Telomerase Activity Correlates with Growth of Transplantable Osteosarcomas in Rats Treated with cis‐Diammine Dichloroplatinum or the Angiogenesis Inhibitor AGM‐1470

To determine the role of telomerase activity in the growth of tumors in rats undergoing chemotherapy, a comparison of the volumes of telomerase‐positive transplantable osteosarcomas was made in rats treated with the antineoplastic agent cis‐diammine dichloroplatinum (CDDP) or the angiogenesis inhibitor O‐(chloroacetylcarbamoyl)fumagillol (AGM‐1470). Male F344 rats, 8 weeks old, received transplants of macroscopic lung metastatic nodules into the subcutaneous back space and treatment was started on day 14 thereafter. CDDP was injected i.v. at doses of 0, 0.625, 1.25 and 2.5 mg/kg body weight (b.w.) and AGM‐1470 was administered at total doses of 0, 2.5, 5 and 10 mg/kg b.w. over 2 weeks by osmotic pumps, also implanted into the subcutaneous back space, but remote from the transplanted tumors. On day 28, all animals were killed for measurement of transplanted tumor size and determination of telomerase activities by telomeric repeat amplification protocol (TRAP) assay. The results showed telomerase activity to be highly correlated with the treated/non‐treated (T/C) tumor size ratio (r=0.96, P<0.0001). In a second experiment, CDDP at 2.5 mg/kg b.w. and AGM‐1470 at 10 mg/kg b.w., these being the most effective doses, were given as in the first experiment, and animals were serially killed on days 14, 21, 28, 35 and 42. Tumors in rats treated with CDDP and AGM‐1470 showed 18.2% and 20.5% of the control telomerase activity on days 35 and 21, respectively, when tumor growth was inhibited. However, on day 42, the activities increased to 46.5% and 92.5%, this correlating with re‐growth (r=0.73, P<0.0001). These results suggest that decline of telomerase activity may be involved in tumor growth retardation induced by chemotherapeutic agents. This possibility clearly warrants further mechanistic studies.