Introduction:
Lung cancer (LC) is a major cause of death among cancer patients worldwide. About 30-55% of LC patients suffer from brain metastasis (BM), with lung adenocarcinoma (LUAD) being one of the main tumor types that develop BM. Consequently, researchers have been increasingly conducting studies related to BM-LUAD in recent years. However, due to the unique characteristics of BM tumors, obtaining genuine BM cells remains challenging. Therefore, researchers often use nude mouse models to establish BM cell lines. Previous methods have several shortcomings, such as high costs, lengthy timeframes, the need for specialized imaging equipment, and difficulties in capturing early features of BM occurrence. To address these issues, we employed an improved method and successfully obtained various BM-LUAD cell lines that exhibit different stage features of BM.

Methods:
By performing low-cell-number (500-4000 cells) circulating intracranial injections in nude mice, we obtained the H1975-BM1, BM2, and BM3 cell lines. We then conducted RNA-Seq and utilized various bioinformatics analyses to reveal the transcriptomic characteristics of the different stages of BM cell lines. Subsequently, we validated our findings through experiments including Transwell assays, CCK8, cell adhesion, and nude mice subcutaneous tumor implantation.

Results:
In the H1975-BM1 cell line, the tumor cells are more focused on proliferation and migration. In contrast, in the H1975-BM3 cell line, the function of the tumor cells shifts more toward cell adhesion and secretion, particularly the secretion of various cytokines related to immune cell recruitment. Subcutaneous tumor implantation also confirmed this finding, as H1975-BM3 exhibited a larger tumor volume and formed a bigger secretion cystic cavity.

Conclusions:
We successfully obtained high-confidence BM-LUAD cell lines through an improved new method, revealing distinct characteristics between the different stage cell lines of BM-LUAD.