922P - A phase II study of SB939 IN patients (pts) with castration resistant prostate cancer (CRPC)

Date 29 September 2012
Event ESMO Congress 2012
Session Poster presentation I
Topics Clinical Research
Prostate Cancer
Basic Scientific Principles
Presenter Bernhard Eigl
Authors B.J. Eigl1, S. North2, E. Winquist3, J. Powers4, J. Good5, M. Sharma6, J. Squire5, M. Cox7, E.A. Eisenhauer8, K.N. Chi9
  • 1Oncology, Tom Baker Cancer Centre, T2N 4N2 - Calgary/CA
  • 2Oncology, Cross Cancer Institute, Edmonton/CA
  • 3University of Western OntarioLondon Regional Cancer Center, CA-N6A 4L6 - London/CA
  • 4Clinical Trials, NCIC Clinical Trials Group, Kingston/CA
  • 5Pathology And Molecular Medicine, Queens University, Kingston/CA
  • 6Urologic Sciences, The Vancouver Prostate Centre, Vancouver/CA
  • 7Urologic Sciences, University of British Columbia, Vancouver/CA
  • 8Clinical Trials, Queen's UniversityNCIC Clinical Trials Group, CA-K7L 3N6 - Kingston/CA
  • 9Oncology, Vancouver Cancer Centre, University of British Columbia, Vancouver/CA



SB939 is a potent oral inhibitor of class 1, 2, and 4 histone deacetylases (HDACs). These 3 HDAC classes are highly expressed in CRPC and associated with poor clinical outcomes. HDAC inhibition abrogates androgen receptor signaling via inactivation of HSP90, and may have particular relevance in prostate cancer with the TMPRSS2-ERG (T2-E) fusion.


Pts with locally recurrent or metastatic CRPC received SB939 60mg every other day 3 times per week x 3 weeks on a 28-day cycle. Primary endpoints were PSA response rate (RR) (>50% decline from baseline for > 4 weeks) and progression-free survival (PFS). Secondary endpoints included objective response rate and duration; overall survival; circulating tumor cell (CTC) enumeration at baseline, 6 and 12 weeks; T2-E fusion analysis; correlative analysis of archival tissue; and safety. In a 2-stage design, a planned maximum of 29 response evaluable patients were to be enrolled.


32 pts were enrolled and have completed study treatment. Median age was 70; 88% of pts had received no prior chemotherapy; and ECOG performance status was 0/1 in 44%/56%. Bone/lymph node/visceral metastases were present in 91%/75%/12%. The median number of SB939 cycles administered was 3 (range 1-8). Adverse events were generally grade 1-2, with 5 pts experiencing one or more grade 3 events (fatigue (5), vomiting (1), dyspnea (1)). One pt died due to myocardial infarction. A confirmed PSA response was noted in 2 pts (6%), lasting 3.0 and 9.4 mo. In 16 pts with measurable disease, there were no objective responses, 7 pts had stable disease lasting 1.6 to 8.0 months. CTC response (from ≥5 at baseline to <5 at 6 or 12 weeks) occurred in 9/14 evaluable patients (64%) and CTC levels >5 at 6 weeks correlated with PSA progression. Correlative studies to evaluate T2-E from whole blood as well as T2-E fusion and PTEN deletion status on archival tissue are ongoing.


SB939 is tolerable at the dose/schedule given, but does not merit further study as a single agent in CRPC based on PSA RR. Activity was observed in terms of CTC declines however. Study of SB939 with cytotoxic or AR targeted therapies may be warranted. Supported by grants from the Canadian Cancer Society and the Ontario Institute for Cancer Research.


All authors have declared no conflicts of interest.