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Traditional chemotherapeutic drugs remain the major treatment for advanced colorectalcancer.Yet, due to the lack of tumor specificity that induces unacceptable systemic toxicity,low solubility and/or low stability has led to the failure of tumor treatment and and mortality.In addition, the development of multidrug resistant (MDR) phenotypes classified into cellularand physiological factors ones is also an important reason for the failure of the traditionalchemotherapy.The MDR is concerned with the over-expressed drug efflux transporters,mutated molecular targets and defective apoptotic mechanisms along with the tumormicroenvironment complications as hypoxia, poor vasculature and low extracellular pH.Targeted drug delivery systems, especially by nanoparticles, have been the focus of cancertherapy research during the last decade to improve bioavailability and specific delivery ofanticancer drugs to tumor sites, thereby reducing toxicity and side effects to normal tissues.However, the positive antitumor effects of these nanocarriers observed in conventionalmonolayer cultures frequently fail during in vivo due to the lack of resembling physical andbiological barriers seen in the actual body.Therefore, in this study, we first developed acollagen based 3-D mul ticellular culture system for new drug nanocarriers screening to obtaina more adequate and better predict therapeutic outcomes in preclinical experiments.This 3-Dculture model was successfully established using optimized density of cells.The resultshowed that 3-D cell colonies were successfully developed from 95-D, U87 and HCT116 celllines respectively after seven day culture in the collagen matrix.The coumarin-conjugatednanoparticles were able to penetrate into the matrix gel to reach tumor cells.The model issupposedly more accurate to reflect/predict the dynamics and therapeutic outcomes of drugtransporting candidates in vivo and/or investigation of tumor biology, thus pacing up thediscovery of novel drug delivery systems for cancer therapy.
In the second place, we synthesized a copolymer by graft epsilon-caprolactone intochitosan via ring-opening polymerization.The efficiency of sustained drug delivery systembased on chitosan and epsilon-caprolactone to overcome multidrug resistance in monolayerand drug resistance associated with the 3-D tumor microenvironment was performed in 2-Dmodels and in our established 3-D models.The 5-FU loaded nanoparticles were characterizedby transmission electron microscope, dynamic light scattering and released property wasdetermined at different pH values.5-FU/NPs exhibited well sustained release properties andmarkedly enhanced the cytotoxicity of 5-FU against HCT116/L-OHP or HCT8/VCR MDRcells in 2-D and its parental cells in 3-D collagen gel culture with 2-to 3-fold decrease in theIC50 values, as demonstrated by MTT assay, Hoechst/PI staining and flow cytomertry analysis.Furthermore, the possible mechanism was explored by HPLC and Rh-123 accumulationexperiment.These results demonstrated that 5-FU/NPs increase intracellular concentration of5-FU and enhance it anticancer efficiency by inducing apoptosis.And more, it was suggestthis novel nanoparticles are a promising carrier to decrease toxic of 5-FU and has the potentialto reverse forms of both intrinsic and acquired drug resistance in 2-D and 3-D cultures. Folate receptor (FR) is a highly selective tumor marker overexpressed in malignanttumors.Folic acid (FA) as one of the most common ligands retains a high affinity for FR.Therefore, folate-based drug delivery systems present an attractive target for tumor-selectivedrug delivery.Folic acids conjugates combine with FR situated at the surface of tumor cellsand are internalized to intracellular compartments to form endosomes.Then folate conjugatesare degraded by lysosome and released drug into the cytosol.In following, we has introduce achemical active group, carbamic acid benzyl easter (CAB), to PEG-b-PCL based materialusing mPEG as an initiator to to make FA conjugated poly(ε-caprolactone)derivatives andincrease the 5-FU loading.FA conjugated mPEG-b-P(CABCL-co-ACL) diblock copolymerswere synthesized and characterized by TEM and NMR.Drug loaded nanoparticles wereprepared using dialysis method and was obtained with a mean diameter of 45.2 nm withsustained in vitro release profile.In vitro cytotoxicity assay indicated that the cytotoxicity offolate modified nanoparticles were significantly increased compared to free drug andnon-folate nanoparticles.In addition, results of hemolytic and histopathologic study suggestedthat the non-loaded nanoparticle (NL/NP) was non-toxic and biocompatible at the testingconcentration.Moreover, in vivo results showed that FA/5-FU/NP effectively inhibitedgrowth of HCT-8 cell-based xenograft tumors in BALB/c mice and revealed strongerantitumor efficacy than other treated groups.Thus, both in vitro and in vivo results exhibitedthat the folate conjugated mPEG-b-P(CABCL-co-ACL) copolymers have great potential to beused as sustainable and specific colon cancer targeting delivery system for anticancer agents.
In the current research, extensive knowledge has been gathered and significant advanceshave been made in the field of nanocarrier delivery systems.Nanocarriers have also provideda great platform for the delivery of chemotherapeutic agents and imaging compounds, or both.Nevertheless, there are many challenges involved with the nanocarrier systems, such asbiodegradation, immune responses, large scale manufacturing, and batch to batch variabilityissues.In respect to testing of efficient delivery systems, more efforts are required to utilize3-D culture for high-throughput screening for potential nanosystems due to the advantages itoffers.Briefly, this study has developed a novel poly(ε-caprolactone) based nanodeliverysystem that carry 5-FU to to the tumor site while limiting exposure to non-target tissues.Still,this study has documented the nanocarrier could improve efficiency of chemotherapy drugsand partly reveal how the nanoparticle reverse drug resistance in cancer cells.Finally, thesefindings contribute to better understanding for the possible therapeutic effects of 5-FUnanoparticles in further clinical research.Moreover, these fmdings may be beneficial forfurther research of utilizing nanopreparations for cancer therapy, especially in the multidrugresistance case.