Inhibition of the NOTCH and mTOR pathways by nelfinavir as a novel treatment for T cell acute lymphoblastic leukemia.

T cell acute lymphoblastic leukemia (T‑ALL), a neoplasm derived from T cell lineage‑committed lymphoblasts, is characterized by genetic alterations that result in activation of oncogenic transcription factors and the NOTCH1 pathway activation. The NOTCH is a transmembrane receptor protein activated by γ‑secretase. γ‑secretase inhibitors (GSIs) are a NOTCH‑targeted therapy for T‑ALL. However, their clinical application has not been successful due to adverse events (primarily gastrointestinal toxicity), limited efficacy, and drug resistance caused by several mechanisms, including activation of the AKT/mTOR pathway. Nelfinavir is an human immunodeficiency virus 1 aspartic protease inhibitor and has been repurposed as an anticancer drug. It acts by inducing endoplasmic reticulum (ER) stress and inhibiting the AKT/mTOR pathway. Thus, it was hypothesized that nelfinavir might inhibit the NOTCH pathway via γ‑secretase inhibition and blockade of aspartic protease presenilin, which would make nelfinavir effective against NOTCH‑associated T‑ALL. The present study assessed the efficacy of nelfinavir against T‑ALL cells and investigated mechanisms of action and in preclinical treatment studies using a transgenic mouse model. Nelfinavir blocks presenilin 1 processing and inhibits γ‑secretase activity as well as the NOTCH1 pathway, thus suppressing T‑ALL cell viability. Additionally, microarray analysis of nelfinavir‑treated T‑ALL cells showed that nelfinavir upregulated mRNA levels of (glutathione‑specific γ‑glutamylcyclotransferase 1, a negative regulator of NOTCH) and sestrin 2 (; a negative regulator of mTOR). As both factors are upregulated by ER stress, this confirmed that nelfinavir induced ER stress in T‑ALL cells. Moreover, nelfinavir suppressed mRNA expression in microarray analyses. These findings suggest that nelfinavir inhibited the NOTCH1 pathway by downregulating mRNA expression, upregulating and suppressing γ‑secretase via presenilin 1 inhibition and the mTOR pathway by upregulating via ER stress induction. Further, nelfinavir exhibited therapeutic efficacy against T‑ALL in an transgenic mouse model. Collectively, these findings highlight the potential of nelfinavir as a novel therapeutic candidate for treatment of patients with T‑ALL.