The emergence of chemoresistance is a major problem for almost all tumour types where chemotherapy remains the frontline therapy. Many theories have been proposed describing the single-cell dynamics of chemotherapy response and expansion of resistant clones. These usually require selection of a pre-existing stem cell population, a low frequency somatic mutation or the de novo acquisition of new mutations. In contrast to these predominantly genetic mechanisms, we have now utilised mathematical modelling and longitudinal single-cell imaging to demonstrate that the propagation of a single cell clone can arise merely through the inherently noisy process of gene expression and the non-linear behaviour of apoptotic signalling pathways.
High-risk neuroblastoma is an aggressive, highly chemoresistant childhood tumour. We previously demonstrated that in silico, patient-specific modelling of apoptotic signalling can stratify neuroblastoma patient cohorts and provide robust biomarkers of patient survival (Fey, 2015, Science Signaling). We now show that application of this patient-focused model to single-cell populations also predicts the presence of this innately chemoresistant cell population, which cannot activate sufficient drug-induced signalling to reach an in-built apoptotic threshold.
Using kinase biosensors and high-content imaging we now confirm the existence of this resistant cell population. In-depth characterisation has also confirmed that these cells are not associated with a distinct cell cycle phase, nor with the expression of phosphatases or drug efflux pumps. We further demonstrate that rationalised therapeutic strategies aimed at lowering the apoptotic threshold can overcome this stochastic single-cell chemoresistance in both cell line and PDX models of primary and relapsed neuroblastoma.