Anticancer activity of mycobacterial DNA: effect of formulation as chitosan nanoparticles

Mycobacterium phlei (M. phlei) DNA inhibits cancer cell division but is susceptible to degradation by DNase. Chitosan forms nanoparticulate polyelectrolyte complexes with DNA, and may thus reduce nuclease degradation. We have characterized chitosan-DNA nanoparticle formation, determined DNase susceptibility, and evaluated their antiproliferative activity. Nanoparticle diameter initially decreased with increasing phosphate charge density. However nanoparticle diameter increased above 6 micromol of phosphate. Particle aggregation occurred at 16.2 micromol phosphate and was related to reduced surface charge. Incorporation of DNA within chitosan nanoparticles significantly decreased degradation by DNase. The ability of M. phlei DNA-chitosan nanoparticles to inhibit melanoma cell division was determined relative to M. phlei DNA and a cationic liposomal M. phlei DNA formulation. M. phlei DNA had antiproliferative activity (MTT reduction, IC50 = 0.9 mg/ml) without intrinsic cytotoxicity (LDH release, ED50 > 50 microg/ml). Cationic polyphosphate chitosan nanoparticles were inert (antiproliferative IC50 > 1 mg/ml, ED50 > 1 mg/ml). M. phlei DNA-chitosan nanoparticles were 20-fold more potent than M. phlei DNA. Cationic DOTAP/DOPE liposomes were cytostatic (IC50 = 49 microg/ml) and cytotoxic (ED50 = 87 microg/ml), and complexation of M. phlei DNA resulted in a significant reduction of antiproliferative activity. Chitosan nanoparticles may therefore be appropriate delivery vehicles for M. phlei DNA.