Triazine Dendrimers for Drug Delivery: Evaluation of Solubilization Properties, Activity in Cell Culture, and In Vivo Toxicity of a Candidate Vehicle

Abstract

Three criteria are evaluated to assess the potential of a dendrimer based on triazines, 1, for use as a vehicle for drug delivery. These criteria are: (1) its ability to solubilize small hydrophobic guests as measured spectrophotometrically; (2) its ability to deliver a drug in vitro as evaluated using a gene reporter assay; and (3) its in vivo toxicity in mice as determined by autopsy and screens of liver and kidney function. Vehicle 1 solubilizes pyrene to a similar extent to dendrimers based on poly(arylether)s, 4, encapsulating approximately 0.2 molecules of pyrene per dendrimer. This activity is approximately 10-fold greater than that of the more polar poly(propyleneimine) and poly(amidoamine) dendrimers, 2 and 3. Gas-phase computational models reveal that both 1 and 4 have cores that are accessible to solvent, suggesting that these dendrimers can occupy much greater volumes than 2 and 3 whose cores are confined toward the interior of the structure. Electrostatic potential maps can be used to rationalize differences in solubilization between 1 and 4. Precipitation results from mixing cationic 1 with the anionic indomethacin, but not with methotrexate, suggesting that the composition of the drug may dictate the scope of delivery applications. Dendrimer 1 solubilizes 10-hydroxycamptothecin and a novel bisindolemethane; approximately four and five molecules of drug per dendrimer are solubilized, respectively. In cell-culture experiments using a luciferase reporter gene assay, the dendrimer:bisindolemethane conjugate shows comparable activity to the bisindolemethane delivered in aqueous DMSO, suggesting that the dendrimer does not preclude delivery of the molecule to an intracellular target. Preliminary toxicology studies of 1 in mice show that this molecule has no adverse toxicity to the kidneys or the liver in single doses delivered intraperitoneally up to 10 mg/kg.

Keywords:

• Dendrimer
• Polymer
• Drug delivery
• Melamine
• Triazine
• Toxicity
• Cell culture
• Solubilization

Acknowledgements

This work was supported by the National Institutes of Health (EES: GM 64650) and the Center for Microencapsulation and Drug Delivery at Texas A&M University.

Notes

^†The strategy adopted combines elements described in Refs [30–33] and was performed in our laboratory.

^‡We investigated a G3 PAMAM dendrimer under the same conditions. The saturated concentration of pyrene in 1.49×10^-4 buffer solution of PAMAM was found to be 1.42×10^-6 M. On average, a single dendrimer molecule can dissolve only 0.0095 molecules of pyrene, which is 19 times lower than 1 (0.18 pyrene/dendrimer).

The Future of Supramolecular ChemistryWhere is supramolecular chemistry going? Bigger. Smarter. Longer. Faster. Cheaper. Useful. These adjectives, or a subset of them with perhaps the most important and most elusive being “useful”, lend themselves to the goals of the community in the diverse areas that the field encompasses. Imagination, creativity and innovation remain key components to success. Ourselves? In hindsight, my own experience with Rinehart as an undergraduate assaying marine natural products using the L1210 antitumor assay, with Whitesides in graduate school studying self-assembly using melamine, and with Wong for post-doctoral studies in drug (and drug paradigm) discovery foreshadowed this area of research. Our dream is to produce a versatile scaffold that will selectively home in on tumors to deliver drugs. The dream provides direction and inspiration. Such a vehicle could increase the therapeutic index of known agents, allow for the use of even more cytotoxic drugs, and ultimately—since this is a dream—enhance and extend the quality of life for those besieged.Eric E. Simanek was born in Tuscola, IL in 1969. He obtained a BS in Chemistry from the University of Illinois in Urbana-Champaign in 1991. Research experience in the laboratories of Professor Kenneth L. Rinehart, Jr and at Abbott Laboratories as well as interactions with Professor Eric N. Jacobsen led him to pursue graduate study. He obtained his PhD in 1996 from Harvard University under the direction of Professor George M. Whitesides. After post-doctoral study with Professor Chi-Huey Wong at Scripps Research Institute in La Jolla, he joined the faculty at Texas A&M University in 1998. His group focuses primarily on dendrimer chemistry, with efforts directed towards separation science and drug delivery.