Vessel normalization and maturation promotes nanoparticle delivery to solid tumors while minimizing metastases

Abstract

Nanoparticle delivery to solid tumors is known to be an inefficient process and various studies have tried to increase efficacy, but mechanistic and comparative studies remain scarce. Here, we use pharmacological agents to study the effect of vessel normalization or vessel disintegration on nanoparticle delivery to solid tumors. Using a multiparametric approach, we find that vessel disintegration fails to improve nanoparticle delivery and instead seems to have a limiting effect. Vessel normalization, however, improves delivery efficacy for nanoparticles ranging from 20 to 60 nm diameter. The normalization of the tumor blood vessels results in reduced hypoxia, reduced necrosis and an increase in Plvap+ CD276+ endothelial cells, which have been linked with nanoparticle delivery. Interestingly, where vessel disintegration stimulated cancer cell intravasation and associated metastases, vessel normalization impeded these processes. Together, these data reveal that, vessel normalization may be a safer and more suited approach for improving nanoparticle delivery to solid tumors, but its efficacy is limited by nanoparticle diameter and tumor parameters.

Gold Nanoparticle Delivery to Solid Tumors by Macrophage Depletion, Hypoxia Inhibition, and Collagen Degradation

“…However, while vessel maturity and coverage were clearly affected, the scale of these effects was somewhat limited. In our previous work, vessel normalization using 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO) had resulted in increased NP levels, 41 which is in line with literature data for other vessel normalization strategies. 60 The lack of an effect here is most likely due to the fact that, while vessel normalization was observed, the extent of it was less outspoken as reported in previous works.…”

“…Given that HIF-1α induces collagen gene expression, 36,37 ECM density was expected to be greatly reduced as a result of acriflavine treatment, and although there is some reduction and the overall distributions for ECM density are lower for this treatment group compared to the control, this difference was not significant. This can be due to the fact that ECM density in Renca tumors is not very high to begin with, and while perfusion in these tumors is relatively good, as already established in our previous studies, 40,41 hypoxia levels may be relatively low, thereby limiting the benefits of acriflavine on secondary outcomes. Blood vessel maturity was significantly Figure 3.…”

“…To measure hypoxia levels, animals were injected IV with Hypoxi-sense680 (2 nmol/100 uL per mouse, PerkinElmer, Life Sciences, Zaventem, Belgium) 24 h after the last pharmacological treatment (together with the Au NPs), and fluorescence signals were measured using the IVIS after 24 h. Levels of (1) tumor necrosis, (2) ECM density, and (3) blood vessel maturity and coverage were obtained by staining tissue slices with (1) hematoxylin and eosin, (2) Picrosirius Red and Fastgreen, and (3) antibodies against CD31 (endothelial cells), laminin, and NG2 (pericytes), respectively, as performed in our previous studies. 40,41 Analysis of Immune Cell Composition in the Tumor. Singlecell suspensions were obtained from isolated tumors using the GentleMACS tissue dissociator and accompanying kit (Miltenyi Biotec, Gladbach, Germany) as per company protocol.…”

“…To measure the amount of Au NPs present in the total tumor, ICP-MS was performed on each of the tumor samples as described in our previous studies. 40,41 Statistics. Statistical analyses were performed using GraphPad Prism 9.0, and comparisons between control and treated groups were obtained using one-way ANOVA.…”

“…Previous work had shown that NP delivery efficacy to solid tumors is linked to various parameters but that the level of TAMs, degree of hypoxia, and extent of ECM in the tumor play important roles. 40,41 In the present study, we study the effect of pharmacological interference with any of those parameters on NP delivery efficacy and uptake by cancer cells. For this, aCSFR1 treatment was chosen as a means to temporarily remove macrophages, as it is known that the majority of NPs are cleared from the blood by Kupffer cells 42,43 and the ones that do reach the tumor mainly end up in TAMs.…”