• ZSM-5/KIT-6 and ZSM-5/SBA-15 were synthesized and modified with COOH and SO 3 H groups. • Verapamil was loaded by incipient wetness impregnation in modified composite nanoparticles. • Verapamil-loaded nanoparticles were coated by a polyelectrolite polymer complex. • Silica structure and polymer complex are the key factors for controlled drug release. • Verapamil-loaded nanocomposites influenced positively efflux pump modulation. ZSM-5/KIT-6 and ZSM-5/SBA-15 nanoparticles were synthesized and further modified by a post-synthesis method with (CH 2) 3 SO 3 H and (CH 2) 3 NHCO(CH 2) 2 COOH groups to optimize their drug loading and release kinetic profiles. The verapamil cargo drug was loaded by incipient wetness impregnation both on the parent and modified nanoporous supports. Nanocarriers were then coated with a three-layer polymeric shell composed of chitosan-k-carrageenan-chitosan with grafted polysulfobetaine chains. The parent and drug loaded formulations were characterized by powder XRD, N 2 physisorption, thermal analysis, AFM, DLS, TEM, ATR-FT-IR and solid state NMR spectroscopies. Loading of verapamil on such nanoporous carriers and their subsequent polymer coating resulted in a prolonged in vitro release of the drug molecules. Quantum-chemical calculations were performed to investigate the strength of the interaction between the specific functional groups of the drug molecule and (CH 2) 3 SO 3 H and CH 2) 3 NHCO(CH 2) 2 COOH groups of the drug carrier. Furthermore, the ability of the developed nanocomposites to positively modulate the intracellular internalization and thereby augment the antitumor activity of the p-gp substrate drug doxorubicin was investigated in a comparative manner vs. free drug in a panel of MDR positive (HL-60/Dox, HT-29) and MDR negative (HL-60) human cancer cell lines using the Chou-Talalay method. [ABSTRACT FROM AUTHOR]