A Ph-sensitive Gold Nanoparticle For Enhancement Of The Radiosensitivity Of Tumors

Radiotherapy is still one of the three main treatments of cancer therapy.Radiosensitizers can enhance the radiotherapy effect and reduce the irradiation dose,which can reduce demage to normal tissues.At the same time,it is very important to reduce side effects of radiosensitizers to normal tissues.Recent study has confimed that GNPs have a good biocompatibility and can enhance radiotherapy effect.Based on this,we choose gold nanoparticles(GNPs)as the radiosensitizer.Meanwhile,small-size nanoparticles are easy to enter tumor tissue,while large-size nanoparticles can enhance the retention effect in tumor.50 we wanted to design an acid-sensitive aggregation of gold nanoparticles using the slightly acidic environment within the tunor.We has designed and synthesized the polypeptide A and polypeptide B through solid phase synthesis.Polypeptide B was modified with 2,3-Dimethylmaleic anhydride(DA)which was pH sensitive.When it came to acidic environment,the 2,3-Dimethylmaleic anhydride was dropped from the polypeptide B and its surface charge was changed.Gold nanoparticles A(GNPs-A)and Gold nanoparticles B(GNPs-B)were synthesized by conjugating polypeptide A and modified polypeptide B to the surface of gold nanoparticles.The polypeptide A and modified polypeptide B was negatively charged at pH 7.4.When polypeptide B reached the slightly acidic environment in the tumor,the modified it occurred the charge inversion and its surface became positive charge.The GNPs system was obtained by mixed the GNPs-A and GNPs-B in equal proportion.When the GNPs system was injected to the body it remained dispered in normal condition to enhance the long circulation in the body.When amving the tumor environment the surface charge reversal occurred and lead to aggregation of GNPs system,so as to enhance the retention in tumors and reducing their diffiision and reflux to normal tissues.This material could achieve better therapeutic effect and has low toxicity to surrounding tissues.The high performance liquid chromatography mass spectrometry and nuclear magnetic resonance hydrogen spectroscopy showed that the conjugate of small molecule DA and polypeptide B was acid sensitive.The polypeptide A and modified polypeptide B was attached to the surface of gold nanoparticles to form GNPs-A and GNPs-B,and then mixed to form GNPs system in equal proportions.When the pH changed from 7.4 to 6.5,the particles size was increased from 32.6 to 912.8 nm.The results of transmission electron microscopy also showed that the GNPs system had obvious aggregation.The UV absorption peak of gold nanoparticles shifted from 520 nm to 600-900 nm by ultraviolet absorption spectroscopy.In vitro characterization experiments showed that the GNPs system has acid-sensitive aggregation characteristics.The transmission electron microscopy,atomic emission spectrometer(ICP-AES),flow cytometry and other in vitro uptake experiments showed that the GNPs system could increase the aggregation and retention in tumor cells.The clone formation experiaent showed that the radiosensitization ratio(SER10)of GNPs system increased from 1.16 and 1.17 to 1,73 compared to GNPs-A and GNPs-B,which indicated that the GNPs system had a good radiosensitization effect.The cell cycle experiments showed that the GNPs system can make cells arrest in G2/M phase,which was the most sensitive to radiation before irradiation,and form G1 phase arrest after irradiation.The apoptosis experiment showed that the GNPs system could increase the apoptotic rate of cells.Comet assay and gamma-H2AX immunofluorescence assay showed that the GNPs system could enhance the anti-tumor effect mainly by increased the irradiation-induced DNA breakage.The GNPs system was injected into nuce through tail vein injection and further treatment was carried out to detect its anti-tumor effect and biological safety in mice with xenografted tumor.In vivo retention experiments such as transmission electron microscopy(TEM)and ICP-AES showed that the GNPs system could increase aggregation and retention in tumors,and had a good photoacoustic imaging effect,In vivo anti-tumor experiments showed that GNPs system had a good radiosensitization effect.The results of hematoxylin-eosin staining(H&E)staining and TUNEL apoptotic staining showed that the apoptotic rate in the treatment group was significantly increased.Hematological analysis and H&E staining showed that the GNPs system had no obvious toxic and side effects on other main tissues.In this study,we designed a GNPs system to enhance the radiotherapy effect of tumors.The results showed that the GNPs system had good pH sensitivity and significantly enhanced the radiotherapy effect.At the same time,it had good biocompatibility,which provide a new therapeutic idea for the treatment of tumors.The photoacoustic imaging and CT imaging showed it has the potential in tumor diagnosis.