大島 将

Guanosine triphosphate (GTP) is increasingly recognized as a critical actor in cancer cell proliferation, yet its regulatory mechanism remains incompletely defined. A key contributor to elevated GTP levels in tumors is inosine monophosphate dehydrogenase 2 (IMPDH2), a rate-limiting enzyme in the de novo guanine nucleotide biosynthetic pathway. Although IMPDH inhibitors, mycophenolic acid (MPA) and mycophenolate mofetil (MMF), have shown potential in cancer therapies, their success has been limited due to their immunosuppressive side effects and several unresolved regulatory mechanisms, including paradoxical control of IMPDH activity by GTP. This review provides a systematic summary of the current understanding of IMPDH biology, emphasizing its complex regulation and therapeutic relevance in cancer. We will outline key unresolved questions, including isozyme-specific roles and mechanisms for escaping regulation, and propose mechanistic and translational strategies to design IMPDH-targeted cancer therapies.

There is currently a global epidemic of obesity and obesity-related diseases such as type 2 diabetes due to decreased physical activity, excessive food intake, and/or genetic predisposition. The Hippo-YAP1 pathway has attracted attention as a potential therapeutic target because YAP1/TAZ activation in murine immature adipocytes in vitro suppresses their differentiation by inhibiting PPARγ activity. However, the role of YAP1 activation in mature adipocytes in vivo remains unclear. MOB1, whose expression is increased in obesity, is the hub of the Hippo core molecule complex and negatively regulates YAP1/TAZ activation. Therefore, we generated aMob1DKO mutant mice, which feature deficiency of Mob1a/b specifically in mature adipocytes. Compared to controls, aMob1DKO mice subjected to a high-fat diet showed beneficial changes consistent with resistance to diet-induced obesity. The mutants exhibited increases in basal lipolysis, "beiging," and energy expenditure, as well as suppression of ROS production and inflammation in white adipose tissue. Insulin sensitivity and glucose tolerance were improved, and ectopic fat accumulation was reduced. Most of these changes were dependent on the YAP1 activation observed in mature white adipose tissue of aMob1DKO mice. FGF21, which improves lipid metabolism, was upregulated directly via YAP1 activation, and many of the phenotypes seen in aMob1DKO mice were also dependent on FGF21. Thus, the aMob1DKO mouse is an interesting model for the study of the metabolic effects of diet-induced obesity and protection against diabetes. Our work suggests that a YAP1-FGF21 axis exists in adipocytes that may be a potential therapeutic target for obesity.

Phosphatidylinositol 5-phosphate 4-kinases (PI5P4K), also known as type II PIPKs or PIPKIIs, convert the lipid second messenger PI5P to PI(4,5)P2. The PI5P4K family consists of three isozymes in mammals-PI5P4Kα, β, and γ-which notably utilize both GTP and ATP as phosphodonors. Unlike the other two isozymes, which can utilize both ATP and GTP, PI5P4Kβ exhibits a marked preference for GTP over ATP, acting as an intracellular GTP sensor that alters its kinase activity in response to physiological changes in GTP concentration. Knockout studies have demonstrated a critical role for PI5P4Kα and β in tumorigenesis, while PI5P4Kγ has been implicated in regulating immune and neural systems. Pharmacological targeting of PI5P4K holds promise for the development of new therapeutic approaches against cancer, immune dysfunction, and neurodegenerative diseases. Although several PI5P4K inhibitors have already been developed, challenges remain in PI5P4K inhibitor development, including a discrepancy between in vitro and cellular efficacy. This discrepancy is attributable to mainly three factors. (a) Most PI5P4K inhibitors were developed at low ATP levels, where these enzymes exhibit minimal activity. (b) Non-catalytic functions of PI5P4K require careful interpretation of PI5P4K depletion studies, as their scaffolding roles suppress class I PI3K signaling. (c) The lack of pharmacodynamic markers for in vivo assessment complicates efficacy assessment. To address these issues and promote the development of effective and targeted therapeutic strategies, this review provides an analytical overview of the distinct roles of individual isozymes and recent developments in PI5P4K inhibitors, emphasizing structural insights and the importance of pharmacodynamic marker identification.

This study aimed to identify the predictive factors associated with the oncological outcomes of metastatic hormone-sensitive prostate cancer-related genes. A nomogram for predicting prostate cancer-specific survival (CSS) was constructed based on biopsy samples obtained from 103 patients with metastatic hormone-sensitive prostate cancer. We analyzed the association between clinical data and mRNA expression levels. The nomogram was externally validated in another cohort (n = 50) by using a concordance index. Based on the cutoff value, determined by a receiver operating characteristic analysis, longer CSS was observed in the high osteoglycin and androgen receptor expression level groups (> 1.133 and > 0.00; median CSS, 85.3 vs. 52.7 months, p = 0.045, and 69.1 vs. 32.1 months, p = 0.034, respectively), compared with that of the low expression level groups. The nomogram predicting CSS included hemoglobin (≥ 13.7 g/dL or < 13.7 g/dL), serum albumin (≥ 3.1 g/dL or < 3.1 g/dL), serum lactate dehydrogenase (≥ 222 IU/L or < 222 IU/L), total Japan Cancer of the Prostate Risk Assessment score, androgen receptor expression level, and osteoglycin expression level. The concordance indices for the internal and external validations were 0.664 and 0.798, respectively. In this study, a nomogram that integrated the expression levels of androgen receptors and osteoglycin to predict CSS in metastatic hormone-sensitive prostate cancer was established.