Discovery of a potent, orally available tricyclic derivative as a novel BRD4 inhibitor for melanoma.

The epigenetic regulation of the protein bromodomain-containing protein 4 (BRD4) has emerged as a compelling target for cancer treatment. In this study, we outline the discovery of a novel BRD4 inhibitor for melanoma therapy. Our initial finding was that benzimidazole derivative 1, sourced from our library, was a powerful BRD4 inhibitor. However, it exhibited a poor pharmacokinetic (PK) profile. To address this, we conducted a scaffold-hopping procedure with derivative 1, which resulted in the creation of benzimidazolinone derivative 5. This new derivative displayed an improved PK profile. To further enhance the BRD4 inhibitory activity, we attempted to introduce hydrogen bond acceptors. This indeed improved the activity, but at the cost of decreased membrane permeability. Our search for a potent inhibitor with desirable permeability led to the development of tricyclic 18. This compound demonstrated powerful inhibitory activity and a favorable PK profile. More significantly, tricyclic 18 showed antitumor efficacy in a mouse melanoma xenograft model, suggesting that it holds potential as a therapeutic agent for melanoma treatment.

Holocrine Secretion Occurs outside the Tight Junction Barrier in Multicellular Glands: Lessons from Claudin-1-Deficient Mice.

Holocrine secretion is a specific mode of secretion involving secretion of entire cytoplasmic materials with remnants of dead cells, as observed in multicellular exocrine glands of reptiles, birds, and mammals. Here, we found that sebaceous glands in mice, representative of multicellular exocrine glands of mammals, exhibit a form of polarized stratified epithelium equipped with tight junctions (TJs), and found that holocrine secretion occurred outside the TJ barriers. Sebaceous glands share characteristics of stratified epithelia with interfollicular epidermis, including basal-layer-restricted cell proliferation, TJ barrier formation at a specific single layer of cells with apico-basolateral plasma membrane polarity, and cell death outside the TJ barrier. Knockout of claudin-1, a transmembrane adhesive protein in TJs, in mice caused leakage of the TJ barrier in sebaceous glands and incomplete degradation of the plasma membrane and nuclei during holocrine secretion. Claudin-1 knockout resulted in the accumulation of incompletely degenerated sebocytes in sebaceous ducts, suggesting that the TJ barrier was necessary for differentiation of holocrine secretion. The redefinition of sebaceous glands as TJ-forming stratified epithelia provides an important framework to understand the molecular mechanism of holocrine secretion.

Collapse of the keratin filament network through the expression of mutant keratin 6c observed in a case of focal plantar keratoderma.

Focal palmoplantar keratoderma (PPK) with severe pain is a hallmark of pachyonychia congenita, a rare autosomal dominant disorder involving PPK and hypertrophic nail dystrophy. Some families present focal PPK with either minimal or no nail changes. Dominant-negative mutations in any of the four identified keratin genes, KRT6A, KRT6B, KRT16 or KRT17, lead to pachyonychia congenita. However, the majority of families with focal PPK showing minimal or no nail changes do not harbor mutations in these genes. Recently, mutations of KRT6C were identified in families with focal PPK alone. Here, we report a 26-year-old Japanese man with focal plantar hyperkeratosis that developed at approximately 10 years of age with no palmar involvement and no nail alterations. We identified a missense KRT6C mutation c.1414G>A resulting in an p.Glu472Lys substitution, as reported in other Japanese patients. When the mutant keratin 6c protein is exogenously expressed in human HaCaT cells, a collapse of the keratin filament network is observed in a dose-dependent manner, suggesting the mutation has a dominant-negative effect on keratin filament network formation. The mutated residue is located at the helix termination motif of keratin 6c. The peptide sequence around this residue is highly conserved among type II, III and IV intermediate filament proteins. Glu to Lys mutations of the equivalent residue have been reported in a variety of inherited diseases, including neurodegenerative diseases, corneal dystrophy and skin disorders, suggesting that this residue is vital to keratin function.