Tumor-specific transcriptional targeting of suicide gene therapy

Area of Science:

• Oncolytic Virotherapy
• Gene Therapy
• Molecular Oncology

Background:

• Tissue-specific promoters often exhibit weak activity, limiting their use in targeted gene expression for cancer therapy.
• Enhancing promoter strength while maintaining tumor specificity is crucial for effective gene therapy vectors.

Purpose of the Study:

• To develop a recombinant adenovirus with a binary promoter system to amplify a tumor-specific promoter (CEA) for enhanced suicide gene expression (HSV-tk).
• To evaluate the in vitro and in vivo efficacy and toxicity of the novel vector (ADV/binary-tk) compared to a control vector (ADV/RSV-tk).

Main Methods:

• Constructed a recombinant adenovirus (ADV/binary-tk) where a CEA promoter drives a transactivator, which then activates a minimal promoter for HSV-tk expression.
• Assessed in vitro cell killing comparing ADV/binary-tk with ADV/RSV-tk (constitutive promoter).
• Utilized noninvasive nuclear imaging with [131I]-FIAU to monitor in vivo HSV-tk gene expression and biodistribution in tumors and liver.

Main Results:

• ADV/binary-tk demonstrated CEA-specific, potent in vitro cell killing, comparable or superior to ADV/RSV-tk.
• [131I]-FIAU accumulation was localized to CEA-positive tumors after ADV/binary-tk injection, with less spread to liver tissue than ADV/RSV-tk.
• Both vectors showed similar efficacy against liver metastases, but ADV/binary-tk exhibited significantly reduced systemic toxicity in vivo.

Conclusions:

• The novel amplified CEA-driven suicide gene therapy vector (ADV/binary-tk) effectively enhances weak tissue-specific promoters for tumor-restricted gene expression.
• This binary promoter system offers an improved therapeutic index, demonstrating significant potential for targeted cancer gene therapy.
• The findings provide a proof of principle for amplifying tissue-specific promoters to overcome limitations in current gene delivery strategies for cancer treatment.