Abrogation of microsatellite-instable tumors using a highly selective suicide gene/prodrug combination

Area of Science:

• Oncology
• Molecular Biology
• Cancer Gene Therapy

Background:

• A significant proportion of human colorectal and endometrial cancers exhibit DNA mismatch repair (MMR) deficiency.
• This deficiency leads to microsatellite instability (MSI), characterized by length alterations in simple sequence repeats.
• Targeting MSI is a key strategy for developing selective cancer therapies.

Purpose of the Study:

• To develop a highly selective gene therapy for MMR-deficient tumors by exploiting the MSI phenotype.
• To engineer a novel suicide gene that is selectively activated in MSI cancer cells.

Main Methods:

• A VP22FCU1 suicide gene was mutated by inserting an out-of-frame microsatellite sequence.
• This mutated gene was introduced into MMR-deficient cancer cells.
• The efficacy of the prodrug 5-fluorocytosine (5-FC) in inducing cytotoxicity and bystander effects was evaluated.
• A mouse model of MMR-deficient tumors was used to assess in vivo therapeutic effects.

Main Results:

• Expression of the full-length suicide protein was observed in MSI cells due to frameshift reversion within the inserted microsatellite.
• Treatment with 5-FC resulted in potent cytotoxicity and significant bystander effects in MSI cells.
• MMR-deficient tumors in mice showed strong remission following 5-FC treatment, with no apparent systemic toxicity.

Conclusions:

• The engineered suicide gene/prodrug system demonstrates high selectivity and potency for MMR-deficient cancers.
• This conditional gene therapy approach holds promise for the treatment and prevention of human MMR-deficient cancers.