In the present study, an open-label, three-treatment, threeperiod clinical study of rosuvastatin (RSV) and rifampicin (RIF) when administered alone and in combination was conducted in 12 male healthy subjects to determine if coproporphyrin I (CP-I) and coproporphyrin III (CP-III) could serve as clinical biomarkers for organic anion transporting polypeptide 1B1 (OATP1B1) and 1B3 that belong to the solute carrier organic anion gene subfamily. Genotyping of the human OATP1B1 gene was performed in all 12 subjects and confirmed absence of OATP1B1*5 and OATP1B1*15 mutations. Average plasma concentrations of CP-I and CP-III prior to drug administration were 0.91 6 0.21 and 0.15 6 0.04 nM, respectively, with minimum fluctuation over the three periods. CP-I was passively eliminated, whereas CP-III was actively secreted from urine. Administration of RSV caused no significant changes in the plasma and urinary profiles of CP-I and CP-III. RIF markedly increased the maximum plasma concentration (C max ) of CP-I and CP-III by 5.7-and 5.4-fold (RIF) or 5.7-and 6.5-fold (RIF1RSV), respectively, as compared with the predose values. The area under the plasma concentration curves from time 0 to 24 h (AUC 0-24h ) of CP-I and CP-III with RIF and RSV increased by 4.0-and 3.3-fold, respectively, when compared with RSV alone. In agreement with this finding, C max and AUC 0-24h of RSV increased by 13.2-and 5.0-fold, respectively, when RIF was coadministered. Collectively, we conclude that CP-I and CP-III in plasma and urine can be appropriate endogenous biomarkers specifically and reliably reflecting OATP inhibition, and thus the measurement of these molecules can serve as a useful tool to assess OATP drug-drug interaction liabilities in early clinical studies.

To identify novel targets for neuropathic pain, 3097 mouse knockout lines were tested in acute and persistent pain behavior assays. One of the lines from this screen, which contained a null allele of the adapter protein-2 associated kinase 1 (AAK1) gene, had a normal response in acute pain assays (hot plate, phase I formalin), but a markedly reduced response to persistent pain in phase II formalin. AAK1 knockout mice also failed to develop tactile allodynia following the Chung procedure of spinal nerve ligation (SNL). Based on these findings, potent, small-molecule inhibitors of AAK1 were identified. Studies in mice showed that one such inhibitor, LP-935509, caused a reduced pain response in phase II formalin and reversed fully established pain behavior following the SNL procedure. Further studies showed that the inhibitor also reduced evoked pain responses in the rat chronic constriction injury (CCI) model and the rat streptozotocin model of diabetic peripheral neuropathy. Using a nonbrain-penetrant AAK1 inhibitor and local administration of an AAK1 inhibitor, the relevant pool of AAK1 for antineuropathic action was found to be in the spinal cord. Consistent with these results, AAK1 inhibitors dose-dependently reduced the increased spontaneous neural activity in the spinal cord caused by CCI and blocked the development of windup induced by repeated electrical stimulation of the paw. The mechanism of AAK1 antinociception was further investigated with inhibitors of α2 adrenergic and opioid receptors. These studies showed that α2 adrenergic receptor inhibitors, but not opioid receptor inhibitors, not only prevented AAK1 inhibitor antineuropathic action in behavioral assays, but also blocked the AAK1 inhibitor–induced reduction in spinal neural activity in the rat CCI model. Hence, AAK1 inhibitors are a novel therapeutic approach to neuropathic pain with activity in animal models that is mechanistically linked (behaviorally and electrophysiologically) to α2 adrenergic signaling, a pathway known to be antinociceptive in humans.

Multiple endogenous compounds have been proposed as candidate biomarkers to monitor organic anion transporting polypeptide (OATP) function in preclinical species or humans. Previously, we demonstrated that coproporphyrins (CPs) I and III are appropriate clinical markers to evaluate OATP inhibition and recapitulate clinical drug-drug interactions (DDIs). In the present study, we investigated bile acids (BAs) dehydroepiandrosterone sulfate (DHEAS), hexadecanedioate (HDA), and tetradecanedioate (TDA) in plasma as endogenous probes for OATP inhibition and compared these candidate probes to CPs. All probes were determined in samples from a single study that examined their behavior and their association with rosuvastatin (RSV) pharmacokinetics after administration of an OATP inhibitor rifampin (RIF) in healthy subjects. Among endogenous probes examined, RIF significantly increased maximum plasma concentration () and area under the concentration-time curve (AUC) of fatty acids HDA and TDA by 2.2- to 3.2-fold. For the 13 bile acids in plasma examined, no statistically significant changes were detected between treatments. Changes in plasma DHEAS did not correlate with OATP1B inhibition by RIF. On the basis of the magnitude of effects for the endogenous compounds that demonstrated significant changes from baseline over interindividual variations, the overall rank order for the AUC change was found to be CP I > CP III > HDA ≈ TDA ≈ RSV > > BAs. Collectively, these results reconfirmed that CPs are novel biomarkers suitable for clinical use. In addition, HDA and TDA are useful for OATP functional assessment. Since these endogenous markers can be monitored in conjunction with pharmacokinetics analysis, the CPs and fatty acid dicarboxylates, either alone or in combination, offer promise of earlier diagnosis and risk stratification for OATP-mediated DDIs.