**1. Introduction**

514 Non-Viral Gene Therapy

Ren Y, et al (2010). MicroRNA-21 inhibitor sensitizes human glioblastoma cells U251 (PTEN-

27, ISSN: 1471-2407

mutant) and LN229 (PTEN-wild type) to taxol. *BMC Cancer*. Vol. 10 , (2010 Jan) pp:

Pharmaceutical nanoparticles were first described in 1970s, and the term "nanotechnology" is now commonly used to refer to the fabrication of new materials with nanoscale dimensions between 1 and 100 nm (Thrall 2004). Several types of nanometer scale systems such as nanoparticles, nanospheres, nanotubes, nanogels and molecular conjugates are being investigated (Lemieux et al. 2000;Liu et al. 2007;Ravi et al. 2004). The field of nanomedicine aims to use the properties and physical characteristics of nanomaterials which have been extensively investigated as novel intravascular or cellular probes for both diagnostic (imaging) and therapeutic purposes (drug/gene delivery). The sub-micron size of nanoparticle delivery systems confers distinct advantages as compared to large sized systems including targeted delivery, higher and deeper tissue penetrability, greater cellular uptake and greater ability to cross the blood-brain barrier (Kreuter et al. 1995;Vinogradov et al. 2002;Vogt et al. 2006). Therapeutic transgene(s) encoded by plasmid or chemically modified DNA can be dissolved, entrapped, chemically conjugated, encapsulated or adsorbed to the surface of nanoparticles. There are, broadly, two main types of nanosized particles with different inner structures: A. Nanoparticle/Nanosphere: Matrix composed of entangled oligomer or polymer units; and B. Nanocapsule: Reservoir consisting of a hydrophobic core surrounded by a polymer wall. Lipids can also be used to generate liposomes or micelles (discussed in detail later). These nanodevices can confer protection to the DNA against a variety of degradative and destabilizing factors, and enhance delivery efficiency to the cells while minimizing the toxic effects.

Nanoparticles are expected to play a critical role in the innovation and development of future cancer treatment modalities. Recent research has developed functional nanoparticles that are covalently linked to biological molecules such as peptides, proteins, nucleic acids, or small-molecule ligands (Alivisatos 2004;Chan et al. 2002;Michalet et al. 2005). Medical applications have also appeared, such as the use of superparamagnetic iron oxide nanoparticles as a contrast agent in the detection of lymph node prostate cancer (Harisinghani et al. 2003) and the use of polymeric nanoparticles for targeted gene delivery to tumor vasculatures (Hood et al. 2002). Target-specific drug/gene delivery and early diagnosis is currently a high priority R&D area, and one in which nanomedicine will inevitably make critical contributions. Current modalities of diagnosis and treatment of various diseases, especially cancer, have major limitations such as poor sensitivity or

Nanomedicine Based Approaches to Cancer Diagonsis and Therapy 517

2000). The *p53* gene product is a sequence-specific nuclear transcription factor that binds to defined consensus sites within DNA as a tetramer and affects the transcription of its target

The loss of *p53* function is of relevance to a broad array of cancer types, including 15–50% of breast cancer cases, 25–70% of metastatic prostate cancers, 25–75% of lung cancers, 33–100% of head and neck cancers and 60-80% advanced ovarian cancers (Ruley, 1996). Furthermore, the null mutation of the gene imparts strongly unfavorable prognosis when associated within human ovarian, lung, colon and breast cancer cases. *P53* also represses genes involved in tumor angiogenesis, and recent evidence suggests that tumor cells possessing a wild-type *p53* allele are more sensitive to chemotherapeutic agents and radiation than *p53* null mutants (Lowe et al. 1994). The pleiotropic abnormalities imparted by deficient *p53* in a significant fraction of human cancers make it one of the primary candidates for cancer gene therapy, whereby the effective expression or replacement of *p53* may re-establish cell growth control, restore appropriate responses to DNA-damaging agents (e.g. chemotherapy and radiotherapy) and preclude tumor angiogenesis. In human neoplasia's that express the wild-type protein, aberrations of p53 regulators, such as MDM2, account for p53 inhibition. For this reason, improved understanding of the p53 pathway should lead to better diagnosis

The *p53* gene therapeutic, Gendicine, is currently approved in China and its US counterpart, Advexin, has shown activity in number of clinical trials. In more conventional approaches a range of small drug like molecules targeting the *p53* mediated system have been developed and several are now in clinical trials. Of critical importance has been the development of small-molecule inhibitors of the p53–Mdm2 protein interaction such as the Nutlins (Vassilev 2004), which have shown activity against human xenografts in preclinical models. Therefore, designing small-molecule inhibitors of the *p53*-MDM2 protein-protein interaction is a promising strategy for the treatment of cancers retaining wild-type *p53* (Lauria et al. 2010). Advanced structural approaches have provided compelling support for the idea that some *p53* mutants can be targets for small molecules that would cause them to regain wildtype function (Joerger et al. 2006). Many adenoviral vectors with cancer specific conditional replication properties have been preclinically evaluated to date. Most promising among these are: i) the Ad dl1520 that possesses a deletion of the 55-kd E1B gene limiting growth to only *p53*-deficient tumor cells. This strategy has shown preclinical efficacy against *p53* deficient nude mouse-human ovarian carcinomatosis xenografts (Vasey et al. 2002); and ii) the integrin-targeted Ad5-D24RGD and serotype 3 receptor-targeted Ad5/3-D24 that possesses a 24 bp deletion in the retinoblastoma binding site of E1A, conferring selective

Suicide gene therapy/molecular chemotherapy is a new experimental form of cancer chemotherapy that is currently being evaluated in human trials (Bhaumik 2011; Onion et al. 2009;Xu et al. 2009). This approach involves intra-tumoral delivery of genes encoding enzymes that convert nontoxic prodrugs into toxic anti-metabolites. Two suicide genes that are being evaluated in the clinic are the *Escherichia coli* CD (*codA* cytosine deaminase) and

replication in cancer cells that are deficient in the Rb/p16 pathway.

genes. These target genes are involved in critical cell processes such as:

3. Apoptosis: Bax, Bcl-xL, Fas, FasL, DR5/Killer, Apaf-1, Puma and Noxa.

1. Growth arrest: P21, Gadd45 and 14-3-3σ.

and treatment of cancer in the future.

**2.2 Molecular chemotherapy**

2. DNA repair: *P53R2*.

specificity and high drug toxicities respectively. The success of nanoparticle delivery systems will ultimately depend on the ability to efficiently deliver the gene of interest and express a therapeutic gene(s) in tumor cells in a targeted manner in order to mitigate toxicity. This chapter examines current existing nanoparticle-based gene therapy approaches to cancer treatment, and assesses their therapeutic utility.
