Enhanced perfusion following exposure to radiotherapy: a theoretical investigation

Tumour angiogenesis leads to the formation of blood vessels that are structurally and spatially heterogeneous. Poor blood perfusion, in conjunction with increased hypoxia and oxygen heterogeneity, impairs a tumour’s response to radiotherapy. The optimal strategy for enhancing tumour perfusion remains unclear, preventing its regular deployment in combination therapies. In this work, we first identify vascular architectural features that correlate with enhanced perfusion following radiotherapy, using in vivo imaging data from vascular tumours. Then, we present a novel computational model to determine the relationship between these architectural features and blood perfusion in silico. If perfusion is defined to be the proportion of vessels that support blood flow, we find that vascular networks with small mean diameters and large numbers of angiogenic sprouts show the largest increases in perfusion post-irradiation for both biological and synthetic tumours. We also identify cases where perfusion increases due to the pruning of hypoperfused vessels, rather than blood being rerouted. These results indicate the importance of considering network composition when determining the optimal irradiation strategy. In the future, we aim to use our findings to identify tumours that are good candidates for perfusion enhancement and to improve the efficacy of combination therapies

Abnormal morphology biases haematocrit distribution in tumour vasculature and contributes to heterogeneity in tissue oxygenation

Oxygen heterogeneity in solid tumors is recognized as a limiting factor for therapeutic efficacy. This heterogeneity arises from the abnormal vascular structure of the tumor, but the precise mechanisms linking abnormal structure and compromised oxygen transport are only partially understood. In this paper, we investigate the role that red blood cell (RBC) transport plays in establishing oxygen heterogeneity in tumor tissue. We focus on heterogeneity driven by network effects, which are challenging to observe experimentally due to the reduced fields of view typically considered. Motivated by our findings of abnormal vascular patterns linked to deviations from current RBC transport theory, we calculated average vessel lengths L⎯⎯ and diameters d⎯⎯ from tumor allografts of three cancer cell lines and observed a substantial reduction in the ratio λ=L⎯⎯/d⎯⎯ compared to physiological conditions. Mathematical modeling reveals that small values of the ratio λ (i.e., λ<6 ) can bias hematocrit distribution in tumor vascular networks and drive heterogeneous oxygenation of tumor tissue. Finally, we show an increase in the value of λ in tumor vascular networks following treatment with the antiangiogenic cancer agent DC101. Based on our findings, we propose λ as an effective way of monitoring the efficacy of antiangiogenic agents and as a proxy measure of perfusion and oxygenation in tumor tissue undergoing antiangiogenic treatment

Differential mechanisms associated with vascular disrupting action of electrochemotherapy: intravital microscopy on the level of single normal and tumor blood vessels.

Electropermeabilization/electroporation (EP) provides a tool for the introduction of molecules into cells and tissues. In electrochemotherapy (ECT), cytotoxic drugs are introduced into cells in tumors, and nucleic acids are introduced into cells in gene electrotransfer. The normal and tumor tissue blood flow modifying effects of EP and the vascular disrupting effect of ECT in tumors have already been determined. However, differential effects between normal vs. tumor vessels, to ensure safety in the clinical application of ECT, have not been determined yet. Therefore, the aim of our study was to determine the effects of EP and ECT with bleomycin on the HT-29 human colon carcinoma tumor model and its surrounding blood vessels. The response of blood vessels to EP and ECT was monitored in real time, directly at the single blood vessel level, by in vivo optical imaging in a dorsal window chamber in SCID mice with 70 kDa fluorescently labeled dextrans. The response of tumor blood vessels to EP and ECT started to differ within the first hour. Both therapies induced a vascular lock, decreased functional vascular density (FVD) and increased the diameter of functional blood vessels within the tumor. The effects were more pronounced for ECT, which destroyed the tumor blood vessels within 24 h. Although the vasculature surrounding the tumor was affected by EP and ECT, it remained functional. The study confirms the current model of tumor blood flow modifying effects of EP and provides conclusive evidence that ECT is a vascular disrupting therapy with a specific effect on the tumor blood vessels

Illustration of FD leakage from blood vessels surrounding the tumor and their constriction after EP and ECT.

<p>Images were acquired at 20×magnification. Control – mice without treatment, Bleomycin – mice treated with bleomycin only, EP – mice treated with EP, ECT – mice treated with ECT. (<b>A</b>) Illustration of FD leakage from blood vessels surrounding the tumor, when FD was injected <i>i.o.</i> before the therapy. Arrows indicate the position of the tumor. Scale bar is 2 mm. (<b>B</b>) Illustration of the constriction of blood vessels surrounding the tumor visualized by FD. The enlarged sections of images were taken at 20×magnification. Scale bar is 500 µm.</p

Characterization of the DWC model.

<p>(<b>A</b>) Filling of tumor blood vessels after <i>i.o.</i> injection of FD and increase of fluorescence intensity in the tumor tissue in control mice. Mean fluorescence intensities were expressed as a percentage of the maximum mean fluorescence intensity (Imax) reached in the observation period. The first image in the series was acquired ∼10 s after the <i>i.o.</i> injection of FD. (<b>B</b>) The timeline of the protocol used in the experiments.</p

Illustration of a “vascular lock” and re-perfusion of tumor blood vessels in the first hour and 4–24 h after EP and ECT.

<p>Tumor blood vessels were visualized by fluorescence microscopy. Control – mice without treatment, EP – mice treated with EP, ECT – mice treated with ECT. (<b>A</b>) FD was injected <i>i.o.</i> 1 min after EP, and images were acquired at 20×magnification at designated times. Arrows indicate the position of the tumor. Scale bar is 2 mm. (<b>B</b>) RhD was injected <i>i.o.</i> at 4, 8 and 24 h after the therapy, and images were acquired 5 min after the injection at 80×magnification. The images are representative of different tumors. Tumors are marked with a dashed line. Scale bar is 500 µm.</p

Timeline of the decrease in FVD and increase in D_V after EP and ECT.

<p>Control – mice without treatment, Bleomycin – mice treated with bleomycin only, EP – mice treated with EP, ECT – mice treated with ECT. (<b>A</b>) The changes in FVD within the tumors are presented as a function of time. (<b>B</b>) The changes of D_V within the tumors are presented as a function of time. n = 3–6. **p<0.05 compared to all other groups, *p<0.05 compared to control and bleomycin groups. Error bars indicate SEM.</p