Lavendustin C, a natural-product derived anticancer lead compound, was modified at its carboxylic group by esterification or amidation (compounds 6–10) and at its amino group by introducing 5-arylidenethiazolin-4-ones (14a–c to 17a–c, 18a and 18b). Two strategies were used to combine these moieties and to optimize the yield. These new compounds were evaluated for their antiproliferative activities against a panel of nine cancer cell lines. The results clearly show that 5-arylidenethiazolin-4-one moiety contributes substantially to the activity. Also, methyl esters are more potent than amides, while N-ethylamides are the most potent among amides. 14b showed the highest potency against all tested cancer cell lines with IC 50 line IC 50 1.4–2.5 µM, while against normal cell >50µM. It showed arrest of HeLa cells at G0/G1, S phases and reduction of the percent of cells in G2/ M. Moreover, 14b triggered death of HeLa cancer cells via apoptosis induction. EGFR inhibitory potency of 14b was found to be comparable to that of erlotinib. Computational docking and in silico pharmacokinetic studies were performed and discussed. In conclusion, 14b might serve as a multitarget lead compound for further development of anticancer agents.