 The on-going dose escalation Phase 1 study has enrolled 44 patients with progressive, metastatic castration-resistant prostate cancer in 11 cohorts. Initial safety data showed that HPN424 is generally well-tolerated, and cytokine-related adverse events have been transient and manageable. Signals of clinical activity include multiple patients remaining on study for more than 24 weeks, and serum PSA declines. 