Small molecule inhibitors of the hedgehog signalling pathway as cancer suppressing agents

The HSP plays a pivotal role in the spatial and temporal regulation of cell proliferation and differentiation. Conversely aberrant Hh signalling is involved in Gorlin syndrome, basal cell carcinoma (the most common cancer in the world), and more than one third of all human medulloblastoma cases. In all of these cases, it is believed that deregulated Hh signalling leads to increased cell proliferation and tumour formation. Inhibition of the Hedgehog Signalling Pathway, is a recently validated anti-cancer drug target, with vismodegib (GDC-0449, Erivedge®) and sonidegib (LDE225, Odomzo®), approved by the U.S. Food and Drug Administration for treatment of early and advanced basal cell carcinomas. We developed three new scaffolds of small molecule inhibitors of the HSP. The first scaffold consisted of 11 quinolone-2-(1H)-ones developed from a sequential Ugi-Knoevenagel reaction pathway (Chapter 3). These analogues not only express their anti-hedgehog activity through the significant inhibition of Gli₂ at both gene and protein expression in SAG-activated Shh LIGHT 2 cells at 10 and 25 μM, respectively, but are able to suppress a panel of nine human HSP expressing cancer cells (GI₅₀ from 2.9 to 18.0 μM). Whilst the exact mechanism remains to be determined, it is probable the inhibition observed is occurring downstream of Smo, due to its activity in the presence of SAG, a potent Smo activator. Subsequent second and third generation analogues were developed on the quinolone-2-(1H)-one pharmacophore, which highlighted the importance of a C3-tethered indole moiety. These new scaffolds were built on tryptophan (9 analogues, Chapter 4) and benzo[1,3]dioxol-5-ylmethyl-[2-(1H-indol-3-yl)-ethyl]-amine derivatives (11 analogues, Chapter 4) displaying superior inhibitory activity against Gli protein expression with the best inhibitors displaying submicromolar IC₅₀ (Chapter 4). Noteworthy, active compounds from the second and third libraries displayed inhibitory activity downstream of Smo, which circumvents the resistance issues experienced by the Smo inhibitors currently in use. We discovered the fourth library of 1,3-thiazine-6-phenylimino-5-carboxylates in a multicomponent one pot synthesis (12 analogues, Chapter 5). These analogues display structural similarities to HPI-1, a non-selective Gli inhibitor, and thus may present themselves as HSP inhibitors. Current biological evaluation is going on to investigate their anti-hedgehog properties.