Herein we describe the first structure-activity relationship study of the broad-range iGluR antagonist (2S,3R)-3-(3-carboxyphenyl)pyrrolidine-2-carboxylic acid (1) by exploring the pharmacological effect of substituents in the 4, 4', or 5' positions and the bioisosteric substitution of the distal carboxylic acid for a phosphonic acid moiety. Of particular interest is a hydroxyl group in the 4' position 2a which induced a preference in binding affinity for homomeric GluK3 over GluK1 (Ki = 0.87 and 4.8 μM, respectively). Two X-ray structures of ligand binding domains were obtained: 2e in GluA2-LBD and 2f in GluK1-LBD, both at 1.9 Å resolution. Compound 2e induces a D1-D2 domain opening in GluA2-LBD of 17.3-18.8° and 2f a domain opening in GluK1-LBD of 17.0-17.5° relative to the structures with glutamate. The pyrrolidine-2-carboxylate moiety of 2e and 2f shows a similar binding mode as kainate. The 3-carboxyphenyl ring of 2e and 2f forms contacts comparable to those of the distal carboxylate in kainate.

Uptake of the major excitatory neurotransmitter in the CNS, (S)-glutamate, is mediated by a family of excitatory amino acid transporters (EAAT). Previously we have explored the structure-activity relationship (SAR) of a series of EAAT1 selective inhibitors, leading to the development of the potent inhibitors UCPH-101 and UCPH-102. In the present study, we set out to improve the solubility properties of these EAAT1 inhibitors with the objective to develop analogs more suited as pharmacological tools for in vivo studies of EAAT1 in terms of their bioavailability. A total of 23 novel UCPH-101/102 analogs were designed, synthesized and characterized pharmacologically at EAAT1-3 in a [(3)H]-D-aspartate uptake assay. Most notably, the potent EAAT1 inhibition displayed of UCPH-101 and UCPH-102 was retained in analog 1d in which the napht-1-yl group in the 7-position of UCPH-102 has been replaced by an o-biphenyl moiety. In contrast, EAAT1 activity was dramatically compromised in analogs 1e and 1f comprising m- and p-biphenyl groups as 7-substituents, respectively. Analog 1d displayed low bioavailability after oral administration in rats, and this problem was addressed by the synthesis of a series of analogs with different chloro, fluoro, methoxy, triflouromethyl and carboxy substitution patterns at the o-biphenyl group of 1d (1h-1s) and m- and p-pyridine analogs of 1d (1t and 1v). Unfortunately, all of the modifications resulted in substantial decreased EAAT1 inhibitory activity, which supports the notion of a very lipophilic binding pocket in EAAT1 for the aromatic 7-substituent in these ligands. In conclusion, while we have not succeeded in developing UCPH-101/102 analogs possessing improved bioavailability properties, this study does offer interesting SAR information about this inhibitor class, and analog 1d seems to be an interesting lead for future SAR studies with focus on the development of more potent EAAT1 inhibitors.

Introduction Pain is a clinical complication to chronic obstructive pulmonary disease (COPD) that interferes negatively with physical activity level (PAL), quality of life (QOL) and pulmonary interventions. Yet, research in pain characteristics including prevalence, localization, and intensity in people with COPD are sparsely researched. Aim To investigate self-reported pain prevalence, localization and intensity of pain in people with and without COPD, and to investigate the association between pain intensity and PAL among participants with COPD. Methods Data were derived from the Danish Health and Morbidity Survey in 2017. The study population was restricted to individuals aged ≥35 years. Data included pain intensity assessed on the Numeric Rating Scale (NRS) and localization, PAL, QoL, sleep disturbance, comorbidities, sociodemographic and behavioral factors. Results In all, 528 participants with COPD and 8184 participants without COPD (51% females, mean ±SD age 67.1±11.4 years) were analyzed. Pain prevalence within the past 14 days was significantly higher in participants with COPD vs nonCOPD (72.7% vs 57.7%, p <0.001) and mainly located in the limbs, thorax, and lower back. COPD was associated with the prevalence of chronic pain (≥6 months) (OR: 2.78, 95%CI: 2.32; 3.34, p <0.001). Participants with COPD reported a higher pain intensity compared to those with nonCOPD with a mean difference of 1.04 points (95%CI: 0.75; 1.32, p <0.001) on the NRS. In the adjusted multiple logistic regression analysis, pain intensity was negatively associated with odds of being physical active (OR: 0.72, 95%CI: 0.61; 0.85, p <0.001). Conclusion Pain is more prevalent in people with self-reported COPD. After adjustment for age and gender, COPD was associated with an elevated pain intensity. Sleep disturbance and multimorbidity had the most pronounced impacts on pain intensity in the multiple linear regression model. In participants with COPD, increased pain intensity was negatively associated with being physically active.

Background Clinicians nominate the distribution of leg pain as being important in diagnosing nerve root involvement. This study aimed to identify: (i) common unisegmental radicular pain patterns and whether they were dermatomal, and (ii) whether these radicular pain patterns assisted clinician discrimination of the nerve root level involved. Methods A cross-sectional diagnostic accuracy study of adult patients with radicular leg pain at a hospital in Denmark. All patients had positive neurological signs (average 2.8 signs - hypoalgesia, diminished reflexes, muscle weakness, positive Straight Leg Raise test). Part 1 (pain patterns) was a secondary analysis of baseline pain pattern data collected during a clinical trial. The pain charts of 93 patients with an MRI and clinically confirmed single-level disc herniation with nerve root compression were digitised and layered to form a composite picture of the radicular patterns for the L5 and S1 nerve roots, which were then compared to published dermatomes. In Part 2 (clinical utility) we prospectively measured the discriminative ability of the identified pain patterns. The accuracy was calculated of three groups of six clinicians at classifying the nerve root affected in a randomized sequence of 53 patients, when not shown, briefly shown or continuously shown the composite pain patterns. In each group were two chiropractors, two medical doctors and two physiotherapists. Results There was a wide overlap in pain patterns from compromised L5 and S1 nerve roots but some distinguishing features. These pain patterns had approximately 50 to 80% overlap with published dermatomes. Clinicians were unable to determine with any accuracy above chance whether an individual pain drawing was from a person with a compromised L5 or S1 nerve root, and use of the composite pain drawings did not improve that accuracy. Conclusions While pain distribution may be an indication of radiculopathy, pain patterns from L5 or S1 nerve root compression only approximated those of sensory dermatomes, and level-specific knowledge about radicular pain patterns did not assist clinicians’ diagnostic accuracy of the nerve root impinged. These results indicate that, on their own, pain patterns provide very limited additional diagnostic information about which individual nerve root is affected.

In the present study, we made further investigations on the structure-activity requirements of the selective excitatory amino acid transporter 1 (EAAT1) inhibitor, 2-amino-4-(4-methoxyphenyl)-7-(naphthalen-1-yl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (UCPH-101), by exploring 15 different substituents (R(1) ) at the 7-position in combination with eight different substituents (R(2) ) at the 4-position. Among the 63 new analogues synthesized, we identified a number of compounds that unexpectedly displayed inhibitory activities at EAAT1 in light of understanding the structure-activity relationship (SAR) of this inhibitor class extracted from previous studies. Moreover, the nature of the R(1) and R(2) substituents were observed to contribute to the functional properties of the various analogues in additive and non-additive ways. Finally, separation of the four stereoisomers of analogue 14 g (2-amino-4-([1,1'-biphenyl]-4-yl)-3-cyano-7-isopropyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene) was carried out, and in agreement with a study of a related scaffold, the R configuration at C4 was found to be mandatory for inhibitory activity, while both the C7 diastereomers were found to be active as EAAT1 inhibitors. A study of the stereochemical stability of the four pure stereoisomers 14 g-A-D showed that epimerization takes places at C7 via a ring-opening, C-C bond rotation, ring-closing mechanism.