Unmasking Drug Resistance: New TP53 Mutations Drive Failure of Cancer Drug Rezatapopt
A recent study conducted by Mass General Brigham investigators has identified specific mutations that lead to clinical resistance against rezatapopt, a drug designed to target the Y220C mutation in the tumor suppressor protein TP53. These findings, published in Cancer Discovery, provide a molecular basis for treatment failure and suggest potential strategies for overcoming acquired drug resistance.
Understanding TP53 and Rezatapopt
The TP53 gene, frequently mutated in approximately 70% of all cancers, plays a critical role as a tumor suppressor. The Y220C mutation, which is the ninth most common TP53 mutation, creates a specific cavity in the mutant protein that is absent in its normal form. This "druggable" pocket has been targeted by small molecules, such as rezatapopt, which aim to restore p53 function and reactivate its tumor suppressor activity.
Early clinical trials for rezatapopt reported an initial response rate of 20%, defined as at least 30% tumor shrinkage, across various cancer types.
These trials included patients with highly advanced cancers who had undergone multiple previous therapies. Advantages noted for rezatapopt included its applicability to diverse cancer types and its oral administration, allowing for home use. Despite this initial efficacy, patients have been observed to develop resistance to the drug over time.
Unraveling Acquired Resistance: The PYNNACLE Trial
To understand the mechanisms behind this acquired resistance, Mass General Brigham investigators analyzed blood and tumor samples from two patients. These patients were participating in the ongoing PYNNACLE clinical trial, which evaluates rezatapopt in individuals with metastatic solid tumors carrying the Y220C mutation. Both patients, who had different types of solid tumors, initially responded to rezatapopt treatment but subsequently developed drug resistance.
Genetic analyses of tumor DNA revealed the emergence of numerous new TP53 mutations during treatment. In one patient's sample, nearly 100 new mutations were observed.
Two Pathways to Resistance
To determine how these newly acquired mutations led to drug insensitivity, the research team expressed the mutations alongside the Y220C mutation in cultured cancer cells. The acquired mutations were categorized into two primary types:
- Mutations altering p53 transcriptional activity: These mutations impaired the overall function of p53. This type of mutation is suggested to cause broader resistance to all agents within the same therapeutic class.
- Mutations modifying the Y220C pocket: These mutations potentially disrupted rezatapopt's ability to bind to its target cavity. This type of resistance may be more drug-specific and potentially addressable with next-generation Y220C reactivators that employ different modes of action.
Future Directions: Overcoming Resistance
Ferran Fece de la Cruz, an instructor at the Krantz Family Center for Cancer Research at the Mass General Brigham Cancer Institute, commented on the significance of the findings:
"These findings establish a molecular basis for therapeutic failure in rezatapopt-treated patients. The study provides clinical evidence that on-target secondary TP53 mutations can lead to acquired resistance."
The researchers suggest that these insights encourage further investigation into next-generation agents or combination therapies aimed at delaying or overcoming the emergence of resistance. Further studies involving larger patient cohorts are considered necessary to fully evaluate the various forms of acquired drug resistance.