Characterization of Signalling Pathways That Link Apoptosis and Autophagy to Cell Death Induced by Estrone Analogues Which Reversibly Depolymerize Microtubules

Abstract

The search for novel anti-cancer compounds which can circumvent chemotherapeutic drug resistance and limit systemic toxicity remains a priority. 2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)15-tetraene-3-ol-17one (ESE-15-one) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) are sulphamoylated 2-methoxyestradiol (2-ME) analogues designed by our research team. Although their cytotoxicity has been demonstrated in vitro, the temporal and mechanistic responses of the initiated intracellular events are yet to be determined. In order to do so, assays investigating the compounds’ effects on microtubules, cell cycle progression, signalling cascades, autophagy and apoptosis were conducted using HeLa cervical- and MDA-MB-231 metastatic breast cancer cells. Both compounds reversibly disrupted microtubule dynamics as an early event by binding to the microtubule colchicine site, which blocked progression through the cell cycle at the G1/S- and G2/M transitions. This was supported by increased pRB and p27Kip1 phosphorylation. Induction of apoptosis with time-dependent signalling involving the p-JNK, Erk1/2 and Akt/mTOR pathways and loss of mitochondrial membrane potential was demonstrated. Inhibition of autophagy attenuated the apoptotic response. In conclusion, the 2-ME analogues induced a time-dependent cross-talk between cell cycle checkpoints, apoptotic signalling and autophagic processes, with an increased reactive oxygen species formation and perturbated microtubule functioning appearing to connect the processes. Subtle differences in the responses were observed between the two compounds and the different cell lines.

The Tubulin Code and Tubulin-Modifying Enzymes in Autophagy and Cancer

“…The decreased cell killing effect, observed when autophagosome formation was inhibited by 3MA, demonstrated that blockage of autophagosome traffic and the accumulation of autophagosomes promotes paclitaxel-induced cancer cell death [144]. In line with these findings, several new tubulin binding agents have been shown to activate apoptosis as a result of autophagic flux inhibition in cancer cells [145][146][147][148]. It could be envisaged that induction of autophagosome formation in response to prolonged mitotic arrest and/or mitotic slippage, together with the reduction of autophagosome turnover by flux blockage, could result in the accumulation of autophagosomes, the intracellular persistence of toxic substances and/or damaged organelles, the production of oxygen reactive species, and cytotoxicity [149].…”

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

“…MTAs like taxotere, epothilone B, discodermolide, vincristine, and colchicine have been shown to inhibit HIF-1α nuclear accumulation and activity by disrupting MT function [194]. Finally, 2-methoxyestradiol (2ME2) is a natural molecule derived from the hormone estradiol that also alters MT dynamics and has antitumor and antiangiogenic properties [195][196][197]. 2ME2 impairs HIF-1α function and therefore inhibits angiogenesis [194,198].…”

Cell Fate following Irradiation of MDA-MB-231 and MCF-7 Breast Cancer Cells Pre-Exposed to the Tetrahydroisoquinoline Sulfamate Microtubule Disruptor STX3451

“…2ME2 and its sulfamoylated analogs address those parameters and indeed have been shown to pre-sensitize prostate and breast cancer cells to radiation whilst selectively sparing non-neoplastic cells [25][26][27][28]. The nonfunctional microtubules result in a G 1 and/or a G 2 -M phase block, which are described as the most radiosensitive phases of the cell cycle [29,30]. Additionally, increased generation of reactive oxygen species (ROS) from exposure to the 2ME2/2ME2 analogs may contribute to those formed by the intracellular water-photon reaction from the radiation, resulting in intrinsic apoptosis and DNA damage.…”