RNA vaccines traditionally consist of messenger RNA synthesized by in vitro transcription using a bacteriophage RNA polymerase and template DNA that encodes the antigen(s) of interest. Once administered and internalized by host cells, the mRNA transcripts are translated directly in the cytoplasm and then the resulting antigens are presented to antigen presenting cells to stimulate an immune response. Alternatively, dendritic cells can be loaded with either tumor associated antigen mRNA or total tumor RNA and delivered to the host to elicit a specific immune response. In this review, we will explain why RNA vaccines represent an attractive platform for cancer immunotherapy, discuss modifications to RNA structure that have been developed to optimize mRNA vaccine stability and translational efficiency, and describe strategies for nonviral delivery of mRNA vaccines, highlighting key preclinical and clinical data related to cancer immunotherapy.

Intratumoral inoculation of viruses with tumor-selective cytotoxicity may induce cancer cell death and, thereby, shrink neoplastic lesions. It is unlikely, however, that viral tumor cell killing alone could produce meaningful, durable clinical responses, as clinically suitable ‘oncolytic’ viruses are severely attenuated and their spread and propagation are opposed by host immunity. Thus, a more propitious event in this context is the innate antiviral response to intratumoral virus administration, in particular for recruiting durable adaptive immune effector responses. It may represent a double-edged sword, as innate immune activation may eliminate infected tumor cells early, intercept viral spread and block any meaningful therapeutic response. The innate response to viral infection of tumors may be very different from that in non-malignant target tissues, owing to the unusual composition/tissue properties of tumor stroma. In this work, we report investigations of the innate immune response to the oncolytic poliovirus recombinant, PVSRIPO, in two mouse xenotransplantation models for breast and prostate cancer. Our observations indicate short-term virus persistence in infected tumors and virus recovery indicative of modest intratumoral propagation and persistence. Yet, a powerful innate inflammatory response coincided with chemokine induction and myeloid cell infiltration into tumors that was, interestingly, dominated by neutrophils. The combined effect of PVSRIPO tumor infection and the innate response it elicits was significant tumor regression in both models.

LBA5009 Background: Pivotal trials of AAP for patients with mCRPC enrolled few B pts, a population with a higher mortality from prostate cancer. Retrospective data suggests B pts may have higher PSA response rates than W pts treated with AAP for mCRPC. Therefore, we prospectively investigated AAP in B vs. W pts with mCRPC. Methods: Abi Race (NCT01940276) is a prospective, multicenter, parallel group study of AP in 100 men (50 B, 50 W) with mCRPC, self-identified by race. All pts received AA 1000 mg/D and P 10 mg/D (AAP) until disease progression or unacceptable adverse events (AE). The primary objective was radiographic progression-free survival (rPFS); key secondary endpoints include PSA kinetics and safety. Exploratory analyses include SNP, metabolomics and hormonal differences by race. Results: Baseline characteristics among pts were similar. The median rPFS for B and W pts was 16.8 months (mo) in each. However, PSA PFS varied by race; median PSA PFS for B and W pts were 16.6 and 11.5 mo [Table]. B pts also had numerically higher rates of ≥30%, ≥50% and ≥90% PSA decline [Table]. AEs were similar in frequency and severity by race including hypertension (42 vs 40%); however, fatigue was higher in W pts (40 vs 26%), and hypokalemia was higher in B pts (36 vs 18%). SNP profiling revealed differences in key genes involved in androgen metabolism and transport. Conclusions: This is the first prospective multicenter study by race of secondary hormonal therapy in mCRPC. B pts may have greater and more durable PSA response to AAP than W pts. SNP patterns vary by race and will be evaluated for prognostic significance. Further prospective studies in B pts are possible and needed to understand the impact of racial determinants on outcome of new hormonal regimens. Clinical trial information: NCT01940276. [Table: see text]

Bone metastases are common in men with metastatic castrate-resistant prostate cancer (mCRPC), occurring in 30% of patients within 2 years of castrate resistance and in >90% of patients over the disease course. There are 6 US Food and Drug Administration-approved therapies for mCRPC with demonstrated survival benefit. Of these, only radium-223 (Ra-223) specifically targets bone metastases, delays development of skeletal-related events, and improves survival. This review discusses key data from the ALSYMPCA trial, which contributed to the approval of Ra-223. Data from other trials are highlighted to provide further insight into which patients might benefit from Ra-223. Special patient populations are described, as well as other considerations for the administration of Ra-223. Finally, ongoing trials of Ra-223 combined with other therapies for mCRPC are discussed. These include combining Ra-223 with sipuleucel-T or immunooncology agents, to enhance immune responses, and trials in mildly symptomatic or asymptomatic patients. To date, the optimal timing, sequence, and combinations of Ra-223 with other agents are yet to be determined. The goals of this review are to provide insight into practical aspects of patient selection for Ra-223 treatment and to discuss key therapeutic strategies using the 6 approved mCRPC agents in patients with bone metastases. Results from ongoing trials should help guide the practitioner in using Ra-223 in patients with mCRPC.

212 Background: Prostate cancer (PC) is the most common malignancy among US men and the 2nd leading cause of cancer-related death. African Americans (AAs) have higher mortality from mCRPC than Whites (W). Despite this disparity, a small prior study suggested AAs may have better PSA response to abiraterone acetate (ABAC) than Ws, though radiographic progression did not differ. We evaluated overall survival (OS) in AA vs W chemotherapy-naïve (CN) mCRPC patients (Ps) treated with ABAC or enzalutamide (ENZ). Methods: This was a retrospective study that used the Veterans Health Administration (VHA) database. Male PC Ps (≥18 years) who had surgical or medical castration were identified from Apr 1, 2013 to Mar 31, 2018. The index date was the first prescription claim date for ABAC or ENZ following castration. Ps had no chemotherapy for 12 months pre-index date and had continuous VA health plan enrollment for ≥12 months pre- and post-index date. Ps were followed until death or disenrollment. Unadjusted and Kaplan-Meier survival analyses adjusted for demographic and clinical characteristics were used to calculate survival time, and multivariate Cox proportional hazards models assessed the relationship between race and OS. Results: This study included 2,123 W and 787 AA mCRPC Ps with mean ages of 74 and 71 years, respectively. The median follow‐up time was 570 days and 561 days for AA and W, respectively. AA were more prone to comorbid hypertension (77.1% vs 67.1%; p<.0001), type II diabetes (38.1% vs 29.3%; p<.0001), and liver damage or abnormality (8.8% vs 5.2%; p=0.0003) than W . From the unadjusted analysis, the median Kaplan-Meier estimated OS was 910 days for AAs and 784 days for Ws; AAs had better OS than Ws (HR=0.887; 95%CI [0.790-0.996]). From the adjusted analysis, the median Kaplan-Meier estimated OS was 918 days for AAs and 781 days for Ws; AAs still had better OS (HR=0.826; 95%CI [0.732-0.933]). Conclusions: This large retrospective study provides the first evidence that AA CN mCRPC Ps may have better OS with ABAC or ENZ than W Ps. Trials are needed to validate this finding and explore the mechanisms of racial disparities in outcomes with new hormonal therapies.

Background A subset of men with metastatic prostate cancer (mPC) responds to immune checkpoint inhibitors, and there is an unmet need to predict those most likely to benefit. We characterized circulating tumor cells (CTCs) for expression of immune checkpoint ligands in men with mPC as a non-invasive biomarker of immune evasion and immunotherapy benefit. Methods Three cohorts of patients were enrolled: 1) men with mCRPC starting abiraterone acetate/prednisone or enzalutamide (pre-ARSI), 2) men with mCRPC who were progressing on enzalutamide or abiraterone acetate/prednisone (post-ARSI), and 3) men with newly diagnosed metastatic hormone sensitive prostate cancer (mHSPC) starting androgen deprivation therapy. CTCs were captured using the CellSearch® system and stained for PD-L1, PD-L2, B7-H3, and CTLA-4 at baseline, on treatment, and disease progression. Summary statistics on mean CTCs per cohort, as well as rates of ligand positivity were used to analyze CTCs by cohort and by timepoint. Results Men in all cohorts and timepoints had prevalent CTC B7-H3 expression (> 80%). We found evidence for CTC PD-L1 expression across disease states, in which > 1 positive CTC or > 50% of CTCs were positive for PD-L1 in 40 and 30% of men with mHSPC, respectively, 60 and 20% of men with mCRPC pre-ARSI, and 70 and 30% of men with mCRPC post-ARSI. CTC PD-L2 expression was present in 20–40% of men in each disease state, while CTC CTLA-4 expression was rare, present in 20% of men with mCRPC pre-ARSI and 10% of men with mCRPC post-ARSI or with mHSPC. CTC immune checkpoint expression was heterogeneous within/between men and across disease states. Conclusions We have identified that CTCs from men with mPC heterogeneously express immune checkpoints B7-H3, PD-L1, PD-L2, and CTLA-4, and the detection of these immune checkpoints may enable monitoring on immunotherapy.

The management of mHSPC is evolving. Abiraterone plus prednisone in addition to ADT has emerged as an alternative standard-of-care to docetaxel plus ADT, and ongoing trials should clarify whether combination vs. sequential approaches with AR-targeting agents and taxane chemotherapy are preferred for initial management in the hormone-sensitive setting.

BackgroundRadium-223 has been shown to improve overall survival in men with metastatic castration-resistant prostate cancer with symptomatic bone metastases. The bone scan response to radium-223 has only been described in one single center trial of 14 patients, none of whom achieved the outstanding bone scan response presented in the current case.Case presentationIn this case report, we describe a 75 year-old white man with extensively pre-treated metastatic castration-resistant prostate cancer and symptomatic bone metastases who experienced a flare in pain and prostate-specific antigen, followed by dramatic clinical (pain), biochemical (prostate-specific antigen), and imaging (bone scan) response.ConclusionThe flare phenomena and bone scan response we observed have not previously been described with radium-223. This case suggests that the degree and duration of bone scan response may be predictive of overall survival benefit.