New insulin-producing pancreatic beta-cells are formed primarily by self-replication during adult life. To identify small molecules that can induce beta cell replication, a large chemical library was screened for proliferation of growth-arrested, reversibly immortalized mouse beta-cells using an automated high-throughput screening platform. A number of structurally diverse, active compounds were identified including phorbol esters, which likely act through protein kinase C, and a group of thiophene-pyrimidines that stimulate beta-cell proliferation by activating the Wnt signaling pathway. A group of dihydropyridine (DHP) derivatives was also shown to reversibly induce beta-cell replication in vitro by activating L-type calcium channels (LTCCs). Our data indicate that the LTCC agonist 2a affects the expression of genes involved in cell cycle progression and cellular proliferation. Furthermore, treatment of beta-cells with both LTCC agonist 2a and the Glp-1 receptor agonist Ex-4 showed an additive effect on beta-cell replication. The identification of small molecules that induce beta-cell proliferation suggests that it may be possible to reversibly expand other quiescent cells to overcome deficits associated with degenerative and/or autoimmune diseases.

Identify small molecules that can induce beta-cell replication. To this end the authors screened a large library for proliferation of growth-arrested, reversibly immortalized mouse beta-cells.

The mouse beta-cell line R7T1 was used. Cells were engineered using the SV40T antigen (TAg) oncoprotein, so that they would proliferate when TAg was induced in the presence of tetracycline (Tet), but they would undergo growth arrest upon withdrawal of Tet. Abour 850K compounds were screened using an automated high-throughput platform for their ability to induce proliferation.

A number of structurally diverse molecules were identified that promote beta-cell replication, including novel Wnt signaling agonists and L-type calcium channel (LTCC) agonists. Furthermore, it was shown that LTCC agonist Bay K 8644 (2a) likely induces beta-cell replication by activating Ras signaling and increased expression of cell cycle regulators, and that cotreatment of beta-cells with 2a and the Glp-1 receptor agonist Exendin-4 (Ex-4) exert an additive effect on beta-cell proliferation. A number of experiments indicate that the proliferative effect of 2a is because of the expansion of the beta-cells per se rather than a dedifferentiated cell type with higher proliferation potential from beta-cells. For example, the beta-cell signature markers Ins 1, Ins 2, and Pdx1 have unchanged expression on R7T1 beta-cells both pretreatment and postreatment with 2a in gene profiling analysis. Irs2, which is critical for beta-cell survival and proliferation had a 1.7-fold increas after 24 hr treatment with 2a. Treatment with 2a led to a large increase in the expression of several immediate-early genes, including Fos, Jun and Egr families. These expression profiles were confirmed by quantitative real-time RT-PCR. Several early response genes, such as Fos, Fosb, Junb, Egr1, Egr2, and Ier2, where expressed at higher levels in cells treated with both 2a and Ex-4 than with either alone. In addition, expression of Ccnd2, an important positive regulator during G1 phase, increased approximately 1.7-fold after treatment with 2a for 24 hr and its expression increased much earlier (at 2 hr) and to a higher level at 24 hr in 2a and Ex-4 cotreated cells. Similarly, combined treatment with 2a and Ex-4 also triggered a higher expression of Rasgrf1 and Rasgef1b, which might contribute to the additive effect of 2a and Ex-4.

A number of small molecules that induce pancreatic beta-cell proliferation were identified. One group of compounds operates by activating Wnt signaling. L-type calcium channel agonists were also identified as inducers of beta-cell proliferation/regeneration. Although analysis of the in vivo efficacy of 2a was hampered by unfavorable pharmacokinetic properties, this class of compounds with improved pharmacokinetics and tolerability may offer a potentially promising avenue for treatment of beta-cell deficiency in diabetes, especially when combined with GLP-1 receptor agonists.

• beta cell proliferation: 1790, 2541, 3465, 3735, 3815,