Background: Heat Shock Protein 27 (Hsp27) is a stress-activated, multi-functional chaperone protein highly expressed in cancer that regulates cell signaling and survival pathways implicated in cancer progression. In prostate cancer models, Hsp27 complexes with androgen receptor (AR) and enhances transactivation of AR-regulated genes. OGX-427 is a 2nd generation antisense that inhibits Hsp27 expression with in vitro and in vivo efficacy. Phase I studies have demonstrated tolerability and single agent activity.
Methods: Patients (pts) with CRPC, no/minimal symptoms and any prior treatment other than chemotherapy were randomized 1:1 to receive prednisone (P) 5 mg PO BID or P with OGX-427 600 mg IV x 3 loading doses followed by 1000 mg IV weekly. Primary endpoint was the proportion of pts progression free (PSAWG 2 criteria) at 12 weeks. A 2-stage MinMax design (H0 = 5%, HA >20%, α=0.1, β=0.1) will enrol 32 pts total per arm and provide 70% power to detect the difference at a 0.10 1-sided significance. Secondary endpoints include PSA decline, measurable disease response, and circulating tumour cell (CTC) enumeration.
Results: In the first 22 pts randomized (11 to OGX-427+P, 11 to P), baseline median age was 71 years (53-86), ECOG PS 0 or 1 in 64% and 36% of pts, median PSA 89 (6-606), metastases in bone/lymph nodes/liver or lung in 77%/64%/10%, 23% had prior treatment with P, and 91% had ≥5 CTC/7.5 ml (median 18/7.5 ml). Thus far, 82% of pts randomized to OGX-427+P have had a PSA decline (55% with ≥30% decline) and 18% a PSA increase; 40% of pts treated with P have had a PSA decline (20% with ≥30% decline), 10% no change and 50% with PSA increase. CTC conversion from ≥5 to <5/7.5 ml has occurred in 60% of pts randomized to OGX-427+P and 20% of pts treated with P alone. Grade 1-2 infusion reactions (e.g., chills, diarrhea, flushing) have occurred in 45% of pts receiving OGX-427+P and 1 pt developed hemolytic uremic syndrome after week 7 probably related to OGX.
Conclusions: Preliminary data provide clinical support for the role of Hsp27 in AR signalling and as a therapeutic target for prostate cancer. Enrolment on this study continues. Funded by a grant from the Terry Fox Research Institute.