KIF20A and neoplasm: The introduction of a methoxy group at the 5-position of the indole ring in compound 9a significantly enhanced its inhibition against human tumor cell lines and improved its biochemical potency, achieving IC50 values of 1.2 μM for 70% inhibition of basal KIF20A ATPase activity and 0.23 μM for 90% inhibition of microtubule-stimulated activity, both markedly better than the original Paprotrain.