Purpose: Imetelstat is a covalently-lipidated 13-mer thiophosphoramidate oligonucleotide that acts as a potent specific inhibitor of telomerase. It binds with high affinity to the template region of the RNA component of human telomerase (hTERC ) and is a competitive inhibitor of telomerase enzymatic activity. The purpose of this study was to determine the recommended phase 2 dose of imetelstat in children with recurrent or refractory solid tumors. Experimental Design: Imetelstat was administered intravenously over two hours on days 1 and 8, every 21 days. Dose levels of 225, 285, and 360 mg/m2 were evaluated, using the rolling-six design. Imetelstat pharmacokinetic and correlative biology studies were also performed during the first cycle. Results: Twenty subjects were enrolled (median age 14 yrs; range 3-21). Seventeen were evaluable for toxicity. The most common toxicities were neutropenia, thrombocytopenia, and lymphopenia, with dose-limiting myelosuppression in two of six patients at 360 mg/m2. Pharmacokinetics were dose dependent with a lower clearance at the highest dose level. Telomerase inhibition was observed in peripheral blood mononuclear cells at 285 and 360 mg/m2. Two confirmed partial responses osteosarcoma (n=1) and Ewing sarcoma (n=1) were observed. Conclusions: The recommended phase 2 dose of imetelstat given on days 1 and 8 of 21-day cycle is 285 mg/m2.
- Received May 8, 2013.
- Revision received September 10, 2013.
- Accepted September 11, 2013.
- Copyright © 2013, American Association for Cancer Research.