Mutations in FMS-like tyrosine kinase 3 (FLT3), such as internal tandem duplications (ITDs), can be found in up to 23% of patients with acute myeloid leukemia (AML) and confer a poor prognosis. Current treatment options for FLT3(ITD)-positive AMLs include genotoxic therapy and FLT3 inhibitors (FLT3i's), which are rarely curative. PARP1 inhibitors (PARP1i's) have been successfully applied to induce synthetic lethality in tumors harboring BRCA1/2 mutations and displaying homologous recombination (HR) deficiency. We show here that inhibition of FLT3(ITD) activity by the FLT3i AC220 caused downregulation of DNA repair proteins BRCA1, BRCA2, PALB2, RAD51, and LIG4, resulting in inhibition of 2 major DNA double-strand break (DSB) repair pathways, HR, and nonhomologous end-joining. PARP1i, olaparib, and BMN673 caused accumulation of lethal DSBs and cell death in AC220-treated FLT3(ITD)-positive leukemia cells, thus mimicking synthetic lethality. Moreover, the combination of FLT3i and PARP1i eliminated FLT3(ITD)-positive quiescent and proliferating leukemia stem cells, as well as leukemic progenitors, from human and mouse leukemia samples. Notably, the combination of AC220 and BMN673 significantly delayed disease onset and effectively reduced leukemia-initiating cells in an FLT3(ITD)-positive primary AML xenograft mouse model. In conclusion, we postulate that FLT3i-induced deficiencies in DSB repair pathways sensitize FLT3(ITD)-positive AML cells to synthetic lethality triggered by PARP1i's. Therefore, FLT3(ITD) could be used as a precision medicine marker for identifying AML patients that may benefit from a therapeutic regimen combining FLT3 and PARP1i's.

Cancer metastasis and secondary tumor initiation largely depend on circulating tumor cell (CTC) and vascular endothelial cell (EC) interactions by incompletely understood mechanisms. Endothelial glycocalyx (GCX) dysfunction may play a significant role in this process. GCX structure depends on vascular flow patterns, which are irregular in tumor environments. This work presents evidence that disturbed flow (DF) induces GCX degradation, leading to CTC homing to the endothelium, a first step in secondary tumor formation. A 2‐fold greater attachment of CTCs to human ECs was found to occur under DF conditions, compared to uniform flow (UF) conditions. These results corresponded to an approximately 50% decrease in wheat germ agglutinin (WGA)‐labeled components of the GCX under DF conditions, vs UF conditions, with undifferentiated levels of CTC‐recruiting E‐selectin under DF vs UF conditions. Confirming the role of the GCX, neuraminidase induced the degradation of WGA‐labeled GCX under UF cell culture conditions or in Balb/C mice and led to an over 2‐fold increase in CTC attachment to ECs or Balb/C mouse lungs, respectively, compared to untreated conditions. These experiments confirm that flow‐induced GCX degradation can enable metastatic CTC arrest. This work, therefore, provides new insight into pathways of secondary tumor formation.

BACKGROUND: The onset of many disease processes depends on the function of the endothelial cell (EC) glycocalyx (GCX) which acts as a flow-dependent barrier to cellular infiltration and molecular transport across the blood vessel wall. OBJECTIVE: This review aims to examine these processes with the potential end goal of implementing GCX repair to restore EC barrier function and slow the progression of disease. METHODS: Cell and mouse studies were employed to examine the state of EC GCX in healthy versus disruptive flow conditions. Correlates of observations of the GCX with a number of EC functions were sought with an emphasis on studies of trans-endothelial barrier integrity against vessel wall infiltration of cells and molecules from the circulation. To demonstrate the importance of GCX as a regulator of trans-endothelial infiltration, assays were performed using ECs with an intact GCX and compared to assays of ECs with an experimentally degraded GCX. Studies were also conducted of ECs in which a degraded GCX was repaired. RESULTS: In healthy flow conditions, the EC GCX was found to be thick and substantially covered the endothelial surface. GCX expression dropped significantly in complex flow conditions and coincided with a disease-like cellular and molecular accumulation in the endothelium or within the blood vessel wall. Therapeutic repair of the GCX abolished this accumulation. CONCLUSIONS: Regenerating the degraded GCX reverses EC barrier dysfunction and may attenuate the progression of vascular disease.

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Purpose The endothelial glycocalyx (GCX) plays a critical role in the health of the vascular system. Degradation of the GCX has been implicated in the onset of diseases like atherosclerosis and cancer because it disrupts endothelial cell (EC) function that is meant to protect from atherosclerosis and cancer. Examples of such EC function include interendothelial cell communication via gap junctions and receptor-mediated interactions between endothelial and tumor cells. This review focuses on GCX-dependent regulation of these intercellular interactions in healthy and diseased states. The ultimate goal is to build new knowledge that can be applied to developing GCX regeneration strategies that can control intercellular interaction in order to combat the progression of diseases such as atherosclerosis and cancer. Methods In vitro and in vivo studies were conducted to determine the baseline expression of GCX in physiologically relevant conditions. Chemical and mechanical GCX degradation approaches were employed to degrade the GCX. The impact of intact versus degraded GCX on intercellular interactions was assessed using cytochemistry, histochemistry, a Lucifer yellow dye transfer assay, and confocal, intravital, and scanning electron microscopy techniques. Results Relevant to atherosclerosis, we found that GCX stability determines the expression and functionality of Cx43 in gap junction-mediated EC-to-EC communication. Relevant to cancer metastasis, we found that destabilizing the GCX through either disturbed flow-induced or enzyme induced GCX degradation results in increased E-selectin receptor-mediated EC-tumor cell interactions. Conclusion Our findings lay a foundation for future endothelial GCX-targeted therapy, to control intercellular interactions and limit the progression of atherosclerosis and cancer.

The endothelium, a crucial homeostatic organ, regulates vascular permeability and tone. Under physiological conditions, endothelial stimulation induces vasodilator endothelial nitric oxide (eNO) release and prevents adhesion molecule accessibility and leukocyte adhesion and migration into vessel walls. Endothelium dysfunction is a principal event in cardiovascular disorders, including atherosclerosis. Minimal attention is given to an important endothelial cell structure, the endothelial glycocalyx (GCX), a negatively charged heterogeneous polysaccharide that serves as a protective covering for endothelial cells and enables endothelial cells to transduce mechanical stimuli into various biological and chemical activities. Endothelial GCX shedding thus plays a role in endothelial dysfunction, for example by increasing vascular permeability and decreasing vessel tone.Consequently, there is increasing interest in developing therapies that focus on GCX repair to limit downstream endothelium dysfunction and prevent further downstream cardiovascular events. Here, we present diosmin (3′,5,7-trihydroxy-4′-methoxyflavone-7-rhamnoglucoside), a flavone glycoside of diosmetin, which downregulates adhesive molecule expression, decreases inflammation and capillary permeability, and upregulates eNO expression. Due to these pleiotropic effects of diosmin on the vasculature, a possible unidentified mechanism of action is through GCX restoration. We hypothesize that diosmin positively affects GCX integrity along with GCX-related endothelial functions. Our hypothesis was tested in a partial ligation left carotid artery (LCA) mouse model, where the right carotid artery was the control for each mouse. Diosmin (50 mg/kg) was administered daily for 7 days, 72 h after ligation. Within the ligated mice LCAs, diosmin How to cite this article: Mitra R, Nersesyan A, Pentland K, Melin MM, Levy RM, Ebong EE. Diosmin and its glycocalyx restorative and anti-inflammatory effects on injured blood vessels.

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