Gene and Drug Delivery System with Soluble Inorganic Carriers

Abstract

Inorganic-based delivery systems are attracting increased attention partially because their inertness gives rise to safety and stability in biosystems and partially because their frameworks can be readily and exactly manipulated. Among the diverse inorganic candidates, such as nanoparticles and clays, we have focused our attention on layered double hydroxides (LDH) with anion-exchange capacity. Diverse anionic molecules can be loaded into the interlayer space of LDH by various routes, such as coprecipitation, anion exchange, and reconstruction. Furthermore, the loaded molecules can be completely discharged by both anion exchange and framework disintegration. When DNA is hybridized with LDH, the intercalated DNA is safely protected against harsh conditions, such as strong alkaline to weakly acidic environments, as well as against DNase attack, which enabled us to develop a novel gene delivery system. HL-60 cells treated with As-myc/LDH hybrids exhibited time-dependent inhibition of cell proliferation, indicating nearly 65% inhibition of growth compared to the untreated cells, after 4 d. On the other hand, LDH itself was noncytotoxic towards HL-60, indicating its biocompatibility. We also demostrated the successful application of a drug-LDH hybrid to in vitro cancer treatment in which LDH played an essential role in the protected delivery of methotrexate (MTX). The initial proliferation of Saos-2 cells was more strongly suppressed by treatment with the MTX-LDH hybrid than with MTX alone. A series of genetic and efficacy assays indicated that LDH does not exert appreciably harmful effects on either normal or cancer cells, and that the action mechanism of MTX is not affected by hybridization. Furthermore, LDH could be vein-injected without any significant effects on tissues or organs below a dose rate of 100 mg/kg. Therefore, we believe that, in the not-so-distant future, LDH will serve as next-generation drug carriers for a broad spectrum of drugs.Key WordsAntisensebio-LDH hybridsinoganic-organic-hybridslayered double hydroxides (LDH)methotrexate