucose as nutrients to fuel core metabolism. These data provide novel mechanistic insights into how mTOR modulates DC metabolism and cellular longevity following TLR activation and provide an explanation for previous findings that mTOR inhibition enhances the efficacy of DCs in autologous vaccination.

Enhancement of the T-cell armamentarium as a cell-based therapy for prostate cancer

Prostate cancer is frequently characterized by a large inflammatory infiltrate that includes T cells. Although T cells traffic to cancer lesions in large numbers, they are unable to generate a therapeutic response because of the immunosuppressive microenvironment. Therefore, arming T cells with a cytotoxic agent that is capable of killing cancer cells independent of these immunosuppressive signals is a rational approach to enhance their potency. Essentially, the T cells would serve as a cell-based vector, or "Trojan Horse," to selectively deliver a protoxin to disseminated prostate cancer lesions. The selective delivery of a protoxin using T cells represents an ideal method to maximize their therapeutic potency through a "field effect." Because systemically infused T cells are expected to traffic to sites of inflammation other than cancer, an additional level of specificity may be needed to prevent toxicity to nontarget tissues. Toward this goal, genetic engineering can be used to make protoxin expression dependent upon T-cell recognition of the prostate-specific membrane antigen by a chimeric antigen receptor. Furthermore, selective activation of the protoxin using a tissue- or tumor-specific protease, such as PSA, can promote further specificity. Thus, T-cell potency can be enhanced by targeted protoxin secretion and greater specificity achieved using combinatorial antigen recognition and protoxin activation.

Inhibition of mechanistic target of rapamycin promotes dendritic cell activation and enhances therapeutic autologous vaccination in mice

Dendritic cells (DCs) are potent inducers of T cell immunity, and autologous DC vaccination holds promise for the treatment of cancers and chronic infectious diseases. In practice, however, therapeutic vaccines of this type have had mixed success. In this article, we show that brief exposure to inhibitors of mechanistic target of rapamycin (mTOR) in DCs during the period that they are responding to TLR agonists makes them particularly potent activators of naive CD8+ T cells and able to enhance control of B16 melanoma in a therapeutic autologous vaccination model in the mouse. The improved performance of DCs in which mTOR has been inhibited is correlated with an extended life span after activation and prolonged, increased expression of costimulatory molecules. Therapeutic autologous vaccination with DCs treated with TLR agonists plus the mTOR inhibitor rapamycin results in improved generation of Ag-specific CD8+ T cells in vivo and improved antitumor immunity compared with that observed with DCs treated with TLR agonists alone. These findings define mTOR as a molecular target for augmenting DC survival and activation, and document a novel pharmacologic approach for enhancing the efficacy of therapeutic autologous DC vaccination.

T cells localized to the androgen-deprived prostate are TH1 and TH17 biased

BACKGROUND

T cells infiltrate the prostates of prostate cancer patients undergoing neoadjuvant androgen deprivation. These prostate-infiltrating T cells have an oligoclonal phenotype, suggesting the development of an antigen-specific T-cell response. We hypothesized that androgen deprivation might elicit a prostate tissue-specific T-cell response that could potentially be combined with other immune-active therapies, and consequently sought to investigate the nature and timing of this T-cell response following castration.

METHODS

We investigated the phenotype and cytokine expression of T cells at various time points in the prostates of Lewis rats following surgical castration, and used adoptive transfer of prostate-infiltrating lymphocytes (PILs) to determine whether the infiltration by T cells was mediated by effects of castration on the prostate or lymphocytes.

RESULTS

Prostate T-cell infiltration shortly after castration was T(H) 1 biased up to approximately 30 days, followed by a predominance of T(H) 17-type cells, which persisted until at least 90 days post castration. PILs from sham-treated or castrate rats localized to the prostates of castrate animals.

CONCLUSIONS

These observations suggest castration elicits a time-dependent prostate-specific T-cell infiltration, and this infiltration is likely mediated by effects of castration on prostate tissue rather than T-cells. These findings have implications for the timing of immunotherapies combined with androgen deprivation as treatments for prostate cancer.

[Immunotherapy for metastatic prostate cancer: do we really need this?]

Following the approval of Sipuleucel-T, the development of new immunomodulatory approaches such as ipilimumab and tasquinimod, and the development of new antihormonal drugs (abiraterone acetate, MDV3100, TAK-700), treatment of castration-resistant prostate cancer is finally reaching a new era of management. Docetaxel based chemotherapy remains the standard treatment of choice for patients with a high tumour burden, rapidly progressiong castration resistant prostate cancer, and poorly differentiated prostate cancer. Sipuleucel-T might be an option in the pre-docetaxel management of castration-resistant prostate cancer resulting in a 4-months improvement of overall survival. However, as with all other modalities of immunotherapy patients with good prognostic factors such as minimal tumour burden, slow PSA doubling time, Gleason score ≤ 7, and a long survival probability of > 1 year might be the best candidates taking into account that immunomodulatory approaches demonstrate positive responses after 4-6 months of therapy. Ipilimumab and tasqunimod as inhibitors of the immune checkpoints are additional, promising therapeutic agents with high clinical potential. It is the aim of the current article to critically review the current options of immune therapy in men with castration resistant prostate cancer.