Farnesyl transferase inhibitor resistance probed by target mutagenesis

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Tyrosine kinase inhibitor resistance is often mediated by oncoprotein mutations (e.g., BCR/ABL in CML).
• The extent to which normal cellular targets of chemotherapy evolve resistance via mutation is less understood.
• Farnesyl protein transferase inhibitors block protein prenylation, impacting cell proliferation.

Purpose of the Study:

• To investigate if normal cellular enzymes develop drug resistance through mutation.
• To identify mutations conferring resistance to lonafarnib, a farnesyl protein transferase inhibitor.
• To assess the clinical relevance of identified mutations in patients.

Main Methods:

• In vitro screening for lonafarnib resistance.
• Identification and characterization of mutations in farnesyl protein transferase.
• Analysis of patient samples treated with imatinib and lonafarnib.
• Cell culture experiments to confirm the proliferative advantage of mutants.

Main Results:

• Nine mutations clustered around the lonafarnib binding site were identified in vitro.
• Farnesyl protein transferase mutations found in patients matched residues from the in vitro screen.
• Substitutions at Y361 were present in pre-treatment patient samples.
• Identified mutants conferred a proliferative advantage to leukemia cells in culture.

Conclusions:

• In vitro mutagenesis of normal cellular enzymes can predict resistance mutations to novel agents.
• Specific farnesyl protein transferase mutations may confer a pre-existing proliferative advantage in leukemia.
• This approach can guide the development of strategies to overcome chemotherapy resistance.