Exploring the Synergistic Effect of Sildenafil and Green Tea Polyphenols on Breast Cancer Stem Cell-like Cells and their Parental Cells: A Potential Novel Therapeutic Approach

BACKGROUND

Many cancer studies have intensely focused on the role of diet, among other factors involved in cancer establishment. The positive effect of green tea polyphenols (GTP) on controlling breast cancer cells has been reported in several studies. Cancer stem cell-like cells (CSC-LCs) possessing self-renewal, metastatic, and drug-resistant capacities are considered prominent therapeutic targets. In many tumors, inducible nitric oxide synthase (iNOS) expression levels are high; however, they have a dual effect on breast cancer pathogenesis.

OBJECTIVE

This study aimed to investigate the cytotoxicity of the iNOS agonist (Sildenafil) and antagonist (LNAME), both alone and in combination with GTP, on MDA-MB-231, CD44+/CD24- CSC-LCs, and their parental cells (MCF-7).

METHODS

The cell viability assay has been studied using the MTT assay. To analyze drug-drug combinations, CompuSyn and Combenefit software were used. The cytotoxicity mechanism was determined using flow cytometric analysis.

RESULTS

L-NAME and GTP showed a synergistic effect on MDA-MB-231 and CSC-LCs. Such an effect was not observed on MCF-7. Sildenafil and GTP, on the other hand, showed synergistic cytotoxicity in all the cells mentioned above. Flow cytometric tests resulted in more than 70% apoptosis in MDA-MB-231 and MCF-7. Also, sub-G1 arrest among MCF-7 cells and a considerable decrease in ROS production by MDA-MB-231 cells following treatment with Sildenafil and GTP were observed.

CONCLUSION

Sildenafil, in combination with flavonoids, may be considered a novel strategy for cancer treatment.

Identification of Sildenafil Compound in Selected Drugs Using X-ray Study and Thermal Analysis

Twelve drugs containing sildenafil compounds (sildenafil citrate and sildenafil base) were examined using X-ray studies and thermal analysis. According to the manufacturer’s information, the presence of sildenafil was confirmed in all investigated drugs. The positions of diffraction lines (value of 2θ angle) agree with the patterns presented in the ICDD database, Release 2018 (ICDD—International Centre of Diffraction Data). The difference expresses the agreement in the position of the diffraction line between the tested substance and the standard. A good agreement is when this difference is less than 0.2°. The values of interplanar distances dhkl are also compatible with the ICDD database. It indicated that the drug examined was genuine. Because all drugs are mixtures of different substances (API and excipients), the various diffraction line intensities were detected in all observed X-ray images for the tested drugs. The intensity of the diffraction line depends on many factors, like the amount of substance, coexisting phases, and mass absorption coefficient of the mixture. The thermal analysis confirmed the results obtained by the X-ray study. On DSC curves, the endothermic peaks for sildenafil compounds were observed. The determined melting points of sildenafil compounds corresponded to the values available in the literature. The results gathered by connecting two methods, X-ray study and thermal analysis, can help identify irregularities that may exist in pharmaceutical specimens, e.g., distinguishing genuine from counterfeit products, the presence of a correct polymorph, a lack of active substance, an inaccurate amount of the active substance, or excipients in the tested drug.

Structural Determination, Biological Function, and Molecular Modelling Studies of Sulfoaildenafil Adulterated in Herbal Dietary Supplement

Unapproved ingredients included in herbal medicines and dietary supplements have been detected as adulterated synthetic drugs used for erectile dysfunction. Extraction from a dietary supplement was performed to isolate the compounds by HPLC analysis. The structural characterization was confirmed using mass spectrometry (ESI-TOF/MS and LC-MS/MS), 1H NMR, and 13C NMR spectroscopy techniques. Results identified the thus-obtained compound to be sulfoaildenafil, a thioketone analogue of sildenafil. The biological activities of this active compound have been focused for the first time by the experimental point of view performance in vitro. The results revealed that sulfoaildenafil can affect the therapeutic level of nitric oxide through the upregulation of nitric oxide synthase and phosphodiesterase type 5 (PDE5) gene expressions. This bulk material, which displays structural similarity to sildenafil, was analyzed for the presence of a PDE5 inhibitor using a theoretical calculation. These unique features of the potential activity of PDE5 protein and its inhibitors, sildenafil and sulfoaildenafil, may play a key consideration for understanding the mode of actions and predicting the biological activities of PDE5 inhibitors.

Analysis of Sildenafil in Liquor and Health Wine Using Surface Enhanced Raman Spectroscopy

The illegal adulteration of sildenafil in herbal food supplements and alcoholic drinks immensely threatens human health due to its harmful side-effects. Therefore, it is important to accurately detect and identify the presence of sildenafil in alcoholic drinks. In this study, Opto Trace Raman 202 (OTR 202) was used as surface enhanced Raman spectroscopy (SERS) active colloids to detect sildenafil. The results demonstrated that the Raman enhancement factor (EF) of OTR 202 colloids reached 1.84 × 10⁷ and the limits of detection (LODs) of sildenafil in health wine and liquor were found to be as low as 0.1 mg/L. Moreover, the SERS peaks of 645, 814, 1235, 1401, 1530 and 1584 cm⁻¹ could be qualitatively determined as sildenafil characteristic peaks and the relationship between Raman peak intensity and sildenafil concentration in health wine and liquor were different. There was a good linear correlation between Raman peak intensity, and sildenafil concentration in health wine ranged 0.1–1 mg/L (0.9687< R² < 0.9891) and 1–10 mg/L (0.9701 < R² < 0.9840), and in liquor ranged 0.1–1 mg/L (0.9662 < R² < 0.9944) and 1–20 mg/L (0.9625 < R² < 0.9922). The relative standard deviations (RSD) were less than 5.90% (sildenafil in health wine) and 9.16% (sildenafil in liquor). The recovery ranged 88.92–104.42% (sildenafil in health wine) and 90.09–104.55% (sildenafil in liquor). In general, the sildenafil in health wine and liquor could be rapidly and quantitatively determined using SERS technique, which offered a simple and accurate alternative for the determination of sildenafil in alcoholic drinks.

Rapid and Quantitative Determination of Sildenafil in Cocktail Based on Surface Enhanced Raman Spectroscopy

Sildenafil (SD) and its related compounds are the most common adulterants found in herbal preparations used as sexual enhancer or man’s virility products. However, the abuse of SD threatens human health such as through headache, back pain, rhinitis, etc. Therefore, it is important to accurately detect the presence of SD in alcoholic beverages. In this study, the Opto Trace Raman 202 (OTR 202) was used as a surface-enhanced Raman spectroscopy (SERS) active colloids to detect SD. The results demonstrated that the limit of detection (LOD) of SD was found to be as low as 0.1 mg/L. Moreover, 1235, 1401, 1530, and 1584 cm⁻¹ could be qualitatively determined as SD characteristic peaks. In a practical application, SD in cocktail could be easily detected using SERS based on OTR 202. Also, there was a good linear correlation between the intensity of Raman peaks at 1235, 1401, 1530, and 1584 cm⁻¹ and the logarithm of SD concentration in cocktail was in the range of 0.1–10 mg/L (0.9822 < R² < 0.9860). The relative standard deviation (RSD) was less than 12.7% and the recovery ranged from 93.0%–105.8%. Moreover, the original 500–1700 cm⁻¹ SERS spectra were pretreated and the partial least squares (PLS) was applied to establish the prediction model between SERS spectra and SD content in cocktail and the highest determination coefficient (Rp²) reached 0.9856. In summary, the SD in cocktail could be rapidly and quantitatively determined by SERS, which was beneficial to provide a rapid and accurate scheme for the detection of SD in alcoholic beverages.

1H NMR determination of adulteration of anabolic steroids in seized drugs

Counterfeiting and adulteration of pharmaceuticals is a prevalent problem worldwide and represents a major health risk to the population, with anabolic steroids being one of the main classes of drugs consumed and obtained from dubious sources. In this work, we propose the use of the ¹H NMR technique to evaluate formulations containing anabolic steroids, with analysis of 40 samples of anabolic drugs that are used in injectable and capsule forms. The samples analyzed presented the following active ingredients: testosterone propionate, testosterone phenylpropionate, testosterone isocaproate, testosterone decanoate, testosterone cypionate, testosterone undecanoate, stanozolol, drostanolone propionate, trenbolone acetate, oxymetholone, and methandrostenolone. The ¹H NMR spectroscopic measurements were performed using a 600 MHz Bruker Avance III spectrometer, with deuterated chloroform (CDCl₃) containing 0.1% TMS as solvent. Of the 40 samples analyzed, eight did not show the presence of the active principle stated on the label. Three types of adulteration were found in the analyzed samples: absence of the active ingredient, adulteration with other substances, and concentration values below those indicated on the label. Sildenafil citrate was found in four samples. The GC-MS technique was used to confirm the adulteration results found using ¹H NMR. Quantitative determination by NMR was performed using internal standard and ERETIC 2 methods, and the results obtained were statistically the same.

Effect of sildenafil on human aromatase activity: From in vitro structural analysis to catalysis and inhibition in cells

Aromatase catalyses the conversion of androgens into estrogens and is a well-known target for breast cancer therapy. As it has been suggested that its activity is affected by inhibitors of phosphodiesterase-5, this work investigates the potential interaction of sildenafil with aromatase. This is carried out both at molecular level through structural and kinetics assays applied to the purified enzyme, and at cellular level using neuronal and breast cancer cell lines. Sildenafil is found to bind to aromatase with a K_D of 0.58±0.05μM acting as a partial and mixed inhibitor with a maximal inhibition of 35±2%. Hyperfine sublevel correlation spectroscopy and docking studies show that sildenafil binds to the heme iron via its 6th axial water ligand. These results also provide information on the starting molecular scaffold for the development of new generations of drugs designed to inhibit aromatase as well as phosphodiesterase-5, a new emerging target for breast cancer therapy.

Nebulized solid lipid nanoparticles for the potential treatment of pulmonary hypertension via targeted delivery of phosphodiesterase-5-inhibitor

Phosphodiesterase type 5 (PDE-5) inhibitors - among which sildenafil citrate (SC) - play a primary role in the treatment of pulmonary hypertension (PH). Yet, SC can be only administered orally or parenterally with lot of risks. Targeted delivery of SC to the lungs via inhalation/nebulization is mandatory. In this study, solid lipid nanoparticles (SLNs) loaded with SC were prepared and characterized in terms of colloidal, morphological and thermal properties. The amount of drug loaded and its release behavior were estimated as a function of formulation variables. The potential of lipid nanocarriers to retain their properties following nebulization and autoclaving was investigated. In addition, toxicity aspects of plain and loaded SLNs on A549 cells were studied with respect to concentration. Spherical SLNs in the size range (100-250nm) were obtained. Particles ensured high encapsulation efficiency (88-100%) and sustained release of the payload over 24h. Cell-based viability experiments revealed a concentration-dependant toxicity for both plain and loaded SLNs recording an IC₅₀ of 516 and 384μg/mL, respectively. Nebulization with jet nebulizer and sterilization via autoclaving affected neither the colloidal stability of SLNs nor the drug entrapment, proving their potential as pulmonary delivery system. Interaction of SLNs with mucin was a function of the emulsifier coating layer. Results yet seeking clinical evidence - might give promises of new therapy for PH of higher safety, better performance and higher patient compliance.

Extended Stability of Morphine and Sildenafil for Oral Use in Infants and Young Children

Morphine and sildenafil are commercially available at high concentrations which may lead to errors in measuring small volumes to provide low doses needed in infants. The purpose of this study was to assess the stability of morphine sulfate and sildenafil citrate in extemporaneously prepared suspensions for oral use. Morphine (0.2 mg/mL) was prepared from dilution of morphine elixir (2 mg/mL) with distilled water and stored in amber, plastic syringes at 25°C for 60 days. The mean concentration of morphine exceeded 95% of the initial concentration for the entire 60-day study period. No marked changes in pH or physical appearance were observed. Sildenafil (2.5 mg/mL) was prepared from Revatio tablets in two groups of suspensions: one group in 1% methylcellulose:simple syrup (1:7) and another in OraPlus:OraSweet (1:1). These were stored in plastic prescription bottles at 4°C and 25°C for a period of 91 days. The mean concentrations of sildenafil exceeded 95% of the original concentrations throughout the 91-day study period. No substantial changes were seen in the pH or physical appearance of the suspensions. These results indicate that the diluted morphine was stable for at least 60 days at room temperature. In addition, sildenafil was stable for 91 days in each of the two suspensions prepared from Revatio tablets and stored under refrigeration or at room temperature.

Optimized nano-transfersomal films for enhanced sildenafil citrate transdermal delivery: ex vivo and in vivo evaluation

Sildenafil citrate (SLD) is a selective cyclic guanosine monophosphate-specific phosphodiesterase type 5 inhibitor used for the oral treatment of erectile dysfunction and, more recently, for other indications, including pulmonary hypertension. The challenges facing the oral administration of the drug include poor bioavailability and short duration of action that requires frequent administration. Thus, the objective of this work is to formulate optimized SLD nano-transfersomal transdermal films with enhanced and controlled permeation aiming at surmounting the previously mentioned challenges and hence improving the drug bioavailability. SLD nano-transfersomes were prepared using modified lipid hydration technique. Central composite design was applied for the optimization of SLD nano-transfersomes with minimized vesicular size. The independent variables studied were drug-to-phospholipid molar ratio, surfactant hydrophilic lipophilic balance, and hydration medium pH. The optimized SLD nano-transfersomes were developed and evaluated for vesicular size and morphology and then incorporated into hydroxypropyl methyl cellulose transdermal films. The optimized transfersomes were unilamellar and spherical in shape with vesicular size of 130 nm. The optimized SLD nano-transfersomal films exhibited enhanced ex vivo permeation parameters with controlled profile compared to SLD control films. Furthermore, enhanced bioavailability and extended absorption were demonstrated by SLD nano-transfersomal films as reflected by their significantly higher maximum plasma concentration (C max) and area under the curve and longer time to maxi mum plasma concentration (T max) compared to control films. These results highlighted the potentiality of optimized SLD nano-transfersomal films to enhance the transdermal permeation and the bioavailability of the drug with the possible consequence of reducing the dose and administration frequency.

Carrier free dry powder formulation of sildenafil for potential application in pulmonary arterial hypertension

The present study was designed to prepare sildenafil carrier free dry powder inhalation (DPI) formulation for the treatment of idiopathic pulmonary arterial hypertension (IPAH). Sildenafil DPI formulations were fabricated by spray drying technique. The ideal formulation was optimized using different solvent type (methanol, dimethyformamide and water), concentration (5 and 50 mg/mL) and pH (2 and 7.4) of feed solution. Particles size distribution, morphology and crystallinity of fabricated microparticles were evaluated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) methods, respectively. The aerosolization efficiency of formulations were assessed by next generation impactor equipped with an Aerolizer. Results indicated that evaluated variables had great impacts on powder characteristics which significantly influenced aerosolization performance of formulations. The aerosolized fraction of formulations was improved from 2 to 70% by changing in solvent type and drug concentration in spray dryer feeding solution. Aerosolization performance of powders were well correlated and interpreted by their morphologies as depicted from SEM images. DSC results also indicated that crystallinity of all formulations were reduced by spray drying procedure. Optimization of spray drying technique for production of Sildenafil carrier free DPI formulation in this study may pave a way for locally treatment of IPAH.

[Identification of a new sildenafil analogue based on Q-TOF-MS]

The drugs such as sildenafil adulterated in herbal products and dietary supplements may endanger human health. The number of the new modified derivatives is increasing recently. Based on Q-TOF-MS, a new sildenafil analogue was found. It was isolated and purified by preparative liquid chromatography. Its structure was determined by NMR, as 1-[4-propoxy-3-(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4, 3-d] pyrimidin-5-yl)phenylsulfonyl]-4-methylpiperazine. Compared with sildenafil, the ethoxy group of the benzene ring moiety was moved to the propoxy group, which had not been reported in China. The mass spectrometric behavior pattern of the structure type was summarized, which can greatly accelerate the structural analysis of novel analogues.