Gold Nanoclusters-Based Nanozymes Modulating Tumor Hypoxia For Enhancing Photodynamic Therapy And Radiotherapy Of Breast Cancer

Breast cancer is the most common cancer in women globally.Currently,its main treatments include surgery,radiotherapy（RT）,and chemotherapy.Photodynamic therapy（PDT）as a novel treatment modality for breast cancer has been a clinical and research hot spot.PDT and RT are local treatment methods for breast cancer,with controllability and minimal systematic side effects.However,tumor hypoxia microenvironment promotes tumor invasion,metastasis,and resistance to PDT and RT,which are dependent on the oxygen level within tumor tissues.Hence,this work developed gold nanoclusters（Au NCs）-based nanozymes for breast cancer theranostics.Due to the high H₂O₂ and low O₂ concentration within breast tumor tissues,Au NCs in situ decomposed H₂O₂ to O₂,which improved hypoxic microenvironment and subsequently enhanced PDT and RT.Furthermore,given that traditional PDT in the first near-infrared window（NIR-Ⅰ,700～900 nm）was hindered by its intrinsic limitations,such as shallow penetration,tissue absorption and scattering,this study investigated the applications of Au NCs-based nanozymes enhancing PDT efficiency against breast cancer in the second near-infrared window（NIR-Ⅱ,1,000～1,700 nm）.（1）The development of NIR-Ⅰ Au NCs-ICG and the investigation of its performance on modulating tumor hypoxia and enhancing breast cancer PDT.Gold atoms were paired with bovine serum albumin（BSA）ligands to form Au NCs,then indocyanine green（ICG）was adsorbed on Au NCs to synthesize Au NCsICG nanozymes with fluorescence（FL）imaging and photoacoustic（PA）imaging capabilities.Au NCs-ICG was characterized by high-resolution transmission electronic microscope（HRTEM）and fluorescent spectrometor,and its catalase-like activity,¹O₂ generation by PDT,DNA damage by RT,in vitro and in vivo FL imaging,hypoxia modulation,biodistribution and metabolism,and biocompatibility were further explored.In addition,anti-tumor effect was investigated on 4T1 tumor-bearing mice.Au NCs-ICG showed high-performance FL/PA imaging,realizing tumor imaging and real-time in vivo monitoring of Au NCs-ICG.And Au NCs-ICG exhibited superior catalase-like activity,¹O₂ generation,and DNA damage ability,which enhanced tumor inhibition.Overall,Au NCs-ICG provided a new solution for imaging-guided PDT and RT against breast cancer.（2）The development of NIR-Ⅱ BSA@Au and the investigation of its performance on modulating tumor hypoxia and enhancing breast cancer PDT.Gold atoms were paired with BSA ligands and reduced by NaBH₄ to form BSA@Au with NIR-Ⅱ FL emission.BSA@Au was comprehensively characterized.Its catalase-like activity,photostability,penetration depth,fluorescent quantum yields（QY）,and ¹O₂ generation were further explored.In vivo FL imaging of BSA@Au was studied by comparing its performance in NIR-Ⅰ and NIR-Ⅱ window.The biodistribution and metabolism,and biocompatibility at cell,tissue,and body levels were also evaluated.In addition,hypoxia modulation and anti-tumor effect was investigated on 4T1 tumor-bearing mice.The results showed that BSA@Au had superior QY（-3.5%）,photostability,penetration depth（>12 mm）,catalase-like activity and ¹O₂ generation,achieving high-performance NIR-Ⅱ FL imaging for breast cancer.Furthermore,BSA@Au catalyzed the H₂O₂ within tumor tissues to produce O₂,improving hypoxia and augmenting PDT efficacy,which provided a new strategy for theranostics of breast cancer.