KML001 Cytotoxic Activity Is Associated with Its Binding to Telomeric Sequences and Telomere Erosion in Prostate Cancer Cells

Abstract

Purpose: KML001 (sodium metaarsenite) is an orally bioavailable arsenic compound that has entered phase I/II clinical trials in prostate cancer. In this study, we elucidated the mode of action of KML001and investigated its effects on telomerase and telomeres. Experimental Design: We compared telomere length to KML001cytotoxic activity in a panel of human solid tumor cell lines. Duration of exposure and concentrations of KML001 that affect telomerase and telomeres were evaluated in relation to established mechanisms of arsenite action such as reactive oxygen species^related DNA damage induction. Binding of KML001 to telomeres was assessed by matrix-assisted laser desorption/ionization mass spectrometry. Results: We established a significant inverse correlation (r 2 = 0.9) between telomere length and cytotoxicity. KML001exhibited activity in tumor cells with short telomeres at concentrations that can be achieved in serum of patients. We found that telomerase is not directly inhibited by KML001. Instead, KML001 specifically binds to telomeric sequences at a ratio of one molecule per three TTAGGG repeats leading to translocation of the telomerase catalytic subunit into the cytoplasm. In prostate cancer cells with short telomeres, KML001 caused telomere-associated DNA damage signaling as shown by g-H2AX induction and chromatin immunoprecipitation assays as well as a rapid telomere erosion shown by metaphase fluorescence in situ hybridization. These effects were not seen in a lung cancer cell line with long telomeres. Importantly, arsenification of telomeres preceded DNA lesions caused by reactive oxygen species production. Conclusions: Sodium metaarsenite is a telomere targeting agent and should be explored for the treatment of tumors with short telomeres.

Telomere and Microtubule Targeting in Treatment-Sensitive and Treatment-Resistant Human Prostate Cancer Cells

“…5, B-D). Figure 5B demonstrates that the SP (primarily Pgp-expressing) and Phatak et al, 2008). KML001 induced phosphorylation of ␥-H2AX in wt DU145 and DU145/Pac200 cells, including the SP and non-SP fractions, and more ␥-H2AX phosphorylation occurred in the SP fraction than in the non-SP fraction (Fig.…”

“…Therefore, we wanted to investigate the effects of targeting microtubules and telomeres in the DU145-derived cells. We showed previously that KML001 is a telomere-targeting agent and its cytotoxic effects depend on telomere length; cell lines with short telomeres (such as prostate cancer cells) are more sensitive to KML001 than are those with longer telomeres (Phatak et al, 2008). The effects of paclitaxel and KML001 on parental DU145 cells were assessed with the SP assay (Fig.…”

“…Approaches that enhance the effects of taxanes and possibly also address Pgprelated and non-Pgp-related resistance and stem cell-like cell subpopulations need to be developed. We showed previously that the telomere-targeting agent KML001 is particularly active in cancer cell lines that have short telomeres and is less active in cell lines with longer telomeres (Phatak et al, 2008). Prostate cancer cell lines in general have relatively short telomeres and maintain endogenous telomerase activity; therefore, they are potential targets for telomere-targeting agents (Phatak et al, 2008).…”

Synergistic interaction between tetra-arsenic oxide and paclitaxel in human cancer cells in vitro

“…TAO and other arsenic compounds also showed potent activity against human solid tumors, such as prostate and cervix cancers (7,17). Similar to ATO, efficacy of TAO may be improved via combination with other chemotherapeutic agents (16,18,19).…”

“…Arsenic sulfide also recently showed an anti-cancer effect against APL (4). Currently, other arsenic anti-cancer agents such as tetra-arsenic oxide [As 4 O 6 , 2,4,6,8,9,10-Hexaoxa-1,3,5,7-tetraarsatricyclo(3.3.1.1 3,7 ) decane, TAO] and sodium meta arsenite are currently being developed (5)(6)(7).…”