PI3K/mTOR inhibitors promote G6PD autophagic degradation and exacerbate oxidative stress damage to radiosensitize small cell lung cancer

Abstract

Our previous study revealed that PI3K/AKT/mTOR signaling was associated with SCLC radioresistance. SBC2 cells were used as primary radioresistance models, while H446 cells were continuously exposed to ionizing radiation (IR) to develop acquired radioresistance. Cell viability and apoptosis assays were used to investigate synergistic effects of BEZ235/GSK2126458 and IR in vitro, while immunoblotting, metabolite quantitative analysis and bioinformatic analyses were utilized to explore the underlying mechanism. Both genetically engineered mouse models (GEMM) and subcutaneous tumor models were used to confirm the synergistic effect in vivo. Key molecules of PI3K/AKT/mTOR signaling were upregulated after IR, which was correlated with primary radioresistance, and they were more expressed in acquired radioresistant cells. BEZ235/GSK2126458 effectively enhanced the cytotoxic effects of IR. BEZ235/GSK2126458 plus IR elevated γ-H2AX and p-Nrf2 expression, suggesting DNA and oxidative stress damage were intensified. Mechanistically, BEZ235/GSK2126458 plus IR significantly reduced the expression of G6PD protein, the rate-limiting enzyme of the pentose phosphate pathway (PPP). In detail, PI3K/mTOR inhibitors reinforced interaction between G6PD and HSPA8/HSC70, and G6PD was degraded by chaperone-mediated autophagy processes. Their metabolites (NADPH and R-5P) were decreased, and ROS levels were indirectly elevated, both of which exacerbated cell death. PI3K/AKT/mTOR signaling activator, insulin, enhanced SCLC radioresistance, while the synergistic effect of BEZ235/GSK2126458 and IR can be attenuated by N-acetylcysteine, and enhanced by 6-amino niacinamide. GEMM and allograft transplantation assays further confirmed their synergistic effect in vivo. This study provided insights into the connection between PI3K/AKT/mTOR signaling and the PPP underlying radioresistance and provided evidence of mechanisms supporting PI3K/mTOR inhibitors as possible therapeutic strategies to abrogate SCLC radioresistance.

Proteomic and metabolomic analysis of GH deficiency-induced NAFLD in hypopituitarism: insights into oxidative stress

“…Using mass spectrometry analysis, we found that the mTOR signaling pathway was activated in the hypophysectomized rats, associated with disturbed lipid homeostasis and oxidative stress. Although there is no clear evidence linking mTOR signals to NADPH regeneration, several studies have shown that mTOR inhibitors can promote G6PD autophagy degradation and exacerbate oxidative stress damage ( 61 ); modulate IDH2 expression ( 62 ). As mTOR’s role in metabolism is context-dependent and integrates various signals, including nutrient availability, growth factors and energy status, its effects on fatty acid oxidation and NADPH regeneration are probably mediated by complex networks of direct and indirect mechanisms.…”

Lactylation stabilizes DCBLD1 activating the pentose phosphate pathway to promote cervical cancer progression

“…Autophagy regulates glycolysis via selective degradation of HK2 [ 26 ]. Additionally, G6PD is degraded by chaperone-mediated autophagy processes [ 27 ]. However, whether DCBLD1 activates autophagy to degrade G6PD, leading to metabolic reprogramming needs to be further investigated.…”

Role of 6-Phosphofructo-2-Kinase/Fructose-2,6-Bisphosphatase-3 in Maintaining Redox Homeostasis and DNA Repair in Non-Small Cell Lung Cancers Under EGFR-Targeting Therapy

“…This oxidative environment promotes the oxidation of macromolecules, including DNA, leading to consequential DNA damage. Glycolysis plays a crucial role in sustaining rapid DNA repair and alleviating oxidative stress by regulating the pentose phosphate pathway in lung cancer (6,7). Metabolic rewiring, coupled with the action of antioxidant defense enzymes such as glutathione peroxidase 4 (GPX4), enables cancer cells tolerate treatment by improving their redox capacity and developing adaptive mechanisms to counteract oxidative stress.…”