N-Acetylcysteine breaks resistance to trastuzumab caused by MUC4 overexpression in human HER2 positive BC-bearing nude mice monitored by 89 Zr-Trastuzumab and 18 F-FDG PET imaging

// Zena Wimana 1, 2 , Geraldine Gebhart 1 , Thomas Guiot 1 , Bruno Vanderlinden 1 , Denis Larsimont 3 , Gilles Doumont 4 , Gaetan Van Simaeys 4 , Serge Goldman 4 , Patrick Flamen 1 and Ghanem Ghanem 1, 2 1 Nuclear Medicine Department, Institut Jules Bordet, Universite Libre de Bruxelles, Brussels, Belgium 2 Laboratory of Oncology and Experimental Surgery, Institut Jules Bordet, Universite Libre de Bruxelles, Brussels, Belgium 3 Pathology Department, Institut Jules Bordet, Universite Libre de Bruxelles, Brussels, Belgium 4 Center for Microscopy and Molecular Imaging (CMMI), Universite Libre de Bruxelles, Brussels, Belgium Correspondence to: Zena Wimana, email: zena.wimana@bordet.be Keywords: HER2, NAC, trastuzumab, resistance, immunoPET Received: September 30, 2016      Accepted: March 30, 2017      Published: April 10, 2017 ABSTRACT Trastuzumab remains an important drug in the management of human epidermal growth factor receptor 2 (HER2) overexpressing breast cancer (BC). Several studies reported resistance mechanisms to trastuzumab, including impaired HER2-accessibility caused by mucin 4 (MUC4). Previously, we demonstrated an increase of Zirconium-89-radiolabeled-trastuzumab ( 89 Zr-Trastuzumab) accumulation when MUC4-overexpressing BC-cells were challenged with the mucolytic drug N-Acetylcysteine (NAC). Hereby, using the same approach we investigated whether tumor exposure to NAC would also enhance trastuzumab-efficacy. Dual SKBr3 (HER2+/MUC4-, sensitive to trastuzumab) and JIMT1 (HER2+/MUC4+, resistant to trastuzumab) HER2-BC-bearing-xenografts were treated with trastuzumab and NAC. Treatment was monitored by molecular imaging evaluating HER2-accessibility/activity ( 89 Zr-Trastuzumab HER2-immunoPET) and glucose metabolism ( 18 F-FDG-PET/CT), as well as tumor volume and the expression of key proteins. In the MUC4-positive JIMT1-tumors, the NAC-trastuzumab combination resulted in improved tumor-growth control compared to trastuzumab alone; with smaller tumor volume/weight, lower 18F-FDG uptake, lower %Ki67 and pAkt-expression. NAC reduced MUC4-expression, but did not affect HER2-expression or the trastuzumab-sensitivity of the MUC4-negative SKBr3-tumors. These findings suggest that improving HER2-accessibility by reducing MUC4-masking with the mucolytic drug NAC, results in a higher anti-tumor effect of trastuzumab. This provides a rationale for the potential benefit of this approach to possibly treat a subset of HER2-positive BC overexpressing MUC4.