CRGD-Functionalized Reversibly Crosslinked Micelles Loaded With Lipophilized Bortezomib For Triple Negative Breast Cancer Chemotherapy

Inhibition of proteasome which disrupts protein homeostasis and attenuates multiple signaling pathways has become a very attractive anticancer therapy.Bortezomib（BTZ）that reversibly binds to the chymotrypsin-like activity of proteasomeβ5 subunit and selectively induces cancer cell apoptosis is the first proteasome inhibitor approved by Food and Drug Administration（FDA）for multiple myeloma and mantle cell lymphoma.In addition,BTZ has been found effectively against lung,prostate,colorectal,and breast cancers.Free BTZ,however,shows fast clearance,low tumor accumulation,and several side effects such as peripheral neuropathy,thrombocytopenia,and gastrointestinal disorder.Various nanocarriers have been designed and prepared for effective delivery of therapeutic agents.However,present BTZ-nanomedicines suffered from low BTZ contents,drug leakage,slow drug release,no targeting ability and so on.In chapter 1,we present a brief literature over mechanism and clinical trial applications of BTZ,tracing the recent progress on BTZ-nanomedicine and multifunctional polymeric nanoparticles.In chapter 2,we designed and developed cRGD-decorated,glutathione-sensitive,lipophilized bortezomib micelles for targeted and efficacious treatment ofα_vβ₃-overexpressing human breast tumor xenografts.Lipophilized bortezomib,bortezomib-pinanediol（BP）,was readily prepared in a high yield.Interestingly,cRGD-decorated micelles based on poly（ethylene glycol）-b-poly（trimethylene carbonate-co-dithiolane trimethylene carbonate）achieved a high drug loading content of 8.05 wt.%BTZ equiv.for BP,which was more than 8-fold higher than for BTZ.BP-loaded cRGD-decorated micelles（BP-cRGD-Ms）exhibited a small size（ca.49 nm）,reduction-triggered drug release,and active targeting ability toα_vβ₃-overexpressing MDA-MB-231 triple-negative breast cancer cells,resulting in a low IC₅₀ of 0.986μM.The in vivo studies displayed that BP-cRGD-Ms had nearly 20-fold improvement in elimination half-life and 20-fold higher maximum-tolerated dose as compared to free BTZ.The biodistribution and therapeutic studies in MDA-MB-231 tumor-bearing nude mice demonstrated that BP-cRGD-Ms induced significantly better tumor accumulation and inhibition while lower adverse effects than free BTZ,leading to greatly improved mice survival rate.This micellar nanoformulation of lipophilized bortezomib appears to be a novel and effective strategy to achieve targeted tumor chemotherapy with bortezomib.Combination chemotherapy with multiple-drugs could effectively slow the cancer cell mutation,overcome drug resistance,diminish toxic side effects and maximize therapeutic outcomes.In chapter 3,we designed and developed lipophilized bortezomib and doxorubicin-encapsulated,cRGD-functionalized,self-crosslinked,and reduction-sensitive polymeric mixed micelles（BP/DOX-cRGD-Ms）for synergistic combination treatment ofα_vβ₃-overexpressing MDA-MB-231 xenografts in nude mice.BP/DOX-cRGD-Ms had a small size about 50 nm and narrow PDI.In vitro drug release revealed that under reduction environment BP and DOX could be fastly released from BP/DOX-cRGD-Ms with similar release profiles.Remarkably,MTT assays revealed BP/DOX-cRGD-Ms exhibited synergistic effects with combination index of 0.71-0.75 in MDA-MB-231 cells at BP/DOX（w/w）ratio from 3/1,1/1,1/3 to 1/6.The in vivo therapeutic studies demonstrated that BP/DOX-cRGD-Ms exhibited the best tumor inhibition as compared to BP-cRGD-Ms and DOX-cRGD-Ms at the corresponding drug concentrations.These smart mixed micelles（BP/DOX-cRGD-Ms）provide a promising nanoplatform for emerging combinatorial cancer chemotherapy.