Constellation Pharmaceuticals Highlights EZH2 Inhibition Program in Prostate Cancer at Biomedical Conference
About EZH2 Inhibition in Prostate Cancer
EZH2 is an enzyme that acts as an epigenetic writer and normally regulates gene expression by placing one or more methyl groups on a histone protein, leading to the suppression of gene expression programs. While this effect of EZH2 on gene expression is a normal part of cellular development, some cancers depend on an abnormal pattern of gene expression and re-direct EZH2 to genes that become abnormally repressed. Cancer cells with these abnormal gene expression programs may be more resistant to anti-cancer therapies.
There is a strong association between EZH2 expression and disease progression in metastatic castration-resistant prostate cancer (mCRPC), and a therapeutic approach that targets EZH2 may result in better outcomes than those achieved with approved therapeutic agents that treat mCRPC. In prostate cancer, the androgen receptor is a key regulator of gene expression and acts as the mediator of androgen signaling in prostate cells. The AR signaling pathway is the primary pathway used by prostate cancer cells to promote tumor growth. We believe that EZH2, by suppressing certain gene sets, enhances AR signaling, which can lead to increased tumor growth. In preclinical studies, we observed enhanced gene expression changes in prostate cancer cells treated with a combination of enzalutamide and CPI-1205 as compared to enzalutamide treatment alone. This corroborates our hypothesis that EZH2 functionally cooperates with androgen receptor signaling to promote prostate cancer growth.
We also believe that EZH2 is utilized by prostate cancer cells to establish resistance to ARS inhibitors. We have observed in preclinical studies that EZH2 inhibitors, such as CPI-1205, in combination with ARS inhibitors synergistically killed tumor cells and demonstrated activity in models that are resistant to ARS inhibitors.
CPI-1205 is a small molecule designed to promote anti-tumor activity by specifically inhibiting EZH2, an enzyme that suppresses target gene expression. In preclinical studies, we observed that CPI-1205 inhibited tumor growth as a single agent and synergistically enhanced the efficacy of cancer therapies, including ARS inhibitors in a prostate cancer model and immune checkpoint inhibitors in other solid tumor models. Based on these observations and the limited options for patients who progress on ARS inhibitors or immune checkpoint inhibitors, we have prioritized clinical development of CPI-1205 as a combination therapy with ARS inhibitors in prostate cancer and immune checkpoint inhibitors in solid tumors. We are currently conducting the ProSTAR trial. We previously completed a Phase 1 clinical trial of CPI-1205 as a monotherapy in patients with relapsed B-cell lymphoma in which CPI-1205 demonstrated clinical activity and was well tolerated.
About the ProSTAR Clinical Trial
ProSTAR is an open-label Phase 1b/2 clinical trial of CPI-1205 for the treatment of metastatic castration-resistant prostate cancer (mCRPC) in combination with enzalutamide or abiraterone acetate, which are second-generation ARS inhibitors, in patients with mCRPC who previously progressed on treatment with either abiraterone acetate or enzalutamide. Patients who have previously progressed on treatment with abiraterone acetate are treated with a combination of enzalutamide and CPI-1205, and patients who previously progressed on treatment with enzalutamide are treated with a combination of abiraterone acetate and CPI-1205. In the Phase 1b portion of this trial, we aim to establish safety, pharmacokinetics, pharmacodynamics, maximum tolerated dose, and a recommended Phase 2 dose of CPI-1205 with these agents. Based on results from the Phase 1b trial, we expect to select either abiraterone acetate or enzalutamide to be combined with the optimal dose regimen of CPI-1205 for the Phase 2 portion of the trial. In the Phase 2 trial, we will assess response rate as the primary endpoint, defined as the proportion of patients who have any of (i) a prostate-specific-antigen reduction of 50% or more from baseline, (ii) a decline of 30% or more in circulating-tumor-cell count from baseline or (iii) for patients with measurable soft tissue disease, an objective response, defined as a complete response or partial response per RECIST 1.1 criteria.
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MacDougall Biomedical Communications
Source: Constellation Pharmaceuticals