Size and surface charge of engineered poly(amidoamine) dendrimers modulate tumor accumulation and penetration: A model study using multicellular tumor spheroids

An enormous effort has been put into designing nanoparticles (NPs) with controlled biodistributions, prolonged plasma circulation times, and/or enhanced tissue targeting. However, little is known about how to design NPs with precise distributions in the target tissues. In particular, understanding NP tumor penetration and accumulation characteristics is crucial to maximizing the therapeutic potential of drug molecules carried by the NPs. In this study, we employed poly(amidoamine) (PAMAM) dendrimers, given their well-controlled size (<10 nm) and surface charge, to understand how the physical properties of NPs govern their tumor accumulation and penetration behaviors. We demonstrate for the first time that the size and surface charge of PAMAM dendrimers control their distributions in both a 3D multicellular tumor spheroid (MCTS) model and a separate extracellular matrix (ECM) model, which mimics the tumor microenvironment. Smaller PAMAM dendrimers not only diffused more rapidly in the ECM model but also efficiently penetrated to the MCTS core compared to their larger counterparts. Furthermore, cationic, amine-terminated PAMAM dendrimers exhibited the greatest accumulation in MCTS compared to either charge-neutral or anionic dendrimers. Our findings indicate that the size and surface charge of PAMAM dendrimers may tailor their tumor accumulation and penetration behaviors. These results suggest that controlled tumor accumulation and distinct intratumoral distributions can be achieved by simply controlling the size and surface charge of dendrimers, which may also be applicable for other similarly sized NPs.