A Synchronous Photothermal-photodynamic Therapy Platform Based On Gold Nanospheres

Malignant tumor and its metastasis have caused an extraordinary high mortality rate of sufferers,and few of them can be cured by commonly used clinical cancer therapies.Phototherapy has attracted widespread focus in the past decade due to its excellent efficacy in treating local cancer with minimal invasiveness.Photothermal therapy(PTT)and photodynamic therapy(PDT)are two major photo therapeutic approaches that employ various photosensitizers,depending on their light conversion ability to produce localized hyperpyrexia(>42?)or reactive oxygen species(ROS,e.g.,singlet oxygen)to kill cancer cells.The photosensitizers employed are minimally toxic in the absence of light;thus their accumulation in non-specific or non-irradiated parts of the body causes little systemic toxicity.Near-infrared(NIR)light can readily penetrate the skin and go deep into the tissues because its tissue absorption is minimal,rendering it highly suitable for in vivo PTT and PDT applications.PTT alone is unlikely to eliminate all tumor cells because the resulting heat distribution is nonuniform,especially in areas near large blood vessels where heat can be rapidly dissipated by circulating blood,which leads to sublethal thermal doses in some areas of the tumor.For PDT alone,the mechanism of which is the generation of reactive oxygen species from tissue oxygen via interactions with the photoactivated agents.However,the oxygen level within tumor tissue can be highly heterogeneous due to dysregulated vascular distribution,leading to severely hypoxic regions.More noteworthily,the generation of ROS during PDT can stimulate the antioxidation balancing system in tumor cells,which causes the photodynamic resistance of the cells,restricting the further efficacy of PDT.Recently,combining PTT and PDT to compensate for the drawbacks of PTT or PDT alone in treating cancer has been widely studied.In this work,we have developed a combined photothermal and photodynamic therapy system based on indocyanine green(ICG)and hollow gold nanospheres(HAuNS)for enhanced antitumor efficacy via one-step NIR irradiation.First,we grafted branched-polyethylenimine(PEI,MW=10 kDa)onto HAuNS to expand the surface area and provide a covering layer of suitable thickness,which could decrease the fluorescence quenching of ICG caused by HAuNS and increase the stereo stability of HAuNS,Then,ICG molecules were covalently conjugated with PEI to obtain a high payload on HAuNS.The physicochemical properties,biodistribution,antitumor effect and metastasis inhibition property of this nanosystem mediated by NIR light were evaluated.Encouragingly,we found that covalently conjugating ICG on HAuNS could induce improved stability of ICG molecules and increased intratumoral accumulation,presenting synchronous PTT and PDT to achieve remarkably enhanced antitumor and metastasis inhibition effect under NIR light irradiation.Second,we further modified the surface of HAuNS with a TNYL peptide to interact with EphB4 receptor,which had been proved an overexpression in various tumor types.The specific tumor targeting as well as synchronous PDT and PTT effect of our nanosystem(TNYL-ICG-HAuNS)led to an excellent antitumor effect.Furthermore,PDT resistance mechanism was investigated.We found that the up-regulated expression of Nrf2 would lead to a PDT resistance to free ICG by activating the transcription of ABCG2,NQO-1 and HIF-la proteins.However,it had little influence on TNYL-ICG-HAuNS,which could still efficiently accumulate into tumor cells and generate a large amount of ROS during PDT.As a result,TNYL-ICG-HAuNS had the capacity of escaping from PDT resistance pathway.In order to supply sufficient oxgen,we prepared an oxygen-laden hemoglobin liposome(Hb-lipo)to support PDT.We found that Hb-lipo could enhance ROS yield as well as the tumor killing efficacy of ICG-HAuNS under hypoxia environment.Besides,it could also efficiently accumulate into the tumor sites through EPR effect so as to be capable of supporting the PDT effect in vivo.In summary,this work proved that compared with PTT or PDT alone,synchronous PTT and PDT induced significantly stronger antitumor and metastasis inhibition effects.Besides,the nanosystem(TNYL-ICG-HAuNS)could overcome the photodynamic resistance of cancer cells.Being supported by an oxygen-delivery Hb-lipo,it could act as a promising modality for simultaneous photothermal and photodynamic cancer therapy.