AKR1B10 (Aldo-keto reductase family 1 B10) promotes brain metastasis of lung cancer cells in a multi-organ microfluidic chip model

Brain metastasis (BM) is a leading cause of mortality in patients with non-small cell lung cancer (NSCLC). However, the molecular mechanisms underlying BM of NSCLC remain largely unknown because of the lack of models to accurately investigate such a dynamic and complex process. Here we developed a multi-organ microfluidic chip as a new methodological platform to study BM. The chip consisted of two bionic organ units - an upstream "lung" and a downstream "brain" characterized by a functional "blood-brain barrier (BBB)" structure, allowing real-time visual monitoring of the entire BM process, from the growth of primary tumor to its breaking through the BBB, and finally reaching the brain parenchyma. The chip was verified by lung cancer cell lines with differing metastatic abilities and then applied for the BM research where we first demonstrated that the protein expression of Aldo-keto reductase family 1 B10 (AKR1B10) was significantly elevated in lung cancer BM. Silencing AKR1B10 in brain metastatic tumor cells suppressed their extravasation through the BBB in the in vitro Transwell model, in our ex vivo microfluidic chip, as well as the in vivo model of brain metastasis in nude mice. Moreover, AKR1B10 downregulated the expression of matrix metalloproteinase (MMP)-2 and MMP-9 via MEK/ERK signaling in metastatic lung cancers. These data suggest that our multi-organ microfluidic chip is a practical alternative to study BM pathogenesis, and AKR1B10 is a diagnostic biomarker and a prospective therapeutic target for NSCLC BM. STATEMENT OF SIGNIFICANCE: Brain metastasis (BM) of non-small cell lung cancer (NSCLC) is a complex cascade, and in particular, the process of lung cancer cells penetrating the blood-brain barrier (BBB) is very unique. However, due to the lack of reliable models that can faithfully mimic the dynamic process of BBB breaking, its molecular mechanisms have not well elucidated so far. In addition, although Aldo-keto reductase family 1 B10 (AKR1B10) has been implicated to the tumor development of liver cancer and many other cancers, little is known on its roles in the BM. Here, we established a multi-organ microfluidic bionic chip platform to recapitulate the entire BM process, and applied it to the BM pathology research, especially BBB extravasation. By using the chip and traditional models synergistically, we first demonstrated that AKR1B10 was significantly elevated in lung cancer BM, and defined the value of AKR1B10 as a diagnostic serum biomarker for lung cancer patients suffering from BM. Further, we investigated the role and mechanisms of AKR1B10 in BM that it promotes the extravasation of cancer cells through the BBB.