Abstract P5-06-06: Hybrid cells generated by Mesenchymal Stem/Stromal Cell Engulfment enhance breast cancer metastasis upon Doxorubicin treatment in mouse model
Authors: Augimeri Giuseppina , Gonzalez Maria E. , Bonofiglio Daniela , Andò Sebastiano , Kleer Celina G. 
Published: March 2022

Abstract
Introduction: Our previous findings evidenced that BCCs engulf MSCs in clinical samples of breast cancer metastasis. Among the BCC-engulfing MSCs, we observed that some of them retain some markers of MSCs, resulting in the generation of hybrid cancer cell population. However, the mechanisms of hybrid cancer cell formation and the phenotypic features of hybrid cancer cells are still unclear. Here, we tested the hypothesis that hybrid cancer cells may acquire in vivo a dormant phenotype, with an increased survival advantage and chemoresistant features. Method: MSC labeled with DsRED (DsRED-MSC) were cultured with MDA-MB-231 labeled with GFP (GFP-231) to generate a hybrid cell-enriched co-culture. Live imaging microscopy, flow cytometry, cytokine array and western blot were used to characterize the hybrid cancer cells. GFP-231 were incubated with phRodo labeled MSC and subjected to phagocytosis assay. In the co-culture of DsRED-MSC with GFP-231 treated with Doxorubicin (Doxo) or untreated, we analyzed the percentage of DsRED+/GFP+ hybrid population. Hybrid-enriched co-culture or GFP-231 in single culture labeled with firefly luciferase were intracardially injected in NOD/SCID mice and monitored for metastases by bioluminescence imaging (BLI), upon Doxo treatment. After collecting the tissues at necropsy, metastases were identified by GFP fluorescence microscopy. Results: In co-cultures, DsRED+/GFP+ hybrid cells had a higher percentage of Ki-67 low in G1 and polyploidy compared to GFP-231+ cells. Hybrid cancer cells have a distinct cytokine profile than control BCCs with increased levels of senescence-associated secretory phenotype (SASP) factors. Hybrid cancer cell formation occurs through a phagocytosis-like mechanism, which involves WNT5A and MSR1. Doxo treatment increased the percentage of DsRED+/GFP+ hybrid cells, whereas reduced the percentage of GFP-231+ cells. In animal study, we observed a lower qualitative BLI intensity in mice injected with hybrid cell-enriched co-cultures compared to control. Doxo treatment increased the metastatic burden in mice inoculated with hybrid cell-enriched co-cultures compared to untreated Conclusions: MSC engulfment by BCCs results in a hybrid multinucleated cell population. Hybrid cells acquire a dormant phenotype characterized by a higher percentage of Ki-67low cells in G1 and a senescent phenotype compared to controls. Hybrid-cell-enriched co-cultures established less metastasis compared to control in vivo, but became resistant and acquire the ability to form metastasis upon doxo treatment.
Citation Format: Giuseppina Augimeri, Maria E. Gonzalez, Daniela Bonofiglio, Sebastiano Andò, Celina G. Kleer. Hybrid cells generated by Mesenchymal Stem/Stromal Cell Engulfment enhance breast cancer metastasis upon Doxorubicin treatment in mouse model [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-06-06.