A phase I dose-escalation study of apatorsen (OGX-427), an antisense inhibitor targeting heat shock protein 27 (Hsp27), in patients with castration-resistant prostate cancer and other advanced cancers.

BACKGROUND: Heat shock protein 27 (Hsp27) is a chaperone protein that regulates cell survival via androgen receptor and other signaling pathways, thereby mediating cancer progression. Apatorsen (OGX-427) is a 2'-methoxyethyl-modified antisense oligonucleotide that inhibits Hsp27 expression. This study evaluated the safety profile and recommended phase II dosing of apatorsen in patients with advanced cancer.

PATIENTS AND METHODS: Patients with castration-resistant prostate (CRPC), breast, ovary, lung, or bladder cancer were enrolled to this phase I dose-escalation study. Apatorsen was administered i.v. weekly in 21-day cycles following 3 loading doses and over 5 dose levels (200-1000 mg). Apatorsen plasma concentrations, circulating tumor cells (CTCs) and CTC Hsp27 expression, and serum Hsp27 levels were evaluated.

RESULTS: Forty-two patients were accrued, of which 52% had CRPC. Patients were heavily pretreated, with 57% having had ≥3 prior chemotherapy regimens. During the loading dose/cycle 1 and overall study period, 93% and 100% of patients (N = 42) experienced treatment-related adverse events, respectively; most were grade 1-2 and included chills, pruritus, flushing, prolonged aPTT, lymphopenia, and anemia. One patient experienced a dose-limiting toxicity at the 600 mg dose level (intracranial hemorrhage in a previously undiagnosed brain metastasis). A maximum tolerated dose was not defined. Apatorsen Cmax increased proportionally with dose. Decreases in tumor markers and declines in CTCs were observed, with a prostate-specific antigen decline >%50% occurring in 10% of patients with CRPC; 29/39 assessable patients (74%) had reductions from ≥5 CTC/7.5 ml at baseline to <5 CTC/7.5 ml post-treatment. Twelve patients had stable measurable disease as best response.

CONCLUSIONS: Apatorsen was tolerated at the highest dose evaluated (1000 mg). Single-agent activity was suggested by changes in tumor markers, CTC, and stable measurable disease. Phase II studies evaluating apatorsen are underway.

CLINICALTRIALSGOV ID: NCT00487786.