A series of 8-substituted alkyl xanthines were evaluated in vitro to test the cytotoxocity in cells. For this experiment, we utilized different mammalian cancer cell lines primarily representing prostrate and lung. One of the compounds synthesized, viz. 8-tertbutyl caffeine showed potent anticancer activity at low concentrations against DU145 when compared to adriamycin. Further experiments were carried out to check the cell cycle arrest in the DU145 cells treated with adriamycin, caffeine and 8-tert butyl caffeine. We observed that there was an arrest in G1 phase of cell cycle at 24 hours while at 48 hours of incubation, the cells were constantly distributed (59.71% -70.79%). We conclude that the effect of 8-tertbutyl caffeine is relatively comparable to caffeine whereas in adriamycin treated cells, we observed the cells underwent G2 arrest. We evaluate the studies on these effects by showing potent analogues which could be used as promising anticancer agents.