Tasneem Cheytan

Neuroendocrine differentiation (NED) promotes lineage plasticity and therapy resistance in prostate and lung cancers. Here we identify NED as a route of treatment escape in breast cancer: neuroendocrine features emerged or increased in 22% of progressive cases, predominantly, but not exclusively, in HER2-positive subtype. Using patient-derived, epithelial/neuroendocrine organoid and xenograft models, we map the epigenetic and transcriptional divergence between epithelial and neuroendocrine states arising from a shared mutational background and define a breast cancer neuroendocrine signature. NED involves epigenetic silencing of EpCAM and amplified HER2, while NEUROD1 functions as a master transcriptional regulator of the neuroendocrine fate. NCAM-positive putative circulating tumor cells were detected in patients in whom EpCAM-based detection had failed. Neuroendocrine tumor cells exhibit an FGFR1 dependency associated with NCAM–FGFR1 interaction and mesenchymal FGFR1 splicing. Together, these findings establish NED as a mechanism of escape from HER2-targeted therapy in breast cancer, with implications for disease monitoring and intervention.

Circulating tumor cells (CTCs) drive metastasis, the leading cause of death in individuals with breast cancer. Due to their low abundance in the circulation, robust CTC expansion protocols are urgently needed to effectively study disease progression and therapy responses. Here we present the establishment of long-term CTC-derived organoids from female individuals with metastatic breast cancer. Multiomics analysis of CTC-derived organoids along with preclinical modeling with xenografts identified neuregulin 1 (NRG1)–ERBB2 receptor tyrosine kinase 3 (ERBB3/HER3) signaling as a key pathway required for CTC survival, growth and dissemination. Genome-wide CRISPR activation screens revealed that fibroblast growth factor receptor 1 (FGFR1) signaling serves a compensatory function to the NRG1–HER3 axis and rescues NRG1 deficiency in CTCs. Conversely, NRG1–HER3 activation induced resistance to FGFR1 inhibition, whereas combinatorial blockade impaired CTC growth. The dynamic interplay between NRG1–HER3 and FGFR1 signaling reveals the molecular basis of cancer cell plasticity and clinically relevant strategies to target it. Our CTC organoid platform enables the identification and validation of patient-specific vulnerabilities and represents an innovative tool for precision medicine.

Biliverdin reductase (BVR)-A is a pleotropic enzyme converting biliverdin to bilirubin and a signaling molecule that has cytoprotective and immunomodulatory effects. We recently showed that biliverdin inhibits the expression of complement activation fragment 5a receptor one (C5aR1) in RAW 264.7 macrophages. In this study, we investigated the role of BVR-A in determining macrophage inflammatory phenotype and function via regulation of C5aR1. We assessed expression of C5aR1, M1-like macrophage markers, including chemokines (RANTES, IP-10), as well as chemotaxis in response to LPS and C5a in bone marrow–derived macrophages from BVR^fl/fl and LysM-Cre:BVR^fl/fl mice (conditional deletion of BVR-A in myeloid cells). In response to LPS, macrophages isolated from LysM-Cre:BVR^fl/fl showed significantly elevated levels of C5aR1 as well as chemokines (RANTES, IP10) but not proinflammatory markers, such as iNOS and TNF. An increase in C5aR1 expression was also observed in peritoneal macrophages and several tissues from LysM-Cre:BVR^fl/fl mice in a model of endotoxemia. In addition, knockdown of BVR-A resulted in enhanced macrophage chemotaxis toward C5a. Part of the effects of BVR-A deletion on chemotaxis and RANTES expression were blocked in the presence of a C5aR1 neutralizing Ab, confirming the role of C5a–C5aR1 signaling in mediating the effects of BVR. In summary, BVR-A plays an important role in regulating macrophage chemotaxis in response to C5a via modulation of C5aR1 expression. In addition, macrophages lacking BVR-A are characterized by the expression of M1 polarization–associated chemokines, the levels of which depend in part on C5aR1 signaling. Key points Myeloid-specific conditional deletion of BVR-A results in increased response to LPS. Macrophages isolated from LysM-Cre:BVR^fl/fl showed elevated levels of C5aR1. Deletion of BVR-A resulted in enhanced macrophage chemotaxis toward C5a. BVR-A–modulated chemotaxis and RANTES levels are dependent in part on C5aR1. Visual Abstract