Novel coumarins and 2-thioxo-coumarins as inhibitors of the tumor-associated carbonic anhydrases IX and XII

A series of coumarins incorporating tert-butyl-dimethylsilyloxy- or allyoxy- moieties in positions 4-, 6 or 7 of the heterocyclic ring have been synthesized and then converted to the corresponding 2-thioxo-coumarins. Other derivatives incorporating hydroxyethyloxy-, tosylethoxy- and 2-fluroethyloxy- moieties in position 7 of the coumarin ring were synthesized together with derivatives of 4-methyl-7-amino coumarin incorporating acetamido, 3,5-dimethylphenylureido- and tert-butyloxycarbonylamido functionalities. All these compounds were assayed as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The human (h) cytosolic isoforms hCA I and II were weakly inhibited (hCA I) or not inhibited at all (hCA II) by these (thioxo)coumarins whereas the tumor-associated transmembrane isoforms hCA IX and XII were inhibited with efficiencies from the submicromolar to the low micromolar range by many of these derivatives. The structure-activity relationship for these classes of less investigated CA inhibitors are delineated, with the potential of using them as leads to obtain isoform-selective inhibitors with excellent affinity for CA IX and XII (validated antitumor targets) which do not significantly inhibit the cytosolic offtarget isoforms hCA I and II.     

Identification of MK-5710 ((8aS)-8a-methyl-1,3-dioxo-2-[(1S,2R)-2-phenylcyclo- propyl]-N-(1-phenyl-1H-pyrazol-5-yl)hexahydro-imidazo[1,5-a]pyrazine-7(1H)-carboxamide), a potent smoothened antagonist for use in Hedgehog pathway dependent malignancies, part 2

The Hedgehog (Hh-) signaling pathway is a key developmental pathway which gets reactivated in many human tumors, and smoothened (Smo) antagonists are emerging as novel agents for the treatment of malignancies dependent on the Hh-pathway, with the most advanced compounds demonstrating encouraging results in initial clinical trials. A novel series of potent bicyclic hydantoin Smo antagonists was reported in the preceding article, these have been resolved, and optimized to identify potent homochiral derivatives with clean off-target profiles and good pharmacokinetic properties in preclinical species. While showing in vivo efficacy in mouse allograft models, unsubstituted bicyclic tetrahydroimidazo[1,5-a]pyrazine-1,3(2H,5H)-diones were shown to epimerize in plasma. Alkylation of the C-8 position blocks this epimerization, resulting in the identification of MK-5710 (47) which was selected for further development.     

Role of spike-frequency adaptation in shaping neuronal response to dynamic stimuli

Spike-frequency adaptation is the reduction of a neuron’s firing rate to a stimulus of constant intensity. In the locust, the Lobula Giant Movement Detector (LGMD) is a visual interneuron that exhibits rapid adaptation to both current injection and visual stimuli. Here, a reduced compartmental model of the LGMD is employed to explore adaptation’s role in selectivity for stimuli whose intensity changes with time. We show that supralinearly increasing current injection stimuli are best at driving a high spike count in the response, while linearly increasing current injection stimuli (i.e., ramps) are best at attaining large firing rate changes in an adapting neuron. This result is extended with in vivo experiments showing that the LGMD’s response to translating stimuli having a supralinear velocity profile is larger than the response to constant or linearly increasing velocity translation. Furthermore, we show that the LGMD’s preference for approaching versus receding stimuli can partly be accounted for by adaptation. Finally, we show that the LGMD’s adaptation mechanism appears well tuned to minimize sensitivity for the level of basal input. This article is part of a special issue on Neuronal Dynamics of Sensory Coding.