CA9 and cancer: Therefore, isatin nucleus was broadly used by our group for the development of diverse effective oxindole-based small molecules (structures I–III29–31, Figure 1) with anticancer activities that target different enzymatic and cellular targets such as inhibition of cancer-related carbonic anhydrase IX isoform32–33, inhibition of different kinases34–35, in addition to apoptosis induction in different human cancer cell lines.36–37