Shu Hsia Chen

Tumor-specific transcriptional targeting of suicide gene therapy.

Transcriptional targeting of gene expression has been plagued by the weakness of tissue-specific promoters. Thus, to increase promoter strength while maintaining tissue specificity, we constructed a recombinant adenovirus containing a binary promoter system with a tumor-specific promoter (CEA; carcinoembryonic antigen) driving a transcription transactivator, which then activates a minimal promoter to express a suicide gene (HSV-tk; herpes simplex virus thymidine kinase). This ADV/binary-tk induced equal or greater cell killing in a CEA-specific manner in vitro compared with the CEA-independent killing of a vector with a constitutive viral promoter driving HSV-tk (ADV/RSV-tk). To monitor adenovirus-mediated HSV-tk gene expression in vivo, we employed noninvasive nuclear imaging using a radioiodinated nucleoside analog ([131I]-FIAU) serving as a substrate for HSV-tk. [131I]-FIAU-derived radioactivity accumulated after intratumoral injection of ADV/binary-tk only in the area of CEA-positive tumors with significantly less spread to the adjacent liver tissue than after administration of the universally expressed ADV/RSV-tk. Both viruses exhibited similar antitumor efficacy upon injection of liver metastases. Importantly, in vivo dose escalation studies demonstrated significantly reduced toxicity after intravenous administration of ADV/binary-tk versus ADV/RSV-tk. In summary, the increased therapeutic index of this novel, amplified CEA-driven suicide gene therapy vector is a proof of principle for the powerful enhancement of a weak tissue-specific promoter for effective tumor restricted gene expression.

NK and CD8+ T cell-mediated eradication of poorly immunogenic B16-F10 melanoma by the combined action of IL-12 gene therapy and 4-1BB costimulation.

In previous reports, systemic administration of a stimulatory monoclonal antibody directed against the 4‐1BB receptor had no effect on survival or tumor burden in mice inoculated with the poorly immunogenic B16‐F10 melanoma. We combined IL‐12 gene transfer with 4‐1BB costimulation to explore a previously noted cooperative anti‐tumor effect against this model tumor. We hypothesize that the innate immune response mediated by IL‐12‐activated natural killer (NK) cells initiates the activation of the immune system, leading to the priming of T cells, whereas 4‐1BB costimulation enhances the function of primed tumor‐specific T cells. The effect of the combination therapy on the growth of subcutaneous (s.c.) tumors and pulmonary metastasis was examined. The combination therapy significantly retarded the growth of subcutaneously‐inoculated tumors, and 50% of tumor‐bearing mice survived with complete tumor regression. In contrast, neither IL‐12 gene transfer nor anti‐4‐1BB antibody administration alone was as effective. Enhanced CTL activity against both B16‐F10 tumor cells and TRP‐2‐pulsed EL4 syngeneic tumor cells was observed in tumor‐bearing animals treated with the combination therapy 2 weeks after treatment and, in long‐term survivors from this combination therapy, at >120 days. In a pulmonary metastatic model, only the combination therapy generated significant protection against metastasis. In vivo depletion of NK or CD8+ but not CD4+ subsets eliminated the protective immunity. Furthermore, NK cell depletion significantly reduced both tumor‐specific CTL activity and the number of tumor‐specific IFN‐γ‐producing cells, suggesting that this synergistic effect requires the participation of both NK and CD8+ T cells.

Adenoviral-mediated herpes simplex virus thymidine kinase gene transfer: Regression of hepatic metastasis of pancreatic tumors

Pancreatic cancer is the fifth leading cause of cancer death in the United States. Most patients have obvious metastases or locally advanced disease at the time of presentation. Surgical resection does not significantly change the clinical outcome. Combination chemotherapy induces a partial response but overall survival remains low. The aim of this study was to evaluate the feasibility of adenovirus-mediated suicide gene transduction as a therapeutic approach for pancreatic cancer. A cell line was established from a murine pancreatic ductal adenocarcinoma and intrahepatic tumors were generated by inoculation of pancreatic cancer cells into the left lateral liver lobe. Transduction efficiency was characterized in vitro and in vivo. Intrahepatic tumors were treated by intratumoral adenovirus injection in combination with intraperitoneal administration of ganciclovir. Adenovirus-mediated herpes simplex virus (HSV)-thymidine kinase (tk) gene expression followed by ganciclovir treatment was highly efficient in inhibiting pancreatic cancer cell proliferation in vitro. The proliferation of nontransduced cells was significantly reduced in the presence of HSV-tk expressing cells. Intrahepatic inoculation of pancreatic cancer cells leads to successful formation of solid adenocarcinomas in syngeneic recipients. Ad.RSV-tk injection of the tumor followed by intraperitoneal ganciclovir application caused highly significant tumor volume reduction and necrosis. These results indicate that transduction of the HSV-tk gene followed by ganciclovir is highly efficient for growth inhibition of hepatic metastases of pancreatic carcinoma.

T cell activation with systemic agonistic antibody versus local 4-1BB ligand gene delivery combined with interleukin-12 eradicate liver metastases of breast cancer

We have shown that interleukin-12 (IL-12) generated a strong, albeit transient, anti-tumor response, mostly mediated by natural killer (NK) cell. T cell participation, in addition to NK cells, was essential for persistence of the anti-tumor response. Ligation of 4-1BB, a co-stimulatory receptor expressed on activated T cells, is known to amplify T cell-mediated immunity. In this study, we compared the effect of a systemically delivered agonistic anti-4-1BB monoclonal antibody (anti-4-1BB mAb) with intra-tumoral adenoviral-mediated gene transfer of the 4-1BB ligand (ADV/4-1BBL) to liver metastases in a syngeneic animal model of breast cancer. Both treatments induced a dramatic regression of pre-established tumor. When combined with intra-tumoral delivery of the IL-12 gene, both anti-4-1BB mAb and ADV/4-1BBL were synergistic and led to survival rates of 87% and 78%, respectively. The anti-tumor immunity is mainly mediated by CD4+ T cells in IL-12 plus 4-1BB ligand-treated animals, and CD8+ T cells in IL-12 plus anti-4-1BB mAb-treated animals. However, only long-term survivors after treatment with IL-12 and 4-1BBL genes have showed significantly potent, systemic, and tumor-specific T cell-mediated immunity.

A novel bystander effect involving tumor cell-derived Fas and FasL interactions following Ad.HSV-tk and Ad.mIL-12 gene therapies in experimental prostate cancer

To enhance the NK population induced by Herpes Simplex virus thymidine kinase (HSV-tk) gene transduction and ganciclovir (GCV) treatment, adenovirus-mediated (Ad) expression of IL-12 was added to Ad.HSV-tk + GCV as combination gene therapy. This approach resulted in improved local and systemic growth suppression in a metastatic model of mouse prostate cancer (RM-1). In vitro assay of tumor infiltrating lymphocytes noted superior lysis of both RM-1 and Yac-1 targets with combination therapy, but in vivo depletion of NK cells only negatively impacted on systemic growth inhibition. TUNEL assay of primary tumors noted induction of apoptosis between two and four times higher than controls lasting for 6–8 days post-vector injection. After demonstrating that Ad.HSV-tk/GCV and Ad.mIL-12-induced IFN-γ independently up-regulated expression of FasL and Fas, respectively, studies examined tumor cell-mediated death through Fas/FasL-induced apoptosis as a mechanism of primary tumor growth suppression. In vitro, combination therapy at low vector doses resulted in synergistic growth suppression, which could be negated by the addition of anti-FasL antibody. In vivo co-inoculation of an adenovirus expressing soluble Fas resulted in combination therapy-treated tumors, which were three times larger than expected, and a reduction in apoptosis to baseline levels. In FasL knockout mice, combination therapy maintained the superior results experienced in wild-type mice, indicating that tumor cell, not host cell FasL, was responsible for Fas transactivation. Therefore, the combination of Ad.HSV-tk/GCV + Ad.mIL-12 results in enhanced local growth control via apoptosis due to tumor cell expression of Fas and FasL and improved anti-metastatic activity secondary to a strong NK response.

Gene therapy of metastatic colon carcinoma: Regression of multiple hepatic metastases by adenoviral expression of bacterial cytosine deaminase

Colon carcinoma accounts for 20% of deaths due to malignancies in the Western world. Once metastases occur, therapeutic options are limited, with an approximate 5-year survival of only 5%. To investigate the potential of new gene therapeutic approaches, a hepatic micrometastasis model of colon carcinoma in BALB/c mice was established. Inoculation of syngeneic MCA26 colon carcinoma cells into the spleens of 18- to 20-week-old mice resulted in the formation of multiple hepatic metastases. Selective transduction of developing hepatic metastases was demonstrated using a β-galactosidase-expressing recombinant adenovirus. Cytosine deaminase (CD) can metabolize 5-fluorocytosine into the chemotherapeutic reagent 5-fluorouracil (5FU). The antitumoral potential of this suicide gene therapy approach was explored by systemic application of a recombinant replication-deficient adenovirus encoding for the bacterial CD gene under the control of the cytomegalovirus promoter (Ad.CMV-CD). Injection into the tail vein of tumor-bearing mice resulted in delayed tumor growth with significant reduction in hepatic metastases. The potential of this experimental approach for possible future clinical applications was evaluated by investigating adenoviral transduction efficiency, 5FU sensitivity, and 5-fluorocytosine-dependent Ad.CMV-CD toxicity in a variety of human colon cancer cell lines. Although the murine cell lines MCA26 and CC36 were highly sensitive to 5FU, the human colon cancer cell lines showed a 1–100 times higher resistance to 5FU. Specific Ad.CMV-CD toxicity correlates with 5FU toxicity. Transduction efficiency in human colon carcinoma cell lines was shown to be 10–1700 times higher compared with murine cell lines, thus compensating for 5FU resistance. In conclusion, suicide gene therapy using CD may be promising as an adjuvant treatment regimen for hepatic micrometastases of human colon carcinoma.

Intratumoral Delivery of Adenovirus-Mediated Interleukin-12 Gene in Mice with Metastatic Cancer in the Liver

Clinical trials of recombinant human interleukin-12 (rhIL-12) delivered by intravenous administration have shown dose-limiting toxicities with limited tumor responses at the doses tested. We have previously reported that intratumoral injection of an adenovirus vector expressing murine interleukin-12 (Adv.RSV-mIL-12) was effective in inducing antitumor immune responses, tumor regression, and long-term survival in mice with established metastatic cancer in the liver. We now report additional studies in the same murine tumor model to assess the safety of intratumoral Adv.RSV-mIL-12 injection. At vector doses that were previously shown to be therapeutically effective, no inflammation in the liver or lungs, and no significant elevations in serum creatinine and aminotransferases were seen after vector injection. Serum elevations of IL-12 and interferon-gamma (IFN-gamma) were 17- and 19-fold lower than peak levels after intravenous recombinant IL-12 at the maximal tolerated dose in clinical trials. No elevations in serum proinflammatory cytokines (interleukin-6, tumor necrosis factor-alpha) were noted up to 2 weeks after vector injection. No systemic dissemination of the vector was detected on polymerase chain reaction (PCR) assays at therapeutically effective vector doses. At higher supratherapeutic vector doses of Adv.RSV-mIL-12, however, inflammation in the liver and lungs with elevation in serum aminotransferases were seen, but not in controls injected with the equivalent particle number of an empty adenoviral vector. These results support the cautious testing in patients with hepatic metastases of adenovirus mediated IL-12 gene delivery by intratumoral injection.