On December 10, 2018 Constellation Pharmaceuticals, Inc. (Nasdaq: CNST), a clinical-stage biopharmaceutical company using its expertise in epigenetics to discover and develop novel therapeutics, reported an update of the ProSTAR study, its ongoing Phase 1b/2 clinical trial of CPI-1205 in patients with metastatic castration-resistant prostate cancer (mCRPC) (Press release, Constellation Pharmaceuticals, DEC 10, 2018, View Source [SID1234532000]).

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The ProSTAR study is evaluating CPI-1205, Constellation’s potent and highly selective small-molecule EZH2 inhibitor, in combination with either enzalutamide or abiraterone / prednisone ("abiraterone"), in mCRPC patients who experienced disease progression while receiving the other ARS inhibitor. Based on encouraging results from the Phase 1b portion of ProSTAR, the Company has initiated dosing in the randomized Phase 2 portion studying CPI-1205 in combination with enzalutamide versus enzalutamide alone. Constellation has also decided to expand the Phase 2 portion of the study by adding an arm evaluating CPI-1205 in combination with abiraterone in the second-line setting.

"We are pleased that CPI-1205 achieved its Phase 1b endpoints in ProSTAR, demonstrating an encouraging safety profile and evidence of clinical activity in both arms," said Adrian Senderowicz, Chief Medical Officer of Constellation

Pharmaceuticals. "As we advance into the Phase 2 portion of the study, we believe combination therapy with CPI-1205 may provide a meaningful second-line treatment option to patients with metastatic castration-resistant prostate cancer, an area of significant unmet medical need. We are excited about expanding our opportunity to include an arm evaluating CPI-1205 in combination with abiraterone in the second-line setting, given that very few patients experience a 50% reduction in PSAs on second-line treatment with abiraterone and that time to progression in this setting is typically short."

Initiation and Expansion of Phase 2 Portion of ProSTAR

As planned, Constellation has already begun dosing patients in the Phase 2 portion of the study, evaluating CPI-1205 in combination with enzalutamide versus enzalutamide alone. The Company continues to expect enrollment of up to 35 patients in both the treatment and the control arms.

Additionally, Constellation is expanding the trial to include a separate Phase 2 arm evaluating CPI-1205 in combination with abiraterone in up to 30 mCRPC patients who progressed on prior enzalutamide therapy. This arm, which will soon begin dosing patients, will not be randomized against a control arm due to the low response rate and lack of durability seen with abiraterone in the second-line setting.

In a recent randomized cross-over trial, only 4% of patients taking abiraterone after disease progression on enzalutamide, and only 31% of patients taking enzalutamide after disease progression on abiraterone, achieved a 50% reduction in PSA levels. Time to PSA progression was only 1.3 months and 2.7 months, respectively. Time to disease progression was only 1.6 months and 2.7 months, respectively.1

Constellation continues to expect to determine proof of concept for CPI-1205 in mid-2019.

1 D. Khalaf et al, Phase 2 randomized cross-over trial of abiraterone + prednisone (ABI) vs enzalutamide (ENZ) for patients (pts) with metastatic castration resistant prostate cancer (mCRPC): results for 2nd-line therapy, poster presented at 2018 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) meeting.

About mCRPC

mCRPC is an advanced form of prostate cancer and is defined by disease progression despite treatment with androgen depletion therapy (ADT). mCRPC may present as one or any combination of the following: a continuous rise in serum levels of PSA, progression of known metastases, or appearance of new metastases. Prognosis is associated with several factors, including the

ability to perform certain daily activities and the presence of bone pain. Additional symptoms commonly include anemia (low healthy red blood cell levels), weight loss, fatigue, hypercoagulability (abnormal blood coagulation), and increased susceptibility to infection. mCRPC presents as a spectrum of disease ranging from patients without symptoms but rising PSA levels despite ADT, to patients with metastases and significant debilitation.