Activated NOTCH–Induced Intratumoral Heterogeneity Drives Lung Cancer

Small-cell lung cancer (SCLC), a neuroendocrine subtype of lung cancer that exhibits aggressive behavior, frequently harbors inactivating genomic alterations in members of the NOTCH pathway, which inhibits neuroendocrine differentiation of precursor cells during lung development and has been implicated as tumor suppressive in SCLC. To elucidate the role of activated NOTCH signaling in SCLC development, Lim and colleagues evaluated tumors from patients with SCLC and a genetically engineered mouse model of SCLC and showed that the majority of both human and mouse SCLC tumors contain cells expressing high levels of HES1, a transcriptional target of NOTCH signaling. Tracking of NOTCH activation and HES1 expression using a transgenic GFP reporter in the SCLC mouse model showed that GFP⁺ cells expressed high levels of Hes1 and the NOTCH receptors Notch1/2/3 and low levels of neuroendocrine genes, whereas GFP⁻ cells expressed high levels of NOTCH ligands and neuroendocrine genes; further, GFP⁻ cells were more proliferative than GFP⁺ cells and formed faster-growing tumors. Single-cell quantitative PCR identified a subset of GFP⁻ cells that express at least one NOTCH receptor, and stimulation with a high-affinity NOTCH ligand induced GFP expression and a non-neuroendocrine morphology in approximately half of GFP⁻ cells. GFP⁺ cells expressed genes involved in extracellular matrix organization and cell adhesion, suggesting that GFP⁺ cell–GFP⁻ cell interactions may be similar to stroma–tumor interactions. Further, bulk mouse tumors were more proliferative than GFP⁺ cells or GFP⁻ cells, and conditioned media from GFP⁺ cells or co-culture with GFP⁺ cells increased the growth of neuroendocrine SCLC cell lines. In vivo, chemotherapy drugs induced apoptosis mostly in GFP⁻ cells, and the combination of chemotherapy drugs with a NOTCH antagonist was more efficacious than either alone in both mouse and human SCLC. These findings describe the dual role of activated NOTCH signaling in driving SCLC and suggest that the selection of NOTCH therapy may be SCLC stage–dependent.

Lim JS, Ibaseta A, Fischer MM, Cancilla B, O'Young G, Cristea S, et al. Intratumoural heterogeneity generated by Notch signaling promotes small-cell lung cancer. Nature 2017;545:360–4.