Growth factor free, peptide-functionalized gelatin hydrogel promotes arteriogenesis and attenuates tissue damage in a murine model of critical limb ischemia.

Critical limb ischemia (CLI) occurs when blood flow is restricted through the arteries, resulting in ulcers, necrosis, and chronic wounds in the downstream extremities. The development of collateral arterioles (i.e. arteriogenesis), either by remodeling of pre-existing vascular networks or de novo growth of new vessels, can prevent or reverse ischemic damage, but it remains challenging to stimulate collateral arteriole development in a therapeutic context. Here, we show that a gelatin-based hydrogel, devoid of growth factors or encapsulated cells, promotes arteriogenesis and attenuates tissue damage in a murine CLI model. The gelatin hydrogel is functionalized with a peptide derived from the extracellular epitope of Type 1 cadherins. Mechanistically, these "GelCad" hydrogels promote arteriogenesis by recruiting smooth muscle cells to vessel structures in both ex vivo and in vivo assays. In a murine femoral artery ligation model of CLI, delivery of in situ crosslinking GelCad hydrogels was sufficient to restore limb perfusion and maintain tissue health for 14 days, whereas mice treated with gelatin hydrogels had extensive necrosis and autoamputated within 7 days. A small cohort of mice receiving the GelCad hydrogels were aged out to 5 months and exhibited no decline in tissue quality, indicating durability of the collateral arteriole networks. Overall, given the simplicity and off-the-shelf format of the GelCad hydrogel platform, we suggest it could have utility for CLI treatment and potentially other indications that would benefit from arteriole development.

Ultrasound Imaging Enables Longitudinal Tracking of Vascular Changes that Correlate with Immune Cell Infiltration After Radiotherapy.

While immunotherapy shows great promise in patients with triple negative breast cancer, many will not respond to treatment, and predicting response is made difficult by significant tumor heterogeneity. Non-invasive imaging of the tumor vasculature enables the monitoring of treatment and has potential to aid in predicting therapeutic response. Here, we use ultrafast power doppler ultrasound (US) to track longitudinal changes in the vascular response to radiotherapy in two breast cancer models to correlate vascular and immune changes in the tumor microenvironment. Tumor volume and vascular index were calculated to evaluate the effects of radiation using US imaging. US tumor measurements and the quantified vascular response to radiation were confirmed with caliper measurements and immunohistochemistry observations, respectively, demonstrating a proof-of-principle method for non-invasive vascular monitoring. Additionally, we found significant infiltration of CD8+ T cells into irradiated tumors 10 days after radiation, which followed a sustained decline in vascular index that was first observed 1 day post-radiation. Taken together, our findings reveal the potential for ultrafast power doppler US to evaluate changes in tumor vasculature that may be indicative of the tumor-immune microenvironment and ultimately improve patient outcomes by predicting response to immunotherapy.