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Epidermal growth factor receptor‐targeted (EGFR‐targeted) therapies show promise for non‐small cell lung cancer (NSCLC), but they are ineffective in a third of patients who lack EGFR mutations. This underlines the need for personalized treatments for patients with EGFR wild‐type NSCLC. A genome‐wide CRISPR/Cas9 screen has identified the enzyme phosphoribosylaminoimidazole carboxylase/phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS), which is vital in de novo purine biosynthesis and tumor development, as a potential drug target for EGFR wild‐type NSCLC. We have further confirmed that PAICS expression is significantly increased in NSCLC tissues and correlates with poor patient prognosis. Knockdown of PAICS resulted in a marked reduction in both in vitro and in vivo proliferation of EGFR wild‐type NSCLC cells. Additionally, PAICS silencing led to cell‐cycle arrest in these cells, with genes involved in the cell cycle pathway being differentially expressed. Consistently, an increase in cell proliferation ability and colony number was observed in cells with upregulated PAICS in EGFR wild‐type NSCLC. PAICS silencing also caused DNA damage and cell‐cycle arrest by interacting with DNA repair genes. Moreover, decreased IMPDH2 activity and activated PI3K–AKT signaling were observed in NSCLC cells with EGFR mutations, which may compromise the effectiveness of PAICS knockdown. Therefore, PAICS plays an oncogenic role in EGFR wild‐type NSCLC and represents a potential therapeutic target for this disease. [ABSTRACT FROM AUTHOR]

Abstract Epidermal growth factor receptor‐targeted (EGFR‐targeted) therapies show promise for non‐small cell lung cancer (NSCLC), but they are ineffective in a third of patients who lack EGFR mutations. This underlines the need for personalized treatments for patients with EGFR wild‐type NSCLC. A genome‐wide CRISPR/Cas9 screen has identified the enzyme phosphoribosylaminoimidazole carboxylase/phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS), which is vital in de novo purine biosynthesis and tumor development, as a potential drug target for EGFR wild‐type NSCLC. We have further confirmed that PAICS expression is significantly increased in NSCLC tissues and correlates with poor patient prognosis. Knockdown of PAICS resulted in a marked reduction in both in vitro and in vivo proliferation of EGFR wild‐type NSCLC cells. Additionally, PAICS silencing led to cell‐cycle arrest in these cells, with genes involved in the cell cycle pathway being differentially expressed. Consistently, an increase in cell proliferation ability and colony number was observed in cells with upregulated PAICS in EGFR wild‐type NSCLC. PAICS silencing also caused DNA damage and cell‐cycle arrest by interacting with DNA repair genes. Moreover, decreased IMPDH2 activity and activated PI3K–AKT signaling were observed in NSCLC cells with EGFR mutations, which may compromise the effectiveness of PAICS knockdown. Therefore, PAICS plays an oncogenic role in EGFR wild‐type NSCLC and represents a potential therapeutic target for this disease.

This is the first case described of transformation from EGFR wild-type non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) during immunotherapy presenting with severe hyponatremia due to paraneoplastic syndrome of inappropriate antidiuretic hormone secretion.