Ubiquitination of Oncogenic Mutant p53 via Attenuation of Ribosome Biogenesis Machinery Effectively Inhibits Pancreatic Tumor Growth.

Dysregulated ribosome biogenesis and p53 mutations are known to play oncogenic roles in various cancers, including pancreatic cancer. In this study, we demonstrated the therapeutic potential of BMH-21, a pharmacologic inhibitor of RNA polymerase I, against pancreatic cancer by uncovering a novel molecular mechanism involving RPA194-mediated ubiquitination of mutant p53 without affecting the ubiquitination of wild-type p53. Our key findings are that (i) BMH-21 selectively induces apoptosis and cell growth inhibition of pancreatic cancer cells with no effect on normal human pancreatic ductal epithelial cells; (ii) BMH-21 degrades RPA194; (iii) BMH-21 inhibits recruitment of both RPA194 and RPA135 on rDNA to suppress pre-rRNA synthesis; (iv) RPA194 physically interacts with p53 and BMH-21-induced degradation of RPA194 selectively exposes truncated and mutated p53 for ubiquitination with no effect on ubiquitination of wild-type p53 in pancreatic cancer cells; and (v) BMH-21 treatment significantly reduces the growth of orthotopic xenograft pancreatic tumors in athymic nude mice with no observed toxicity. Altogether, these findings suggest that BMH-21 is a promising, nontoxic therapeutic agent for patients with pancreatic cancer with aberrant ribosome biogenesis and mutant p53, offering a potential new avenue for targeted treatment.