CC-401 Promotes ß-Cell Replication via Pleiotropic Consequences of DYRK1A/B Inhibition.

Pharmacologic expansion of endogenous ß cells is a promising therapeutic strategy for diabetes. To elucidate the molecular pathways that control ß-cell growth we screened ∼2400 bioactive compounds for rat ß-cell replication-modulating activity. Numerous hit compounds impaired or promoted rat ß-cell replication, including CC-401, an advanced clinical candidate previously characterized as a c-Jun N-terminal kinase inhibitor. Surprisingly, CC-401 induced rodent (in vitro and in vivo) and human (in vitro) ß-cell replication via dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) 1A and 1B inhibition. In contrast to rat ß cells, which were broadly growth responsive to compound treatment, human ß-cell replication was only consistently induced by DYRK1A/B inhibitors. This effect was enhanced by simultaneous glycogen synthase kinase-3ß (GSK-3ß) or activin A receptor type II-like kinase/transforming growth factor-ß (ALK5/TGF-ß) inhibition. Prior work emphasized DYRK1A/B inhibition-dependent activation of nuclear factor of activated T cells (NFAT) as the primary mechanism of human ß-cell-replication induction. However, inhibition of NFAT activity had limited effect on CC-401-induced ß-cell replication. Consequently, we investigated additional effects of CC-401-dependent DYRK1A/B inhibition. Indeed, CC-401 inhibited DYRK1A-dependent phosphorylation/stabilization of the ß-cell-replication inhibitor p27Kip1. Additionally, CC-401 increased expression of numerous replication-promoting genes normally suppressed by the dimerization partner, RB-like, E2F and multivulval class B (DREAM) complex, which depends upon DYRK1A/B activity for integrity, including MYBL2 and FOXM1. In summary, we present a compendium of compounds as a valuable resource for manipulating the signaling pathways that control ß-cell replication and leverage a DYRK1A/B inhibitor (CC-401) to expand our understanding of the molecular pathways that control ß-cell growth.

Genetic Disruption of Adenosine Kinase in Mouse Pancreatic ß-Cells Protects Against High-Fat Diet-Induced Glucose Intolerance.

Islet ß-cells adapt to insulin resistance through increased insulin secretion and expansion. Type 2 diabetes typically occurs when prolonged insulin resistance exceeds the adaptive capacity of ß-cells. Our prior screening efforts led to the discovery that adenosine kinase (ADK) inhibitors stimulate ß-cell replication. Here, we evaluated whether ADK disruption in mouse ß-cells affects ß-cell mass and/or protects against high-fat diet (HFD)-induced glucose dysregulation. Mice targeted at the Adk locus were bred to Rip-Cre and Ins1-Cre/ERT1Lphi mice to enable constitutive (ßADKO) and conditional (ißADKO) disruption of ADK expression in ß-cells, respectively. Weight gain, glucose tolerance, insulin sensitivity, and glucose-stimulated insulin secretion (GSIS) were longitudinally monitored in normal chow (NC)-fed and HFD-fed mice. In addition, ß-cell mass and replication were measured by immunofluorescence-based islet morphometry. NC-fed adult ßADKO and ißADKO mice displayed glucose tolerance, insulin tolerance and ß-cell mass comparable to control animals. By contrast, HFD-fed ßADKO and ißADKO animals had improved glucose tolerance and increased in vivo GSIS. Improved glucose handling was associated with increased ß-cell replication and mass. We conclude that ADK expression negatively regulates the adaptive ß-cell response to HFD challenge. Therefore, modulation of ADK activity is a potential strategy for enhancing the adaptive ß-cell response.

A High-content In Vitro Pancreatic Islet ß-cell Replication Discovery Platform.

Loss of insulin-producing ß-cells is a central feature of diabetes. While a variety of potential replacement therapies are being explored, expansion of endogenous insulin-producing pancreatic islet ß-cells remains an attractive strategy. ß-cells have limited spontaneous regenerative activity; consequently, a crucial research effort is to develop a precise understanding of the molecular pathways that restrain ß-cell growth and to identify drugs capable of overcoming these restraints. Herein an automated high-content image-based primary-cell screening method to identify ß-cell replication-promoting small molecules is presented. Several, limitations of prior methodologies are surmounted. First, use of primary islet cells rather than an immortalized cell-line maximizes retention of in vivo growth restraints. Second, use of mixed-composition islet-cell cultures rather than a ß-cell-line allows identification of both lineage-restricted and general growth stimulators. Third, the technique makes practical the use of primary islets, a limiting resource, through use of a 384-well format. Fourth, detrimental experimental variability associated with erratic islet culture quality is overcome through optimization of isolation, dispersion, plating and culture parameters. Fifth, the difficulties of accurately and consistently measuring the low basal replication rate of islet endocrine-cells are surmounted with optimized immunostaining parameters, automated data acquisition and data analysis; automation simultaneously enhances throughput and limits experimenter bias. Notable limitations of this assay are the use of dispersed islet cultures which disrupts islet architecture, the use of rodent rather than human islets and the inherent limitations of throughput and cost associated with the use of primary cells. Importantly, the strategy is easily adapted for human islet replication studies. This assay is well suited for investigating the mitogenic effect of substances on ß-cells and the molecular mechanisms that regulate ß-cell growth.

Repurposing cAMP-modulating medications to promote ß-cell replication.

Loss of ß-cell mass is a cardinal feature of diabetes. Consequently, developing medications to promote ß-cell regeneration is a priority. cAMP is an intracellular second messenger that modulates ß-cell replication. We investigated whether medications that increase cAMP stability or synthesis selectively stimulate ß-cell growth. To identify cAMP-stabilizing medications that promote ß-cell replication, we performed high-content screening of a phosphodiesterase (PDE) inhibitor library. PDE3, -4, and -10 inhibitors, including dipyridamole, were found to promote ß-cell replication in an adenosine receptor-dependent manner. Dipyridamole's action is specific for ß-cells and not α-cells. Next we demonstrated that norepinephrine (NE), a physiologic suppressor of cAMP synthesis in ß-cells, impairs ß-cell replication via activation of α(2)-adrenergic receptors. Accordingly, mirtazapine, an α(2)-adrenergic receptor antagonist and antidepressant, prevents NE-dependent suppression of ß-cell replication. Interestingly, NE's growth-suppressive effect is modulated by endogenously expressed catecholamine-inactivating enzymes (catechol-O-methyltransferase and l-monoamine oxidase) and is dominant over the growth-promoting effects of PDE inhibitors. Treatment with dipyridamole and/or mirtazapine promote ß-cell replication in mice, and treatment with dipyridamole is associated with reduced glucose levels in humans. This work provides new mechanistic insights into cAMP-dependent growth regulation of ß-cells and highlights the potential of commonly prescribed medications to influence ß-cell growth.