Date Published: July 26, 2017
Publisher: Public Library of Science
Author(s): Navin Sarin, Florian Engel, Ganna V. Kalayda, Mareike Mannewitz, Jindrich Cinatl, Florian Rothweiler, Martin Michaelis, Hisham Saafan, Christoph A. Ritter, Ulrich Jaehde, Roland Frötschl, Aamir Ahmad.
The efficacy of cisplatin-based chemotherapy in cancer is limited by the occurrence of innate and acquired drug resistance. In order to better understand the mechanisms underlying acquired cisplatin resistance, we have compared the adenocarcinoma-derived non-small cell lung cancer (NSCLC) cell line A549 and its cisplatin-resistant sub-line A549rCDDP2000 with regard to cisplatin resistance mechanisms including cellular platinum accumulation, DNA-adduct formation, cell cycle alterations, apoptosis induction and activation of key players of DNA damage response. In A549rCDDP2000 cells, a cisplatin-induced G2/M cell cycle arrest was lacking and apoptosis was reduced compared to A549 cells, although equitoxic cisplatin concentrations resulted in comparable platinum-DNA adduct levels. These differences were accompanied by changes in the expression of proteins involved in DNA damage response. In A549 cells, cisplatin exposure led to a significantly higher expression of genes coding for proteins mediating G2/M arrest and apoptosis (mouse double minute 2 homolog (MDM2), xeroderma pigmentosum complementation group C (XPC), stress inducible protein (SIP) and p21) compared to resistant cells. This was underlined by significantly higher protein levels of phosphorylated Ataxia telangiectasia mutated (pAtm) and p53 in A549 cells compared to their respective untreated control. The results were compiled in a preliminary model of resistance-associated signaling alterations. In conclusion, these findings suggest that acquired resistance of NSCLC cells against cisplatin is the consequence of altered signaling leading to reduced G2/M cell cycle arrest and apoptosis.
Non-small cell lung cancer (NSCLC) is associated with high incidence and mortality . Cisplatin (cis-diamminedichloroplatinum (II)) is one of the common constituents of first-line treatment after surgery . The absolute effect of cisplatin chemotherapy after five years was shown to be a decrease of lung cancer associated death by 6.9% compared to an untreated control group . The precise antineoplastic mechanism of cisplatin remains not completely understood . Cisplatin cytotoxicity has been suggested to be predominantly mediated by nuclear DNA binding, mainly via intrastrand DNA crosslinks leading to cell cycle arrest and subsequent apoptosis . However, this view may be an oversimplification since only around 1% of the intracellular cisplatin binds to nuclear DNA. Cisplatin becomes intracellularly activated into an aquatic complex that reacts with numerous membrane and cytoplasmic components, suggesting that the drug may also exert cytotoxic effects by mechanisms independent of nuclear DNA binding .
We intended to elucidate molecular key events shading more light on the potential mechanistic background of the cellular development of cisplatin resistance. Cisplatin treatment leads to cisplatin-DNA adducts and DNA crosslinks. Major cellular responders to Pt-DNA adduct formation are pATM and p53. We therefore focused our investigation on genes and proteins which are potential effectors of these proteins and also assumed to be involved in cell cycle and apoptosis control. MDM2 was considered of importance due to its major activity in p53 homoeostasis and SIP for its kinase activity on p53. p21 is an effector of p53 and a major cell cycle checkpoint control protein . XPC was in our interest as it is involved in DNA repair but mainly also because it has been suggested to predict treatment outcome in patients with NSCLC [16,17].