The long-term objectives of this application are to understand the molecular mechanisms of resistance to androgen-directed therapies and to develop effective strategies to overcome the resistance. Recent significant advances in our understanding of continued androgen receptor (AR) signaling in castration-resistant prostate cancer have led to the development and FDA approval of two next-generation androgen-directed therapies, abiraterone and enzalutamide (MDV3100), which heralded a new era of prostate cancer therapy. However, disease progression after androgen-directed therapies remains the most critical challenge in the clinical management of prostate cancer. Upregulated expression of constitutively-active, alternatively-spliced AR variants (AR-Vs) that lack the ligand binding-domain has been implicated to play an important role in disease progression. However, the precise mechanism by which androgen-directed therapies increase AR-V expression and the precise mechanism by which AR-Vs regulate target-gene expression in mediating therapeutic resistance remain poorly understood. These are two issues vital to understanding resistance to androgen-directed therapies and developing effective means to overcome the resistance, and therefore are the main focus of investigation of the proposed study. Based on the findings from ours and others, we propose that upregulation of AR-Vs is an inevitable response of prostate cancers to all androgen-directed therapies currently accepted in the clinic and that a shift from androgen-dependent full-length AR (AR-FL) homodimerization to androgen-independent AR-FL/AR-V and AR-V/AR-V dimerization leads to unleashed AR activity, driving disease progression. Given the potency of abiraterone and enzalutamide and the evidence for ongoing suppression of androgen synthesis at the time of progression on abiraterone, this resistance mechanism may be especially critical for abiraterone and enzalutamide.
Three specific aims are proposed to test the hypotheses.
Aim 1 : Delineate the mechanism of AR-V induction following androgen-directed therapies.
Aim 2 : Elucidate the mechanism by which AR-Vs regulate target-gene expression.
Aim 3 : Correlate AR-V expression in circulating tumor cells with abiraterone/enzalutamide response. The proposed research is relevant to public health because it addresses a resistance mechanism that is inherent to all current androgen-directed therapies, including the new drugs abiraterone and enzalutamide. Moreover, we hope to establish AR-Vs as a prognostic marker to guide the selection of patients who will likely benefit from abiraterone and enzalutamide therapies. Overall, the outcome of this study is expected to have a direct impact on rational drug design and combination to overcome the shortcoming of current therapies and on reducing suffering and improving quality of life of the patients.

Public Health Relevance

Despite recent development and FDA approval of two new hormonal therapies for metastatic castration-resistant prostate cancer, abiraterone and enzalutamide, disease progression after hormonal therapies remains the most critical challenge in the clinical management of prostate cancer. The proposed research is relevant to public health because it addresses a resistance mechanism that is inherent to all current hormonal therapies, including abiraterone and enzalutamide, and is expected to establish a prognostic marker to guide the selection of patients for treatment. Overall, the outcome of this study is expected to have a direct impact on rational drug design and combination to overcome the shortcoming of current hormonal therapies and on reducing suffering and improving quality of life of the patients.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA188609-03
Application #
9122338
Study Section
Tumor Cell Biology Study Section (TCB)
Program Officer
Sathyamoorthy, Neeraja
Project Start
2014-09-01
Project End
2019-08-31
Budget Start
2016-09-01
Budget End
2017-08-31
Support Year
3
Fiscal Year
2016
Total Cost
Indirect Cost
Name
Tulane University
Department
Biology
Type
Schools of Medicine
DUNS #
053785812
City
New Orleans
State
LA
Country
United States
Zip Code
70118
Bai, Shanshan; Zhang, Bryan Y; Dong, Yan (2018) Impact of taxanes on androgen receptor signaling. Asian J Androl :
Li, Jianzhuo; Fu, Xueqi; Cao, Subing et al. (2018) Membrane-associated androgen receptor (AR) potentiates its transcriptional activities by activating heat shock protein 27 (HSP27). J Biol Chem 293:12719-12729
Luo, Jun; Attard, Gerhardt; Balk, Steven P et al. (2018) Role of Androgen Receptor Variants in Prostate Cancer: Report from the 2017 Mission Androgen Receptor Variants Meeting. Eur Urol 73:715-723
Zhan, Yang; Zhang, Guanyi; Wang, Xiaojie et al. (2017) Interplay between Cytoplasmic and Nuclear Androgen Receptor Splice Variants Mediates Castration Resistance. Mol Cancer Res 15:59-68
Cao, Subing; Zhan, Yang; Dong, Yan (2016) Emerging data on androgen receptor splice variants in prostate cancer. Endocr Relat Cancer 23:T199-T210
Liu, Xichun; Ledet, Elisa; Li, Dongying et al. (2016) A Whole Blood Assay for AR-V7 and ARv567es in Patients with Prostate Cancer. J Urol 196:1758-1763
Zhang, Guanyi; Liu, Xichun; Li, Jianzhuo et al. (2015) Androgen receptor splice variants circumvent AR blockade by microtubule-targeting agents. Oncotarget 6:23358-71
Xu, Duo; Zhan, Yang; Qi, Yanfeng et al. (2015) Androgen Receptor Splice Variants Dimerize to Transactivate Target Genes. Cancer Res 75:3663-71
Cao, Bo; Qi, Yanfeng; Yang, Yan et al. (2014) 20(S)-protopanaxadiol inhibition of progression and growth of castration-resistant prostate cancer. PLoS One 9:e111201