[18F]BTK-1: A Novel Positron Emission Tomography Tracer for Imaging Bruton's Tyrosine Kinase

PURPOSE

Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signaling, and as such a critical regulator of cell proliferation and survival. Aberrant BCR signaling is important in the pathogenesis of various B cell malignancies and autoimmune disorders. Here, we describe the development of a novel positron emission tomography (PET) tracer for imaging BTK expression and/or occupancy by small molecule therapeutics.

METHODS

Radiochemistry was carried out by reacting the precursor with [¹⁸F]fluoride on a GE FX-FN TracerLab synthesis module to produce [¹⁸F]BTK-1 with a 6% decay-corrected radiochemical yield, 100 ± 6 GBq/µmol molar activity, and a radiochemical purity of 99%. Following intravenous administration of [¹⁸F]BTK-1 (3.63 ± 0.59 MBq, 0.084 ± 0.05 µg), 60-min dynamic images were acquired in two xenograft models: REC-1, an efficacious mantle cell lymphoma model, and U87MG, a non-efficacious glioblastoma model. Subsequent studies included vehicle, pretreatment (10 min prior to tracer injection), and displacement (30 min post-tracer injection) studies with different reversible BTK inhibitors to examine BTK binding. Human radiation dosimetry was estimated based on PET imaging in healthy rats.

RESULTS

Uptake of [¹⁸F]BTK-1 was significantly higher in BTK expressing REC-1 tumors than non-BTK expressing U87MG tumors. Administration of BTK inhibitors prior to tracer administration blocked [¹⁸F]BTK-1 binding in the REC-1 tumor model consistent with [¹⁸F]BTK-1 binding to BTK. The predicted effective dose in humans was 0.0199 ± 0.0007 mSv/MBq.

CONCLUSION

[¹⁸F]BTK-1 is a promising PET tracer for imaging of BTK, which could provide valuable information for patient selection, drug dose determination, and improving our understanding of BTK biology in humans.

Synthesis of [H-3]- and [C-14]-labeled elagolix

Gonadotropin-releasing hormone (GnRH) receptor antagonists are an important class of compounds designed to block the pituitary gland from synthesizing follicle-stimulating hormone and luteinizing hormone for the treatment of sex hormone dependent disorders. Elagolix (ABT-620) is currently approved for the treatment of pain associated with endometriosis and as a combination with estradiol and norethindrone acetate is approved for management of heavy menstrual bleeding due to uterine fibroids. In order to support the development of elagolix, we prepared [³ H]elagolix for preclinical metabolism studies and [¹⁴ C]elagolix for environmental risk assessment studies.

Clostridioides difficile carriage in animals and the associated changes in the host fecal microbiota

The relationship between the gut microbiota and Clostridioides difficile, and its role in the severity of C. difficile infection in humans is an area of active research. Intestinal carriage of toxigenic and non-toxigenic C. difficile strains, with and without clinical signs, is reported in animals, however few studies have looked at the risk factors associated with C. difficile carriage and the role of the host gut microbiota. Here, we isolated and characterized C. difficile strains from different animal species (predominantly canines (dogs), felines (cats), and equines (horses)) that were brought in for tertiary care at North Carolina State University Veterinary Hospital. C. difficile strains were characterized by toxin gene profiling, fluorescent PCR ribotyping, and antimicrobial susceptibility testing. 16S rRNA gene sequencing was done on animal feces to investigate the relationship between the presence of C. difficile and the gut microbiota in different hosts. Here, we show that C. difficile was recovered from 20.9% of samples (42/201), which included 33 canines, 2 felines, and 7 equines. Over 69% (29/42) of the isolates were toxigenic and belonged to 14 different ribotypes including ones known to cause CDI in humans. The presence of C. difficile results in a shift in the fecal microbial community structure in both canines and equines. Commensal Clostridium hiranonis was negatively associated with C. difficile in canines. Further experimentation showed a clear antagonistic relationship between the two strains in vitro, suggesting that commensal Clostridia might play a role in colonization resistance against C. difficile in different hosts.

Strain-Dependent Inhibition of Clostridioides difficile by Commensal Clostridia Carrying the Bile Acid-Inducible (bai) Operon

Clostridioides difficile is one of the leading causes of antibiotic-associated diarrhea. Gut microbiota-derived secondary bile acids and commensal Clostridia that carry the bile acid-inducible (bai) operon are associated with protection from C. difficile infection (CDI), although the mechanism is not known. In this study, we hypothesized that commensal Clostridia are important for providing colonization resistance against C. difficile due to their ability to produce secondary bile acids, as well as potentially competing against C. difficile for similar nutrients. To test this hypothesis, we examined the abilities of four commensal Clostridia carrying the bai operon (Clostridium scindens VPI 12708, C. scindens ATCC 35704, Clostridium hiranonis, and Clostridium hylemonae) to convert cholate (CA) to deoxycholate (DCA) in vitro, and we determined whether the amount of DCA produced was sufficient to inhibit the growth of a clinically relevant C. difficile strain. We also investigated the competitive relationships between these commensals and C. difficile using an in vitro coculture system. We found that inhibition of C. difficile growth by commensal Clostridia supplemented with CA was strain dependent, correlated with the production of ∼2 mM DCA, and increased the expression of bai operon genes. We also found that C. difficile was able to outcompete all four commensal Clostridia in an in vitro coculture system. These studies are instrumental in understanding the relationship between commensal Clostridia and C. difficile in the gut, which is vital for designing targeted bacterial therapeutics. Future studies dissecting the regulation of the bai operon in vitro and in vivo and how this affects CDI will be important.IMPORTANCE Commensal Clostridia carrying the bai operon, such as C. scindens, have been associated with protection against CDI; however, the mechanism for this protection is unknown. Herein, we show four commensal Clostridia that carry the bai operon and affect C. difficile growth in a strain-dependent manner, with and without the addition of cholate. Inhibition of C. difficile by commensals correlated with the efficient conversion of cholate to deoxycholate, a secondary bile acid that inhibits C. difficile germination, growth, and toxin production. Competition studies also revealed that C. difficile was able to outcompete the commensals in an in vitro coculture system. These studies are instrumental in understanding the relationship between commensal Clostridia and C. difficile in the gut, which is vital for designing targeted bacterial therapeutics.

Metabolism and Disposition of a Novel Selective α7 Neuronal Acetylcholine Receptor Agonist ABT-126 in Humans: Characterization of the Major Roles for Flavin-Containing Monooxygenases and UDP-Glucuronosyl Transferase 1A4 and 2B10 in Catalysis

Mass balance, metabolism, and excretion of ABT-126, an α7 neuronal acetylcholine receptor agonist, were characterized in healthy male subjects (n = 4) after a single 100-mg (100 μCi) oral dose. The total recovery of the administered radioactivity was 94.0% (±2.09%), with 81.5% (±10.2%) in urine and 12.4% (±9.3%) in feces. Metabolite profiling indicated that ABT-126 had been extensively metabolized, with 6.6% of the dose remaining as unchanged parent drug in urine. Parent drug accounted for 12.2% of the administered radioactivity in feces. The primary metabolic transformations of ABT-126 involved aza-adamantane N-oxidation (M1, 50.3% in urine) and aza-adamantane N-glucuronidation (M11, 19.9% in urine). M1 and M11 were also major circulating metabolites, accounting for 32.6% and 36.6% of the drug-related material in plasma, respectively. These results demonstrated that ABT-126 is eliminated primarily by hepatic metabolism, followed by urinary excretion. Enzymatic studies suggested that M1 formation is mediated primarily by human liver flavin-containing monooxygenase (FMO)3 and, to a lesser extent, by human kidney FMO1; M11 is generated mainly by human uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A4, whereas UGT 2B10 also contributes to ABT-126 glucuronidation. Species-dependent formation of M11 was observed in hepatocytes; M11 was formed in human and monkey hepatocytes, but not in rat and dog hepatocytes, suggesting that monkeys constitute an appropriate model for predicting the fate of compounds undergoing significant N-glucuronidation. M1 and M11 are not expected to have clinically relevant on- or off-target pharmacologic activities. In summary, this study characterized ABT-126 metabolites in the circulation and excreta and the primary elimination pathways of ABT-126 in humans.

Intensive mobility training postcerebral hemispherectomy: early surgery shows best functional improvements

BACKGROUND

Limited research exists on rehabilitative techniques focused on reducing disabilities after cerebral hemispherectomy despite persistent hemiparesis.

OBJECTIVES

The efficacy of Intensive Mobility Training (IMT) for improving gait, balance and mobility was evaluated in patients after cerebral hemispherectomy and compared with clinical variables for signs of developmental neuroplasticity.

METHODS

Participants (N.=19; 13.8±5.7 years) postcerebral hemispherectomy received IMT, three hours/day for 10 days. Outcomes measures were assessed pre- and post-intervention using the GAITRite electronic walkway® (velocity, toe in/out, step length of affected an unaffected leg), Dynamic Gait Index, Fugl-Meyer Scale, Berg Balance Scale, Timed Up and Go and Six-Minute Walk Test. Six of the nine measures that showed moderate effect sizes were incorporated into a Combined Functional Index (CFI) to assess global impact of therapy.

RESULTS

After IMT, improvements were identified for toe in/out, step length of unaffected leg, Dynamic Gait Index, Berg Balance Scale and Six-Minute Walk (P<0.05; Effect Size 0.36-0.50). Using CFI for these six measures, patients improved from 77.3% to 82.7% (+5.3±3.7%) of normal following IMT. Improvements in CFI were greater in patients five years or younger at time of surgery (+7.7±3.6%) compared with older patients (+3.2±2.5%), and this accounted for 22% of variability in the change in score.

CONCLUSION

The younger the participant at time of surgery correlated with the greatest improvements following IMT. These findings support the concept that the remaining hemisphere retains greater neuroplasticity if the contralateral surgery occurs earlier in cerebral development.