Anaphase catastrophe is a target for cancer therapy

Abstract

Neoplastic cells are genetically unstable. Strategies that target pathways affecting genome instability can be exploited to disrupt tumor cell growth, potentially with limited consequences to normal cells. Chromosomal instability (CIN) is one type of genome instability characterized by mitotic defects that increase the rate of chromosome mis-segregation. CIN is frequently caused by extra centrosomes that transiently disrupt normal bipolar spindle geometry needed for accurate chromosome segregation. Tumor cells survive with extra centrosomes because of biochemical pathways that cluster centrosomes and promote chromosome segregation on bipolar spindles. Recent work shows that targeted inhibition of these pathways prevents centrosome clustering and forces chromosomes to segregate to multiple daughter cells, an event triggering apoptosis that we refer to as anaphase catastrophe. Anaphase catastrophe specifically kills tumor cells with more than 2 centrosomes. This death program can occur after genetic or pharmacologic inhibition of cyclin dependent kinase 2 (Cdk2) and is augmented by combined treatment with a microtubule inhibitor. This proapoptotic effect occurs despite the presence of ras mutations in cancer cells. Anaphase catastrophe is a previously unrecognized mechanism that can be pharmacologically induced for apoptotic death of cancer cells and is, therefore, appealing to engage for cancer therapy and prevention.

Figure 1. Fates of mitotic cells

Cells can undergo diverse fates according to their status at anaphase. (A) Proper segregation of chromosomes in mitosis leads to the generation of two genetically identical daughter cells. (B) Gradual degradation of cyclin B in the presence of prolonged spindle checkpoint activation causes cells to exit mitosis without dividing chromosomes in anaphase, termed slippage. Cells that exit mitosis via slippage enter G1 as tetraploid cells. These cells may continue to cycle, senesce, or undergo apoptosis. (C) Anaphase catastrophe occurs when a cell with multiple centrosomes fails to coalesce centrosomes into two spindle poles and enters anaphase with a multipolar spindle. Segregation of chromosomes to more than two daughter cells causes cell death.

Figure 2. Inhibition of Cdk2 and other pathways triggers anaphase catastrophe in lung cancer cells

Mouse lung cancer cells overexpressing cyclin E were treated with control siRNA (A) or Cdk2 targeting siRNA (B) for 24 hr. Cells were stained for microtubules in red and DNA in blue. A representative bipolar anaphase (A) and a representative multipolar anaphase leading to anaphase catastrophe (B) are shown. Scale bar, 10µm. (C) Pharmacologic or genetic inhibition of numerous pathways affects mitotic fidelity and can trigger anaphase catastrophe leading to cell death. Centrosome amplification leads to supernumerary centrosomes. This can be prevented with a Plk4 inhibitor. Centrosome clustering enables cancer cells to survive through mitosis in the presence of supernumerary centrosomes. Inhibition of Cdk2, HSET, or ILK inhibits centrosome clustering, resulting in multipolar spindle formation. This causes multipolar anaphases that trigger anaphase catastrophe.