Abstract

Despite the introduction of a number of new treatment options (such as abiraterone acetate and enzalutamide) for castration resistant prostate cancer (CRPC), patients with this disease eventually progress. In order to understand how to help such patients, it is paramount to understand the biological characteristics of the resistant disease that emerges in response to new lines of therapy. Unfortunately, repeat biopsy samples are difficult to attain and may not reflect the full complexity of the disease. Circulating tumor cells (CTCs) provide a powerful alternative to biopsies for determining the molecular characteristics of cells that emerge following development of resistance. The presence of ≥ 5 CTCs measured with the CellSearch system is associated with poor survival in patients with CRPC and increases in the number of CTCs following treatment with abiraterone acetate or enzalutamide appears to be indicative of a lack of clinical response. Such association with clinical outcome suggests that CTCs play an important role in metastatic process. Moreover, detailed molecular characterization of CTCs at various points of the disease course may be useful in understanding of evolution of tumors and aid in selection of optimal therapeutic regimens. To better characterize resistant phenotypes that emerge following treatment with abiraterone acetate or enzalutamide, we collected blood from CRPC patients that prior to starting abiraterone acetate or enzalutamide, or upon a switch between the two therapies. We also collected blood at 4, 8, 12 weeks and at progression. CTCs were enumerated using CellSearch and also stained for synaptophysin (SYP) expression. Blood was also collected for analysis of myeloid derived suppressor cells (MDSCs) that are often associated with cancer progression. Like most other CTC isolation instruments, CellSearch is a CTC-enrichment device that efficiently captures CTCs while also retaining a few thousand non-specifically captured white blood cells. To obtain molecular profiles of CTCs, we isolated single tumor cells and performed RNA sequencing of pools of a small number of cells, which enabled us to track changes of molecular characteristics of CRPC upon progression. Initial observations suggest that CRPC is an evolving heterogeneous disease that utilizes several escape mechanisms upon application of specific treatments.

By Jaymala Patel, Vipul Bhargava, Miaoling He, Brad Foulk, Denis A. Smirnov, Przemyslaw Twardowski, Marcin Kortylewski, Sumanta Kumar Pal & Jeremy O. Jones