Tracking the cell cycle origins for escape from topotecan action by breast cancer cells

Abstract

The anticancer agent topotecan is considered to be S-phase specific. This implies that cancer cells that are not actively replicating DNA could resist the effects of the drug. The cycle specificity of topotecan action was investigated in MCF-7 cells, using time-lapse microscopy to link the initial cell cycle position during acute exposures to topotecan with the antiproliferative consequences for individual cells. The bioactive dose range (0.5 -10 mM) for 1-h topotecan exposures was defined by rapid drug delivery and topoisomerase I trapping. Topotecan caused pan-cycle induction and activation of p53. Lineage analysis of the time-lapse sequences identified cells initially in S-phase and G2, and defined the time to mitosis for cells originating from G2, S-phase and G1. Topotecan prevented all mitoses from S-phase cells and G1 cells (half-maximal effects at 0.14 mM and 0.96 mM, respectively). No dose of topotecan completely prevented mitosis among G2 cells, and at saturating doses of topotecan about half the cells of G2 origin continued dividing (the half-maximal effects was at 0.31 mM). Overall, topotecan differentially targeted G1-, S-and G2-phase cells, but many G2 cells were resistant to topotecan, presenting a clear route for cell cycle-mediated drug resistance.

Poly(ADP-ribose) polymerase signaling of topoisomerase 1-dependent DNA damage in carcinoma cells

“…For our experiments we performed 1 h treatment with up to 10 M TPT that was already reported to be sufficient for trapping TOP1 in MCF7 cells [26]. PJ34 was used at a concentration (5 M) that was capable of inhibiting PARP activity but devoid of cytotoxic effects We found that TPT toxicity was higher when PAR synthesis was strongly reduced by either PARP-1 silencing (HeLa …”

Cytostatic and Cytotoxic Effects of Topotecan Decoded by a Novel Mathematical Simulation Approach

“…Agents in this pathway might also be engaged outside G 1 , with a role in cell cycle delays or cell death in S and G 2 -M phases; these are the effects experienced by many BrdUrd-positive cells, which never had a chance to reach G 1 . Feeney et al (13) found that after TPT treatment, p53 expression increased more in S and G 2 -M cells than in G 1 cells, and the high level lasted a long time. There is also evidence of activation of p53-dependent responses outside G 1 (20).…”

“…Feeney et al (13) investigated cell cycle effects of TPT by timelapse microscopy. They suggested that cells treated with TPT while in G 1 and S phase were unable to duplicate in 48 h, whereas part of G 2 -M cells could divide.…”

Exploration of the intercellular heterogeneity of topotecan uptake into human breast cancer cells through compartmental modelling

“…Cells might vary according to their structure (e.g., growth rate and morphology) and/or behaviour (e.g., invasion and metastasis) [23]. The verification and importance of heterogeneity of these cells is therefore explored using a new mathematical multi-cell compartmental model [24,25] of the interaction between TPT and a population of MCF-7 breast cancer cells [8].…”

“…The cancer cells are characterised by a rapid proliferation rate which is paralleled by topoisomerase I activity. Since TPT activity is sensitive to proliferating cells and is S-phase specific [8], cancer cells are more likely to be targeted by the drug due to the increased levels of topoisomerase I.…”