Subcutaneous or intrahepatic injection of suicide gene modified tumour cells induces a systemic antitumour response in a metastatic model of colon carcinoma in rats

Abstract

Background: Suicide gene therapy consists of the transfer into tumour cells of a "suicide" gene that can convert a non-toxic compound into a lethal drug. Expression of the cytosine deaminase gene leads to the conversion of the non-toxic compound 5-fluorocytosine to 5-fluorouracil. We have recently shown that "suicide cell based vaccination" consisting of intrahepatic injection of cytosine deaminase expressing colon cancer cells followed by 5-fluorocytosine treatment induces regression of a distant wild-type liver tumour in rats.

Aims: This study was conducted to test if (i) a distant bystander effect on a liver tumour can be induced after subcutaneous suicide cell based vaccination and (ii) suicide cell based vaccination is efficient in limiting tumour dissemination to extrahepatic compartments.

Methods: An aggressive variant of rat colon carcinoma cells was selected after successive passages in vitro. Rats carrying an experimental liver "metastasis" generated by injection of these cells were vaccinated by subcapsular or subcutaneous injection of cytosine deaminase expressing cells followed by 5-fluorocytosine treatment.

Results: Subcutaneous and subcapsular vaccination induced 70% regression in the median volume of the pre-established liver tumour (p=0.001) and abolished tumour dissemination compared with control animals.

Conclusions: This study has compared for the first time the efficiency of subcutaneous and intrahepatic suicide cell based vaccination in a metastatic colorectal carcinoma model in rats. The results indicate that both modes of vaccination are equally efficient in inducing a systemic antitumour response, suggesting that this strategy is a powerful approach against the development and dissemination of metastatic colon carcinoma.

Figure 1

(A) Intrahepatic suicide cell based vaccination in an advanced liver metastasis model. Left: five days after subcapsular PROb tumour cell injection in the right liver lobe, all rats received subcapsular injection of PRObCD tumour cells in the left liver lobe. Animals were then either treated (+; n=7) or not treated (−; n=7) with 5-fluorouracil (5-FC) for 30 days. The volumes of the PROb and PRObCD liver tumours in each group at the end of treatment are presented for the control and treated groups. Right: five days after unique subcapsular PROb tumour cell injection in the right liver lobe, rats were treated with saline or 5-FC for 30 days. The volumes of the PROb liver tumours in both groups at the end of the treatment are presented for the saline treated and 5-FC treated groups. (B) Subcutaneous suicide cell based vaccination in an advanced liver metastasis model. Five days after subcapsular PROb tumour cell injection in the right liver lobe, all rats received subcutaneous injection of PRObCD tumour cells. Animals were then either treated (n=9) or not treated (n=10) with 5-FC for 30 days. The volumes of the hepatic PROb and subcutaneous PRObCD tumours in each group at the end of the treatment are presented for the control and treated groups.

Figure 2

(A) Suicide cell based vaccination protocol. Five days after intrahepatic wild-type tumour cell injection, rats were randomised to one of three groups and treated as indicated. (B) Comparison of the therapeutic effect of subcapsular or subcutaneous vaccination on a pre-existing wild-type liver tumour. Volumes of PROb liver tumours in each group at the end of the treatment are presented for the control group, subcapsular vaccination group, and subcutaneous vaccination group.

Figure 3

(A) Wound metastasis observed in control and vaccinated rats. The tumours are indicated by arrows. (B) Effect of suicide cell based vaccination on wound tumours. The volumes of the wound tumour nodules in each group are presented for the control group, subcapsular vaccination group, and subcutaneous vaccination group.