Construction Of PH-responsive Bone-targeted Nano-drug Delivery System And Its Anti-breast Cancer Bone Metastasis

Breast cancer is one of the common malignant tumors in women.With the development of living standards,breast cancer incidence and mortality are at the forefront of female malignancy.Studies have shown that the leading cause of death in breast cancer patients is distal metastasis,mainly including bone,lung,and liver metastases.Because the bone tissue has a special structure and physiological function,it is suitable for the growth of tumor cells,making it the most common metastatic site of breast cancer.Bone metastasis of breast cancer not only endangers the patient’s life,but also causes bone-related events,such as pathological fractures,bone pain,hypercalcemia,etc.,which increase the patient’s pain and reduce the patient’s quality of life.However,according to the conventional administration method,since the drug is not selective and the permeability to bone is low,it is difficult to effectively deliver the drug to the site of bone metastasis,and therefore it is often required to increase the dose,and the large-dose administration is easy causes damage to other organs.Therefore,it is of great theoretical and practical significance to develop appropriate carriers and delivery systems for bone metastases in breast cancer.With the development of nanotechnology,environmental responsive polymer micelles are increasingly favored by pharmaceutical workers.Polyethylene glycol-polylysine(PEG-b-PLL)is widely used for the delivery of DNA,RNA and chemotherapeutic drugs because of its good biocompatibility and chemical modification.In this study,PEG-b-PLL was used as the basic carrier polymer.Through chemical bonding,the chemotherapeutic agent bortezomib(BTZ)and the bone-targeting ligand alendronate sodium(ALN)were modified to PEG-b-PLL.A nano-drug delivery system(ALN-NPs)with bone targeting and pH responsive drug release was designed.ALN-NPs can be stably transported in the blood circulation without releasing the drug.The effect of ALN is that the capillary wall of the bone tissue reaches the surface of the bone,and is transported to the tumor tissue under the enhanced permeability and retention effect(EPR effect)of the solid tumor.After being taken up by tumor cells,BTZ is released and kills tumor cells.Based on the above design,the synthesized polymers(PEG-b-PLL,PEG-b-P(LL-g-Cat-BTZ),ALN-PEG-b-PLLZ)were first characterized by ~1H NMR and infrared light scanning;Nanoparticles for bone-targeting nanoparticles(ALN-NPs)were prepared by nano-coprecipitation method.The particle size is about 95±15 nm,appearance,roundness,drug loading is about 3.06%±0.5,and obvious pH response and bone targeting in vitro.Secondly,cell experiments showed that compared with free BTZ,the same drug dose of ALN-NPs was more toxic after 48 h;In addition,after ALN was modified,the uptake of ALN-NPs by RAW 264.7 cells was not significantly different from that of unmodified ALN,indicating that modification of ALN did not affect the properties of the micelles;and the CLSM results show that after the nanoparticles are taken up by MDA-MB-231 cells,the drug can escape from the lysosomes.Finally,in vivo imaging of small animals showed that ALN-NPs can effectively increase the accumulation and residence time of nanoparticles in the bone and tumor tissues of tumor-bearing mice.In vivo efficacy experiments showed that ALN-NPs group can significantly inhibit tumor growth in mice;Compared with the free BTZ group,the body weight of the ALN-NPs group had no significant changes after treatment.Micro-CT results showed that after treatment with ALN-NPs,the tibial destruction of mice was significantly smaller than that of the boneless-targeted group.In summary,the pH-responsive bone-targeting nano-drug delivery system constructed in this project has good bone targeting and anti-tumor activity.