Metformin for biochemical recurrence of prostate cancer: Immune data from a phase 2 study

377

Background: Metformin impacts immune response in several ways. It protects CD8 TILs from apoptotic death, downregulates CD39 and CD73, reduces MDSC activity and suppresses the transcription of PD1 thus enhancing CD8+ T cell antitumor activity (Ma et al, 2000, Nature). There is limited data on the immunologic impact of metformin treatment in hormone sensitive prostate cancer. Methods: We conducted an open label, randomized, phase II trial of bicalutamide with or without metformin of patients with high risk, biochemically recurrent prostate cancer (NCT02614859). Patients were randomized 1:2 to observation for an initial 8 weeks or metformin 1000 mg twice daily. Bicalutamide 50 mg/day was added after 8 weeks to both arms. The study discontinued accrual after interim analysis indicated no difference in PSA at 32 weeks between the two arms; however, metformin monotherapy for 8 weeks induced modest PSA declines observed in 40% of patients. Here we report immune responses in a subgroup of patients (N=12), including systemic cytokine levels and 158 circulating immune cell subsets after 8 weeks of metformin monotherapy. Results: Twelve patients treated at the NCI were analyzed. After 8 weeks, the metformin arm showed increased pDCs and lower Tregs compared to baseline. Significant differences in the percent change of immune parameters after 8 weeks of metformin monotherapy compared to 8 weeks of observation are summarized. Conclusions: Metformin has been shown to reduce markers of immune exhaustion in hormone sensitive prostate cancer which is supported by a greater reduction of PD-1+ and Tim3+ NK cells. Additional immune changes included increases in activated subpopulations of natural killer (NK) cells, which have been reported as a potential predictive biomarker of prolonged treatment response to hormone therapy in prostate cancer (Pasero et al, Oncotarget, 2015). Clinical trial information: NCT02614859 . [Table: see text]

Effects of docetaxel on circulating immune cell subsets and association with outcomes in metastatic castration-sensitive prostate cancer

207

Background: Docetaxel with androgen deprivation therapy (ADT) has been shown to improve survival in metastatic castration-sensitive prostate cancer (mCSPC). There is limited data on the immunologic effects of docetaxel in mCSPC. Greater knowledge of the immune impact of docetaxel could inform future trials in prostate cancer. Methods: A clinical trial in mCSPC evaluated sequencing docetaxel and ADT with Prostvac, a poxviral vaccine targeting prostate-specific antigen (PSA). Eligibility criteria included mCSPC within 4 months of ADT and ECOG performance status 0-2. Patients given 6 cycles of docetaxel 75mg/m2 with ADT alone for mCSPC were included in this analysis. Peripheral blood mononuclear cells (PBMCs) were sampled at baseline and at 3 weeks after commencing docetaxel. Immune cell subsets analyzed included CD4+ and CD8+ T-cells, T regulatory cells (Tregs), natural killer (NK) cells, dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs). Analyses were performed to determine if the baseline immune status or immune changes induced by therapy associate with PSA at 2 years. Results: Fifteen patients were evaluated for peripheral immune responses in this study. Median age was 63 years (range 50-73). Fourteen were white and 1 was black. ECOG performance status was 0 in 11 patients, 1 in 4 patients. Disease volume was high in 7 and low in 8 patients. Among 158 immune cell subsets assessed, only changes in Tregs and activated NK cells with a lytic and cytokine producing phenotype (CD16+ CD56br) were noted after initiation of docetaxel in addition to ADT. Patients with PSA ≤0.2 at 2 years had higher baseline frequencies of total CD4+ T cells, several activated CD4+ T-cell subsets, plasmacytoid DCs, and CD49d- Tregs. They also had lower baseline frequencies of total CD8+ T cells, naïve CD8+ T cells, and CD73+CD8+ T-cells. Patients with PSA ≤0.2 at 2 years also had greater percent increases in CD8+ effector memory (EM) PD-1+ T-cells after treatment. Conclusions: This is the first study to demonstrate increases in activated NK cells with lytic and cytokine producing potential after treatment with docetaxel. Given that NK cells are associated with clinical outcomes in prostate cancer (Zhao SG, JNCI, 2019) and that increased NK cells were seen after treatment with enzalutamide as well (Madan, JITC, 2021), developing immunotherapy combinations to capitalize on NK cell activity may be a path forward for developing immunotherapy in prostate cancer. Clinical trial information: NCT02649855 . [Table: see text]

Incorporation of intrapatient response heterogeneity using 18F-NaF PET/CT imaging improves outcome prediction models for metastatic prostate cancer patients

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Background: Quantitative 18F-NaF PET/CT imaging metrics have been shown to be prognostic in metastatic prostate cancer (mPC) patients. However, previous studies have shown conflicting results in which metrics could be prognostic. This study investigates if current methods from literature generalize to external datasets and explores which combination of features are necessary to for survival models to generalize across datasets. Methods: Imaging and progression-free survival (PFS) data from 118 patients with mPC from four separate prospective clinical trials were gathered retrospectively. Patients received 18F-NaF PET/CT imaging at baseline and at follow-up, between eight and thirteen weeks. TRAQinform IQ technology (AIQ Solutions) was used to identify, segment, and track individual lesions from baseline to follow-up. Eighty-four imaging features were extracted from each patient and sorted into baseline, follow-up, response, patient-level (no inter-lesion comparison), and intrapatient heterogeneity (comparisons between lesions). The data was split into two training and testing sets, 44 patients from one study and 73 patients from the remaining 3 studies. As they can utilize large number of inputs without overfitting, random survival forest (RSF) models were chosen to evaluate performance of feature sets in predicting PFS. Different combinations of features were used as inputs to RSF models to compare single timepoint features with response features and patient-level features with intrapatient heterogeneity features. The performance of the RSF models, together with other methods identified in literature, were evaluated in each dataset using Kaplan-Meier analysis for categorical variables and the c-index for continuous variables. Results: No patient-level imaging features highlighted by literature displayed significant association to PFS across all four clinical trials (c-index < 0.62 in at least one dataset). Other criteria from literature did not generalize across all datasets (P > 0.05). The RSF model trained with all features had high c-indices in all four datasets (range: 0.66-0.80). RSF models built with response features (min: 0.63) performed better on average than models built with features obtained from single timepoints (min: 0.55). Patient-level features (min: 0.56) were not sufficient in all testing scenarios as compared to intrapatient heterogeneity features (min: 0.63). Conclusions: The candidate imaging biomarkers from previous 18F-NaF PET/CT imaging studies of mPC patients did not generalize across all datasets. Incorporating response and heterogeneity features with single-timepoint and patient-level features resulted in RSF prediction models which were generalizable across all datasets. Use of such models hold promise for improving outcome prediction in mPC patients.

Combining IL-12 immunocytokine (M9241) with docetaxel in metastatic prostate cancer: A phase I study

e17033

Background: M9241 is an immunocytokine that targets single- and double-stranded DNA which allows the treatment to localize IL-12 to necrotic tumor (Xu, CCR 2017). M9241 was well-tolerated as a monotherapy in a Phase I study with solid tumors (Strauss J, CCR 2019). Additional preclinical data has demonstrated synergy of M9241 with cytotoxic therapy. This is the first study to examine the safety of a novel combination of chemotherapy and immunocytokines in metastatic prostate cancer. Methods: This safety analysis included patients with mCSPC or mCRPC. Patients were enrolled in a 2-dose level (DL) escalation cohort of M9241 (DL 1: 12mcg/kg, DL 2: 16.8mcg/kg) combined with docetaxel (75mg/m2) with 6 patients planned per DL. A third DL of 8mcg/kg will enroll 6 more patients after the 16.8mcg/kg DL has fully enrolled. All patients were treated with ADT. Patients were initiated on treatment with docetaxel with a plan for mCSPC patients to receive six 3-week cycles of combined treatment and mCRPC patients to continue until progression or unacceptable toxicity. M9241 was given starting with the second cycle of treatment for each patient. Dose-limiting toxicity (DLT) was evaluated in the first 6 weeks after start of docetaxel (from cycle 1 day 1 through the end of the first cycle with M9241). Results: The study has enrolled 10 patients out of a planned 18 for the safety portion. Age range is 58-82 with a median of 69 years. Race distribution is 80% White and 20% Black. Gleason scores for patients were 8 (40%), 9 (40%), and 10 (20%). No DLTs were seen with either dose-level. Only 1 patient had a Grade 4 AE, neutropenia. Grade 3 toxicities included anemia, diarrhea, leukopenia, and hypotension (each occurring in 10% of the patients). The most frequent adverse events (AEs) of any grade were anemia (40%) and lymphopenia (40%), followed by fatigue (30%), diarrhea (20%), and fever (20%). Conclusions: We established a safe dose-level of M9241 at ≥ 12mcg/kg. Updated clinical data from the safety cohort (n = 18) will be presented. This demonstrates that an immunocytokine and chemotherapy can be safely combined for treatment in metastatic prostate cancer. Two planned expansion cohorts will evaluate docetaxel and M9241 in mCSPC and mCRPC, respectively. Clinical trial information: NCT04633252.

PSMA PET findings in patients with undetectable PSA more than 3 years after docetaxel for metastatic castration-sensitive prostate cancer (mCSPC)

e17046

Background: Multiple treatment options combined with androgen deprivation therapy (ADT) provide a survival advantage in mCSPC. In this prospective study, mCSPC patients were treated with docetaxel and Prostvac, a therapeutic cancer vaccine. Since initiation of the study, a phase 3 trial of Prostvac did not show independent clinical activity in metastatic castration-resistant prostate cancer. Still, this study offers a chance to evaluate responses to docetaxel-based therapy in mCSPC. More specifically, with FDA approval of prostate-specific membrane antigen (PSMA) PET imaging in just the last year, there is a paucity of data regarding the use of this scan in long-term responders to therapies for mCSPC. Methods: Eligible patients included those with mCSPC and ECOG PS of ≤ 2. As per the CHAARTED regimen, patients started docetaxel within 4 months of initiating ADT with a plan to receive 75mg/m2 for 6 cycles. Patients were randomized to receive Prostvac prior to, concurrent with, or after docetaxel. Restaging was done annually with CT and Tc99 bone scan. The study was powered to evaluate immune responses, which is being reported separately. For this analysis, patients were evaluated as one group. Ten patients are in follow up with continued PSA values of ≤ 0.2 ng/mL and 7/10 were evaluated with 18F-DCFPyL PSMA PET. Results: Seventy-three patients enrolled. Median age was 63 years with a range of 41-86 years. Race distribution was 71.6% White, 20.3% Black, 4.1% other, and 4.1% unknown. Gleason 6, 7, and 8 to 10 was 4.1%, 21.6%, and 68.9% of patients, respectively, with 5.4% being unknown. Median pre-ADT PSA was 34.75 ng/mL. Low-volume disease represented 41.1% of patients and high-volume was 58.9%. After 2 years from the start of ADT, 22% of patients had PSA values of ≤ 0.2 ng/mL. This included 37% of the low-volume group and 12% of the high-volume group. Three years from starting ADT, 14% of patients had PSA values ≤ 0.2 ng/mL (20% of the low-volume group, 9% of the high-volume group). Of the 7 patients who remain in follow-up with PSA values ≤ 0.2 ng/mL and who were evaluated with PSMA PET, median time from start of ADT was 4 years with a range of 3.5-6 years. These patients either had no evidence of disease or minimal residual findings on CT/Tc99 bone scan. Four of the 7 patients still had residual areas of uptake on PSMA PET. Conclusions: Patients treated with docetaxel for mCSPC have the potential for long-term clinical responses. In these long-term responders, despite prolonged PSA response and minimal findings on conventional CT and Tc99 scans, more than half of patients still had findings on PSMA PET imaging. Further studies are required to better understand the clinical implications of these findings and the role of PSMA PET in mCSPC. Clinical trial information: NCT02649855.

Phase II evaluation of the combination of PDS0101, M9241, and bintrafusp alfa in patients with HPV 16+ malignancies

2518

Background: More than 630,000 cases of HPV related cancer occur worldwide annually. About 15-20% of cases respond to PD-(L)1 inhibitors and about 30% respond to dual PD-L1/TGF-β blockade including 10% of checkpoint refractory pts, but for the majority of pts with checkpoint refractory disease there is no effective standard therapy. Preclinical studies show that the combination of PDS0101, a therapeutic vaccine targeting HPV 16 E6/E7, M9241, a tumor-targeting IL-12 immunocytokine, and bintrafusp alfa (BA), a bifunctional fusion protein targeting TGF-β and PD-L1, resulted in maximum T cell infiltration and tumor reduction compared to any 1 or 2 of these agents alone. Prior clinical data suggests that the combination is preferentially active in HPV 16+ disease. Methods: 30 pts with advanced HPV 16+ cancer were treated with PDS0101, M9241 and BA (NCT04287868). Pts received BA at 1200 mg IV q2wks, M9241 at 16.8 mcg/kg SC q4wks or 8 mcg/kg SC q2wks, and PDS0101 as two 0.5 ml SC injections q4wks. Dose reductions or skipped doses for toxicities of BA and M9241 were allowed. 5 pts had surgical resection of tumor for disease control and were censored for PD but not survival. Results: 30 pts (9 cervical, 2 vaginal/vulvar, 6 anal, 13 oropharyngeal) were treated. 13/30 had grade 3 treatment related AEs including grade 3 anemia in 9 pts associated with grade 3 hematuria in 3 pts and grade 3 GI bleeding in 3 pts. 2 pts had grade 3 AST/ALT elevation. Grade 3 flu like symptoms and grade 3 hemophagocytic lymphohistiocytosis were each seen in 1 pt. One pt had grade 3 lymphopenia/leukopenia plus grade 4 neutropenia and one pt had grade 4 AST/ALT elevation. There were no grade 5 treatment related AEs. 7/8 (88%) pts with checkpoint naïve disease had objective responses (OR) including 1 delayed response after initial PD with 4/7 (57%) responses ongoing (median 17 months follow up). 10/22 (45%) with checkpoint refractory disease have had disease reduction including 6/22 (27%) with OR and 4/6 (67%) responses ongoing (median 12 months follow up). 6/8 (75%) pts with checkpoint naïve disease and 17/22 (77%) pts with checkpoint refractory disease are alive after a median of 17 and 12 months follow up respectively. For checkpoint refractory pts, M9241 dosing appears to affect response rates. 5/8 (63%) pts receiving M9241 at 16.8 mcg/kg had an OR compared to 1/14 (7%) who received M9241 at 8 mcg/kg with an OR. However, despite differences in response rates with higher vs lower M9241 dose, survival outcomes were similar irrespective of M9241 dose (p = 0.99 by Kaplan Meier analysis). Conclusions: The combination of PDS0101, M9241 and BA appears to have a manageable safety profile along with early evidence of clinical activity for pts with checkpoint naïve and refractory advanced HPV 16+ cancer. Moreover, growing data suggest that all 3 drugs in the combination contribute to the encouraging outcomes being observed. Clinical trial information: NCT04287868.

Evaluating the optimal sequence of immunotherapy and docetaxel in men with metastatic castration-sensitive prostate cancer

130

Background: Docetaxel is a standard of care for metastatic castration-sensitive prostate cancer (mCSPC). PROSTVAC is a pox viral-based therapeutic cancer vaccine encoding for PSA and three T-cell co-stimulatory molecules. Pox viral-based vaccines had previously demonstrated potential immune synergy with docetaxel. This clinical trial evaluated the optimal sequence of immunotherapy and chemotherapy in mCSPC. Methods: Key eligibility criteria were mCSPC within 4 months of ADT and ECOG performance status 0-2. Patients were randomized between Arms A (6 cycles of docetaxel 75mg/m2 followed by 6 doses of PROSTVAC) and B (docetaxel concurrent with PROSTVAC). After rapid accrual to the first 2 arms, Arm C was added by protocol amendment (6 doses of PROSTVAC prior to 6 cycles of docetaxel). ADT was continued throughout the treatment period. The primary endpoint was to evaluate antigen-specific responses to the tumor antigens, PSA and MUC1, and brachyury, a transcription factor implicated in the metastatic process, after patients completed their respective sequence of docetaxel and PROSTVAC. This was done using intracellular cytokine staining of 4 established markers in both CD4+ and CD8+ T-cells, for a total of 8 measures of activation per antigen. Results: The study enrolled 73 patients with a median age of 63 years (range 41-86). Gleason scores for patients were 6 (4.1%), 7 (21.6%) and 8-10 (68.9%), with 5.4% being unknown. Median pre-ADT PSA was 34.75 ng/mL. Per CHAARTED criteria, disease volume was low in 41.1% and high in 58.9% of patients. Numbers of patients evaluable for immune responses in arms A, B, and C were 16, 12 and 18, respectively. Clinical responses have previously been presented (Atiq, MO et al., ASCO 2021), with 22% of all patients having PSA <0.2 at 2 years. Conclusions: This data provides some insights into the potential of immune activating therapies in relation to chemotherapy in patients with prostate cancer. This preliminary analysis suggests the greatest magnitude of immune activation is seen when immunotherapy is followed by chemotherapy. Additional analysis of the breadth of immune responses and associations with clinical outcomes is ongoing and will be presented. Clinical trial information: NCT02649855. [Table: see text]

The immunocytokine M9241 in the treatment of prostate cancer (PCa): Clinical and immune data from a phase 1 study

127

Background: Interleukin-12 (IL-12) is a proinflammatory cytokine that plays a critical role in regulating the transition from innate to adaptive immunity but has toxicity with systemic administration. M9241 is an immunocytokine composed of 2 IL-12 heterodimers, each fused to one of the H-chains of the NHS76 antibody, which has affinity for both single and double stranded DNA. Thus, M9241 targets delivery to regions of tumor necrosis where DNA has become exposed. NCT01417546, a phase I trial of M9241 at escalating doses, established safety and dosing (Strauss J et al, CCR 2019). This was the first use of M9241 in human subjects with solid tumors including PCa. Methods: Nine patients (pts) with PCa enrolled in the phase 1 study, not all of which were presented previously. M9241 was given subcutaneously every 4 weeks (0.1-21.8mcg/kg) or every 2 weeks (12-16.8mcg/kg). PSA declines and immune responses were evaluated including systemic cytokine levels and 30 markers on 158 circulating immune cell subsets. Results: Nine PCa pts were treated with NHS-IL12 and 8 were evaluable for response, including 6 pts with biochemical recurrence and 2 with metastatic castration resistant prostate cancer (one patient discontinued the study treatment after 1 dose due to grade 3 elevation in ALT). There were no adverse events (AEs) of grade >4. Additional grade 3 toxicities included one each of: leukopenia, neutropenia and lymphopenia. The most common AEs of any grade were lymphopenia (77.8%), fatigue (55.6%), and ALT elevation (55.6%). 5 of 8 (62.5%) had PSA declines ranging from 8-42%. After treatment with M9241, evaluable pts had increases in systemic IL-10, TNF and INFg. Additional immune changes included increases in activated subpopulation of natural killer (NK) cells, consistent with the phase 1 experience. Conclusions: M9241 was found to be safe and well tolerated in PCa pts. PSA declines occurred in 5 of 8 evaluable pts. As with the phase 1 study, increases in NK subpopulations were seen in the small number of evaluable pts. These preliminary findings of a necrosis-targeting immunocytokine will be evaluated further in combination studies with cytotoxic therapy. M9241 is currently being evaluated in combination with docetaxel in metastatic prostate cancer (NCT04633252). Clinical trial information: NCT01417546.

Safety evaluation of M9241 in combination with docetaxel in metastatic prostate cancer

93

Background: M9241 is an immunocytokine that targets single- and double-stranded DNA which allows the treatment to localize IL-12 to necrotic tumor (Xu, CCR 2017). M9241 was well-tolerated as a monotherapy in a Phase I study with solid tumors (Strauss J, CCR 2019). Additional preclinical data has demonstrated synergy of M9241 with cytotoxic therapy. This is the first study to examine the safety of a novel combination of chemotherapy and immunocytokines in metastatic prostate cancer. Methods: This safety analysis included patients with mCSPC or mCRPC. Patients were enrolled in a 2-dose level (DL) escalation cohort of M9241 (DL 1: 12mcg/kg, DL 2: 16.8mcg/kg) combined with docetaxel (75mg/m2) with 6 patients planned per DL. A third DL of 8mcg/kg will enroll 6 more patients after the 16.8mcg/kg DL has fully enrolled. All patients were treated with ADT. Patients were initiated on treatment with docetaxel with a plan for mCSPC patients to receive six 3-week cycles of combined treatment and mCRPC patients to continue until progression or unacceptable toxicity. M9241 was given starting with the second cycle of treatment for each patient. Dose-limiting toxicity (DLT) was evaluated in the first 6 weeks after start of docetaxel (from cycle 1 day 1 through the end of the first cycle with M9241). Results: The study has enrolled 10 patients out of a planned 18 for the safety portion. Age range is 58-82 with a median of 69 years. Race distribution is 80% White and 20% Black. Gleason scores for patients were 8 (40%), 9 (40%), and 10 (20%). No DLTs were seen with either dose-level. Only 1 patient had a Grade 4 AE, neutropenia. Grade 3 toxicities included anemia, diarrhea, leukopenia, and hypotension (each occurring in 10% of the patients). The most frequent adverse events (AEs) of any grade were anemia (40%) and lymphopenia (40%), followed by fatigue (30%), diarrhea (20%), and fever (20%). Conclusions: We established a safe dose-level of M9241 at ≥ 12mcg/kg. Updated clinical data from the safety cohort (n = 18) will be presented. This demonstrates that an immunocytokine and chemotherapy can be safely combined for treatment in metastatic prostate cancer. A planned expansion cohort will evaluate docetaxel and M9241 in mCRPC. Clinical trial information: NCT04633252.

Phase II evaluation of the triple combination of PDS0101, M9241, and bintrafusp alfa in patients with HPV 16 positive malignancies

2501

Background: There are more than 630,000 cases of HPV associated malignancies including cervical, oropharyngeal and anal cancer worldwide annually. HPV 16 is responsible for the majority of these cases. About 15-20% of HPV associated malignancies respond to PD-(L)1 inhibitors, but for the overwhelming majority of patients who progress on these immunotherapies there is no effective standard of care therapy. Preclinical studies have shown that the triple combination of PDS0101 (Versamune-HPV), a liposomal multipeptide therapeutic vaccine targeting HPV 16 E6/E7, M9241, a tumor-targeting immunocytokine composed of IL-12 heterodimers fused to a monoclonal antibody targeting free DNA in necrotic tumor regions, and bintrafusp alfa, a bifunctional fusion protein targeting TGF-β and PD-L1, resulted in maximum HPV-specific T cell responses, T cell tumor infiltration and tumor reduction as compared to any one or two of these agents alone. Methods: Fourteen pts with HPV 16+ relapsed or refractory advanced cancer were enrolled to the triple combination of PDS0101, M9241 and bintrafusp alfa (NCT04287868). Pts received bintrafusp alfa at 1200 mg flat dose i.v. every 2 weeks, M9241 at 16.8 mcg/kg s.c. every 4 weeks and PDS0101 given as two separate 0.5 ml s.c. injections every 4 weeks. Dose reductions of M9241 to 8 mcg/kg were allowed as well as skipped doses of any agent for ongoing toxicities. Results: Fourteen pts with advanced HPV 16+ cancers (5 cervical, 2 vaginal/vulvar, 4 anal, 3 oropharyngeal) were treated. 4/14 (28.6%) pts had a grade 3 treatment related toxicity including grade 3 hematuria in 2 pts with cervical ca and prior pelvic radiation and grade 3 AST/ALT elevation in 2 pts, one with anal ca and one with vaginal ca. For one patient with grade 3 AST/ALT elevation dose reduction of M9241 from 16.8 to 8 mcg/kg allowed for continued treatment with AST/ALT remaining at grade 1 or less. One additional patient had transient asymptomatic grade 4 neutropenia. No other treatment related grade 3 or greater toxicities were noted. 10/14 (71%) pts have had objective responses: 1 CR (anal ca) and 9 PRs (3 cervical, 2 vulvar/vaginal, 2 anal, 2 oropharyngeal) with 9/10 of these responses ongoing after a median 5 month of follow up. Of the 14 pts, 6 pts have checkpoint naïve disease and 8 pts have checkpoint refractory disease. 5/6 (83%) pts with checkpoint naïve disease and 5/8 (63%) pts with checkpoint refractory disease have had objective responses. Analyses of immune responses and other immune correlates are ongoing. Conclusions: Triple combination of PDS0101, M9241 and bintrafusp alfa appears to have a manageable safety profile along with early evidence of notable clinical activity for pts with both checkpoint naïve as well as checkpoint refractory HPV 16+ advanced malignancies. Clinical trial information: NCT04287868.

A phase 1 open label trial of intravenous administration of MVA-BN-Brachyury vaccine in patients with advanced cancer

2617

Background: Brachyury is a member of the T-box family of transcription factors which is overexpressed in several tumor types and has been associated with treatment resistance, epithelial to mesenchymal transition and metastatic potential. MVA-BN-Brachyury vaccine is a vector-based therapeutic cancer vaccine which demonstrated immunogenicity and safety in previous clinical trials. Preclinical studies suggested that IV administration of vaccines can induce superior CD8 + T-cell responses as compared with SC or IM routes. This is the first-in-human study to evaluate safety and tolerability of IV administration of this vaccine. Methods: Patients with metastatic or unresectable locally advanced malignant solid tumors were treated with MVA-BN-Brachyury vaccine in a phase 1, open-label, 3+3 dose-escalation study. Eligible patients received a total of three vaccine doses intravenously Q3W at 1x107 (DL1), 1x108 (DL2), or 1x109 infections units (Inf.U) (DL3). Patients were admitted for 48 hours for observation after each dose and had imaging at baseline and 1 and 3 months after the last vaccine dose. Primary objective was to determine the safety and tolerability and establish the recommended phase 2 dose (RP2D). Immune assays were performed in the first 10 enrolled patients. Results: In 13 patients (10 chordoma, 1 small cell breast, 1 prostate, 1 colorectal cancer), no dose-limiting toxicities were observed. Right upper quadrant abdominal pain was the only grade 3 TRAE. All other TRAEs were grade 1 or 2; most common was cytokine release syndrome (four grade 2 and one grade 1. As of Feb 2021, 9 patients completed treatment and two planned restaging scans: 5 patients had PD (3 in DL1 and 2 in DL2), 3 had SD (2 in DL2 and 1 in DL3) and 1 had PR (DL3) as their best treatment response per RECIST 1.1. One patient with advanced sacral chordoma had significant reduction of ulcerated skin metastases after 2 doses, followed by 33% shrinkage at the end of trial. Two chordoma patients with SD reported significant pain improvement. Multifunctional Brachyury, CEA, and MUC1 specific T cells were increased after vaccination in in 60%, 67%, and 50% of patients, respectively. Conclusions: MVA-BN-Brachyury IV vaccine is safe across all tested dose levels and suggesting activity in chordoma at DL3 for which this vaccine was granted FDA orphan drug designation. Mild cytokine release syndrome (rigors, chills, fever and hypotension) has been observed in 5 patients and managed with IV fluids and steroids in 2 patients. A dose 1 x 109 Inf.U (DL3) was selected for RP2D based upon available safety data. Further research is pending to evaluate clinical benefit and immunogenicity. Clinical trial information: NCT04134312.

Patients with undetectable PSA 2 years after docetaxel for metastatic castration sensitive prostate cancer (mCSPC)

e17044

Background: Patients with mCPSC have multiple treatment options to combine with androgen deprivation therapy (ADT) including docetaxel, abiraterone, enzalutamide and apalutamide, all of which have demonstrated a survival advantage. While oral anti-androgens are administered daily until progression but are less toxic, docetaxel has more upfront side effects. One of the advantages of using docetaxel is that the 6-cycle regimen (over approximately 4 months) potentially affords patients a respite from daily therapies thereafter. Furthermore, docetaxel may be more cost-effective. In this prospective study, mCSPC patients were treated with docetaxel and Prostvac, a therapeutic cancer vaccine. Since this study was initiated, Prostvac did not demonstrate independent clinical activity in a phase 3 trial in metastatic castration resistant prostate cancer. Nonetheless, this study provides an opportunity to evaluate responses to docetaxel-based therapy in mCSPC. Methods: Eligible patients included those with mCSPC and ECOG of ≤ 2. All patients were treated with docetaxel and were planned to receive 75mg/m2 for 6 cycles within 4 months of starting ADT, as per the CHAARTED regimen. Patients were randomized to receive Prostvac prior to, concurrent with or after docetaxel. Patients were restaged annually with CT and Tc99 bone scan. The study was powered to evaluate immunologic responses, which is ongoing. For the purposes of this analysis, all patients were analyzed as one group and long-term PSA responses were evaluated. Results: The study enrolled 73 patients. Age range was 41-86 with a median of 63 years. Race distribution was 71.6% White, 20.3% Black, 4.1% other, and 4.1% unknown. Gleason scores were 6 (4.1%), 7 (21.6%), and 8-10 (68.9%), with 5.4% being unknown. Median pre-ADT PSA was 34.75 ng/mL. Low-volume disease represented 41.1% of patients and high-volume was 58.9%. After 2 years from the start of ADT, 22% of all patients had PSA values of ≤ 0.2 ng/mL. This included 37% of the low-volume group and 12% of the high-volume group. Three years from the start of ADT, 14% of all patients had PSA values ≤ 0.2 ng/mL (20% of the low-volume group, 9% of the high-volume group). Conclusions: These data highlight long-term outcomes of 6 cycles of docetaxel for men with mCSPC. Although there are concerns about the short-term toxicity of docetaxel, there is potential for prolonged stable disease after ̃4 months of chemotherapy that allows these patients to defer additional oral anti-androgen therapy for years in some patients. The proportions of patients presented here are an underestimate of those who could continue to be monitored for slowly rising, but low PSAs, before starting the next line of therapy. Additional research is required to determine the optimal therapeutic sequence for men diagnosed with mCSPC and long-term implications for quality of life and cost-effectiveness. Clinical trial information: NCT02649855.

First-in-human phase I/II trial of PRGN-2009 vaccine as monotherapy or with bintrafusp alfa in patients with recurrent/metastatic (R/M) human papillomavirus (HPV)-associated cancers (HPVC) and as neoadjuvant/induction therapy in locoregionally advanced (LA) HPV oropharyngeal (OP) and sinonasal (SN) squamous cell cancer (SCC)

TPS6092

Background: R/M HPVC (cervical, anal, oropharyngeal, etc.) are incurable by current therapies. For newly diagnosed LA HPV-OPSCC standard-of-care (SOC) is radiotherapy ± chemotherapy (C/RT) or surgery ± adjuvant C/RT, with considerable risk of relapse. Newly diagnosed LA SNSCC treatment follows the OPSCC paradigm, and detection of HPV appears to confer improved prognosis. Neoadjuvant PD-1 immune checkpoint blockade (ICB) before surgery may improve RFS and is being evaluated in a multicenter phase III clinical trial (Keynote-689). PRGN-2009 (P) is a novel gorilla adenovirus vaccine containing 35 non-HLA-restricted epitopes of HPV 16 and 18 shown to induce HPV specific responses (preclinical models). Bintrafusp alfa (BA) is a bifunctional fusion protein targeting TGF-β and PD-L1 with promising activity in HPVC. This trial will evaluate the safety and activity of P/ P + BA in patients with previously treated R/M HPVC and as neoadjuvant/induction therapy before SOC surgery or C/RT in newly diagnosed LA HPV-OPSCC and HPV-SNSCC. Methods: This is a first-in-human, investigator-initiated, single-center phase I/II trial. Pts with previously treated (incl. ICB) R/M HPVC are eligible for Phase I: P dose escalation arm (3+3 design, 6-12 patients) testing 2 dose levels (1x1011, 5x1011 viral particle units, SC Q2W three times, then Q4W), and combination arm (10 patients) testing P (recommended phase 2 dose (RP2D), same schedule) + BA (1200 mg IV Q2W). Treatment (both arms) will continue until disease progression, unacceptable toxicity, decision to withdraw. Primary endpoint is safety. Secondary endpoints include ORR (RECIST 1.1), PFS, and OS. For Phase II, patients with newly diagnosed stage II/III (AJCC Cancer Staging Manual, 8th ed.) HPV-OPSCC and stage II/III/IVA/IVB HPV-SNSCC planned for SOC C/RT or surgery will be eligible for two treatment arms of 20+2 patients each (sequential): P arm and P + BA, to evaluate the treatment activity. All patients will have pre-treatment biopsy, receive two cycles of the study treatment at the NCI Clinical Center two weeks apart, followed by post-treatment biopsy and SOC treatment (at the referring institution) 4 weeks after the first study treatment. Primary endpoint is post-treatment ≥2-fold increase in tumor-infiltrating CD3+ cells. Secondary endpoints include RFS, OS. Exploratory endpoints for both arms include analyses of immune subsets, soluble factors, and HPV-specific immune responses in peripheral blood and tissue where available, and in Phase II sequencing (exome, scRNA), immune spatial profiling with multiplex immunofluorescence, and salivary HPV DNA. Clinical trial registry: NCT04432597. Clinical trial information: NCT04432597.

A phase I/II study of bintrafusp alfa and NHS-IL12 in combination with docetaxel in adults with metastatic castration sensitive (mCSPC) and castration-resistant prostate cancer (mCRPC)

TPS5096

Background: Immune checkpoint inhibition is successful in a small subpopulation of men with prostate cancer. This could be related to barriers to immune response in the tumor microenvironment. Immunocytokines present an opportunity to specifically target the pleiotropic tumor microenvironment impacting immune cells beyond T-cells. NHS-IL12 is an immunocytokine that carries IL-12 (shown to impact natural killer and myeloid cells) and binds to necrotic tissue with exposed histones. Phase 1 studies have indicated immune and even PSA responses in prostate cancer to NHS-IL12 (Strauss J, CCR 2019). Preclinical data has demonstrated synergy with docetaxel, which is standard therapy in both mCSPC and mCRPC. Further synergy has been shown with a novel first-in-class bifunctional fusion protein (bintrafusp alfa) composed of the extracellular domain of human TGF-β receptor II (TGFβRII), which effectively functions to sequester or “trap” all three TGF-β isoforms (Lind H, JITC 2020), fused to a monoclonal antibody against PD-L1. This study will examine the potential of a novel combination of chemotherapy, checkpoint inhibition, and immunocytokines in metastatic prostate cancer. Methods: The study will evaluate safety of NHS-IL12 with docetaxel at escalating doses followed by the addition of bintrafusp alfa in all metastatic patients. Once safety of the combination is established, patients will enroll in 2 cohorts with either mCSPC or mCRPC. Eligible patients include mCSPC (≤134 days of starting ADT) and mCRPC (must have been previously treated with abiraterone or enzalutamide), with good performance status (ECOG of ≤ 2). Patients with brain metastases or who are immunocompromised are excluded. For mCSPC, the primary endpoint will evaluate the increase in the proportion of patients who have a PSA less than 0.2 ng/mL 7 months after the start of ADT, which is based on the prognostic value of PSA less than 0.2 ng/mL at 7 months in mCSPC (Harshman L, JCO 2017). The secondary endpoint is biochemical and radiographic time to progression. The primary endpoint for the mCRPC patients will evaluate progression free survival with secondary endpoints examining the percentage of patients with a 50% PSA decline from baseline and radiographic response rates per RECIST. Exploratory analysis will analyze changes in immune cell subsets after treatment as well as immune status of the tumor microenvironment. Clinical trial information: NCT04633252.

Anaplastic features (AnaF) and DNA-damage repair pathway (DDR) mutations in metastatic castration-resistant prostate cancer (mCRPC)

92

Background: Anaplastic prostate cancer displays features of small-cell carcinoma, a type of neuroendocrine tumor. Treatments for anaplastic prostate cancer are based on small cell lung cancer regimens. Both AnaF and mutations in DDR pathways, including BRCA2 confer an aggressive phenotype. For patients (pts) with certain DDR mutations, olaparib (O) was recently FDA approved, and an ongoing study is evaluating whether the addition of durvalumab (D) confers additional benefit in mCRPC (NCT02484404). We evaluate a potential preliminary relationship between DDR mutations, treatment with D and O, and AnaF. Methods: This is a phase II study of O plus D in pts with mCRPC with disease that is amenable to biopsy. On-study core biopsies undergo mutational analysis. Prior treatment with enzalutamide (enza) and/or abiraterone (abi) is required. D is given at 1500 mg iv q28 days + O 300 mg tablets po q12 hours. The primary endpoint is PFS. Pts were categorized into those with and without AnaF as defined by Aparicio et al. (2013). AnaF include small-cell histology; exclusively visceral metastases; predominantly lytic bone metastases; bulky lymphadenopathy (≥5 cm) or high-grade (Gleason ≥8) mass in prostate/pelvis; low PSA (≤10 ng/mL) at initial presentation with high volume (≥20) bone metastases; neuroendocrine markers in histology or serum plus elevated LDH, malignant hypercalcemia, or elevated serum CEA; or short interval (≤6 months) to androgen-independent progression. Results: Of 55 pts accrued, 24 had prior abi and enza; 19 pts had prior taxane. Common adverse events include anemia, fatigue, and nausea. Also, 11 pts (20.0%) displayed clear AnaF (Table) and 43 pts lacked AnaF, including 8 (14.5%) with partial AnaF that did not meet the full criteria, 4 (7.3%) who likely did not have AnaF due to difficulty in quantifying disease burden, 29 (52.7%) who did not have AnaF, and 2 (3.6%) had unknown status. Four pts (36.4%) with clear AnaF had DDR aberrations, including 3 (27.3%) with BRCA2, 1 (9.1%) with both BRCA2 and CHEK2, and 1 (9.1%) with ATM. Conclusions: Pts with mCRPC with DDR mutations can also have AnaF. This preliminary data demonstrates that pts with anaplastic prostate cancer and pts with DDR mutations are two distinct populations with some degree of overlap. O+D is well-tolerated, and future studies should focus on finding optimal treatments for pts with AnaF without and without DDR mutations. Clinical trial information: NCT02484404. [Table: see text]

Evaluating biomarkers in metastatic castration-resistant prostate cancer patients treated with enzalutamide: PSA, circulating tumor cell counts, AR-V7 status and radiographic progression

e17569

Background: Enzalutamideis ahighly effective treatment in metastatic castration resistant prostate cancer (mCRPC). Although Prostate Cancer Working Group (PCWG) guidelines recommend continuing treatment until radiographic/clinical progression (rPD/cPD), many patients discontinue therapy for rising PSA alone. Methods: We conducted an open label, randomized phase 2 trial in mCRPC patients untreated with docetaxel, abiraterone, or enzalutamide, comparing enzalutamide alone or in combination with PROSTVAC, a therapeutic cancer vaccine designed to induce an anti-tumor immune response. The study discontinued accrual after planned interim analysis indicated no difference in progression between the two arms. Patients were followed beyond 1st of 3 confirmed PSA rises until rPD. 49 patients were analyzed for Circulating Tumor Cell (CTC) count and AR-V7 status at 1st PSA rise and at rPD/cPD or last follow up. Results: 57 patients were enrolled with median follow up time of 55.4 mo. 49/57 (86%) patients had rising PSA; median time to 1st PSA rise for all patients was 6.4 mo (95% CI: 3.7-11.0 mo) after starting enzalutamide. 38/57 (67%) patients had progressive disease (majority with rPD; 1/38 (3%) with cPD); median time to progression for all patients was 23.3 mo (95% CI: 16.1-27.8 mo). 5 patients tested positive for AR-V7 within 30 days of rPD. In patients who experienced rPD/cPD, CTCs were detected in 11/24 (46%) samples taken at rPD vs. in only 3/24 (13%) samples taken at rising PSA. CTC counts were higher at rPD compared to samples taken at rising PSA (P = 0.004, Wilcoxon unpaired test). Of the 7 patients still being treated (median time on drug = 4.2 yrs), 2 experienced rising PSA; however none of the patients had detectable CTCs at a median of 30 days from last follow up. Conclusions: These data suggest that a rising PSA may not be a warning of near-term clinically significant disease progression in mCRPC patients treated with enzalutamide, given the 17-month difference between the first rise in PSA and ultimate rPD/cPD seen in this analysis. Further, CTCs and AR-V7 status associate strongly with rPD but not with rising PSA, adding biological rationale to the hypothesis that CTC counts and AR-V7 status are associated with disease progression. Collectively, these data highlight the need to continue to educate patients and providers on PCWG criteria for progression and appropriately-timed utilization of both therapies and diagnostic tests to maximize drug efficacy in mCRPC. Clinical trial information: NCT01867333 .

A randomized, double-blind, phase II clinical trial of GI-6301 (yeast-brachyury vaccine) versus placebo in combination with standard of care definitive radiotherapy in locally advanced, unresectable, chordoma

11527

Background: Chordoma is a rare neoplasm of the notochord that overexpresses brachyury, a transcription factor associated with epithelial-to-mesenchymal transition, metastasis, poor prognosis, and chemotherapy resistance. GI-6301 is a recombinant yeast-brachyury vaccine shown to demonstrate brachyury-specific immunogenicity, excellent safety profile, and some evidence of clinical activity in patients with chordoma in a previous phase I trial. Radiation therapy (RT) can modulate the tumor to become an immunostimulatory milieu. Preclinical studies have shown a synergistic effect combining RT with vaccine, thus prompting this clinical trial evaluating the combination of GI-6301 with RT in chordoma (NCT02383498). Methods: Adults with locally advanced, unresectable chordoma were treated on a randomized, double-blind, placebo controlled, phase 2 clinical trial. Patients received 3 doses of GI-6301 (80 x 107 yeast cells) vs placebo followed by photon or proton RT, followed by GI-6301 vs placebo until disease progression. Primary outcome was overall response rate (ORR) defined as a complete response or partial response in the irradiated tumor site at 24 months. Immune assays were conducted to evaluate immunogenicity. Due to slow accrual, an unplanned interim analysis was undertaken. Results: 24 pts were randomized and treated between May 2015 and September 2019. Vaccine was well tolerated with no dose reductions or treatment discontinuation. Treatment-related serious adverse events included: nausea/emesis (2); fatigue (2); dehydration (2); diarrhea (1); radiation necrosis (1); stroke (1); sepsis (1). There was no difference in ORR between the two arms. Pre-existing brachyury-specific T-cells were detected in the majority of patients but did not correlate with response to therapy. Most patients developed T-cell responses during therapy, regardless of treatment arm. Conclusions: There was no difference in ORR between the two arms. GI-6301 was well tolerated with toxicities related to RT, not vaccine. The trial was stopped early due to low conditional power for finding a statistical difference at the planned end of accrual, based on findings to date. Future studies will define utility of vaccines targeting brachyury in chordoma. Clinical trial information: NCT02383498 . [Table: see text]

Artificial intelligence assisted bone lesion detection and classification in computed tomography scans of prostate cancer patients

e17567

Background: Patients diagnosed with prostate cancer undergo computed tomography (CT) for pretreatment staging to rule out bone metastases. However, detection and classification of bone lesions on CT is challenging and subject to inter-reader variability. We present a cascaded deep learning algorithm for automatic detection and classification of bone lesions on staging CT in patients diagnosed with prostate cancer. Methods: CT scans from 56 patients with histopathologically proven prostate cancer were included. An expert radiologist annotated the extent of individual bone lesions (N = 4217) and labelled all regions as either benign or malignant. All scans were anonymized and normalized at the patient-level prior to training. Our method can be described as a two-stage framework, 1) A detection algorithm: Inspired by Yolo-v3 detection method, we designed a network with a backbone of darknet-53 pretrained on Coco dataset and four final scaling blocks to compensate for wide range of lesion diameters, 2) A classification algorithm: we formed a binary classifier based on ResNet-50 pretrained using the ImageNet dataset. We used a train/validation split equal to 90%/10% for this study. To facilitate the learning process, horizontal flipping, relative zooming and mean weighted averaging were used for data augmentation in stage 1. Instead, the classification algorithm took advantage of synthesized patches generated by Deep Convolutional Generative Adversarial Network (DC-GAN) for augmentation. Results: We could achieve a real-time (~120ms per slice) performance on our validation set with a median penalty of 0.3(0.02-0.78) false positives per true positive within each patient. Overall performance of our detection algorithm was 81% sensitivity and 86% positive predictive value. In stage 2, we obtained an accuracy of 89% for correct classification of benign from malignant bone lesions with no augmentation which was improved to 91% when we incorporated the augmented data for training. Conclusions: Our 2-stage algorithm sequentially detects and classifies bone lesions on CT of prostate cancer patients with a significant performance. To further improve our results and for generalizability we are accruing more data from different centers. Eventually, with greater dataset, both algorithms will be cascaded and trained as a whole unit to become one single tool for fully automatic detection and classification which serves as an aid for radiologists who read the staging CTs.

Spatial analysis of tumor immune microenvironment (TIME) in patients treated with Bintrafusp alfa

3070

Background: Bintrafusp alfa is a first-in-class bifunctional fusion protein composed of the extracellular domain of TGF-βRII receptor (TGF-β “trap”) fused to a human IgG1 mAb blocking PD-L1. In preclinical models, bintrafusp alfa treatment promoted CD8+ T cell and NK cell activation, and both immune cell (IC) populations were required for optimal bintrafusp alfa mediated tumor control. However, the effect of bintrafusp alfa on TIME in humans has not been reported. Methods: In this unplanned interim analysis of a biomarker expansion cohort (NCT 02517398), patients (pts) with advanced non-small cell lung cancer (NSCLC) underwent paired biopsies (bx) before and on treatment with bintrafusp alfa (~ 50 days apart). The objective was to evaluate frequency and localization of tumor infiltrated ICs by IHC. Out of 12 pts, 7 had matched (Pre vs Post) tumor-containing specimens sufficient for multiplex immunofluorescence (MxIF) analysis of TIME. Four pts were excluded as Post bx histology for 3/12 [2 PR (partial response), 1 SD (stable disease)] was negative for tumor (necrosis or fibrosis) and 1/12 did not have a Post bx performed. Results: TIME study shows CD8 T cell infiltrates were increased in Post compared to Pre bx (median 161 vs 62/mm²; interquartile range [IQR] 65–396/mm² vs 31–135/mm²; p = 0·04). While M2 macrophages were also increased (median 800 vs 367/mm²; IQR 776–1131/mm² vs 171–831/mm²; p = 0·04), the ratio of M1/M2 was reversed in pts with SD (↑) compared to pts with PD (↓). Other ICs such as CD4, T-regs, NK cells and M1 macrophages were not changed. On average compared to baseline, M2 macrophages were > 2 fold closer to every other IC in pts with PD, but > 2 fold further from any IC in pts with SD. Tregs were relatively closer to other IC in PD pts. Linear Discriminant Analysis was also performed and results indicate that differential IC densities (mainly M1 macrophages and CD4 T cells) do perform as classifiers between long ( > 5 months) and short ( < 5 months) term responses. Conclusions: This study suggests that bintrafusp alfa not only can enhance intratumoral effector IC infiltrates (CD8) but also has a modulating effect on the spatial distribution of both M1/M2 macrophages within the NSCLC TIME. The differential proximity of M2 macrophages to other IC infiltrates and changes in M1/M2 ratios in association with response suggests that an M1/M2 macrophage balance is directly involved in response and/or resistance to bintrafusp alfa. Given the limited number of patients in this cohort, we intend to study effects of bintrafusp alfa in a larger cohort of patients. Clinical trial information: 02517398 .

A tale of lineage plasticity: Intense neoadjuvant testosterone lowering therapy in localized prostate cancer (PCa) harboring high-risk genomic signatures

368

Background: PCa is driven by androgen receptor (AR) signaling and neoadjuvant therapy with AR inhibitors offer an opportunity to improve cure rates in high-risk PCa particularly with utilization of multiparametric MRI (mpMRI). A loss of AR-regulated lineage characteristics and genomic loss of tumor suppressors RB1 and TP53 or mutations in DNA damage repair (DDR) genes can represent aggressive prostate variants. We conducted a feasibility study using mpMRI to evaluate tumor responses and resistance in newly diagnosed, high-risk PCa (NCT02430480). Methods: Pts were treated with androgen deprivation therapy (ADT) + enzalutamide (enza) 160 mg daily for 6 months (mos). Pts underwent 2 mpMRIs: baseline and post 6 mos treatment (trt). Post-trt mpMRI was followed by radical prostatectomy (RP). Primary endpoint: feasibility of mpMRI for localization and detection of PCa before and after ADT + enza. Results: 39 pts were enrolled on-study with 36 pts completing 6 mos trt and undergoing RP. Of 39 pts, 3 had disease progression. Conclusions: Neoadjuvant intense testosterone lowering therapy shows activity in PCa but a subset of pts not respond to AR-targeted therapies through lineage plasticity enabled by characteristic loss of RB1 and TP53 or due to genetic alterations. Identification of this high-risk patient population, along with development of treatment options, needs further investigation. Clinical trial information: NCT02430480. [Table: see text]

Bicalutamide with or without metformin for biochemical recurrence in prostate cancer patients (BIMET-1)

85

Background: Metformin (MET) may play a role as an anti-proliferative and anti-carcinogenic agent. Epidemiological studies have demonstrated that MET is associated with decreased prostate cancer (PCa) incidence, including decreased PCa specific mortality in diabetic men with PCa. Preclinical studies have shown synergistic effect of MET with bicalutamide, thus prompting this clinical trial evaluating the combination (NCT02614859). Methods: This was an open label, randomized, phase II trial of pts with biochemically recurrent PCa, PSA doubling time 3-9 months, normal testosterone, and BMI > 25. Pts were randomized (2:1) either to MET 1000 mg twice daily orally or observation for initial 8 weeks. Bicalutamide 50 mg orally daily was added to both arms after 8 weeks. Total duration of treatment was 32 weeks. The primary objective was to determine number of pts with undetectable PSA ( < 0.2 ng/mL) at the end of study with key secondary objectives of evaluating PSA declines of ≥ 85%, PSA responses to MET alone and safety. An early stopping rule for futility was set at 39 pts, but due to slow accrual, an unplanned interim analysis was undertaken. Results: 28 patients were randomized between December 2015 and September 2019. Treatment was well tolerated with no dose reductions or treatment discontinuation. No Grade 3 treatment-related adverse events were observed. Conclusions: PSA responses were seen in 50% pts with MET monotherapy after 8 weeks. Although well tolerated, there was no difference in PSA at 32 weeks between the two arms. The trial will be stopped early due to poor accrual and inability to achieve its primary endpoint. Ongoing larger studies of MET in PCa (STAMPEDE) will define it’s utility in prostate cancer. Clinical trial information: NCT02614859. [Table: see text]

The effect of deep AR suppression with enzalutamide or apalutamide on endogenous glucocorticoids: Implications for adverse effects and development of combination therapies

17

Background: Metabolic consequences of potent AR suppression with enzalutamide and apalutamide are unresolved. Endocrine perturbations induced by potent AR antagonists may promote adverse effects and impinge on the potential efficacy of combination therapies, including for example, immunotherapies. We hypothesized that enzalutamide and apalutamide will block 11β-HSD2, the major enzyme that inactivates cortisol in peripheral tissues and results in increased systemic exposure to endogenous active glucocorticoids. We further hypothesized that AR is co-expressed with 11β-HSD2, suggesting a mechanism of suppression. Methods: Cortisol and cortisol/cortisone ratio (substrate/product of 11β-HSD2) were measured in serum using mass spectrometry before and on-treatment in 3 clinical trials: 1) neoadjuvant apalutamide + leuprolide 2) enzalutamide +/- PROSTVAC for metastatic castration-resistant prostate cancer 3) enzalutamide +/- PROSTVAC for non-metastatic castration-sensitive prostate cancer. AR and 11β-HSD2 expression were assessed in kidneys of 13 men and 9 women. Results: A rise in cortisol concentration and cortisol/cortisone ratio occurs uniformly across all 3 trials of potent AR antagonists. For example, a rise in cortisol/cortisone ratio occurred in 23/25 (92%) patients (p<0.001), 30/38 (79%) patients (p=0.051), and 36/64 (67%) patients (p<0.001), in the 3 respective trials. AR is only expressed alongside 11β-HSD2 in the kidneys of men but not women. Conclusions: Treatment with enzalutamide or apalutamide increases systemic exposure to active glucocorticoids. This effect is likely mediated by AR suppression of 11β-HSD2 in the kidney. These findings have potential consequences for immune suppression, the efficacy of treatment combinations using next-generation AR antagonists, and adverse effects of these drugs.

PSA progression compared to radiographic or clinical progression in metastatic castration-resistant prostate cancer patients treated with enzalutamide

105

Background: Enzalutamideis ahighly effective treatment in patients with metastatic castration resistant prostate cancer (mCRPC). Although Prostate Cancer Working Group Guidelines (PCWG) recommend continuing treatment until radiographic progression of disease (rPD) or clinical progression (cPD), many patients discontinue therapy for rising PSA alone. Methods: We conducted an open label, randomized phase 2 clinical trial in mCRPC patients (on testosterone suppression therapy) previously untreated with docetaxel, abiraterone, or enzalutamide, comparing enzalutamide alone or in combination with PROSTVAC, a therapeutic cancer vaccine designed to induce an anti-tumor immune response. The study discontinued accrual after a planned interim analysis indicated no difference in progression between the two arms. Patients were followed beyond PSA progression (first of three confirmed PSA rises, evaluated monthly) until rPD per PCWG (scans done every 3 months per protocol). Results: A total of 57 patients were enrolled with a median follow up time of 55.4 months. Of those, 47 (82%) patients were Caucasian and seven (12%) patients were African American. The median age of patients on enrollment was 67.2 years. 49/57 (86%) patients had PSA progression and the median time to first PSA rise for all 57 patients combined was 6.4 months (95% CI: 3.7-11.0 months) after starting enzalutamide. 38/57 (67%) patients experienced progressive disease (majority with rPD and 1/38 (3%) with cPD), with the median time to progression for all 57 patients of 23.3 months (95% CI: 16.1-27.8 months). Conclusions: Consistent with PCWG recommendations, these data suggest that a rising PSA may not be a warning of near-term clinically significant disease progression in mCRPC patients given the nearly 17-month difference between the first rise in PSA and ultimate rPD or cPD seen in this analysis. These data highlight the need to continue to educate patients and providers on PCWG criteria for progression, which were also used in original trials that led to the FDA approval of enzalutamide, so as not to substantially limit the potential efficacy of mCRPC therapies such as enzalutamide. Clinical trial information: NCT01867333.

Deep androgen receptor suppression in prostate cancer exploits sexually dimorphic renal expression for systemic glucocorticoid exposure

BACKGROUND

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Metabolic, hormonal and immunologic effects of deep AR suppression are unknown. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations, increased ratio of active to inactive glucocorticoids and possibly suboptimal response to immunotherapy. On-treatment glucocorticoid changes might serve as an indicator of active glucocorticoid exposure and resultant adverse consequences.

PATIENTS AND METHODS

Human kidney tissues were stained for AR and 11β-HSD2 expression. Patients in three trials [neoadjuvant apalutamide plus leuprolide, enzalutamide ± PROSTVAC (recombinant poxvirus prostate-specific antigen vaccine) for metastatic castration-resistant prostate cancer (CRPC) and enzalutamide ± PROSTVAC for non-metastatic castration-sensitive prostate cancer] were analyzed for cortisol and its metabolites using liquid chromatography-mass spectrometry (LC-MS/MS). Progression-free survival was determined in the metastatic CRPC study of enzalutamide ± PROSTVAC for those with glucocorticoid changes above and below the median.

RESULTS

Concurrent AR and 11β-HSD2 expression occurs only in the kidneys of men. A statistically significant rise in cortisol concentration, cortisol/cortisone ratio and tetrahydrocortisol/tetrahydrocortisone ratio with AR antagonist treatment occurred uniformly across all three trials. In the trial of enzalutamide ± PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed.

CONCLUSION

Enzalutamide and apalutamide treatment toggles renal 11β-HSD2 and significantly increases indicators of and exposure to biologically active glucocorticoids, which is associated with clinical outcomes.

Phase I trial of a modified vaccinia ankara (MVA) priming vaccine followed by a fowlpox virus (FPV) boosting vaccine modified to express brachyury and costimulatory molecules in advanced solid tumors

2640

Background: Brachyury, a transcription factor, plays an integral role in epithelial-to-mesenchymal transition, metastasis, poor prognosis, and resistance to chemotherapy. It is expressed in many tumor types, and rare in normal tissue, making it an ideal immunologic target. BN-Brachyury comprises heterologous vaccination with recombinant MVA priming followed by FPV boosting, each encoding transgenes for brachyury and three costimulatory molecules (B7-1, ICAM1, and LFA-3). Heterologous prime boost approach is intended to optimize immunogenicity, as previously observed. Methods: Pts with metastatic solid tumors were treated with 2 monthly doses of MVA-brachyury SC at the previously tested dose, 2.2 x 109 infectious units (IU), followed by FPV-brachyury SC, 1 x 109 IU, for 6 monthly doses and then every 3 months for up to 2 years. The primary objective was to determine safety and tolerability and establish the RP2D. Immune assays were conducted to evaluate immunogenicity. Results: In 10 pts (3 chordoma, 6 GI, 1 papillary thyroid), no dose-limiting toxicities or serious treatment-related adverse events (TRAEs) were observed. The only Grade 3 TRAE was sedation associated with fever, which resolved spontaneously and did not recur with subsequent cycles. All other TRAEs were Grade 1 or 2; the most common was injection-site reaction in all patients. Five pts have had stable disease for > 24 wks (per RECIST v1.1) and remain on treatment. One pt with chordoma, for which BN-Brachyury was granted orphan drug designation, has had a 13.2% reduction in tumor size. As previously demonstrated, brachyury-specific T cell responses were observed, as were responses against cascade antigens (non-encoded antigens) CEA and MUC-1. Conclusions: Heterologous MVA- and FPV-brachyury is well tolerated and induced immune responses to brachyury and cascade antigens, suggesting induction of immunologically relevant tumor cell destruction. These data have informed combining BN-Brachyury with checkpoint inhibition (NCT03493945) and radiation (NCT03595228) to evaluate potential for synergetic activity in selected populations. Clinical trial information: NCT03349983.

Clinical efficacy of abiraterone and enzalutamide metastatic castration sensitive prostate cancer patients who progressed rapidly on docetaxel with a genomic analysis

e16536

Background: Docetaxel has become a standard of care for mCSPC. Enzalutamide and abiraterone have been proven to improve survival in metastatic castration-resistant prostate cancer (mCRPC) patients. Little is known about patients who have been treated with docetaxel for mCSPC and subsequent therapeutic responses. This retrospective analysis is to evaluate the response duration of abiraterone and enzalutamide in patients who previously received docetaxel for mCSPC but developed mCRPC within 12 months. Methods: Clinical Trial NCT02649855 enrolled patients with newly diagnosed mCSPC who were treated with standard androgen deprivation therapy (ADT) and docetaxel (75 mg/m2 every 3 weeks for 6 cycles) sequenced with immunotherapy (PROSTVAC) from February 2016 to present. Patients who had progression (based on consecutive PSA rises or imaging) within 1 year of completing docetaxel and went on to subsequent abiraterone/enzalutamide were evaluated. (Note these are different PSA progression criteria than used in CHAARTED, Sweeney, NEJM, 2015). A PCR-based NGS panel (OncoMine Comprehensive Assay v3) will evaluate available tissue from these patients. Results: Of the 46 patients evaluated regardless of immunotherapy sequence, 15 (33%) went on subsequent therapy after progression on docetaxel for mCSPC, with 12 patients starting abiraterone/enzalutamide (7 with high volume disease and 5 with low volume disease). The median age was 62 (41-83) years. 6/12 patients (50%) initiated enzalutamide and 6/12 patients (50%) initiated abiraterone. The median duration of treatment for both was 7.43 (1.53 – 16.0) months, the median time to prostate-specific antigen (PSA) progression was 2 (0 – 11) months; the median duration of PSA decline was 2 months in patients with both high and low volume disease. Of note, 3/12 (25%) of patients did not have PSA response, all of them had high volume disease. Conclusions: These data from a small cohort suggest that patients who have progression within 12 months of completing docetaxel for mCSPC have limited subsequent benefit from enzalutamide or abiraterone. Additional studies are required to determine optimal timing and treatment sequence for patients with mCSPC who rapidly develop mCRPC. Clinical trial information: NCT02649855.

A phase I and randomized phase II study of cabozantinib plus docetaxel and prednisone (C+DP) versus docetaxel and prednisone (DP) alone in metastatic castrate-resistant prostate cancer (mCRPC)

173

Background: A phase I study of Cabozantinib (C) in combination with docetaxel (D) and prednisone (P) in patients (pts) with mCRPC determined that 40 mg daily was the maximum tolerated dose of C in combination with D and P (C+DP). We report a pooled analysis of the phase I and randomized phase II study comparing C+DP to DP alone. Methods: Eligible pts had mCRPC without prior chemotherapy in the castrate setting. All pts received a fixed dose of D (75 mg/m2IV day one of each 21 day cycle) and P (5 mg PO twice daily), and in the C+DP group, C at three escalating dose levels: 20 mg, 40 mg, or 60 mg in the phase I cohort (all PO daily) and 40 mg daily in the phase II cohort. Results: A total of 32 pts received C+DP (19 pts in phase I and 13 pts in the phase II cohort). 12 pts received DP alone. Baseline characteristics for C+DP vs DP included median age 69 (45 – 84) vs 69 (50-83) and median PSA 74.8 ng/ml (0.01-4093.7) vs 309.5 ng/ml (94.6 – 2649) respectively. Clinical trial information: NCT01683994. 18/32 C+DP pts had previous enzalutamide or abiraterone, with a median PFS of 13.6 months (95% CI: 5.2 – 21.0). 23/32 pts (72%) treated with C+DP required dose reduction or discontinuation of C, and 10/32 (31%) required C discontinuation. 2/32 patients (6%) in the C+DP group died on protocol, possibly related to study drug (sudden death NOS/venous thromboembolism). Grade 4 adverse events (AEs) in the C+DP group included: neutropenia (28%), leukopenia (6%), pulmonary embolism (3%), and mucositis (3%) and in DP: hyperglycemia (8%). Grade 3 AEs (>10%) in C+DP included: neutropenia (31%), febrile neutropenia (16%), leukopenia (13%), hypophosphatemia (13%) and in DP: anemia (17%). Conclusions: In pts with mCRPC, C+DP is associated with a greater PFS and PSA responses compared to DP alone. Toxicities with the combination were manageable. Further study is required to better define the potential benefits of C+DP in mCRPC.[Table: see text]

A study of intense neoadjuvant testosterone lowering therapy with goserelin and enzalutamide (Enza) in high-risk prostate cancer (PC) with multiparametric MRI (mpMRI)

63

Background: Neoadjuvant therapy with novel androgen receptor inhibitors, like enza, offer an opportunity to improve cure rates in men with high risk PC but also emphasizes the need for improved imaging techniques and genomic studies to evaluate treatment (trt) responses. We conducted a feasibility study using mpMRI to evaluate tumor responses and resistance in newly diagnosed, high-risk PC. Methods: Patients (pts) were treated with androgen deprivation therapy (ADT) + enza 160 mg po qdaily for 6 months (mos). Pts underwent 2 mpMRI: baseline and post 6 mos of therapy. Post-trt mpMRI was followed by radical prostatectomy (RP). Primary endpoint was feasibility of mpMRI for localization and detection of PC before and after therapy with ADT + enza. Results: 31 out of 33 pts completed 6 mos of therapy and underwent RP. Median on-study PSA was 9.58 (1.18-984.72 ng/dL). Median PSA post 6 mos of ADT + enza was <0.02 (0.02-0.35 ng/mL). No pt was taken off-trt for adverse events. Median residual cancer burden (RCB) defined as volume of tumor corrected by tumor cellularity was 0.1584 (0.0001-12.32 cc). Using RCB of <0.05 cc, 12 patients had minimal residual disease of which 4 pts were pathologic complete responses. Post-trt mpMRI volume correlated with final pathology in all cases. Conclusions: Neoadjuvant enza + ADT is tolerable and shows activity in a newly-diagnosed, high-risk population. mpMRI can be utilized to assess responses to trt. Analysis of genomic characteristics and resistance mechanisms is on-going. Clinical trial information: NCT02430480.

Molecular and imaging correlates of exceptional pathologic response to neoadjuvant ADT plus enzalutamide

61

Background: AR directed therapies are standard of care for metastatic prostate cancer, and their use for high-risk localized disease may improve survival. Previous trials showed that suppression of AR activity resulting in greater pathologic responses improved survival rates. However, the underlying biology and molecular features of exceptionally responding tumors remain unknown. Methods: Men with locally advanced prostate cancer (median Gleason score 8, median PSA 9.58 ng/dl) received mpMRI and MRI/US-fusion targeted biopsies at baseline. Patients received 6 months of ADT plus enzalutamide, then received a second mpMRI, and underwent radical prostatectomy. RP specimens were whole mounted in the same plane as MRI. The location of each tumor on biopsy was mapped to prostatectomy specimens using pathologic and imaging hallmarks. FFPE sections of baseline and post-treatment tumor were stained, laser capture microdissected, and analyzed using whole exome sequencing. Amongst nonresponding patients (residual tumor burden > 0.05 cc) comparison of pre- and post-treatment tumor specimens identified evolutionary phylogenies over space and time representing intrinsic or clonal selection of pre-existing cells. Amongst responding patients, clonal extinction was confirmed by sequencing and immunostaining of surgical specimens. Results: Gleason score at baseline did not differentiate responding and nonresponding patients. Focal ERG staining in biopsies was absent in 100% of responders and present in 60% of responders. Intraductal carcinoma architecture was also absent in all responding tumors. Focal PTEN loss was observed in all nonresponders at baseline. Responding tumor foci were enriched for deletion of chromosome 6q. Comparison of baseline mpMRI sequences indicated a trend towards lower variance on dynamic contract enhanced (DCE) MR and lower local texture heterogeneity metrics in responding lesions. Conclusions: Response to neoadjuvant intense ADT correlates with distinctive pathologic, molecular, and imaging features that can be observed prior to treatment. Selection of patients based on these parameters may improve overall responses to treatment in subsequent clinical trials. Clinical trial information: NCT02430480.

Efficacy of abiraterone and enzalutamide in patients who had disease progression within twelve months of completing docetaxel for metastatic castration sensitive prostate cancer

241

Background: Docetaxel is a standard of care for mCSPC. Enzalutamide and abiraterone have been proven to improve survival in metastatic castration-resistant prostate cancer (mCRPC) patients. Little is known about patients who have been treated with docetaxel for mCSPC and subsequent therapeutic responses. This retrospective analysis is to evaluate the response duration of abiraterone and enzalutamide in patients who previously received docetaxel for mCSPC but developed mCRPC within 12 months. Methods: Clinical Trial NCT02649855 enrolled patients with newly diagnosed mCSPC who were treated with standard androgen deprivation therapy (ADT) and docetaxel (75 mg/m2 every 3 weeks for 6 cycles) sequenced with immunotherapy (PROSTVAC) from February 2016 to present. Patients who had progression (based on consecutive PSA rises or imaging) within 1 year of completing docetaxel and went on to subsequent abiraterone/enzalutamide were evaluated. (Note these are different PSA progression criteria than used in CHAARTED, Sweeney, NEJM, 2015). Results: Of the 46 patients evaluated regardless of immunotherapy sequence, 15 (33%) went on subsequent therapy after progression on docetaxel for mCSPC, with 12 patients starting abiraterone/enzalutamide (6 each with high and low volume disease). The median age was 62 (41-83) years. 7/12 patients (58.3%) initiated enzalutamide and 5/12 patients (41.7%) initiated abiraterone. The median duration of treatment for both was 7.12 (1.53–16.0) months, the median time to prostate-specific antigen (PSA) progression was 5.54 (0–15.83) months; 5/12 (41.7%) of patients did not have PSA response. Of note, patients with low volume disease had a median treatment duration of 5.88 months, 3 of them did not have PSA response. Conclusions: These data from a small cohort suggest that patients who have progression within 12 months of completing docetaxel for mCSPC have limited subsequent benefit from enzalutamide or abiraterone. Additional studies are required to determine optimal timing and treatment sequence for patients with mCSPC who rapidly develop mCRPC. Clinical trial information: NCT02649855.

Immunotherapy for biochemically recurrent prostate cancer

215

Background: Annually about 30-50,000 men are diagnosed with biochemically recurrent prostate cancer (BCRpc), defined by a rising PSA after radical prostatectomy (RP) or definitive radiation therapy (RT) with negative conventional imaging (CT and bone scan). Standard treatments include salvage therapies, androgen deprivation or surveillance. The role of immunotherapy in BCRpc is undefined. Methods: This study evaluates PROSTVAC, a pox-viral based therapeutic cancer vaccine targeting PSA, in BCRpc. Key eligibility criteria include PSA > 0.8 after RP or > 2.0 after RT with a maximum PSA of 30, PSA doubling time (DT): 5-15 months; testosterone > 100, negative CT and bone scan. Patients (pts) are randomized to vaccine for 6 months or 6 months surveillance followed by 6 months of vaccine. In a post hoc analysis delayed PSA declines were characterized as a confirmed PSA decline after an intra-study apex PSA (ISAP) defined by a peak PSA affirmed by a contiguous PSA within 10% (to exclude lab variations). 80 pts will be enrolled at NCI, Dana-Farber Cancer Institute and Memorial Sloan Kettering Cancer Center. Results: Of the 26 pts enrolled thus far, 22 have been followed for > 9 months after vaccine and are evaluable. On-study median values were age 66.8 years (54-78), PSA 2.67 ng/ml (0.83-28.5), PSA DT 7.5 months (5.1-14.9). 8 pts (38%) had delayed PSA declines after ISAP (-12% to -99%). Of 13 pts on surveillance for 6 months, only one pt had a similar decline lasting only 56 days. Conclusions: Preliminary data from this study suggests that PROSTVAC may be associated with delayed, but sustained PSA declines in BCRpc which are rarely seen in surveillance alone. Additional data will be acquired from this study, but this provides rationale to develop immunotherapy combinations in BCRpc. Clinical trial information: NCT02649439. [Table: see text]

A phase 2 study of olaparib and durvalumab in metastatic castrate-resistant prostate cancer (mCRPC) in an unselected population

163

Background: Data suggests 25-30% of sporadic mCRPC has defects in DNA repair pathways which may confer sensitivity to PARP inhibition (PARPi). Immune checkpoint blockade may increase the proportion of patients that respond to PARPi. We hypothesize that increased DNA damage by olaparib (O) will complement anti-tumor activity of immune checkpoint blocking antibody, durvalumab (D), in mCRPC (NCT02484404). Methods: Single arm pilot study with accrual of 25 patients (pts) with mCRPC and disease that is amenable to biopsy. Prior treatment with enzalutamide and/or abiraterone is required. D is given at 1500 mg iv q28 days + O 300 mg tablets po q12 hours. The primary endpoint is PFS. Core biopsies undergo mutational analysis. Results: In the first 17 pts, median age is 66 (range 45-79 years), median baseline PSA is 79.67 ng/mL [3.93-2356 ng/mL]). Median Gleason score is 8. 6 patients have bone only disease and 11 patients have bone and soft tissue/visceral disease. Median number of cycles is 7 (2-17). Grade 3/4 adverse events include anemia 4/17 (24%), lymphopenia 2/17 (12%), infection 2/17 (12%), thrombocytopenia, leukopenia, neutropenia, nausea, vomiting, UTI, hypertension, hearing impairment, fatigue, syncope, oral mucositis, muscle weakness, and muscle cramps [1/17 each, (6%)]. 8/17 pts (47%) had PSA responses >50%. 6 of these pts had mutations in the DNA damage repair pathways (DNAdr). 2/17 pts (11%) had PSA responses >30% with no known mutations in DNAdr. 4 pts had a PR. The 12 month PFS is 51.5% (95% CI: 25.7-72.3%). Conclusions: Preliminary data shows D+O is well tolerated with activity in an unselected population. Accrual is ongoing with biomarker analysis. Clinical trial information: NCT02484404.

Avelumab in metastatic castration-resistant prostate cancer (mCRPC)

5037

Background: Despite recent progress, mCRPC remains a lethal disease. While programmed cell death 1 (PD-1) and PD-1 ligand (PD-L1) inhibitors have shown activity in variety of cancers, to this point there is minimal evidence of activity in mCRPC. This is a report of avelumab, anti-PDL1 in mCRPC patients (pts). Methods: This is an expansion cohort of the first in human, phase I trial (JAVELIN Solid Tumor; EMR100070-001) that evaluated 10 mg/kg of avelumab in pts with mCRPC who had progressive disease (PD) on previous treatment. Pts who had PD on an androgen receptor antagonist (ARA) could enroll on trial and continue their ARA. Avelumab was administered as a 1-hour intravenous infusion every 2 weeks (w) with restaging scans every 6 w. Prostate cancer working group 2 criteria were used to determine PD. Results: 18 patients were enrolled on this cohort; the median age of pts was 67 years. Median on study PSA was 11ng/mL. 11 pts had Gleason score (GS) ≥ 8 and 7 had GS of 7. 3 pts had previous chemotherapy with docetaxel, 8 pts received previous vaccine treatment including 4 pts with sipuleucel-T and 4 pts with Prostvac. Overall avelumab treatment appears safe and tolerable. 15 pts experienced grade ≤ 2 treatment related adverse events (TRAEs), fatigue being the most common one. 4 pts developed treatment related hypothyroidism, 3 with grade 2 and 1 with grade 1. In addition, 2 pts had grade 3 asymptomatic TRAEs (amylase & lipase elevations). 7 pts had stable disease (SD) > 24 w post treatment, 6 pts had PD after first restaging scans at 6 w which was reconfirmed in 2nd restaging scan at 12 w. PSA doubling time (PSADT) prior to avelumab was compared with PSADT after 3 months (m) of treatment. Among 17 pts with available data, 3 pts had a prolonged PSADT which was defined at 3 m (twice as high as on-study PSADT), 7 pts had stable PSADT and 7 had decreased PSADT. 5 of 18 pts enrolled while on enzalutamide with a rising PSA. Among these pts 1 had prolonged PSADT, 2 had a stable PSADT and 2 with decreased PSADT after 3 m of follow up. 3 of 5 pts had SD > 24 m, 1 had SD for 13 w and 1 had PD at first restaging scans. Conclusions: These data provide safety data of avelumab on a population of pts with mCRPC. Immune analysis is under way to determine correlation with immune responses in the pts on this trial that had prolonged SD. Clinical trial information: NCT01772004.

Combination of PDL-1 and PARP inhibition in an unselected population with metastatic castrate-resistant prostate cancer (mCRPC)

5026

Background: About 30% of sporadic mCRPC has defects in DNA repair pathways which may confer sensitivity to PARP inhibition. There is limited data about PDL1 inhibition in mCRPC. We hypothesize increased DNA damage by olaparib (O) will complement anti-tumor activity of immune checkpoint blocking antibody, durvalumab (D), in mCRPC:NCT02484404. Methods: Single arm pilot study with accrual of 25 patients (pts) with mCRPC and biopsiable disease. Prior treatment with enzalutamide and/or abiraterone is required. D is given at 1500 mg iv q28 days + O 300 mg po q12 h. Primary endpoint is PFS. Pretreatment and on-study core biopsies undergo mutational analysis. Results: 10 pts have enrolled (median age 65 yr [range 51-79], median baseline PSA: 85.78 [22.17-809.9 ng/mL]). 7 pts have GS ≥ 8. Grade 3/4 adverse events include anemia 2/7 (29%), thrombocytopenia, lymphopenia, neutropenia, nausea, fatigue, UTI, and lung infection [1/7 each, (14%)]. 5/7 pts (71%) on-study >2 months (mos) have PSA declines > 50%. Median PFS is 7.8 mos (95% CI: 1.8 mos-undefined). Conclusions: Preliminary data shows D+O is well tolerated with activity in an unselected population. Accrual is ongoing with biomarker analysis. Clinical trial information: NCT02484404. [Table: see text]

Preliminary results from a phase 1 trial of M7824 (MSB0011359C), a bifunctional fusion protein targeting PD-L1 and TGF-β, in advanced solid tumors

3006

Background: M7824 (MSB0011359C) is a novel bifunctional fusion protein comprised of a fully human IgG1 monoclonal antibody against programmed death ligand 1 (PD-L1) fused to the soluble extracellular domain of transforming growth factor-β (TGF-β) receptor II, which acts as a TGF-β trap. We report preliminary data from a phase 1 trial of M7824 in patients (pts) with advanced solid tumors. Methods: NCT02517398 is a phase 1, open-label, 3+3 dose-escalation study. Eligible pts receive M7824 at 1, 3, 10, or 20 mg/kg Q2W until confirmed progressive disease, unacceptable toxicity, or trial withdrawal; treatment beyond progression is generally allowable. The primary objective is to determine the safety and maximum tolerated dose of M7824; secondary objectives include pharmacokinetics (PK), immunogenicity, and best overall response per RECIST v1.1. Results: 16 heavily pretreated pts with ECOG performance status 0-1 have received M7824. Our PK data show a dose-linear increase in exposure starting at a dose of 3 mg/kg; furthermore, M7824 saturates peripheral PD-L1 and sequesters any released plasma TGF-β1, -β2, and -β3 throughout the dosing period in a dose-dependent manner. Grade 3 drug-related treatment-emergent adverse events (TEAEs) occurred in 3 pts (skin infection secondary to grade 2 bullous pemphigoid [BP], lipase increased, and colitis with associated anemia); there were no grade 4-5 drug-related TEAEs. BP and colitis responded well to steroids. Colitis and its secondary events of anemia and rectal hemorrhage (in a previously radiated area) were considered dose limiting in 1 pt. There was preliminary evidence of efficacy across all dose levels, including 1 ongoing confirmed complete response (cervical), 1 durable partial response (pancreatic), a 25% reduction in the sum of diameters of target lesions after 2 doses of M7824 (cervical), and 2 cases of prolonged stable disease (pancreatic; carcinoid). Conclusions: Preliminary data from this phase 1 dose-escalation study suggest that M7824 has a manageable safety profile in pts with heavily pretreated advanced solid tumors. Early signs of clinical efficacy warrant further study. Clinical trial information: NCT02517398.

Changes in multiparametric prostate MRI and immune subsets in patients (Pts) receiving neoadjuvant immunotherapy and androgen deprivation therapy (ADT) prior to radiation

30

Background: Endorectal(er) MRI is an emerging tool in assessing intraprostatic tumors. Immunotherapy development in prostate cancer has been limited due to the lack of intermediate (bio)markers of response. Methods: Untreatedpts with high-risk prostate cancer were randomized in a trial (NCT01496131) of standard ADT+Radiation + an immunotherapy targeting MUC1 (tecemotide, aka L-BLP25). Pts had erMRI at baseline and after 2 months of ADT+/- biweekly immunotherapy. Low dose (300 mg/m2, maximum 600 mg) cyclophosphamide for regulatory T-cell depletion preceded first immunotherapy. Multiparametric MRI included evaluation of apparent diffusion coefficient (ADC) maps from diffusion-weighted MRI. Monthly peripheral blood assessments utilized flow cytometry to evaluate immune cell subsets. This analysis focuses on the 2 month neoadjuvant period of ADT+/-immunotherapy before radiation. Results: 28 pts (n = 14/arm) with high risk prostate cancer (Gleason 8-10, PSA > 20, or stage T3) were enrolled. PSA declined in all pts 2 months after ADT. erMRI findings at 2 months indicated greater improvements in ADC values in pts receiving immunotherapy+ADT vs. ADT alone. Improved ADC on MRI suggests improvements in intratumoral diffusion and has been associated with decreased tumor density. This relative improvement between the groups occurred both per patient (p = 0.16) and per lesion (p = 0.031). Relative to baseline, pts receiving immunotherapy+ADT had increases in CTLA4+ CD8+ T-cells consistent with immune activation (p = 0.0134) and decreases in myeloid derived suppressor cells (MDSCs; p = 0.0353) during the neoadjuvant period corresponding to the erMRI changes. These immune findings were not seen in the ADT alone group. Conclusions: Pts who received immunotherapy+ADT for 2 months had greater improvements in ADC values on erMRI, consistent with decreased tumor density, relative to pts receiving ADT alone. Corresponding increases in activated CD8+ T-cells and decreases in MDSCs were seen in pts receiving vaccine+ADT. These preliminary findings suggest that ADC on MRI may be useful in assessing immunologic impact. Further study is warranted. Clinical trial information: NCT01496131.

A phase II study of the anti-programmed death ligand-1 antibody durvalumab (D; MEDI4736) in combination with PARP inhibitor, olaparib (O), in metastatic castration-resistant prostate cancer (mCRPC)

162

Background: Recent data suggests 25-30% of sporadic mCRPC has defects in DNA repair pathways which may confer sensitivity to PARP inhibition. Immune checkpoint blockade is a promising avenue in mCRPC treatment. We hypothesize that increased DNA damage by O will complement anti-tumor activity of immune checkpoint inhibitor, D, in mCRPC (NCT02484404). Methods: Eligible pts have mCRPC with adequate end organ function and biopsiable disease (bone or soft tissue). Prior treatment with enzalutamide and/or abiraterone is required. D is administered at 1500 mg iv q28 days with O at 300 mg po q12 h. Primary endpoint is PFS. Secondary endpoints include PSA responses, safety and ORR. Single arm pilot study with a total accrual of 25 pts. On-study core biopsies undergo mutational analysis. Results: 6 pts have enrolled (median age 67 yr [range 60-79], median ECOG PS 1 [1-2]). Median baseline PSA: 258.1 (54.1-809.9 ng/mL). 4 pts have Gleason score (GS) > 8 and 2 pts have GS of 7. Grade 3/4 adverse events include anemia 2/6 (33%), thrombocytopenia, lymphopenia, nausea, febrile neutropenia, aspiration pneumonia [1 each, (17%)]. Conclusions: Exploiting synergy of D+O is a treatment option for heavily pre-treated pts. Preliminary data shows D+O is tolerable and active in mCRPC pts without germline BRCA mutation. Paired tumor biopsies and blood samples including ctDNA are being collected. Accrual is ongoing. Clinical trial information: NCT02484404. [Table: see text]

Avelumab in metastatic castration-resistant prostate cancer (mCRPC)

159

Background: Despite recent progress, mCRPC remains a lethal disease. While programmed cell death 1 (PD-1) and PD-1 ligand (PD-L1) inhibitors have shown activity in variety of malignancies, to this point there is minimal evidence of activity in mCRPC. This is a report of avelumab, anti-PDL1 in mCRPC patients (pts). Methods: This is an expansion cohort of the first in human, phase I trial (JAVELIN Solid Tumor; EMR100070-001) that evaluated 10 mg/kg of avelumab in pts with mCRPC who had progressive disease (PD) on previous treatment. Pts who had PD on an androgen receptor antagonist (ARA) could enroll on trial and continue their ARA. Avelumab was administered as a 1-hour intravenous infusion every 2 weeks (w) with restaging scans every 6 w. Prostate cancer working group 2 criteria were used to determine PD. Results: 18 patients were enrolled on this cohort; the median age of pts was 67 years. Median on study PSA was 11ng/mL. 11 pts had Gleason score (GS) ≥ 8 and 7 had GS of 7. 3 pts had previous chemotherapy with docetaxel, 8 pts received previous vaccine treatment including 4 pts with sipuleucel-T and 4 pts with Prostvac. Overall avelumab treatment was safe and tolerable. 15 pts experienced grade ≤ 2 treatment related adverse events (TRAEs), fatigue being the most common one. 4 pts developed treatment related hypothyroidism, 3 with grade 2 and 1 with grade 1. In addition, 2 pts had grade 3 asymptomatic TRAEs (amylase & lipase elevations). 7 pts had stable disease (SD) > 24 w post treatment, 6 pts had PD after first restaging scans at 6 w which was reconfirmed in 2nd restaging scan at 12 w. PSA doubling time (PSADT) prior to avelumab was compared with PSADT after 3 months (m) of treatment. Among 17 pts with available data, 3 pts had a prolonged PSADT which was defined at 3 m (twice as high as on-study PSADT), 7 pts had stable PSADT and 7 had decreased PSADT. 5 of 18 pts enrolled while on enzalutamide with a rising PSA. Among these pts 1 had prolonged PSADT, 2 had a stable PSADT and 2 with decreased PSADT after 3 m of follow up. 3 of 5 pts had SD > 24 m, 1 had SD for 13 w and 1 had PD at first restaging scans. Conclusions: These data provide safety data of avelumab on a population of pts with mCRPC. Immune analysis is under way to determine correlation with immune responses in the pts on this trial that had prolonged SD. Clinical trial information: NCT01772004.

Imaging metastatic prostate cancer with 18F-DCFBC PET/CT (DCFBC) and 18F-NaF PET/CT (NaF)

231

Background: Conventional imaging of advanced prostate cancer (computerized tomography and nuclear bone scintigraphy) is limited and indicates a need for a more specific molecular imaging probe. DCFBC is a radiolabeled PET agent that binds with high affinity to prostate specific membrane antigen (PSMA), which is overexpressed in almost all prostate cancers and through whole-body non-invasive functional imaging, may provide new information on the expression of PSMA. We compare the uptake of DCFBC in bone with respect to NaF PET/CT in metastatic prostate cancer patients. DCFBC has added capability to detect soft tissue metastasis whereas NaF is confined to secondary effects of bone disease. Methods: Subjects with known or suspected prostate cancer metastasis underwent DCFBC PET/CT imaging performed at 1 hour and 2 hours after IV bolus injection of 8 mCi of DCFBC. Patients also underwent a whole body NaF PET/CT scan within 3 weeks of DCFBC PET/CT to assess for bone metastases. Patients received 3 mCi of NaF IV bolus and then were imaged 1hour post injection. PSA levels and antiandrogen therapy status were obtained at the time of DCFBC imaging. Results: Fifteen patients have been preliminarily analyzed. PSA ranged from < .01 to 4379 ng/mL. NaF identified bone lesions in 10 patients but matching focal DCFBC uptake was only seen in 3 patients. DCFBC additionally showed lymph node metastasis in 1of these 3 patient. There were 5 patients without focal abnormal bone uptake on NaF or DCFBC. In this group, 4 of 5 patients had focal DCFBC uptake in lymph nodes or soft tissue lesions. Ten patients were on some form of androgen deprivation therapy (ADT). For those on ADT, 7 of 10 patients had positive findings on NaF, compared to 2 of 10 patients on DCFBC. Conclusions: DCFBC uptake in bone metastasis does not routinely correspond to focal NaF uptake which could be due to distinct mechanisms of tracer uptake and tumor biology. There is an inverse association in focal bone findings when comparing each tracer on antiandrogen therapy. Through whole-body non-invasive functional imaging and further study, DCFBC may prove useful in characterizing prostate cancer based on PSMA expression. Clinical trial information: NCT02190279.

Clinical and immunologic impact of short course enzalutamide without androgen deprivation therapy for biochemically recurrent prostate cancer

214

Background: Enzalutamide (enz) is FDA approved for advanced prostate cancer, but studies are evaluating enz in earlier stages of disease. We have conducted a clinical trial (NCT01875250) of enz ± a therapeutic vaccine in biochemically recurrent prostate cancer. Methods: Eligible patients (pts) had a PSA between 2.0-20.0 ng/ml, no metastatic disease and normal testosterone (T). Treatment for all pts included enz 160 mg daily for 84 days (D), but no T lowering therapy was permitted. This analysis evaluated all pts for the impact of enz on PSA and T regardless of randomization. Pts treated with Enz alone were evaluated for immune responses.The impact of the vaccine will be evaluated after protocol-defined requisite follow-up. Results: Median age for all pts (n = 34) was 66 years (range: 52-87), with a median on-study baseline PSA of 4.55 ng/ml (2.02-19.43). Common adverse events included fatigue and breast tenderness, but no pts discontinued enz for toxicity. The median PSA decline was 99% (range: 52% to > 99%) with 11/34 pts having undetectable nadirs. Median time to first PSA rise after 84 D course of enz was 29 D (13-70) and median recovery to baseline PSA in 25 evaluable pts was 190 D (84-469). T increased above normal limits in 18/34 pts (median Tmax = 802 ng/dl). Immune analysis (n = 12) indicated enz alone increased naïve T-cells and NK cells, and decreased several subsets of myeloid derived suppressor cells with a highly suppressive phenotype. Conclusions: The preliminary findings from this study suggest that short-course enz is well tolerated, leads to prolonged PSA suppression and enhanced immune responses in patients with biochemically recurrent prostate cancer. These immune studies provide the rationale for the use of enz in combination with immunotherapeutics in this and other malignancies. Clinical trial information: NCT01875250.

An analysis of sodium 18f-fluoride PET/CT and prostate specific antigen (PSA) changes in men with metastatic castration resistant prostate cancer (mCRPC)

203

Background: Recently there has been growing evidence that 18F-Fluoride PET/CT has increased sensitivity relative to technetium-99m diphosphonate (Tc-99m MDP) bone scan for evaluating metastatic bone disease. This analysis studied changes in 18F-Fluoride PET/CT and evaluated associations with PSA changes for mCRPC patients (pts) on enzalutamide (enz). Methods: As part of a randomized phase II study evaluating enz with or without vaccine therapy, men with mCRPC electively underwent 18F-Fluoride PET/CT at 3 month (mos) intervals [NCT01867333]. At these points serum PSA was collected. Data was taken on max SUV and volume of presumed cancerous lesions and a variable, ΣSUV*Volume, was calculated which was defined as the sum of the products of SUV max and volume of cancerous lesions. Results: At the time of our analysis, 19 pts had PSA and PET/CT data for at least 2 time points within 1 year of initiating therapy. The median baseline PSA was 19.6 ng/ml (0.76-587). All pts had predominantly bone disease with 10 having small volume lymphadenopathy. Only 1/19 pts progressed by PSA Working Group criteria. An analysis found that 18/19 pts (95%) had an association between changes in PSA and ΣSUV*Volume. Of these 18 pts, 13 had a major ( > 50%) and 1 had a minor ( > 30%) PSA response and all 14 had an accompanying decrease in ΣSUV*Volume. For 11/14 pts with PSA responses, the change in ΣSUV*Volume paralleled the change in PSA at all time points, while for 3 pts an associated change between ΣSUV*Volume and PSA was delayed by 3 mos. 4/14 pts had short term responses lasting only 3 mos followed by PSA increases. For these 4 pts the changes in ΣSUV*Volume paralleled PSA changes, decreasing at 3 mos and increasing thereafter. Finally 4/18 patients had no PSA response to therapy. All 4 pts had increases in ΣSUV*Volume which paralleled rising PSA values. Conclusions: Preliminary data from a small cohort suggests that findings on 18F-Fluoride PET/CT are associated with PSA changes. This represents a substantial difference from standard Tc-99m MDP and further suggests that 18F-Fluoride PET/CT may provide a more sensitive analysis of bone disease. Additional data from this and other studies are required.

Comparison of survival of African-American (AA) patients (pts) in docetaxel (D)-based combination therapies in metastatic castrate-resistant prostate cancer (mCRPC)

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Background: AA pts experience greater prostate cancer (PC) incidence and mortality compared to Caucasian (C) pts but are underrepresented in clinical trials (CTs). Greater representation of AAs is required to explore differences in clinical benefit in advanced disease where recent data has reaffirmed the role of D. Methods: In a retrospective analysis, baseline characteristics, Gleason score (GS), ECOG PS, number of cycles (cys), maximum prostate-specific antigen (PSA) declines, radiographic responses, overall survival (OS) and progression-free survival (PFS) were captured in 2 recent D based CTs. Results: Of 136 pts, 28 (21%) self-identified as Black or AA. Median age of AA pts is 66 (50-78 yrs). Median GS is 8 (5-10). Median ECOG PS is 1 (0-2). 15 pts have bone and soft tissue disease; 13 pts have bone only disease. Median number of cys is 28.5 (1-63). Of 27 evaluable pts, 26 had PSA declines (-26 to -99%). Radiographic responses include 11 (39%) partial responses and 16 (57%) pts with stable disease. Median OS for AAs is 29.0 months (mos) (95% CI: 20.9-34.7 mos); median PFS is 21.5 mos (95% CI: 13.7-28.9 mos). Median OS for all non-AA pts is 24.8 mos (95% CI: 21.8-29.5 mos); median PFS is 16.1 mos (95% CI: 14.1-20.1 mos). The VEGF-634G > C SNP, associated with a more aggressive phenotype of PC, was evaluated in 54 pts. No evidence was found that genotype frequency varies between C and AA pts. Conclusions: In this analysis, AA pts did not have inferior OS (29 mos) or PFS (21.5 mos) outcomes compared to non-AA pts (24.8, 16.1 mos). Further analysis from larger studies is required to determine differential benefits of D for AA pts compared to non-AA pts. Clinical trial information: NCT00089609, NCT00942578.