The Development Of Novel Anticancer Strategies Targeting The Tumor Acidic Microenvironment

Cancer is one of the main causes of human death and seriously endangers human life.Tumor microenvironment（TME）is a steady-state environment during the development and progression of tumors,composed of tumor cells,stromal cells and extracellular matrix,etc.It has the characteristics of hypoxia,acidity,low glucose and high permeability.In recent years,TME not only plays a key role in the development and metastasis of tumors,but also can seriously affect the therapeutic effect of tumors,causing a serious burden to patients.For example,TME can cause serious problems such as drug insensitivity,immune tolerance and immune escape,infiltration and metastasis in tumors.At present,TME targeting strategy exhibits an ability to improve the anticancer effects and is recognized as the hot research topics.Acidic microenvironment is an important therapeutic target of TME.This subject focuses on the in-depth study of acidic microenvironment associated anticancer strategy,and is mainly divided into the following three parts.In the first part,we investigated and compared the effects of three major factors of TME on DOX resistance,and demonstrated that the effect of acid on promoting DOX resistance was superior to hypoxia and low glucose.In addition,the neutralization of Na₂CO₃could significantly restore the sensitivity of tumor cells to DOX.Furthermore,a series of studies were conducted to identify the mechanism of acid-induced DOX resistance.It was found that acidity could significantly reduce DOX uptake,induce cell cycle arrest at the G0/G1 phase and inhibit glucose uptake.Meanwhile,neutralizing with Na₂CO₃could reverse these effects induced by acidity.Therefore,Na₂CO₃is a good therapeutic adjuvant,which can be used to improve drug resistance mediated by acidic microenvironment,and provides the necessary research foundation and new ideas for the development of anti-tumor nanomedicine.In the second part,we developed an ultrasound-responsive PLGA nanoparticle（PLGA-DSP）,co-loaded with DOX,Na₂CO₃,and perfluorocarbon（PFC）,for recovering acid-induced DOX resistance.PLGA-DSP were uniform spherical nanoparticles with the mean sizes of 150 nm.In particular,PLGA-DSP nanoparticles had good serum stability and insensitivity to p H changes,but could quickly release DOX and Na₂CO₃under ultrasound stimulation,indicating that PLGA-DSP have ultrasonic response performance.In addition,the in vitro anti-tumor effects of PLGA-DSP under ultrasound stimulation were studied.PLGA-DSP triggered by ultrasound stimulation,could significantly improve the acidic microenvironment and promote the sensitivity of tumor cells to DOX.Finally,the anti-tumor effects of PLGA-DSP in vivo were further investigated.PLGA-DSP could not only effectively release Na₂CO₃to neutralize the acidic microenvironment under ultrasound stimulation,but also significantly inhibit tumor growth,thereby enhancing the antitumor effects of DOX.In the third part,we mainly explored the molecular mechanism of acidic microenvironment on metastasis of hepatocellular carcinoma.Receptor typosine kinase-like orphan receptor 1（ROR1）is type-I membrane protein and plays a critical role in tumor invasion and migration at a variety of cancers,including breast cancer,hepatocellular carcinoma,ovarian carcinaoma,leukemia,and melanoma.Therefore,q RT-PCR and western blot were performed to examine the expression of ROR1 and Wnt5a under acidic conditions.It was found that acidity could significantly upregulate the expression of ROR1 and Wnt5a.In addition,the effects of ROR1 knockdown on acidic microenvironment-mediated tumor metastasis were investigated.ROR1knockdown could effectively inhibit acid-induced epithelial mesenchymal transformation（EMT）,cell invasion and migration.Furthermore,we investigated the effects of Na HCO₃treatment on ROR1 expression and tumor metastasis,and demonstrated that Na HCO₃treatment could inhibit acid-induced cell metastasis by downregulating ROR1 expression in vitro and in vivo.In summary,this thesis focuses on acidic microenvironment related anticancer studies.We have developed an ultrasound-responsive PLGA nanoparticle,which could effectively neutralize the acidic microenvironment and improve the anti-cancer effect.In addition,we confirmed that acidic microenvironment could modulate Wnt5a/ROR1signaling pathway to promote tumor metastasis,and Na HCO₃treatment could neutralize the acidic microenvironment and downregulate the expression of acid-induced ROR1,thereby inhibiting tumor metastasis.The study shows that the tumor acidic microenvironment related anti-tumor strategy is of great significance for improving the anti-tumor therapeutic effect,and provides new ideas and directions for the effective clinical treatment of tumors.