Supplementary Figure 4. Overexpression of IL13Rα2 does not increase metastatic colonization in poorly invasive BT474M1 BC cells. Poorly metastatic ER+HER2+ BT474M1 cells expressing EV or OE-IL13RA2 and a luciferase reporter, were induced with doxycycline for 48 h prior to injecting in dox-treated NSG mice implanted with 1 mg E2 pellets (N=12 per group). Brain metastatic colonization was measured via IVIS at the indicated times. Head total flux for each animal was normalized to brain signal at time 0 (Fold Change FC). Graph shows Log-transformed FC {plus minus}SEM over time for EV vs OE-IL13RA2 injected mice. Normally distributed Log-transformed FC values were analyzed using Repeated Measures Mixed effects.*P=0.02 at 7 days. Ns at other time points
ARTICLE ABSTRACT
The survival of women with brain metastases (BM) from breast cancer remains very poor, with over 80% dying within a year of their diagnosis. Here, we define the function of IL13Rα2 in outgrowth of breast cancer brain metastases (BCBM) in vitro and in vivo, and postulate IL13Rα2 as a suitable therapeutic target for BM.
We performed IHC staining of IL13Rα2 in BCBM to define its prognostic value. Using inducible shRNAs in TNBC and HER2+ breast–brain metastatic models, we assessed IL13Rα2 function in vitro and in vivo. We performed RNAseq and functional studies to define the molecular mechanisms underlying IL13Rα2 function in BCBM.
High IL13Rα2 expression in BCBM predicted worse survival after BM diagnoses. IL13Rα2 was essential for cancer-cell survival, promoting proliferation while repressing invasion. IL13Rα2 KD resulted in FAK downregulation, repression of cell cycle and proliferation mediators, and upregulation of Ephrin B1 signaling. Ephrin-B1 (i) promoted invasion of BC cells in vitro, (ii) marked micrometastasis and invasive fronts in BCBM, and (iii) predicted shorter disease-free survival and BM-free survival (BMFS) in breast primary tumors known to metastasize to the brain. In experimental metastases models, which bypass early tumor invasion, downregulation of IL13Rα2 before or after tumor seeding and brain intravasation decreased BMs, suggesting that IL13Rα2 and the promotion of a proliferative phenotype is critical to BM progression.
Non-genomic phenotypic adaptations at metastatic sites are critical to BM progression and patients' prognosis. This study opens the road to use IL13Rα2 targeting as a therapeutic strategy for BM.
