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Purpose: Trastuzumab-emtansine (T-DM1) is a standard treatment in advanced HER2-positive breast cancer. However, resistance inevitably occurs. We aimed to identify mechanisms of acquired T-DM1 resistance. Experimental Design: HER2-positive breast cancer cells (HCC1954, HCC1419, SKBR3, and BT474) were treated in a pulse-fashion with T-DM1 to induce a resistant phenotype. Cellular and molecular effects of T-DM1 in parental versus resistant cells were compared. CDK1 kinase activity and cyclin B1 expression were assayed under various conditions. Genetic modifications to up- or downregulate cyclin B1 were conducted. Effects of T-DM1 on cyclin B1 levels, proliferation, and apoptosis were assayed in human HER2 -positive breast cancer explants. Results: We obtained three cell lines with different levels of acquired T-DM1 resistance (HCC1954/TDR, HCC1419/TDR, and SKBR3/TDR cells). HER2 remained amplified in the resistant cells. Binding to HER2 and intracellular uptake of T-DM1 were maintained in resistant cells. T-DM1 induced cyclin B1 accumulation in sensitive but not resistant cells. Cyclin B1 knockdown by siRNA in parental cells induced T-DM1 resistance, while increased levels of cyclin B1 by silencing cdc20 partially sensitized resistant cells. In a series of 18 HER2-positive breast cancer fresh explants, T-DM1 effects on proliferation and apoptosis paralleled cyclin B1 accumulation. Conclusions: Defective cyclin B1 induction by T-DM1 mediates acquired resistance in HER2-positive breast cancer cells. These results support the testing of cyclin B1 induction upon T-DM1 treatment as a pharmacodynamic predictor in HER2-positive breast cancer. Clin Cancer Res; 23(22); 7006-19. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Spermatogenesis, which involves mitosis and meiosis of male germ cells, is a highly complicated and coordinately ordered process. Cyclin B1 (CCNB1), an important regulator in cell cycle machinery, is proved essential for mouse embryonic development. However, the role of CCNB1 in mammalian spermatogenesis remains unclear. Here we tested the requirement for CCNB1 using conditional knockout mice lacking CCNB1 in male germ cells. We found that ablation of CCNB1 in gonocytes and spermatogonia led to mouse sterile caused by the male germ cells' depletion. Gonocyte and spermatogonia without CCNB1 is unable to proliferate normally and apoptosis increased. Moreover, CCNB1 ablation in spermatogonia may promote their differentiation by downregulating Lin28a and upregulating let-7 miRNA. However, ablation of CCNB1 in premeiotic male germ cells did not have an effect on meiosis of spermatocytes and male fertility, suggesting that CCNB1 may be dispensable for meiosis of spermatocytes. Collectively, these results indicate that CCNB1 is critically required for the proliferation of gonocytes and spermatogonia but may be redundant in meiosis of spermatocytes in mouse spermatogenesis.

Cyclins B1 and B2 are frequently elevated in human cancers and are associated with tumour aggressiveness and poor clinical outcome; however, whether and how B-type cyclins drive tumorigenesis is unknown. Here we show that cyclin B1 and B2 transgenic mice are highly prone to tumours, including tumour types where B-type cyclins serve as prognosticators. Cyclins B1 and B2 both induce aneuploidy when overexpressed but through distinct mechanisms, with cyclin B1 inhibiting separase activation, leading to anaphase bridges, and cyclin B2 triggering aurora-A-mediated Plk1 hyperactivation, resulting in accelerated centrosome separation and lagging chromosomes. Complementary experiments revealed that cyclin B2 and p53 act antagonistically to control aurora-A-mediated centrosome splitting and accurate chromosome segregation in normal cells. These data demonstrate a causative link between B-type cyclin overexpression and tumour pathophysiology, and uncover previously unknown functions of cyclin B2 and p53 in centrosome separation that may be perturbed in many human cancers.