NOTCH signaling promotes the survival of irradiated basal airway stem cells

Abstract

Radiation-induced lung injury to normal airway epithelium is a frequent side-effect and dose-limiting factor in radiotherapy of tumors in the thoracic cavity. NOTCH signaling plays key roles in self-renewal and differentiation of upper airway basal lung stem cells during development, and the NOTCH pathway is frequently deregulated in lung cancer. In preclinical lung cancer models, NOTCH inhibition was shown to improve the radiotherapy response by targeting tumor stem cells, but the effects in combination with irradiation on normal lung stem cells are unknown. NOTCH/γ-secretase inhibitors are potent clinical candidates to block NOTCH function in tumors, but their clinical implementation has been hampered by normal tissue side-effects. Here we show that NOTCH signaling is active in primary human- and murine-derived airway epithelial stem cell models and when combined with radiation NOTCH inhibition provokes a decrease in S-phase and increase in G1-phase arrest. We show that NOTCH inhibition in irradiated lung basal stem cells leads to a more potent activation of the DNA damage checkpoint kinases pATM and pCHK2 and results in an increased level of residual 53BP1 foci in irradiated lung basal stem cells reducing their capacity for self-renewal. The effects are recapitulated in ex vivo cultured lung basal stem cells after in vivo whole thorax irradiation and NOTCH inhibition. These results highlight the importance of studying normal tissue effects that may counteract the therapeutic benefit in the use of NOTCH/γ-secretase inhibitors in combination with radiation for antitumor treatment.

FLASH Irradiation Spares Lung Progenitor Cells and Limits the Incidence of Radio-induced Senescence

“…In the lung, recent work from Stripp and colleagues showed that radiation reduces the in vitro colonyforming ability of epithelial progenitor cells from distal airways (27,28). We recently demonstrated that NOTCH signaling promotes the survival of irradiated P63 þ basal stem cells through activation of the 53BP1/DNA damage response pathway (29). Whether this also impacts on the protective response of FLASH is not known.…”

Targeting Notch to Maximize Chemotherapeutic Benefits: Rationale, Advanced Strategies, and Future Perspectives

“…It is worth mentioning that combining Notch inhibitors with radiotherapy had quite contrasting consequences for airway epithelium regeneration in experimental works. Radiation damages the DNA of progenitor cells, and Notch signaling inactivation increases the phosphorylation of ATM and CHK2 and alters DNA damage response, but it could result both in decreased and improved renewal capacity of basal stem cells in different conditions [608,609].…”

The Radiation-Induced Regenerative Response of Adult Tissue-Specific Stem Cells: Models and Signaling Pathways

“…Indeed, this system better resembles the in vivo structure of the lung and allows the coculture with different cell types such as tumor cells, fibroblasts, or immune cells. For instance, lung SC response to radiation was studied by Giuranno et al using this model [ 8 , 10 ]. Inhibition of the Notch SC pathway was shown to increase lung SC self-renewal upon IR, contributing to a more intact epithelium as assessed in a completely differentiated setting [ 8 ].…”

“…Inhibition of the Notch SC pathway was shown to increase lung SC self-renewal upon IR, contributing to a more intact epithelium as assessed in a completely differentiated setting [ 8 ]. This effect was not observed in 2D models, which do not permit the culture of the differentiated cells, suggesting the contribution of the luminal cells to SC response to RT [ 10 ]. This indicates that the choice of the right model may be crucial for translating preclinical research findings to clinical practice.…”

“…The role of the Notch pathway in the lung SC in response to RT has been investigated in only a few papers [ 8 , 10 ]. Giuranno et al [ 8 ] showed that Notch inhibition increased the proliferation of the irradiated primary lung SCs, reduced DNA damage, and contributed to a more intact epithelium ( Figure 2 b).…”