Lydia Amari , you should always run a pilot experiment treating your cells with different concentrations of camptothecin. You can assess the viability by either trypan blue exclusion assay or MTT/MTS (Cell Titer) assays. You can use the doses in the literature as a baseline, but that can drastically change depending on your regents (e.g. different brands/purity, supplements interference, etc) and culture conditions.