While bortezomib has significant benefits in multiple myeloma (MM) therapy, the disease remains incurable due to the invariable development of bortezomib resistance. This emphasises the need for advanced models for preclinical evaluation of new therapeutic approaches for bortezomib-resistant MM. Here, we describe the development of an orthotopic syngeneic bortezomib-resistant MM mouse model based on the most well-characterised syngeneic MM mouse model derived from spontaneous MM-forming C57BL/KaLwRij mice. Using bortezomib-resistant 5TGM1 cells, we report and characterise a robust syngeneic mouse model of bortezomib-resistant MM that is well suited to the evaluation of new therapeutic approaches for proteasome inhibitor-resistant MM.
8000 Background: Carfilzomib (CFZ) is a highly selective proteasome inhibitor with single-agent activity in patients (pts) with R/R MM. Methods: In this ongoing study of single-agent CFZ in R/R MM, pts were stratified based on prior exposure to BTZ and CFZ dose level (Table). CFZ IV was administered on days 1, 2, 8, 9, 15, and 16 every 28 d for up to 12 cycles. Study endpoints included overall response rate (ORR), defined as ≥ partial response (PR), duration of response (DOR), and safety. Results: The BTZ-treated cohort included 35 pts (14 refractory to most recent treatment). For BTZ-naive pts, cohort 1 included 59 pts and cohort 2 included 20 pts. Pts received a mean of 5 cycles of CFZ (range 1–12). Thirty-three BTZ-treated pts were evaluable with an ORR of 18%. For BTZ-naive pts, 54 pts in cohort 1 and 19 pts in cohort 2 were evaluable with ORRs of 46% and 53%, respectively. Median DOR (≥MR) was ≥8.8 months (mo). Treatment groups and patient responses are shown in the Table. In the combined pt population, the most common adverse events (AEs) included fatigue (66%), nausea (49%), dyspnea (40%), anemia (34%), diarrhea (32%) and were primarily ≤ Gr 2 in severity. The most common ≥ Gr 3 AEs were anemia, thrombocytopenia, and neutropenia (10% each). Febrile neutropenia and treatment-emergent peripheral neuropathy (PN) were uncommon. Of 23 pts who completed the 12 cycle protocol, 7 chose to continue CFZ therapy on an extended treatment protocol. Updated results for all cohorts will be presented. Conclusions: Single-agent CFZ is active in pts with R/R MM. AEs were generally mild and thereby durable disease control was obtained with continued dosing. Severe PN is rare and does not limit therapy. BTZ-treated N=35 BTZ-naive Cohort 1 N=54 Cohort 2 N=19 CFZ administration 20 mg/m2 20 mg/m2 20 mg/m2 cycle 1, 27 mg/m2 cycle 2+ Best response CR 1 1 0 VGPR 1 5 1 PR 4 19 9 MR 4 8 0 SD 13 12 6 Median DOR (≥MR) 9.0 mo 8.8 mo TBD Median TTP 5.3 mo 7.6 mo TBD Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Onyx Bristol-Myers Squibb, Celgene, Centocor Ortho Biotech, Exelixis, Genzyme, Millennium, Onyx Pharmaceuticals Onyx Bristol-Myers Squibb, Celgene, Centocor Ortho Biotech, Exelixis, Johnson & Johnson, Merck, Millennium, Onyx Celgene, Merck, Millennium, Novartis, Onyx
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.
// Craig T. Wallington-Beddoe 1,2,3 , Melissa K. Bennett 1,2,3 , Kate Vandyke 2,3,4 , Lorena Davies 1,2 , Julia R. Zebol 1,2 , Paul A.B. Moretti 1,2 , Melissa R. Pitman 1,2 , Duncan R. Hewett 3,4 , Andrew C.W. Zannettino 1,2,3,4,* and Stuart M. Pitson 1,2,3,* 1 Center for Cancer Biology, University of South Australia, Adelaide, Australia 2 SA Pathology, Adelaide, Australia 3 School of Medicine, University of Adelaide, Australia 4 South Australian Health and Medical Research Institute, Adelaide, Australia * Co-senior authorship of this article Correspondence to: Andrew C.W. Zannettino, email: // Stuart M. Pitson, email: // Keywords : myeloma, endoplasmic reticulum, proteasome inhibitor, sphingosine kinase Received : March 29, 2017 Accepted : April 04, 2017 Published : April 14, 2017 Abstract The 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.
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