Antitumor agent-173 (Compound 4b) is a prodrug of Cycloicaritin. Antitumor agent-173 is a substrate for OATP2B1. Antitumor agent-173 selectively inhibits the growth of tumor Antitumor agent-173 significantly increases the oral bioavailability of Cycloicaritin and exerts good antitumor activity and safety.