Forchlorfenuron (FCF) is a synthetic plant cytokinin widely used in agriculture to promote fruit size, that paradoxically inhibits proliferation, migration, and invasion in human cancer cell lines. FCF has also been shown to affect HIF-1α and HER2, which are both known to play a crucial role in cancer cell survival. In this study, we have developed potent FCF analogs through structural modification of FCF, coined UR214-1, UR214-7, and UR214-9. Compared to parental FCF, these analogs are more effective in decreasing viability and proliferation in both ovarian and endometrial cancer cell lines. These FCF analogs also suppress HER2 expression at a concentration lower than that of FCF. In addition, we found that treatment with either FCF or its analogs decreases the expression of human epididymis protein 4 (HE4), which is commonly upregulated in ovarian and endometrial cancers. Given the association between cancer behavior and HE4 production in gynecologic cancers, our findings may provide insight useful in the development of new treatment strategies for gynecologic cancers.