![]() ![]() Besides, similar pattern in G2/M and cyclin B1 was verified in vivo and in patients explants. Lack of these effects appeared in acquired T-DM1 resistant cells. Our results showed that T-DM1 induced G2/M cell cycle arrest in a cyclin B1/CDK1 dependent-manner. By cyclin B1 induction pattern, we could categorize T-DM1 responsive/non-responsive in fresh breast cancer explants from HER2 positive breast cancer patients. Finally, cyclin B1 induction by T-DM1 was confirmed in in vivo and ex vivo xenograft animal model and patients’ explants, respectively. Furthermore, the silencing of cdc20, a protein mainly involved in APC complex related cyclin B1 degradation, could sensitize the resistant cells to T-DM1. CDK1 activity assay was also correlated with cyclin B1 expression, increasing following T-DM1 treatment in the parental cells, but not in the resistant cells.įunctional analysis revealed that cyclin B1 knock down in the parental cells induced a significant T-DM1 resistance. Cyclin B1 accumulation induced by T-DM1 in the parental cells was not observed in the resistant cells. Expression/activity analysis of cyclin B1/CDK1 complex, the main apparatus involve in G2/M cell cycle arrest induction, showed a remarkable decrease in the basal level of cyclin B1 in the resistant cells. Analysis of T-DM1 effects on cell cycle showed a significant induction of G2/M arrest in the parental cells, while this effect was not observed in the resistant cells. We generated acquired resistant cells with different level of resistance to T-DM1 evaluated by 3, 7 and 10 days proliferation assay, using automated cell counting in SKBR3, HCC1419 and HCC1954 parental and the acquired resistant cells. resistant cells) generated by an established protocol of T-DM1 exposure, increasing the concentration of T-DM1, 3days on/3days off, for 54 days overall. Here, we focused on finding mechanisms of acquired resistance to T-DM1 in a panel of HER2 positive breast cancer cell lines (HCC1954, HCC1419 and SKBR3 parental vs. Looking for the mechanisms of resistance is necessary to improve patient selection and to develop novel treatment strategies. Although T-DM1 is approved for the treatment of HER2 positive metastatic breast cancer patients, primary and acquired resistance towards this drug is still a main challenge. ![]() DM1 delivery by trastuzumab inside the HER2 positive cells affects microtubule polymerization, cell cycle arrest and finally cell death. Trastuzumab-emtansine (T-DM1) is an antibody-cytotoxic agent (DM1) conjugated drug.
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