First-in-human, phase 1 study of PF-06753512, a vaccine-based immunotherapy regimen (VBIR), in non-metastatic hormone-sensitive biochemical recurrence and metastatic castration-resistant prostate cancer (mCRPC)

BACKGROUND

This phase 1 study evaluated PF-06753512, a vaccine-based immunotherapy regimen (PrCa VBIR), in two clinical states of prostate cancer (PC), metastatic castration-resistant PC (mCRPC) and biochemical recurrence (BCR).

METHODS

For dose escalation, patients with mCRPC received intramuscular PrCa VBIR (adenovirus vector and plasmid DNA expressing prostate-specific membrane antigen (PSMA), prostate-specific antigen (PSA), and prostate stem cell antigen (PSCA)) with or without immune checkpoint inhibitors (ICIs, tremelimumab 40 or 80 mg with or without sasanlimab 130 or 300 mg, both subcutaneous). For dose expansion, patients with mCRPC received recommended phase 2 dose (RP2D) of PrCa VBIR plus tremelimumab 80 mg and sasanlimab 300 mg; patients with BCR received PrCa VBIR plus tremelimumab 80 mg (Cohort 1B-BCR) or tremelimumab 80 mg plus sasanlimab 130 mg (Cohort 5B-BCR) without androgen deprivation therapy (ADT). The primary endpoint was safety.

RESULTS

Ninety-one patients were treated in dose escalation (mCRPC=38) and expansion (BCR=35, mCRPC=18). Overall, treatment-related and immune-related adverse events occurred in 64 (70.3%) and 39 (42.9%) patients, with fatigue (40.7%), influenza-like illness (30.8%), diarrhea (23.1%), and immune-related thyroid dysfunction (19.8%) and rash (15.4%), as the most common. In patients with mCRPC, the objective response rate (ORR, 95% CI) was 5.6% (1.2% to 15.4%) and the median radiographic progression-free survival (rPFS) was 5.6 (3.5 to not estimable) months for all; the ORR was 16.7% (3.6% to 41.4%) and 6-month rPFS rate was 45.5% (24.9% to 64.1%) for those who received RP2D with measurable disease (n=18). 7.4% of patients with mCRPC achieved a ≥50% decline in baseline PSA (PSA-50), with a median duration of 4.6 (1.2-45.2) months. In patients with BCR, 9 (25.7%) achieved PSA-50; the median duration of PSA response was 3.9 (1.9-4.2) and 10.1 (6.9-28.8) months for Cohorts 5B-BCR and 1B-BCR. Overall, antigen specific T-cell response was 88.0% to PSMA, 84.0% to PSA, and 80.0% to PSCA.

CONCLUSIONS

PrCa VBIR overall demonstrated safety signals similar to other ICI combination trials; significant side effects were seen in some patients with BCR. It stimulated antigen-specific immunity across all cohorts and resulted in modest antitumor activity in patients with BCR without using ADT.

TRIAL REGISTRATION NUMBER

NCT02616185.

PF-06939999, a potent and selective PRMT5 inhibitor, in patients with advanced or metastatic solid tumors: A phase 1 dose escalation study

3019

Background: Protein arginine methyltransferase 5 (PRMT5) methylates multiple substrates known to be dysregulated in cancer, including components of the spliceosome machinery. PF-06939999 is a selective small-molecule inhibitor of PRMT5. Here we report the safety, PK, PD, and preliminary activity of PF-06939999 in patients (pts) with selected advanced/metastatic solid tumors. Methods: This phase 1 dose escalation trial (NCT03854227) enrolled pts with solid tumor types marked by potential frequent splicing factor mutations, including advanced/metastatic endometrial cancer, head and neck squamous cell carcinoma (HNSCC), non-small cell lung cancer (NSCLC), urothelial cancer, cervical cancer, or esophageal cancer. PF-06939999 monotherapy was continuously administered orally QD or BID in 28-day cycles. A Bayesian Logistic Regression Model was used to inform dose level decisions. Primary objectives were to assess dose limiting toxicities (DLTs), AEs and laboratory abnormalities. Tumor response was assessed using RECIST v1.1. PK and PD were assessed by determining PF-06939999 plasma concentration after dosing and changes in plasma levels of symmetric di-methyl arginine (SDMA), the product of PRMT5 enzymatic activity. Results: 28 pts received PF-06939999 at doses from 0.5-12 mg daily (QD or BID) during dose escalation. Median number of cycles was 2 (range, 1-13). Most were female (54%) with a median age of 61.5 (range, 32-84) y. Median number of prior therapies was 4. Overall, 4/24 (17%) pts reported DLTs: thrombocytopenia (n=2, 6 mg BID); anemia (n=1, 8 mg QD); and neutropenia (n=1, 6 mg QD). Treatment-related AEs occurred in 24 (86%) pts. Most common (≥20%) treatment-related AEs across all cycles were anemia (43%), thrombocytopenia (32%), dysgeusia, fatigue and nausea (29% each). Grade ≥3 treatment-related AEs included anemia (25%), thrombocytopenia (21%), fatigue, neutropenia and lymphocyte count decreased (4% each). One pt (6mg BID) had Grade 4 treatment-related thrombocytopenia. All cytopenias were dose-dependent and reversible with dose modification. No pts discontinued treatment for treatment-related toxicity. There were no treatment-related deaths. Exposure to PF-06939999 increased with doses in the dose range tested. Plasma SDMA was reduced at steady state (58.4-87.5%), indicating robust PD target inhibition. Two pts had confirmed partial response (HNSCC and NSCLC). 6 mg QD was identified as the recommended monotherapy dose for expansion. Conclusions: PF-06939999 showed dose-dependent and manageable toxicities in this phase 1 dose escalation study. Objective tumor responses were observed in pts with HNSCC and NSCLC. Analysis of archival tissue for the presence of splicing factor mutations and other potential predictive biomarkers is ongoing. Enrollment to part 2 dose expansion is ongoing in pts with NSCLC, HNSCC and urothelial cancer. Clinical trial information: NCT03854227.

First-in-human, phase I study of PF-06753512, a vaccine-based immunotherapy regimen (PrCa VBIR), in biochemical relapse (BCR) and metastatic castration-resistant prostate cancer (mCRPC)

2612

Background: Therapeutic vaccines targeting PC-associated antigens represent attractive approaches in combination with immune checkpoint inhibitors (ICI). Safety/antitumor activity of PF-06753512 (PrCa VBIR) was evaluated in a phase I, dose-escalation and expansion study in patients (pts) with BCR prior to ADT and in pts with mCRPC either prior to or after failure of novel hormone therapy. PrCa VBIR consists of: 1) priming immunization with a replication-deficient adenoviral vector (AdC68) expressing PSA, prostate-specific membrane antigen and prostate stem cell antigen; 2) boosts with plasmid DNA (pDNA) encoding the same antigens by IM electroporation; 3) ICI given subcutaneously, including anti CTLA-4 antibody tremelimumab (TRM) and anti PD-1 antibody sasanlimab (SSL). Methods: AdC68 ± ICI(s) were given on months (mos) 1 and 5 and pDNA ± ICI(s) on mos 2–4 and 6–8. After 8 mos, maintenance pDNA + ICI(s) were given every 1 or 2 mos. In Part A (6 escalation cohorts), pts with mCRPC received AdC68 (4 or 6x10e11 viral particles) + pDNA 5 mg ± ICIs (TRM alone 80 mg; TRM 40 or 80 mg + SSL 130 or 300 mg). In Part B (3 expansion cohorts), pts with mCRPC received AdC68 6x10e11 + pDNA 5 mg + TRM 80 mg + SSL 300 mg; pts with BCR received similar vector and pDNA + TRM 80 mg ± SSL 130 mg. Primary objectives: Assess overall safety (CTCAE v4.03), determine expansion dose. Secondary objectives: Anti-tumor activity (RECIST v1.1, Prostate Cancer Working Group 3, PSA 50 response) and immune response. (Note: Database remains open, some queries pending). Results: As of Sept 15, 2020, 91 pts were treated in dose-escalation (n=38) and expansion (n=53; BCR=35, mCRPC=18). Immune responses (ELISpot) were positive in some pts. Grade (G) 3 or 4 treatment-related adverse events (TRAEs) developed in 38.5% (35/91) of pts. G5 TRAEs occurred in 2 pts (n=1 G4 myasthenia gravis + G5 pulmonary embolism; n=1 G5 myocarditis). irAEs were more frequent in BCR compared to mCRPC. See the table for efficacy data. Conclusions: Vaccination with PrCa VBIR had a manageable safety profile. TRAEs increased when 2 ICIs were given. Some pts with BCR experienced durable PSA-50 responses without ADT; patients with mCRPC had few objective tumor responses, but had prolonged median rPFS. PrCa VBIR appears to stimulate antigen-specific immunity and results in noticeable antitumor activity, particularly in androgen sensitive disease. Clinical trial information: NCT02616185. [Table: see text]

Outcomes in 370 patients with mantle cell lymphoma treated with ibrutinib: a pooled analysis from three open-label studies

Ibrutinib is highly active in treating mantle cell lymphoma (MCL), an aggressive B-cell lymphoma. We pooled data from three ibrutinib studies to explore the impact of baseline patient characteristics on treatment response. Patients with relapsed/refractory MCL (n = 370) treated with ibrutinib had an objective response rate (ORR) of 66% (20% complete response; 46% partial response); median duration of response (DOR), progression-free survival (PFS) and overall survival (OS) were 18·6, 12·8 and 25·0 months, respectively. Univariate analyses showed patients with one versus >one prior line of therapy had longer OS. Multivariate analyses identified that one prior line of therapy affected PFS; Eastern Cooperative Oncology Group (ECOG) performance status, simplified MCL international prognostic index (sMIPI) score, bulky disease, and blastoid histology affected OS and PFS. Patients with blastoid versus non-blastoid histology had similar time to best response, but lower ORR, DOR, PFS and OS. OS and PFS were longer in patients with better sMIPI, patients with ECOG performance status 0-1, non-bulky disease and non-blastoid histology. Additionally, the proportion of patients with poor prognostic factors increased with increasing lines of therapy. Together, results suggest that patient outcomes following treatment failure with ibrutinib are related to the natural biological evolution of the disease.