Diverse microtubule-targeted anticancer agents kill cells by inducing chromosome missegregation on multipolar spindles

Abstract

Microtubule-targeted agents are commonly used for cancer treatment, though many patients do not benefit. Microtubule-targeted drugs were assumed to elicit anticancer activity via mitotic arrest because they cause cell death following mitotic arrest in cell culture. However, we recently demonstrated that intratumoral paclitaxel concentrations are insufficient to induce mitotic arrest and rather induce chromosomal instability (CIN) via multipolar mitotic spindles. Here, we show in metastatic breast cancer and relevant human cellular models that this mechanism is conserved among clinically useful microtubule poisons. While multipolar divisions typically produce inviable progeny, multipolar spindles can be focused into near-normal bipolar spindles at any stage of mitosis. Using a novel method to quantify the rate of CIN, we demonstrate that cell death positively correlates with net loss of DNA. Spindle focusing decreases CIN and causes resistance to diverse microtubule poisons, which can be counteracted by addition of a drug that increases CIN without affecting spindle polarity. These results demonstrate conserved mechanisms of action and resistance for diverse microtubule-targeted agents. Trial registration: clinicaltrials.gov, NCT03393741.

Suppressing Anaphase-Promoting Complex/Cyclosome–Cell Division Cycle 20 Activity to Enhance the Effectiveness of Anti-Cancer Drugs That Induce Multipolar Mitotic Spindles

“…Paclitaxel is approved in the USA for the treatment of more than 20 types of adult cancers [ 27 ]. The therapeutic index of 10 nM paclitaxel, the clinically relevant amount to work with in lab-cultured MDA-MB-231 cell lines [ 14 ], is now hypothesized not to involve cell-cycle arrest in mitosis, but rather may be derived from the formation of multipolar mitotic spindles that can lead to two different cell death fates after a mother cell with a multipolar spindle executes an aberrant mitosis [ 4 , 5 , 9 , 10 , 14 , 15 , 16 ] ( Figure 1 ).…”

“…Elevated levels of chromosome mis-segregation on the multipolar spindle may induce necrosis/apoptosis/quiescence in the daughter cells due to a loss of genetic information and/or cell stress induced by imbalances in transcriptional networks, resulting in dysfunctional and proteo-toxic protein expression levels [ 9 , 14 , 15 , 16 ]. Second, a lagging chromosome(s) in anaphase on the multipolar spindle of the mother cell may lead to a chromatin bridge(s) in cytokinesis that activates the cGAS-STING pathway in the daughter cells, which may promote type I interferon secretion, resulting in leukocyte recruitment into solid tumors which execute immunogenic cell death, a pathway that can also be activated during apoptosis and/or necrosis [ 4 , 5 , 9 , 10 , 28 , 29 ].…”

“…Furthermore, to make matters more confounding, to our knowledge, the clinically relevant doses for eribulin and vinorelbine have also not yet been established in this compelling way for in vitro cell culture-based experimentation. However, progress in the right direction is being made [ 16 ].…”

“…Thus, the current hypothesis is that the therapeutic index of 10 nM paclitaxel, the clinically relevant amount to expose MDA-MB-231 breast cancer cell lines to in vitro [ 14 ], does not involve substantial cell-cycle arrest in mitosis, but rather may be derived from the formation of multipolar mitotic spindles that can lead to two different cell death fates after a mother cell with a multipolar spindle executes an aberrant mitosis, namely (i) an apoptosis/necrosis/quiescence pathway and (ii) an immunogenic cell death pathway [ 4 , 5 , 9 , 10 , 14 , 15 , 16 ]. Eribulin and vinorelbine, two other anti-cancer, anti-mitotic agents, like paclitaxel, were recently observed to promote multipolar spindles in situ in tumor biopsy samples and in vitro in tissue culture cells, even though they induce microtubule depolymerization instead of microtubule stability like paclitaxel [ 16 ]. The implications of the results of these clinical trials [ 9 , 14 , 15 , 16 ] and cell-line studies on paclitaxel, eribulin and vinorelbine are profound: post-treatment in situ tumor cell analyses revealed only small increases in mitotic indices (5% or less) and large increases in the number of multipolar mitotic spindles (between 10 and 60%) in the cancer cells.…”

“…Eribulin and vinorelbine, two other anti-cancer, anti-mitotic agents, like paclitaxel, were recently observed to promote multipolar spindles in situ in tumor biopsy samples and in vitro in tissue culture cells, even though they induce microtubule depolymerization instead of microtubule stability like paclitaxel [ 16 ]. The implications of the results of these clinical trials [ 9 , 14 , 15 , 16 ] and cell-line studies on paclitaxel, eribulin and vinorelbine are profound: post-treatment in situ tumor cell analyses revealed only small increases in mitotic indices (5% or less) and large increases in the number of multipolar mitotic spindles (between 10 and 60%) in the cancer cells. For paclitaxel, these levels correspond to 10 nM paclitaxel in MDA-MB-231 and CAL-51 breast cancer cell lines, with a limited increase in mitotic index (20% or less) as the key factor which establishes this limit in the mitotic index as an experimental cut-off for clinical relevancy.…”