Sphingosine kinase 2 inhibition synergises with bortezomib to target myeloma by enhancing endoplasmic reticulum stress

Published: April 14, 2017The proteasome inhibitor bortezomib has proven to be invaluable in the treatment of myeloma. By exploiting the inherent high immunoglobulin protein production of malignant plasma cells, bortezomib induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), resulting in myeloma cell death. In most cases, however, the disease remains incurable highlighting the need for new therapeutic targets. Sphingosine kinase 2 (SK2) has been proposed as one such therapeutic target for myeloma. Our observations that bortezomib and SK2 inhibitors independently elicited induction of ER stress and the UPR prompted us to examine potential synergy between these agents in myeloma. Targeting SK2 synergistically contributed to ER stress and UPR activation induced by bortezomib, as evidenced by activation of the IRE1 pathway and stress kinases JNK and p38MAPK, thereby resulting in potent synergistic myeloma apoptosis in vitro. The combination of bortezomib and SK2 inhibition also exhibited strong in vivo synergy and favourable effects on bone disease. Therefore, our studies suggest that perturbations of sphingolipid signalling can synergistically enhance the effects seen with proteasome inhibition, highlighting the potential for the combination of these two modes of increasing ER stress to be formally evaluated in clinical trials for the treatment of myeloma patients.Craig T. Wallington-Beddoe, Melissa K. Bennett, Kate Vandyke, Lorena Davies, Julia R. Zebol, Paul A.B. Moretti, Melissa R. Pitman, Duncan R. Hewett, Andrew C.W. Zannettino and Stuart M. Pitso

The E3 ligase HUWE1 inhibition as a therapeutic strategy to target MYC in multiple myeloma

Proteasome inhibitors have provided a significant advance in the treatment of multiple myeloma (MM). Consequently, there is increasing interest in developing strategies to target E3 ligases, de-ubiquitinases, and/or ubiquitin receptors within the ubiquitin proteasome pathway, with an aim to achieve more specificity and reduced side-effects. Previous studies have shown a role for the E3 ligase HUWE1 in modulating c-MYC, an oncogene frequently dysregulated in MM. Here we investigated HUWE1 in MM. We identified elevated expression of HUWE1 in MM compared with normal cells. Small molecule-mediated inhibition of HUWE1 resulted in growth arrest of MM cell lines without significantly effecting the growth of normal bone marrow cells, suggesting a favorable therapeutic index. Studies using a HUWE1 knockdown model showed similar growth inhibition. HUWE1 expression positively correlated with MYC expression in MM bone marrow cells and correspondingly, genetic knockdown and biochemical inhibition of HUWE1 reduced MYC expression in MM cell lines. Proteomic identification of HUWE1 substrates revealed a strong association of HUWE1 with metabolic processes in MM cells. Intracellular glutamine levels are decreased in the absence of HUWE1 and may contribute to MYC degradation. Finally, HUWE1 depletion in combination with lenalidomide resulted in synergistic anti-MM activity in both in vitro and in vivo models. Taken together, our data demonstrate an important role of HUWE1 in MM cell growth and provides preclinical rationale for therapeutic strategies targeting HUWE1 in MM

Once-weekly selinexor, bortezomib, and dexamethasone versus twice-weekly bortezomib and dexamethasone in patients with multiple myeloma (BOSTON): a randomised, open-label phase 3 trial

Background Selinexor with dexamethasone has demonstrated activity in patients with heavily pretreated multiple myeloma (MM). In a phase 1b/2 study, the combination of oral selinexor with the proteasome inhibitor (PI) bortezomib, and dexamethasone (SVd) induced high response rates with low rates of peripheral neuropathy, the main dose-limiting toxicity of bortezomib. The aim of this trial was to evaluate the clinical benefit of weekly SVd versus standard bortezomib and dexamethasone (Vd) in patients with previously treated MM. Methods This phase 3, randomised, open label trial was conducted at 123 sites in 21 countries. Patients who were previously treated with one to three lines of therapy, including PIs were randomised (1:1) to selinexor (100 mg once-weekly) plus bortezomib (1·3 mg/m2 once-weekly) and dexamethasone (20 mg twice-weekly) [SVd] or bortezomib (1·3 mg/m2 twice-weekly) and dexamethasone (20 mg 4 times per week) [Vd]. Randomisation was done using interactive response technology and stratified by previous PI therapy, lines of treatment, and MM stage. The primary endpoint was progression-free survival (PFS) in the intention-to-treat population. Patients who received at least one dose of study treatment were included in the safety population. This trial is registered at ClinicalTrials.gov, NCT03110562. Findings Between June 2017 and February 2019, 402 patients were randomised: 195 to SVd and 207 to Vd. Median PFS was 13·93 (95% CI 11·73–NE) with SVd versus 9·46 months (8·11–10·78) with Vd; HR 0·70, [95% CI 0·53–0·93]; P=0.0075. Most frequent grade ≥3 adverse events (SVd vs Vd) were thrombocytopenia (77 [40%] vs 35 [17%]), fatigue (26 [13%] vs 2 [1%]), anaemia (31 [16%] vs 20 [10%]), and pneumonia (22 [11%] vs 22 [11%]). Peripheral neuropathy rates (overall, 32·3% vs 47·1%; OR 0·52, [95% CI 0·35-0·79]; P=0.0010 and grade ≥2, 21·0% vs 34·3%; OR 0·50, [95% CI 0·32-0·79]; P=0.0013) were lower with SVd. There were 47 (24%) deaths on SVd and 62 (30%) on Vd. Interpretation Once-weekly SVd is a novel, effective, and convenient treatment option for patients with MM who have received 1-3 prior therapies. Funding Karyopharm Therapeutics In

Sphingolipids and the unfolded protein response

The unfolded protein response (UPR) is a response by the endoplasmic reticulum to stress, classically caused by any disruption to cell homeostasis that results in an accumulation in unfolded proteins. However, there is an increasing body of research demonstrating that the UPR can also be activated by changes in lipid homeostasis, including changes in sphingolipid metabolism. Sphingolipids are a family of bioactive lipids with important roles in both the formation and integrity of cellular membranes, and regulation of key cellular processes, including cell proliferation and apoptosis. Bi-directional interactions between sphingolipids and the UPR have now been observed in a range of diseases, including cancer, diabetes and liver disease. Determining how these two key cellular components influence each other could play an important role in deciphering the causes of these diseases and potentially reveal new therapeutic approaches.Melissa K. Bennett, Craig T. Wallington-Beddoe, Stuart M. Pitso

Oncogenic properties of sphingosine kinases in haematological malignancies

The sphingosine kinases (SphKs) have relatively recently been implicated in contributing to malignant cellular processes with particular interest in the oncogenic properties of SPHK1. Whilst SPHK1 has received considerable attention as a putative oncoprotein, SPHK2 has been much more difficult to study, with often conflicting data surrounding its role in cancer. Initial studies focused on non-haemopoietic malignancies, however a growing body of literature on the role of sphingolipid metabolism in haemopoietic malignancies is now emerging. This review provides an overview of the current state of knowledge of the SphKs and the bioactive lipid sphingosine 1-phosphate (S1P), the product of the reaction they catalyse. It then reviews the current literature regarding the roles of S1P and the SphKs in haemopoietic malignancies and discusses the compounds currently available that modulate sphingolipid metabolism and their potential and shortcomings as therapeutic agents for the treatment of haematological malignancies.Craig T. Wallington-Beddoe, Kenneth F. Bradstock and Linda J. Bendal

Resistance to proteasome inhibitors and other targeted therapies in myeloma

The number of novel therapies for the treatment of myeloma is rapidly increasing, as are the clinical trials evaluating them in combination with other novel and established therapies. Proteasome inhibitors, immunomodulatory agents and monoclonal antibodies are the most well known and studied classes of novel agents targeting myeloma, with histone deacetylase inhibitors, nuclear export inhibitors and several other approaches also being actively investigated. However, in parallel with the development and clinical use of these novel myeloma therapies is the emergence of novel mechanisms of resistance, many of which remain elusive, particularly for more recently developed agents. Whilst resistance mechanisms have been best studied for proteasome inhibitors, particularly bortezomib, class effects do not universally apply to all class members, and within-class differences in efficacy, toxicity and resistance mechanisms have been observed. Although immunomodulatory agents share the common cellular target cereblon and thus resistance patterns relate to cereblon expression, the unique cell surface antigens to which monoclonal antibodies are directed means these agents frequently exhibit unique within-class differences in clinical efficacy and resistance patterns. This review describes the major classes of novel therapies for myeloma, highlights the major clinical trials within each class and discusses known resistance mechanisms.Craig T. Wallington‐Beddoe, Magdalena Sobieraj‐Teague, Bryone J. Kuss Stuart M. Pitso

Targeting sphingolipid metabolism as an approach for combination therapies in haematological malignancies

Facts • Efficacy of many chemotherapeutics and targeted therapies is dictated by cellular ceramide levels. • Oncogene activation skews sphingolipid metabolism to favour the production of pro-survival sphingolipids. • Inhibitors of enzymes involved in ceramide metabolism exhibit promise in the relapsed-refractory setting. • Anti-cancer activity of sphingosine kinase inhibitors provides several options for new drug combinations. Open Questions • What other clinically utilised drugs rely on increases in ceramide levels for their efficacy and can they be effectively partnered with other ceramide inducing agents? • How does ceramide modulate the Bcl-2 family proteins, Mcl-1 and Bcl-2? • Are sphingolipid enzyme inhibitors best suited in the frontline or relapsed-refractory setting

Sphingosine kinase 2 promotes acute lymphoblastic leukemia by enhancing MYC expression

Abstract not availableCraig T. Wallington-Beddoe, Jason A. Powell, Daochen Tong, Stuart M. Pitson, Kenneth F. Bradstock and Linda J. Bendal

Identification of sphingosine kinase 1 as a therapeutic target in B-lineage acute lymphoblastic leukaemia

Abstract not availableCraig T. Wallington‐Beddoe, Vicki Xie, Daochen Tong, Jason A. Powell, Alexander C. Lewis, Lorena Davies, Stuart M. Pitson, Kenneth F. Bradstock Linda J. Bendal