Sphingosine kinase 2 supports the development of BCR/ABL-independent acute lymphoblastic leukemia in mice

Sphingosine kinase (SphK) 2 has been implicated in the development of a range of cancers and inhibitors of this enzyme are currently in clinical trial. We have previously demonstrated a role for SphK2 in the development of acute lymphoblastic leukemia (ALL).In this and our previous study we use mouse models: in the previous study the disease was driven by the proto-oncogene BCR/ABL1, while in this study cancer risk was elevated by deletion of the tumor suppressor ARF.Mice lacking ARF and SphK2 had a significantly reduced incidence of ALL compared mice with wild type SphK2.These results show that the role of SphK2 in ALL development is not limited to BCR/ABL1 driven disease extending the potential use of inhibitors of this enzyme to ALL patients whose disease have driver mutations other than BCR/ABL1.Vicki Xie, Daochen Tong, Craig T. Wallington-Beddoe, Ken F. Bradstock and Linda J. Bendal

Ceramide-induced integrated stress response overcomes Bcl-2 inhibitor resistance in acute myeloid leukemia.

Inducing cell death by the sphingolipid ceramide is a potential anti-cancer strategy, but the underlying mechanisms remain poorly defined. Here, we show that triggering accumulation of ceramide in acute myeloid leukaemia (AML) cells by inhibition of sphingosine kinase induces an apoptotic integrated stress response (ISR) through protein kinase R-mediated activation of the master transcription factor ATF4. This leads to transcription of the BH3-only protein, Noxa, and degradation of the pro-survival Mcl-1 protein on which AML cells are highly dependent on for survival. Targeting this novel ISR pathway in combination with the Bcl-2 inhibitor venetoclax synergistically killed primary AML blasts, including those with venetoclax-resistant mutations, as well as immunophenotypic leukemic stem cells, and reduced leukemic engraftment in patient-derived AML xenografts. Collectively, these findings provide mechanistic insight into the anti-cancer effects of ceramide and pre-clinical evidence for new approaches to augment Bcl-2 inhibition in the therapy of AML and other cancers with high Mcl-1 dependency.Alexander C. Lewis, Victoria S. Pope, Melinda N. Tea, Manjun Li, Gus O. Nwosu, Thao M. Nguyen, Craig T. Wallington-Beddoe, Paul A. B. Moretti, Dovile Anderson, Darren J. Creek, Maurizio Costabile, Saira R. Ali, Chloe A. L. Thompson-Peach, B. Kate Dredge, Andrew G. Bert, Gregory J. Goodall, Paul G. Ekert, Anna L. Brown, Richard D'Andrea, Nirmal Robinson, Melissa R. Pitman, Daniel Thomas, David M. Ross, Briony L. Gliddon, Jason A. Powell, and Stuart M. Pitso

Desmoglein-2 expression is an independent predictor of poor prognosis patients with multiple myeloma

accepted 9 July 2021 OnlinePublMultiple myeloma (MM) is the second most common hematological malignancy and is an incurable disease of neoplastic plasma cells (PC). Newly-diagnosed MM patients currently undergo lengthy genetic testing to match chromosomal mutations with the most potent drug/s to decelerate disease progression. With only 17% of MM patients surviving 10-years post diagnosis, faster detection and earlier intervention would unequivocally improve outcomes. Here, we show that the cell surface protein desmoglein-2 (DSG2) is overexpressed in ~20% of bone marrow biopsies from newly-diagnosed MM patients. Importantly, DSG2 expression was strongly predictive of poor clinical outcome, with patients expressing DSG2 above the 70th percentile exhibiting an almost 3-fold increased risk of death. As a prognostic factor, DSG2 is independent of genetic subtype as well as the routinely measured biomarkers of MM activity (e.g. paraprotein). Functional studies revealed a non-redundant role for DSG2 in adhesion of MM PC to endothelial cells. Together, our studies suggest DSG2 to be a potential cell surface biomarker that can be readily detected by flow cytometry to rapidly predict disease trajectory at the time of diagnosis.Lisa M. Ebert, Kate Vandyke, M. Zahied Johan, Mark DeNichilo, Lih Y. Ta

Resensitising proteasome inhibitor-resistant myeloma with sphingosine kinase 2 inhibition.

The introduction of the proteasome inhibitor bortezomib into treatment regimens for myeloma has led to substantial improvement in patient survival. However, whilst bortezomib elicits initial responses in many myeloma patients, this haematological malignancy remains incurable due to the development of acquired bortezomib resistance. With other patients presenting with disease that is intrinsically bortezomib resistant, it is clear that new therapeutic approaches are desperately required to target bortezomib-resistant myeloma. We have previously shown that targeting sphingolipid metabolism with the sphingosine kinase 2 (SK2) inhibitor K145 in combination with bortezomib induces synergistic death of bortezomib-naïve myeloma. In the current study, we have demonstrated that targeting sphingolipid metabolism with K145 synergises with bortezomib and effectively resensitises bortezomib-resistant myeloma to this proteasome inhibitor. Notably, these effects were dependent on enhanced activation of the unfolded protein response, and were observed in numerous separate myeloma models that appear to have different mechanisms of bortezomib resistance, including a new bortezomib-resistant myeloma model we describe which possesses a clinically relevant proteasome mutation. Furthermore, K145 also displayed synergy with the next-generation proteasome inhibitor carfilzomib in bortezomib-resistant and carfilzomib-resistant myeloma cells. Together, these findings indicate that targeting sphingolipid metabolism via SK2 inhibition may be effective in combination with a broad spectrum of proteasome inhibitors in the proteasome inhibitor resistant setting, and is an approach worth clinical exploration.Melissa K. Bennett, Manjun Li, Melinda N. Tea, Melissa R. Pitman, John Toubia, Paul P.-S. Wang, Dovile Anderson, Darren J. Creek, Robert Z. Orlowski, Briony L. Gliddon, Jason A. Powell, Craig T. Wallington-Beddoe, Stuart M. Pitso