The Synthesis Of Self-powered Bone Targeting And Multifunctional Potential Ultra-small Photothermal Nanomaterial And Its Application In Bone Tumor Therapy

ObjectiveBone tumor is a serious disease threatening human life and health.Due to high blood flow in the red marrow,bone is one of the most common sites for metastasis,with around 60-80% malignant tumor patients suffering from bone metastasis in their advanced stage.Tumor can cause bone to be destroyed and weakened to the extent that it breaks,resulting in severe pain,pathological fracture,spinal-cord compression and other skeletal-related events,reducing patients' quality of life and increasing mortality significantly.Excisional surgery causes serious operation related injury and complications and it is not suitable for patients with multiple metastases.On the other hand,bone marrow microenvironment provides not only a fertile soil for cancer cell survival and growth but also a protective niche for cancer cells to resist clinical treatments including chemotherapy and radiotherapy.Therefore,novel and efficient therapeutic regimens are urgently needed in the clinical treatment of bone tumors.Photothermal therapy(PTT)has recently emerged as an attractive alternative approach for the treatment of solid tumors.Compared with the conventional therapeutic modalities,PTT exhibits unique advantages including high specificity,minimal invasiveness and precise spatial-temporal selectivity,etc.Though efficacies of these materials in PTT therapy in vitro and in vivo were demonstrated,their clinical applications are limited by relatively large sizes and multiple functionalization.The developed photothermal agents with size of >40 nm are difficult to penetrate deeply in the tumor tissues and be cleared out of the body post-treatment.Besides,multiple functionalization endows photothermal agents with synergistic enhanced therapeutic efficacy.But multifunctionality,lining with additional costs and multiple synthetic steps,is still a huge challenge.In view of the poor permeability of bone tissue,it is difficult for drugs to reach and accumulate in the bone tumor site through the traditional way of administration,which calls for bone targeting nanoparticles.According to Yadav's research,anionic moieties are expected to respond to the diffusion-induced electric field by moving towards the bone crack,self-powered bone targeting nanomaterial could be designed.Herein,we used dendrimers and platinum(Pt)nanoparticles to synthesize self-powered bone targeting and multifunctional potential ultra-small photothermal nanomaterial and apply it to bone tumor therapy.MethodsIn this study,dendrimers with different terminal groups was used as single dispersing templates and stabilizers,and a proper amount of K2PtCl6 was added.After fully reaction,NaHB4 was used to reduce Pt ions,so as to synthesize photothermal nanomaterials of different terminal groups.Transmission electron microscope(TEM)and dynamic light scattering(DLS)were used for characterization of nanomaterials.Furthermore,the bone targeting properties of the nanomaterials were verified by in vitro nano-artificial bone absorption and in vivo distribution experiments.In vitro lighting and heating experiments are used to verify photothermal properties.The biocompatibility of the materials were confirmed by cytotoxicity tests and stability in serum tests.Last but not least,we built tibia tumor model in nude mice.The above mentioned photothermal materials were applied to treat tibia tumors in nude mice.The whole course of treatment consisted of three times of the injection of photothermal materials together with twice ten-minute near infrared irradiation treatments 12 h and 24 h after each injection.Relative luminescence intensity,tumor maximum circumference and weight,bone volume,bone surface,trabecular number and trabecular separation were regarded as observed indicators.Results(?)Synthesis and characterization of self-powered bone targeting and multifunctional potential ultra-small photothermal nanomaterialsPhotothermal nanomaterials of carboxyl-terminated(negatively charged),amine-terminated(positively charged)and acetylated amino-terminated(no charge)were successfully synthesized,with the name of G4.5-COOH-Pt ? G5-NH2-Pt and G5-NH2-AC-Pt,respectively.TEM showd that the three materials were similar in morphology and uniform in size with diameters ranging from 1-2 nm.DLS indicated that the hydration diameters of the three materials are all about 10 nm,and G4.5-COOH-Pt has a negative charge,G5-NH2-Pt is positively charged,and G5-NH2-AC-Pt has a slight positive charge.(?)The bone targeting property,photothermal property and biocompatibility of self-powered bone targeting and multifunctional potential ultra-small photothermal nanomaterialsBoth in vitro nano-artificial bone absorption and in vivo distribution experiments demonstrated that the platinum content of G4.5-COOH-Pt group was much higher than that of other two control groups in terms of bone absorption(** P < 0.01 or *** P < 0.001).In vitro lighting and heating experiments showed that all these three materials have light conversion properties,but because of the higher platinum content of G4.5-COOH-Pt group,the temperature was higher and rose faster than that of the other groups,with 45? after one-minute irradiation and nearly 70? in maximum.Cytotoxicity test proved that in G4.5-COOH-Pt and G5-NH2-AC-Pt groups,cell survival rate is still higher than 90% culturing in a material concentration of 300 ?M,cell survival rate of G5-NH2-Pt group is around 80% at the same concentration.Stability in serum tests revealed that there was no change in the size of three kinds of materials dissolved in 50% PBS and 50% serum solution for 72 hours.(?)Therapeutic effect evaluation of self-powered bone targeting and multifunctional potential ultra-small photothermal nanomaterials in tibia tumor models in nude miceDuring the photothermal therapy,the maximum temperature of the tumor site from high to low was G4.5-COOH+NIR group,G5-NH2-AC+NIR group,G5-NH2+NIR group,and PBS group.In G4.5-COOH+NIR group,the highest temperature(45? in 12 h and 44? in 24 h)can be reached within 2 minutes after irradiation.The maximum temperature of G5-NH2-AC+NIR group,G5-NH2+NIR group,and PBS group was 41?,40?,39?,respectively.After therapy,relative luminescence intensity of G4.5-COOH+NIR group is the lowest,around 2.5,comparing to 12.5-15 of other groups(*** P < 0.001).Tumor maximum circumference and weight of G4.5-COOH+NIR group is far less than those of other four groups(*** P < 0.001).Moreover,according to Micro-CT three-dimensional reconstruction,bone volume,bone surface and trabecular number of G4.5-COOH+NIR group were significantly higher than those in the other four groups(** P < 0.01 or *** P < 0.001),while trabecular separation of G4.5-COOH+NIR group is minimum(* P < 0.05 or ** P < 0.01).ConclusionsIn summary,taking advantage of dendrimer and platinum nanoparticles,we successfully synthesized the ultra-small photothermal nanomaterials.Specially,the carboxyl-terminated nanomaterial,G4.5-COOH-Pt,exhibited excellent photothermal property,self-powered bone targeting property and biocompatibility.Meanwhile,G4.5-COOH-Pt also presented brilliant efficacy in the treatment of bone tumor.All in all,self-powered bone targeting and multifunctional potential ultra-small photothermal nanomaterial would contribute to provide a new effective choice for the treatment of bone tumor in the future.