PhiKan 083 Inhibits MYCN Expression in Liver Cancer Cells Independent of p53 Pathways

MYCN is a key oncogenic driver in hepatocellular carcinoma (HCC) and a therapeutic challenge due to the historical undruggability of MYC transcription factors (TFs). Using a high-throughput MYCN promoter-luciferase reporter, we identified PhiKan 083 (PK83), a small molecule previously recognized as a mutant p53 activator, that dose-dependently suppresses MYCN expression in HCC cells. PK83 impaired the proliferation and survival of MYCN-high HCC cells, inducing DNA damage, apoptosis, and loss of clonogenic and spheroid growth potential, while sparing MYCN-low HCC cells and normal hepatocytes. Structure-activity analysis revealed that polar, hydrogen-bond-capable substituents on PK83's tricyclic scaffold are critical for its activity. Although PK83 broadly activates p53 signaling, its cytotoxicity in MYCN-high cells is not strictly dependent on intact p53, as confirmed in p53-knockout systems. Transcriptome profiling and pathway analysis demonstrated robust suppression of MYC/MYCN targets along with modulation of pathways linked to stress, differentiation, and metabolism. In primary HCC tumors, PK83-downregulated TFs, including oncogenic TFs ZMIZ1 and TARBP1, positively correlated with MYCN, whereas upregulated stress-responsive TFs ATF3 and FOSL2 showed a negative correlation. These findings suggest that PK83 suppresses MYCN expression and preferentially affects MYCN-high HCC cells in a p53-independent manner, warranting further preclinical investigation of PK83 and related compounds in MYCN-associated cancers.