Targeting mitotic exit in solid tumors.

Targeting mitosis by taxanes is one of the most common chemotherapeutic approaches in various malignant solid tumors, but cancer cells may survive antimitotic treatment with attainable concentrations due to mitotic slippage with a residual activity of the ubiquitin ligase anaphase-promoting complex (APC/C) and a continuous slow ubiquitin-proteasome-dependent cyclin B-degradation leading to mitotic exit. Therefore, blocking cyclin B-proteolysis via additional proteasome (PI) or APC/C-inhibition may have the potential to enhance tumor cell eradication by inducing a more robust mitotic block and mitotic cell death. Here, we analyzed this approach in different cell lines and more physiological patient-derived xenografts (PDX) from lung and breast cancer.

Structural centrosome aberrations sensitize polarized epithelia to basal cell extrusion.

Centrosome aberrations disrupt tissue architecture and may confer invasive properties to cancer cells. Here we show that structural centrosome aberrations, induced by overexpression of either Ninein-like protein (NLP) or CEP131/AZI1, sensitize polarized mammalian epithelia to basal cell extrusion. While unperturbed epithelia typically dispose of damaged cells through apical dissemination into luminal cavities, certain oncogenic mutations cause a switch in directionality towards basal cell extrusion, raising the potential for metastatic cell dissemination.

Impact of Centrosome Aberrations on Chromosome Segregation and Tissue Architecture in Cancer.

Centrosomes determine the disposition of microtubule networks and thereby contribute to regulate cell shape, polarity, and motility, as well as chromosome segregation during cell division. Additionally, centrioles, the core components of centrosomes, are required for the formation of cilia and flagella. Mutations in genes coding for centrosomal and centriolar proteins are responsible for several human diseases, foremost ciliopathies and developmental disorders resulting in small brains (primary microcephaly) or small body size (dwarfism).

Structural centrosome aberrations promote non-cell-autonomous invasiveness.

Centrosomes are the main microtubule-organizing centers of animal cells. Although centrosome aberrations are common in tumors, their consequences remain subject to debate. Here, we studied the impact of structural centrosome aberrations, induced by deregulated expression of ninein-like protein (NLP), on epithelial spheres grown in Matrigel matrices.

Proteasome inhibition enhances the efficacy of volasertib-induced mitotic arrest in AML in vitro and prolongs survival in vivo.

Elderly and frail patients, diagnosed with acute myeloid leukemia (AML) and ineligible to undergo intensive treatment, have a dismal prognosis. The small molecule inhibitor volasertib induces a mitotic block via inhibition of polo-like kinase 1 and has shown remarkable anti-leukemic activity when combined with low-dose cytarabine. We have demonstrated that AML cells are highly vulnerable to cell death in mitosis yet manage to escape a mitotic block through mitotic slippage by sustained proteasome-dependent slow degradation of cyclin B.

Suppression of APC/CCdh1 has subtype specific biological effects in acute myeloid leukemia.

The E3 ubiquitin ligase and tumor suppressor APC/CCdh1 is crucial for cell cycle progression, development and differentiation in many cell types. However, little is known about the role of Cdh1 in hematopoiesis. Here we analyzed Cdh1 expression and function in malignant hematopoiesis.

Metadherin exon 11 skipping variant enhances metastatic spread of ovarian cancer.

Metastatic ovarian cancer has a dismal prognosis and current chemotherapeutic approaches have very limited success. Metadherin (MTDH) is expressed in human ovarian cancer tissue and its expression inversely correlates with patients overall survival. Consistent with these studies, we observed MTDH expression in tissue specimens of FIGO Stage III ovarian carcinomas (72/83 cases).

The 3' untranslated region of the cyclin B mRNA is not sufficient to enhance the synthesis of cyclin B during a mitotic block in human cells.

Antimitotic agents are frequently used to treat solid tumors and hematologic malignancies. However, one major limitation of antimitotic approaches is mitotic slippage, which is driven by slow degradation of cyclin B during a mitotic block. The extent to which cyclin B levels decline is proposed to be governed by an equilibrium between cyclin B synthesis and degradation.

BubR1 is frequently repressed in acute myeloid leukemia and its re-expression sensitizes cells to antimitotic therapy.

Spindle poison-based therapy is of only limited benefit in acute myeloid leukemia while lymphoblastic leukemia/lymphoma responds well. In this study, we demonstrated that the spindle assembly checkpoint protein BubR1 was down-regulated in the vast majority of cases of acute myeloid leukemia whereas its expression was high in lymphoblastic cells. Correct function of the spindle assembly checkpoint is pivotal in mediating mitotic delay in response to spindle poisons.

Potent in vitro and in vivo activity of sorafenib in multiple myeloma: induction of cell death, CD138-downregulation and inhibition of migration through actin depolymerization.

Despite considerable advances, multiple myeloma (MM) remains incurable and the development of novel therapies targeting the interplay between plasma cells (PCs) and their bone marrow (BM) microenvironment remains essential. We investigated the effect of various agents in vitro on the proliferation, phenotype, morphology, actin polymerization and migration of MM cells and, in vivo, the tumour growth of L363-bearing non-obese diabetic severe combined immunodeficient mice with a deficient interleukin-2 receptor gamma chain (NSG). In vitro, we observed a dose-dependent cytotoxicity with bortezomib and sorafenib.

Studying proteolysis of cyclin B at the single cell level in whole cell populations.

Equal distribution of chromosomes between the two daughter cells during cell division is a prerequisite for guaranteeing genetic stability. Inaccuracies during chromosome separation are a hallmark of malignancy and associated with progressive disease. The spindle assembly checkpoint (SAC) is a mitotic surveillance mechanism that holds back cells at metaphase until every single chromosome has established a stable bipolar attachment to the mitotic spindle.

Cell cycle control in acute myeloid leukemia.

Acute myeloid leukemia (AML) is the result of a multistep transforming process of hematopoietic precursor cells (HPCs) which enables them to proceed through limitless numbers of cell cycles and to become resistant to cell death. Increased proliferation renders these cells vulnerable to acquiring mutations and may favor leukemic transformation. Here, we review how deregulated cell cycle control contributes to increased proliferation in AML and favors genomic instability, a prerequisite to confer selective advantages to particular clones in order to adapt and independently proliferate in the presence of a changing microenvironment.

Monitoring APC/C activity in the presence of chromosomal misalignment in unperturbed cell populations.

Chromosome segregation is under strict control of the spindle assembly checkpoint (SAC). The SAC regulates anaphase-promoting complex/cyclosome (APC/C)-dependent proteolysis of securin and cyclin B. Unattached or misaligned chromosomes trigger SAC-mediated mitotic delay by stabilizing securin and cyclin B due to inhibition of APC/C until the problem is solved.

Management of multiple myeloma in pregnancy: strategies for a rare challenge.

Multiple myeloma is the second most commonly diagnosed hematologic malignancy. It is characterized by the accumulation of monoclonal plasma cells. It typically manifests in the sixth decade of life or later, whereas the incidence in patients who are younger than 40 years old is extremely rare.