D-peptide inhibitors of the p53–MDM2 interaction for targeted molecular therapy of malignant neoplasms

Abstract

The oncoproteins MDM2 and MDMX negatively regulate the activity and stability of the tumor suppressor protein p53, conferring tumor development and survival. Antagonists targeting the p53-binding domains of MDM2 and MDMX kill tumor cells both in vitro and in vivo by reactivating the p53 pathway, promising a class of antitumor agents for cancer therapy. Aided by native chemical ligation and mirror image phage display, we recently identified a D-peptide inhibitor of the p53-MDM2 interaction termed The tumor suppressor protein p53 is a transcription factor that transactivates, in response to cellular stresses, the expression of various target genes that mediate cell cycle arrest, senescence, or apoptosis (1). Dubbed the "guardian of the genome" (2), p53 is critical for maintaining genetic stability and preventing tumor development (3). Not surprisingly, loss of p53 activity resulting from point mutations in the TP53 gene is responsible for approximately 50% of human tumors. Although p53 retains WT status in many other tumors, its tumor suppressor activity and in vivo stability are abrogated by regulatory molecules such as the E3 ubiquitin ligase MDM2 and its homologue MDMX (4, 5). Amplified or over-expressed in a significant fraction of cancers without concomitant TP53 mutation, MDM2 and MDMX directly contribute to p53 inactivation and tumor survival.MDM2 itself is transcriptionally inducible by p53 in a negative feedback loop (6). MDM2 binds the N-terminal transactivation domain of p53 with high affinity to block p53 regulating responsive gene expression (7). More importantly, MDM2 controls p53 stability by targeting the tumor suppressor protein for ubiquitinmediated constitutive degradation (8-10). Although MDMX lacks E3 ubiquitin ligase activity, the MDM2 homologue acts as an effective transcriptional antagonist of p53, and nonredundantly impedes p53-induced growth inhibitory and apoptotic responses (4, 5). In addition, MDMX forms heterodimers with MDM2 through their C-terminal RING finger domains, stimulating MDM2-mediated ubiquitination and degradation of p53 and MDMX itself (11-13). The interplay between MDM2 and MDMX confers a robust p53 inactivation in tumorigenesis (14).Recent studies show that restoring endogenous p53 activity can halt the growth of cancerous tumors in mice through cell typedependent multiple mechanisms, including apoptosis, senescence, and senescence-triggered innate inflammatory responses (15-17). Thus, antagonists of MDM2 and MDMX that activate the p53 pathway can potentially be developed into a class of therapeutic agents for cancer treatment (14). Much of the current efforts have been focused on combinatorial library search for and structurebased rational design of low molecular weight antagonists of MDM2 (18). Successful examples include a cis-imidazoline analogue, termed nutlin-3, and, a spiro-oxindole-derived compound, termed 20). For optimal efficacy, however, dual specific inhibitors may be needed to target both MDM2 and MDMX (14).We previously reported the synthesis of the p53...

High-resolution structures of a heterochiral coiled coil

“…"Mirror-image phage display," a powerful method pioneered by Kim and co-workers, has identified D peptides that bind tightly to L proteins (6). A few of these heterochiral complexes have been characterized at atomic resolution (7,8), but no general principles of heterochiral recognition have emerged. Shai and co-workers have reported that D peptides corresponding to transmembrane helices of several integral membrane proteins can pair with the natural L-peptide helix within a lipid bilayer (9-11).…”

Chemical synthesis and X-ray structure of a heterochiral {D-protein antagonist plus vascular endothelial growth factor} protein complex by racemic crystallography

“…Such D-peptide ligands would be resistant to proteolytic digestion in vivo, and for that reason they have excited a great deal of interest. Although mirror image phage display has been used in a number of academic studies (12)(13)(14), it has not yet led to the development of D-peptides as therapeutics.…”

Destabilization of the Epidermal Growth Factor Receptor (EGFR) by a Peptide That Inhibits EGFR Binding to Heat Shock Protein 90 and Receptor Dimerization

“…Although most therapeutic peptides are directed toward extracellular targets (38), the increasing use of cell-penetrating peptide sequences to transport "cargo," including peptide therapeutics, across the cell membrane has opened the door to many intracellular targets, including many proteins implicated in cancer (39,40). Recently, small peptides have shown efficacy in blocking the interaction of Bcl-XL with Bax (34) and of p53 with MDM2 (36) in preclinical cancer therapy models. At present, we have no indication that the use of Disruptin would be therapeutically viable, either alone or by potentiating the effects of radiation or chemotherapy.…”