Figure 4.

Cytotoxic effect of unconjugated cryptophycin-55 glycinate (4), conjugates 10, 11, and metabolite 12 against M21 and M21-L human melanoma cells after 72 h (2 h treatment and additional 70 h incubation). Curves obtained by non-linear regression (four-parameter dose-response, error bars represent the standard deviation of triplicates, the measurements were repeated twice).