Halda emergence heralds new ‘TAC’ type

Halda Therapeutics, founded by Yale University chemistry professor Craig Crews, has emerged from stealth to join a crowded scene of protein-targeting start-ups. The New Haven, Connecticut–based company is developing a new class of therapies called regulated induced proximity targeting chimeras (RIPTACs) to treat cancer. The company, which so far has raised $76 million, presented its RIPTAC data for the first time publicly at the 2023 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium in San Francisco Feb. 16–18. RIPTACs are bifunctional molecules that draw two different proteins together. On one end is a ligand that grabs a tumor-specific protein; on the other end is a ligand that binds a protein necessary for the cancer cell to survive. The RIPTAC and the two proteins form a complex within cancer cells that inhibits the protein with the essential function. The company calls the mechanism “hold and kill”—the ternary complexes hold