Src controls castration recurrence of CWR22 prostate cancer xenografts

Bing Su,Kevin H Eng,Bryan Gillard,Irwin H Gelman,Lingqiu Gao

doi:10.1002/cam4.144

Abstract

Recurrence of prostate cancer (CaP) after androgen-deprivation therapy continues to have the greatest impact on patient survival. Castration-recurrent (CR)-CaP is likely driven by the activation of androgen receptor (AR) through multiple mechanisms including induction of AR coregulators, AR mutants or splice variants, and AR posttranslational modification such as phosphorylation by Src-family and Ack1 tyrosine kinases. Here, we address whether Src is required for the CR growth of human CWR22 CaP xenografts. The shRNA-mediated Src knockdown or treatment with the Src inhibitors, dasatinib or KXO1, reduced CaP recurrence over controls and increased time-to-recurrence following castration. Moreover, CR-CaP [Src-shRNA] tumors that recurred had similar Src protein and activation levels as those of parental cells, strengthening the notion that Src activity is required for progression to CR-CaP. In contrast, the ability of dasatinib or KXO1 to inhibit Src kinase activity in vitro did not correlate with their ability to inhibit serum-driven in vitro proliferation of CR and androgen-dependent stable cell lines derived from CWR22 tumors (CWR22Rv1 and CWR22PC, respectively), suggesting that the in vitro proliferation of these CaP lines is Src independent. Taken together, these findings strongly suggest that Src is a potent and specific therapeutic target for CR-CaP progression.

Highlights

Prostate cancer (CaP), the second leading cause of cancer deaths in U.S men, progresses from localized to invasive disease associated with metastasis to local lymph nodes and bones
Using Src-specific shRNA, the pan-tyrosine kinase inhibitor, dasatinib, and the Src-family tyrosine kinases (SFK)/tubulin inhibitor, KXO1, we show that Src antagonism decreased spontaneous CR-CaP formation and increased time to recurrence
The well established human CWR22 xenograft model [18] can recapitulate initial AD CaP growth in vivo followed by castration-induced regression and the recurrence in 40– 50% of hosts of CR-CaP that express and are driven by androgen receptor (AR) [32] (Fig. 1A)

Summary

Introduction

Prostate cancer (CaP), the second leading cause of cancer deaths in U.S men (http://seer.cancer.gov/statfacts/html/ prost.html), progresses from localized to invasive disease associated with metastasis to local lymph nodes and bones. Newer studies have corroborated the involvement of activated Src in progression to androgen independence [21,22,23] or increased invasiveness [24] These data as well as preclinical studies demonstrating critical roles for SFK in CaP metastasis [25,26,27,28,29,30] have spawned clinical trials using SFK-specific or pan-tyrosine kinase inhibitors (reviewed in [1, 31]). CR-CaP lesions recurring after Src shRNAmediated knockdown exhibited control Src protein and activity levels, suggesting that sustained Src activity is required for CR growth in this model These data suggest a role for SFK targeting in some CR-CaP

Material and Methods

Results and Discussion

50 Vehicle

B Control shSrc