GTMB 7 - Gene Therapy & Molecular Biology

Cai et al: Lung cancer gene therapyantiangiogenic gene therapy; and immunotherapy. Clinicaltrials have already been initiated. The number of approvedprotocols in clinical trials has increased, and at least 50%are designed for cancer (Folkman, 1998). Nervethless, acentral challenge is perfecting methods for deliveringtherapeutic genes to the appropriate cells. The ideal genetransfer systems should be tailored to the specific tissue orcells requiring modification, to the needed duration ofgene action and to the desired physiological effect of thegene product. Practical and theoretical limitationscurrently exist for the application of gene therapy incancer patients, Most of these approaches have yet to passeven the most preliminary clinical tests demonstratingtheir overall safety and efficacy, but these ideas may leadto better cancer treatments in the future.The molecular changes and underlying mechanismsof lung cancer have been continuously identified. Theaccumulation of the progresses may actually offer athorough understanding of the disease and clinical context,and offer many targets for gene therapy. Theimprovements in gene transfer systems offer promise forthe development of an efficient, specific-targeted andnontoxic gene delivery system, and thus there is very goodreason to believe that greater success will be achieved inthe near future.II. Alteration of mutated genesGene alteration therapy is potentially a very powerfultool, targeting intracellular mutant genes of lung tumors.These gene products are specific molecular mediators ofcancer development and progression.A. Tumor suppressor genes1. p53p53 mutations, with frequencies up to 50% inNSCLC and 80% in SCLC, are the most common geneticlesions observed in lung cancers (Salgia et al, 1998).Mitsudomi et al, (2000) have shown by meta-analysis thatp53 mutation or overexpression was an indicator of poorprognosis, especially in patients with adenocarcinoma.Roth et al, (1996) first reported the use of the strategy ofreplacing p53 in the treatment of nine lung cancer patientsby local injection of retroviral vectors encoding wild typep53. Tumor regression was noted in three patients, andtumor growth stabilized in three other patients. In thesecond Phase I trial performed by this group, anadenoviral vector was used. Repeated intratumoralinjections of Ad-p53 appeared to be well tolerated,resulted in transgene expression of wild-type p53, andmediated antitumor activity in a subset of patients withadvanced NSCLC (Swisher et al, 1999). Because thesecompleted studies have demonstrated only modestresponse rates, several protocols have been developed thatcombine the p53 gene transfer approach with othertreatment modalities. No enhanced radiosensitivity ofnormal cells was noted when the ability of Ad-p53 (INGN201) in NSCLC cell lines and human fibroblast cells wascompared (Kawabe et al, 2001).Recently, the same group reported the results of theirPhase II study on 19 patients with NSCLC. The groupfound that intratumoral injection of Ad-p53 (INGN 201) incombination with radiation therapy was well tolerated, andalso demonstrated evidence of tumor regression in primaryinjected tumors. Additionally, they found BAK expressionwas significantly increased 24h after injection of Ad-p53(INGN 201), providing the first demonstration ofinduction of an apoptotic pathway by tumor suppressorgene expression in actual human cancers (Swisher et al,2003). Schuler et al, (1998) reported the results of anotherPhase II trial, in which Ad-p53 gene therapy appeared toprovide no additional benefit in patients receiving first-linechemotherapy for advanced NSCLC. To elucidate thecombined effects of p53 gene transfer, chemotherapy, andradiation therapy on lung cancer growth in vitro and invivo, Nishizaki et al, (2001) evaluated the synergistic,additive, or antagonistic efficacy of these therapeuticagents in four human NSCLC cell lines at the ID50 andID80 levels. Synergistic inhibitory effects on tumor cellgrowth were noted both in an in vitro and a murine modelwith H1299 and A549 xenografts. Using two humancancer cell lines, H157 and H1299, Osaki et al, (2000)evaluated several anticancer agents, and suggested thatcisplatin (CDDP) and an active metabolite of irinotecan(CPT-11) would be suitable candidates for a combinationof chemotherapy and gene therapy for NSCLC.Srivenugopal et al, (2001) demonstrated that enforcedexpression of wild-type p53 curtailed the transcription ofO(6)-methylguanine-DNA methyltransferase (MGMT), aDNA repair protein that confers tumor resistance on manyanticancer alkylating agents. This finding suggests that acombination of MGMT-directed alkylators with the p53gene should achieve improved antitumor efficacy. Severalstudies (see below) have indicated the benefits ofcombination therapy on lung cancer, as one of thefunctions of p53 is to keep the cell from progressingthrough the cell cycle if there is damage to DNA present(Lowe et al, 1993).Since wild type p53 reconstitution was notcompletely effective in all cases, mutants of p53 wereexplored for their ability to prevent p53 inactivation. Ap53 derivative vector, in which the p53 domains bound byits inhibitor (murine double minute-2, MDM2) werereplaced, was significantly more efficient than the p53vector in tumor models overexpressing MDM2. Both invitro and in vivo, a higher inhibition of tumor growth withthe mutant p53 vector correlated with a higher induction ofapoptosis (Bougeret et al, 2000).2. RBAbnormalities of retinoblastoma (RB), consisting ofthe tumor suppressor pRb/p105 and related protein p107and pRB2/p130, are detected in more than 90% of SCLCsand in 15% to 30% of NSCLCs (Forgacs et al, 2001).Immunohistochemical studies of the expression patterns ofthe Rb family members in 235 specimens of lung cancersuggest an independent role for pRB2/p130 in thedevelopment and/or progression of human lung carcinoma(Baldi et al, 1996; 1997). Loss of pRb2/p130 expression is256