Abstract LB074: Chymostatin, a cathepsin L inhibitor, inhibits lung cancer cell proliferation and COVID-19 Mpro in vitro

Abstract

Abstract Lung cancer patients are more vulnerable to COVID-19 infection. Treatment of patients with lung cancer during the current COVID-19 pandemic is challenging and development of drugs for COVID-19 and lung cancer is urgently needed. Cathepsin L plays key role in lung cancer progression, invasion and more so, endocytosis of SARS-Cov-2 virus into the lung epithelial cells. Importantly, patients with KrasG12V mutation show agreessive disease and high-resistance to chemotherapy due to over-expression of Cathepsin L. Thus, Cathepsin L is a common target for lung cancer and COVID-19 infection. Chymostatin is a known cathepsin L inhibitor, here we screened it for dual inhibition of COVID-19 Mpro and lung cancer patients with COVID-19. In vitro COVID-19 Mpro fluorometric assay was performed to evaluate its inhibitory efficacy by chymostatin. Chymostatin showed dose-dependent inhibition of COVID-19 Mpro activity with IC50 of 15.81 µM (P<0.0001). Isothermal titration calorimetry based binding studies determined that chymostatin strongly bound to COVID-19 Mpro (KD=22.45 µM). CD spectrum analysis demonstrated that chymostatin (10 µM)-induced changes in the secondary structure of COVID-19 Mpro. A unit cell crystal parameter COVID-19 Mpro co-crystalized with chymostatin (a = 49.926 Å, b = 108.71 Å, c = 56.49 Å, α = 90.0°, β = 102.7553°, γ = 90.0°; unit cell volume: 299.03 Ao) was determined using X-ray diffractometer. Molecular docking studies demonstrated that chymostatin interacts with active site amino acids (Cys145). Pro-apoptotic effect of chymostatin was evaluated on human H441 lung cancer cells and mouse lung normal epithelial cells using Annexin V/propidium iodide staining. Chymostatin did not show any cytotoxicity on normal mouse lung epithelial cells up to 100 µM, where as it inhibited proliferation of human H441 lung cancer cells (KrasG12V mutant) with IC50 of 1.2 µM. In conclusion, preliminary in vitro studies demonstrated that naturally occurring cathepsin L inhibitor chymostatin is a SARS-CoV-2 Mpro inhibitor and exhibited anticancer activity against lung cancer cells. The results of the study warranted detailed studies to develop as drugs for lung cancer patients during COVID-19 pandemic (supported by VPR-PHF, the University of Oklahoma Health Sciences Centre for financial support through COVID-19 seed grant program). Citation Format: Nagendra Sastry Yarla, Gopal Pathuri, Simon Terzyan, Yuting Zhang, Anil Singh, Marcus T. Scotti, Venkateshwar Madka, Chinthalapally V. Rao. Chymostatin, a cathepsin L inhibitor, inhibits lung cancer cell proliferation and COVID-19 Mpro in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB074.