seq id no 6 and seq id no 9 was studied by mtt assay which is based on the principle of uptake of mtt 3 4 5 dimethylthiazol 2 yl 2 5 diphenyl tetrazolium bromide a tetrazolium salt by the metabolically active cells where it is metabolized by active mitochondria into a blue colored formazan product which can be read spectrophotometrically briefly tumor cells ptc primary human colon cancer cell line kb oral squamous u87mg glioblastoma hbl100 breast hep2 laryngeal ecv304 endothelial pa 1 ovary and l132 lung were incubated with the peptide analogs for 48 hours at 37 u00b0 c in a 96 well culture plate followed by the addition of 100 u03bcg mtt and further incubation of 1 hour the formazan crystals formed inside the cells were dissolved with a detergent comprising 10 sodium dodecyl sulfate and 0 01 n hcl and optical density read on a multiscan elisa reader the optical density was directly proportional to the number of proliferating and metabolically active cells percent cytotoxicity of peptide analogs is shown in the following tables in vivo antitumor activity of the novel synthesized somatostatin analogs on primary tumor colon xenografted mice the antitumor activity of seq id no 2 and seq id no 3 was studied in human colon adenocarcinoma ptc xenografts in nude mice ptc tumor xenografts were grown in balb c athymic.