Design, Synthesis, and Investigation of Novel Nitric Oxide (NO)-Releasing Aromatic Aldehydes as Drug Candidates for the Treatment of Sickle Cell Disease.

Sickle cell disease (SCD) is caused by a single-point mutation, and the ensuing deoxygenation-induced polymerization of sickle hemoglobin (HbS), and reduction in bioavailability of vascular nitric oxide (NO), contribute to the pathogenesis of the disease. In a proof-of-concept study, we successfully incorporated nitrate ester groups onto two previously studied potent antisickling aromatic aldehydes, TD7 and VZHE039, to form TD7-NO and VZHE039-NO hybrids, respectively. These compounds are stable in buffer but demonstrated the expected release of NO in whole blood in vitro and in mice. The more promising VZHE039-NO retained the functional and antisickling activities of the parent VZHE039 molecule. Moreover, VZHE039-NO, unlike VZHE039, significantly attenuated RBC adhesion to laminin, suggesting this compound has potential in vivo RBC anti-adhesion properties relevant to vaso-occlusive events. Crystallographic studies show that, as with VZHE039, VZHE039-NO also binds to liganded Hb to make similar protein interactions. The knowledge gained during these investigations provides a unique opportunity to generate a superior candidate drug in SCD with enhanced benefits.

Design, Synthesis, and Antisickling Investigation of a Nitric Oxide-Releasing Prodrug of 5HMF for the Treatment of Sickle Cell Disease.

5-hydroxyfurfural (5HMF), an allosteric effector of hemoglobin (Hb) with an ability to increase Hb affinity for oxygen has been studied extensively for its antisickling effect in vitro and in vivo, and in humans for the treatment of sickle cell disease (SCD). One of the downstream pathophysiologies of SCD is nitric oxide (NO) deficiency, therefore increasing NO (bio)availability is known to mitigate the severity of SCD symptoms. We report the synthesis of an NO-releasing prodrug of 5HMF (5HMF-NO), which in vivo, is expected to be bio-transformed into 5HMF and NO, with concomitant therapeutic activities. In vitro studies showed that when incubated with whole blood, 5HMF-NO releases NO, as anticipated. When incubated with sickle blood, 5HMF-NO formed Schiff base adduct with Hb, increased Hb affinity for oxygen, and prevented hypoxia-induced erythrocyte sickling, which at 1 mM concentration were 16%, 10% and 27%, respectively, compared to 21%, 18% and 21% for 5HMF. Crystal structures of 5HMF-NO with Hb showed 5HMF-NO bound to unliganded (deoxygenated) Hb, while the hydrolyzed product, 5HMF bound to liganded (carbonmonoxy-ligated) Hb. Our findings from this proof-of-concept study suggest that the incorporation of NO donor group to 5HMF and analogous molecules could be a novel beneficial strategy to treat SCD and warrants further detailed in vivo studies.

Rational modification of vanillin derivatives to stereospecifically destabilize sickle hemoglobin polymer formation.

Increasing the affinity of hemoglobin for oxygen represents a feasible and promising therapeutic approach for sickle cell disease by mitigating the primary pathophysiological event, i.e. the hypoxia-induced polymerization of sickle hemoglobin (Hb S) and the concomitant erythrocyte sickling. Investigations on a novel synthetic antisickling agent, SAJ-310, with improved and sustained antisickling activity have previously been reported. To further enhance the biological effects of SAJ-310, a structure-based approach was employed to modify this compound to specifically inhibit Hb S polymer formation through interactions which perturb the Hb S polymer-stabilizing αF-helix, in addition to primarily increasing the oxygen affinity of hemoglobin. Three compounds, TD-7, TD-8 and TD-9, were synthesized and studied for their interactions with hemoglobin at the atomic level, as well as their functional and antisickling activities in vitro. X-ray crystallographic studies with liganded hemoglobin in complex with TD-7 showed the predicted mode of binding, although the interaction with the αF-helix was not as strong as expected. These findings provide important insights and guidance towards the development of molecules that would be expected to bind and make stronger interactions with the αF-helix, resulting in more efficacious novel therapeutics for sickle cell disease.

Rational design of pyridyl derivatives of vanillin for the treatment of sickle cell disease.

Hypoxia-induced polymerization of sickle hemoglobin (Hb S) is the principal phenomenon that underlays the pathophysiology and morbidity associated with sickle cell disease (SCD). Opportunely, as an allosteric protein, hemoglobin (Hb) serves as a convenient and potentially critical druggable target. Consequently, molecules that prevent Hb S polymerization (Hb modifiers), and the associated erythrocyte sickling have been investigated-and retain significant interest-as a viable therapeutic strategy for SCD. This group of molecules, including aromatic aldehydes, form high oxygen affinity Schiff-base adducts with Hb S, which are resistant to polymerization. Here, we report the design and synthesis of novel potent antisickling agents (SAJ-009, SAJ-310 and SAJ-270) based on the pharmacophore of vanillin and INN-312, a previously reported pyridyl derivative of vanillin. These novel derivatives exhibited superior in vitro binding and pharmacokinetic properties compared to vanillin, which translated into significantly enhanced allosteric and antisickling properties. Crystal structure studies of liganded Hb in the R2 quaternary state in complex with SAJ-310 provided important insights into the allosteric and antisickling properties of this group of compounds. While these derivatives generally show similar in vitro biological potency, significant structure-dependent differences in their biochemical profiles would help predict the most promising candidates for successful in vivo pre-clinical translational studies and inform further structural modifications to improve on their pharmacologic properties.

Developing a stable aqueous enteric coating formulation with hydroxypropyl methylcellulose acetate succinate (HPMCAS-MF) and colloidal silicon dioxide as anti-tacking agent.

The purpose of this study was to use statistical design of experiments to develop a stable aqueous enteric coating formulation containing stabilizing excipients, such as polyethylene glycol that can minimize hydroxypropyl methylcellulose acetate succinate aggregation and minimize spray-nozzle clogging at elevated processing temperatures. The mechanisms of stabilization (i.e. charge stabilization and molecular interactions) were studied by performing zeta potential and FTIR studies. Electrostatic stabilization by sodium lauryl sulfate and hydrogen bonding by polyethylene glycol provided dispersion stability and yielded a stable aqueous coating formulation that prevented spray-nozzle clogging. An enteric coated tablet with better gastric resistance was obtained by incorporating fumed silica (Aerosil® R972) as the anti-tacking agent instead of talc. Dissolution testing on the riboflavin enteric coated tablets showed a good enteric release profile without releasing riboflavin in 0.1 N HCl, and completely disintegrating within 10 min in phosphate buffer (pH 6.8).

Impact of formulation excipients on the thermal, mechanical, and electrokinetic properties of hydroxypropyl methylcellulose acetate succinate (HPMCAS).

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) has been widely used in amorphous solid dispersions and as an enteric coating polymer. Under aqueous coating conditions and at elevated coating temperatures, HPMCAS particles tend to aggregate and clog the spray-nozzle, hence interrupting the coating process. This research focused on how plasticizers and surfactants, excipients used for aqueous coating, affect the properties and stability of HPMCAS. This information would be useful in identifying suitable excipients for developing a stable HPMCAS aqueous enteric coating formulation. Triethyl citrate was found to be the most compatible plasticizer with HPMCAS, and displayed suitable thermal and mechanical properties. PEG 4000, the co-plasticizer, provided dispersion stability by yielding a dispersible sediment without aggregation at the elevated processing temperatures. Zeta potential measurements indicated sodium lauryl sulfate (SLS) could be used as a potential stabilizing agent at concentrations above its critical micelle concentration (CMC). This study facilitated the understanding of the HPMCAS aggregation mechanism, in addition to identifying suitable stabilizing agents. These stabilizing excipients could potentially be used to develop a stable aqueous coating formulation that does not exhibit polymer aggregation and nozzle clogging during the coating process.

Investigation of Polymer/Surfactant Interactions and Their Impact on Itraconazole Solubility and Precipitation Kinetics for Developing Spray-Dried Amorphous Solid Dispersions.

Methods were developed to systematically screen different polymer-surfactant combinations for the purpose of enhancing amorphous active pharmaceutical ingredient (API) solubility while maintaining its physical stability. Itraconazole (ITZ) was chosen as the model API mostly due to its low aqueous solubility. Special attention was paid to determine the effect of a reduction in the critical micelle concentration (CMC) by specific polymer/surfactant combinations on the ITZ solubility and physical stability. However, only a slight correlation was actually found. Only the polymer/surfactant combinations with the smallest effect on CMC improved solubility and stability of ITZ in simulated intestinal fluids (SIF). Surfactants were found to negate the stabilizing effects of polymers. ITZ crystallization tendency generally depended on the degree of supersaturation and the type of polymer/surfactant combinations used. In general, we found that instead of focusing solely on reducing the CMC, a systematic screening of systems that maintain high ITZ supersaturation proved to be a successful approach.

Design, Synthesis, and Investigation of Novel Nitric Oxide (NO)-Releasing Prodrugs as Drug Candidates for the Treatment of Ischemic Disorders: Insights into NO-Releasing Prodrug Biotransformation and Hemoglobin-NO Biochemistry.

We have developed novel nitric oxide (NO)-releasing prodrugs of efaproxiral (RSR13) for their potential therapeutic applications in a variety of diseases with underlying ischemia. RSR13 is an allosteric effector of hemoglobin (Hb) that decreases the protein's affinity for oxygen, thereby increasing tissue oxygenation. NO, because of its vasodilatory property, in the form of ester prodrugs has been found to be useful in managing several cardiovascular diseases by increasing blood flow and oxygenation in ischemic tissues. We synthesized three NO-donor ester derivatives of RSR13 (DD-1, DD-2, and DD-3) by attaching the NO-releasing moieties nitrooxyethyl, nitrooxypropyl, and 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate, respectively, to the carboxylate of RSR13. In vitro studies demonstrated that the compounds released NO in a time-dependent manner upon being incubated with l-cysteine (1.8-9.3%) or human serum (2.3-52.5%) and also reduced the affinity of Hb for oxygen in whole blood (ΔP50 of 4.9-21.7 mmHg vs ΔP50 of 25.4-32.1 mmHg for RSR13). Crystallographic studies showed RSR13, the hydrolysis product of the reaction between DD-1 and deoxygenated Hb, bound to the central water cavity of Hb. Also, the hydrolysis product, NO, was observed exclusively bound to the two α hemes, the first such HbNO structure to be reported, capturing the previously proposed physiological bis-ligated nitrosylHb species. Finally, nitrate was observed bound to ßHis97. Ultraperformance liquid chromatography-mass spectrometry analysis of the compounds incubated with matrices used for the various studies demonstrated the presence of the predicted reaction products. Our findings, beyond the potential therapeutic application, provide valuable insights into the biotransformation of NO-releasing prodrugs and their mechanism of action and into hemoglobin-NO biochemistry at the molecular level.