HUMAN GENE THERAPY 12:193–204 (January 20, 2001) Mary Ann Liebert, Inc. Systemic Administration of a Matrix-Targeted Retroviral Vector Is Efficacious for Cancer Gene Therapy in Mice ERLINDA M. GORDON, 1–3 ZHEN HAI CHEN, 1,2 LING LIU, 1,2 MICHELLE WHITLEY, 1,2 LIQIONG LIU, 1,2 DENICE WEI, 4,5 SUSAN GROSHEN, 4,5 DAVID R. HINTON, 6 W. FRENCH ANDERSON, 1,3,5,7 ROBERT W. BEART, JR., 2,5,8 and FREDERICK L. HALL 1,2,8,9 ABSTRACT Targeting cytocidal vectors to tumors and associated vasculature in vivo is a long-standing goal of human gene therapy. In the present study, we demonstrated that intravenous infusion of a matrix (i.e., collagen)-targeted retroviral vector provided efficacious gene delivery of a cytocidal mutant cyclin G1 construct (designated Mx- dnG1) in human cancer xenografts in nude mice. A nontargeted CAE-dnG1 vector (p 5 0.014), a control ma- trix-targeted vector bearing a marker gene (Mx-nBg; p 5 0.004), and PBS served as controls (p 5 0.001). En- hanced vector penetration and transduction of tumor nodules (35.7 6 1.4%, mean 6 SD) correlated with therapeutic efficacy without associated toxicity. Kaplan–Meier survival studies were conducted in mice treated with PBS placebo, the nontargeted CAE-dnG1 vector, and the matrix-targeted Mx-dnG1 vector. Using the Tarone log-rank test, the overall p value for comparing all three groups simultaneously was 0.003, with a trend that was significant to a level of 0.004, indicating that the probability of long-term control of tumor growth was significantly greater with the matrix-targeted Mx-dnG1 vector than with the nontargeted CAE- dnG1 vector or PBS placebo. The present study demonstrates that a matrix-targeted retroviral vector de- ployed by peripheral vein injection (1) accumulated in angiogenic tumor vasculature within 1 hr, (2) trans- duced tumor cells with high-level efficiency, and (3) enhanced therapeutic gene delivery and long-term efficacy without eliciting appreciable toxicity. 193 OVERVIEW SUMMARY The development of targeted injectable vectors for thera- peutic gene delivery in vivo is critical for the progress of cancer gene therapy to the clinic. Retroviral vectors incor- porating a matrix (i.e., collagen)-binding motif target ex- tracellularmatrix (ECM) exposed during tumor growth, an- giogenesis, and metastasis. Here we report the inhibition of subcutaneous tumor growth in nude mice by intravenous administration of a matrix-targeted retroviral vector bear- ing a cytocidal/cytostatic cyclin G1 construct (designated Mx-dnG1 vector). Enhanced vector penetration and trans- duction of tumor nodules were demonstrated and correlated with therapeutic efficacy without associated toxicity. These results provide the first proof-of-principle that matrix-tar- geted retroviral vectors may be safely and effectively de- ployed in pursuit of solid tumors by direct injection into a peripheral vein. INTRODUCTION T ARGETING CYTOCIDAL VECTORS to tumors is an important goal of human gene therapy. Retroviral vectors are particularly suitable for cancer gene therapy because they integrate and ex- press packaged genes only in actively dividing cells, that is, can- cer cells and neovasculature, allowing the expression of cytoci- dal gene constructswhile sparing normal nondividingcells (Miller et al., 1990; Gordon and Anderson, 1994). However, the devel- opment of targeted retroviral vectors for gene delivery in vivo has been hampered by the inability to insert appropriate targeting mo- tifs into the retroviral envelope protein that would confer a gain- of-function phenotype without loss of native infectivity. Hence, many attempts to target retroviral vectors to specific cell types, by the display of various polypeptides on retroviral envelopes (Kasahara et al., 1994; Nilson et al., 1996; Martin et al ., 1998; Boerger et al., 1999; Peng and Russell, 1999), have not produced a clinicallyusefulvectorbecauseof associatedpostbindingblock 1 Gene Therapy Laboratories, 2 Division of Colon and Rectal Surgery, 3 Department of Pediatrics, 4 Department of Preventive Medicine, 5 Nor- ris Comprehensive Cancer Center, 6 Department of Pathology, 7 Department of Biochemistry, 8 Department of Surgery, and 9 Department of Mo- lecular Pharmacology and Toxicology, Keck School of Medicine of the University of Southern California, Los Angeles, CA 90033.