Tunneling nanotube formation promotes survival against 5-fluorouracil in MCF-7 breast cancer cells

Abstract

Tunneling nanotubes (TNTs) are F-actin-based open-ended tubular extensions that form following stresses, such as nutritional deprivation and oxidative stress. The chemotherapy agent 5-fluorouracil (5-FU) represents a significant stressor to cancer cells and induces thymidine deficiency, a state similar to nutritional deprivation. However, the ability of 5-FU to induce TNT formation in cancer cells and potentially enhance survival has not been explored. In this study, we examined whether 5-FU can induce TNT formation in MCF-7 breast cancer cells. Cytotoxic doses of 5-FU (150-350 μm) were observed to significantly induce TNT formation beginning at 24 h after exposure. TNTs formed following 5-FU treatment probably originated as extensions of gap junctions as MCF-7 cells detach from cell clusters. TNTs act as conduits for exchange of cellular components and we observed mitochondrial exchange through TNTs following 5-FU treatment. 5-FU-induced TNT formation was inhibited by over 80% following treatment with the F-actin-depolymerizing agent, cytochalasin B (cytoB). The inhibition of TNTs by cytoB corresponded with increased 5-FU-induced cytotoxicity by 30-62% starting at 48 h, suggesting TNT formation aides in MCF-7 cell survival against 5-FU. Two other widely used chemotherapy agents, docetaxel and doxorubicin induced TNT formation at much lower levels than 5-FU. Our work suggests that the therapeutic targeting of TNTs may increase 5-FU chemotherapy efficacy and decrease drug resistance in cancer cells, and these findings merits further investigation.

Keywords: 5-fluorouracil; chemotherapy; cytochalasin B; doxorubicin; drug resistance; tunneling nanotubes.