Methotrexate-loaded PEGylated gold nanoparticles as hemocompatible and pH-responsive anticancer drug nanoconjugate

Methotrexate (MTX) is a well-known chemotherapeutic agent for solid tumor. However, its clinical usage is limited due to low permeability, cellular drug efflux, and non-specific drug delivery. These constraints require dose dumping and result in dose-dependent toxic effects. In the current study, MTX-loaded PEGylated gold nanoparticles (PEG-MTX-AuNPs) exposed to acidic pH (tumor cell) trigger a significant drug release profile. MTX was conjugated to citrate functionalized AuNP and stabilized by thiolated methyl polyethylene glycol (mPEG-SH). PEG-MTX-AuNP was cationic with 39.5 +/- 1.2 mV zeta potential and a particle size of 39 nm, as revealed by DLS and TEM. AuNP size ranging from 40 to 50 nm was favorable for maximum endosomal uptake and fast drug release. MTX-AuNP showed 39.4% (22.28 mu g/ml) drug loading efficiency. Spectroscopic examinations confirmed MTX chemisorption onto AuNPs via carboxyl (-COOH) and gold dative bond. In vitro release study indicated a 6.5-fold increased MTX release in the acidic environment (pH 4.5) compared to physiological pH. The terminal mPEG provided stability in a biological medium, refrained from protein deactivation, and exhibited significant hemocompatibility (less than 5% hemolysis up to 10 mu M concentration). In vitro cytotoxicity against human rhabdomyosarcoma (RD) cells indicated significant (p < 0.0001) anticancer activity of PEG-MTX-AuNPs with low median growth inhibition concentration (GI(50) = 3.61 +/- 0.94 mu M) compared to MTX (13.12 +/- 0.98 mu M) and AuNPs (5.24 +/- 0.98 mu M) alone. In conclusion, PEG-MTX-AuNPs offer higher stability in ionic and biological media, hemocompatibility, and acidic pH-dependent MTX release, and mediate enhanced in vitro anticancer activity that makes them a potential candidate for skeletal muscle sarcomas.