Purpose: Therapeutic strategies against hormonal receptor-positive (HR+)/HER2+ breast
cancers with poor response to
trastuzumab need to be optimized.Experimental Design: Two HR+/HER2+ patient-derived xenograft (PDX) models named as COH-SC1 and COH-SC31 were established to explore targeted
therapies for HER2+ breast
cancers.
RNA sequencing and RPPA (reverse phase
protein array) analyses were conducted to decipher molecular features of the two PDXs and define the therapeutic strategy of interest, validated by in vivo drug efficacy examination and in vitro cell proliferation analysis.Results:
Estrogen acted as a growth driver of
trastuzumab-resistant COH-SC31
tumors but an accelerator in the
trastuzumab-sensitive COH-SC1 model. In vivo
trastuzumab efficacy examination further confirmed the consistent responses between PDXs and the corresponding
tumors. Integrative omics analysis revealed that
mammalian target of rapamycin (mTOR) and ERĪ± signaling predominantly regulate
tumor growth of the two HR+/HER2+ PDXs. Combination of the dual mTOR complex inhibitor
MLN0128 and anti-HER2
trastuzumab strongly suppressed
tumor growth of COH-SC1 PDX accompanied by increasing ER-positive cell population in vivo Instead,
MLN0128 in combination with
antiestrogen fulvestrant significantly halted the growth of HR+/HER2+
cancer cells in vitro and
trastuzumab-resistant COH-SC31 as well as
trastuzumab-sensitive COH-SC1
tumors in vivoConclusions: Compared with the standard
trastuzumab treatment, this study demonstrates alternative therapeutic strategies against HR+/HER2+
tumors through establishment of two PDXs coupled with integrative omics analyses and in vivo drug efficacy examination. This work presents a prototype of future "co-clinical" trials to tailor
personalized medicine in clinical practice. Clin
Cancer Res; 24(2); 395-406. ©2017 AACR.