The Telomere Targeting Agent sodium metaarsenite Can Eradicate The Side Population Of Hormone
Silke Suer1, Bin Zhang2, Arif Hussain2, Angelika M. Burger1. 1Karmanos Cancer Institute, Detroit, MI; 2University of Maryland Greenebaum Cancer Center, Baltimore, MD
Cancer stem cells share properties with normal stem cells such as self-renewal, protection from cytotoxic insult, and quiescence. Due to
the latter, conventional chemotherapies are ineffective against cancer stem cells (CSCs) and drug resistant tumors have an even higher
CSC fraction as a result of clonal selection. Activation of telomerase in more than 90 % of all cancers ensures endless self-renewal and
enables the maintenance of telomeres at a stable length after their rapid shortening during early tumorigenesis. In this study we examined
the potential of sodium metaarsenite which can target telomeres and the catalytic subunit of telomerase (hTERT), to eradicate the mature
and the CSC population in drug sensitive and resistant prostate cancer cell lines. We have shown earlier, that prostate cancer cells are
sensitive to sodium metaarsenite. We analyzed various prostate cancer cell lines reflecting hormone responsive (LnCaP and LAPC-4),
hormone resistant (LAPC-4/CSS100 and LNCaP/C81) chemonaïve (DU145) and taxane resistant (DU145/Pac200) lines for the
existence of a CSC subpopulation by using the side population assay which is based on the property of stem cells to express drug efflux
pumps such as Pgp (P-glycoprotein) and BCRP (Breast Cancer Resistant Protein) that are responsible for the resistance to standard
chemotherapies. Fluorescence activated cell sorting (FACS) was used to separate the side population (SP) from the mature cell
population. We have tested the effect of sodium metaarsenite on cell growth in a standard MTT. Cells were treated with IC50 and IC100
concentrations of the compound for 72 hrs and analyzed for its effect on the SP and telomerase activity by a PCR ELISA assay as well as
hTERT expression level by real-time PCR. DNA damage induction was analyzed by γH2AX immunfluorescence staining. Cell growth
curves showed that all tested cancer cell lines respond with similar sensitivity to sodium metaarsenite (IC50 = 2-7μM) but that the sorted
SP respond better (IC50 = 1μM) to this compound. The taxane resistant cell line Du145/Pac200 had the highest percentage of a SP of
about 65% which was reduced to 89% at IC50 and to 52% at IC100 concentrations of sodium metaarsenite to controls. The sorted side
population showed higher telomerase activity as well as hTERT expression. The compound induced telomere-associated DNA damage
signaling which was more intense in the sorted side population than in the mature cell population. Our data suggest that resulting from a
reduction in telomerase activity and hTERT expression particularly in the CSC population, sodium metaarsenite treatment is responsible
for the decrease of the prostate cancer stem cell fraction and that this agent may be useful in the treatment of drug as well as hormone
resistant prostate cancers.
