A New Generation of Dihydropyridine Calcium Channel Blockers: Photostabilization of Liquid Formulations Using Nonionic Surfactants

Cyclodextrins and their applications in pharmaceutical and related fields

This chapter presents an overall account of cyclodextrins (CDs) with a brief description of the history, classification, and properties of these macromolecules. CDs act as complexing agents for drugs to form CD-drug inclusion complexes by various techniques. These complexes lead to the modification of the physicochemical properties of drugs to make them more soluble, chemically, and photochemically stable, and less toxic. It focuses in detail on various pharmaceutical uses of CDs and their derived forms in drug solubility, bioavailability, drug stability, drug delivery, and drug safety which have been specifically highlighted. The role of CDs and derivatives as excipients in the drug formulation of solid dosage forms, parenteral dosage forms, and anticancer drugs has been emphasized. Some other applications of CDs in cosmetics, environmental protection, food technology, and analytical methods have been described.

Multivariate Approaches in Quantitative Structure-Property Relationships Study for the Photostability Assessment of 1,4-Dihydropyridine Derivatives

1,4-dihydropyridines (1,4-DHPs) are widely recognized as highly effective L-type calcium channel blockers with significant therapeutic benefits in the treatment of cardiovascular disorders. 1,4-DHPs can also target T-type calcium channels, making them promising drug candidates for neurological conditions. When exposed to light, all 1,4-DHPs tend to easily degrade, leading to an oxidation product derived from the aromatization of the dihydropyridine ring. Herein, the elaboration of a quantitative structure-property relationships (QSPR) model was carried out by correlating the light sensitivity of structurally different 1,4-DHPs with theoretical molecular descriptors. Photodegradation experiments were performed by exposing the drugs to a Xenon lamp following the ICH rules. The degradation was monitored by spectrophotometry, and experimental data were elaborated by Multivariate Curve Resolution (MCR) methodologies to assess the kinetic rates. The results were confirmed by the HPLC-DAD method. PaDEL-Descriptor software was used to calculate molecular descriptors and fingerprints related to the chemical structures. Seventeen of the 1875 molecular descriptors were selected and correlated to the photodegradation rate by means of the Ordinary Least Squares (OLS) algorithm. The chemometric model is useful to predict the photosensitivity of other 1,4-DHP derivatives with a very low relative error percentage of 5.03% and represents an effective tool to design new analogs characterized by higher photostability.

Synthesis and Evaluation of Novel Substituted N-Aryl 1,4-Dihydropyridines as Antituberculostatic Agents

BACKGROUND

Tuberculosis has been the main cause of mortality of infectious diseases worldwide, with strongly limited therapeutic options. With increasing resistance and missing suitable drugs in those cases, there is a strong need for novel antituberculostatic drugs. We developed novel N-aryl 1,4-dihydropyridines with various substitution patterns to evaluate them as antituberculostatic agents.

METHODS

1,4-Dihydropyridine derivatives were synthesized and purified by column chromatography or recrystallization. The mycobacterial growth inhibition was determined in a fluorescent mycobacterial growth assay.

RESULTS

The compounds were prepared in a simple one-pot reaction under acidic conditions with structurally varied components. The substituent effects on the determined mycobacterial growth inhibitory properties are discussed.

CONCLUSION

Lipophilic diester substituted derivatives show promising activities that were additionally affected by the aromatic substituent functions. Thus, we identified compounds with activities almost reaching that of the used antimycobacterial drug as control.

Use of Pluronic Surfactants in Gel Formulations of Photosensitive 1,4-Dihydropyridine Derivatives: A Potential Approach in the Treatment of Neuropathic Pain

1,4-Dihydropyridines (DHPs) are the most important class of L-type calcium channel blockers that are employed for the treatment of cardiovascular diseases, particularly hypertension. Various modifications on this scaffold lead to the discovery of new DHPs blocking different types of calcium channels. Among them, the T-type calcium channel has recently attracted great interest due to its role in chronic pain conditions. In this study, we selected three newly synthesized DHPs (HM8, HM10 and MD20) with different selectivity profiles to the T-type calcium channel and formulated them in micellar solutions and micellar-in-gel matrices to be tested for potential topical use in the treatment of neuropathic pain. To prevent the well-known sensitivity to light of the DHPs, the studied compounds were entrapped in colloidal aggregates obtained by using edible Pluronic^® surfactants and adding α-tocopherol as an antioxidant. All the prepared formulations were exposed to stressing light, according to international rules. Along with the degradation experiments, the concentrations of the parent compounds and by-products were calculated by multivariate curve resolution—alternating least squares (MCR-ALS) applied to the spectral data. The defined formulations proved suitable as light-stable matrices for the DHP compounds, showing an increase in stability for HM8 and MD20 and an almost complete photoprotection for HM10, compared to ethanol solutions and standard gel formulations.

Gel Formulation of Nabumetone and a Newly Synthesized Analog: Microemulsion as a Photoprotective Topical Delivery System

Photostability studies were performed on topical formulations containing the anti-inflammatory drug Nabumetone and an analog newly synthesized in order to achieve better photostability and pharmacokinetic profile. Stability tests, according to the International Conference on Harmonization rules, were applied on ethanol solutions and topical gel formulations of both compounds. The photodegradation profiles were monitored by Multivariate curve resolution applied to the UV spectral data. The inclusion of the compounds in microemulsion was investigated to improve light stability and, at the same time, to ensure a sustained release system for skin delivery. All the formulations in solution, gel, microemulsion, and microemulsion-in-gel were exposed to a forced irradiation of 350 W/m², corresponding to a 21 kJ/m² min, for up to 300 min. Photostability increased significantly for both drugs in the liquid microemulsion and microemulsion-in-gel, compared to the ethanol solution and plain gel, reaching a residual drug of 97% and 98% for Nabumetone and analog in microemulsion-in-gel, respectively. Permeation experiments on the microemulsion-in-gel showed a better performance of the analog formulated at 0.2%, compared to the same formulation of Nabumetone at 0.7%. These results highlight the potential of the designed matrices as delayed drug delivery systems along with the use of lower drug doses leading to reduced side effects.

Development of a UV-Stabilized Topical Formulation of Nifedipine for the Treatment of Raynaud Phenomenon and Chilblains

Raynaud’s Phenomenon is a vascular affliction resulting in pain and blanching of the skin caused by excessive and prolonged constriction of arterioles, usually due to cold exposure. Nifedipine is a vasodilatory calcium channel antagonist, which is used orally as the first-line pharmacological treatment to reduce the incidence and severity of attacks when other interventions fail to alleviate the condition and there is danger of tissue injury. Oral administration of nifedipine, however, is associated with systemic adverse effects, and thus topical administration with nifedipine locally to the extremities would be advantageous. However, nifedipine is subject to rapid photodegradation, which is problematic for exposed skin such as the hands. The goal of this project was to analyze the photostability of a novel topical nifedipine cream to UVA light. The effect of incorporating the photoprotectants rutin, quercetin, and/or avobenzone (BMDBM) into the nifedipine cream on the stability of nifedipine to UVA light exposure and the appearance of degradation products of nifedipine was determined. Rutin and quercetin are flavonoids with antioxidant activity. Both have the potential to improve the photostability of nifedipine by a number of mechanisms that either quench the intermolecular electron transfer of the singlet excited dihydropyridine to the nitrobenzene group or by preventing photoexcitation of nifedipine. Rutin at either 0.1% or 0.5% (w/w) did not improve the stability of nifedipine 2% (w/w) in the cream after UVA exposure up to 3 h. Incorporation of quercetin at 0.5% (w/w) did improve nifedipine stability from 40% (no quercetin) to 77% (with quercetin) of original drug concentration after 3 h UVA exposure. A combination of BMDBM and quercetin was the most effective photoprotectant for maintaining nifedipine concentration following up to 8 h UVA exposure.

Discovery of Michael acceptor containing 1,4-dihydropyridines as first covalent inhibitors of L-/T-type calcium channels

1,4-Dihydropyridines (DHPs) are an important class of blockers targeting different calcium channel subtypes and have great therapeutic value against cardiovascular and neurophysiologic conditions. Here, we present the design of DHP-based hexahydroquinoline derivatives as either selective or covalent inhibitors of calcium channels. These compounds were synthesized via a modified Hantzsch reaction under microwave irradiation and characterized by IR, ¹H NMR, ¹³C NMR and mass spectra. Additionally, the proposed structure of HM12 was resolved by single crystal X-ray analysis. The abilities of the target compounds to block both L- and T-type calcium channels were evaluated by utilizing the whole-cell patch clamp technique. Our results identified covalent inhibitors of calcium channels for the first time, which could be achieved by introducing a Michael acceptor group into the ester side chain of the compounds. The proposed covalent binding between the compounds and the cysteine amino acid (Cys1492) within the DHP binding pocket of L-type calcium channel was supported by docking and pharmacophore analysis as well as a glutathione reactivity assay.