Identification of the APC/C co-factor FZR1 as a novel therapeutic target for multiple myeloma

Abstract

Multiple Myeloma (MM) is a haematological neoplasm characterised by the clonal proliferation of malignant plasma cells in the bone marrow. The success of proteasome inhibitors in the treatment of MM has highlighted the importance of the ubiquitin proteasome system (UPS) in the pathogenesis of this disease. In this study, we analysed gene expression of UPS components to identify novel therapeutic targets within this pathway in MM. Here we demonstrate how this approach identified previously validated and novel therapeutic targets. In addition we show that FZR1 (Fzr), a cofactor of the multi-subunit E3 ligase complex anaphase-promoting complex/cyclosome (APC/C), represents a novel therapeutic target in myeloma. The APC/C associates independently with two cofactors, Fzr and Cdc20, to control cell cycle progression. We found high levels of FZR1 in MM primary cells and cell lines and demonstrate that expression is further increased on adhesion to bone marrow stromal cells (BMSCs). Specific knockdown of either FZR1 or CDC20 reduced viability and induced growth arrest of MM cell lines, and resulted in accumulation of APC/CFzr substrate Topoisomerase IIα (TOPIIα) or APC/CCdc20 substrate Cyclin B. Similar effects were observed following treatment with proTAME, an inhibitor of both APC/CFzr and APC/CCdc20. Combinations of proTAME with topoisomerase inhibitors, etoposide and doxorubicin, significantly increased cell death in MM cell lines and primary cells, particularly if TOPIIα levels were first increased through pre-treatment with proTAME. Similarly, combinations of proTAME with the microtubule inhibitor vincristine resulted in enhanced cell death. This study demonstrates the potential of targeting the APC/C and its cofactors as a therapeutic approach in MM.

The therapeutic potential of cell cycle targeting in multiple myeloma

“…Recently, we showed that Cdc20 is significantly higher expressed in high-risk myeloma patients and this elevated Cdc20 correlates with a poor prognosis [ 79 ]. This was later on confirmed by Crawford et al [ 140 ]. In contrast to our observations, Crawford et al also showed that elevated Cdh1 levels are found in newly diagnosed myeloma patients.…”

“…In contrast to our observations, Crawford et al also showed that elevated Cdh1 levels are found in newly diagnosed myeloma patients. An explanation for this contradiction could be the different data sets used in both studies [ 79 , 140 ]. Nevertheless, we and Crawford et al both demonstrated that APC/C inhibition using the small molecule inhibitor proTAME induced a cell cycle arrest and caspase-mediated apoptosis in human cell lines and primary MM cells.…”

“…Nevertheless, we and Crawford et al both demonstrated that APC/C inhibition using the small molecule inhibitor proTAME induced a cell cycle arrest and caspase-mediated apoptosis in human cell lines and primary MM cells. Moreover, combinations with conventional anti-myeloma drugs such as melphalan, doxorubicin and vincristine resulted in enhanced anti-myeloma effect [ 79 , 140 ]. These data indicate that the APC/C could be a promising new target for MM therapy.…”

“…by inhibition of APC/C) seems a better strategy than inhibiting mitotic entry [ 75 , 153 ]. Based on preclinical data reported on the APC/C inhibitor proTAME, it seems that targeting APC/C could indeed be an efficient strategy in myeloma treatment, especially in combination with standard of care agents [ 79 , 140 ]. However, so far, it remains impossible to evaluate proTAME in clinical trials [ 141 ].…”

The Identification of Potential Therapeutic Targets for Cutaneous Squamous Cell Carcinoma

“…These data suggest that CDC20 rather than CDH1 has potential as a therapeutic target for cSCC. CDC20 is essential for mitosis, but a high level of suppression is required to block cell-cycle progression in normal cells and in many tumor cells (Baumgarten et al, 2009;Crawford et al, 2016;Jin et al, 2010;Kidokoro et al, 2008;Li et al, 2014, Li et al, 2007Taniguchi et al, 2008;Wirth et al, 2004;Zhang et al, 2014). The robust effects of targeting APC/C core subunits and CDC20 in SCCRDEB4 cells likely reflects sensitivity to partial suppression of APC/C.…”