SUMMARY In a screen of drugs previously tested in humans we identified itraconazole, a systemic antifungal, as a potent antagonist of the Hedgehog (Hh) signaling pathway that acts by a mechanism distinct from its inhibitory effect on fungal sterol biosynthesis. Systemically administered itraconazole, like other Hh pathway antagonists, can suppress Hh pathway activity and the growth of medulloblastoma in a mouse allograft model and does so at serum levels comparable to those in patients undergoing antifungal therapy. Mechanistically, itraconazole appears to act on the essential Hh pathway component Smoothened (Smo) by a mechanism distinct from that of cyclopamine and other known Smo antagonists, and prevents the ciliary accumulation of Smo normally caused by Hh stimulation.

Epithelial integrity in metazoan organs is maintained through the regulated proliferation and differentiation of organ-specific stem and progenitor cells. Although the epithelia of organs such as the intestine regenerate constantly and thus remain continuously proliferative1, other organs, such as the mammalian urinary bladder, shift from near-quiescence to a highly proliferative state in response to epithelial injury2–4. The cellular and molecular mechanisms underlying this injury-induced mode of regenerative response are poorly defined. Here we show in mice that the proliferative response to bacterial infection or chemical injury within the bladder is regulated by signal feedback between basal cells of the urothelium and the stromal cells that underlie them. We demonstrate that these basal cells include stem cells capable of regenerating all cell types within the urothelium, and are marked by expression of the secreted protein signal Sonic hedgehog (Shh). On injury, Shh expression in these basal cells increases and elicits increased stromal expression of Wnt protein signals, which in turn stimulate the proliferation of both urothelial and stromal cells. The heightened activity of this signal feedback circuit and the associated increase in cell proliferation appear to be required for restoration of urothelial function and, in the case of bacterial injury, may help clear and prevent further spread of infection. Our findings provide a conceptual framework for injury-induced epithelial regeneration in endodermal organs, and may provide a basis for understanding the roles of signalling pathways in cancer growth and metastasis.

An RNA model system consisting of an oligomer binding to a 4-nt overhang at the 5' end ofa hairpin stem provides thermodynamic parameters for helix-helix interfaces. In a sequence-dependent manner, oligomers bind up to 1000-fold more tightly adjacent to the hairpin stem than predicted for binding to a free tetramer at 370C. For reaction (19, 20). Synthetic details will be provided elsewhere.Measurement of Thermodynamic Parameters. The buffer for melting experiments was 1 M NaCl/10 mM sodium cacodylate/0.5 mM EDTA. Absorbance versus temperature curves were measured at 280 nm with a heating rate of 10C/min. These curves were analyzed by fitting to a two-state model with sloping base lines through use of a nonlinear least-squares program (21).Predictions of Secondary Structure. Sets of 20 secondary structures were generated with the program of Zuker (12), kcal/mol, and internal loops of three were given a AG'7 for loop closure of 5.1 + 0.3 = 5.4 kcal/mol (23). (iii) Stacking and pairing of terminal mismatches were included in calculating free energies of internal loops in the following manner. Single mismatches were given AG7 = 0.8 kcal/mol. For larger internal loops, terminal GA, UU, and other mismatches adjacent to COG pairs were given favorable free energy increments of -2.7, -2.5, and -1.5 kcal/mol, respectively (24). These mismatches adjacent to A-U pairs were given AG' values of -2. 9218The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Diffuse intrinsic pontine gliomas (DIPGs) are highly aggressive tumors of childhood that are almost universally fatal. Our understanding of this devastating cancer is limited by a dearth of available tissue for study and by the lack of a faithful animal model. Intriguingly, DIPGs are restricted to the ventral pons and occur during a narrow window of middle childhood, suggesting dysregulation of a postnatal neurodevelopmental process. Here, we report the identification of a previously undescribed population of immunophenotypic neural precursor cells in the human and murine brainstem whose temporal and spatial distributions correlate closely with the incidence of DIPG and highlight a candidate cell of origin. Using early postmortem DIPG tumor tissue, we have established in vitro and xenograft models and find that the Hedgehog (Hh) signaling pathway implicated in many developmental and oncogenic processes is active in DIPG tumor cells. Modulation of Hh pathway activity has functional consequences for DIPG selfrenewal capacity in neurosphere culture. The Hh pathway also appears to be active in normal ventral pontine precursor-like cells of the mouse, and unregulated pathway activity results in hypertrophy of the ventral pons. Together, these findings provide a foundation for understanding the cellular and molecular origins of DIPG, and suggest that the Hh pathway represents a potential therapeutic target in this devastating pediatric tumor.Hedgehog pathway | cancer stem cells | brainstem glioma