Loss of Notch1 Activity Inhibits Prostate Cancer Growth and Metastasis and Sensitizes Prostate Cancer Cells to Antiandrogen Therapies.

Prostate cancer remains among the leading causes of cancer-related deaths in men. Patients with aggressive disease typically undergo hormone deprivation therapy. Although treatment is initially very successful, these men commonly progress to lethal, castration-resistant prostate cancer (CRPC) in 2 to 3 years. Standard therapies for CRPC include second-generation antiandrogens, which prolong patient lifespan by only several months. It is imperative to advance our understanding of the mechanisms leading to resistance to identify new therapies for aggressive prostate cancer. This study identifies Notch1 as a therapeutic target in prostate cancer. Loss of in aggressive prostate cancer cells decreases proliferation, invasion, and tumorsphere formation. Therapeutic inhibition of Notch1 activity with gamma secretase inhibitors RO4929097 or DAPT in prostate cancer cells further results in decreased proliferative abilities. Loss of and treatment of immunocompromised mice bearing prostate cancer xenografts with RO4929097 display significantly impaired tumor growth. Loss of additionally decreased metastatic potential of prostate cancer cells in invasion assays as well as experiments. Moreover, treatment with gamma secretase inhibitors or gene deletion synergized with antiandrogen therapies, enzalutamide or abiraterone, to decrease the growth of prostate cancer cells. Combination of gamma secretase inhibitors with abiraterone significantly inhibited cell migration and invasion, while combination with enzalutamide reversed enzalutamide-induced migration and invasion. These collective findings suggest loss of delays growth of CRPC and inhibits metastasis, and inhibition of Notch1 activation in conjunction with second-generation antiandrogen therapies could delay growth and progression of prostate cancer.