Rigosertib

INTRODUCTION: ;Ovarian cancer is a difficult to treat cancer entity with a high relapse rate. After initial surgery and chemotherapy, only a few options for therapeutic treatment remain in case of cancer recurrence. New treatment options with improved efficacies to circumvent acquired or pre-existing drug resistance are needed.;MATERIALS: ;This survey focuses on new prospective drugs for ovarian cancer treatment that either cause direct damage to the nuclear DNA or inhibit chromosome segregation by acting as mitotic spindle inhibitors.;RESULTS: ;Among a plethora of currently tested and proposed new drugs for ovarian cancer treatment, only a few appear to meet the criteria of sufficient and reliable efficacy with tolerable toxicity. These include the naturally occurring DNA-alkylating alkaloid trabectedin, the nitrogen mustard prodrug canfosfamide, and the synthetic kinase inhibitor ON-01910. The latter inhibits mitotic spindle formation without a direct tubulin interaction, avoiding adverse neurotoxic reactions common to the taxanes. Further, epothilones and oxaliplatin, already approved drugs for other cancer entities, show promising activity against ovarian cancer; they are even of interest as a first-line treatment option.

ESPL1/separase, a cysteine endopeptidase, is a key player in centrosome duplication and mitotic sister chromatid separation. Aberrant expression and/or altered separase proteolytic activity are associated with centrosome amplification, aneuploidy, tumorigenesis and disease progression. Since centrosome alterations are a common and early detectable feature in patients with myelodysplastic syndrome (MDS) and cytogenetic aberrations play an important role in disease risk stratification, we examined separase activity on single cell level in 67 bone marrow samples obtained from patients with MDS, secondary acute myeloid leukemia (sAML), de novo acute myeloid leukemia (AML) and healthy controls by a flow cytometric separase activity assay. The separase activity distribution (SAD) value, a calculated measure for the occurrence of cells with prominent separase activity within the analyzed sample, was tested for correlation with the centrosome, karyotype and gene mutation status. We found higher SAD values in bone marrow cells of sAML patients than in corresponding cells of MDS patients. This concurred with an increased incidence of aberrant centrosome phenotypes in sAML vs. MDS samples. No correlation was found between SAD values and the karyotype/gene mutation status.

Mammalian erythroblasts undergo enucleation through a process thought to be similar to cytokinesis. Microtubule-organizing centers (MTOCs) mediate organization of the mitotic spindle apparatus that separates the chromosomes during mitosis and are known to be crucial for proper cytokinesis. However, the role of MTOCs in erythroblast enucleation remains unknown. We therefore investigated the effect of various MTOC inhibitors on cytokinesis and enucleation using human colony-forming units-erythroid (CFU-Es) and mature erythroblasts generated from purified CD34(+) cells. We found that erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA), a dynein inhibitor, and monastrol, a kinesin Eg5 inhibitor, as well as various inhibitors of MTOC regulators, including ON-01910 (Plk-1), MLN8237 (aurora A), hesperadin (aurora B), and LY294002 (PI3K), all inhibited CFU-E cytokinesis. Among these inhibitors, however, only EHNA blocked enucleation. Moreover, terminally differentiated erythroblasts expressed only dynein; little or none of the other tested proteins was detected. Over the course of the terminal differentiation of human erythroblasts, the fraction of cells with nuclei at the cell center declined, whereas the fraction of polarized cells, with nuclei shifted to a position near the plasma membrane, increased.