Measurement of Cdk1/Cyclin B Kinase Activity by Specific Antibodies and Western Blotting

Abemaciclib Is Effective in Palbociclib-Resistant Hormone Receptor-Positive Metastatic Breast Cancers

Cyclin-dependent kinases 4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) is standard of care for patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC). However, resistance to CDK4/6is plus ET remains a clinical problem with limited therapeutic options following disease progression. Different CDK4/6is might have distinct mechanisms of resistance, and therefore using them sequentially or targeting their differentially altered pathways could delay disease progression. To understand pathways leading to resistance to the CDK4/6is palbociclib and abemaciclib, we generated multiple in vitro models of palbociclib-resistant (PR) and abemaciclib-resistant (AR) cell lines as well as in vivo patient-derived xenografts (PDX) and ex vivo PDX-derived organoids (PDxO) from patients who progressed on CDK4/6i. PR and AR breast cancer cells exhibited distinct transcriptomic and proteomic profiles that sensitized them to different classes of inhibitors; PR cells upregulated G2-M pathways and responded to abemaciclib, while AR cells upregulated mediators of the oxidative phosphorylation pathway (OXPHOS) and responded to OXPHOS inhibitors. PDX and organoid models derived from patients with PR breast cancer remained responsive to abemaciclib. Resistance to palbociclib while maintaining sensitivity to abemaciclib was associated with pathway-specific transcriptional activity but was not associated with any individual genetic alterations. Finally, data from a cohort of 52 patients indicated that patients with HR-positive/HER2-negative MBC who progressed on palbociclib-containing regimens can exhibit a meaningful overall clinical benefit from abemaciclib-based therapy when administered after palbociclib. These findings provide the rationale for clinical trials evaluating the benefit of abemaciclib treatment following progression on a prior CDK4/6i.

SIGNIFICANCE

Palbociclib-resistant breast cancers respond to abemaciclib and express pathway-specific signatures of sensitivity, providing a biomarker-driven therapeutic option for patients with metastatic breast cancer following disease progression on cyclin-dependent kinases 4/6 inhibitors.

Pulchelloid A, a sesquiterpene lactone from the Canadian prairie plant Gaillardia aristata inhibits mitosis in human cells

BACKGROUND

The Canadian prairie ecosystem presents a rich source of natural products from plants that are subjected to herbivory by grazing mammals. This type of ecological competition may contribute to the production of natural products of interest in cell biology and medical research. We provide the first biological description of the sesquiterpene lactone, pulchelloid A, which we isolated from the prairie plant, Gaillardia aristata (Asteraceae) and report that it inhibits mitosis in human cells.

METHODS AND RESULTS

We found that G. aristata (Blanket flower) extracts were cytotoxic to human cell lines and used phenotypic assays to characterize the bioactivity of extracts. Before dying, cells were characterized by a rounded morphology, phospho-histone H3 signals, mitotic spindles, and active Cdk1. By biology-guided fractionation of Gaillardia extracts, we isolated a sesquiterpene lactone named pulchelloid A. We used immunofluorescence microscopy and observed that cells treated with pulchelloid A have phospho-histone H3 positive chromosomes and a mitotic spindle, confirming that they were in mitosis. Treated cells arrest with an unusual phenotype; they enter a prolonged mitotic arrest in which the spindles become multipolar and the chromosomes acquire histone γH2AX foci, a hallmark of damaged DNA.

CONCLUSIONS

We propose that pulchelloid A, a natural product present in the prairie plant Gaillardia aristata, delays cells in mitosis. There is a growing body of evidence that a small number of members of the sesquiterpene lactone chemical family may target proteins that regulate mitosis.

Upregulation of Myt1 Promotes Acquired Resistance of Cancer Cells to Wee1 Inhibition

Adavosertib (also known as AZD1775 or MK1775) is a small-molecule inhibitor of the protein kinase Wee1, with single-agent activity in multiple solid tumors, including sarcoma, glioblastoma, and head and neck cancer. Adavosertib also shows promising results in combination with genotoxic agents such as ionizing radiation or chemotherapy. Previous studies have investigated molecular mechanisms of primary resistance to Wee1 inhibition. Here, we investigated mechanisms of acquired resistance to Wee1 inhibition, focusing on the role of the Wee1-related kinase Myt1. Myt1 and Wee1 kinases were both capable of phosphorylating and inhibiting Cdk1/cyclin B, the key enzymatic complex required for mitosis, demonstrating their functional redundancy. Ectopic activation of Cdk1 induced aberrant mitosis and cell death by mitotic catastrophe. Cancer cells with intrinsic adavosertib resistance had higher levels of Myt1 compared with sensitive cells. Furthermore, cancer cells that acquired resistance following short-term adavosertib treatment had higher levels of Myt1 compared with mock-treated cells. Downregulating Myt1 enhanced ectopic Cdk1 activity and restored sensitivity to adavosertib. These data demonstrate that upregulating Myt1 is a mechanism by which cancer cells acquire resistance to adavosertib. SIGNIFICANCE: Myt1 is a candidate predictive biomarker of acquired resistance to the Wee1 kinase inhibitor adavosertib.

Experimental Determination of Checkpoint Adaptation by Mitotic Shake-Off and Microscopy

Cells that undergo checkpoint adaptation arrest at and then abrogate the G2/M cell cycle checkpoint to enter mitosis with damaged DNA. Cells surviving this process frequently contain micronuclei, which can lead to genomic change and chromothripsis. In this chapter we describe how to induce checkpoint adaptation and detect it by time-lapse video and immunofluorescence microscopy and how to isolate cells undergoing checkpoint adaptation from a total cell population.

Antibody Engineering for Pursuing a Healthier Future

Since the development of antibody-production techniques, a number of immunoglobulins have been developed on a large scale using conventional methods. Hybridoma technology opened a new horizon in the production of antibodies against target antigens of infectious pathogens, malignant diseases including autoimmune disorders, and numerous potent toxins. However, these clinical humanized or chimeric murine antibodies have several limitations and complexities. Therefore, to overcome these difficulties, recent advances in genetic engineering techniques and phage display technique have allowed the production of highly specific recombinant antibodies. These engineered antibodies have been constructed in the hunt for novel therapeutic drugs equipped with enhanced immunoprotective abilities, such as engaging immune effector functions, effective development of fusion proteins, efficient tumor and tissue penetration, and high-affinity antibodies directed against conserved targets. Advanced antibody engineering techniques have extensive applications in the fields of immunology, biotechnology, diagnostics, and therapeutic medicines. However, there is limited knowledge regarding dynamic antibody development approaches. Therefore, this review extends beyond our understanding of conventional polyclonal and monoclonal antibodies. Furthermore, recent advances in antibody engineering techniques together with antibody fragments, display technologies, immunomodulation, and broad applications of antibodies are discussed to enhance innovative antibody production in pursuit of a healthier future for humans.