Abstract 4225: Dynamic control of tumor vasculature with direct observation using intravital microscopy

Abstract

Abstract Introduction Intravital microscopy (IVM) provides in vivo real-time imaging of tumor-associated vasculature. Our group was the first to use IVM successfully in human subjects to image melanoma associated vessels. In this preclinical study, we hypothesized that intravenous (IV) nicardipine increases observable blood flow to tumor through vasodilatation and therefore may facilitate drug delivery. Methods Standard window chambers for IVM were implanted into female BALB/c mice. The murine colon cancer cell line CT26HA was inoculated in the skin within the chamber. Fluorescein isothiocyanate dextran (FITC-dex) was injected IV to enhance vessel observation prior to nicardipine (8 μg/mouse). Observations were performed at 100x magnification using a modified Olympus microscope for 10 minutes. Naïve mice were used for control observations. Mice bearing CT26HA were observed on post-inoculation day 5, 12 and 20. Vessel architecture and vessel diameter in response to nicardipine were compared. Results In non-CT26HA bearing mice, nicardipine resulted in a greater than 10% increase in skin vessel diameters directly measured using IVM (pre-nicardipine diameter 82.4 ± 3.6 μm versus post-nicardipine diameter 93.0 ± 3.9 μm. In CT26HA bearing mice, abnormal vessels were observed as early as day 7 even in the absence of a solid tumor mass. Vessel abnormalities included haphazard areas of increased vessel density, aberrant vessel branching patterns, nonfunctional vessels, and altered flow rates. Following nicardipine injection, the diameter of larger tumor-associated vessels did not increase and remained constant (pre: 111.2 ± 2.7 μm vs post: 109.1 ± 3.3 μm). Paradoxically, for smaller vessels (< 20 μm), tumor-associated vessels vasoconstricted following nicardipine injection and returned to baseline diameter after approximately five minutes. Blood flow in these small vessels decreased or stopped during this observation. Conclusions Observation of dynamic vessel changes from vasoactive agents is feasible using IVM. For tumor-associated vessels, nicardipine was not shown to increase vessel diameter and counterintuitively decreased diameters of smaller vessels. Implication on drug delivery from vasoactive agents will lead to further pre-clinical study of applications for human IVM. Citation Format: Emmanuel M. Gabriel, Daniel Fisher, Minhyung Kim, Colin Powers, Anthony Visioni, Jason Muhitch, Joseph Skitzki. Dynamic control of tumor vasculature with direct observation using intravital microscopy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4225.