Reactive oxygen species (ROS) are metabolic byproducts that regulate various cellular processes. However, at high levels, ROS induce oxidative stress, which in turn can trigger cell death. Cancer cells alter the redox homeostasis to facilitate protumorigenic processes; however, this leaves them vulnerable to further increases in ROS levels. This paradox has been exploited as a cancer therapeutic strategy with the use of pro-oxidative drugs. Many chemotherapeutic drugs presently in clinical use, such as cisplatin and doxorubicin, induce ROS as one of their mechanisms of action. Further, various drugs, including phytochemicals and small molecules, that are presently being investigated in preclinical and clinical studies attribute their anticancer activity to ROS induction. Consistently, this review aims to highlight selected pro-oxidative drugs whose anticancer potential has been characterized with specific focus on phytochemicals, mechanisms of ROS induction, and anticancer effects downstream of ROS induction.

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The role of autophagy in lung cancer cells exposed to waterpipe smoke (WPS) is not known. Because of the important role of autophagy in tumor resistance and progression, we investigated its relationship with WP smoking. We first showed that WPS activated autophagy, as reflected by LC3 processing, in lung cancer cell lines. The autophagy response in smokers with lung adenocarcinoma, as compared to non-smokers with lung adenocarcinoma, was investigated further using the TCGA lung adenocarcinoma bulk RNA-seq dataset with the available patient metadata on smoking status. The results, based on a machine learning classification model using Random Forest, indicate that smokers have an increase in autophagy-activating genes. Comparative analysis of lung adenocarcinoma molecular signatures in affected patients with a long-term active exposure to smoke compared to non-smoker patients indicates a higher tumor mutational burden, a higher CD8+ T-cell level and a lower dysfunction level in smokers. While the expression of the checkpoint genes tested—PD-1, PD-L1, PD-L2 and CTLA-4—remains unchanged between smokers and non-smokers, B7-1, B7-2, IDO1 and CD200R1 were found to be higher in non-smokers than smokers. Because multiple factors in the tumor microenvironment dictate the success of immunotherapy, in addition to the expression of immune checkpoint genes, our analysis explains why patients who are smokers with lung adenocarcinoma respond better to immunotherapy, even though there are no relative differences in immune checkpoint genes in the two groups. Therefore, targeting autophagy in lung adenocarcinoma patients, in combination with checkpoint inhibitor-targeted therapies or chemotherapy, should be considered in smoker patients with lung adenocarcinoma.

Smoking is the number one risk factor for lung cancer and tobacco smokers are at 20 to 40 times higher risk of developing lung cancer in comparison to non-smokers. We have previously shown that exposing lung cancer cell lines to tobacco smoke condensate generated from waterpipe (WP) interferes with cell proliferation, cell plasticity, DNA damage and tumor cell recognition and killing by natural killer (NK) cells. Global transcriptomic analysis identified an expression profile of genes that best distinguished treated and non-treated cells involving several pathways including those involved in epithelial to mesenchymal transition (EMT) and stemness. Because of the important role of autophagy in tumor resistance and progression, we investigated its relationship with WP smoking. We first showed an activation of autophagy as reflected by LC3 and P62 in lung cancer cell lines in response to WPS. Interestingly, our data revealed that WPS-induced EMT and cancer stemness involved autophagy induction. The autophagy response in smokers with lung adenocarcinoma as compared to non-smokers with lung adenocarcinoma was investigated using TCGA lung adenocarcinoma bulk RNA-seq dataset with the available patient metadata on smoking status. Preliminary results based on a machine learning classification model using Random Forest indicate that smokers have an increase in autophagy activating genes as compared to non-smokers. Comparative analysis of lung adenocarcinoma molecular signatures in affected patients with a long-term active exposure to smoke compared to patients who have not had any active exposure to smoke indicate a higher tumor mutational burden, CD8+ T-cell level and lower dysfunction level in smokers. Multivariate regression analyses confirm these results even after controlling for confounding factors like age, gender, and tumor stage. While the checkpoint genes tested PD1, PDL1, PDL2 and CTLA-4, had no difference between smokers and non-smokers, B7-1, B7-2, IDO1 and CD200R1 had higher expression in non-smokers than smokers. Because multiple factors in the tumor microenvironment dictate the success of immunotherapy, in addition to the expression of immune checkpoint genes, our analysis explains why patients who are smokers with lung adenocarcinoma respond better to immunotherapy, even though there are no relative differences in immune checkpoint genes in the two cohorts. Therefore, targeting autophagy in lung adenocarcinoma patients in combination with checkpoint inhibitors, targeted therapies or chemotherapy should be considered in smoker patients with lung adenocarcinoma. Citation Format: Rania F. Zaarour, Mohak Sharda, Bilal Azakir, Goutham Hassan Venkatesh, Raefa Abou Khouzam, Ayesha Rifath, Zohra Nizami, Fatima Abdullah, Fatin Mohammad, Husam Nawafleh, Yehia ElSayed, Salem Chouaib. Autophagy as a key driver of waterpipe smoke-induced lung cancer cell plasticity and resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2995.