A novel HER2 inhibitor TAK-285 overcomes trastuzumab resistance of HER2-over-expressing breast cancer.

Abstract

Abstract Abstract #3143 Background: The anti-HER2 antibody trastuzumab has been proven highly effective in the treatment of HER2-expressing breast cancers clinically. However, the continuous administration often leads to drug resistance, the mechanism of which is not well understood. Here we present a new mechanism for trastuzumab-resistance. We also show TAK-285, a novel small molecule HER2/EGFR kinase inhibitor under clinical evaluation, overcomes the resistance to trastuzumab.
 Methods: A trastuzumab-resistant sub-clone (BT-474TR) of the HER2-positive human breast cancer line, BT-474, was established in house by serial passage in the presence of 5 μg/mL trastuzumab for over 5 months. Gene expression profiles of the clones were assessed using Affymetrix HG-U133 plus 2.0 human gene arrays and confirmed by real-time PCR. Target genes were depleted by siRNA-mediated knockdown and confirmed by real time-PCR and immunoblot. Effects on cell growth were assessed by the CellTiter-Glo luminescent cell viability assay (Promega).
 Results: BT-474TR cells exhibited modified expression of several genes including cofilin, compared to the parental BT-474 cells. Although immunoblotting using anti-cofilin antibody revealed no clear change in protein level, BT-474TR displayed significant increase in phosphorylation of cofilin. Gene-specific knockdown of cofilin-1 led to re-sensitization of BT-474TR to trastuzumab, though the cofilin-2 knockdown did not. Likewise, knockdown of either LIMK1 or PAK1, known to regulate cofilin-phosphorylation, resulted in similar re-sensitization of BT-474TR to trastuzumab. BT-474TR also exhibited increase in phosphorylation of both LIMK1 and PAK1. TAK-285 showed almost equivalent inhibitory activity against both BT-474 and BT-474TR proliferation in cell culture and in xenograft study, while trastuzumab did not affect the proliferation of BT-474TR in either condition
 Conclusions: These data suggest that activation of cofilin signaling pathway is a probable mechanism of trastuzumab resistance. PAK1/LIMK1/cofilin-1 inhibitors might therefore be useful in preventing or reversing trastuzumab resistance. The phosphorylation status of PAK1/LIMK1/cofilin might also serve as a biomarker of Trastuzumab-sensitivity. Moreover a novel HER2 inhibitor, TAK-285, might show benefit in the treatment of trastuzumab-resistant HER2-expressing breast cancers. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3143.