Design and Evaluation of [18F]CHDI-650 as a Positron Emission Tomography Ligand to Image Mutant Huntingtin Aggregates.

Therapeutic interventions are being developed for Huntington's disease (HD), a hallmark of which is mutant huntingtin protein (mHTT) aggregates. Following the advancement to human testing of two [11C]-PET ligands for aggregated mHTT, attributes for further optimization were identified. We replaced the pyridazinone ring of CHDI-180 with a pyrimidine ring and minimized off-target binding using brain homogenate derived from Alzheimer's disease patients. The major in vivo metabolic pathway via aldehyde oxidase was blocked with a 2-methyl group on the pyrimidine ring. A strategically placed ring-nitrogen on the benzoxazole core ensured high free fraction in the brain without introducing efflux. Replacing a methoxy pendant with a fluoro-ethoxy group and introducing deuterium atoms suppressed oxidative defluorination and accumulation of [18F]-signal in bones. The resulting PET ligand, CHDI-650, shows a rapid brain uptake and washout profile in non-human primates and is now being advanced to human testing.

Spirocycle MmpL3 Inhibitors with Improved hERG and Cytotoxicity Profiles as Inhibitors of Mycobacterium tuberculosis Growth.

With the emergence of multi-drug-resistant strains of Mycobacterium tuberculosis, there is a pressing need for new oral drugs with novel mechanisms of action. A number of scaffolds with potent anti-tubercular in vitro activity have been identified from phenotypic screening that appear to target MmpL3. However, the scaffolds are typically lipophilic, which facilitates partitioning into hydrophobic membranes, and several contain basic amine groups. Highly lipophilic basic amines are typically cytotoxic against mammalian cell lines and have associated off-target risks, such as inhibition of human ether-à-go-go related gene (hERG) and IKr potassium current modulation. The spirocycle compound 3 was reported to target MmpL3 and displayed promising efficacy in a murine model of acute tuberculosis (TB) infection. However, this highly lipophilic monobasic amine was cytotoxic and inhibited the hERG ion channel. Herein, the related spirocycles (1-2) are described, which were identified following phenotypic screening of the Eli Lilly corporate library against M. tuberculosis. The novel N-alkylated pyrazole portion offered improved physicochemical properties, and optimization led to identification of a zwitterion series, exemplified by lead 29, with decreased HepG2 cytotoxicity as well as limited hERG ion channel inhibition. Strains with mutations in MmpL3 were resistant to 29, and under replicating conditions, 29 demonstrated bactericidal activity against M. tuberculosis. Unfortunately, compound 29 had no efficacy in an acute model of TB infection; this was most likely due to the in vivo exposure remaining above the minimal inhibitory concentration for only a limited time.

Essential but Not Vulnerable: Indazole Sulfonamides Targeting Inosine Monophosphate Dehydrogenase as Potential Leads against Mycobacterium tuberculosis.

A potent, noncytotoxic indazole sulfonamide was identified by high-throughput screening of >100,000 synthetic compounds for activity against Mycobacterium tuberculosis (Mtb). This noncytotoxic compound did not directly inhibit cell wall biogenesis but triggered a slow lysis of Mtb cells as measured by release of intracellular green fluorescent protein (GFP). Isolation of resistant mutants followed by whole-genome sequencing showed an unusual gene amplification of a 40 gene region spanning from Rv3371 to Rv3411c and in one case a potential promoter mutation upstream of guaB2 (Rv3411c) encoding inosine monophosphate dehydrogenase (IMPDH). Subsequent biochemical validation confirmed direct inhibition of IMPDH by an uncompetitive mode of inhibition, and growth inhibition could be rescued by supplementation with guanine, a bypass mechanism for the IMPDH pathway. Beads containing immobilized indazole sulfonamides specifically interacted with IMPDH in cell lysates. X-ray crystallography of the IMPDH-IMP-inhibitor complex revealed that the primary interactions of these compounds with IMPDH were direct pi-pi interactions with the IMP substrate. Advanced lead compounds in this series with acceptable pharmacokinetic properties failed to show efficacy in acute or chronic murine models of tuberculosis (TB). Time-kill experiments in vitro suggest that sustained exposure to drug concentrations above the minimum inhibitory concentration (MIC) for 24 h were required for a cidal effect, levels that have been difficult to achieve in vivo. Direct measurement of guanine levels in resected lung tissue from tuberculosis-infected animals and patients revealed 0.5-2 mM concentrations in caseum and normal lung tissue. The high lesional levels of guanine and the slow lytic, growth-rate-dependent effect of IMPDH inhibition pose challenges to developing drugs against this target for use in treating TB.

Tetrahydroxanthones by sequential Pd-catalyzed C-O and C-C bond construction and use in the identification of the "antiausterity" pharmacophore of the kigamicins.

Readily available C-acylated cycloalkanones undergo efficient Pd catalyzed ring closure/cross-coupling providing 7-substituted tetrahydroxanthones in a single operation. One of the synthesized derivatives (depicted) is shown to selectively kill pancreatic cancer (PANC-1) cells under conditions of nutrient deprivation indicating that the tetrahydroxanthone is responsible, in part, for the "antiausterity" effects of the naturally occurring kigamicins.