Exportin1 (XPO1; also known as chromosome maintenance region 1, or CRM1) controls nucleo-cytoplasmic transport of most tumor suppressors and is overexpressed in many cancers, including multiple myeloma, functionally impairing tumor suppressive function via target mislocalization. Selective inhibitor of nuclear export (SINE) compounds block XPO1-mediated nuclear escape by disrupting cargo protein binding, leading to retention of tumor suppressors, induction of cancer cell death, and sensitization to other drugs. Combined treatment with the clinical stage SINE compound selinexor and the irreversible proteasome inhibitor (PI) carfilzomib induced synergistic cell death of myeloma cell lines and primary plasma cells derived from relapsing/refractory myeloma patients and completely impaired the growth of myeloma cell line-derived tumors in mice. Investigating the details of SINE/PI-induced cell death revealed (i) reduced Bcl-2 expression and cleavage and inactivation of Akt, two prosurvival regulators of apoptosis and autophagy; (ii) intracellular membrane-associated aggregation of active caspases, which depended on caspase-10 protease activity; and (iii) novel association of caspase-10 and autophagy-associated proteins p62 and LC3 II, which may prime activation of the caspase cascade. Overall, our findings provide novel mechanistic rationale behind the potent cell death induced by combining selinexor with carfilzomib and support their use in the treatment of relapsed/refractory myeloma and potentially other cancers. Mol Cancer Ther; 15(1); 60-71. Ó2015 AACR.

SummaryToward our goal of personalized medicine, we comprehensively profiled pre-treatment malignant plasma cells from multiple myeloma patients and prospectively identified pathways predictive of favourable response to bortezomib-based treatment regimens. We utilized two complementary quantitative proteomics platforms to identify differentially-regulated proteins indicative of at least a very good partial response (VGPR) or complete response/near complete response (CR/nCR) to two treatment regimens containing either bortezomib, liposomal doxorubicin and dexamethasone (VDD), or lenalidomide, bortezomib and dexamethasone (RVD). Our results suggest enrichment of 'universal response' pathways that are common to both treatment regimens and are probable predictors of favourable response to bortezomib, including a subset of endoplasmic reticulum stress pathways. The data also implicate pathways unique to each regimen that may predict sensitivity to DNA-damaging agents, such as mitochondrial dysfunction, and immunomodulatory drugs, which was associated with acute phase response signalling. Overall, we identified patterns of tumour characteristics that may predict response to bortezomib-based regimens and their components. These results provide a rationale for further evaluation of the protein profiles identified herein for targeted selection of anti-myeloma therapy to increase the likelihood of improved treatment outcome of patients with newly-diagnosed myeloma.

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Introduction High rates of complete response (CR) have previously been demonstrated in KRd-treated NDMM pts in a phase 1/2 trial (trial 1; NCT01029054) and a phase 2 trial that combined KRd with autologous stem cell transplant (ASCT) (trial 2; NCT01816971). Here, we report results of extended follow-up from the 2 trials and correlate response and PFS with GEP performed using the MMprofiler GEP assay, which provides results for the SKY92 signature, 7 virtual karyotyping markers (t[4;14], t[11;14], t[14;16]/t[14;20], gain[1q], del[13q], del[17p], H-MM [virtual gain(9q)]), and 3 clusters (MF, MS, CD2). Previously, a combination of 5 markers (SKY92, virtual gain[1q], virtual t[14;16]/t[14;20], MF and CD2 clusters) was identified that predicts improved outcomes when treated with the proteasome inhibitor (PI) bortezomib (van Vliet et al, EHA 2014). We evaluated the SKY92 prognostic signature, virtual karyotyping markers, and this 5-marker PI predictor signature in order to confirm these markers as predictive signatures in the KRd setting. Materials and Methods In the consecutive trials 1 and 2, pts received 4 cycles of KRd induction, followed by extended KRd treatment with deferred ASCT (trial 1; NCT01029054) or ASCT followed by extended KRd treatment (trial 2; NCT01816971). In both trials, pts received single-agent lenalidomide as maintenance after completion of KRd. The MMprofiler GEP assay was performed on RNA from CD138+ purified plasma cells. As depth of response with KRd is associated with improved time-to-event outcomes (Jasielec et al, ASH 2013), data were analyzed for associations between any of the MMprofiler markers and the groups that achieved ≥near CR (nCR) vs <nCR by the end of 4 cycles (Fisher exact test). For progression-free survival (PFS), Kaplan-Meier curves were constructed, median survival estimates were calculated, and the Cox proportional hazards model was used to calculate hazard ratios (HR) and associated p-values. Results Based on a July 1, 2014 cutoff date, 91 pts were enrolled (53 in trial 1; 38 in trial 2). CD138+ RNA was available from 27 pts (16 from trial 1; 11 from pts in trial 2 who completed ≥4 KRd cycles). Pts with H-MM (virtual gain[9q]) were significantly less likely to achieve nCR (p=0.027) (Table 1). None of the other markers were found to have a statistically significant association with response; several markers, however, showed a trend for predictive value at the current sample size. PFS data were available for 16 pts (median follow-up: trial 1, 40 months [mo]; trial 2, 6.7 mo [with no events at the cutoff date]). Two markers were found to be significantly prognostic (Figure 1): SKY92 (5/16 pts [31%]; HR=5.7; p=0.023) and virtual gain (1q) (6/16 pts [38%]; HR=5.5; p=0.017). Virtual t(4;14) was marginally significant (HR=3.7, p=0.055). When considering the 5-marker PI predictor signature, none of the 16 pts were positive for virtual t(14;16)/t(14;20), MF or CD2 clusters. Combining the SKY92 and virtual gain(1q) markers identified a highly significant subgroup of high-risk pts (7/16; 44%) with a median PFS of 26 mo (HR=8.7; p=0.0088; Figure 1). In no-risk pts (9/16), estimated 4-year PFS was 78%. Conclusions Absence of H-MM (virtual gain[9q]) identified pts more likely to achieve ≥nCR by the end of 4 cycles of KRd, with other markers awaiting validation from ongoing enrollment to the KRd + ASCT trial. Based on combined SKY92 high-risk and virtual gain(1q) signatures, the MMprofiler assay detected a highly significant group of high-risk pts with inferior PFS compared to the no-risk group. Despite the inferior outcome, these high-risk pts appeared to have benefited from KRd when compared to historical data of treatment without PIs, suggesting that the 5-marker PI predictor signature (Van Vliet et al, EHA 2014) may also apply to carfilzomib-based treatment. We observed a 4-year PFS rate in no-risk pts in the KRd trials which trended higher than the historical outcome of the PAD arm in the HOVON65/GMMG-HD4 trial (78% vs 34%, respectively), suggesting a benefit for KRd without ASCT in this group of pts compared with other strategies with PIs; further study is needed, however. With ongoing enrollment into the KRd + ASCT trial, the findings reported here will be further validated. Updated results will be presented at the meeting. Acknowledgments This research was performed within the framework of CTMM, the Center for Translational Molecular Medicine, project BioCHIP grant 03O-102. Disclosures van Vliet: SkylineDx: Employment. Vij:Celgene: Honoraria, Research Funding; Onyx: Honoraria, Research Funding; Sanofi: Honoraria; Janssen: Honoraria; Novartis: Honoraria; Millennium: Honoraria; Array: Honoraria. Dumee:SkylineDx: Employment. Bosman:SkylineDx: Employment. deBest:SkylineDx: Employment. van Beers:SkylineDx: Employment. Jakubowiak:Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Onyx: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; SkylineDX: Honoraria, Membership on an entity's Board of Directors or advisory committees.

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