Highlights d Ras-ERK signaling controls cell shape in mitosis d Activation of Ras alters cell mechanics to enhance mitotic stiffening d Cells expressing Ras are better able to round up to divide under stiff gels d Ras limits DNA segregation errors normally observed in confined cell division
When cells enter mitosis, they become spherical and mechanically stiffen. We used MCF10A cell lines as a model system in which to investigate the effect of induced oncogene expression on mitotic entry. We find that activation of oncogenic Ras V12 , for as little as five hours, changes the way cells divide. Ras V12 -dependent activation of the MEK-ERK signalling cascade alters acto-myosin contractility to enhance mitotic rounding. Ras V12 also affects cell mechanics, so that Ras V12 expressing cells are softer in interphase but stiffen more upon entry into mitosis. As a consequence, Ras V12 expression augments the ability of cells to round up and divide faithfully when confined underneath a stiff hydrogel. Conversely, inhibition of the Ras-ERK pathway reduces mitotic rounding under confinement, resulting in chromosome segregation defects. These data suggest a novel mechanism by which oncogenic Ras-ERK signalling can aid division in stiff environments like those found in tumours.
2566 Background: BAL101553, a pro-drug of the small molecule BAL27862, is a novel microtubule targeting agent (MTA) with cytotoxic and vascular disrupting properties. Pre-clinical data showed anti-proliferative activity in several in vitro and xenograft tumour models, including tumours refractory to conventional MTAs through diverse resistance mechanisms. Primary objectives of this FIH study were determination of the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT). Secondary objectives included the evaluation of PK, PD and anti-tumour activity. Methods: An accelerated titration dose-escalation design was used. Eligible patients (pts) with advanced solid tumours, who had failed standard therapy, received BAL101553 as a 2-h intravenous infusion on days 1, 8 and 15 of a 28-day cycle. Adverse events (AEs) were assessed according to CTCAEv4. Disease response was assessed by RECIST 1.1 every 2 cycles. Results: 16 pts (7 male; median age 52 years; range 29-80) with solid tumours were treated at 4 dose levels (15, 30, 45 and 60 mg/m2). DLTs were observed at 60 mg/m2 and included rapidly reversible grade (G) 3 hypertension (HTN) and G3 reduced mobility/ dizziness. DLT criteria for HTN were subsequently modified. Frequent drug-related AEs were injection site reactions, nausea, vomiting (all G1-2), and G2-3 HTN (transient during the infusion; responding to nifedipine). One pt experienced G2 peripheral neuropathy at 60 mg/m2. PK analyses indicated conversion of BAL101553 to the active BAL27862, dose proportional exposure for both compounds and a half-life of BAL27862 in a range of 11 to 27 h. Preliminary tumour PD data comparing pre/post biopsies showed loss of CD34+ capillaries and focally decreased proliferation. A confirmed partial response was demonstrated in 1 pt with ampullary (pancreaticobiliary) cancer maintained on treatment for >16 cycles with intra-pt dose escalation. 2 pts (laryngeal and rectal cancer) demonstrated stable disease >16 weeks. Conclusions: BAL101553 is well tolerated up to 60 mg/m2 with evidence of anti-tumour activity. Dose escalation continues to determine the MTD. Clinical trial information: NCT01397929.
Oncogenic Ras has been shown to change the way cancer cells divide by increasing the forces generated during mitotic rounding. In this way, RasV12 enables cancer cells to divide across a wider range of mechanical environments than normal cells. Here, we identify a further role for oncogenic Ras-ERK signalling in division by showing that RasV12 expression alters the shape, division orientation and respreading dynamics of cells as they exit mitosis, in a manner that depends on MEK and ERK. Many of these effects appear to result from the impact of RasV12 signalling on actomyosin contractility, since RasV12 induces the severing of retraction fibres that normally guide spindle positioning and provide a memory of the interphase cell shape. In support of this idea, the RasV12 phenotype is reversed by inhibition of actomyosin contractility, and can be mimicked by the loss of cell-substrate adhesion during mitosis. Thus, the induction of oncogenic Ras-ERK signalling leads to rapid changes in division orientation that, along with the effects of RasV12 on cell growth and cell cycle progression, are likely to disrupt epithelial tissue organisation and contribute to cancer dissemination.
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