Sequencing of Sipuleucel-T and Androgen Deprivation Therapy in Men with Hormone-Sensitive Biochemically Recurrent Prostate Cancer: A Phase II Randomized Trial

New Combination Strategies Using Programmed Cell Death 1/Programmed Cell Death Ligand 1 Checkpoint Inhibitors as a Backbone

The discovery of immune checkpoints and subsequent clinical development of checkpoint inhibitors have revolutionized the field of oncology. The durability of the antitumor immune responses has raised the hope for long-term patient survival and potential cure; however, currently, only a minority of patients respond. Combination strategies to help increase antigen release and T-cell priming, promote T-cell activation and homing, and improve the tumor immune microenvironment, all guided by predictive biomarkers, can help overcome the tumor immune-evasive mechanisms and maximize efficacy to ultimately benefit the majority of patients. Great challenges remain because of the complex underlying biology, unpredictable toxicity, and accurate assessment of response. Carefully designed clinical trials guided by translational studies of paired biopsies will be key to develop reliable predictive biomarkers to choose which patients would most likely benefit from each strategy.

Overcoming Oncogenic Mediated Tumor Immunity in Prostate Cancer

Immunotherapy is being tested intensively in clinical trials for prostate cancer; it includes immune checkpoint inhibition, prostate specific antigen (PSA) vaccines and dendritic cell-based strategies. Despite increasing evidence for clinical responses, the consensus of multiple trials is that prostate cancers are poorly responsive to immunotherapy. Prostate cancer has a high degree of pathological and genetic heterogeneity compared to other cancer types, which may account for immunotherapeutic resistance. This hypothesis also implies that select types of prostate tumors may be differentially responsive to immune-based strategies and that the clinical stage, pathological grade and underlying genetic landscape may be important criteria in identifying tumors that respond to immune therapies. One strategy is to target oncogenic driver pathways in combination with immunotherapies with the goal of overcoming tumor immunity and broadening the number of patients achieving a clinical response. In this analysis, we address the hypothesis that driver oncogenic signaling pathways regulate cancer progression, tumor immunity and resistance to current immune therapeutics in prostate cancer. We propose that increased responsiveness may be achieved through the combined use of immunotherapies and inhibitors targeting tumor cell autonomous pathways that contribute towards anti-tumor immunity in patients with prostate cancer.

Phase I clinical trial of sipuleucel-T combined with escalating doses of ipilimumab in progressive metastatic castrate-resistant prostate cancer

Background

Sipuleucel-T (SIP-T), which functions by stimulating cancer-specific dendritic cells, prolongs survival in men with prostate cancer. Ipilimumab (IPI) achieved a borderline survival advantage in a large randomized trial. SIP-T and IPI are potentially synergistic.

Patients and Methods

Nine men with progressive metastatic castrate-resistant prostate cancer (mCRPC) were treated prospectively with SIP-T followed immediately by IPI with one of the following doses of IPI: 1 mg/kg at 1 week after SIP-T; 1 mg/kg at 1 and 4 weeks after SIP-T; or 1 mg/kg at 1, 4, and 7 weeks after SIP-T. Three patients were evaluated at each level. Cancer-specific immunoglobulins directed at granulocyte-macrophage-colony-stimulating factor/prostatic acid phosphatase (PAP) fusion protein (PA2024) and PAP were measured prior to SIP-T, after SIP-T, 1 week after IPI, every other month for 5 months, then every 3 months for an additional 12 months.

Results

Adverse events of SIP-T were consistent with previous reports. IPI only caused a transient grade 1 rash in one patient. Median age, Gleason score, and number of previous hormonal interventions were 77 years, 8, and 3, respectively. Eight men had bone metastases and one had lymph node metastasis. Statistically significant increases in serum immunoglobulin G (IgG) and IgG-IgM specific for PA2024 and PAP occurred after SIP-T. An additional statistically significant increase in the aforementioned immunoglobulins – above the levels achieved by SIP-T – occurred after IPI. Median clinical follow-up was 36 months (range: 26–40). Three patients died from progressive disease after 9, 18, and 20 months. Out of the remaining six patients, five of them needed further treatment that included abiraterone acetate, enzalutamide, radium-223 dichloride, and spot radiation. One patient had an undetectable PSA, who did not receive any other treatment except spot radiation. Median PSA at last follow-up for the surviving patients was 3.8 (range: 0.6–7.47).

Conclusion

In this small trial, the addition of IPI to SIP-T was well tolerated. IPI increased immunoglobulins specific for the PA2024 protein and PAP above the level achieved with SIP-T alone.