Tumor

Tumor-selective targeted delivery of genes and antisense oligodeoxyribonucleotides via the folate receptorXiaobin B. Zhao, Robert J. Lee*Division of Pharmaceutics, College of Pharmacy, The Ohio State University, Room 542, LM Parks Hall,500 W. 12th Avenue, Columbus, OH 43210, USAReceived 28 September 2003; accepted 5 January 2004AbstractGene therapy is a promising approach for the treatment of cancer. The main obstacle for the clinical application of cancer gene therapy is the lack of gene transfer vectors that are safe, efficacious, and tumor-selective. In recent years, targeted gene delivery through cellular receptors, using either viral or nonviral vectors, is emerging as a novel approach to enhance the efficacy of tumor-selective gene delivery. The folate receptor (FR), which is absent in most normal tissues and elevated in over 90% of ovarian carcinomas and at a high frequency in other human malignancies, is an attractive tumor-selective target. FRtargeted vectors include folate-derivatized adenoviruses, cationic polymers, cationic liposomes, and pH-sensitive liposomes. In addition, FR-targeted liposomes have been evaluated for the targeted delivery of antisense oligodeoxyribonucleotides (ODNs). These vectors have invariably shown impressive FR-selectivity in cell culture assays and, in addition, shown promising tumorspecificgene transfer activity in several in vivo models. There are important theoretical advantages for FR-targeted vectors over traditional non-targeted vectors in therapeutic gene and oligodeoxyribonucleotides delivery in vivo to cancer cells. Further preclinical characterization of these vectors is, therefore, warranted to determine their potential utility in cancer gene therapy.D 2004 Elsevier B.V. All rights reservedKeywords: Folate receptor; Targeted delivery; Gene therapy; Gene transfer; TumorAbbreviations: ATRA, all-trans-retinoic acid; CHEMS, cholesteryl hemisuccinate; Chol, cholesterol; DC-Chol, dimethylaminoethane carbamoyl cholesterol; DDAB, dioctadecyl dimethyl ammonium bromide; DODAP,1,2-dioleoyl-3-(dimethylamino) propane; DOPE, dioleoyl phosphatidylethanolamine; DOSPA,2,3-dioleyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanaminium trifluoroacetate;DOTAP, dioleoyl trimethylammonium propane; DOTMA, dioleylpropyl trimethylammonium chloride; DPPE, dipalmitoyl phosphatidylethanolamine;DSP, dithio-bis-(succinimidylpropionate); DSPE, distearoyl phosphatidylethanolamine; DTBP,dimethyl-3,3V-dithio-bis-propionimidate;EGF, epidermal growth factor; FR, folate receptor; LPD, lipid–polycation–DNA ternary complex; ODN, oligodeoxyribonucleotide;PE, phosphatidylethanolamine; PEG, polyethylene glycol; PEI, polyethylenimine; PLL, poly-L-lysine; RT-PCR, reverse transcriptionpolymerase chain reaction.* Corresponding author. Tel.: +1-614-292-4172; fax: +1-614-292-7766.E-mail address: lee.1339@ (R.J. Lee).0169-409X/$ - see front matter D 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.addr.2004.01.0051. Introduction1.1. Cancer gene therapySince the first human gene therapy trial in 1989, several hundred clinical protocols involving genetransfer have been initiated worldwide. In general terms, ‘‘gene therapy’’ refers to the transfer of genetic material into target cells for therapeutic purpose. This approach has originally been proposed as a means to correct inherited genetic diseases，such as hemophilia，cystic fibrosis, and metabolic disorders. However, perhaps as a reflection of the scope of the clinical problem, most present clinical studies involving gene transfer protocols have been for the treatment of cancer. Potential therapeutic genes for cancer include tumor suppressor genes,suicide genes, and cytokine genes. The advances in cancer genetics and the expanding selection of therapeutic genes provides a plethora of potential mechanisms of tumor in hibition. Gene therapy, either as monotheraphy or used in combination with other clinical modalities, offers new hope for overcoming drug resistance and providing alternative treatment for tumors that are refractory to existing standard therapeutic regimens. There are three general approaches to somatic gene therapy. In the first approach, cells from patient are transfected ex -vivo and re-administered into the patient. In the second approach, therapeutic genes are locally introduced into the target tissue in situ. In the third approach, therapeutic gene is administered systemically. The first two approaches have been adopted in most existing clinical protocols. Thisis despite the fact that local vector administration typically results in poor and uneven distribution in tissues due to the relatively large size of gene transfer vectors, and, therefore, their limited ability to diffuse from the needle track. In contrast, i.v. administration provides the potential for efficient vector distribution through the vasculature. This systemic delivery method is, therefore, perhaps the most promising route for clinical application. The successful clinical application of gene therapy has thus far been limited by the lack of safe, efficient, and well characterized gene transfer vectors that are suitable for systemic administration.The large size and polyanionic nature of DNA molecules poses a formidable challenge for the development of gene transfer vectors. Early efforts in vector design have focused primarily on vectors derived from genetically engineered viruses, including retroviruses, adenoviruses, adeno-associated viruses, and several other viral types. Several obstacles limit the usefulness of viral vectors in gene therapy. These include (1) immunogenicity of viral proteins, which precludes repeated administration, (2) lack of desired tissue selectivity, (3) potential for oncogenesis due to chromosomal integration and (4) generation of infectious viruses due to recombination. In order to bypass these obstacles, nonviral gene transfer vectors composed of synthetic components are being developed as potential alternatives to viral vectors.1.2. Nonviral gene therapy vectorsSynthetic vectors provide flexibility in formulation design and can be tailored to the size and topology of the DNA cargo and the specific route of vector administration, and can be delivered selectively to a specific tissue type through the incorporation of a targeting ligand. Compared to viral vectors, synthetic vectors potentially are less immunogenic, relatively easy to produce in clinically relevant quantities, and associated with fewer safety concerns [15]. Synthetic vectors designed for parenteral administration encompass a wide range of formulations. These include unmodified (naked) DNA, which is designed for direct intra-tissue injection, cationic polymer–DNA complexes (polyplexes), cationic lipid–DNA complexes (lipoplexes), and cationic polymer–lipid–DNA ternary complexes (lipopolyplexes), which are mostly aimed at systemic administration.。