Estrogen(s) and Analogs as a Non-Immunogenic Endogenous Ligand in Targeted Drug/DNA Delivery

The maximum therapeutic potentials of pharmacologically active molecules are generally not attained due to their non specific delivery. Ligands associated with drug or delivery system through which it is delivered provide navigation and direction to the carrier system(s) so as to reach and release bioactive(s) at the desired site of action in a optimum therapeutic concentration vis a vis minimizing the undesired side effects associated with non specific delivery. Many ligands employed and implicated in targeted drug delivery have been reportedly found to be mild to strong immunogenic. Hence, their potential utility is considered to be compromised in achieving concept of magic bullet. Therefore endogenous ligand (bio self molecules) based drug/DNA delivery may be a better alternative they being biocomponents so are non-immunogenic and biocompatible per se. Estrogens and their receptors are over expressed in the several pathophysiological conditions including cardiovascular, osteoarthritis and cancer of prostate and ovaries etc. The selective high density of such portal may be utilized for targeting such estrogen receptor rich sites. The several scientific communities from various fields of specialization of science have explored estrogen(s) and their analogs for the purpose of targeting of bioactive(s) either by preparing estrogen-drug conjugates of using estrogens as sitedirecting ligands attached with various carrier system(s). This review presents an exhaustive account of how hormones especially estrogens and their derivatives could be used for site-specific delivery of bioactive(s), as diagnostic agents and also the future prospects of these bioligands in controlled and targeted clinical pharmacology. Estrogen-drug conjugates and various carrier systems that utilized estrogens as ligands for site-specific delivery have been reviewed and are discussed in detail.