Intracellular Processing of Riboflavin in Human Breast Cancer Cells

Riboflavin Crystals with Extremely High Water Solubility

New insights into the unique biochemical properties of riboflavin (Rf), also known as vitamin B2, are leading to the development of its use not only as a vitamin supplement but also as a potential anti-inflammatory, immunomodulatory, antioxidant, anticancer, and antiviral agent, where it may play a role as an inhibitor of viral proteinases. At the same time, the comparison of the pharmacoactivity of Rf with its known metabolites, namely, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is very complicated due to its poor water solubility: 0.1-0.3 g/L versus 67 g/L for FMN and 50 g/L for FAD, which is the limiting factor for its administration in clinical practice. In this study, we report the recrystallization procedure of the type A Rf crystals into the slightly hydrophobic type B/C and a new hydrophilic crystal form that has been termed the P type. Our method of Rf crystal modification based on recrystallization from dilute alkaline solution provides an unprecedented extremely high water solubility of Rf, reaching 23.5 g/L. A comprehensive study of the physicochemical properties of type P riboflavin showed increased photodynamic therapeutic activity compared to the known types A and B/C against clinical isolates of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Salmonella typhimurium. Importantly, our work not only demonstrates a simple and inexpensive method for the synthesis of riboflavin with high solubility, which should lead to increased bioactivity, but also opens up opportunities for improving both known and new therapeutic applications of vitamin B2.

Theoretical Analysis of Riboflavin Adsorption on Hexagonal Boron Nitride for Drug Delivery Applications: Unveiling the Influence of Point Defects

This research delves into the intriguing realm of investigating the stability of vitamin B2 (riboflavin, Rf) on hexagonal boron nitride (h-BN), both in its pristine state and in the presence of vacancy defects, with the aim of harnessing their potential as carriers for drug delivery applications. Employing the density functional theory (DFT), we perform binding energy calculations and analyze the electronic structure of the BN@Rf system to unravel the nature of their interactions. Our comprehensive DFT calculations unequivocally demonstrate the spontaneous physical sorption of the drug onto the h-BN surface, facilitated by the formation of π-π stacking interactions. The adsorption energy spans a range from -1.15 to -4.00 eV per system, emphasizing the robust nature of the BN@Rf bonding. The results show that the HOMO and LUMO of riboflavin are located exactly in the region of the iso-alloxazine rings of riboflavin. This arrangement fosters the formation of π-π stacking between riboflavin and boron nitride, effectively facilitating the transfer of electron density within the BN@Rf system. Furthermore, our investigations reveal the significant impact of vacancy defects within the boron nitride lattice. These vacancies alter the behavior of the structure, prompting riboflavin to metamorphose from an electron donor to an electron acceptor, expanding our understanding of the interplay between boron nitride defects and riboflavin sorption. Therefore, it is imperative to exert meticulous oversight of the structural integrity of h-BN, given that the existence of vacancies may lead to a noticeable change in its adsorption properties. The obtained data could amplify our capacity to conceive and refine drug delivery h-BN-based systems.

Dual Functions of Riboflavin-functionalized Poly(lactic-co-glycolic acid) Nanoparticles for Enhanced Drug Delivery Efficiency and Photodynamic Therapy in Triple-negative Breast Cancer Cells

Combating triple-negative breast cancer (TNBC) is one of the greatest challenges in cancer therapy. This is primarily due to the difficulties in developing drug delivery systems that can effectively target cancer sites. In this study, we demonstrated a proof-of-principle concept using modified surfaces of poly(lactic-co-glycolic acid) nanoparticles linked with a riboflavin analogue (PLGA-CSRf) to obtain a dual-functional material. PLGA-CSRf nanoparticles were able to function as a drug delivery ligand and a photodynamic therapy agent for TNBC cells (MDA-MB-231). Biocompatibility of novel PLGA-CSRf nanoparticles was evaluated with both breast cancer and normal breast (MCF-10A) cells. In vitro studies revealed a six-fold increase in the cellular uptake of PLGA-CSRf nanoparticles in cancer cells compared with normal cells. The results demonstrate the ability of riboflavin (Rf) to enhance the delivery of PLGA nanoparticles to TNBC cells. The viability of TNBC cells was decreased following treatment with doxorubicin-encapsulated PLGA-CSRf nanoparticles in combination with UV irradiation, due to the photosensitizing property of Rf on the surface of the nanoparticles. This work demonstrated the ability of PLGA-CSRf to function both as an effective drug delivery carrier and as a therapeutic entity, with the potential to enhance photodynamic effects in the highly aggressive TNBC model.

Influence of Riboflavin Targeting on Tumor Accumulation and Internalization of Peptostar Based Drug Delivery Systems

Riboflavin carrier protein (RCP) and riboflavin transporters (RFVTs) have been reported to be highly overexpressed in various cancer cells. Hence, targeting RCP and RFVTs using riboflavin may enhance tumor accumulation and internalization of drug delivery systems. To test this hypothesis, butyl-based 3-arm peptostar polymers were synthesized consisting of a lysine core (10 units per arm) and a sarcosine shell (100 units per arm). The end groups of the arms and the core were successfully modified with riboflavin and the Cy5.5 fluorescent dye, respectively. While in phosphate buffered saline the functionalized peptostars showed a bimodal behavior and formed supramolecular structures over time, they were stable in the serum maintaining their hydrodynamic diameter of 12 nm. Moreover, the polymers were biocompatible and the uptake of riboflavin targeted peptostars in A431 and PC3 cells was higher than in nontargeted controls and could be blocked competitively. In vivo, the polymers showed a moderate passive tumor accumulation, which was not significantly different between targeted and nontargeted peptostars. Nonetheless, at the histological level, internalization into tumor cells was strongly enhanced for the riboflavin-targeted peptostars. Based on these results, we conclude that passive accumulation is dominating the accumulation of peptostars, while tumor cell internalization is strongly promoted by riboflavin targeting.

A comprehensive analysis of metabolomics and transcriptomics reveals new biomarkers and mechanistic insights on DEHP exposures in MCF-7 cells

Di-(2-ethylhexyl) phthalate (DEHP) is one of the most important environmental pollutants and affects multiple pathways upon human exposure. DEHP could induce MCF-7 cell proliferation at a very low dose; however, the possible linkage between DEHP and the cell proliferation effect is still unclear. Here, we carried out a comprehensive metabolome and transcriptome analysis to depict the possible molecular mechanisms of the effect of DEHP exposure on MCF-7 proliferation. In this paper, MCF-7 cells treated with DEHP at a dose of 1 μM for 48 h were selected for metabolome and transcriptome analysis. Untargeted and targeted metabolomics identified 8 differential metabolites, including amino acids, purine, pyrimidine and nucleotides. The metabolite changes were associated with 9 metabolic pathways. Disorders in riboflavin, histidine, beta-alanine metabolism, and nitrogen metabolism caused by DEHP exposure are important concerns for MCF-7 proliferation. Moreover, a transcriptomics study of the MCF-7 cells found a total of 500 differentially expressed genes (DEGs). KEGG enrichment analyses showed that pathways in cancer had stronger responses. The results of integrated analysis of the interactions between the DEGs and metabolites revealed significant changes in the purine metabolism pathway, which will shed light on the mechanism of MCF-7 cell proliferation after DEHP exposure. Overall, this study depicts the possible contribution of DEHP exposure to MCF-7 cell proliferation and highlights the power of omics platforms to deepen the mechanistic understanding of toxicity caused by endocrine disrupting chemicals.

Designing Stimuli-Responsive Upconversion Nanoparticles that Exploit the Tumor Microenvironment

Tailoring personalized cancer nanomedicines demands detailed understanding of the tumor microenvironment. In recent years, smart upconversion nanoparticles with the ability to exploit the unique characteristics of the tumor microenvironment for precise targeting have been designed. To activate upconversion nanoparticles, various bio-physicochemical characteristics of the tumor microenvironment, namely, acidic pH, redox reactants, and hypoxia, are exploited. Stimuli-responsive upconversion nanoparticles also utilize the excessive presence of adenosine triphosphate (ATP), riboflavin, and Zn²⁺ in tumors. An overview of the design of stimulus-responsive upconversion nanoparticles that precisely target and respond to tumors via targeting the tumor microenvironment and intracellular signals is provided. Detailed understanding of the tumor microenvironment and the personalized design of upconversion nanoparticles will result in more effective clinical translation.

Riboflavin: The Health Benefits of a Forgotten Natural Vitamin

Riboflavin (RF) is a water-soluble member of the B-vitamin family. Sufficient dietary and supplemental RF intake appears to have a protective effect on various medical conditions such as sepsis, ischemia etc., while it also contributes to the reduction in the risk of some forms of cancer in humans. These biological effects of RF have been widely studied for their anti-oxidant, anti-aging, anti-inflammatory, anti-nociceptive and anti-cancer properties. Moreover, the combination of RF and other compounds or drugs can have a wide variety of effects and protective properties, and diminish the toxic effect of drugs in several treatments. Research has been done in order to review the latest findings about the link between RF and different clinical aberrations. Since further studies have been published in this field, it is appropriate to consider a re-evaluation of the importance of RF in terms of its beneficial properties.

Riboflavin-Targeted Drug Delivery

Active targeting can improve the retention of drugs and drug delivery systems in tumors, thereby enhancing their therapeutic efficacy. In this context, vitamin receptors that are overexpressed in many cancers are promising targets. In the last decade, attention and research were mainly centered on vitamin B9 (folate) targeting; however, the focus is slowly shifting towards vitamin B2 (riboflavin). Interestingly, while the riboflavin carrier protein was discovered in the 1960s, the three riboflavin transporters (RFVT 1-3) were only identified recently. It has been shown that riboflavin transporters and the riboflavin carrier protein are overexpressed in many tumor types, tumor stem cells, and the tumor neovasculature. Furthermore, a clinical study has demonstrated that tumor cells exhibit increased riboflavin metabolism as compared to normal cells. Moreover, riboflavin and its derivatives have been conjugated to ultrasmall iron oxide nanoparticles, polyethylene glycol polymers, dendrimers, and liposomes. These conjugates have shown a high affinity towards tumors in preclinical studies. This review article summarizes knowledge on RFVT expression in healthy and pathological tissues, discusses riboflavin internalization pathways, and provides an overview of RF-targeted diagnostics and therapeutics.

Riboflavin-Terminated, Multivalent Quantum Dot as Fluorescent Cell Imaging Probe

Bioconjugated nanoparticles are commonly used for targeting cellular/subcellular components, and labeling performance is known to depend on multivalency, i.e., the number of attached biomolecule per particle. However, these multivalency effects are largely unexplored. Here, we show that multivalency of nanoparticle-bound riboflavin controls the cellular interaction, cellular entry/exit mechanism, and subcellular trafficking property. We have synthesized riboflavin-functionalized quantum dot (QD) of 15-25 nm hydrodynamic size with average riboflavin multivalencies of 15, 30, and 70 [designated as QD(RF)₁₅, QD(RF)₃₀, and QD(RF)₇₀, respectively] and investigated their uptake mechanism in riboflavin receptor overexpressed KB cells. We found that increased multivalency from 15 to 70 increases the cellular interaction with QD, shifts the cell uptake mechanism from caveolae-clathrin to exclusive clathrin-mediated endocytosis, and enhances lysosomal trafficking. This work demonstrates the importance of multivalency of bioconjugated molecule at the nanoparticle surface toward biolabeling performance and should be optimized for best performance of designed nanobioconjugate.

Riboflavin immobilized Fe3O4 magnetic nanoparticles carried with n-butylidenephthalide as targeting-based anticancer agents

n-Butylidenephthalide (BP) is a potential anti-cancer drug, which can be extracted from Angelica sinensis (Danggui). Previous reports have shown the effectiveness of BP in treating cancer diseases. However, BP has no targeting capacity towards specific cancer cells. To improve treatment efficiency and reduce the dose of BP used in cancer treatment, targeting-based approaches should be developed. In the present study, we used riboflavin-5'-phosphate (RFMP) immobilized iron oxide magnetic nanoparticles (Fe₃O₄ MNPs) as carriers for BP to treat cancer cell lines derived from liver, prostate and breast. These model cancer cells overexpress riboflavin receptors on their cell membrane and are also sensitive to BP treatment. Thus, BP-binding free RFMP on MNPs can be used as probes to target these model cells, whereas BP can be readily released on target cancer cells. Cell viability was twofold lower by using Fe₃O₄@RFMP MNPs immobilized with BP than that achieved by using free-form BP at a similar amount. Moreover, BP-Fe₃O₄@RFMP MNPs have no apparent harmful effects on non-target cells. In addition, we evaluated the level of cysteine-aspartic acid protease 3 (caspase 3) in the resultant cell lysate obtained after treatment by BP-Fe₃O₄@RFMP MNPs to demonstrate that apoptosis is mainly involved in the growth inhibition of target cells.

Evaluation of Riboflavin Transporters as Targets for Drug Delivery and Theranostics

The retention and cellular internalization of drug delivery systems and theranostics for cancer therapy can be improved by targeting molecules. Since an increased uptake of riboflavin was reported for various cancers, riboflavin and its derivatives may be promising binding moieties to trigger internalization via the riboflavin transporters (RFVT) 1, 2, and 3. Riboflavin is a vitamin with pivotal role in energy metabolism and indispensable for cellular growth. In previous preclinical studies on mice, we showed the target-specific accumulation of riboflavin-functionalized nanocarriers in cancer cells. Although the uptake mechanism of riboflavin has been studied for over a decade, little is known about the riboflavin transporters and their expression on cancer cells, tumor stroma, and healthy tissues. Furthermore, evidence is lacking concerning the representativeness of the preclinical findings to the situation in humans. In this study, we investigated the expression pattern of riboflavin transporters in human squamous cell carcinoma (SCC), melanoma and luminal A breast cancer samples, as well as in healthy skin, breast, aorta, and kidney tissues. Low constitutive expression levels of RFVT1-3 were found on all healthy tissues, while RFVT2 and 3 were significantly overexpressed in melanoma, RFVT1 and 3 in luminal A breast cancer and RFVT1-3 in SCC. Correspondingly, the SCC cell line A431 was highly positive for all RFVTs, thus qualifying as suitable in vitro model. In contrast, activated endothelial cells (HUVEC) only presented with a strong expression of RFVT2, and HK2 kidney cells only with a low constitutive expression of RFVT1-3. Functional in vitro studies on A431 and HK2 cells using confocal microscopy showed that riboflavin uptake is mostly ATP dependent and primarily driven by endocytosis. Furthermore, riboflavin is partially trafficked to the mitochondria. Riboflavin uptake and trafficking was significantly higher in A431 than in healthy kidney cells. Thus, this manuscript supports the hypothesis that addressing the riboflavin internalization pathway may be highly valuable for tumor targeted drug delivery.

Biological activity of PtIV prodrugs triggered by riboflavin-mediated bioorthogonal photocatalysis

We have recently demonstrated that riboflavin (Rf) functions as unconventional bioorthogonal photocatalyst for the activation of Pt^IV prodrugs. In this study, we show how the combination of light and Rf with two Pt^IV prodrugs is a feasible strategy for light-mediated pancreatic cancer cell death induction. In Capan-1 cells, which have high tolerance against photodynamic therapy, Rf-mediated activation of the cisplatin and carboplatin prodrugs cis,cis,trans-[Pt(NH₃)₂(Cl)₂(O₂CCH₂CH₂CO₂H)₂] (1) and cis,cis,trans-[Pt(NH₃)₂(CBDCA)(O₂CCH₂CH₂CO₂H)₂] (2, where CBDCA = cyclobutane dicarboxylate) resulted in pronounced reduction of the cell viability, including under hypoxia conditions. Such photoactivation mode occurs to a considerable extent intracellularly, as demonstrated for 1 by uptake and cell viability experiments. ¹⁹⁵Pt NMR, DNA binding studies using circular dichroism, mass spectrometry and immunofluorescence microscopy were performed using the Rf-1 catalyst-substrate pair and indicated that cell death is associated with the efficient light-induced formation of cisplatin. Accordingly, Western blot analysis revealed signs of DNA damage and activation of cell death pathways through Rf-mediated photochemical activation. Phosphorylation of H₂AX as indicator for DNA damage, was detected for Rf-1 in a strictly light-dependent fashion while in case of free cisplatin also in the dark. Photochemical induction of nuclear pH₂AX foci by Rf-1 was confirmed in fluorescence microscopy again proving efficient light-induced cisplatin release from the prodrug system.

Riboflavin and health: A review of recent human research

There has lately been a renewed interest in Riboflavin owing to insight into its recognition as an essential component of cellular biochemistry. The knowledge of the mechanisms and regulation of intestinal absorption of riboflavin and its health implications has significantly been expanded in recent years. The purpose of this review is to provide an overview of the importance of riboflavin, its absorption and metabolism in health and diseased conditions, its deficiency and its association with various health diseases, and metabolic disorders. Efforts have been made to review the available information in literature on the relationship between riboflavin and various clinical abnormalities. The role of riboflavin has also been dealt in the prevention of a wide array of health diseases like migraine, anemia, cancer, hyperglycemia, hypertension, diabetes mellitus, and oxidative stress directly or indirectly. The riboflavin deficiency has profound effect on iron absorption, metabolism of tryptophan, mitochondrial dysfunction, gastrointestinal tract, brain dysfunction, and metabolism of other vitamins as well as is associated with skin disorders. Toxicological and photosensitizing properties of riboflavin make it suitable for biological use, such as virus inactivation, excellent photosensitizer, and promising adjuvant in chemo radiotherapy in cancer treatment. A number of recent studies have indicated and highlighted the cellular processes and biological effects associated with riboflavin supplementation in metabolic diseases. Overall, a deeper understanding of these emerging roles of riboflavin intake is essential to design better therapies for future.

Metabolomic alterations in invasive ductal carcinoma of breast: A comprehensive metabolomic study using tissue and serum samples

Invasive ductal carcinoma (IDC) is the most common type of breast cancer and the leading cause of breast cancer related mortality. In the present study, metabolomic profiles of 72 tissue samples and 146 serum samples were analysed using targeted liquid chromatography multiple reaction monitoring mass spectrometry (LC-MRM/MS) and untargeted gas chromatography mass spectrometry (GC-MS) approaches. Combination of univariate and multivariate statistical treatment identified significant alterations of 42 and 32 metabolites in tissue and serum samples of IDC, respectively when compared to control. Some of the metabolite changes from tissue were also reflected in serum, indicating a bi-directional interaction of metabolites in IDC. Additionally, 8 tissue metabolites and 9 serum metabolites showed progressive change from control to benign to IDC suggesting their possible role in malignant transformation. We have identified a panel of three metabolites viz. tryptophan, tyrosine, and creatine in tissue and serum, which could be useful in screening of IDC subjects from both control and benign. The metabolomic alterations in IDC showed perturbations in purine and pyrimidine metabolism, amino sugar metabolism, amino acid metabolism, fatty acid biosynthesis etc. Comprehensively, this study provides valuable insights into metabolic adaptations of IDC, which can help to identify diagnostic markers as well as potential therapeutic targets.

Riboflavin photoactivation by upconversion nanoparticles for cancer treatment

Riboflavin (Rf) is a vitamin and endogenous photosensitizer capable to generate reactive oxygen species (ROS) under UV-blue irradiation and kill cancer cells, which are characterized by the enhanced uptake of Rf. We confirmed its phototoxicity on human breast adenocarcinoma cells SK-BR-3 preincubated with 30-μM Rf and irradiated with ultraviolet light, and proved that such Rf concentrations (60 μM) are attainable in vivo in tumour site by systemic intravascular injection. In order to extend the Rf photosensitization depth in cancer tissue to 6 mm in depth, we purpose-designed core/shell upconversion nanoparticles (UCNPs, NaYF₄:Yb³⁺:Tm³⁺/NaYF₄) capable to convert 2% of the deeply-penetrating excitation at 975 nm to ultraviolet-blue power. This power was expended to photosensitise Rf and kill SK-BR-3 cells preincubated with UCNPs and Rf, where the UCNP-Rf energy transfer was photon-mediated with ~14% Förster process contribution. SK-BR-3 xenograft regression in mice was observed for 50 days, following the Rf-UCNPs peritumoural injection and near-infrared light photodynamic treatment of the lesions.

In vivo evaluation of riboflavin receptor targeted fluorescent USPIO in mice with prostate cancer xenografts

Riboflavin (Rf) receptors bind and translocate Rf and its phosphorylated forms (e.g. flavin mononucleotide, FMN) into cells where they mediate various cellular metabolic pathways. Previously, we showed that FMN-coated ultrasmall superparamagnetic iron oxide (FLUSPIO) nanoparticles are suitable for labeling metabolically active cancer and endothelial cells in vitro. In this study, we focused on the in vivo application of FLUSPIO using prostate cancer xenografts. Size, charge, and chemical composition of FLUSPIO were evaluated. We explored the in vitro specificity of FLUSPIO for its cellular receptors using magnetic resonance imaging (MRI) and Prussian blue staining. Competitive binding experiments were performed in vivo by injecting free FMN in excess. Bio-distribution of FLUSPIO was determined by estimating iron content in organs and tumors using a colorimetric assay. AFM analysis and zeta potential measurements revealed a particulate morphology approximately 20-40 nm in size and a negative zeta potential (-24.23 ± 0.15 mV) in water. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry data confirmed FMN present on the USPIO nanoparticle surface. FLUSPIO uptake in prostate cancer cells and human umbilical vein endothelial cells was significantly higher than that of control USPIO, while addition of excess of free FMN reduced accumulation. Similarly, in vivo MRI and histology showed specific FLUSPIO uptake by prostate cancer cells, tumor endothelial cells, and tumor-associated macrophages. Besides prominent tumor accumulation, FLUSPIO accumulated in the liver, spleen, lung, and skin. Hence, our data strengthen our hypothesis that targeting riboflavin receptors is an efficient approach to accumulate nanomedicines in tumors opening perspectives for the development of diagnostic and therapeutic systems.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available for this article at 10.1007/s12274-016-1028-7 and is accessible for authorized users.

Molecular expression and functional activity of vitamin C specific transport system (SVCT2) in human breast cancer cells

The main goal of this study is to investigate the expression of sodium dependent vitamin C transport system (SVCT2). Moreover, this investigation has been carried out to define uptake mechanism and intracellular regulation of ascorbic acid (AA) in human breast cancer cells (MDA-MB231, T47D and ZR-75-1). Uptake of [(14)C] AA was studied in MDA-MB231, T47D and ZR-75-1 cells. Functional parameters of [(14)C] AA uptake were delineated in the presence of different concentrations of unlabeled AA, pH, temperature, metabolic inhibitors, substrates and structural analogs. Molecular identification of SVCT2 was carried out with reverse transcription-polymerase chain reaction (RT-PCR). Uptake of [(14)C] AA was studied and found to be sodium, chloride, temperature, pH and energy dependent in all breast cancer cell lines. [(14)C] AA uptake was found to be saturable, with Km values of 53.85 ± 6.24, 49.69 ± 2.83 and 45.44 ± 3.16 μM and Vmax values of 18.45 ± 0.50, 32.50 ± 0.43 and 33.25 ± 0.53 pmol/min/mg protein, across MDA-MB231, T47D and ZR-75-1, respectively. The process is inhibited by structural analogs (l-AA and d-iso AA) but not by structurally unrelated substrates (glucose and PAHA). Ca(++)/calmodulin and protein kinase pathways appeared to play a crucial role in modulating AA uptake. A 626 bp band corresponding to a vitamin C transporter (SVCT2) based on the primer design was detected by RT-PCR analysis in all breast cancer cell lines. This research article describes AA uptake mechanism, kinetics, and regulation by sodium dependent vitamin C transporter (SVCT2) in MDA-MB231, T47D and ZR-75-1 cells. Also, MDA-MB231, T47D and ZR-75-1 cell lines can be utilized as a valuable in vitro model to investigate absorption and permeability of AA-conjugated chemotherapeutics.

Riboflavin carrier protein-targeted fluorescent USPIO for the assessment of vascular metabolism in tumors

Riboflavin (Rf) and its metabolic analogs flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are essential for normal cellular growth and function. Their intracellular transport is regulated by the riboflavin carrier protein (RCP), which has been shown to be over-expressed by metabolically active cancer cells. Therefore, FAD-decorated ultrasmall superparamagnetic iron oxide nanoparticles (FAD USPIO) were developed as the first carrier-protein-targeted molecular MR agents for visualizing tumor metabolism. FAD USPIO were synthesized using an adsorptive, fluorescent and non-polymeric coating method, and their physicochemical properties were characterized using TEM, SEM, FTIR, MRI and fluorescence spectroscopy. In vitro analyses showed the biocompatibility of FAD USPIO, and confirmed that they were strongly and specifically taken up by cancer (LnCap) and endothelial (HUVEC) cells. In vivo molecular MRI together with subsequent histological validation finally demonstrated that FAD USPIO efficiently accumulate in tumors and tumor blood vessels, indicating that RCP-targeted diagnostic nanoparticles are interesting new materials for the assessment of vascular metabolism in tumors.

Riboflavin ameliorates cisplatin induced toxicities under photoillumination

Background

Cisplatin is an effective anticancer drug that elicits many side effects mainly due to induction of oxidative and nitrosative stresses during prolonged chemotherapy. The severity of these side effects consequently restricts its clinical use under long term treatment. Riboflavin is an essential vitamin used in various metabolic redox reactions in the form of flavin adenine dinucleotide and flavin mononucleotide. Besides, it has excellent photosensitizing property that can be used to ameliorate these toxicities in mice under photodynamic therapy.

Methods and Findings

Riboflavin, cisplatin and their combinations were given to the separate groups of mice under photoilluminated condition under specific treatment regime. Their kidney and liver were excised for comet assay and histopathological studies. Furthermore, Fourier Transform Infrared Spectroscopy of riboflavin-cisplatin combination in vitro was also conducted to investigate any possible interaction between the two compounds. Their comet assay and histopathological examination revealed that riboflavin in combination with cisplatin was able to protect the tissues from cisplatin induced toxicities and damages. Moreover, Fourier Transform Infrared Spectroscopy analysis of the combination indicated a strong molecular interaction among their constituent groups that may be assigned for the protective effect of the combination in the treated animals.

Conclusion

Inclusion of riboflavin diminishes cisplatin induced toxicities which may possibly make the cisplatin-riboflavin combination, an effective treatment strategy under chemoradiotherapy in pronouncing its antineoplastic activity and sensitivity towards the cancer cells as compared to cisplatin alone.

Non-inclusion complexes between riboflavin and cyclodextrins

Objectives

To investigate the molecular interaction between β-cyclodextrin (βCD) or hydroxypropyl-β-cyclodextrin (HPβCD) and riboflavin (RF), and to test the anticancer potential of these formulations.

Methods

The physicochemical characterization of the association between RF and CDs was performed by UV-vis absorption, fluorescence, differential scanning calorimetry and NMR techniques. Molecular dynamics simulation was used to shed light on the mechanism of interaction of RF and CDs. Additionally, in-vitro cell culture tests were performed to evaluate the cytotoxicity of the RF–CD complexes against prostate cancer cells.

Key findings

Neither βCD nor HPβCD led to substantial changes in the physicochemical properties of RF (with the exception of solubility). Additionally, rotating frame Overhauser effect spectroscopy experiments detected no spatial correlations between hydrogens from the internal cavity of CDs and RF, while molecular dynamics simulations revealed ‘out-of-ring’ RF–CD interactions. Notwithstanding, both RF–βCD and RF–HPβCD complexes were cytotoxic to PC3 prostate cancer cells.

Conclusions

The interaction between RF and either βCD or HPβCD, at low concentrations, seems to be made through hydrogen bonding between the flavonoid and the external rim of both CDs. Regardless of the mechanism of complexation, our findings indicate that RF–CD complexes significantly increase RF solubility and potentiate its antitumour effect.