Medulloblastoma is the most common type of childhood malignant brain tumour. Recent global collaborative efforts to comprehensively characterise the medulloblastoma genome revealed at least four distinct molecular subgroups with differing clinical characteristics and demographics. These seminal findings now provide a platform for the development of subgroup specific targeted therapies that are more effective with less damaging side-effects. Deregulated sonic hedgehog (SHH) signalling is a hallmark of one of the best-characterised medulloblastoma subgroups, representing approximately one-third of cases. Importantly, targeted inhibition of Smoothened, an integral component of the SHH signalling cascade, is clinically effective for treating patients with sonic hedgehog dependent medulloblastoma. Deregulated SHH signalling is also associated with the pathogenesis of a broad range of other tumours, raising the possibility that inhibitors of the SHH pathway may be broadly effective for cancer treatment in diverse contexts.
Methods: Functionally important domains of the SHH pathway regulators, Smoothened and KIF7, were used in a proprietary yeast two-hybrid screening platform to isolate interacting peptides from libraries of protein fragments generated from the genomes of a diverse group of bacterial species. The ability of Smoothened- and KIF7- interacting peptides to inhibit SHH pathway activity was assessed in transfection based assays using the murine SHHLightII and C3H10T1/2 cell lines.
Results: A total of 64 Smoothened peptides and 49 KIF7 peptides were identified from two independent yeast two-hybrid screens. Thirty peptides inhibited SHH pathway activity by >25% in the SHHLightII assay, and a subset also inhibited SHH pathway activity in C3H10T1/2 cells.
Conclusion: Several putative Smoothened- and KIF7- interacting peptides exhibited SHH pathway inhibitory activity in cell line models in vitro. Further detailed characterisation of these, and other novel peptides isolated in this study, may provide suitable candidates for preclinical testing in animal models of medulloblastoma and other SHH driven cancers.