Changing perspectives of the role of chemotherapy in advanced prostate cancer

β2-adrenoreceptor Signaling Increases Therapy Resistance in Prostate Cancer by Upregulating MCL1

There is accumulating evidence that continuous activation of the sympathetic nervous system due to psychosocial stress increases resistance to therapy and accelerates tumor growth via β2-adrenoreceptor signaling (ADRB2). However, the effector mechanisms appear to be specific to tumor type. Here we show that activation of ADRB2 by epinephrine, increased in response to immobilization stress, delays the loss of MCL1 apoptosis regulator (MCL1) protein expression induced by cytotoxic drugs in prostate cancer cells; and thus, increases resistance of prostate cancer xenografts to cytotoxic therapies. The effect of epinephrine on MCL1 protein depended on protein kinase A (PKA) activity, but was independent from androgen receptor expression. Furthermore, elevated blood epinephrine levels correlated positively with an increased MCL1 protein expression in human prostate biopsies. In summary, we demonstrate that stress triggers an androgen-independent antiapoptotic signaling via the ADRB2/PKA/MCL1 pathway in prostate cancer cells. IMPLICATIONS: Presented results justify clinical studies of ADRB2 blockers as therapeutics and of MCL1 protein expression as potential biomarker predicting efficacy of apoptosis-targeting drugs in prostate cancer.

Castration-resistant prostate cancer: systemic therapy in 2012

Prostate cancer is the most common non-cutaneous neoplasm in the male population worldwide. It is typically diagnosed in its early stages, and the disease exhibits a relatively indolent course in most patients. Despite the curability of localized disease with prostatectomy and radiation therapy, some patients develop metastatic disease and die. Although androgen deprivation is present in the majority of patients with metastatic prostate cancer, a state of androgen resistance eventually develops. Castration-resistant prostate cancer, defined when there is progression of disease despite low levels of testosterone, requires specialized care, and improved communication between medical and urologic oncologists has been identified as a key component in delivering effective therapy. Despite being considered a chemoresistant tumor in the past, the use of a prostate-specific antigen has paved the way for a new generation of trials for castration-resistant prostate cancer. Docetaxel is a life-prolonging chemotherapy that has been established as the standard first-line agent in two phase III clinical trials. Cabazitaxel, a novel taxane with activity in cancer models resistant to paclitaxel and docetaxel, is the only agent that has been compared to a chemotherapy control in a phase III clinical trial as a second-line therapy; it was found to prolong the overall survival of patients with castration-resistant prostate cancer previously treated with docetaxel when compared to mitoxantrone. Other agents used in this setting include abiraterone and sipuleucel-T, and novel therapies are continually being investigated in an attempt to improve the outcome for patients with castration-resistant prostate cancer.