Background aims: Previously, we showed that human mesenchymal stromal cells (hMSCs) were activated to express tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) upon TNF-α stimulation, induced cell death in triple-negative breast cancer (TNBC) MDA-MB-231 cells (MDA), and RNA released from apoptotic MDA further increased TRAIL expression in hMSCs. This feed-forward stimulation increased apoptosis in MDA cells. Here, we tested whether TRAIL-expressing hMSCs, in combination with a sub-toxic-dose of a chemotherapy drug doxorubicin, would overcome TRAIL resistance and create synergistic effects on targeting metastatic TNBC.
Methods: To optimize conditions for the combination treatment, we (i) selected an optimal condition to activate hMSCs for TRAIL expression, (ii) selected an optimal dose of doxorubicin treatment, (iii) examined underlying mechanisms in vitro and (iv) tested the efficacy of the optimized conditions in a xenograft mouse model of human breast cancer lung metastasis.
Results: The results showed that DNA fragments from apoptotic MDA triggered hMSCs to increase further TRAIL expression in an absent in melanoma 2 (AIM2)-dependent manner, and thus higher TRAIL-expressing hMSCs stimulated with synthetic DNA, poly(deoxyadenylic-deoxythymidylic) acid [poly(dA:dT)], more effectively suppressed tumor progression in vivo. Furthermore, activated hMSCs increased apoptosis in MDA cells when combined with a sub-toxic dose of doxorubicin, which was mediated by up-regulating TRAIL and Fas-related pathways. When we combined the optimized conditions, pre-activated hMSCs with poly (dA:dT) synergistically reduced tumor burden even with minimal doxorubicin treatment in a xenograft mouse model of human breast cancer lung metastasis.
Conclusions: These results suggest that the treatment of hMSCs with a sub-toxic dose of doxorubicin can overcome TRAIL resistance and be a potential novel therapy for TNBC metastasis treatment.
Keywords: IFIH1; Poly (I:C); bone marrow; multipotent stromal cells.
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