The design, synthesis, and evaluation of novel drug delivery systems

Biological barriers are fundamental to both the prevention and the treatment of disease. These barriers prevent the uptake of many xenobiotics harmful to the body, but also limit or preclude the uptake, and therefore the therapeutic benefit, of a variety of drugs. The perceived effectiveness of barriers is so great that most approaches to drug design select only drug candidates that fall into a rather narrow log P range so as to allow passage of the molecule through the polar extracellular milieu and diffusion across the relatively nonpolar membrane of a cell. Yet this approach dramatically reduces the diversity of drug discovery and would remove from consideration many interesting polar drugs (e.g., siRNA) as well as highly nonpolar drugs (e.g., taxol). Molecular transporters can be used to address these problems.;Molecular transporter conjugates of otherwise poorly soluble or poorly bioavailable drugs exhibit excellent solubility in water and at the same time an enhanced ability to cross tissue and cell barriers and with modification to do so selectively. The Wender group has developed arginine and guanidinium transporters that exhibit superior uptake to those found in nature (e.g. Tat 49-57) and that can be synthesized in a step-economical fashion. Significantly, the arginine transporters have been advanced to phase II clinical trials.;The work discussed herein focuses on the development of releasable conjugates of the molecular transporters and a variety of probes and drugs. Novel assays for the real-time quantification of transporter conjugate uptake and cargo release in transfected cells and transgenic animals were developed utilizing the small molecule probe luciferin. This process effectively emulates drug-conjugate delivery, drug release, and drug turnover by an intracellular target, critical for both fundamental studies and therapeutic applications.;Releasable transporter conjugates of the immunosuppressant drug Cyclosporin A were developed for topical delivery. The conjugates varied greatly in structure and function, utilizing guanidinium-rich and lipid transporters, reductive and esterase bioactivation, and cyclization, 1,6-elimination, and acetal self-immolating linkers.;While the cell membrane prevents some xenobiotics from entering simply by log P, there are more advanced barrier mechanisms that arise in cancer cells. One of these is the increased expression of membrane proteins (e.g. P-glycoprotein or Pgp) that mediate unidirectional energy-dependent drug efflux, thereby intercepting and exporting the drug before it reaches its intracellular target. A releasable octaarginine-conjugate of the Pgp-substrate and probe, coelenterazine H, was prepared and shown to overcome Pgp-mediated efflux. Releasable octaarginine-taxol conjugates were prepared and overcame resistance in cell culture and animal models of ovarian cancer.