760 Phosphorylation of the Androgen Receptor by Cdk1 Predicts Outcome in Prostate Cancer Patients with PSA ⩽ 20 ng/ml

Abstract

The use of targeted therapies for cancer treatment has significantly grown in the last years and many clinical trials with new drugs are ongoing. In order to study the molecular mechanisms of both drug response and resistance, appropriate pre-clinical models are required. In our Institute, a vast collection of colorectal cancer liver metastases has been implanted and expanded into immunocompromised mice, thus generating a panel of so-called ‘xenopatients’. These mice have been used to evaluate response and resistance to targeted therapies, including Cetuximab, an antiEGFR antibody currently used in clinics, proving to be a robust pre-clinical model. We systematically processed tumors from xenopatients to generate colosphere cultures (’xenospheres’), which displayed the properties of tumorinitiating cells. Newly established xenospheres could be long-term propagated in vitro, and maintained the same genetic lesions as the corresponding xenopatients. Upon re-injection into immunocompromised mice, they generated a tumor xenograft (spheropatient) that displayed the same tumor histology and, most importantly, the same response to cetuximab treatment of the original xenopatient, which correlated with the KRAS gene mutational status. We could subdivide xenospheres in two subgroups that displayed distinctive proliferation requirements. KRAS xenospheres grew almost independently of exogenous growth factors (GFs), and were not inhibited by cetuximab. On the contrary, proliferation of KRAS xenospheres required exogenous GFs and was strongly impaired by cetuximab treatment. Of note, the extent of KRAS xenosphere response to cetuximab was modulated by both autocrine loops of EGFR ligands and exogenous GFs concentration and combinations. Interestingly, we observed that a conditioned medium obtained by human fibroblasts cell lines, including cancer-associated fibroblasts, contained high amount of HGF and was able to sustain proliferation of KRAS , but not KRAS, xenospheres. Addition of the small molecule MET inhibitor JnJ38877605 abrogated proliferation and induced cell death, while cetuximab was completely ineffective, suggesting a role for the microenvironment in modulating the cancer response to the drug. We have thus generated a robust system that allow to integrate in vivo with in vitro data of the same tumor of origin, and that will be a powerful tool to elucidate the molecular mechanisms of both response and resistance to targeted therapies, and to test new potential therapeutic strategies.