Novel Platform for Predicting Drug Effects in Patients with Acromegaly: Translational Exposure-Response Evaluation of Growth Hormone-Inhibitory Effect of Octreotide after Growth Hormone-Releasing Hormone Stimulation.

Acromegaly is a chronic systemic disease characterized by facial and peripheral changes caused by soft tissue overgrowth and is associated with multiple comorbidities. Despite available surgical and medical therapies, suitable treatments for acromegaly are still lacking. Efficient drug development requires an understanding of the exposure-response (E-R) relationship based on nonclinical and early clinical studies. We aimed to establish a platform to facilitate the development of novel drugs to treat acromegaly. We evaluated the E-R relationship of the growth hormone (GH)-inhibitory effect of the somatostatin analog octreotide under growth hormone-releasing hormone + arginine stimulation in healthy participants and compared the results with historical data for patients with acromegaly. This randomized five-way crossover study included two placebo and three active-treatment periods with different doses of octreotide acetate. GH secretion in the two placebo periods was comparable, which confirmed the reproducibility of the response with no carryover effect. GH secretion was inhibited by low-, medium-, and high-dose octreotide acetate in a dose-dependent manner. We also examined the E-R relationship in monkeys as a preclinical drug evaluation study and in rats as a more convenient and simple system for screening candidate drugs. The E-R relationships and EC50 values were similar among animals, healthy participants, and patients with acromegaly, which suggests that GH stimulation studies in early research and development allowed simulation of the drug response in patients with acromegaly. SIGNIFICANCE STATEMENT: This study demonstrated similar exposure-response relationships in terms of the growth hormone-inhibitory effect of octreotide after growth hormone-releasing hormone stimulation among healthy participants, monkeys, and rats. The research methods and analyses utilized in this study will be useful for simulating the dosages and therapeutic effects of drugs for acromegaly and will facilitate the research and development of novel therapeutic agents with similar modes of action.

Design, synthesis, and biological evaluation of novel somatostatin receptor subtype-2 agonists: Optimization for potency and risk mitigation of hERG and phospholipidosis.

Somatostatin receptors are members of G-protein coupled receptor superfamily. Receptors can be classified into five subtypes, SSTR1 to 5. The highly potent and orally active SSTR2 agonist 7, which had been identified by our group, was found out to have toxicological liabilities such as hERG inhibition and phospholipidosis (PLD). We investigated the relationship between in silico physicochemical properties and hERG and PLD, and explored well-balanced agonists to identify amide 19 and benzimidazole 30. As a result of this exploration, we found out that the value of (cLogP) [2] + (pKa) [2] needs to be less than 110 to mitigate the liabilities.

Discovery and SAR Studies of Orally Active Somatostatin Receptor Subtype-2 (SSTR2) Agonists for the Treatment of Acromegaly.

Acromegaly is a disease caused by the oversecretion of growth hormone. It is currently treated by intravenous injection with cyclic peptide drugs that activate somatostatin receptor subtype 2 (SSTR2). Here, novel nonpeptidic, small-molecule, and orally active SSTR2 agonists were identified from a hit compound (13). Pharmacophore studies enabled scaffold hopping to obtain a unique 3,4,5-trisubstituted pyridine motif. Further optimization conferred potent SSTR2 agonistic activity and metabolic stability. Several compounds were evaluated and these showed good oral pharmacokinetic profiles in rats, and one representative compound (25) showed highly potent inhibition of growth hormone secretion induced by growth hormone-releasing hormone in rats. Based on these results, 25 was identified as a promising lead for further optimization. A structure-activity relationship (SAR) study and the metabolic stability data for this compound are also described.

Endogenous prostaglandin E2 inhibits aberrant overgrowth of rheumatoid synovial tissue and the development of osteoclast activity through EP4 receptor.

OBJECTIVE: We recently developed an ex vivo cellular model of pannus, the aberrant overgrowth of human synovial tissue. This study was undertaken to use that model to investigate the role of prostaglandin E2 (PGE2) and its receptor subtypes in the development of pannus growth and osteoclast activity in rheumatoid arthritis (RA). METHODS: Inflammatory cells that infiltrated pannus from patients with RA were collected without enzyme digestion and designated synovial tissue-derived inflammatory cells. Their single-cell suspensions were cultured in medium alone to observe an aberrant overgrowth of inflammatory tissue in vitro. Levels of cytokines produced in culture supernatants were measured using enzyme-linked immunosorbent assay kits. Osteoclast activity was assessed by the development of resorption pits in calcium phosphate-coated slides. RESULTS: Primary culture of the synovial tissue-derived inflammatory cells resulted in spontaneous reconstruction of inflammatory tissue in vitro within 4 weeks, during which tumor necrosis factor α, PGE2, macrophage colony-stimulating factor, and matrix metalloproteinase 9 were produced in the supernatant. This aberrant overgrowth was inhibited by antirheumatic drugs including methotrexate and infliximab. On calcium phosphate-coated slides, synovial tissue-derived inflammatory cells showed numerous resorption pits. In the presence of inhibitors of endogenous prostanoid production such as indomethacin and NS398, exogenous PGE1 and EP4-specific agonists significantly inhibited all these activities of synovial tissue-derived inflammatory cells in a dose-dependent manner. Addition of indomethacin, NS398, or EP4-specific antagonist resulted in the enhancement of these cells' activities. EP2-specific agonist had a partial effect, while EP1- and EP3-specific agonists had no significant effects. CONCLUSION: These results suggest that endogenous PGE2 produced in rheumatoid synovium negatively regulates aberrant synovial overgrowth and the development of osteoclast activity via EP4.

Analysis of the mechanism regulating the stability of rat macrophage inflammatory protein-2 mRNA in RBL-2H3 cells.

Using rat peritoneal neutrophils, the complete nucleotide sequence of rat macrophage inflammatory protein-2 (MIP-2) mRNA including 5'untranslated region (UTR) and 3'UTR was determined (GenBank Accession number, AB060092). It was found that the MIP-2 mRNA has a 70 bp 5'UTR, a 303 bp coding region and a 728 bp 3'UTR which contains adenylate/uridylate (AU)-rich areas defined as AU-rich elements (AREs). Site-directed mutagenesis studies using the tetracycline-sensitive transactivator protein-expressing rat basophilic leukemia cells (RBL-2H3-TO cells) revealed that MIP-2 mRNA mutants which lack the 3'UTR are more stable than MIP-2-wild-type (wt) mRNA. A MIP-2 mRNA mutant in which some mutations were introduced to the ARE was also stable. The stability of MIP-2 mRNA was low in untreated RBL-2H3-TO cells, but it increased in the antigen-stimulated immunoglobulin E (IgE)-sensitized cells. The antigen-induced MIP-2 mRNA stabilization was counteracted by the highly specific p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 and the MAPK/ERK kinase (MEK-1) inhibitor PD98059. These findings indicate that ARE is the cis-element which mediates the rapid decay of MIP-2 mRNA, and the antigen stimulation stabilizes MIP-2 mRNA and the p38 MAPK and p44/42 MAPK pathways are involved in the antigen-induced stabilization of MIP-2 mRNA.