Targeted Bortezomib Therapy Of Multiple Myeloma By Hyaluronic Acid-Shelled And Core-Disulfide-Crosslinked Micelles

Multiple myeloma(MM)is one of the most frequently occurred hematological cancers and is characterized by an expansion of abnormal plasma cells in the bone marrow and excessive production of monoclonal immunoglobulin,which often leads to pathologic fractures and hematopoietic function failure.Bortezomib(BTZ)is a potent proteasome inhibitor that is approved for the treatment of MM and other hematologic malignancies.BTZ binds to the threonine residues in the active sites if the active sites of the proteasome via boronic acid to block the degradation of ubiquitinated proteins.The current clinical formulation of BTZ,however,shows fast clearance,low tumor accumulation,and several side effects including thrombocytopenia and peripheral neuropathy which occurs in approximately 30%of patients and are the most problematic dose limiting toxicities.Therefore,various BTZ nanomedicines including polymer-BTZ conjugates,micelles,liposomes and nanoparticles have been designed and explored for increasing the therapeutic efficacy and reducing the toxicity of BTZ.However,low drug loading and low tumor selectivity are critical issue for the development of BTZ nanomedicines.In chapter 2,we reported on targeted BTZ therapy of MM in vivo by hyaluronic acid-shelled and core-disulfide-crosslinked biodegradable micelles(HA-CCMs)encapsulating lipophilized BTZ,bortezomib-pinanediol(BP).HA-CCMs loaded with 7.3 BTZ equiv.wt.%exhibited a small size of 78 nm,good stability in 10%FBS,and glutathione-triggered drug release.MTT assays in CD44 positive LP-1 multiple myeloma cells revealed that BP encapsulated in HA-CCMs caused enhanced antiproliferative effect compared with free BP,with a half inhibitory concentration(IC50)of 0.023 ?g/mL.Flow cytometry,confocal microscopy and MTT assays indicated that BP-loaded HA-CCMs(HA-CCMs-BP)could actively target to LP-1 cells and induce high antitumor effect.Proteasome activity assays in vitro showed HA-CCMs-BP had a similar proteasome activity inhibition as compared to free BTZ at 18 h.The fluorescence imaging using Cy5-labeled HA-CCMs showed that HA-CCMs had a longer circulation time than free HA pretreated control group and HA shell played a critical role in tumor accumulation.The therapeutic efficacy of HA-CCMs-BP was investigated in LP-1 tumor-bearing mice.HA-CCMs-BP(0.5 mg BTZ equiv./kg)exhibited more effective inhibition of tumor growth than free BTZ at the same dosage.Importantly,HA-CCMs-BP at 3 mg BTZ equiv./kg brought about significant tumor growth inhibition(TIR:72.5%)and survival benefits(median survival times:62 d).Loading of lipophilized BTZ into HA-shelled multifunctional micelles appears to be an interesting approach for bortezomib therapy of MM.Drug combinations with different mechanisms have become one of the effective treatments for cancer.BTZ and Lipo-DOX combination chemotherapy has been approved by FDA for the therapy for multiple myeloma.However,clinical trials showed that a lack of therapeutic effect was observed using BTZ and Lipo-DOX as combination chemotherapy.The reason is likely associated with the difference of pharmacokinetic between BTZ and Lipo-DOX.BTZ can be cleared rapidly by red blood cells,while Lipo-DOX has a long half-life(55 h).In chapter 3,we used HA-CCMs encapsulating bortezomib-pinanediol(BP)and doxorubicin(HA-CCMs-BP/DOX)for targeted therapy of MM.HA-CCMs-BP/DOX exhibited a small size of 90 nm and high drug loading content of BP and DOX(7.3 wt.%and 8.9 wt.%).The in vitro drug release studies showed that HA-CCMs-BP/DOX had similar drug release behavior.MTT assays revealed that the best synergistic effect was observed at BP/DOX molar ratio of 1/3.The therapeutic studies in LP-1 MM-bearing mice revealed superior treatment efficacy of HA-CCMs-BP/DOX at a dosage of 1/4.2 mg/kg(molar ratio:1/3)compared to BTZ and Lipo-DOX,in which TIR of 72.5%and 32.5%were observed.The HA-CCMs-BP/DOX can realize certain drug proportion release in tumor cells,improve treatment effect,and afford a fascinating platform for targeted combination chemotherapy of multiple myeloma cancer.