Design, synthesis and biological evaluation of novel homocamptothecin analogues as potent antitumor agents

Fifteen novel homocamptothecin derivatives with α-OMe substituted E-rings were designed and synthesized. All of the derivatives exhibited similar or superior cytotoxicities compared with that of SN-38, and they inhibited Topo I activity in a cell-free assay in a manner similar to that of SN-38, confirming that they represent a new class of Topo I inhibitors. Notably, the water soluble compound 36o (1.2 mg/mL) exhibited increased lactone stability, and at 0.5 mg/kg and 3.0 mg/kg, it demonstrated significant antitumor activity in mice bearing a xenograft model using human colon cancer cell line HT-29. On the basis of these positive results, further development of 36o-related compounds as potential anticancer clinical trial candidates is definitely warranted.