Lactoferrin selectively triggers cell death in highly metastatic breast cancer cells through inhibition of the plasmalemmal proton pump V-H+-ATPase

Breast cancer is the most common type of cancer affecting women. Despite the good prognosis when detected early, the treatment of the metastatic breast cancer is still a huge challenge. The recruitment of the proton pump V-ATPase to the plasma membrane, where it contributes to the acidity of the tumor microenvironment, is a recognized feature involved in the acquisition of a metastatic phenotype in breast cancer. Therefore, inhibitors of this pump have emerged as promising anticancer drugs.

Lactoferrin is a pro-apoptotic protein derived from milk that has strong anticancer activity whose mechanism of action is not fully understood. We show that bovine lactoferrin (bLf) preferentially induces cell death in the highly metastatic breast cancer cell lines, which display V-ATPase at the plasma membrane, but not in lowly metastatic or in non-tumorigenic cell lines. We also demonstrate that bLf decreases the extracellular acidification rate, causes intracellular acidification in metastatic breast cancer cells and inhibits V-H⁺-ATPase in sub-cellular fractions.

These data demonstrate that bLf targets V-ATPase and explain the selectivity of this protein for highly metastatic breast cancer cells. Our results pave the way for in vivo studies aiming to explore this protein for metastatic breast cancer therapy.

Authors and Affiliations:

Cátia S. Pereira^1,2, Joana P. Guedes^1,2, Marília Gonçalves¹, Luís Loureiro¹, Lisandra Castro¹, Hernâni Gerós^1,3, Lígia R. Rodrigues², Manuela Côrte-Real¹

¹Centre of Molecular and Environmental Biology (CBMA), Department of Biology, University of Minho, Braga, Portugal

²Centre of Biological Engineering (CEB), Department of Biological Engineering, University of Minho, Braga, Portugal

³Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), Department of Biology, University of Minho, Braga, Portugal

Abstract:

Breast cancer is the most common type of cancer affecting women. Despite the good prognosis when detected early, significant challenges remain in the treatment of metastatic breast cancer. The recruitment of the vacuolar H⁺-ATPase (V-H⁺-ATPase) to the plasma membrane, where it mediates the acidification of the tumor microenvironment (TME), is a recognized feature involved in the acquisition of a metastatic phenotype in breast cancer. Therefore, inhibitors of this pump have emerged as promising anticancer drugs. Lactoferrin (Lf) is a natural pro-apoptotic iron-binding glycoprotein with strong anticancer activity whose mechanism of action is not fully understood. Here, we show that bovine Lf (bLf) preferentially induces apoptosis in the highly metastatic breast cancer cell lines Hs 578T and MDA-MB-231, which display a prominent localisation of V-H⁺-ATPase at the plasma membrane, but not in the lowly metastatic T-47D or in the non-tumorigenic MCF-10-2A cell lines. We also demonstrate that bLf decreases the extracellular acidification rate and causes intracellular acidification in metastatic breast cancer cells and, much like the well-known proton pump inhibitors concanamycin A and bafilomycin A1, inhibits V-H⁺-ATPase in sub-cellular fractions. These data further support that bLf targets V-H⁺-ATPase and explain the selectivity of bLf for cancer cells, especially for highly metastatic breast cancer cells. Altogether, our results pave the way for more rational in vivo studies aiming to explore this natural non-toxic compound for metastatic breast cancer therapy.

Journal: Oncotarget

Link: http://www.impactjournals.com/oncotarget/index.php?journal=oncotarget&page=article&op=view&path[]=11394&pubmed-linkout=1