Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Pathology and Laboratory Medicine, 2020.
Prostate cancer (PCa) is the most common cancer and the second-leading cause of cancer deaths for men in the U.S. Around 30% of men over 50 years have histological evidence of PCa. In early stages, PCa normally does not have obvious symptoms. However when PCa travels through the blood or lymphatic system to spread to other organs, it will severely affect patients’ life quality and in some cases also threaten their life. In the early stages of PCa, there are many primary therapeutic options for patients including surgery, hormone therapy, and radiotherapy (RT). Because it is non-invasive and has a low risk, nearly 50% patients will choose RT as primary treatment, and the majority of them will recieve external beam radiotherapy (EBRT). EBRT mainly works though direct or indirect (producing reactive oxygen species) mechanisms to break double strand DNA to kill tumors or shrink tumor sizes. Hence, studying the DNA damage repairing system and oxygen concentration inside tumors are extremely important for increasing RT efficacy. Besides, there are still certain unrevealed areas of treatment after RT. Although RT provides significant benefits to PCa patients, it is also associated with risks of toxicity, including proctitis (rectal inflammation), cystitis (bladder inflammation), urinary or rectal bleeding, and in some extreme cases even can result in death. Intreatment, patients who receive EBRT need to be exposed to 75.6 to 81.0 Gy total cumulative dose of gamma rays, which will result in unavoidable adverse effects. In addition, clinician employed 3D image guided radiotherapy (IGRT) to partly reduce the surrounding tissue damage, how to increase RT efficacy, and minimize post RT response still needs to be well studied. For this thesis, we focused on the function and role of androgen receptor (AR) in RT. We dissected the AR role in RT and demonstrated how to use radiosensitizers to increase RT efficacy through targeting AR. On the other hand, we investigated the drug sensitivity after RT and selected several clinically available compounds to restore/recover the drug sensitivity.
First of all, based on previous studies and our observation, we knew AR expression level and activity will increase after RT, which might upregulate the expression of AR-mediated DNA damage response (DDR) genes and futher reduce the RT efficacy. Therefore, we used the AR degradation enhancer, ASC-J9®, as a radiosensitizer that can suppress the expression and function of AR and AR mediated DDR genes. In addition, ASC-J9® pre-treatment could help PCa bypass the IR induced cell cycle arrest, which will lead to genomic instablity and further trigger AR mediated apoptotic pathway. In addition, it is known that the low oxygen area at the core of solid tumors would make EBRT less effective than expected. ASC-J9® shares the polyphenol structure with other curcumin derivatives, therefore its polyphenol structure could regulate the gutathione pathway and further elevate IR induced ROS production that increases DNA double strand breaks (DSB). All above evidence demonstrate that targeting AR with ASC-J9® is an effective strategy to enhance RT efficacy.
In our second set of studies, we investigated how RT impacts the sensitivity of the anti-adrogen drug, Enzalutamide (Enz). Enz was the last developed and currently most powerful anti-androgen compound in PCa therapy, it can extend metastasis free survival from 14.7 to 36.6 months. According to the last NCCN guidlines Enz could be used alone or combined with other chemotherapy drugs after primary therapies (eg. surgery, hormone therapy, and radiotherapy). As we mentioned, patients receive 34-42 daily fractions of 1.8- to 2.0-Gy EBRT (75.6 to 81.0 Gy total cumulative dose), which might change gene expression profiles and cell behavior. In our cell line model, we found that multiple times of RT would gradually increase lncRNA MALAT1 expression levels and further increase the AR splicing variant 7 (ARv7) production, which might result in PCa cells becoming less sensitive to Enz. The similar tendency was also shown in our circulating tumor cells mRNA samples, we found that in nearly 40% of patients we coulddetect increased mRNA levels of ARv7 after RT. Futhermore, the existence of ARv7 could change the fate of PCa cells, withPCa cells transforming to CD133+, CD44+ prostate cancer stem like cells (PCSLCs). RT induced PCSLCs have relatively higher ABCG2 expression and activity, which will result in PCa cells becoming resistant to several therapeutic compounds. Finally, through our different xenograft nude mice models, we have demonstrated that ASC-J9®, as a radiosensitizer could effectively increase RT efficacy, multiple RT treatments could reduce Enz sensitivity through inducing ARv7, and platinum drugs combined with Enz might restore Enz sensitivity. Using all of the above studies, we point out insightful information how to reduce RT resistance and RT-induced Enz resistance, as well as provide new therapeutic strategies to better treat PCa.
