The impact of S- and G2-checkpoint response on the fidelity of G1-arrest by cisplatin and its comparison to a non-cross-resistant platinum(IV) analog

Abstract

Objective Cisplatin is a DNA-damaging antitumor agent that is highly effective in treating ovarian cancer. It activates the p53/p21 pathway for its cytotoxic mode of action, but it does not induce p21-dependent cell cycle arrest in G1. Therefore, we investigated this paradox, and used the model analog DAP as a positive control for p21-dependent G1-arrest. Methods Studies were conducted in p53-proficient ovarian A2780 tumor cells to examine Cdk activity, cell cycle distribution and DNA damage signaling after cisplatin or DAP in combination with the mitotic inhibitor nocodazole. Results Cisplatin consistently induced transient S-phase arrest by inhibiting Cdk2/cyclin A complex in S-phase at 12 h and then a durable G2/M-arrest by inhibiting Cdc2/cyclin B complex at 12–18 h. These inhibitions were associated with Chk1 and Chk2 activation and resultant increase in inhibitory tyrosine phosphorylation of Cdk2 and Cdc2. Cisplatin also potently inhibited G1-phase Cdk4/cyclin D1 and Cdk2/cyclin E activities at ~18 h. In agreement, exposure of cisplatin-treated A2780, HCT-116p53−/− and HCT-116p21−/− tumor cells to nocodazole revealed limited G1-arrest that was dependent on p53 and p21. In contrast, the durable G1-arrest by DAP, which failed to activate Chk1 and Chk2, was unaffected by nocodazole. Conclusions Cisplatin induced G1-arrest, but at an attenuated level. This was primarily due to orchestration of Cdk inhibition in S-phase first, then in G2, and finally in G1 that effectively blocked cells in G2 and prevented cells from progressing and arresting in G1. These studies demonstrate that cisplatin unequivocally activates G1-checkpoint response, but the fidelity of G1-arrest is compromised by Chk1/2 activation and checkpoint response in S- and G2/M-phase.

Cyclin-dependent kinase 4 may be expressed as multiple proteins and have functions that are independent of binding to CCND and RB and occur at the S and G2/M phases of the cell cycle

“…Cisplatin, a chemotherapeutic agent, has been reported to decrease CDK4, 30 but in our RT-PCR assay it slightly increased the wt mCDK4 mRNA in NMuMG benign mouse mammary epithelial cells and 5 mouse breast cancer cell lines, with a proportional increase in the ΔE2 level in most of these cell lines (Fig. 2D).…”

Compound K, a Ginsenoside Metabolite, Inhibits Colon Cancer Growth via Multiple Pathways Including p53-p21 Interactions

“…Two of the major mechanisms involve inhibitory binding of p21 to the CDK via the p53/p21 pathway and an increase in inhibitory phosphotyrosine levels of CDK [43–45]. A previous study demonstrated that the p53/p21 pathway is critical for chemotherapy-induced G1 phase arrest [46]. Since p53 can inhibit the cell cycle and induce apoptosis, pharmacological strategies to control or restore wild-type p53 function could have great therapeutic potential.…”

Functional Activation of Mutant p53 by Platinum Analogues in Cisplatin-Resistant Cells Is Dependent on Phosphorylation

“…At this point, it is unknown if a specific kinase fails to be activated by cisplatin in resistant cells to prevent Ser20 phosphorylation and, conversely, if a distinctly different kinase is activated by the two platinum analogs to restore this phosphorylation. The implication that independent kinases may likely be involved is based on our previous report that cisplatin is dependent on ATR, Chk1 and Chk2 for activating DNA damage-dependent signaling pathways, whereas DAP is independent of these kinases (37). Thus, additional studies may be needed to identify the key kinase associated with induction of Ser20 phosphorylation with each platinum drug.…”