Protective roles of cytoplasmic p21^Cip1/Waf1 in senolysis and ferroptosis of lung cancer cells

Abstract

Objective Therapy‐induced senescent cancer cells increase the expression of the cyclin‐dependent kinase inhibitors p16Ink4a and p21Cip1/Waf1. Given that p21 regulates not only the cell cycle but also cell death, we investigated the roles of p21 in cell death using a p16‐negative A549 human lung adenocarcinoma cell line. Methods Senescence was induced by doxorubicin (DXR) or pemetrexed (PEM). The protein expression of p21 was examined by immunoblot. Cell death, reactive oxygen species (ROS) and lipid peroxidation were determined by flow cytometry. ABT‐263 and ABT‐737 were used as senolytic drugs. In vivo growth of A549 cells with different levels of p21 and their sensitivity to PEM were examined in xenograft models. Results DXR‐induced senescent A549 cells increased the expression of cytoplasmic p21, and the sensitivity to ABT‐263 was augmented in p21‐knockout A549 (A549‐KOp21) cells. A similar senolytic effect was observed when PEM was combined with ABT‐737. PEM alone induced a higher level of non‐apoptotic cell death, ferroptosis, in A549‐KOp21 cells than in A549 cells. Although there was no difference in the level of lipid peroxidation, ROS levels were higher in PEM‐treated A549‐KOp21 cells than in PEM‐treated A549 cells. A loss of p21 increased the sensitivity of A549 cells to PEM both in vitro and in vivo. A clinical database analysis showed that CDKN1Ahigh lung adenocarcinoma patients had a poorer prognosis compared to CDKN1Alow patients. Conclusion Cytoplasmic p21, which was increased in therapy‐induced senescent lung cancer cells, plays protective roles in senolysis and ferroptosis.

Senolysis of gemcitabine‐induced senescent human pancreatic cancer cells

“…In the xenograft model, we used ABT‐737 rather than ABT‐263, as they have identical specificity, 27 whereas the former can be systemically administered. We previously reported that ABT‐737 exhibited antitumor effects against drug‐induced human breast and lung cancer cells both in vitro and in vivo when combined with a CDK4/6 inhibitor and pemetrexed, respectively 29,30 . In this study, combined treatment with GEM and ABT‐737 retarded the in vivo tumor growth of AsPC‐1 cells to a greater extent than either GEM or ABT‐737 monotherapy (Figure 6).…”

“…We previously reported that ABT-737 exhibited antitumor effects against drug-induced human breast and lung cancer cells both in vitro and in vivo when combined with a CDK4/6 inhibitor and pemetrexed, respectively. 29,30 In this study, combined treatment with GEM and ABT-737 retarded the in vivo tumor growth of AsPC-1 cells to a greater extent than either GEM or ABT-737 monotherapy (Figure 6). We performed in vivo experiments to test the AsPC-1 combinations because a prior study reported combined effects of GEM and ABT-263 against PANC-1 cells.…”

“… 27 , 28 In this regard, we previously reported that ABT‐263 and its analog ABT‐737 had senolytic activity against drug‐induced senescent human breast and lung cancer cells both in vitro and in vivo. 29 , 30 We also found that GEM could induce senescence in some human pancreatic cancer cell lines. These findings led us to test whether senolytic drugs could effectively induce cell death in GEM‐treated senescent human pancreatic cancer cells.…”

“…Recently, ABT‐263 was shown to be a senolytic drug, that is, lethal to senescent cells 23–25 . We previously found that senescent breast and lung cancer cells were lysed by ABT‐263 29,30 . Therefore, we explored whether GEM‐treated pancreatic cancer cells could be lysed by ABT‐263.…”

“…ABT‐263 (navitoclax), an oral inhibitor of Bcl‐2, Bcl‐xL, and Bcl‐w, is a representative drug that can lyse senescent cells 27,28 . In this regard, we previously reported that ABT‐263 and its analog ABT‐737 had senolytic activity against drug‐induced senescent human breast and lung cancer cells both in vitro and in vivo 29,30 . We also found that GEM could induce senescence in some human pancreatic cancer cell lines.…”