Folate receptor function is regulated in response to different cellular growth rates in cultured mammalian cells

Folic-Acid-Conjugated Thermoresponsive Polymeric Particles for Targeted Delivery of 5-Fluorouracil to CRC Cells

Colorectal cancer is the fourth most common cancer worldwide and the third most frequently diagnosed form of cancer associated with high mortality rates. Recently, targeted drug delivery systems have been under increasing attention owing to advantages such as high therapeutic effectiveness with a significant depletion in adverse events. In this report, we describe the biocompatible and thermoresponsive FA-conjugated PHEA-b-PNIPAAm copolymers as nanocarriers for the delivery of 5-FU. The block copolymers were obtained using RAFT (Reversible Addition-Fragmentation chain Transfer) polymerization and were characterized by methods such as SEC (Size Exclusion Chromatography), NMR (Nuclear Magnetic Resonance), UV-Vis (Ultraviolet-Visible), FT-IR (Fourier Transform Infrared) spectroscopy, and TGA (Thermogravimetric Analysis). Nanoparticles were formed from polymers with and without the drug-5-fluorouracil, which was confirmed using DLS (Dynamic Light Scattering), zeta potential measurements, and TEM (Transmission Electron Microscopy) imaging. The cloud points of the polymers were found to be close to the temperature of the human body. Eventually, polymeric carriers were tested as drug delivery systems for the safety, compatibility, and targeting of colorectal cancer cells (CRC). The biological evaluation indicated high compatibility with the representative host cells. Furthermore, it showed that proposed nanosystems might have therapeutic potential as mitigators for 5-FU-induced monocytopenia, cardiotoxicity, and other chemotherapy-associated disorders. Moreover, results show increased cytotoxicity against cancer cells compared to the drug, including a line with a drug resistance phenotype. Additionally, the ability of synthesized carriers to induce apoptosis and necrosis in treated CRC cells has been confirmed. Undoubtedly, the presented aspects of colorectal cancer therapy promise future solutions to overcome the conventional limitations of current treatment regimens for this type of cancer and to improve the quality of life of the patients.

Chlorotoxin and Lung Cancer: A Targeting Perspective for Drug Delivery

In the generational evolution of nano-based drug delivery carriers, active targeting has been a major milestone for improved and selective drug accumulation in tissues and cell types beyond the existing passive targeting capabilities. Among the various active targeting moieties, chlorotoxin, a peptide extracted from scorpions, demonstrated promising tumor cell accumulation and selection. With lung cancer being among the leading diagnoses of cancer-related deaths in both men and women, novel therapeutic methodologies utilizing nanotechnology for drug delivery emerged. Given chlorotoxin's promising biological activity, we explore its potential against lung cancer and its utilization for active targeting against this cancer's tumor cells. Our analysis indicates that despite the extensive chlorotoxin's research against glioblastoma, lung cancer research with the molecule has been limited, despite some promising early results.

Estrone-Conjugated PEGylated Liposome Co-Loaded Paclitaxel and Carboplatin Improve Anti-Tumor Efficacy in Ovarian Cancer and Reduce Acute Toxicity of Chemo-Drugs

Purpose

Ovarian cancer is the most lethal gynecologic malignancy. The combination of paclitaxel (PTX) and carboplatin (CBP) is the first-line remedy for clinical ovarian cancer. However, due to the limitations of adverse reaction and lacking of targeting ability, the chemotherapy of ovarian cancer is still poorly effective. Here, a novel estrone (ES)-conjugated PEGylated liposome co-loaded PTX and CBP (ES-PEG-Lip-PTX/CBP) was designed for overcoming the above disadvantages.

Methods

ES-PEG-Lip-PTX/CBP was prepared by film hydration method and could recognize estrogen receptor (ER) over-expressing on the surface of SKOV-3 cells. The characterizations, stability and in vitro release of ES-PEG-Lip-PTX/CBP were studied. In vitro cellular uptake and its mechanism were observed by fluorescence microscope. In vivo targeting effect in tumor-bearing mice was determined. Pharmacokinetics and biodistribution were studied in ICR mice. In vitro cytotoxicity and in vivo anti-tumor efficacy were evaluated on SKOV-3 cells and tumor-bearing mice, respectively. Finally, the acute toxicity in ICR mice was explored for assessing the preliminary safety of ES-PEG-Lip-PTX/CBP.

Results

Our results showed that ES-PEG-Lip-PTX/CBP was spherical shape without aggregation. ES-PEG-Lip-PTX/CBP exhibited the optimum targeting effect on uptake in vitro and in vivo. The pharmacokinetics demonstrated ES-PEG-Lip-PTX/CBP had improved the pharmacokinetic behavior. In vitro cytotoxicity showed that ES-PEG-Lip-PTX/CBP maximally inhibited SKOV-3 cell proliferation and its IC₅₀ values was 1.6 times lower than that of non-ES conjugated liposomes at 72 h. The in vivo anti-tumor efficacy study demonstrated that ES-PEG-Lip-PTX/CBP could lead strong SKOV-3 tumor growth suppression with a tumor volume inhibitory rate of 81.8%. Meanwhile, acute toxicity studies confirmed that ES-PEG-Lip-PTX/CBP significantly reduced the toxicity of the chemo drugs.

Conclusion

ES-PEG-Lip-PTX/CBP was successfully prepared with an optimal physicochemical and ER targeting property. The data of pharmacokinetics, anti-tumor efficacy and safety study indicated that ES-PEG-Lip-PTX/CBP could become a promising therapeutic formulation for human ovarian cancer in the future clinic.

Different Serum, Different Protein Corona! The Impact of the Serum Source on Cellular Targeting of Folic Acid-Modified Chitosan-Based Nanoparticles

The nanoparticle (NP) protein corona represents an interface between biological components and NPs, dictating their cellular interaction and biological fate. To assess the success of cellular targeting, NPs modified with targeting ligands are incubated with target cells in serum-free culture medium or in the presence of fetal bovine serum (FBS). In the former, the role of the corona is overlooked, and in the latter, the effects of a corona that does not represent the one forming in humans nor the respective disease state are considered. Via proteomic analysis, we demonstrate how the difference in the composition of FBS, sera from healthy human volunteers, and breast cancer patients (BrCr Pt) results in the formation of completely different protein coronas around the same NP. Successful in vitro targeting of breast cancer cells was only observed when NPs were incubated with target cells in the presence of BrCr Pt sera only. In such cases, the success of targeting was not attributed to the targeting ligand itself, but to the adsorption of specific serum proteins that facilitate NP uptake by cancer cells in the presence of BrCr Pt sera. This work therefore demonstrates how the serum source affects the reliability of in vitro experiments assessing NP-cell interactions and the consequent success or failure of active targeting and may in fact indicate an additional reason for the limited clinical success of drug targeting by NPs in cancer.

A Novel Method of Magnetic Nanoparticles Functionalized with Anti-Folate Receptor Antibody and Methotrexate for Antibody Mediated Targeted Drug Delivery

Therapeutic effects of anticancer medicines can be improved by targeting the specific receptors on cancer cells. Folate receptor (FR) targeting with antibody (Ab) is an effective tool to deliver anticancer drugs to the cancer cell. In this research project, a novel formulation of targeting drug delivery was designed, and its anticancer effects were analyzed. Folic acid-conjugated magnetic nanoparticles (MNPs) were used for the purification of folate receptors through a novel magnetic affinity purification method. Antibodies against the folate receptors and methotrexate (MTX) were developed and characterized with enzyme-linked immunosorbent assay and Western blot. Targeting nanomedicines (MNP-MTX-FR Ab) were synthesized by engineering the MNP with methotrexate and anti-folate receptor antibody (anti-FR Ab). The cytotoxicity of nanomedicines on HeLa cells was analyzed by calculating the % age cell viability. A fluorescent study was performed with HeLa cells and tumor tissue sections to analyze the binding efficacy and intracellular tracking of synthesized nanomedicines. MNP-MTX-FR Ab demonstrated good cytotoxicity along all the nanocomposites, which confirms that the antibody-coated medicine possesses the potential affinity to destroy cancer cells in the targeted drug delivery process. Immunohistochemical approaches and fluorescent study further confirmed their uptake by FRs on the tumor cells' surface in antibody-mediated endocytosis. The current approach is a useful addition to targeted drug delivery for better management of cancer therapy along with immunotherapy in the future.

The other side to the use of active targeting ligands; the case of folic acid in the targeting of breast cancer

Due to its overexpression in cancer cells, the folate receptor (FR) is heavily exploited in the active targeting of nanoparticles (NPs). Its ligand, folic acid (FA) is as a consequence widely used as a NP targeting ligand. Although rather popular and successful in principle, recent data has shown that FA may result in breast cancer initiation and progression, which questions the suitability of FA as NP cancer targeting ligand. In this work, intravenous administration of free FA to healthy female mice resulted in breast tissue dysplasia, hyperplasia and in the increased expression of human epidermal growth factor receptor-2 (HER2), folate receptor (FR), cancer antigen 15-3 (CA15.3), vascular endothelial growth factor (VEGF), signal transducer and activator of transcription 3 (STAT3) and the pro-inflammatory cytokines, tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6) and interleukin-1β. In addition to the reduction in IL2. To evaluate the suitability and safety of FA as NP targeting ligand in breast cancer, small (≈ 150 nm) and large (≈ 500 nm) chitosan NPs were formulated and decorated with two densities of FA. The success of active targeting by FA was confirmed in two breast cancer cell lines (MCF-7 and MDA-MB-231 cells) in comparison to HEK293 cells. FA modified NPs that demonstrated successful active targeting in-vitro were assessed in-vivo. Upon intravenous administration, large NPs modified with a high density of FA accumulated in the breast tissue and resulted in similar effects as those observed with free FA. These results therefore question the suitability of FA as a targeting ligand in breast cancer and shed light on the importance of considering the activity (other than targeting) of the ligands used in NP active targeting.

Synergistic effect of folate-conjugated polymers and 5-fluorouracil in the treatment of colon cancer

Background

In recent years, targeted drug delivery strategies have received special attention from the scientific world due to advantages such as more effective therapy and reduction of side effects. The principle of operation is delayed excretion from the bloodstream of the drug delivery system compared to the drug itself, as well as facilitated penetration into diseased cells thanks to the use of ligands recognized by appropriate receptors. Particularly interesting drug carriers are amphiphilic copolymers that form nano-sized micelles with a drug, which can release the drug at a specific place in the body under the influence of appropriate stimuli.

Results

We describe the synthesis of the diblock polymer, poly(2-hydroxyethyl acrylate)-b-poly(N-vinylcaprolactam) using RAFT/MADIX (Reversible Addition-Fragmentation chain Transfer/MAcromolecular Design by Interchange of Xanthate) controlled polymerization affording polymers with good dispersity according to SEC (Size-Exclusion Chromatography). Some post-modifications of the polymer with folic acid were then performed as evidenced by NMR (Nuclear Magnetic Resonance), UV–Vis (UltraViolet–Visible) and FT-IR (Fourier-Transform Infrared) spectroscopy, and TGA (ThermoGravimetric Analysis). The formation of stable micellar systems from polymers with and without the drug, 5-fluorouracil, was confirmed by DLS (Dynamic Light Scattering) and zeta potential measurements, and TEM (Transmission Eelectron Microscopy) imaging. Finally, the cloud point of the polymers was investigated, which turned out to be close to the temperature of the human body. Most importantly, these micellar systems have been explored as a drug delivery system against colon cancer, showing increased cytotoxicity compared to the drug alone. This effect was achieved due to the easier cellular uptake by the interaction of folic acid and its receptors on the surface of cancer cells.

Conclusions

The presented results constitute a solid foundation for the implementation of a nano-sized drug delivery system containing folic acid for practical use in the treatment of drug-resistant cancer, as well as more effective therapy with fewer side effects.

Graphical Abstract

Highly Sensitive Electrochemical Biosensor Using Folic Acid-Modified Reduced Graphene Oxide for the Detection of Cancer Biomarker

The detection of cancer biomarkers in the early stages could prevent cancer-related deaths significantly. Nanomaterials combined with biomolecules are extensively used in drug delivery, imaging, and sensing applications by targeting the overexpressed cancer proteins such as folate receptors (FRs) to control the disease by providing earlier treatments. In this investigation, biocompatible reduced graphene oxide (rGO) nanosheets combined with folic acid (FA)-a vitamin with high bioaffinity to FRs-is utilized to develop an electrochemical sensor for cancer detection. To mimic the cancer cell environment, FR-β protein is used to evaluate the response of the rGO-FA sensor. The formation of the rGO-FA nanocomposite was confirmed through various characterization techniques. A glassy carbon (GC) electrode was then modified with the obtained rGO-FA and analyzed via differential pulse voltammetry (DPV) for its specific detection towards FRs. Using the DPV technique, the rGO-FA-modified electrode exhibited a limit of detection (LOD) of 1.69 pM, determined in a linear concentration range from 6 to 100 pM. This excellent electrochemical performance towards FRs detection could provide a significant contribution towards future cancer diagnosis. Moreover, the rGO-FA sensing platform also showed excellent specificity and reliability when tested against similar interfering biomolecules. This rGO-FA sensor offers a great promise to the future medical industry through its highly sensitive detection towards FRs in a fast, reliable, and economical way.

Oral absorption enhancement of the amyloid-β oligomer eliminating compound RD2 by conjugation with folic acid

Amyloid-β (Aβ) plays a central role in the development and progression of Alzheimer's disease (AD) with Aβ oligomers representing the most toxic species. The all-d-enantiomeric peptide RD2, which recently successfully completed clinical phase I, specifically eliminates Aβ oligomers in vitro as well as in vivo and improves cognitive deficits in various transgenic AD mouse models even after oral administration. To further enhance the oral absorption of RD2, folic acid has been conjugated to the d-peptide promoting an endocytosis-mediated uptake via a folate receptor located in the intestine. Two different conjugation strategies were selected to obtain prodrugs with folic acid being cleaved after intestinal absorption releasing unmodified RD2 in order to enable RD2's unaltered systemic efficacy. Both conjugates remained stable in simulated gastrointestinal fluids. But only one of them was suitable as prodrug as it was cleaved to RD2 in vitro in human blood plasma and liver microsomes and in vivo in mice after intravenous injection leading to a systemic release of RD2. Furthermore, the conjugate's permeability in vitro and after oral administration in mice was strongly enhanced compared to unconjugated RD2 demonstrating the prodrug's functionality. However, the conjugate seemed to have impaired the mice's wellbeing shortly after oral administration possibly resulting from strain-specific hypersensitivity to folic acid. Nevertheless, we assume that the prodrug is actually non-toxic, especially in lower concentrations as verified by a cell viability test. Furthermore, lower dosages can be applied with unaltered efficacy due to its enhanced oral absorption.

Gestational folate deficiency alters embryonic gene expression and cell function

Folic acid is a nutrient essential for embryonic development. Folate deficiency can cause embryonic lethality or neural tube defects and orofacial anomalies. Folate receptor 1 (Folr1) is a folate binding protein that facilitates the cellular uptake of dietary folate. To better understand the biological processes affected by folate deficiency, gene expression profiles of gestational day 9.5 (gd9.5) Folr1^-/- embryos were compared to those of gd9.5 Folr1^+/+ embryos. The expression of 837 genes/ESTs was found to be differentially altered in Folr1^-/- embryos, relative to those observed in wild-type embryos. The 837 differentially expressed genes were subjected to Ingenuity Pathway Analysis. Among the major biological functions affected in Folr1^-/- mice were those related to 'digestive system development/function', 'cardiovascular system development/function', 'tissue development', 'cellular development', and 'cell growth and differentiation', while the major canonical pathways affected were those associated with blood coagulation, embryonic stem cell transcription and cardiomyocyte differentiation (via BMP receptors). Cellular proliferation, apoptosis and migration were all significantly affected in the Folr1^-/- embryos. Cranial neural crest cells (NCCs) and neural tube explants, grown under folate-deficient conditions, exhibited marked reduction in directed migration that can be attributed, in part, to an altered cytoskeleton caused by perturbations in F-actin formation and/or assembly. The present study revealed that several developmentally relevant biological processes were compromised in Folr1^-/- embryos.

Functionalized layer-by-layer assembled film with directional 5-fluorouracil release to target colon cancer

The objective of this work was to prepare and characterize pH-sensitive capsule containing functionalized layer-by-layer (LbL) assembled polymeric film with directional drug release and evaluate its effectiveness against colon cancer. 5-Fluorouracil (5FU) loaded LbL film was prepared by sequential adsorption of chitosan and alginate polyelectrolytes. This LbL film was coated with polycaprolactone (PCL, 95% w/w) as a backing layer to restrict 5FU release on one-side. The other side constituted the folic acid conjugated chitosan layer for cancer targeting. This film was encapsulated into a gelatin capsule coated with pH-sensitive Eudragit S100. 5FU loaded LbL film was characterized for physical and mechanical properties. Mucoadhesion studies performed using excised rabbit colon showed that chitosan-side of LbL film adhered with significantly (p < 0.05) greater strength compared with PCL-side. Non-everted rat colon-sac model and open colon membrane model studies showed greater permeation of 5FU across the colon wall when adhered to chitosan-side of LbL film compared with PCL-side of the film. Cell monolayer and 3D-spheroid model studies using Caco-2 and COLO 320DM colorectal cancer cells showed significant (p < 0.05) growth inhibition by 5FU loaded LbL film compared with free 5FU solution. In conclusion, pH-sensitive capsule containing 5FU loaded LbL film can be developed to target colorectal cancer for regional drug delivery.

Poloxamer 407 based-nanoparticles for controlled release of methotrexate

Poloxamer 407 (P407)-based nanoparticles were produced by the high pressure homogenization method for the encapsulation and delivery of methotrexate (MTX), aiming intravenous therapeutic applications. The surface of these nanoparticles was functionalized by conjugation of P407 with folic acid (FA) or with MTX, which served as targeting ligand agents. MTX-P407 conjugate was also developed to increase the final drug cargo. Two hydrophobic derivatives of MTX, MTX di-ethylated ester (MTX-OEt) and the ionic complex MTX-dimethyldioctadecylammonium bromide (MTX-DODAB) were produced and entrapped onto P407-based nanoparticles. All formulations developed revealed a monodisperse character comprising small and narrow nanoparticles (<100 nm). P407 nanoparticles (functionalized with FA) and MTX-P407 nanoparticles, both loaded with MTX-OEt, demonstrated a slow drug release profile. The effect of lipase from Aspergillus oryzae on the hydrolysis of the linkage between the P407 and MTX, and consequent MTX release profile, was also evaluated. We observed a controlled and slow release of MTX (<50% of release after 11 days) in the presence of enzyme. These MTX-P407 nanoparticles loaded with MTX-OEt induced a great effect against Caco-2 cancer cells (≈40% of cell death after 72 h of incubation), demonstrating higher efficiency than the free MTX at the same concentration.

Investigating the effect of near infrared photo thermal therapy folic acid conjugated gold nano shell on melanoma cancer cell line A375

Nowadays, there is growing interest regarding the use of metal Nanoshells as targeted agents of Nano-photo thermal cancer therapy. This study was aimed at synthesis the folic acid (FA)-conjugated with silica @gold core-shell nanoparticles (FA-SiO₂@AuNPs) for improving the treatment of melanoma cancer cells. The characterization data showed that the FA-SiO₂@AuNPs is spherical in shape and its size is ∼73.7 nm. The intracellular uptake of FA-SiO₂@AuNPs into melanoma cells (A375) was measured through the inductively coupled plasma, (∼47.7%). The cytotoxicity of nanoparticles was investigated on A375 and HDF (Human dermal fibroblast) cell lines. Cytotoxicity results indicated that there is no significant cytotoxicity in HDF cell lines treated with nanoparticles. MTT and flow cytometry results showed that the viability of A375 cells treated by SiO₂@Au and FA-SiO₂@AuNPs was decreased significantly to about 31% and 16% respectively. The higher toxicity of cancer cells was obtained for the cells exposed to 808 nm near-infrared (NIR) laser after incubation with FA-SiO₂@AuNPs rather than the non-targeted SiO₂@AuNPs. Furthermore, about 64% more cell death was observed for A-375 cells using both photothermal therapy and treatment with FA-SiO₂@AuNPs compared to photothermal therapy. Additionally, the majority of the cell deaths were related to the apoptosis process, not necrosis. It can be concluded that FA-SiO₂@AuNPs was an effective targeting agent for photothermal therapy in the treatment of melanoma.

Next-Generation Multimodality of Nanomedicine Therapy: Size and Structure Dependence of Folic Acid Conjugated Copolymers Actively Target Cancer Cells in Disabling Cell Division and Inducing Apoptosis

Nanomedicine as a multimodality treatment of cancer utilizes the advantages of nanodelivery systems of drugs. They are superior to the clinical administration of different therapeutic agents in several aspects, including simultaneous delivery of drugs to the active site, precise ratio control of the loading drugs and overcoming multidrug resistance. The role of nanopolymer size and structural shape on the internalization process and subsequent intracellular toxicity is limited. Here, the size and shape dependent mechanism of a functionalized copolymer was investigated using folic acid (FA) covalently bonded to the copolymer poly (styrene-alt-maleic anhydride) (SMA) on its hydrophilic exterior via a biological linker 2,4-diaminobutyric acid (DABA) to target folic acid receptors (FR) overly expressed on cancer cells actively. We recently reported that unloaded FA-DABA-SMA copolymers significantly reduced cancer cell viability, suggesting a secondary therapeutic mechanism of action of the copolymer carrier post-internalization. Here, we investigated the size and shape dependent secondary mechanism of unloaded 350 kDa and 20 kDa FA-DABA-SMA. The 350 kDa and 20 kDa copolymers actively target folic acid receptors (FR) to initialize internationalization, but only the large size and sheet shaped copolymer disables cell division by intracellular disruptions of essential oncogenic proteins including p53, STAT-3 and c-Myc. Furthermore, the 350 kDa FA-DABA-SMA activates early and late apoptotic events in both PANC-1 and MDA-MB-231 cancer cells. These findings indicate that the large size and structural sheet shape of the 350 kDa FA-DABA-SMA copolymer facilitate multimodal tumor targeting mechanisms together with the ability to internalize hydrophobic chemotherapeutics to disable critical oncogenic proteins controlling cell division and to induce apoptosis. The significance of these novel findings reveals copolymer secondary cellular targets and therapeutic actions that extend beyond the direct delivery of chemotherapeutics. This report offers novel therapeutic insight into the intracellular activity of copolymers critically dependent on the size and structural shape of the nanopolymers.

Folic Acid Receptor-Mediated Targeting Enhances the Cytotoxicity, Efficacy, and Selectivity of Withania somnifera Leaf Extract: In vitro and in vivo Evidence

Nanomedicine holds great potential for drug delivery to achieve more effective and safer cancer treatment. Earlier, we reported that the alcoholic extract of Withania somnifera leaves (i-Extract) has selective cancer cell killing activity. Herein, we developed a folate receptor-targeting i-Extract nanocomplex (FRi-ExNC) that suspends well in water and possesses enhanced selective anticancer activity in both in vitro and in vivo assays. Comparative analyses of folate receptor (FR)-positive and -negative cells revealed that FRi-ExNC caused a stronger decrease in Cyclin D/Cdk4 and anti-apoptotic protein Bcl-2, as well as a higher increase in the growth arrest regulating protein p21^WAF1 and pro-apoptotic protein PARP-1, in FR-enriched cancer cells. Our results demonstrate that FRi-ExNC could be a natural source-based nanomedicine for targeted cancer therapy.

Receptor mediated transcytosis in biological barrier: The influence of receptor character and their ligand density on the transmembrane pathway of active-targeting nanocarriers

Active-targeting nanocarriers can significantly improve the transcytosis of poorly water-soluble or bio-macromolecular drugs across biological barrier. However, reasons for the improvement are not understood enough, which hampered the reasonable design of active targeting nanocarriers. To illustrate how different factors influence the transport of active-targeting nanocarriers, we established ligand-decorated micelles targeting different receptors to study how the decorations influence the transcytosis of the micelles by comparing the endocytosis, transport pathway and exocytosis process. Three different kinds of receptors, Neonatal Fc receptor (FcRn), transferrin receptor (TfR) and αvβ3 integrin were selected. They presented three different transport pathways, mainly mediating transcytosis, recycling pathway and cell binding, respectively. Their corresponding ligand FcBP, 7pep and c(RGDfK) decorated micelles with different ligand densities were prepared first. Then the effects of receptor and ligand density on the transcytosis across biological barrier were investigated. The results showed that the uptake rate of active micelles was higher than passive micelles and an optimum ligand density with most endocytosis appeared in all functional micelles. Transport pathway study showed 7pep decorated micelles were transferred into apical recycling endosome (ARE) and exocytosed to apical plasma membrane in a ligand depended way. c(RGDfK) decorated micelles were transferred through common recycling endosome (CRE) and Golgi complex to basolateral plasma membrane instead of ARE. While FcBP decorated micelles took both the recycling pathway and transcytosis through CRE, but not Golgi complex. Proper ligand density, not the higher the better, led the most uptake. Also the apical to basolateral transcytosis ratio may not be in accordance with the uptake. Among all the itineraries, transcytosis through CRE is the best itinerary for transcytosis. So, in the design of active targeting nanocarriers to overcome biological barrier, receptor character should be considered priorly, and then ligand density should be optimized.

Methyl-donor depletion of head and neck cancer cells in vitro establishes a less aggressive tumour cell phenotype

PURPOSE

DNA methylation plays a fundamental role in the epigenetic control of carcinogenesis and is, in part, influenced by the availability of methyl donors obtained from the diet. In this study, we developed an in-vitro model to investigate whether methyl donor depletion affects the phenotype and gene expression in head and neck squamous cell carcinoma (HNSCC) cells.

METHODS

HNSCC cell lines (UD-SCC2 and UPCI-SCC72) were cultured in medium deficient in methionine, folate, and choline or methyl donor complete medium. Cell doubling-time, proliferation, migration, and apoptosis were analysed. The effects of methyl donor depletion on enzymes controlling DNA methylation and the pro-apoptotic factors death-associated protein kinase-1 (DAPK1) and p53 upregulated modulator of apoptosis (PUMA) were examined by quantitative-PCR or immunoblotting.

RESULTS

HNSCC cells cultured in methyl donor deplete conditions showed significantly increased cell doubling times, reduced cell proliferation, impaired cell migration, and a dose-dependent increase in apoptosis when compared to cells cultured in complete medium. Methyl donor depletion significantly increased the gene expression of DNMT3a and TET-1, an effect that was reversed upon methyl donor repletion in UD-SCC2 cells. In addition, expression of DAPK1 and PUMA was increased in UD-SCC2 cells cultured in methyl donor deplete compared to complete medium, possibly explaining the observed increase in apoptosis in these cells.

CONCLUSION

Taken together, these data show that depleting HNSCC cells of methyl donors reduces the growth and mobility of HNSCC cells, while increasing rates of apoptosis, suggesting that a methyl donor depleted diet may significantly affect the growth of established HNSCC.

Folate Receptor-Positive Gynecological Cancer Cells: In Vitro and In Vivo Characterization

The folate receptor alpha (FR) is expressed in a variety of gynecological cancer types. It has been widely used for tumor targeting with folic acid conjugates of diagnostic and therapeutic probes. The cervical KB tumor cells have evolved as the standard model for preclinical investigations of folate-based (radio) conjugates. In this study, a panel of FR-expressing human cancer cell lines—including cervical (HeLa, KB, KB-V1), ovarian (IGROV-1, SKOV-3, SKOV-3.ip), choriocarcinoma (JAR, BeWo) and endometrial (EFE-184) tumor cells—was investigated in vitro and for their ability to grow as xenografts in mice. FR-expression levels were compared in vitro and in vivo and the cell lines were characterized by determination of the sensitivity towards commonly-used chemotherapeutics and the expression of two additional, relevant tumor markers, HER2 and L1-CAM. It was found that, besides KB cells, its multiresistant KB-V1 subclone as well as the ovarian cancer cell lines, IGROV-1 and SKOV-3.ip, could be used as potentially more relevant preclinical models. They would allow addressing specific questions such as the therapeutic efficacy of FR-targeting agents in tumor (mouse) models of multi-resistance and in mouse models of metastases formation.

Folate-based single cell screening using surface enhanced Raman microimaging

Recent progress in nanotechnology and its application to biomedical settings have generated great advantages in dealing with early cancer diagnosis. The identification of the specific properties of cancer cells, such as the expression of particular plasma membrane molecular receptors, has become crucial in revealing the presence and in assessing the stage of development of the disease. Here we report a single cell screening approach based on Surface Enhanced Raman Scattering (SERS) microimaging. We fabricated a SERS-labelled nanovector based on the biofunctionalization of gold nanoparticles with folic acid. After treating the cells with the nanovector, we were able to distinguish three different cell populations from different cell lines (cancer HeLa and PC-3, and normal HaCaT lines), suitably chosen for their different expressions of folate binding proteins. The nanovector, indeed, binds much more efficiently on cancer cell lines than on normal ones, resulting in a higher SERS signal measured on cancer cells. These results pave the way for applications in single cell diagnostics and, potentially, in theranostics.

Role of the folate receptor in ovarian cancer treatment: evidence, mechanism, and clinical implications

Folate can be transported into the cell by the reduced folate carrier (RFC), the proton-coupled folate transporter (PCFT), or the folate receptor (FR), of which various isoforms exist. While the RFC and PCFT are expressed by many normal cells, the FR is present only in a small proportion of normal tissues. In these tissues, the FR expression level is often low and restricted to the apical surface of polarized epithelial cells. In contrast, FR is expressed on the blood-accessible basal and lateral membranes of many types of epithelial cancer. Considering that FR is expressed in few nonmalignant cell types on luminal membranes generally not accessible for molecules transported in the blood, FR is considered a promising antitumor target. As FR expression seems associated with tumor progression and prognosis, anticancer therapies targeting FR are currently being developed, such as farletuzumab (Morphotek, Exton, PA, USA), IMGN853 (ImmunoGen, Waltham, MA, USA), vintafolide, and EC1456 (both Endocyte Inc., West Lafayette, IN, USA). FR expression could be used as a response-predictive biomarker for these treatments. The ability to identify patients and treat them with an effective therapy based on the known expression of the tumor marker would, indeed, be the next step in predictive medicine for these patients. This review summarizes the role of FR in ovarian cancer and the value of FR as a prognostic biomarker for ovarian cancer and a response-predictive biomarker for folate-targeted therapeutics.

Targeted delivery of 5-aminolevulinic acid by multifunctional hollow mesoporous silica nanoparticles for photodynamic skin cancer therapy

5-Aminolevulinic acid (5-ALA) is a precursor of a strong photosensitizer, protoporphyrin IX (PphIX), for photodynamic therapy (PDT). Developing appropriate delivery carriers that can assist 5-ALA in bypassing the lipophilic barrier to directly enter into cancer cells is a research focus. The improved delivery of 5-ALA is even important for skin cancer therapy through PDT process. In this work, targeting ligand folic acid (FA)-functionalized hollow mesoporous silica nanoparticles (HMSNPs) were fabricated to deliver 5-ALA for PDT against B16F10 skin cancer cells. The FA targeting ligand enabled selective endocytosis of 5-ALA loaded HMSNPs into cancer cells. PphIX formed from delivered 5-ALA exhibited high photocytotoxicity to the cancer cells in vitro.

Integrated hollow mesoporous silica nanoparticles for target drug/siRNA co-delivery

A hollow mesoporous silica nanoparticle (HMSNP) based drug/siRNA co-delivery system was designed and fabricated, aiming at overcoming multidrug resistance (MDR) in cancer cells for targeted cancer therapy. The as-prepared HMSNPs have perpendicular nanochannels connecting to the internal hollow cores, thereby facilitating drug loading and release. The extra volume of the hollow core enhances the drug loading capacity by two folds as compared with conventional mesoporous silica nanoparticles (MSNPs). Folic acid conjugated polyethyleneimine (PEI-FA) was coated on the HMSNP surfaces under neutral conditions through electrostatic interactions between the partially charged amino groups of PEI-FA and the phosphate groups on the HMSNP surfaces, blocking the mesopores and preventing the loaded drugs from leakage. Folic acid acts as the targeting ligand that enables the co-delivery system to selectively bind with and enter into the target cancer cells. PEI-FA-coated HMSNPs show enhanced siRNA binding capability on account of electrostatic interactions between the amino groups of PEI-FA and siRNA, as compared with that of MSNPs. The electrostatic interactions provide the feasibility of pH-controlled release. In vitro pH-responsive drug/siRNA co-delivery experiments were conducted on HeLa cell lines with high folic acid receptor expression and MCF-7 cell lines with low folic acid receptor expression for comparison, showing effective target delivery to the HeLa cells through folic acid receptor meditated cellular endocytosis. The pH-responsive intracellular drug/siRNA release greatly minimizes the prerelease and possible side effects of the delivery system. By simultaneously delivering both doxorubicin (Dox) and siRNA against the Bcl-2 protein into the HeLa cells, the expression of the anti-apoptotic protein Bcl-2 was successfully suppressed, leading to an enhanced therapeutic efficacy. Thus, the present multifunctional nanoparticles show promising potentials for controlled and targeted drug and gene co-delivery in cancer treatment.

DNA methyltransferase mediates dose-dependent stimulation of neural stem cell proliferation by folate

The proliferative response of neural stem cells (NSCs) to folate may play a critical role in the development, function and repair of the central nervous system. It is important to determine the dose-dependent effects of folate in NSC cultures that are potential sources of transplantable cells for therapies for neurodegenerative diseases. To determine the optimal concentration and mechanism of action of folate for stimulation of NSC proliferation in vitro, NSCs were exposed to folic acid or 5-methyltetrahydrofolate (5-MTHF) (0-200 μmol/L) for 24, 48 or 72 h. Immunocytochemistry and methyl thiazolyl tetrazolium assay showed that the optimal concentration of folic acid for NSC proliferation was 20-40 μmol/L. Stimulation of NSC proliferation by folic acid was associated with DNA methyltransferase (DNMT) activation and was attenuated by the DNMT inhibitor zebularine, which implies that folate dose-dependently stimulates NSC proliferation through a DNMT-dependent mechanism. Based on these new findings and previously published evidence, we have identified a mechanism by which folate stimulates NSC growth.

Folic acid modified gelatine coated quantum dots as potential reagents for in vitro cancer diagnostics

BACKGROUND

Gelatine coating was previously shown to effectively reduce the cytotoxicity of CdTe Quantum Dots (QDs) which was a first step towards utilising them for biomedical applications. To be useful they also need to be target-specific which can be achieved by conjugating them with Folic Acid (FA).

RESULTS

The modification of QDs with FA via an original "one-pot" synthetic route was proved successful by a range of characterisation techniques including UV-visible absorption spectroscopy, Photoluminescence (PL) emission spectroscopy, fluorescence life-time measurements, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS). The resulting nanocomposites were tested in Caco-2 cell cultures which over-express FA receptors. The presence of FA on the surface of QDs significantly improved the uptake by targeted cells.

CONCLUSIONS

The modification with folic acid enabled to achieve a significant cellular uptake and cytotoxicity towards a selected cancer cell lines (Caco-2) of gelatine-coated TGA-CdTe quantum dots, which demonstrated good potential for in vitro cancer diagnostics.

A comparative study of two folate-conjugated gold nanoparticles for cancer nanotechnology applications

We report a comparative study of synthesis, characteristics and in vitro tests of two folate-conjugated gold nanoparticles (AuNP) differing in linkers and AuNP sizes for selective targeting of folate-receptor positive cancerous cells. The linkers chosen were 4-aminothiophenol (4Atp) and 6-mercapto-1-hexanol (MH) with nanoconjugate products named Folate-4Atp-AuNP and Folate-MH-AuNP. We report the folate-receptor tissue distribution and its endocytosis for targeted nanotechnology. Comparison of the two nanoconjugates’ syntheses and characterization is also reported, including materials and methods of synthesis, UV-visible absorption spectroscopic measurements, Fourier Transform Infra Red (FTIR) measurements, Transmission electron microscopy (TEM) images and size distributions, X-ray diffraction data, elemental analyses and chemical stability comparison. In addition to the analytical characterization of the nanoconjugates, the cell lethality was measured in HeLa (high level of folate receptor expression) and MCF-7 (low level of folate receptor expression) cells. The nanoconjugates themselves, as well as the intense pulsed light (IPL) were not harmful to cell viability. However, upon stimulation of the folate targeted nanoconjugates with the IPL, ~98% cell killing was found in HeLa cells and only ~9% in MCF-7 cells after four hours incubation with the nanoconjugate. This demonstrates that folate targeting is effective in selecting for specific cell populations. Considering the various comparisons made, we conclude that Folate-4Atp-AuNP is superior to Folate-MH-AuNP for cancer therapy.

A novel splice variant of FR4 predominantly expressed in CD4+CD25+ regulatory T cells

Folate receptor 4 (FR4) is recently found as a lymphoid tissue specific protein. In this study, we have identified an alternative splicing variant of the FR4 gene from murine splenocytes, termed FR4v, which is almost identical to FR4 cDNA sequence except with the retained 108 bp intron 3 between exon 3 and 4 of FR4 gene. FR4v mRNA encodes a larger protein than FR4 and is constitutively expressed on CD4(+)CD25(+) regulatory T cell (Treg) membrane via a GPI anchor mechanism. Whether FR4v plays a redundant or unique functional role in Tregs should be investigated further in the future.

Melanoma activation of 3-o-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin to a potent irreversible inhibitor of dihydrofolate reductase

Human melanoma is a significant clinical problem because it is resistant to treatment by most chemotherapeutic agents, including antifolates. It is therefore a desirable goal to develop a second generation of low-toxicity antifolate drugs to overcome acquired resistance to the prevention and treatment of this skin pathology. In our efforts to improve the stability and bioavailability of green tea polyphenols for cancer therapy, we synthesized a trimethoxy derivative of epicatechin-3-gallate, which showed high antiproliferative and proapoptotic activity against melanoma. This derivative, 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG), is a prodrug that is selectively activated by the specific melanocyte enzyme tyrosinase. Upon activation, TMECG generates a stable quinone methide product that strongly inhibits dihydrofolate reductase in an irreversible manner. The treatment of melanoma cells with TMECG also affected cellular folate transport and the gene expression of DHFR, which supported the antifolate nature of this compound. In addition, its pharmacological efficacy has been confirmed in a mouse melanoma model, in which tumor growth and metastasis were inhibited, significantly enhancing the mean survival of the treated groups. TMECG, therefore, shows a potential for clinical use in melanoma therapy.

Regulation of folate receptor 1 gene expression in the visceral endoderm

BACKGROUND

Nutrient supply to the developing mammalian embryo is a fundamental requirement. Before completion of the chorioallantoic placenta, the visceral endoderm plays a crucial role in nurturing the embryo. We have found that visceral endoderm cells express folate receptor 1, a high-affinity receptor for the essential micronutrient folic acid, suggesting that the visceral endoderm has an important function for folate transport to the embryo. The mechanisms that direct expression of FOLR1 in the visceral endoderm are unknown.

METHODS

Sequences were tested for transcriptional activation capabilities in the visceral endoderm utilizing reporter gene assays in a cell model for extraembryonic endoderm in vitro, and in transgenic mice in vivo.

RESULTS

With F9 embryo carcinoma cells as a model for extraembryonic endoderm, we demonstrate that the P4 promoter of the human FOLR1 gene is active during differentiation of the cells towards visceral endoderm. However, transgenic mouse experiments show that promoter sequences alone are insufficient to elicit reporter gene transcription in vivo. Using sequence conservation as guide to choose genomic sequences from the human FOLR1 gene locus, we demonstrate that the sequence termed F1CE2 exhibits specific enhancer activity in F9 cells in vitro, in the visceral endoderm, and later the yolk sac in transgenic mouse embryos in vivo. We further show that the transcription factor HNF4-alpha can activate this enhancer sequence.

CONCLUSIONS

We have identified a transcriptional enhancer sequence from the FOLR1 locus with specific activity in vitro and in vivo, and suggest that FOLR1 is a target for regulation by HNF4-alpha.

Targeted Receptor Trafficking Affects the Efficiency of Retrovirus Transduction

We describe the development of an experimental system to test the hypothesis that the efficiency of retrovirus transduction is dependent on the pathway of virus entry into the host cell and the intracellular trafficking itinerary of the cellular receptor with which it interacts. The experimental system consists of three model target cell lines, derived from HeLa cells, that stably express one of three interleukin-2 receptor alpha chain (CD25) chimeras, TAC, TAC-CD16, and TAC-DKQTLL, which have identical extracellular domains but different intracellular trafficking itineraries, and a targeted amphotropic murine leukemia retrovirus whose envelope proteins were modified to include a binding site for TAC at their N-termini. We found that the efficiency of retrovirus transduction was affected by the distribution and trafficking itinerary of the TAC receptors. Transduction of cells that expressed TAC-DKQTLL was nearly 4-fold lower than transduction of control cells that did not express any of the TAC receptors. In contrast, transduction of cells that expressed TAC was 1.6-fold higher than transduction of control cells, whereas transduction was not significantly affected by the expression of TAC-CD16. Our results suggest that in the course of designing a targeted retrovirus it may be prudent to target only those receptors that internalize retroviruses via pathways that most efficiently support post-binding steps of infection.

Folate receptor expression in pituitary adenomas cellular and molecular analysis

Clinically nonfunctional pituitary adenomas cause hypopituitarism or compression of regional structures. Unlike functional tumors, there is no available medical treatment or specific imaging technique for these tumors. We have recently discovered that both folate receptor (FR)alpha mRNA and protein are uniquely overexpressed in nonfunctional pituitary tumors, but not in functional adenomas. We hypothesized that FRalpha may hold significant promise for medical treatment by enabling novel molecular imaging and targeted therapy. Here, we used murine pituitary tumor cell line alphaT3-1 as a model to investigate the biological significance of FRalpha and its mutant FR67. We demonstrate that overexpression of FR facilitated tumor cell growth and anchorage-independent growth in soft agar. More colonies were observed in FR overexpressing cells than in mutant FR67 clones in soft agar. Cell proliferation rate was increased, the percentage of cells in S-phase was increased, and high PCNA staining was detected in cells overexpressing the receptor. In alphaT3-1 cells transfected with mutant FR67, cell proliferation rate was reduced, the percentage of cells residing in S-phase was slightly decreased, and low PCNA staining was observed. By real-time quantitative PCR, the genes involved in NOTCH3 pathway including NOTCH3, HES-1, and TLE2 were altered; the mRNA expression of FGFR1 was upregulated, and ERbeta mRNA was downregulated in FR overexpressing cells. Our findings suggest that FRalpha plays a role in pituitary tumor formation, and this effect may in part be due to its regulation of the NOTCH3 pathway.

Polyplex Nanogel formulations for drug delivery of cytotoxic nucleoside analogs

Hydrophilic nanosized particles consisting of the cross-linked cationic polymer network (Nanogels) are suggested as a drug delivery system for nucleoside analog 5'-triphosphates, an active form of cytotoxic anticancer drugs. Preparation, properties, and cellular effects of several polyplex Nanogel formulations with the 5'-triphosphate of cytotoxic 5-fluoroadenine arabinoside (fludarabine) (FATP) were examined and discussed here. The polyplexes have formed spontaneously by mixing solutions of FATP and Nanogels because of ionic interactions between protonated polyethylenimine (PEI) chains in Nanogel network with polyphosphate groups of the drug. Subsequent compaction of the flexible Nanogel network has resulted in an encapsulation of the FATP/PEI complex in a dense core surrounded by hydrophilic poly(ethylene glycol) (PEG) envelope. This structure has provided a sustained release of the drug, as well as an efficient protection of FATP against enzymatic degradation. The drug loading could reach up to 33% by weight of the drug-Nanogel formulation. In vitro 35% of loaded drug has released from Nanogel formulations during the first 24 h, and a slower additional release was observed during the next 2 days. Nanogels have protected 90% of the encapsulated FATP from enzymatic dephosphorylation during the first 60 min of incubation in vitro. The drug-Nanogel formulation compared to the drug has demonstrated a significantly enhanced cytotoxicity in cultured cancer cells. Cancer cell-targeting molecules, such as folate, could be easily attached to Nanogels and this modification has resulted in a strong 10-fold increase of the carrier's internalization in human breast carcinoma MCF-7 cells. Moreover, transcellular transport of the folate-Nanogel polyplexes was found to be 4 times more effective compared to the drug alone using Caco-2 cell monolayers as an in vitro intestinal model. The data demonstrate that this carrier-based approach to delivery of cytotoxic drugs may enhance tumor specificity and significantly reduce side effects related to systemic toxicity usually observed during cancer chemotherapy.

Folate targeting of drug carriers: A mathematical model

The binding of folate-targeted drug carriers to a receptor-bearing cell surface is modeled using a deterministic approach. The model accounts for the presence of multiple folate ligands on the carrier surface, the anchoring and presentation of the ligands on flexible polymeric tethers, and the combination of both clustered and homogeneous spatial distributions of receptors on the cell surface. The model was validated against an experimental system where folate-bearing liposomes were used as delivery vehicles to deliver drug to tumor cells in vitro. Unknown parameters of the model were then estimated by a least-squares fit to the experimental data. A parametric study systematically varying the estimated parameters around the best-fit values indicated that the model was sensitive to these parameters, lending credence to their estimated values. This study indicates that drug uptake is dependent on several factors including the ligand number, the exposure time, and carrier concentration. For the specific case of folate targeting, the cumulative uptake of folate ligands is important, causing a decrease in the carrier uptake rate once a threshold cumulative uptake is crossed.

Downstream effects on human low density lipoprotein of homocysteine exported from endothelial cells in an in vitro system

A model system is presented using human umbilical vein endothelial cells (HUVECs) to investigate the role of homocysteine (Hcy) in atherosclerosis. HUVECs are shown to export Hcy at a rate determined by the flux through the methionine/Hcy pathway. Additional methionine increases intracellular methionine, decreases intracellular folate, and increases Hcy export, whereas additional folate inhibits export. An inverse relationship exists between intracellular folate and Hcy export. Hcy export may be regulated by intracellular S-adenosyl methionine rather than by Hcy. Human LDLs exposed to HUVECs exporting Hcy undergo time-related lipid oxidation, a process inhibited by the thiol trap dithionitrobenzoate. This is likely to be related to the generation of hydroxyl radicals, which we show are associated with Hcy export. Although Hcy is the major oxidant, cysteine also contributes, as shown by the effect of glutamate. Finally, the LDL oxidized in this system showed a time-dependent increase in uptake by human macrophages, implying an upregulation of the scavenger receptor. These results suggest that continuous export of Hcy from endothelial cells contributes to the generation of extracellular hydroxyl radicals, with associated oxidative modification of LDL and incorporation into macrophages, a key step in atherosclerosis. Factors that regulate intracellular Hcy metabolism modulate these effects.

Point mutations alter the cellular distribution of the human folate receptor in cultured Chinese hamster ovary cells

Diminished cellular need for folate results in decreased function of the human folate receptor (FR) but increased expression of this protein in cells grown at different rates. Much of this FR is intracellular and not available for vitamin transport, raising the following question: what is the function of this excess receptor? In this study, we characterized the effects of three point mutations on FR regulation in Chinese hamster ovary cells stably transfected to express either wild-type receptor or FR containing mutations at positions 67(S-->P),144(E-->D), and/or 201(N-->D). The 201(N-->D) FR responded functionally like the wild-type receptor but was localized predominantly at the cell surface (>90% vs. <40% for wild-type). This mutation disrupted a N-linked glycosylation site and generated a partially deglycosylated receptor. The 67(S-->P) mutation also shifted the cellular distribution such that more FR was surface accessible ( approximately 80%) but did not affect glycosylation. Because previous results showed that these mutations influence the conformation of FR, our findings suggest that structural changes in the receptor facilitate its trafficking to the cell surface. FR containing the 67(S-->P) mutation with either a 144(E-->D) or 201(N-->D) change was not processed from the high-mannose to complex glycoform but was still transported to the cell surface and able to transport folates. Thus, conformational changes introduced by specific point mutations can influence FR processing and/or trafficking to the cell surface. Furthermore, the fact that mutated FR can be trafficked to the cell surface more efficiently suggests that the native receptor may be retained intracellularly to perform some function there.