Porphyrin Modified Trastuzumab Improves Efficacy of HER2 Targeted Photodynamic Therapy of Gastric Cancer

Abstract

Gastric cancer (GC) is the 3^rd deadliest cancer worldwide, due to limited treatment options and late diagnosis. Human epidermal growth factor receptor-2 (HER2) is overexpressed in ∼20% of GC cases and anti-HER2 antibody trastuzumab in combination with conventional chemotherapy, is recognized as standard therapy for HER2-positive metastatic GC. This strategy improves GC patients' survival by 2-3 months, however its optimal results in breast cancer indicate that GC survival may be improved. A new photoimmunoconjugate was developed by conjugating a porphyrin with trastuzumab (Trast:Porph) for targeted photodynamic therapy in HER2-positive GC. Using mass spectrometry analysis, the lysine residues in the trastuzumab structure most prone for porphyrin conjugation were mapped. The in vitro data demonstrates that Trast:Porph specifically binds to HER2-positive cells, accumulates intracellularly, co-localizes with lysosomal marker LAMP1, and induces massive HER2-positive cell death upon cellular irradiation. The high selectivity and cytotoxicity of Trast:Porph based photoimmunotherapy is confirmed in vivo in comparison with trastuzumab alone, using nude mice xenografted with a HER2-positive GC cell line. In the setting of human disease, these data suggest that repetitive cycles of Trast:Porph photoimmunotherapy may be used as an improved treatment strategy in HER2-positive GC patients. This article is protected by copyright. All rights reserved.

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