Shortening of telomeres along with an up-regulation of
telomerase is implicated in the immortality of
tumor cells. Targeting either telomeres or
telomerase with specific compounds has been proposed as an anticancer strategy. Because
telomerase activity and telomeres are found in normal cells, telomere or
telomerase targeting agents could induce side effects in normal tissues. We evaluated the effects of telomere and
telomerase interactive agents in human
tumor and normal cell lines to try to determine the potential side effects those agents might induce in patients. Toxicity of the G-quadruplex interactive
porphyrins (
TMPyP4, TMPyP2) and
azidothymidine (AZT) were tested using a cell-counting technique against normal human cell lines (CRL-2115 and CRL-2120, fibroblasts; NHEK-Ad, adult keratinocytes; CCL-241, small intestinal cells; NCM 460, colonic mucosal epithelial cells) and human tumor cell lines (MDA-MB 231 and Hs 578T,
breast cancer; SK-N-FI,
neuroblastoma; HeLa,
cervix cancer; MIA PaCa-2,
pancreatic cancer; HT-29 and HCT-116,
colon cancer; DU 145,
prostatic cancer cell line).
Telomerase activity of these cell lines was measured by a non-PCR-based conventional assay. The effects of TMPgammaP2,
TMPyP4, and AZT were also evaluated against normal human bone marrow specimens, using a granulocyte-macrophage colony-forming assay (CFU-GM). AZT showed very low cytotoxic effects against normal and tumor cell lines, with the IC50 values above 200 microM. The IC50 values for TMPyP2 and
TMPyP4 in normal human cell lines were in the range of 2.9-48.3 microM and 1.7-15.5 microM, respectively, whereas in tumor cell lines the IC50 values were 11.4-53 microM and 9.0-28.2 microM, respectively. Within the tissue types, keratinocytes were more sensitive to
TMPyP4 than fibroblasts, and small intestinal cells were more sensitive than colonic mucosal epithelial cells. The IC50 for TMPyP2 and
TMPyP4 in the normal marrow colony-forming assays were 19.3 +/- 5.1 microM and 47.9 +/-1.0 microM, respectively. In conclusion, the in vitro cytotoxicity of the telomere interactive agent
TMPyP4 is comparable in human
tumor and normal cell lines, which indicates that
TMPyP4 could have effects on normal tissues.