Nano-branched Gold-mediated Photothermal Therapy Induces Cell Apoptosis And Its Molecular Mechanism

Photothermal therapy?PTT?is a novel strategy to cancer treatment,in which photothermal agents translocated in the tumor converts light energy into heat energy under the irradiation of near-infrared light to generate hyperthermia at the tumor site to kill cancer cells.Compared with traditional cancer treatment methods,photothermal treatment has the advantages of high specificity and small side effects,so it has attracted widespread attention.However,recent researches on PTT were focused more on the design and development of photothermal reagents,while little attention has been paid to the molecular mechanism of the death of cancer cells in PTT remains unclear.At present,there are two distinct pathways of cancer cell death:apoptosis and necrosis.Compared to cell necrosis,apoptosis is a more"clean"way of death.Therefore,finding a feasible solution to induce apoptosis by photothermal therapy and understanding the molecular mechanism of apoptosis is very important to improve the effect of photothermal therapy and advance its clinical application.Therefore,this dissertation aims to screen out photothermal treatment conditions that can specifically induce apoptosis of cancer cells,and to elucidate the molecular mechanism of PTT-induced apoptosis.The main research contents of this thesis are as follows:1.In order to selectively induce cancer cell apoptosis.First,we synthesized coral-like gold nanoparticles?Au NCs?with strong absorption capacity in the near infrared?NIR?region,which has a very high near infrared light-to-heat conversion efficiency?32%?.Then using Au NCs as the photothermal agents,the in vitro experiments showed that laser irradiation with low power density(0.5 W cm^-2)for 15 min selectively induced apoptosis of human breast cancer cells?MCF-7?.In addition,the results of Western blot experiments showed that photothermal therapy-induced apoptosis was mediated by Bak-2 activation and Bcl-2 protein inhibition in the Bcl-2 family.Moreover,the use of Au NCs as heaters can effectively ablate MCF-7 xenograft tumors and prevent the return of cancer.Immunohistochemical analysis of tumor tissue sections further confirmed that the death pathway of MCF-7 cells in mice was through an apoptotic pattern,and that apoptosis was mediated by Bak protein and Bcl-2 protein.These results offer a feasible protocol to selectively induce apoptotic cell death,which is beneficial to improve the effect of PTT.2.Raman observation of a molecular signaling pathway of apoptotic cells induced by photothermal therapy.In this work,MCF-7 cells,human lung cancer cells?A549?,and human cervical cancer cells?He La?were chose as study models,nuclear-targeting Au nanostars?Au NSs?were used as both a photothermal agent to specifically induce apoptosis in cancer cells and as a SERS probe to monitor the time-dependent SERS spectra of cancer cells which are undergoing apoptosis.Through SERS spectra and their synchronous and asynchronous SERS correlation maps,the occurrence and dynamics of a cascade of molecular events have been investigated,and a molecular signaling pathway of PTT-induced apoptosis,including release of cytochrome c,protein degradation,and DNA fragmentation,was revealed,which was also demonstrated by metabolomics,agarose gel electrophoresis,and western blot analysis,respectively.These results indicated that PTT-induced apoptosis undergoes an intrinsic mitochondria-mediated apoptosis pathway.Combined with western blot results,this intrinsic mitochondria-mediated apoptosis pathway was further demonstrated to be initiated by a BH3-only protein,BID.The experimental results of this work reveal the molecular mechanism of PTT inducing apoptosis,which has important theoretical guiding significance on how to adjust the parameters of PTT to optimize its therapeutic effect.