Functional diversity and co-operativity between subclonal populations of paediatric glioblastoma and diffuse intrinsic pontine glioma cells

The failure to develop effective therapies for paediatric glioblastoma (pGBM) and diffuse intrinsic pontine glioma (DIPG) is in part due to their intrinsic heterogeneity. We aimed to quantitatively map assess the extent to which this was present in these tumours through subclonal genomic analyses, and to determine whether distinct tumour subpopulations may interact to promote tumorigenesis by generating novel subclonal patient-derived models in vitro and in vivo. Analysis of 142 sequenced cases revealed multiple tumour subclones, spatially and temporally co-existing in a stable manner as observed by multiple sampling strategies. We isolated genotypically and phenotypically distinct subpopulations which we propose co-operate to enhance tumorigenicity and resistance to therapy. Inactivating mutations in the H4K20 histone methyltransferase KMT5B (SUV420H1), present in <1% of cells, confer an abrogated DNA repair pathway and increased invasion/migration of neighbouring cells, in vitro and in vivo, through chemokine signalling and modulation of integrins. These data indicate that even rare tumour subpopulations may exert profound effects on tumorigenesis as a whole, and may represent a novel avenue for therapeutic development. Unravelling the mechanisms of subclonal diversity and communication in pGBM/DIPG will be an important step to overcoming barriers to effective treatments.