Plasticity of squamous differentiation drives drug resistance in HNSCC

A critical hallmark of carcinogenesis is the ability of cancer cells to evade the loss of self-renewal normally imposed by terminal differentiation. However, therapies directly attempting to promote differentiation have shown limited efficacy in solid tumours and the cellular mechanisms behind cancer cell persistence are poorly understood. Here we established a patient-derived orthotopic head and neck squamous cell carcinoma (HNSCC) model in vivo that recapitulates the genetic, cellular and histopathological heterogeneity of HNSCC. Experimental induction of differentiation and clonal lineage tracing by fluorescent barcoding revealed a heterogeneous response to terminal differentiation stimuli, enabling subsets of cancer cells to escape differentiation-associated loss of self-renewal. While pharmacological inhibition of ErbB-MEK1/2-ERK1/2 pathway by afatinib could induce the differentiation of patient-derived cancer cells, some highly clonogenic cells remained refractory to differentiation signals even though they were capable of differentiating. Differentiation reporter IVLmCherry further confirmed that differentiation and loss of self-renewal ability were partially uncoupled in patient-derived HNSCC cells. These findings identify differentiation-resistant clonogenic populations as a key barrier to therapeutic efficacy and provide a framework for improving differentiation-based strategies in HNSCC.