Engineering Photoswitchable Microtubule Inhibition Nanosystems For Site-Specific Cancer Therapy

Azobenzene is a photo-responsive molecule with a N=N moiety that can be isomerized from trans to cis state upon ultraviolet（UV）light irradiation.In pharmacotherapy,the poor drug selectivity leads to the side effects and reduced tolerance.Azobenzene-based prodrugs offer incomparable opportunities to achieve precise spatiotemporal treatment and decrease the side effects via light-triggered activity of azobenzene isomer.However,the poor tissue penetration and phototoxicity of UV light limit the application of azo-based prodrugs.The employment of visible light to near-infrared light（NIR）to regulate the isomerization of azobenzene derivatives is useful to expand the application of azo-based prodrugs in clinical settings.Meanwhile,it is challenging to prolong the half-life of active cis isomer to extend the therapy duration.In this thesis,we designed a NIR-sensitive upconversion nanocarrier to regulate the activity of a photo-responsive microtubule inhibitor,Azo combretastatin A-4（Azo-CA4）,for precise tumor treatment.To prolong the relaxation time of active cis Azo-CA4,a series of borides together with singlet oxygen（¹O₂）were investigated to lock the cis structure through coordination interaction or the formation of new four-atom ring.The main contents of this thesis are as follows:An upconversion nanocarrier was constructed to trigger the activity of the microtubule inhibitor Azo-CA4 and concurrent ferroptosis for the treatment of triple-negative breast cancer（TNBC）.Despite the resistance of TNBC to targeted hormone therapy,the discovery of Azo-CA4,as well as the TNBC microenvironment that is susceptible to ferroptosis,provides prospective therapeutic opportunities for this devastating disease.Here,the activation of Azo-CA4 depended on the trans-cis isomerization upon UV light that is generated from upconverting nanocarriers with a light irradiation at 980 nm.The NIR-triggered Azo-CA4-loaded nanocarrier significantly reduced the viability of TNBC cells（MDA-MB-231）via both apoptotic and ferroptotic mechanisms.The former is induced by the conformational trans-cis transition of Azo-CA4,accompanied with microtubule breakdown and cell cycle arrest at G₂/M phase.The latter is caused by the UV light-induced reduction of Fe³⁺to Fe²⁺that facilitates the peroxidation of tailored lipids.The cooperation between apoptosis and ferroptosis in eliminating TNBC is further demonstrated in a xenograft mice model in terms of histological staining,tumor growth inhibition and animal survival.Since the NIR light is only applied to the tumor site,the adverse effects of such triggered nanocarriers to the healthy organs are negligible.To regard the relaxation of cis Azo-CA4,a strategy of locked cis Azo-CA4molecule was first proposed through coordination interaction with electron acceptor or oxidation by singlet oxygen.Tris（pentafluorophenyl）borane,a strong electron acceptor,was verified to lock cis isomer via coordination bonding,resulting in the longer relaxation time of cis Azo-CA4.On the other hand,the hypothetical Azo-CA4containing N₂O₂ four-membered ring group has not been found in the reaction of ¹O₂and cis Azo-CA4.In summary,we developed a NIR-triggered drug delivery system to achieve the photoswitchable activity of Azo-CA4 for precise treatment of tumors.At the same time,the locking of cis azobenzene was first proposed to increase its stability.The successful locking provides a novel approach for improving the potency of azobenzene-based（pro）drugs.