A Difluorinated Derivative of ARC-111 Suppresses Intrahepatic Cholangiocarcinoma Growth via Targeting Topoisomerase I

Intrahepatic cholangiocarcinoma (ICC) has limited treatment options and a poor prognosis. Thus, novel therapeutics are urgently needed. Topoisomerase I (Top I), an essential DNA regulatory enzyme, is commonly upregulated in malignancies and contributes to their aggressive growth. ARC-111 derivative <b>YCJ-02</b> is a new synthesized Top I inhibitor with a structure different from camptothecin, but its potential for ICC treatment is not clear. In this study, we investigated the potential of <b>YCJ-02</b> to inhibit the growth of ICC cells in vitro and verified its antitumor activity in vivo by using an AKT/NICD-induced ICC preclinical mouse model. We found that Top I was overexpressed in human ICC tissues and cell lines and knockdown of Top I inhibited ICC cell growth. Consistently, Top I inhibitor <b>YCJ-02</b> blocked the proliferation of ICC cells and showed superior cytotoxic activity compared to reference drugs ARC-111, topotecan, and SN-38. Mechanistically, <b>YCJ-02</b> arrested the cell cycle at the G2/M phase and elevated p21 expression. Subsequently, apoptosis was induced, characterized by increased Bax, Bad, and cleaved caspase3 and decreased Bcl-2. <b>YCJ-02</b> also induced DNA damage, as shown with increased γ-H2AX. Interestingly, DNA relaxation assay and Western blotting showed that <b>YCJ-02</b> not only functions as a Top I poison but also promotes its degradation via a ubiquitin/26S proteasome pathway. Critically, <b>YCJ-02</b> dramatically suppressed AKT/NICD-induced ICC growth in mice and decreased the expression of Top I. Together, this study demonstrates that <b>YCJ-02</b> is an effective Top I inhibitor with high potency in inhibiting ICC growth and merits further preclinical evaluation.