Synchrotron Radiation: A Key Tool for Drug Discovery

Synchrotron radiation is extensively utilized in the domains of materials science, physical chemistry, and life science, resulting from its high intensity, exceptional monochromaticity, superior collimation, and broad wave spectrum. This top-notch light source has also made significant contributions to the progress of biomedicine. The advancement of synchrotron radiation-based X-ray and protein crystallography technologies has created new prospects for drug discovery. These innovative techniques have opened up exciting avenues in the field. The investigation of protein crystal structures and the elucidation of the spatial configuration of biological macromolecules have revealed intricate details regarding the modes of protein binding. Furthermore, the screening of crystal polymorphs and ligands has laid the groundwork for rational drug modification and the improvement of drug physicochemical properties. As science and technology continue to advance, the techniques for analyzing structures using synchrotron radiation sources and the design of corresponding crystallographic beamline stations are undergoing continuous enhancement. These cutting-edge tools and facilities are expected to expedite the drug development process and rectify the current situation of a lack of targeted drugs.

New perspectives in macromolecular powder diffraction using single-photon-counting strip detectors: high-resolution structure of the pharmaceutical peptide octreotide

Advances in instrumentation, as well as the development of powerful crystallographic software have significantly facilitated the collection of high-resolution diffraction data and have made X-ray powder diffraction (XRPD) particularly useful for the extraction of structural information; this is true even for complex molecules, especially when combined with synchrotron radiation. In this study, in-line with past instrumental profile studies, an improved data collection strategy exploiting the MYTHEN II detector system together with significant beam focusing and tailored data collection options was introduced and optimized for protein samples at the Material Science beamline at the Swiss Light Source. Polycrystalline precipitates of octreotide, a somatostatin analog of particular pharmaceutical interest, were examined with this novel approach. XRPD experiments resulted in high angular and d-spacing (1.87 Å) resolution data, from which electron-density maps of enhanced quality were extracted, revealing the molecule's structural properties. Since microcrystalline precipitates represent a viable alternative for administration of therapeutic macromolecules, XRPD has been acknowledged as the most applicable tool for examining a wide spectrum of physicochemical properties of such materials and performing studies ranging from phase identification to complete structural characterization.

Insulin polymorphism induced by two polyphenols: new crystal forms and advances in macromolecular powder diffraction

This study focuses on the polymorphism of human insulin (HI) upon the binding of the phenolic derivativesp-coumaric acid ortrans-resveratrol over a wide pH range. The determination of the structural behaviour of HI via X-ray powder diffraction (XRPD) and single-crystal X-ray diffraction (SCXRD) is reported. Four distinct polymorphs were identified, two of which have not been reported previously. The intermediate phase transitions are discussed. One of the novel monoclinic polymorphs displays the highest molecular packing among insulin polymorphs of the same space group to date; its structure was elucidated by SCXRD. XRPD data collection was performed using a variety of instrumental setups and a systematic comparison of the acquired data is presented. A laboratory diffractometer was used for screening prior to high-resolution XRPD data collection on the ID22 beamline at the European Synchrotron Radiation Facility. Additional measurements for the most representative samples were performed on the X04SA beamline at the Swiss Light Source (SLS) using the MYTHEN II detector, which allowed the detection of minor previously untraceable impurities and dramatically improved thed-spacing resolution even for poorly diffracting samples.

Exploring the complex map of insulin polymorphism: a novel crystalline form in the presence ofm-cresol

In this study, the first crystal structure of a novel crystal form of human insulin bound tometa-cresol in an acidic environment is reported. The combination of single-crystal and powder X-ray diffraction crystallography led to the detection of a previously unknown monoclinic phase (P21). The structure was identified from the powder patterns and was solved using single-crystal diffraction data at 2.2 Å resolution. The unit-cell parameters at pH 6.1 area= 47.66,b = 70.36,c = 84.75 Å, β = 105.21°. The structure consists of two insulin hexamers per asymmetric unit. The potential use of this insulin form in microcrystalline drugs is discussed.

Applications of X-ray Powder Diffraction in Protein Crystallography and Drug Screening

Providing fundamental information on intra/intermolecular interactions and physicochemical properties, the three-dimensional structural characterization of biological macromolecules is of extreme importance towards understanding their mechanism of action. Among other methods, X-ray powder diffraction (XRPD) has proved its applicability and efficiency in numerous studies of different materials. Owing to recent methodological advances, this method is now considered a respectable tool for identifying macromolecular phase transitions, quantitative analysis, and determining structural modifications of samples ranging from small organics to full-length proteins. An overview of the XRPD applications and recent improvements related to the study of challenging macromolecules and peptides toward structure-based drug design is discussed. This review congregates recent studies in the field of drug formulation and delivery processes, as well as in polymorph identification and the effect of ligands and environmental conditions upon crystal characteristics. These studies further manifest the efficiency of protein XRPD for quick and accurate preliminary structural characterization.

Unit-cell response of tetragonal hen egg white lysozyme upon controlled relative humidity variation

Variation of relative humidity (rH) greatly affects the internal order of solvent-based protein crystals, and the rearrangement of molecules can be efficiently recorded in distinct diffraction patterns. This study focuses on this topic, reporting the effect of rH variation experiments on hen egg white lysozyme (HEWL) polycrystalline precipitates of tetragonal symmetry using X-ray powder diffraction (XRPD). In situ XRPD data were collected on HEWL specimens during dehydration and rehydration processes using laboratory instrumentation. A known polymorph [space group P43212, a = 79.07181 (1), c = 38.0776 (1) Å] was identified during gradual dehydration from 95 to 63% rH and vice versa. Pawley analysis of collected data sets and accurate extraction of unit-cell parameters indicated a characteristic evolution of the tetragonal axes with rH. In addition, there is a low humidity level below which samples do not retain their crystallinity. This work illustrates the accuracy of laboratory XRPD as a probe for time-resolved studies of proteins and in situ investigations of gradual structural modifications upon rH variation. These experiments provide essential information for improving production and post-production practices of microcrystalline protein-based pharmaceuticals.

Revisiting the structure of a synthetic somatostatin analogue for peptide drug design

Natural or artificially manufactured peptides attract scientific interest worldwide owing to their wide array of pharmaceutical and biological activities. X-ray structural studies are used to provide a precise extraction of information, which can be used to enable a better understanding of the function and physicochemical characteristics of peptides. Although it is vulnerable to disassociation, one of the most vital human peptide hormones, somatostatin, plays a regulatory role in the endocrine system as well as in the release of numerous secondary hormones. This study reports the successful crystallization and complete structural model of octreotide, a stable octapeptide analogue of somatostatin. Common obstacles in crystallographic studies arising from the intrinsic difficulties of obtaining a suitable single-crystal specimen were efficiently overcome as polycrystalline material was employed for synchrotron and laboratory X-ray powder diffraction (XPD) measurements. Data collection and preliminary analysis led to the identification of unit-cell symmetry [orthorhombic, P212121, a = 18.5453 (15), b = 30.1766 (25), c = 39.798 (4) Å], a process which was later followed by complete structure characterization and refinement, underlying the efficacy of the suggested (XPD) approach.

In situ detection of a novel lysozyme monoclinic crystal form upon controlled relative humidity variation

The effect of relative humidity (rH) on protein crystal structures, an area that has attracted high scientific interest during the past decade, is investigated in this study on hen egg-white lysozyme (HEWL) polycrystalline precipitates via in situ laboratory X-ray powder diffraction (XRPD) measurements. For this purpose, HEWL was crystallized at room temperature and pH 4.5, leading to a novel monoclinic HEWL phase which, to our knowledge, has not been reported before. Analysis of XRPD data collected upon rH variation revealed several structural modifications. These observations, on a well-studied molecule like HEWL, underline not only the high impact of humidity levels on biological crystal structures, but also the significance of in-house XRPD as an analytical tool in industrial drug development and its potential to provide information for enhancing manufacturing of pharmaceuticals.