Article pubs.acs.org/molecularpharmaceutics
Size and Surface Charge of Engineered Poly(amidoamine) Dendrimers Modulate Tumor Accumulation and Penetration: A Model Study Using Multicellular Tumor Spheroids Jason Bugno,† Hao-Jui Hsu,† Ryan M. Pearson,† Hyeran Noh,‡ and Seungpyo Hong*,†,§ †
Department of Biopharmaceutical Sciences, College of Pharmacy, University of Illinois, Chicago, Illinois 60612, United States Department of Optometry, Seoul National University of Science and Technology, Seoul 139-743, Korea § Departments of Integrated OMICs for Biomedical Science and Pharmacy and Underwood International College, Yonsei University, Seoul 120-749, Korea ‡
S Supporting Information *
ABSTRACT: 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 ( G7-Ac. G2-Ac exhibited greater than a 2-fold decrease in the recovery half-life compared to G4-Ac and G7-Ac (47.89 s−1 vs 100.60 and 111.63 s−1, respectively). These findings indicate that the diffusion through the ECM is strongly dependent on the dendrimer size and appears related to their ability to penetrate into the MCTS.
neutral or negatively charged dendrimers, we further investigated the permeation behaviors of G2-NH2, G4-NH2, and G7-NH2 in large MCF-7 MCTS to elucidate the role that dendrimer size plays in governing their tumor penetration (Figure 3). The penetration depth of PAMAM dendrimers into the MCTS was inversely proportional to the dendrimer size (Figure 3a). G2-NH2 exhibited significantly greater spheroid penetrating capabilities (214 ± 36 μm) compared to the larger G4-NH2 (105 ± 12 μm) and G7-NH2 (81 ± 8.31 μm). In contrast, the overall accumulation of fluorescent signal was directly related to the dendrimer generation (Figure 3c), which corresponds well temporally with the 2D cellular interaction kinetics (SI Figures 7−9). The MCTS surface accumulation and 2D cellular interaction kinetics were proportional to dendrimer generation with G7-NH2 > G4-NH2 > G2-NH2. This trend likely reflects the greater numbers of charged surface terminal groups of higher generation PAMAM dendrimers, as measured by the increase in zeta potential (SI Table 1). This increased surface charge causes them to interact more strongly with the cellular membranes, leading to greater MCTS accumulation.21,22 This effect is best evidenced by the migration of the dendrimer diffusion front from the outer edge of the spheroids (Figure 3di−iv). G7-NH2 displayed the most rapid accumulation in MCTS and was most prominent following 9 h of treatment (Figure 3diii). By 24 h a clear difference in the migration fronts of the dendrimers (indicated by the arrows in Figure 3div) was observed across the treatment groups with the penetration depth into the MCTS being inversely proportional to dendrimer size: G2-NH2 > G4-NH2 > G7-NH2. These results again support that the size and surface charge of PAMAM dendrimers can be engineered to tune their tumor penetration and accumulation, generating tailored tumor distributions. 3.4. Dendrimer Diffusion in a Model Extracellular Matrix. The ECM surrounding the tumor makes up a large portion of the local microenvironment and represents a significant barrier to efficient tumor penetration.2,25−28 Therefore, we were also interested in characterizing the effect of dendrimer size on their ability to permeate through constituents of the ECM. To accomplish this, we loaded PAMAM dendrimers into a collagen type I gel, a major component of the ECM and known networking protein, and performed a fluorescence recovery after photobleaching (FRAP) experiment (Figure 4). In order to exclude any charge-based effect, RHO-labeled acetylated (charge-neutral)
4. DISCUSSION While we have demonstrated that dendrimer size is intricately tied to their ability to penetrate the tumor and components of the microenvironment, it is not clear if the difference is due to the hydrodynamic diameters or the increased number of branched groups at higher generations. Reports regarding optimal NP size and tumor penetration vary widely, suggesting that several factors other than the hydrodynamic radius and size govern their penetration. For instance, Tang et al. have found that particles up to 50 nm in diameter are still capable of maintaining favorable tumor penetration.6,7 Other groups have demonstrated that 15 nm gold particles are approximately the cutoff for efficient tumor penetration.3 Based on these reports and the small hydrodynamic diameters of our dendrimers (
