Fig. 3: The synthetic MNs (scaffold implants) eradicate tumor cells and drive metastatic dormancy, while the endogenous lungs promote metastatic outgrowth in BALB/c mice with 4T1 metastatic breast cancer.

a, b Different fates of 4T1-Luc2-tdTomato cells recruited to diseased scaffolds and lungs of BALB/c mice bearing 4T1 tumor in experimental (a) and spontaneous (b) metastasis models. In the experimental metastasis model, 4T1-Luc2-tdTomato cells were transfused to BALB/c mice bearing non-fluorescent 4T1 tumor through intracardiac injection, and then tdTomato⁺ cells in MNs were measured by flow cytometry at day 1 and day 12 after injection. In the spontaneous metastasis model, 4T1-Luc2-tdTomato cells were orthotopically inoculated to BALB/c mice, and then tdTomato⁺ cells in the MNs were quantified at days 14, 21, and 28 after tumor inoculation. c Antitumor and pro-tumor transcription factors are differentially overexpressed in 4T1 cells co-cultured with diseased scaffold and lung cells. Activities of transcription factors were measured by TRACER (TRanscriptional Activity CEll aRrays). d Apoptosis and in vitro proliferation of 4T1-Luc2-tdTomato cells co-cultured with cells derived from diseased scaffolds or lungs. e Lung metastases of BALB/c mice without or with scaffold implants at days 10, 15, and 20 after orthotopic inoculation of 4T1-Luc2-tdTomato, representing early, intermediate, and late stages of cancer, respectively. Mice were immediately imaged after surgically resecting the primary tumor at the desired time. Mice bearing scaffold implants were less likely to have detectable metastases than mice without implants (top panel, p value is from Fisher’s exact test). Mice bearing scaffolds had reduced luminescence localized to the lung in the day 15 and day 20 groups (lower panel, p values are from non-parametric Mann–Whitney test). Data are shown as Mean ± SEM. p values are from student’s two-tailed t test when not otherwise specified. n = 6 for (a), (b), n = 3 for (d, top and lower panels), and n = 8 for (e, lower panel). Source data are provided as a Source Data file.