Objectives
The Walensky laboratory focuses on the chemical biology of deregulated apoptotic, transcriptional, and metabolic pathways in cancer. To achieve our objectives, we take a multidisciplinary approach that employs synthetic chemistry techniques, structural biology analyses, and biochemical, cellular, and mouse modeling experiments to systematically dissect the pathologic signaling pathways of interest. By interrogating BCL-2 family signaling proteins using a diversity of analytical approaches, we aim to uncover the interaction surfaces and mechanisms that regulate apoptotic function. We strive to conduct structure-function studies that will advance our fundamental understanding of these oncogenic proteins so that new therapeutic strategies can be developed to overcome cancer chemoresistance.
Stapled Peptide Design
We specialize in the design, synthesis, and application of stapled alpha-helical peptides for cancer research. These chemical tools and prototype therapeutics recapitulate the native alpha-helical fold of critical protein-protein interactions domains, making them valuable bioactive domains for modulating signaling pathways in vitro, in cellulo, and in vivo. We have a longstanding history of collaborating with research groups in the Dana-Farber community as well as laboratories outside the Institute to advance cancer, infectious diseases, and metabolic research. We design and generate stapled peptides for a host of research needs. Our goal is to remain fully engaged with our collaborators to provide ongoing input on experimental design, data analysis, and project development. Best-practices in advancing and applying stapled peptide technologies are outlined in our methodologic publications and have been adopted by dozens of unaffiliated research groups nationally and around the world.
Please submit your project proposals by email to Greg Bird.
greg_bird@dfci.harvard.edu
Research Projects
Dissecting and targeting the BCL-2 family interaction network
BCL-2 family proteins are critical regulators of apoptosis or programmed cell death. Whereas the pro-apoptotic members such as BAX and BAK function to induce cell death by permeabilizing the mitochondrial outer membrane, other members like BCL-2 and MCL-1 protect from cell death by intercepting the pro-apoptotic members. Because so many human diseases are classified by either too little cell death (such as in cancer) or too much cell death (such as in heart attack, stroke, or neurogenerative diseases), rigorously understanding the interplay between BCL-2 family proteins is critical to advancing new therapeutic strategies to alternatively restore or reduce cell death. We use a host of chemical, analytical, and biological techniques to investigate and target BCL-2 family proteins, providing blueprints for the development of selective pharmacologic agents to modulate cell death pathways in cancer and other human diseases. For example, we developed the first stapled peptide and small molecule direct activators of BAX, selective stapled peptide inhibitors of MCL-1, and selective covalent stapled peptide and small molecule inhibitors of BFL-1. A key facet of our work in this area is to also uncover unexpected roles of BCL-2 family proteins in human physiology and pathophysiology.
Dual targeting of HDM2 and HDMX to maximally reactivate p53 in human cancer
Alpha-helical motifs are commonly involved in mediating the signaling interactions between proteins. p53 is a critical protein known as the guardian of the human genome and functions to monitor and maintain the integrity of DNA. As such, p53 is a tumor suppressor protein, which works to prevent the development of cancer by ridding the body of cells that contain damaged DNA. Since cancer cells thrive on errors in DNA, such as mutations and translocations, p53 is itself often mutated, deleted, or suppressed in human cancer. A key mechanism involved in p53 suppression involves two negative regulators, called HDM2 and HDMX. Whereas HDM2 binds and degrades p53, HDMX binds and sequesters p53. HDM2 and HDMX bind to the same “transactivation domain” alpha-helix in p53. We previously generated a stapled peptide modified after this essential p53 helix, yielding the first inhibitor of its kind to block both HDM2 and HDMX, and thereby maximally reactivate p53 in cancer. Because so many adult cancers (~50%) and especially pediatric cancers (~90%) maintain the expression of wild-type p53, typically by upregulating HDM2 and HDMX, our stapled p53 peptide approach has the potential to reactivate cell death in a host of human cancers for therapeutic benefit. We have demonstrated preclinical proof-of-concept for this therapeutic activity in mouse models of choriocarcinoma, Ewing sarcoma, and rhabdoid tumors, motivating ongoing translational studies.
Interrogating oncogenic protein interactions using a broad spectrum of discovery technologies
The results of our stapled p53 projects demonstrate the potential broad impact of stapled peptides in general as a platform technology that yields chemical tools and prototype therapeutics for cancer. For example, we have reported stapled peptides that target (1) EED to inhibit the PRC2 complex, (2) β-catenin to block aberrant Wnt signaling, (3) KRAS and its mutant isoforms to block pathologic nucleotide exchange activity, and (4) E1 to block the ubiquitin-proteasome pathway. Ongoing projects in the lab continue to explore the breadth of applications of stapled peptide, small molecule, and recombinant protein designs for investigating and modulating a host of disease targets, incorporating a host of “omics” technologies to drive our in-depth analyses.
Stapled peptides as viral fusion inhibitors and prototype immunogens
New therapeutic strategies are needed to prevent and treat viral infections, as the threat of new viruses and widespread outbreaks is ever-present. Stapled peptides have demonstrated potential as viral fusion inhibitors in diverse infections that employ a fusogenic six-helix bundle mode of entry, such as HIV, RSV, and coronaviruses. Similarly, we have demonstrated that stapled peptides can serve as high fidelity, protease-resistant mimics of highly conserved antigenic structures recognized by the broadly neutralizing HIV-1 antibodies, 4e10 and 10e8, highlighting their potential utility as prototype immunogens for the development of an HIV-1 vaccine.
Stapled peptides as next-generation antibiotics to combat multidrug resistant infections
Cationic α-helical antimicrobial peptides (AMPs) hold great promise for the treatment of multidrug-resistant (MDR) bacteria, which are less likely to develop resistance to membrane lysis, the mechanism of action of such AMPs. However, linear AMPs are typically unstructured in solution, proteolytically labile, and can non-specifically lyse mammalian cells. We have generated more stable, membrane-selective AMPs termed stapled AMPs (StAMPs; alpha-helical AMPs stabilized using hydrocarbon linkers), which can kill antibiotic-resistant bacteria in culture and in mice.
To determine the optimal placement of the staple in designing StAMPs, we tested the lytic activity of a 58-member staple-scanning library of the 23-residue AMP magainin II (Mag2; from the African clawed frog, Xenopus laevis) against bacteria and red blood cells (RBCs; a model for lysis of mammalian membranes). Staple placement that expanded the continuity of the hydrophobic landscape of the amphipathic helix, regardless of the change in overall hydrophobicity, resulted in increased hemolytic activity. These insights were used to design an algorithm for creating StAMPs that selectively target bacterial membranes while minimizing hemolysis, expressed as a lyticity index (LI).
Visit the Lyticity Index & Hydrophobicity Network Map (HNM) to learn more.