GTMB 7 - Gene Therapy & Molecular Biology

Gene Therapy and Molecular Biology Vol 7, page 261(Tb), can serve as a suicide gene, as it convertsallopurinol, a purine analogue, to a cytotoxic metabolite.Retrovirus-mediated TbHGPRT expression can sensitizefive NSCLC cell lines to allopurinol to levels 2.1 to 7.6higher than control values, and represents a practicalapproach in lung cancer therapy (Trudeau et al, 2001).2. Thyroperoxidase-mediated retention ofradioiodideIn much the same way as such gene-prodrugtreatment strategy, the sodium iodide symporter (NIS)gene, that allows rapid internalization of iodide into cells,can be used to obtain radionuclide accumulation byradioactive iodide administration for tumor cell killing. Acombination of the NIS gene and the thyroperoxidase(TPO) gene, which can catalyze iodination of protein,resulted in an augmentation of radioiodide uptake andretention and subsequent effective tumor cell death intransfected NSCLC cell lines (Huang et al, 2001).Although there have so far been few reports on thetreatment of lung cancer with NIS gene, it promises to bean effective approach for cancer treatment.IV. AntiangiogenesisTargeting angiogenesis is an attractive strategy totreat cancer. As progressive growth and metastasis of solidtumors is dependent on the formation of new blood vessels(Folkman, 1971), antiangiogenic therapy is a broadspectrum treatment for cancer. Two strategies used in thedevelopment of antiangiogenic agents involve therapywith endogenous inhibitors of angiogenesis as well as theinhibition of proangiogenic factors.A. Endogenous inhibitors of angiogenesis1. EndostatinEndostatin, a 20-kDa C-terminal fragment ofcollagen XVIII (O’Reilly et al, 1997), is the leadingmember of a class of physiologic inhibitors ofangiogenesis with potent antitumor activity. Boehm et al,(1997) have also reported that when three different mousetumors were subjected to chronic, intermittent therapywith endostatin, there were no traces of acquiredresistance. To establish a constant therapeuticconcentration of circulating endostatin, investigations intoendogenetic expression by a gene therapy approach havebeen prompted. Many viral vectors are actively understudy in endostatin delivery. After systemic administrationof a recombinant adenovirus to nude mice, persistent highserum levels of murine endostatin were achieved. Theendostatin vector treatment not only resulted in significantreduction of the growth rates and volumes of Lewis lungcarcinoma, but also completely prevented the formation ofpulmonary micrometastases (Sauter et al, 2000).Intramuscular injection of adeno-associated viral vectorexpressing human endostatin led to a sufficient level ofserum endostatin to inhibit angiogenesis and tumor growth(Shi et al, 2002). High-level endostatin was also detectedin the vasculature of mice in which hematopoietic stemcells were implanted after being transduced by retrovirusencoding a secretable form of endostatin (Pawliuk et al,2002). In addition, Lentiviral vector (Shichinohe et al,2001) and Semliki Forest viral vector (Yamanaka et al,2001) have been developed to express endostatin, andwere first evaluated in T24 human bladder cancer cells andmice bearing B 16 brain tumor respectively. Some othernonviral transgene delivery approaches also involveendostatin transfer. Utilizing cationic vector, Nakashima etal, (2003) found that intravenous endostatin gene deliverysignificantly inhibited murine lung metastases.Intramuscular injection of polymerized endostatin plasmidinhibited syngeneic tumor growth and lung metastases inmice (Blezinger et al, 1999), and was also shown to inhibitmurine metastatic brain tumor growth (Oga et al, 2003).When electroporation was used to enhance endostatin genetransfer into muscle tissues, the electrotransfer resulted inreduced numbers of experimental melanoma metastases inthe lungs, while intratumoral electrotransfer significantlyinhibited tumor growth (Cichon et al, 2002). Recently,engineered Bifidobacterium, a type of nonpathogenicanaerobic bacterial vector, was applied to bear endostatinby Li X et al, (2003), who demonstrated that vectorscentered in tumors only, and inhibited local tumor growthafter delivery by tail vein injection.2. AngiostatinAngiostatin is another specific endogenous inhibitorof endothelial cell proliferation. It is an internal fragmentof plasminogen, isolated from the urine of mice bearingLewis lung carcinoma (LLC) (O’Reilly et al, 1994).Tanaka et al, (1998) have demonstrated that retroviral andadenoviral vectors transducing angiostatin cDNA can beused to inhibit endothelial cell growth in vitro andangiogenesis in vivo. In a pulmonary metastatic breastcancer model, the delivery of Ad-angiostatin (1x10 9 pfu)to the lung significantly delayed tumor growth, asmeasured by the number of visible surface tumor nodules(Gyorffy et al, 2001). Intratumoral injection of a high-titerAAV-angiostatin vector effectively suppressed tumors andresulted in long-term survival in 40% of a group of treatedrats, whereas the control AAV-GFP vector had notherapeutic benefits (Ma et al, 2002a). As angiostatin is anendogenous internal fragment of plasminogen, effectivesystemic gene therapy could be obtained by angiostatingene transfer. Studies on liposome-coated plasmidcarrying murine and human angiostatin showed that repeatintraperitoneal vector injection resulted in tumor growthsuppression and delay in the onset of tumor growth to thesame degree as intratumoral injection in a nude micemelanoma xenograft model (Rodolfo et al, 2001). Genetransfer of AAV-angiostatin via the portal vein led tosignificant suppression of the growth of both nodular andmetastatic EL-4 lymphoma tumors established in the liver,and prolonged the survival time of the mice (Xu et al,2003). Similar long-term therapeutic effects have alsobeen demonstrated by Ma et al, (2002b), who used a singlei.m. injection of AAV-angiostatin to effectively suppresshuman glioma growth in the brain of nude mice. Thegeneration of angiostatin from endogenous plasminogen261