A designed equine herpes thymidine kinase (EHV4 TK) variant improves ganciclovir-induced cell-killing

Area of Science:

• Biochemistry
• Molecular Biology
• Gene Therapy

Background:

• The ganciclovir (GCV)/herpes simplex virus thymidine kinase (HSV1 TK) system is a widely studied suicide gene therapy approach.
• Limitations exist in the GCV/HSV1 TK system, prompting research into alternative thymidine kinase (TK) variants.

Purpose of the Study:

• To enhance the cytotoxic profile of the GCV/equine herpes virus-4 thymidine kinase (EHV4 TK) system.
• To engineer EHV4 TK through structure-guided mutagenesis to preferentially phosphorylate GCV over its natural substrate, deoxythymidine (dT).

Main Methods:

• Structure-guided mutagenesis of EHV4 TK.
• Steady-state kinetic analysis.
• Genetic complementation in thymidine kinase-deficient Escherichia coli.
• Isothermal titration calorimetry.
• Generation of HEK 293 stable cell lines expressing EHV4 TK mutants and wild-type EHV4 TK.
• Analysis of GCV-induced cell killing.

Main Results:

• The EHV4 TK S144H-GFP mutant demonstrated a preferential phosphorylation of GCV compared to deoxythymidine (dT).
• This mutant conferred significantly increased GCV-induced cytotoxicity in HEK 293 cells compared to wild-type EHV4 TK.
• Kinetic and biophysical analyses supported the altered substrate specificity of the mutant enzyme.

Conclusions:

• The engineered EHV4 TK S144H-GFP mutant represents a promising advancement for suicide gene therapy.
• This modified enzyme exhibits improved GCV phosphorylation and enhanced GCV-induced cytotoxicity, potentially leading to more effective cancer treatments.