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Research Highlights

Luo, Xunrong1

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doi: 10.1097/TP.0000000000003826
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Pazopanib Ameliorates Acute Lung Injuries via Inhibition of MAP3K2 and MAP3K3

Yuan Q, Basit A, Liang W, et al. Sci Transl Med. 2021;13:eabc2499.

Acute lung injury (ALI) can result from microbial infections and airway aspiration. In lung transplantation, ALI can be the result of ischemia followed by reperfusion after recipient organ implantation. No current therapeutic intervention can effectively treat or prevent ALI, representing a clear unmet need. A hallmark of ALI is the infiltration of neutrophils in the lungs.1 While their production of reactive oxygen species (ROS) is critically important for clearing pathogens during infections, its role in sterile lung inflammation is more controversial. In neutrophils, ROS is produced through the action of an NADPH oxidase, which consists of 4 cytosolic and 2 membrane components that come together under inflammatory stimuli. A key step in the activation of the NADPH oxidase is the phosphorylation of the cytosolic component p47phox subunit. However, aberrant phosphorylation of p47phox could result in functional impairment of the NADPH oxidase and consequent inhibition of ROS production. In neutrophils, such an aberrant phosphorylation can be accomplished by 2 nonredundant kinases: mitogen-activated protein kinase 2 (MAP3K2) and MAP3K3.

In the present study, Yuan et al first demonstrated in mice that myeloid cell-specific genetic deletion of MAP3K2 and MAP3K3 or a point mutation in p47phox that rendered it resistant to phosphorylation by MAP3K2 and MAP3k3 resulted in enhanced ROS production, and protected mice in experimental models of ALI induced either by orotracheal LPS (mimicking microbial infections) or by orotracheal HCL (mimicking acid aspiration). The mechanism of protection appeared to involve the elimination of aberrant phosphorylation as a potential impediment to subunit interaction necessary for NADPH oxidase activation. Importantly, they showed that the protective effect depended on enhanced local production of H2O2, which, in turn, led to reduced apoptosis and increased proliferation of lung epithelial cells. The authors then performed a screening of chemical compounds for specific MAP3K2/3 inhibitors, and unexpectedly identified pazopanib, an FDA-approved oral drug for renal cell carcinoma,2 as a highly specific and potent MAP3K2/3 inhibitor which in mice ameliorated ALI in both the LPS and the HCL models by inhibiting aberrant p47phox phosphorylation and increasing neutrophil ROS production. To demonstrate the clinical utility of pazopanib in ALI, the authors treated 5 pairs of lung transplant recipients (each pair receiving 1 lung from the same donor) with 1 perioperative oral dose of pazopanib, and followed their chest X-ray film for pulmonary edema for 5 consecutive days posttransplant. Remarkably, a single dose of pazopanib given at the time of lung transplant resulted in consistently reduced pulmonary edema from the first day (day 1) to the last day (day 5) of the follow-up.

This study provides a novel mechanistic insight for repurposing an FDA-approved anticancer drug pazopanib for use in ALI with relevance for lung transplantation. Given the encouraging results in the 1 perioperative oral dose regimen in lung allograft recipients, a pragmatic question that should now be addressed is whether repetitive dosing and possibly via a more direct route (eg, airway delivery and intravenous delivery) may enhance the therapeutic efficacy. A more counter-intuitive aspect of these observations, as the authors pointed out, is that excessive amounts of ROS are generally considered to be proinflammatory, and yet a “moderate” increase in myeloid cell ROS favors protection in settings of ALI. Therefore, whether the protection seen here is exquisitely dependent on the level and the specific cell source of ROS in these models will need to be carefully examined. A more granulated understanding of this question would have a significant impact on how best to use pazopanib for the desired effect of ameliorating ALI.

In summary, the current study demonstrates an unexpected benefit of myeloid cell ROS in promoting pulmonary vascular and epithelial cell integrity in ALI. A detailed examination of the mechanisms of protection of this approach is now warranted and will provide useful insight in exploiting this pathway in the treatment of ALI.

Advancing the Ethical Dialogue About Monkey/Human Chimeric Embryos and Chimeric Contribution of Human Extended Pluripotent Stem Cells to Monkey Embryos Ex Vivo

Greely HT, Farahany NA. Cell. 2021;184:1962–1963; Tan T, Wu J, Si C, et al. Cell. 2021;184:2020–2032.e14.

In transplantation, organ shortage and long waitlist have motivated researchers to seek alternative sources of organs, such as xenogeneic sources and regenerated organs. One potential approach for generating large quantities of regenerated human organs is the use of human pluripotent stem cells (hPSCs) for interspecies organogenesis via blastocyte complementation.1 This is because PSCs can not only self-renew but also differentiate into all adult cell types. It is well known that the ability of forming chimeras between hPSCs, and host species cells are a requirement for successful interspecies organogenesis, and it is speculated that species that are evolutionarily closer to humans would be better hosts for a higher success rate for forming chimeras. Furthermore, hPSCs in different pluripotency states also differ in their chimeric potential when introduced into animal embryos.

A type of hPSCs called human “extended” PSCs (hEPSCs) have been generated via inhibiting critical differentiation pathways and have recently been shown to demonstrate improved chimeric capability in murine embryos.2 In the present study, Tan et al tested such hEPSCs for chimera formation within cynomolgus monkey (CM) embryos cultured ex vivo. They injected hEPSCs into early blastocytes from CMs 6 d postfertilization, and took advantage of a method that allowed prolonged ex vivo cultures of such embryos for up to 20 d, and determined the presence of human-CM chimerism in the cultured embryos. Remarkably, at 10th day after fertilization, the majority of the chimeric embryos were still alive in cultures. Although the number of surviving chimeric embryos dropped precipitously between days 15 and 19, progenies from hEPSCs were readily detectable in epiblasts and hypoblasts of the surviving chimeras. Importantly, the authors uncovered signaling events underlying the interspecies cross-talk that may have shaped the developmental trajectories of hEPSCs within the chimeric embryos. These studies coupled with techniques allowing effective gene editing will likely have enormous implications in both investigating developmental questions as well as in regenerative organogenesis for transplantation.

However, this unconventional research has clearly also yet again pushed the limits of current ethical and social boundaries. As poignantly discussed in a Commentary accompanying this paper, the introduction of hEPSCs into CM blastocytes will allow human cells to potentially integrate and differentiate into discrete cell populations throughout the developing chimeric embryos; and if implanted into a uterus, potentially lead to living chimeric fetuses. Whether this possibility can occur in reality is largely unknown at the moment, but the mere possibility most certainly raises anxiety and important issues that should be discussed by the scientific and ethics community in anticipation. At the most basic level, animal welfare and consent from human subjects providing hEPCSs for such research should be ensured by special committees with the needed scientific and ethics expertise. But in entirely uncharted territory are issues stemming from mixing human and monkey cells, and the potential of true living chimeric creatures developed from chimeric embryos. Mixed in these considerations are sentiments from the general public with highly varying degrees of preparedness.

In summary, the current study provides useful cellular and molecular insights for human/non-human chimeric embryo development. In addition to advancing the scientific frontier, important ethical and social concerns are once again brought to the forefront for consideration by our society at large.

REFERENCES

1. Matthay MA, Zemans RL. The acute respiratory distress syndrome: pathogenesis and treatment. Annu Rev Pathol. 2011; 6:147–163
2. Zivi A, Cerbone L, Recine F, et al. Safety and tolerability of pazopanib in the treatment of renal cell carcinoma. Expert Opin Drug Saf. 2012; 11:851–859

REFERENCES

1. Suchy F, Nakauchi H. Interspecies chimeras. Curr Opin Genet Dev. 2018; 52:36–41
2. Gao X, Nowak-Imialek M, Chen X, et al. Establishment of porcine and human expanded potential stem cells. Nat Cell Biol. 2019; 21:687–699
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