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Wei-Jie Cheng,1,* Shyr-Yi Lin,2,3,* Kuo-Hsiang Chuang,4,5,* Michael Chen,4 Hsiu-O Ho,1 Ling-Chun Chen,6 Chien-Ming Hsieh,1 Ming-Thau Sheu1 1School of Pharmacy, College of Pharmacy, Taipei Medical University, Taipei, Taiwan; 2Division of Gastroenterology, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan; 3Department of General Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan; 4Graduate Institute of Pharmacognosy, Taipei Medical University, Taipei, Taiwan; 5PhD Program in Clinical Drug Development of Chinese Herbal Medicine, Taipei Medical University, Taipei, Taiwan; 6Department of Biotechnology and Pharmaceutical Technology, Yuanpei University of Medical Technology, Hsinchu, Taiwan*These authors contributed equally to this workCorrespondence: Chien-Ming Hsieh; Ming-Thau Sheu, Email cmhsieh@tmu.edu.tw; mingsheu@tmu.edu.twIntroduction: Approximately 15%~30% of breast cancers have gene amplification or overexpression of the human epidermal growth factor receptor 2 (HER2), resulting in the chemotherapy resistance, a more-aggressive phenotype and poor prognosis.Methods: We propose a strategy of nanocarriers co-loaded with docetaxel (DTX) and pictilisib (PIC) at a synergistic ratio and non-covalently bound with dual anti-HER2 epitopes bispecific antibodies (BsAbs: anti-HER2-IV/methoxy-polyethylene glycol (mPEG) and anti-HER2-II/methoxy-PEG) for synergistic targeting to overcome the therapeutic dilemmas of the resistance for HER2-targetable chemodrugs. DTX/PIC-loaded nanocarriers (D/P_NCs) were prepared with single emulsion methods and characterized using dynamic light scattering analysis, and the drug content was assayed by high-performance liquid chromatographic method. The integrity and function of BsABs were evaluated using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and enzyme-linked immunosorbent assay (ELISA). The in vitro cell studies and in vivo breast tumor-bearing mice model were used to evaluate the anti-cancer effect and biosafety of formulations.Results: D/P_NCs optimally prepared exhibited a spherical morphology with small particle sizes (~140 nm), high drug loading (~5.5%), and good colloidal stability. The synergistic tumor cytotoxicity of loading DTX and PIC at 2:1 ratio in D/P_NCs was discovered. The BsAbs are successfully decorated on mPEGylated DTX/PIC-loaded nanocarriers via anti-mPEG moiety. In vitro studies revealed that non-covalent decoration with dual BsAbs on D_P-NCs significantly and synergistically increased cellular uptake, while with loading DTX and PIC at a synergistic ratio of 2:1 in D/P_NCs further resulted in synergistic cytotoxicity. In vivo tumor inhibition studies showed the comparable results for synergistic antitumor efficacy while minimizing systemic toxicity of chemodrugs.Conclusion: Non-covalent modification with dual distinct epitopes BsAbs on the nanocarriers loaded with dual chemodrugs at a synergistic ratio was expected to be a promising therapeutic platform to overcome the chemoresistance of various cancers and warrants further development for future therapy in the clinical.Graphical Abstract: Keywords: docetaxel, pictilisib, nanocarriers, bispecific antibodies, dual epitopes, HER2-positive breast cancer