Synthesis and Pharmacological Evaluation of Natural Product Diphyllin Derivatives against Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is one of the most common malignant tumors, but clinical drug treatments are limited. The natural product diphyllin was identified as a lead compound suppressing the proliferation of HNSCC cells through phenotypic screening of natural product library. However, further developments of diphyllin as an anti-HNSCC agent were restricted by the weak bioactivity and poor metabolic stability. Herein, we designed and synthesized two series of novel diphyllin derivatives that were achieved by introducing various pyranose rings or hydrophilic groups to block the easily metabolic C-4 site with the aim to improve antitumor activity and drug-like properties. Among these compounds, compound A3 showed the most potent inhibitory effects against HNSCC cells with IC₅₀ values ranging from 4.37 to 77.81 nM and much less potent cytotoxicity against normal cells (IC₅₀ > 10 μM). Mechanistically, it effectively inhibited cell proliferation and migration and induced the cell cycle arrest and apoptosis in a concentration-dependent manner. Besides, A3 possessed greatly improved pharmacokinetic properties including over 10-fold higher plasma exposure (AUC_0-t: 541 vs 43.6 h*ng/mL) and better oral bioavailability (F: 20.85% vs 2.70%), lower systemic plasma clearance (CL:1897 vs 24523 mL/h/kg), as well as longer half-life (T_1/2: 0.530 vs 0.108 h) when compared to diphyllin. In a tumor cell xenograft model, A3 significantly suppressed the CAL27 tumor growth with a TGI of 42.2% without obvious safety concern, which is superior to that of diphyllin (TGI = 23.3%), suggesting great potential for treatment of HNSCC.