The secretome of non-tumorigenic mammary cells MCF-10A elicits DNA damage in MCF-7 and MDA-MB-231 breast cancer cells.

Radiotherapy is used in breast cancer to destroy tumor cells lingering after surgery. It is accepted that lethal effects of ionizing radiation occur as a result of damage to DNA in irradiated (IR) cells. However, response mechanisms may promote cell survival with efficient DNA repair or genomic alterations. Chromosomal aberrations are frequent in surviving cells and may enhance chromosomal instability (CIN) which is associated with increased risk of recurrence and metastasis. Intercellular communication can affect the response in IR cells and cause damage in non-irradiated (N-IR) cells. We evaluated the effect of the secretome of non-tumorigenic mammary cells (MCF-10A) on proliferation and DNA damage in breast cancer cells (MCF-7 and MDA-MB-231). Results showed that conditioned media from IR and N-IR MCF-10A cells produced cycles of DNA double-strand breaks in N-IR and IR tumor cells leaving them with residual damage. CIN markers (micronuclei, nucleoplasmic bridges, nuclear buds) were also increased in IR and N-IR tumor cells, being the effect of conditioned media from IR MCF-10A greater in many cases. The inhibition of phosphorylation/activation of Src kinase in cancer cells hindered CIN markers' increment. Besides, clonogenic survival of tumor cells was differentially modulated by conditioned media from MCF-10A: decreased in MCF-7 and enhanced in MDA-MB-231 cells. These results signal the relevance of tumor-host interaction in tumor behavior and the response to radiotherapy.