Tipifarnib Inhibits HRAS-Driven Dedifferentiated Thyroid Cancers

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapeutics

Background:

• HRAS is a RAS oncoprotein uniquely susceptible to farnesyltransferase inhibitors (FTIs).
• FTI therapy for HRAS-driven cancers remains clinically underexploited.
• Thyroid cancers driven by HRAS present a potential target for FTI intervention.

Purpose of the Study:

• To evaluate the efficacy of the FTI tipifarnib in Hras-driven thyroid cancer models.
• To investigate mechanisms of resistance to tipifarnib treatment.
• To identify combination strategies to overcome FTI resistance.

Main Methods:

• Treatment of mice with Hras-driven thyroid cancer using tipifarnib.
• Assessment of tumor regression, survival, and resistance mechanisms.
• In vitro and in vivo testing of combination therapies (tipifarnib with RTK or MEK inhibitors).
• Whole-exome sequencing of resistant tumors to identify genetic alterations.

Main Results:

• Tipifarnib treatment led to sustained tumor regression and improved survival in mice.
• Acquired resistance to tipifarnib was observed, associated with RAS-MAPK pathway reactivation.
• Combination therapy with the MEK inhibitor AZD6244 significantly improved outcomes compared to monotherapy.
• NF1 nonsense mutations and GNAS activating mutations were identified as drivers of acquired resistance.

Conclusions:

• Targeting Ras membrane association with FTIs is a feasible strategy for HRAS-driven cancers.
• Combination therapy, particularly with MEK inhibitors, can overcome adaptive resistance.
• NF1 and GNAS mutations are key mechanisms conferring acquired resistance to HRAS inhibition.