Now a day, cancer is one of the major causes of patients’ deaths all over the world due to lack of appropriate diagnostic techniques. Successful prevention and treatment of cancer depends on the precise detection at of cancer the early stage. Only large size (bigger than a centimeter in diameter) tumors can be detected by conventional anatomic imaging techniques like computed tomography (CT) and magnetic resonance imaging (MRI) (Weissleder, 2006; Pomper, 2005). Smaller tumors cannot be detected by these techniques so there is the need to develop more effective and sensitive imaging techniques for early and exact diagnosis of cancer. Therefore, molecular imaging technologies are developed for early diagnosis of cancer cells so that the cancer may be treated more effectively. These imaging techniques help in identifying the nature and progression of various diseases at the molecular and cellular levels, and help in determining the molecular target for treatment of diseases (Weissleder, 2006; Liu et al., 2011). Conventional imaging techniques are mainly based on anatomical structures of organs, while molecular imaging technologies use molecules as the targeting probe for specific receptors present on the diseased tissues which form the images of high contrast (Sun et al., 2010). Thus, it becomes the key point to identify and generate the tumor-specific molecular ligands with high binding affinity.
Not only proper diagnosis, but effective treatment also required for the improvement of patient’s health. Likewise, as far as cancer treatment is concerned, targeted drug delivery is attracting intensive attention because it can not only enhance the local drug concentration, but also reduce the systemic side effect due to nonspecific exposure of anti-cancer drugs to normal tissues. The “magic bullet or smart bullet” concept has been introduced for targeted drug delivery in which anticancer drug is attached with the suitable tumor-targeting ligand and show their effects only at the tumor site (Brown, 2010). Tumor-specific ligands are the major need for these both purposes, i.e. molecular diagnosis and targeted drug delivery to the tumor site. So we can say that there is need to identify or diagnose tumor specific ligand which has the capability of distinguishing between tumor cells from the normal cells.
Conventionally, the most common molecular targeting agents are antibodies or their fragments for the targeted delivery of imaging contrast agents and anti-cancer drugs to tumor tissues. Different types of monoclonal antibodies have been developed for the various types of cancer treatment, such as Trastuzumab (for breast cancer), Bevacizumab (for colorectal cancer), Cetuximab (for colorectal cancer/head and neck cancer) and Ibritumomab tiuxetan (for Non-Hodgkin lymphoma) (Brown, 2010; Deutscher, 2010; Lu et al., 2011; Mancuso and Sternberg, 2005; Trail et al., 2003; Adams and Weiner, 2005). But, there are two major drawbacks associated with the of antibody application as tumor targeting ligand. Because of the large size of molecules their tumor tissue penetrating ability is very low and they can be nonspecifically phagocytosed by the mononuclear phagocyte systems (MPS) (Deutscher, 2010; Li and Cho, 2010).
On the other hand various type of peptide receptors are over-expressed on the tumor cells which can be used as molecular target for the effective cancer therapy. Hence, peptide based targeting delivery system has been developed for the effective tumor targeting. When peptide system compared with monoclonal antibody, the peptide moiety has wider range of targets with a vast coverage and show many exclusive distinctiveness. Peptides exhibit several advantages over antibody such as, good tissue penetrating ability due to small molecular weight (average less than 50 amino acids), high affinity to targets, low immunogenicity, acceptable stability and integrity in vivo and easy to manipulate for synthesis and conjugation with other agents and drugs (Deutscher, 2010; Li and Cho, 2010; Lee et al., 2010).
The use of recent advances of nanotechnology is the one of the most appropriate targeting strategy for cancer diagnosis and treatment. Recently, researchers are trying to develop various applications of peptide-based nanomaterials, which may help to kill cancer cells, or regenerate severely damaged nerves or stop bleeding in clinics. Currently, peptide-based nanoparticles (pepNPs) are emerging the most sophisticated, green structures with several advantages over other type of nanoparticles (organic or inorganic NPs) for cancer diagnosis as well as for therapy.
The RGD peptide can be combined with integrins receptors, which are overexpressed on the newly formed blood vessels on to the tumor cells with a certain affinity, and hence found to be attractive target for diagnotic agents, drugs, and gene delivery for tumor treatment. Further, RGD as a biomimetic peptide can also enhance cell adhesion to the matrix, prevent cell apoptosis and increase the formation of new tissue. It is also reported that the RGD modified nanoparticulate system can increase cell and system interaction which may be helpful in tissue engineering in the formation of new tissue or a part of organ.
With this review, the authors try to discuss about the peptide-based nanoparticles, with their advantages and functions of RGD peptide. The review also describes the applications of RGD as imaging agents, gene delivery for tumor therapy, drugs, and underlines the importance of RGD in the development of tissue engineering like cornea repair, bone regeneration, artificial neovascularization in current scenario.