Fibroblast growth factor receptor 2 (FGFR2) is a membrane‐spanning tyrosine kinase that mediates FGF signaling. Various FGFR2 alterations are detected in breast cancer, yet it remains unclear if activation of FGFR2 signaling initiates tumor formation. In an attempt to answer this question, a mouse model berrying an activation mutation of FGFR2 (FGFR2‐S252W) in the mammary gland is generated. It is found that FGF/FGFR2 signaling drives the development of triple‐negative breast cancer accompanied by epithelial‐mesenchymal transition that is regulated by FGFR2‐STAT3 signaling. It is demonstrated that FGFR2 suppresses BRCA1 via the ERK‐YY1 axis and promotes tumor progression. BRCA1 knockout in the mammary gland of the FGFR2‐S252W mice significantly accelerated tumorigenesis. It is also shown that FGFR2 positively regulates PD‐L1 and that a combination of FGFR2 inhibition and immune checkpoint blockade kills cancer cells. These data suggest that the mouse models mimic human breast cancers and can be used to identify actionable therapeutic targets.

Cancer metastasis is an extremely complex process affected by many factors. An acidic microenvironment can drive cancer cell migration toward blood vessels while also hampering immune cell activity. Here, we identified a mechanism mediated by sialyltransferases that induces an acidic tumor-permissive microenvironment (ATPME) in BRCA1-mutant and most BRCA1-low breast cancers. Hypersialylation mediated by ST8SIA4 perturbed the mammary epithelial bilayer structure and generated an ATPME and immunosuppressive microenvironment with increased PD-L1 and PD1 expressions. Mechanistically, BRCA1 deficiency increased expression of VEGFA and IL6 to activate TGFβ–ST8SIA4 signaling. High levels of ST8SIA4 led to accumulation of polysialic acid (PSA) on mammary epithelial membranes that facilitated escape of cancer cells from immunosurveillance, promoting metastasis and resistance to αPD1 treatment. The sialyltransferase inhibitor 3Fax-Peracetyl Neu5Ac neutralized the ATPME, sensitized cancers to immune checkpoint blockade by activating CD8 T cells, and inhibited tumor growth and metastasis. Together, these findings identify a potential therapeutic option for cancers with a high level of PSA. Significance: BRCA1 deficiency generates an acidic microenvironment to promote cancer metastasis and immunotherapy resistance that can be reversed using a sialyltransferase inhibitor.

Breast cancer–associated gene 1 ( Brca1 ) deficiency induces the onset of breast cancer formation, accompanied with extensive genetic alterations. Here, we used both the sleeping beauty transposon mutagenesis system and CRISPR-Cas9–mediated genome-wide screening in mice to identify potential genetic alterations that act synergistically with Brca1 deficiency to promote tumorignesis. Both approaches identified Cullin-5 as a tumor suppressor, whose mutation enabled Brca1 -deficient cell survival and accelerated tumorigenesis by orchestrating tumor microenvironment. Cullin-5 suppresses cell growth through ubiquitylating and degrading adenosine 3′,5′-monophosphate–responsive element binding protein 1 (CREB1), especially under protein damage condition. Meanwhile, Cullin-5 deficiency activated CREB1-CCL2 signaling and resulted in the accumulation of monocytes and polymorphonuclear myeloid–derived suppressor cells, reduction of T cells that benefit tumor progression in both Brca1 -deficient cells and wild-type cells. Blocking CREB1 activity either through gene knockout or specific inhibitor treatment suppressed changes in the tumor microenvironment caused by Cullin-5 deficiency and blocked tumor progression.

Breast cancer is a major global health burden with the highest incidence in women, and triple-negative breast cancer (TNBC) stands out as the most malignant subtype. Effective therapeutic targets are urgently needed to develop new therapies for TNBC. Nicotinic acetylcholine receptor is a ligand-gated ion channel receptor that is associated with the advancement of multiple cancers. Notably, α9 nicotinic acetylcholine receptor (α9 nAChR) is less investigated towards its role in cancer. This study sought to clarify the significance of α9 nAChR in TNBC. Firstly, our results uncovered that the expression of CHRNA9 was notably elevated in TNBC tissues and was associated with poor prognosis of TNBC patients. Further, our data indicated that overexpression of α9 nAChR facilitated the growth of TNBC cells, via mechanisms of simultaneously activating AKT-, ERK- and STAT3-mediated proliferation and negatively regulating ferroptosis through promoting SLC7A11/GSH/GPX4 and Keap1/Nrf2/HO1 signaling. Conversely, CHRNA9 knockdown would completely reverse all this signaling, ultimately inhibiting TNBC tumor growth both in vitro and in vivo. Finally, we reported a specific polypeptide antagonist of α9 nAChR, GeXIVA[1,2] and exerted good anti-tumor effects in tumor-bearing mice of TNBC, which indicated a great potential of GeXIVA[1,2] to be further studied as a novel targeted therapy for TNBC. This study provides a scientific basis for establishing α9 nAChR as a novel therapeutic target for TNBC, which is worthy of further development in the future.

The cryopreservation of cancer tissues to generate frozen libraries is a common practice used worldwide for storing patient samples for later applications. However, frozen samples stored by existing methods cannot be used for initiating living cell cultures, such as patient-derived tumor organoids (PDOs), which offer great potential for personalized treatment. To overcome this challenge, we developed a novel procedure for culturing PDOs using frozen live tumor tissues. We show that tumor specimens stored using this technique maintain their viability and can be successfully used to generate organoids even after long-term freezing, with an impressive success rate of 95.2 %. Importantly, we found that the structural features, tumor marker expression, and drug responses of organoids derived from frozen tissues are similar to those derived from fresh tissues. Moreover, organoids derived from frozen tissues can be routinely passaged and frozen, making them ideal for high-throughput drug screening at any time. Notably, cryopreserved tumor tissues can also be utilized in air-liquid interface (ALI) culture. This method allows for preserving the original tumor microenvironment, making it an invaluable resource for conducting tests on antitumor drug responses, including immune checkpoint inhibitors (ICIs). This innovation has the potential to enable the identification of potentially effective drugs for patients and facilitate the development of novel therapeutic drugs. Thus, we have established protocols for the long-term cryopreservation of cancer tissues to maintain their viability and microenvironment, which are useful for personalized therapy.