Combination inhibition of PI3K and mTORC1 yields durable remissions in mice bearing orthotopic patient-derived xenografts of HER2-positive breast cancer brain metastases.

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Combination inhibition of PI3K and mTORC1 yields durable remissions in mice bearing orthotopic patient-derived xenografts of HER2-positive breast cancer brain metastases.

Nat Med. 2016 Jul;22(7):723-6

Authors: Ni J, Ramkissoon SH, Xie S, Goel S, Stover DG, Guo H, Luu V, Marco E, Ramkissoon LA, Kang YJ, Hayashi M, Nguyen QD, Ligon AH, Du R, Claus EB, Alexander BM, Yuan GC, Wang ZC, Iglehart JD, Krop IE, Roberts TM, Winer EP, Lin NU, Ligon KL, Zhao JJ

Abstract
Brain metastases represent the greatest clinical challenge in treating HER2-positive breast cancer. We report the development of orthotopic patient-derived xenografts (PDXs) of HER2-expressing breast cancer brain metastases (BCBM), and their use for the identification of targeted combination therapies. Combined inhibition of PI3K and mTOR resulted in durable tumor regressions in three of five PDXs, and therapeutic response was correlated with a reduction in the phosphorylation of 4EBP1, an mTORC1 effector. The two nonresponding PDXs showed hypermutated genomes with enrichment of mutations in DNA-repair genes, which suggests an association of genomic instability with therapeutic resistance. These findings suggest that a biomarker-driven clinical trial of PI3K inhibitor in combination with an mTOR inhibitor should be conducted for patients with HER2-positive BCBM.

PMID: 27270588 [PubMed - indexed for MEDLINE]

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