A Phase I/IB, Open Label, Dose Finding Study to Evaluate Safety, Pharmacodynamics and Efficacy of Pembrolizumab in Combination With Vorinostat in Patients With Advanced Prostate, Renal or Urothelial Carcinoma.

BACKGROUND

Immunosuppressive factors such as regulatory T cells and myeloid-derived suppressive cells (MDSCs) limit the efficacy of immunotherapies. Histone deacetylase (HDAC) inhibitors have been shown to have immunomodulatory effects. Thus, we conducted a Phase Ib clinical study with the HDAC inhibitor vorinostat and the PD-1 inhibitor pembrolizumab in patients (pts) with metastatic urothelial (UC), renal (RCC) and prostate (PCA) carcinoma.

METHODS

The phase I portion consisted of two dose levels of vorinostat (100 and 200 mg, PO daily 2 weeks ON and 1 week OFF) and a fixed dose of pembrolizumab (200 mg IV every 21 days). Patients (pts) were assigned to three cohorts: Cohort A (previously treated, anti-PD1/PD-L1 naïve UC and RCC), Cohort B (previously treated, anti-PD1/PD-L1 resistant UC and RCC pts), and Cohort C (PCA pts).

RESULTS

Dose levels 1 and 2 were completed without DLTs. We have enrolled 44 pts. (36 evaluable) in the dose expansion cohorts, and the most common resolved grade 3/4 toxicities were diarrhea, hypophosphatemia, acute kidney injury, anemia, and hypothyroidism. For Cohort A (13 pts), B (11 pts), and C (12 pts) the objective response rate was 8%, 0%, and 17%, and the median progression-free survival was 2.9, 3.5, and 3.5 months, respectively. Four partial responses were observed, and two PCA pts. had a complete biochemical response with undetectable PSA. Persistent lower levels of peripheral CD11, CD14 HLA-DR monocytic MDSCs were associated with clinical benefit.

CONCLUSION

The combination of vorinostat and pembrolizumab is relatively well tolerated and may be active in a subset of immune checkpoint-resistant UC/RCC pts. and immune checkpoint-naïve PCA pts.

TRIAL REGISTRATION

NCT02619253.