Bystander-mediated regression of murine neuroblastoma via retroviral transfer of the HSV-TK gene

Immunotherapy and gene therapy as novel treatments for cancer

The immune system interacts closely with tumors during the disease development and progression to metastasis. The complex communication between the immune system and the tumor cells can prevent or promote tumor growth. New therapeutic approaches harnessing protective immunological mechanisms have recently shown very promising results. This is performed by blocking inhibitory signals or by activating immunological effector cells directly. Immune checkpoint blockade with monoclonal antibodies directed against the inhibitory immune receptors CTLA-4 and PD-1 has emerged as a successful treatment approach for patients with advanced melanoma. Ipilimumab is an anti-CTLA-4 antibody which demonstrated good results when administered to patients with melanoma. Gene therapy has also shown promising results in clinical trials. Particularly, Herpes simplex virus (HSV)-mediated delivery of the HSV thymidine kinase (TK) gene to tumor cells in combination with ganciclovir (GCV) may provide an effective suicide gene therapy for destruction of glioblastomas, prostate tumors and other neoplasias by recruiting tumor-infiltrating lymphocytes into the tumor. The development of new treatment strategies or combination of available innovative therapies to improve cell cytotoxic T lymphocytes trafficking into the tumor mass and the production of inhibitory molecules blocking tumor tissue immune-tolerance are crucial to improve the efficacy of cancer therapy.

NT-polyplex: a new tool for therapeutic gene delivery to neuroblastoma tumors

Neurotensin (NT)-polyplex is a nonviral system for the targeted gene delivery to cells that express and internalize the high-affinity NT receptor (NTSR1). In hemiparkinsonian rats, we previously demonstrated the morphological and functional recovery from dopaminergic neurodegeneration using the NT-polyplex as a vehicle to transfect a neurotrophic gene. The main objective of this work was to demonstrate the feasibility of NT-polyplex to transfect reporter or therapeutic genes into neuroblastoma tumors through the blood stream or by intratumoral injection. N1E-115 cells known to express NTSR1 were allografted into athymic mice to generate the neuroblastoma tumor model. Both routes of administration allowed the NT-polyplex to reach and transfect tumoral cells. A low transgene expression was also detected in intestinal tract cells only after the injection into the blood stream. The transfection of the thymidine kinase (HSVTK) suicide gene followed by ganciclovir (GCV) treatment decreased the size and weight of neuroblastoma tumors by 30-50% and increased apoptosis compared to controls. This study shows the potential of the NT-polyplex as specific gene-transfer system for NTSR1 cancer cells.

Inhibitory effect of HSV1-TK suicide gene system induced by retrovirus on murine transplanted hepatocarcinoma

AIM: To establish the HSV1-tk/GCV tumor suicide system by constructing a recombinant retroviral vector, and to determine the inhibitory effect of this system on murine transplanted hepetocarcinoma in vivo.

METHODS: The HSV-tk cDNA was orientationally cloned into the retroviral vector plasmid (pLXSN) using DNA recombinant technique. The recombinant plasmid (pLXSN-tk) was mixed with PolyFect Transfection reagent and was transfected into the packaging cell line PT67. Then, a stable virus-producing packaging cell lines was obtained by G418 screening, and was transfected into murine hepatocarcinomatous H22 cells. An anti-G418 clone named H22/tk was obtained by G418 screening. H22/tk and H22 wild type cells were mixed in a proportion of 1∶4. Then the mixed cells were inoculated subcutaneously into Kunming mice. The tumor-bearing mice were randomly divided into model control group and GCV treated group, and the tumor inhibitory effect was observed by measuring tumor sizes.

RESULTS: HSV1-tk was inserted into recombinant plasmid pLXSN-tk successfully. The anti-G418 positive cell strain PT67/tk, which could excrete retrovirus recombinant, was obtained. The titer of the virus was 4×10⁷cfu/L. After the infection of H22, the anti-G418 positive cell strain H22/tk was also obtained. The sensibility to GCV showed in H22/tk cells was much higher than that in H22. Nearly all the cells lysed and became granule-like after treated with GCV (1 000 mg/L) for 72 h. The tumor growth in the GCV treated group was significantly inhibited as compared with that in the control group. There was no significant difference in tumor size between the two groups before the mice were treated with GCV. But at the 8^th, 10^th, 12^th, 14^th day after treatment with GCV, the tumor sizes in the GCV treated group were obviously decreased as compared with those in the control group (231±155 mm³vs 356±205 mm³, t = -2.25, P = 0.03; 413±252 mm³vs 635±382 mm³, t = -2.14, P = 0.04; 592±420 mm³vs 963±580 mm³, t = -2.38, P = 0.02; 939±847 mm³vs 1 509±1 105 mm³, t = -1.92, P = 0.06),and the tumor inhibitory rates were 35.0%, 35.0%, 38.5% and 37.8%, respectively.

CONCLUSION: The recombinant retrovirus expressing HSV1-tk is obtained successfully, and the HSV1-tk/GCV suicide gene system shows marked inhibitory effect on murine transplanted hepatocarcinoma.

Antitumor effects and radiosensitization of cytosine deaminase and thymidine kinase fusion suicide gene on colorectal carcinoma cells

AIM

To investigate the killing effect and radiosensitization of double suicide gene mediated by adenovirus on colorectal carcinoma cells.

METHODS

Colorectal carcinoma cell line SW480 was transfected with adenovirus expression vector containing cytosine deaminase (CD) and thymidine kinase (TK) fusion gene. The expression of CD-TK fusion gene was detected by reverse transcriptase-polymerase chain reaction. The toxic effect of ganciclovir (GCV) and 5-fluorocytosine (5-FC) on infected cells was determined by MTT assay. The radiosensitization of double suicide gene was evaluated by clonogenic assay.

RESULTS

After prodrugs were used, the survival rate of colorectal carcinoma cells was markedly decreased. When GCV and 5-FC were used in combination, the cytotoxicity and bystander effect were markedly superior to a single prodrug (chi2 = 30.371, P<0.01). Both GCV and 5-FC could sensitize colorectal carcinoma cells to the toxic effect of radiation, and greater radiosensitization was achieved when both prodrug were used in combination.

CONCLUSION

CD-TK double suicide gene can kill and radiosensitize colorectal carcinoma cells.