A dual-exposure drug treatment of cell lines in tissue culture provides a possible method for determining schedule dependency. This is suggested by results of treatment of human small cell lung carcinoma NIH H209 and murine L1210 leukemia cell lines with cisplatin, a non-schedule-dependent drug, and etoposide, a schedule-dependent drug. Nonlinear least squares was used to estimate the dose-response surface. The estimated regression coefficients for the effect of the first dose compared to that of the second dose support the premise that cisplatin is not schedule dependent. Unlike cisplatin, the second dose of etoposide was shown to be more effective than the first dose in the human small cell carcinoma line. This agrees with known clinical results where multiple etoposide dosing has been shown to be more effective and confirms schedule dependency. This methodology, or a refinement, may offer another tool for studying schedule dependency of drugs using tissue culture methods.
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