Identification of Novel p53 Pathway Activating Small-Molecule Compounds Reveals Unexpected Similarities with Known Therapeutic Agents

Abstract

Manipulation of the activity of the p53 tumor suppressor pathway has demonstrated potential benefit in preclinical mouse tumor models and has entered human clinical trials. We describe here an improved, extensive small-molecule chemical compound library screen for p53 pathway activation in a human cancer cell line devised to identify hits with potent antitumor activity. We uncover six novel small-molecule lead compounds, which activate p53 and repress the growth of human cancer cells. Two tested compounds suppress in vivo tumor growth in an orthotopic mouse model of human B-cell lymphoma. All compounds interact with DNA, and two activate p53 pathway in a DNA damage signaling-dependent manner. A further screen of a drug library of approved drugs for medicinal uses and analysis of gene-expression signatures of the novel compounds revealed similarities to known DNA intercalating and topoisomerase interfering agents and unexpected connectivities to known drugs without previously demonstrated anticancer activities. These included several neuroleptics, glycosides, antihistamines and adrenoreceptor antagonists. This unbiased screen pinpoints interference with the DNA topology as the predominant mean of pharmacological activation of the p53 pathway and identifies potential novel antitumor agents.

p53 and ribosome biogenesis stress: The essentials

“…Another small molecule, BMH-21, was recently reported to target PolI activity through its ability to promote the proteasomal degradation of RPA194, the large catalytic subunit of PolI holocomplex [126]. Although BMH-21 intercalates into DNA with high affinity to GC-rich regions, it does not elicit a DNA damage response [127] and its ability to activate p53 is probably mediated by ribosome biogenesis stress. This promising agent was shown to effectively impede the growth of different cancer cells, both in vitro and in vivo [126].…”

Wild type p53 reactivation: From lab bench to clinic

“…Interestingly, a recent chemical library screen lead to the discovery of several molecules which activate the p53 pathway and kill cancer cells via interference with the DNA topology [65]. One of the compounds, BMH-21, binds to GC-rich sequences, in particular in ribosomal DNA genes, leading to the inhibition of RNA Pol I via proteasome-dependent degradation of Pol I subunit RPA194 and segregation of nucleolar proteins [66].…”

Small Molecule BMH-Compounds That Inhibit RNA Polymerase I and Cause Nucleolar Stress

“…Lead molecules arising from large unbiased screens have a diversity of action mechanisms including inhibition of sirtuins, and regulation of p53 folding and binding (1, 2). We conducted a cell-based high-throughput imaging screen to identify small molecule p53-activators and discovered and validated six lead compounds as activators of p53 based on their ability to stabilize p53, activate p53 reporter and p53 target genes and transcriptional profiling consistent with p53 responses (8). Characterization of their mechanism of p53 activation revealed that two of the compounds caused DNA-damage and mediated p53 stabilization through activation of ATM-signaling pathway.…”

“…The present study focused on characterization of the mechanism of action of compounds BMH-9, BMH-22 and BMH-23 arising from our initial high-throughput screen for p53 activators (8). We show here that these compounds function as Pol I inhibitors and similarly to BMH-21, cause proteasome-dependent degradation of RPA194.…”