Abstract
Prodrug-activating suicide gene therapy (PA suicide gene therapy for short) for cancer is to introduce cancer cells with suicide genes. The enzyme encoded by suicide gene is not toxic but is able to kill cancer cells by converting a non-toxic prodrug into a toxic compound. This approach is a promising cancer gene therapy that could reduce non-specific toxicity to normal tissue. However, there is no quantitative method to evaluate efficacy of suicide gene therapy in preclinical study. The aim of this study is to develop a new method to quantitatively evaluate and compare prodrug-activating suicide gene therapies. This study was carried out on an oral squamous cell carcinoma (OSCC) cell line CAL-27. Suicide genes were integrated into ROSA26 locus of CAL-27 by CRISPR-Cas9. CAL-27 cell lines stably expressing herpes simplex virus-thymidine kinase (TK) or yeast cytosine deaminase (CD) were used to evaluate and compare PA suicide gene therapies. The efficacies of PA suicide gene therapies were quantitatively evaluated from three aspects: effective prodrug concentration, prodrug treatment time, and bystander effect. This method also could be used for different types of suicide gene therapies and different types of cancer. When the prodrug concentration, treatment time, and rate of suicide gene-positive cells (related to bystander effect) are fixed, anti-cancer effects could be quantitatively measured. This information is important for suicide gene therapy preclinical development.