Synergistic effects of ion transporter and MAP kinase pathway inhibitors in melanoma.

Ugur Eskiocak,Meng Wang,Elsa Quintana,Jennifer G Gill,Vijayashree Ramesh,Stacy W Yuan,Zhiyu Zhao,Ralph J Deberardinis,Travis Vandergriff,Sean J Morrison,Timothy M Johnson,Mark Shackleton,Arthur E Frankel

doi:10.1038/ncomms12336

Abstract

New therapies are required for melanoma. Here, we report that multiple cardiac glycosides, including digitoxin and digoxin, are significantly more toxic to human melanoma cells than normal human cells. This reflects on-target inhibition of the ATP1A1 Na+/K+ pump, which is highly expressed by melanoma. MEK inhibitor and/or BRAF inhibitor additively or synergistically combined with digitoxin to induce cell death, inhibiting growth of patient-derived melanomas in NSG mice and synergistically extending survival. MEK inhibitor and digitoxin do not induce cell death in human melanocytes or haematopoietic cells in NSG mice. In melanoma, MEK inhibitor reduces ERK phosphorylation, while digitoxin disrupts ion gradients, altering plasma membrane and mitochondrial membrane potentials. MEK inhibitor and digitoxin together cause intracellular acidification, mitochondrial calcium dysregulation and ATP depletion in melanoma cells but not in normal cells. The disruption of ion homoeostasis in cancer cells can thus synergize with targeted agents to promote tumour regression in vivo.

Highlights

Similar results were obtained when tumours were treated with digoxin rather than digitoxin (Supplementary Fig. 3a,b) or when the MAPK pathway was inhibited with BRAF inhibitor rather than MEK inhibitor (Supplementary Fig. 3c,d)
Mice xenografted with a BRAF mutant melanoma treated with digitoxin plus BRAF inhibitor had significantly smaller tumours than mice treated with BRAF inhibitor or digoxin alone
To test whether digitoxin plus MEK inhibitor would prolong the survival of xenografted mice with metastatic disease we subcutaneously injected melanoma cells derived from two patients (M491, M481), allowed tumours to grow to 2 cm in diameter, surgically removed the melanomas and initiated treatment with digitoxin and/or MEK inhibitor (Fig. 2b)

Summary

Introduction

We report that multiple cardiac glycosides, including digitoxin and digoxin, are significantly more toxic to human melanoma cells than normal human cells. This reflects on-target inhibition of the ATP1A1 Na þ /K þ pump, which is highly expressed by melanoma. Stage III melanomas that metastasize efficiently in NSG mice form distant metastases in patients despite surgical resection, whereas melanomas that metastasize inefficiently in mice are generally cured by surgery in patients[10]. We used this assay to test new therapies. This improves cardiomyocyte contractility in the failing heart[15]

Methods

Results

Conclusion