Etoposide (VP16-213) and teniposide (VM26) comparative in vitro activities in human tumors.

In order to determine if any inherent sensitivity differences may exist between VP16-213 and VM26 individual human tumors were grown in vitro and drug sensitivities were determined using the soft agar clonogenic assay method. Only nine of the 34 tumors tested so far showed a differing sensitivity to VP16-213 and VM26 as measured by a 25% or greater colony number reduction. However in none of these tumors did this added reduction result in a 70% decrease over control plate colony numbers. As yet we have been unable to demonstrate any clinically meaningful inherent in vitro sensitivity difference between VP16-213 and VM26 in any tumor type tested.