Correlation of indoleamine-2,3-dioxigenase 1 inhibitory activity of 4,6-disubstituted indazole derivatives and their heme binding affinity.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-containing enzyme that acts on the first and rate-limiting step of the tryptophan/kynurenine pathway. Since the pathway is one of the means of cancer immune evasion, IDO1 inhibitors have drawn interest as potential therapeutics for cancers. We found a 4,6-disubstituted indazole 1 as a hit compound that showed both IDO1 inhibitory activity and binding affinity for IDO1 heme. Structural modification of 1 yielded compound 6, whose relatively large substituent at the 4-position and proper size substituent at the 6-position were found to be important for the enhancement of IDO1 inhibitory activity and heme affinity. A series of compounds synthesized in this work were evaluated by in silico docking simulations and by in vitro experiments using a C129Y mutant of the pocket-A of IDO1. Our results revealed that proper substituents at the 6- and 4-positions of the compounds interact with pockets A and B, respectively, and that, in particular, a good fit in pocket-A is important for the compounds' biological activities. Absorption spectral analysis of these compounds showed that they strongly bound to the ferrous heme rather than its ferric heme. Furthermore, we observed that the heme affinities of these compounds strongly correlate with their IDO1 inhibitory activities.

Evaluation of Brown Adipose Tissue Using Near-Infrared Time-Resolved Spectroscopy.

Human brown adipose tissue (BAT) activity (SUVmax) has been typically evaluated by 18F-fluorodeoxy glucose (FDG)-positron emission tomography (PET) combined with computed tomography (CT). In this study, the objective was to detect human BAT by near-infrared time-resolved spectroscopy (NIRTRS), a noninvasive and simple method for measuring total hemoglobin concentration [total-Hb] and reduced scattering coefficient (µs') in the tissue. The [total-Hb] in the supraclavicular region of the BAT (+) (SUVmax≥2.0) group was 95.0±28.2 µM (mean+/-SD), which was significantly higher than that of the BAT (-) (SUVmax<2.0) group (52.0±14.8 µM), but not in other regions apart from the BAT deposits. The µs' in the supraclavicular region of the BAT (+) group was 8.4±1.7 cm(-1), which was significantly higher than that of BAT (-) group (4.3±1.0 cm(-1)), but not in other regions. The area under the receiver operating characteristic curve closest to (0, 1) for [total-Hb] and µs' to discriminate BAT (+) from BAT (-) was 72.5 µM and 6.3 cm(-1), respectively. The sensitivity, specificity, and accuracy for both parameters were 87.5, 100, and 93.3%, respectively. Our novel NIRTRS method is noninvasive, simple, and inexpensive compared with FDG-PET/CT, and is reliable for detecting human BAT.