The Route of the Malignant Plasma Cell in Its Survival Niche: Exploring "Multiple Myelomas".

Growing evidence points to multiple myeloma (MM) and its stromal microenvironment using several mechanisms to subvert effective immune and anti-tumor responses. Recent advances have uncovered the tumor-stromal cell influence in regulating the immune-microenvironment and have envisioned targeting these suppressive pathways to improve therapeutic outcomes. Nevertheless, some subgroups of patients include those with particularly unfavorable prognoses. Biological stratification can be used to categorize patient-, disease- or therapy-related factors, or alternatively, these biological determinants can be included in a dynamic model that customizes a given treatment to a specific patient. Genetic heterogeneity and current knowledge enforce a systematic and comprehensive bench-to-bedside approach. Given the increasing role of cancer stem cells (CSCs) in better characterizing the pathogenesis of solid and hematological malignancies, disease relapse, and drug resistance, identifying and describing CSCs is of paramount importance in the management of MM. Even though the function of CSCs is well-known in other cancer types, their role in MM remains elusive. With this review, we aim to provide an update on MM homing and resilience in the bone marrow micro milieu. These data are particularly interesting for clinicians facing unmet medical needs while designing novel treatment approaches for MM.

68Ga-Pentixafor PET/CT for Detection of Chemokine Receptor CXCR4 Expression in Myeloproliferative Neoplasms.

C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for cancer diagnosis and treatment, as it is overexpressed in many solid and hematologic malignancies. This study investigated the feasibility of CXCR4-directed imaging with PET/CT using 68Ga-pentixafor to visualize and quantify disease involvement in myeloproliferative neoplasms (MPNs). Methods: Twelve patients with MPNs (4 with primary myelofibrosis, 6 with essential thrombocythemia, and 2 with polycythemia vera) and 5 controls underwent 68Ga-pentixafor PET/CT. Imaging findings were compared with immunohistochemical stainings, laboratory data, and splenic volume. Results:68Ga-pentixafor PET/CT was visually positive in 12 of 12 patients, and CXCR4 target specificity could be confirmed by immunohistochemical staining. A significantly higher tracer uptake could be detected in the bone marrow of MPN patients (SUVmean, 6.45 ± 2.34 vs. 4.44 ± 1.24). Dynamic changes in CXCR4 expression determined by 68Ga-pentixafor PET/CT corresponded with treatment response. Conclusion:68Ga-pentixafor PET/CT represents a novel diagnostic tool to noninvasively detect and quantify the extent of disease involvement in MPNs.

Halting the vicious cycle within the multiple myeloma ecosystem: blocking JAM-A on bone marrow endothelial cells restores angiogenic homeostasis and suppresses tumor progression.

Interactions of malignant multiple myeloma (MM) plasma cells (MM-cells) with the microenvironment control MM-cell growth, survival, drug-resistance and dissemination. As in MM microvascular density increases in the bone marrow (BM), we investigated whether BM MM endothelial cells (MMECs) control disease progression via the junctional adhesion molecule A (JAM-A). Membrane and cytoplasmic JAM-A levels were upregulated in MMECs in 111 newly diagnosed (NDMM) and 201 relapsed-refractory (RRMM) patients compared to monoclonal gammopathy of undetermined significance (MGUS) and healthy controls. Elevated membrane expression of JAM-A on MMECs predicted poor clinical outcome. Mechanistically, addition of recombinant JAM-A to MMECs increased angiogenesis whereas its inhibition impaired angiogenesis and MM growth in 2D and 3D in vitro cell culture and chorioallantoic membrane-assays. To corroborate these findings, we treated MM bearing mice with JAM-A blocking mAb and demonstrated impaired MM progression corresponding to decreased MM-related vascularity. These findings support JAM-A as an important mediator of MM progression through facilitating MM-associated angiogenesis. Collectively, elevated JAM-A expression on bone marrow endothelial cells is an independent prognostic factor for patient survival in both NDMM and RRMM. Blocking JAM-A restricts angiogenesis in vitro, in embrio and in vivo and represents a suitable druggable molecule to halt neoangiogenesis and MM progression.

RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

Oncogenic RAS provides crucial survival signaling for up to half of multiple myeloma cases, but has so far remained a clinically undruggable target. RAL is a member of the RAS superfamily of small GTPases and is considered to be a potential mediator of oncogenic RAS signaling. In primary multiple myeloma, we found RAL to be overexpressed in the vast majority of samples when compared with pre-malignant monoclonal gammopathy of undetermined significance or normal plasma cells. We analyzed the functional effects of RAL abrogation in myeloma cell lines and found that RAL is a critical mediator of survival. RNAi-mediated knockdown of RAL resulted in rapid induction of tumor cell death, an effect which was independent from signaling via mitogen-activated protein kinase, but appears to be partially dependent on Akt activity. Notably, RAL activation was not correlated with the presence of activating RAS mutations and remained unaffected by knockdown of oncogenic RAS. Furthermore, transcriptome analysis yielded distinct RNA expression signatures after knockdown of either RAS or RAL. Combining RAL depletion with clinically relevant anti-myeloma agents led to enhanced rates of cell death. Our data demonstrate that RAL promotes multiple myeloma cell survival independently of oncogenic RAS and, thus, this pathway represents a potential therapeutic target in its own right.

Exon-4 Mutations in KRAS Affect MEK/ERK and PI3K/AKT Signaling in Human Multiple Myeloma Cell Lines.

Approximately 20% of multiple myeloma (MM) cases harbor a point mutation in KRAS. However, there is still no final consent on whether KRAS-mutations are associated with disease outcome. Specifically, no data exist on whether KRAS-mutations have an impact on survival of MM patients at diagnosis in the era of novel agents. Direct blockade of KRAS for therapeutic purposes is mostly impossible, but recently a mutation-specific covalent inhibitor targeting KRASp.G12C entered into clinical trials. However, other KRAS hotspot-mutations exist in MM patients, including the less common exon-4 mutations. For the current study, the coding regions of KRAS were deep-sequenced in 80 newly diagnosed MM patients, uniformely treated with three cycles of bortezomib plus dexamethasone and cyclophosphamide (VCD)-induction, followed by high-dose chemotherapy and autologous stem cell transplantation. Moreover, the functional impact of KRASp.G12A and the exon-4 mutations p.A146T and p.A146V on different survival pathways was investigated. Specifically, KRASWT, KRASp.G12A, KRASp.A146T, and KRASp.A146V were overexpressed in HEK293 cells and the KRASWT MM cell lines JJN3 and OPM2 using lentiviral transduction and the Sleeping Beauty vector system. Even though KRAS-mutations were not correlated with survival, all KRAS-mutants were found capable of potentially activating MEK/ERK- and sustaining PI3K/AKT-signaling in MM cells.

Protocol for M3P: A Comprehensive and Clinical Oriented Targeted Sequencing Panel for Routine Molecular Analysis in Multiple Myeloma.

Over the past 10 years next generation sequencing (NGS) approaches deciphered a large number of genomes from a wide variety of tumor types. However, despite most relevant findings, this technology has not yet been implemented into standard diagnostic workflows. Broad access to NGS technology is still limited, sequencing/analysis times exceed clinically relevant timeframes and despite huge cuts, costs remain significant. We proposed a custom-tailored gene panel, which focuses on a selected number of relevant genes and developed a clinically oriented NGS targeted sequencing approach for the molecular characterization of Multiple Myeloma (MM) tumors, allowing the description of the tumor genetic heterogeneity and its changes under selective pressure of antitumor therapy, in a more cost effective and faster turnaround timeframe.

Rare SNPs in receptor tyrosine kinases are negative outcome predictors in multiple myeloma.

Multiple myeloma (MM) is a plasma cell disorder that is characterized by a great genetic heterogeneity. Recent next generation sequencing studies revealed an accumulation of tumor-associated mutations in receptor tyrosine kinases (RTKs) which may also contribute to the activation of survival pathways in MM. To investigate the clinical role of RTK-mutations in MM, we deep-sequenced the coding DNA-sequence of EGFR, EPHA2, ERBB3, IGF1R, NTRK1 and NTRK2 which were previously found to be mutated in MM, in 75 uniformly treated MM patients of the "Deutsche Studiengruppe Multiples Myelom". Subsequently, we correlated the detected mutations with common cytogenetic alterations and clinical parameters. We identified 11 novel non-synonymous SNVs or rare patient-specific SNPs, not listed in the SNP databases 1000 genomes and dbSNP, in 10 primary MM cases. The mutations predominantly affected the tyrosine-kinase and ligand-binding domains and no correlation with cytogenetic parameters was found. Interestingly, however, patients with RTK-mutations, specifically those with rare patient-specific SNPs, showed a significantly lower overall, event-free and progression-free survival. This indicates that RTK SNVs and rare patient-specific RTK SNPs are of prognostic relevance and suggests that MM patients with RTK-mutations could potentially profit from treatment with RTK-inhibitors.

A GRP78-Directed Monoclonal Antibody Recaptures Response in Refractory Multiple Myeloma with Extramedullary Involvement.

PURPOSE: Glucose-regulated protein (GRP) 78 is overexpressed in multiple myeloma, and both its surface expression and its biologic significance as key sensor of the unfolded protein response make GRP78 an ideal candidate for immunotherapeutic intervention. The monoclonal antibody PAT-SM6 targets surface GRP78 and leads to disease stabilization when used as single agent in a clinical trial. In this article, we evaluated expression of GRP78 in relapsed-refractory disease and explored PAT-SM6 therapy in combination regimens. EXPERIMENTAL DESIGN: GRP78 expression was immunohistochemically analyzed during disease progression and development of drug resistance throughout different stages of multiple myeloma. Activity of PAT-SM6 was evaluated in combination with anti-multiple myeloma agents lenalidomide, bortezomib, and dexamethasone in vitro Finally, we report on a multiple myeloma patient with relapsed-refractory disease treated with PAT-SM6 in combination with bortezomib and lenalidomide. RESULTS: Although sGRP78 expression was present at all stages, it increased with disease progression and was even strongly elevated in patients with drug-resistant and extramedullary disease. Pretreatment with dexamethasone as well as dual combination of PAT-SM6/lenalidomide further increased sGRP78 expression and consecutively showed synergistic anti-multiple myeloma effects with PAT-SM6 in proliferation assays. As proof of concept, a 62-year-old male with triple resistant multiple myeloma treated with PAT-SM6, bortezomib, and lenalidomide experienced partial remission of both intra- and extramedullary lesions. CONCLUSIONS: PAT-SM6 therapy in combination regimens showed efficacy in relapsed-refractory multiple myeloma. Clin Cancer Res; 22(17); 4341-9. ©2016 AACR.

Efficient transient transfection of human multiple myeloma cells by electroporation--an appraisal.

Cell lines represent the everyday workhorses for in vitro research on multiple myeloma (MM) and are regularly employed in all aspects of molecular and pharmacological investigations. Although loss-of-function studies using RNA interference in MM cell lines depend on successful knockdown, no well-established and widely applied protocol for efficient transient transfection has so far emerged. Here, we provide an appraisal of electroporation as a means to introduce either short-hairpin RNA expression vectors or synthesised siRNAs into MM cells. We found that electroporation using siRNAs was much more efficient than previously anticipated on the basis of transfection efficiencies deduced from EGFP-expression off protein expression vectors. Such knowledge can even confidently be exploited in "hard-to-transfect" MM cell lines to generate large numbers of transient knockdown phenotype MM cells. In addition, special attention was given to developing a protocol that provides easy implementation, good reproducibility and manageable experimental costs.

PI3K-dependent multiple myeloma cell survival is mediated by the PIK3CA isoform.

Constitutive phosphatidylinositide 3-kinase (PI3K) signalling has been implicated in multiple myeloma (MM) pathophysiology and is regarded as an actionable target for pharmacological intervention. Isoform-specific PI3K inhibition may offer the most focused treatment approach and could result in greater clinical efficacy and reduced side effects. We therefore performed isoform-specific knockdown of PIK3CA, PIK3CB, PIK3CD, and PIK3CG to analyse their individual contributions to MM cell survival and downstream signalling. In addition, we tested the effectivity of the novel PI3K isoform-specific inhibitors BYL-719 (PIK3CA), TGX-221 (PIK3CB), CAL-101 (PIK3CD), and CAY10505 (PIK3CG). We found the PIK3CA isoform to be of paramount importance for constitutive Akt activity in MM cells, and - in contrast to inhibition of other class I isoforms - only the blockade of PIK3CA was sufficient to induce cell death in a sizeable subgroup of MM samples. Furthermore, pharmacological PIK3CA inhibition in combination treatments of BYL-719 and established anti-myeloma agents resulted in strongly enhanced MM cell death. Our data thus clearly indicate therapeutic potential of PIK3CA inhibitors and support their clinical evaluation in multiple myeloma.

The PI3K/Akt signaling pathway regulates the expression of Hsp70, which critically contributes to Hsp90-chaperone function and tumor cell survival in multiple myeloma.

Despite therapeutic advances multiple myeloma remains largely incurable, and novel therapeutic concepts are needed. The Hsp90-chaperone is a reasonable therapeutic target, because it maintains oncogenic signaling of multiple deregulated pathways. However, in contrast to promising preclinical results, only limited clinical efficacy has been achieved through pharmacological Hsp90 inhibition. Because Hsp70 has been described to interact functionally with the Hsp90-complex, we analyzed the suitability of Hsp72 and Hsp73 as potential additional target sites. Expression of Hsp72 and Hsp73 in myeloma cells was analyzed by immunohistochemical staining and western blotting. Short interfering RNA-mediated knockdown or pharmacological inhibition of Hsp72 and Hsp73 was performed to evaluate the role of these proteins in myeloma cell survival and for Hsp90-chaperone function. Furthermore, the role of PI3K-dependent signaling in constitutive and inducible Hsp70 expression was investigated using short interfering RNA-mediated and pharmacological PI3K inhibition. Hsp72 and Hsp73 were frequently overexpressed in multiple myeloma. Knockdown of Hsp72 and/or Hsp73 or treatment with VER-155008 induced apoptosis of myeloma cells. Hsp72/Hsp73 inhibition decreased protein levels of Hsp90-chaperone clients affecting multiple oncogenic signaling pathways, and acted synergistically with the Hsp90 inhibitor NVP-AUY922 in the induction of death of myeloma cells. Inhibition of the PI3K/Akt/GSK3ß pathway with short interfering RNA or PI103 decreased expression of the heat shock transcription factor 1 and down-regulated constitutive and inducible Hsp70 expression. Treatment of myeloma cells with a combination of NVP-AUY922 and PI103 resulted in additive to synergistic cytotoxicity. In conclusion, Hsp72 and Hsp73 sustain Hsp90-chaperone function and critically contribute to the survival of myeloma cells. Translation of Hsp70 inhibition into the clinic is therefore highly desirable. Treatment with PI3K inhibitors might represent an alternative therapeutic strategy to target Hsp70.

Combined targeting of MEK/MAPK and PI3K/Akt signalling in multiple myeloma.

So-called RAS-dependent pathways, such as those signalling via mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) and phosphoinositide-3 kinase (PI3K)/Akt, are implicated in proliferation and survival of multiple myeloma (MM) cells. However, the effects of their combined blockade and its potential therapeutic utility for the treatment of RAS-mutated MM have not systematically been analysed. Here, we tested the functional consequences of single versus combined inhibition of the MEK/MAPK and PI3K/Akt pathways in a large series of primary MM samples (n = 55) and MM cell lines (n = 11). Additionally, the anti-myeloma activity of different treatments was analysed with respect to the RAS mutation status. PI3K/Akt blockade was generally more pro-apoptotic than blockade of MEK/MAPK both in cell lines and in primary MM samples. Simultaneous blockade of both pathways led to significantly enhanced anti-myeloma activity in 75% of primary MM samples, whereas the remainder was largely resistant. Resistance to combination blockade was exclusively observed in RAS wildtype cases, whereas sensitivity was noted in RAS wildtype and in RAS mutated MM. These results suggest that oncogenic RAS is a predictor of sensitivity to combination treatment with PI3K/Akt and MEK/MAPK inhibitors and that such an approach might therefore be beneficial for this genetically well-defined subgroup of MM patients.

Integrin-linked kinase is dispensable for multiple myeloma cell survival.

We investigated the utility of integrin-linked kinase (ILK) as a target for therapeutic intervention in multiple myeloma (MM). ILK (over-)expression was assessed in primary samples and MM cell lines, and the molecular and physiological consequences of siRNA-mediated ILK ablation were compared to treatment with the small molecule inhibitor QLT0267. Whereas ILK expression was ubiquitous, overexpression was only rarely observed in patient biopsies. ILK knockdown had no effect on the viability or survival pathway activity pattern of MM cells. Conversely, QLT0267 induced cell death in MM cell lines and most primary tumor samples via the intrinsic apoptotic pathway. Although this effect was largely tumor cell-specific it is unlikely to have been mediated via ILK. We conclude that ILK does not play a prominent role in the promotion or sustenance of established MM.

Mutated RAS and constitutively activated Akt delineate distinct oncogenic pathways, which independently contribute to multiple myeloma cell survival.

We have recently shown that approximately half of primary multiple myeloma (MM) samples display constitutive Akt activity, which disposes them for sensitivity to Akt inhibition. The Akt pathway counts among the signaling conduits for oncogenic RAS and activating mutations of K- and N-RAS frequently occur in MM. We therefore analyzed the relation between RAS mutation and Akt dependency in biopsies and CD138-purified cells from MM patients (n = 65) and the function of oncogenic RAS for MM cell survival in a range of MM cell lines with differing RAS status. Whereas RAS mutations do not predict Akt dependency, oncogenic RAS retains an important role for MM cell survival. Knockdown of either K- or N-RAS strongly decreased the viability of MM cells that harbored the respective oncogenic isoform, whereas ablation of wild-type RAS isoforms had little or no effect. Silencing of oncogenic RAS did not affect the Akt pathway, again indicating lack of a direct link. Combined inhibition of RAS and Akt strongly enhanced MM cell death. These data suggest that oncogenic RAS and Akt may independently contribute to MM cell survival. Targeting of both pathways could provide an attractive therapeutic strategy for patients with oncogenic RAS and dysregulated Akt signaling.