Introduction: Prostate cancer progenitor cells (PCPCs) are undifferentiated tumor cells that can self-renew and generate tumors in the face of standard therapies. Here we show that telomerase, known to be critical for benign stem cell function, also plays an important role in PCPCs and can be exploited to neutralize these cells using novel telomerase-interfering constructs. Methods: A putative PCPC population was isolated from human prostatectomy specimens via collagen attachment and FACS selection for integrin \#945;2\#946;1 and CD44. PCPCs were characterized for gene expression (RT-PCR), clonogenicity (colony formation), and invasiveness (matrigel chamber). PCPC telomerase activity was measured by RT-PCR-based telomeric repeat amplification protocol (qPCR-TRAP). PCPC telomerase interference was accomplished by lentiviral expression of 2 constructs: telomerase RNA with an altered template region (MT-Ter) and siRNA targeting wild-type telomerase RNA (anti-Ter siRNA). The effects of these constructs were assessed by measuring PCPC viability and apoptosis (TUNEL assay). Results: An integrin \#945;2\#946;1+CD44+ putative PCPC population was isolated from 6 human prostate tumors. This population expressed high levels of \#8220;progenitor phenotype\#8221; genes (ABCG2, \#946;-catenin, NANOG, Oct3/4) and low levels of \#8220;differentiated phenotype\#8221; genes (AR and PSA). Functionally, PCPCs yielded >50 colonies per 1000 cells seeded on collagen after 3 weeks vs. no colonies from FACS- cells. Similarly, matrigel chamber assay showed 10% of the PCPC population invading through the chamber over 24 hours vs. none of the FACS- population. Most importantly, PCPCs possessed at least 20-fold greater telomerase activity than FACS- cells, and induction of telomerase interference in PCPCs via MT-hTer and anti-hTer siRNA expression elicited a brisk apoptotic response (TUNEL) by day 3 in >90% of cells, with concomitant near-complete growth inhibition. Conclusion: We have shown that human prostate tumors contain a subpopulation of prostate cancer progenitor cells (PCPCs) marked by an undifferentiated gene expression profile, vigorous clonogenicity and invasiveness, and high levels of telomerase activity that can be successfully exploited to neutralize these cells. Ongoing studies are investigating the in vivo effects of telomerase interference on PCPCtumorigenicity in mouse models. Our findings suggest that telomerase interference may constitute a unique therapeutic strategy capable of eradicating the progenitor cancer cells thought to mediate tumor recurrence and progression.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1072.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009