Targeting SRC enhances differentiation and promotes multifaceted cell death mechanisms in recurrent group 3...

Medulloblastoma (MB) is the most common childhood brain cancer, with Group 3 (G3) as the most aggressive subgroup, being prone to relapse and treatment resistance. A small subset of stem-like cells contributes to this recurrence, but the mechanisms behind their transformation are not fully understood. In this study, we employed therapeutically relevant in vitro and in vivo chemoradiotherapy (CRT) models of G3 MB and discovered a significant activation of SRC kinase following CRT treatment, while other kinases such as AKT and ERK were unaffected. Remarkably, SRC activation was exclusive to G3 MB cells and was absent in the less aggressive Sonic Hedgehog and Group 4 MB, as well as in normal brain cells. SRC activation in CRT-treated G3 MB cell and tumors corresponded with increased stemness, as evidenced by elevated levels of stemness factors SOX2, NOTCH1, OCT4, Nanog and phosphorylated STAT3, alongside a reduction in the differentiation marker βIII-tubulin/TUBB3. Conversely, SRC knockout or pharmacological inhibition promoted differentiation and reduced aggressiveness in CRT-resistant G3 MB cells, which could be rescued by re-expression of SRC in SRC knockout cells. Additionally, SRC inhibition significantly reduced the viability of CRT-treated G3 MB cells by inducing both apoptosis and necroptosis, while sparing the proliferation and stem-like properties of normal neural stem cells, indicating a promising toxicity profile. Importantly, in a therapeutically relevant orthotopic G3 MB model, administration of the re-purposed blood-brain-barrier permeable SRC inhibitor, Saracatinib, in conjunction with CRT, significantly reduced tumor burden and improved animal survival compared to CRT treatment alone without any neurotoxic side effects. Overall, our results underscore the pivotal role of SRC in enhancing stemness and aggressive behavior in CRT-resistant recurrent G3 MB. Targeting SRC not only promotes cell death through apoptosis and necroptosis but also encourages differentiation, positioning it as a promising therapeutic target for rapid clinical interventions.