Steppogenin, a natural flavonoid, has been reported to exert antitumor activity through the dual inhibition of HIF-1α in cancer cells and DLL4 in endothelial cells. However, its anticancer efficacy compared with FDA-approved or investigational tyrosine kinase inhibitors (TKIs) has yet to be identified.

 In this study, we evaluated the antitumor effects of steppogenin in the Lewis Lung Carcinoma (LLC) mouse model, comparing it to two TKIs—Rivoceranib, a VEGFR2 TKI and Lazertinib, a third-generation EGFR TKI. In addition, we examined the effect of the different administration routes and assessed the synergistic effects of combining steppogenin with an immune checkpoint inhibitor (ICI), specifically an anti-PD-1 antibody.

 Oral administration of steppogenin exhibited tumor growth inhibition comparable to that of Rivoceranib and Lazertinib, despite being administered at 20-fold and 10-fold lower doses, respectively. Additionally, oral administration of steppogenin showed antitumor efficacy similar to that of subcutaneous administration. Immunohistochemical (IHC) analysis revealed that steppogenin significantly inhibited CD31⁺ tumor vasculature and suppressed the expression of VEGF and HIF-1α compared to the vehicle control. Moreover, steppogenin promoted the infiltration of CD8⁺GZMB⁺ cytotoxic T cells and increased the population of TUNEL-positive apoptotic cells within the tumor microenvironment. Finally, the combination of steppogenin with an ICI significantly increased both apoptotic cells counts and the recruitment of cytotoxic T cells compared to the Rivoceranib-ICI combination, though this was not observed with the Lazertinib-ICI combination.

Collectively, these results indicate that oral administration of steppogenin is a viable alternative to subcutaneous injection, demonstrating high antitumor efficacy even when compared to established or developing anticancer agents. Therefore, we suggest that steppogenin is a promising candidate for an oral anticancer agent or supplement derived from the natural products.