Increased anti-tumor effect by a combination of HSV thymidine kinase suicide gene therapy and interferon-gamma/GM-CSF cytokine gene therapy in CT26 tumor model

Abstract

The potential therapeutic benefit of introducing IFN-gamma and GM-CSF genes in combination with the HSVtk suicide gene into subcutaneously implanted CT26 tumor cells was compared with that from each treatment alone. Cells, unmodified or retrovirally transduced with HSVtk or IFN-gamma/GM-CSF genes, were inoculated subcutaneously into syngeneic BALB/c mice in various combinations. HSVtk gene, with intraperitoneal ganciclovir treatment, reduced tumor volume by 81% at locally inoculated tumor sites (p < 0.01) and by 25% at distantly inoculated tumor sites (p = 0.052). IFN-gamma/GM-CSF genes showed a 56% tumor volume reduction at local tumor sites (p < 0.01) and 15% volume reduction at remote tumor sites, although this was not statistically significant. The combination of HSVtk (with GCV) and IFN-gamma/GM-CSF genes showed an 81% volume reduction at local tumor sites (p < 0.01) and a 43% volume reduction at remote tumor sites (p < 0.01). Thus, the combination of HSVtk and IFN-gamma/GM-CSF gene therapy produced greater therapeutic efficacy than either treatment alone.

Fig. 1

Expression of MHC class I molecules in untransduced or transduced CT26 cells. INF-γ transduced cells only showed increased expression. Cells were stained for FITC-labeled H-2 K^dD^d. MFI, mean fluorescence intensity in region C.

Fig. 2

In vitro growth of untransduced or transduced CT26 cells used in animal study. There is no difference of growth rate in different cell lines.

Fig. 3

Tumor volumes of transduced CT26 cells at locally inoculated tumor. (A) control vs. suicide gene therapy, (B) control vs. cytokine gene therapy, (C) control vs. combined gene therapy. Differences were significant: ^*p<0.05, ^†p<0.01. Results were expressed as mean±SD.

Fig. 4

Tumor volumes of untransduced CT26 cells at distantly inoculated tumor. (A) control vs. suicide gene therapy, (B) control vs. cytokine gene therapy, (C) control vs. combined gene therapy. Differences were significant: ^*p=0.052, ^†p<0.05, ^‡p<0.01. Results were expressed as mean±SD.

Fig. 5

The therapeutic effects of HSVtk and cytokines expression on tumor growth at distantly inoculated tumor.