Pazopanib reveals a role for tumor cell B-Raf in the prevention of HER2+ breast cancer brain metastasis

Clin Cancer Res. 2011 Jan 1;17(1):142-53. doi: 10.1158/1078-0432.CCR-10-1603. Epub 2010 Nov 16.

Abstract

Purpose: Brain metastases of breast cancer contribute significantly to patient morbidity and mortality. We have tested pazopanib, a recently approved antiangiogenic drug that targets VEGFR1, VEGFR2, VEGFR3, PDGFRβ, PDGFRα, and c-kit, for prevention of experimental brain metastases and mechanism of action.

Experimental design: In vitro assays included B-Raf enzymatic assays, Western blots, and angiogenesis assays. For in vivo assays, HER2 transfectants of the brain seeking sublines of MDA-MB-231 cells (231-BR-HER2) and MCF7 cells (MCF7-HER2-BR3, derived herein) were injected into the left cardiac ventricle of mice and treated with vehicle or pazopanib beginning on day 3 postinjection. Brain metastases were counted histologically, imaged, and immunostained.

Results: Treatment with 100 mg/kg of pazopanib resulted in a 73% decline in large 231-BR-HER2 metastases (P < 0.0001) and a 39% decline in micrometastases (P = 0.004). In vitro, pazopanib was directly antiproliferative to 231-BR-HER2 breast cancer cells and inhibited MEK and ERK activation in vitro despite B-Raf and Ras mutations. Enzymatic assays demonstrated that pazopanib directly inhibited the wild type and exon 11 oncogenic mutant, but not the V600E mutant forms of B-Raf. Activation of the B-Raf targets pERK1/2 and pMEK1/2 was decreased in pazopanib-treated brain metastases whereas blood vessel density was unaltered. In the MCF7-HER2-BR3 experimental brain metastasis model, pazopanib reduced overall brain metastasis volume upon magnetic resonance imaging (MRI) by 55% (P = 0.067), without affecting brain metastasis vascular density.

Conclusions: The data identify a new activity for pazopanib directly on tumor cells as a pan-Raf inhibitor and suggest its potential for prevention of brain metastatic colonization of HER2(+) breast cancer.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents / therapeutic use
  • Brain Neoplasms / genetics
  • Brain Neoplasms / prevention & control*
  • Brain Neoplasms / secondary*
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Disease Models, Animal
  • Endothelial Cells / drug effects
  • Extracellular Signal-Regulated MAP Kinases / antagonists & inhibitors
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Female
  • Humans
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Mutation
  • Proto-Oncogene Proteins B-raf / antagonists & inhibitors*
  • Proto-Oncogene Proteins B-raf / metabolism
  • Pyrimidines / pharmacology*
  • Pyrimidines / therapeutic use
  • Receptor, ErbB-2 / genetics*
  • Signal Transduction / drug effects
  • Sulfonamides / pharmacology*
  • Sulfonamides / therapeutic use
  • Xenograft Model Antitumor Assays

Substances

  • Antineoplastic Agents
  • Pyrimidines
  • Sulfonamides
  • pazopanib
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Proto-Oncogene Proteins B-raf
  • Extracellular Signal-Regulated MAP Kinases