Background: Galeterone is a first-in-class multitargeted oral steroid analog; it suppresses prostate cancer by a combination of AR modulation (antagonism and degradation) and CYP17 inhibition. Safety and proof of concept of galeterone in CRPC was assessed in ARMOR1. Galeterone was reformulated by spray dry dispersion technology (SDD) to optimize PK and remove food effect. ARMOR2 (NCT 01709734) is an open label, 2-part phase 2 trial that evaluates safety and efficacy of SDD galeterone in 4 populations of CRPC patients. These results report Part 1. Methods: Objectives of Part 1: confirm dose equivalence of SDD formulation with evaluation of PK, safety and PSA response. Metastatic (M1) and non-metastatic (M0) treatment naïve CRPC pts enrolled to groups of 1,700, 2,550 or 3,400 mg PO daily. An abiraterone refractory (Abi-R) group of 3 patients opened at 2,550mg. Results: 28 were enrolled in part 1. Safety: All groups were safe by IMC assessment. There were 4 grade 3 adverse events. 2 were unrelated to study drug. 2 had transient G3 ALT elevations (did not recur with rechallenge). There was no AME: supplemental steroids were not required. G4 angioedema occurred in a pt receiving lisinopril (known association with angioedema). Efficacy: PSA response was improved compared to ARMOR1 (AACR 2012. Taplin et al abstract: CT-07). At early follow up Abi-R pts showed improvements in PSA with 1 PSA30% response, 2 with stablized PSA (decline in PSA-V from +0.44 to -0.39 ng/day). Conclusions: Galeterone in SDD formulation is tolerated at doses up to 3,400mg daily. SDD galeterone provides improved PSA response and durability vs. prior formulation. There is evidence of activity in abiraterone refractory patients. Clinical trial information: 01709734.

* Of evaluable. ** Ongoing evaluation.