Design and Evaluation of Nucleoside Derivatives for Targeted Drug Delivery and Therapeutic Applications

Abstract

2',3'-Dideoxynucleoside analogs are commonly used as anti-HIV, anti-HBV, and anti-cancer drugs. Despite of their potent activities, there are some major limitations in using 2',3'-dideoxynucleosides as therapeutic agents. The nucleosides have usually poor cellular uptake because of their hydrophilic nature. Some of the nucleoside analogs, such as anti-HIV agents, become ineffective after multiple administrations because of the development of the drug resistance, and therefore they must be administered in combination therapy. It is hard to deliver the nucleoside analogs to a particular tissue for site specific targeting. Furthermore, nucleoside analogs undergo three intracellular phosphorylation steps to become active. The first phosphorylation step is slow and a rate-limiting process for several compounds. Herein, we report the synthesis and evaluation of 2',3'-dideoxynucleoside conjugates with fatty acids, peptides, other nucleosides, fatty acyl phosphotriesters, or polymer derivatives. The primary hypothesis of this project was that conjugation of nucleosides with other compounds offers a novel strategy in designing compounds with enhanced anti-HIV activity. This combination may result in development of anti-HIV agents having enhanced lipophilicity, longer duration of action by sustained intracellular release of active substrates at adequate concentrations, higher uptake into infected cells, and/or site specificity. The development of viral resistance to the nucleosides would occur at a slower rate than to either compound alone. Furthermore, some of the compounds may be used to bypass first rate-limiting phosphorylation step. In the first two chapters, synthesis and anti-HIV activities of fatty acyl derivatives of Zidovudine (AZT), Allovudine (FLT), Emtricitabine (FTC), Lamivudine (3TC), and Stavudine (d4T) are discussed. Among all the compounds, 5'-0-myristoyl derivative of FTC (2.31, EC50 = 70 nM against cell-free virus) exhibited the best anti- HIV profile when compared with other fatty acyl derivatives of other nucleosides and the physical mixture of FTC and myristic acid. 5'-0-Fatty acyl derivatives of FLT, 5'-0-(12-azidododecanoyl) derivative of FLT (KP-1), and 5'-0-(12-thioethyldodecanoyl)thymidine (KP-17), also displayed good activity against cell-free (EC50 values of 0.9 to 1.0 μM, respectively) virus and minimal cellular toxicity. Cellular uptake studies for 5’-O-fatty acyl derivatives of FLT and 3TC were conducted on CCRF-CEM cell line using a 5(6)-carboxyfluorescein derivative attached through 12-aminododecanoic acid as a linker to the nucleosides. The fluorescence-based studies indicated that the fatty acyl derivatives of FLT and 3TC have a higher cellular uptake versus that of the corresponding parent nucleoside substituted with a short alkyl group, such as β-alanine the cellular uptake with concentration-and-time-dependent. In the third chapter, the synthesis