Mesenchymal transformation of pulmonary endothelial cells contributes to the formation of a metastatic microenvironment, but it is not known whether this precedes or follows early metastasis formation. In the present work, we characterize the development of nitric oxide (NO) deficiency and markers of endothelial–mesenchymal transition (EndMT) in the lung in relation to the progression of 4T1 metastatic breast cancer injected orthotopically in mice. NO production, endothelial nitric oxide synthase (eNOS) phosphorylation status, markers of EndMT in the lung, pulmonary endothelium permeability, and platelet activation/reactivity were analyzed in relation to the progression of 4T1 breast cancer metastasis to the lung, as well as to lung tissue remodeling, 1–5 weeks after 4T1 cancer cell inoculation in Balb/c mice. Phosphorylation of eNOS and NO production in the lungs of 4T1 breast cancer-bearing mice was compromised prior to the development of pulmonary metastasis, and was associated with overexpression of Snail transcription factor in the pulmonary endothelium. These changes developed prior to the mesenchymal phenotypic switch in the lungs evidenced by a decrease in vascular endothelial-cadherin (VE-CAD) and CD31 expression, and the increase in pulmonary endothelial permeability, phenomena which coincided with early pulmonary metastasis. Increased activation of platelets was also detected prior to the early phase of metastasis and persisted to the late phase of metastasis, as evidenced by the higher percentage of unstimulated platelets binding fibrinogen without changes in von Willebrand factor and fibrinogen binding in response to ADP stimulation. Decreased eNOS activity and phosphorylation resulting in a low NO production state featuring pulmonary endothelial dysfunction was an early event in breast cancer pulmonary metastasis, preceding the onset of its phenotypic switch toward a mesenchymal phenotype (EndMT) evidenced by a decrease in VE-CAD and CD31 expression. The latter coincided with development of the first metastatic nodules in the lungs. These findings suggest that early endothelial dysfunction featured by NO deficiency rather than EndMT, might represent a primary regulatory target to prevent early pulmonary metastasis.

Dual antiplatelet therapy with clopidogrel and aspirin increases mortality in 4T1 metastatic breast cancer-bearing mice by inducing vascular mimicry in primary tumour Dual antiplatelet therapy with clopidogrel and aspirin increases mortality in 4T1 metastatic breast cancer-bearing mice by inducing vascular mimicry in primary tumour

Overwhelming evidence suggests that platelets have a detrimental role in promoting cancer spread via platelet-cancer cell interactions linked to thrombotic mechanisms. On the other hand, a beneficial role of platelets in the preservation of the endothelial barrier in inflammatory conditions has been recently described, a phenomenon that could also operate in cancer-related inflammation. It is tempting to speculate that some antiplatelet strategies to combat cancer metastasis may impair the endogenous platelet-dependent mechanisms preserving endothelial barrier function. If the protective function of platelets is impaired, it may lead to increased endothelial permeability and more efficient cancer cell intravasation in the primary tumor and cancer cell extravasation at metastatic sites. In this commentary, we discuss current evidence that could support this hypothesis.

The characteristic feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19 disease) is that its course is asymptomatic or mild in the majority of cases, while increasing age and/or underlying cardiovascular diseases predispose for a severalfold increased case fatality rate. ¹ This association has not been explained as yet, and several potential mechanisms have been put forward to uncover why the course of the disease is more severe in elderly patients with underlying cardiovascular risk factors and/or cardiovascular diseases. Some hypotheses have been proposed, including the role of angiotensin-converting enzyme 2 (ACE2) (a functional receptor for SARS-CoV-2), accelerated ageing of the immune system, or other mechanisms linked to comorbidities. ¹ However, it has been recently reported that SARS-CoV-2 virus-induced endotheliitis and microvascular endothelium pathology could contribute to vascular bed dysfunction in different organs and to fatal clinical sequelae in COVID-19 patients. ² Indeed, in patients who died from COVID-19, severe endothelial injury, widespread thrombosis, and microangiopathy were detected, ³ pointing to the important role of vascular pathophysiology and alterations in endothelial function in COVID-19 disease. In fact, a biomarker of endothelial activation and altered endothelial permeability, angiopoietin-2, was found to be a good predictive factor for severe cases of COVID-19 ⁴ disease underscoring important pathophysiological role of vascular endothelial dysfunction in COVID-19, with its distinct vascular endotype. ⁵