Cytotoxicity of 2-chlorodeoxyadenosine in a human tumor colony-forming assay.

We have utilized a human tumor colony forming assay to test the antitumor activity of 2-chlorodeoxyadenosine and to compare its activity with that of 9-beta-D-arabinofuranosyl-2-fluoroadenine, a related analog now in phase I/II clinical trials. The overall in vitro response rate (defined as less than 50% survival of tumor colony forming units) for 2-chlorodeoxyadenosine was: 8% and 23% at 1.0 and 10.0 micrograms/ml as a 1 hour pulse exposure, respectively; 11% and 31% at 1.0 and 10.0 micrograms/ml, as a continuous exposure, respectively. 2-Chlorodeoxyadenosine and 9-beta-D-arabinofuranosyl-2-fluoroadenine did not have identical spectra of antitumor activities in vitro, suggesting that both may be worthy of further clinical trial.