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Objectives: The prognostic value of kinetics of response to multiple myeloma (MM) therapy is controversial. We aimed to expand the knowledge on this topic by reviewing the kinetics of response to both first‐ and second‐line MM therapy, utilizing a homogeneously treated cohort and analyzing separately both M‐spike and light chain (LC) responses for each patient. Methods: We reviewed all patients who received first‐line cyclophosphamide, bortezomib and dexamethasone induction followed by autologous transplant with melphalan and lenalidomide maintenance in our center between 2007 and 2019. Results: Analyzing 360 patients, we observed no correlation between response kinetics to first‐ versus second‐line therapy at the individual patient level. Time to best response to first‐line therapy was not a predictor of outcome; however, longer time to best response was highly predictive of a favorable outcome in the second‐line setting, independent of other factors. Patients with IgA‐MM cleared their M‐spike faster than IgG‐MM, probably reflecting different half‐lives of these isotypes rather than disease biology, as the clearance of LC in both subtypes was similar. Conclusions: Analyzing both M‐spike and LC responses in a homogenously treated cohort, we identified important insights regarding the prognostic value of kinetic patterns. Prospective analysis may shed more light on unsolved questions. [ABSTRACT FROM AUTHOR]

Chromosome copy number variations (CNVs) are a near-universal feature of cancer; however, their individual effects on cellular function are often incompletely understood. Single-cell ribonucleic acid (RNA) sequencing (scRNA-seq) might be leveraged to reveal the function of intra-clonal CNVs; however, it cannot directly link cellular gene expression to CNVs. Here, we report a high-throughput scRNA-seq analysis pipeline that provides paired CNV profiles and transcriptomes for single cells, enabling exploration of the effects of CNVs on cellular programs. RTAM1 and -2 normalization methods are described, and are shown to improve transcriptome alignment between cells, increasing the sensitivity of scRNA-seq for CNV detection. We also report single-cell inferred chromosomal copy number variation (sciCNV), a tool for inferring single-cell CNVs from scRNA-seq at 19–46 Mb resolution. Comparison of sciCNV with existing RNA-based CNV methods reveals useful advances in sensitivity and specificity. Using sciCNV, we demonstrate that scRNA-seq can be used to examine the cellular effects of cancer CNVs. As an example, sciCNV is used to identify subclonal multiple myeloma (MM) cells with +8q22–24. Studies of the gene expression of intra-clonal MM cells with and without the CNV demonstrate that +8q22–24 upregulates MYC and MYC-target genes, messenger RNA processing and protein synthesis, which is consistent with established models. In conclusion, we provide new tools for scRNA-seq that enable paired profiling of the CNVs and transcriptomes of single cells, facilitating rapid and accurate deconstruction of the effects of cancer CNVs on cellular programming. [ABSTRACT FROM AUTHOR]

Background: The prevalence of multiple myeloma is increasing and there is a need to evaluate escalating therapy costs (Canadian Cancer Statistics A, 2020). The MYX.1 phase II trial showed that high‐dose weekly carfilzomib, cyclophosphamide, and dexamethasone (wKCD) is efficacious in relapsed and refractory disease. We conducted a descriptive cost analysis, from the perspective of the Canadian public healthcare system, using trial data. Methods: The primary outcome was the mean total cost per patient. Resource utilization data were collected from all 75 trial patients over a trial time horizon. Costs are presented in Canadian dollars (2020). Results: The cost of treatment was calculated from the time of patient (pt) enrollment until the second data lock. The mean total cost was $203 336.08/pt (range $17 891.27‐$505 583.55) Canadian dollars (CAD, where 1 CAD = 0.67 Euro (EUR)) and $14 081.45/pt per cycle. The median number of cycles was 15. The predominant cost driver was the cost of chemotherapy accounting for an average of $179 332.78/pt or $12 419.17/pt per cycle. Carfilzomib acquisition accounted for the majority of chemotherapy costs – $162 471.65/pt or $11 251.50/pt per cycle. Fifty‐six percent (56%) of patients had at least one hospitalization during the trial period with an average cost of $12 657.86 per hospitalization. Three patients developed thrombotic microangiopathy (TMA) with an average cost of $18 863.32/pt including the cost of hospitalizations and therapeutic plasma exchange. Conclusions: High‐dose wKCD is an active triplet regimen for relapsed and refractory multiple myeloma (RRMM) associated with reduced total cost compared with twice‐weekly carfilzomib‐based regimens. [ABSTRACT FROM AUTHOR]

High dose chemotherapy followed by autologous stem cell transplant (ASCT) is a cornerstone of frontline therapy for multiple myeloma (MM) [[1]]. Four of the ten transplants were performed as second-line therapy, including two for relapsed disease 42 and 48 months after frontline ASCT (Patients #4 and #5 on Table 1) and one relapsing 47 months after frontline syngeneic transplant (Patient #3). GVHD was questioned in 2 patients (Patients #3 and #5), both receiving allogeneic-like conditioning and cyclosporine prophylaxis. Two of nine patients developed a secondary cancer during follow up (Patient #5 myelodysplastic syndrome 7 years post-syngeneic transplant; Patient #4 transitional cell carcinoma 11 years post-syngeneic transplant). [Extracted from the article]

Follicular lymphoma ( FL) in young adults ( YA, <40 years old) is uncommon, and the clinical characteristics and outcomes of this group are not well defined. We conducted a retrospective database review of 427 patients with newly diagnosed FL aged 65 years or less registered at Princess Margaret Cancer Centre between 1995 and 2010. YA ( n = 61) and those 40-65 ( n = 366) were compared with regards to clinical stage at diagnosis, FL International Prognostic Index ( FLIPI) score, and the following clinical outcomes: time to second treatment, cause-specific survival (CSS) and overall survival (OS). At diagnosis, stage and FLIPI score were similar, as were the proportion of patients requiring therapy ( YA 75% versus older adults 71%). Median follow-up was 8·1 years. Time to second therapy was similar in both age groups (5-year probability 23% YA versus 27% older adults; Gray's P-value = 0·76). Ten-year OS was significantly higher for YA (87% versus older adults 72%; P = 0·029). On multivariate analysis, age <40 years, low FLIPI score and observation as initial management were favourable prognostic factors for OS and CSS. We conclude that YA with FL have a favourable prognosis compared to older patients; whether this reflects competing mortality risks or age-related differences in lymphoma biology warrants further investigation. [ABSTRACT FROM AUTHOR]

Autologous stem-cell transplant has been widely used to treat patients with AL amyloidosis. However, transplant-related mortality rates are high, and a recent randomized trial suggested that non-transplant regimens produced comparable results with less toxicity. In order to define the role of patient selection in stem cell transplantation, we evaluated 78 consecutive AL amyloidosis patients transplanted at our centre. Transplant-related mortality occurred in 11·5%. Complete haematological response and organ response were achieved in 56% and 60%. Median overall survival was significantly lower for patients with brain-type natriuretic peptide ( BNP) >300 pg/ml (17·5 months vs. not-reached) ( P = 0·0004), troponin-I >0·07 ng/ml (13·5 months vs. not-reached) ( P = 0·00001) and those not achieving a complete haematological response (88 months vs. not-reached) ( P = 0·0345); high BNP and troponin-I were the most important predictive factors in a multivariate analysis. Based on this study, patients with BNP <300 pg/ml and/or normal levels of troponin-I should be considered transplant candidates. [ABSTRACT FROM AUTHOR]

Involvement of the central nervous system ( CNS) in multiple myeloma ( MM) is a rare complication, with reported survival of <6 months. This report describes 37 MM patients with leptomeningeal and/or parenchymal brain involvement treated at our institution and identifies factors associated with long-term survival. From January 1999 to December 2010, 37 patients with CNS MM were evaluated at our institution. Clinical characteristics, treatment and survival were retrospectively collected. CNS disease was present at MM diagnosis in 24% and at relapse in 76%. Plasma cell leukemia (40%) and skull plasmacytomas (65%) were common, suggesting haematological and contiguous spread. Intrathecal ( IT) chemotherapy was used in 81%, cranial and/or spinal irradiation in 78%, and various systemic therapies [immunomodulatory agents ( IMiDs) (51%), cisplatin-based ( DPACE; cisplatin, doxorubicin, cyclophosphamide, etoposide) (27%), bortezomib (19%), alkylators (11%), dexamethasone alone (8%), auto-transplant (5%)]. Median survival from CNS disease was only 4·6 months [95% confidence interval ( CI): 2·8-6·7]; however, nine patients had prolonged survival (median: 17·1 months, 95% CI: 13·2-67·4). In general, these long-term survivors were treated with radiotherapy, multi-dosing IT chemotherapy, and IMi D-containing therapy. CNS MM is a highly aggressive disease but in our experience, long-term survival can be achieved with the combination of multi-dosing IT chemotherapy, radiation and IMi D-based therapy. [ABSTRACT FROM AUTHOR]

Summary: By misdirecting the activity of Activation-Induced Deaminase (AID) to a conditional MYC transgene, we have achieved sporadic, AID-dependent MYC activation in germinal center B cells of Vk∗MYC mice. Whereas control C57BL/6 mice develop benign monoclonal gammopathy with age, all Vk∗MYC mice progress to an indolent multiple myeloma associated with the biological and clinical features highly characteristic of the human disease. Furthermore, antigen-dependent myeloma could be induced by immunization with a T-dependent antigen. Consistent with these findings in mice, more frequent MYC rearrangements, elevated levels of MYC mRNA, and MYC target genes distinguish human patients with multiple myeloma from individuals with monoclonal gammopathy, implicating a causal role for MYC in the progression of monoclonal gammopathy to multiple myeloma. [Copyright &y& Elsevier]

Summary: Activation of NF-κB has been noted in many tumor types, however only rarely has this been linked to an underlying genetic mutation. An integrated analysis of high-density oligonucleotide array CGH and gene expression profiling data from 155 multiple myeloma samples identified a promiscuous array of abnormalities contributing to the dysregulation of NF-κB in approximately 20% of patients. We report mutations in ten genes causing the inactivation of TRAF2, TRAF3, CYLD, cIAP1/cIAP2 and activation of NFKB1, NFKB2, CD40, LTBR, TACI, and NIK that result primarily in constitutive activation of the noncanonical NF-κB pathway, with the single most common abnormality being inactivation of TRAF3. These results highlight the critical importance of the NF-κB pathway in the pathogenesis of multiple myeloma. [Copyright &y& Elsevier]

The article presents a study on cyclophosphamide, bortezomib and dexamethasone induction therapy for newly diagnosed patients with multiple myeloma (MM). It discusses the development of new therapies for MM, method used to calculate the patients' survival, and the overall response for all patients in the study.

Introduction: According to previous data, higher yields of stem-cells collected to support autologous transplantation may predict for improved outcomes. We aimed to assess the association between high stem-cells collection and survival outcomes in multiple myeloma (MM) MATERIALS AND METHODS: We reviewed all patients who underwent autologous transplantation for MM at our center over a 10-year period, and initially used a predefined threshold of 8 × 10 6 /kg used in previous studies., Results: Six hundred twenty-one patients were analyzed. Higher mobilization did not correlate with favorable outcomes post-transplant. The most efficient mobilizers, collecting ≥8 × 10 6 /kg (n = 478) achieved a shorter median progression-free survival (PFS) of 24.1m versus 34.5m in patients collecting 4.5 to 8 × 10 6 /kg (n = 129). A small group (n = 14) collecting ≤4.5 × 10 6 /kg but minimum of 2 × 10 6 /kg to support autologous transplantation exhibited the worst outcomes (median PFS 11.4m). Further analysis of potential confounders identified greater use of bortezomib induction in the lower mobilizers, however, sensitivity analysis in patients receiving bortezomib revealed similar results- worst outcomes to the most efficient mobilizers., Conclusion: Although bortezomib is not considered stem-cell toxic, it may be associated with lower stem cell collection yields. Bortezomib's efficacy at induction may partially explain the improved outcomes, however, other factors may be involved, and are discussed. We can conclude that with our large cohort and long follow-up, high stem-cell mobilization does not appear to predict for a long-term survival advantage., Competing Interests: Disclosure The authors had no conflict of interests to disclose., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Genomic characterization of cancer has enabled identification of numerous molecular targets, which has led to significant advances in personalized medicine. However, with few exceptions, precision medicine approaches in the plasma cell malignancy multiple myeloma (MM) have had limited success, likely owing to the subclonal nature of molecular targets in this disease. Targeted therapies against FGFR3 have been under development for the past decade in the hopes of targeting aberrant FGFR3 activity in MM. FGFR3 activation results from the recurrent transforming event of t(4;14) found in ∼15% of MM patients, as well as secondary FGFR3 mutations in this subgroup. To evaluate the effectiveness of targeting FGFR3 in MM, we undertook a phase 2 clinical trial evaluating the small-molecule FGFR1-4 inhibitor, erdafitinib, in relapsed/refractory myeloma patients with or without FGFR3 mutations (NCT02952573). Herein, we report on a single t(4;14) patient enrolled on this study who was identified to have a subclonal FGFR3 stop-loss deletion. Although this individual eventually progressed on study and succumbed to their disease, the intended molecular response was revealed through an extensive molecular characterization of the patient's tumor at baseline and on treatment using single-cell genomics. We identified elimination of the FGFR3 -mutant subclone after treatment and expansion of a preexisting clone with loss of Chromosome 17p. Altogether, our study highlights the utility of single-cell genomics in targeted trials as they can reveal molecular mechanisms that underlie sensitivity and resistance. This in turn can guide more personalized and targeted therapeutic approaches, including those that involve FGFR3-targeting therapies., (© 2023 Croucher et al.; Published by Cold Spring Harbor Laboratory Press.)

Background: Salvage transplant has been historically considered effective therapy for myeloma patients relapsing after first transplant, if they achieved adequate remission duration. However, the efficacy of novel agent combinations has called this paradigm into question., Materials and Methods: We performed a retrospective analysis in a homogeneously treated cohort of 106 patients undergoing ASCT2 at our institution, all of whom received novel agent-based chemotherapy (immunomodulatory agent [IMiD] and/or proteasome inhibitor [PI]) for both induction and relapse. As an exploratory objective we assessed whether predictive thresholds of progression free survival post first transplant (ASCT1) for benefit post ASCT2 vary with use of IMiD maintenance post ASCT1., Results: The overall response rate (ORR) was 98% post-ASCT2 and treatment-related mortality (TRM) was low at 1.8%. With a median follow-up of 26 months (range 0.5-85) from ASCT2, median overall survival (OS) is estimated at 80 months (95% CI: ≥ 49-months) and median progression-free survival after ASCT2 (PFS2) at 24 months (95% CI 19-39). PFS post first transplant (PFS1) at >/= 50 months was associated with improved OS. Predictors of PFS2 included PFS1 ≤42 months and progression on IMiD-based maintenance post- ASCT1., Conclusion: ASCT2 continues to offer acceptable outcomes for most patients treated within modern day treatment paradigms, with longer PFS after ASCT1 and IMiD non-refractory disease being associated with improved outcomes., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Purpose: The efficacy of EZH2 inhibition has been modest in the initial clinical exploration of diffuse large B-cell lymphoma (DLBCL), yet EZH2 inhibitors are well tolerated. Herein, we aimed to uncover genetic and pharmacologic opportunities to enhance the clinical efficacy of EZH2 inhibitors in DLBCL., Experimental Design: We conducted a genome-wide sensitizing CRISPR/Cas9 screen with tazemetostat, a catalytic inhibitor of EZH2. The sensitizing effect of IKZF1 loss of function was then validated and leveraged for combination treatment with lenalidomide. RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing analyses were performed to elucidate transcriptomic and epigenetic changes underlying synergy., Results: We identified IKZF1 knockout as the top candidate for sensitizing DLBCL cells to tazemetostat. Treating cells with tazemetostat and lenalidomide, an immunomodulatory drug that selectively degrades IKAROS and AIOLOS, phenocopied the effects of the CRISPR/Cas9 screen. The combined drug treatment triggered either cell-cycle arrest or apoptosis in a broad range of DLBCL cell lines, regardless of EZH2 mutational status. Cell-line-based xenografts also showed slower tumor growth and prolonged survival in the combination treatment group. RNA-seq analysis revealed strong upregulation of interferon signaling and antiviral immune response signatures. Gene expression of key immune response factors such as IRF7 and DDX58 were induced in cells treated with lenalidomide and tazemetostat, with a concomitant increase of H3K27 acetylation at their promoters. Furthermore, transcriptome analysis demonstrated derepression of endogenous retroviruses after combination treatment., Conclusions: Our data underscore the synergistic interplay between IKAROS degradation and EZH2 inhibition on modulating epigenetic changes and ultimately enhancing antitumor effects in DLBCL., (©2021 American Association for Cancer Research.)

Both previous and additional genetic knockdown studies reported herein implicate G protein-coupled receptor kinase 6 (GRK6) as a critical kinase required for the survival of multiple myeloma (MM) cells. Therefore, we sought to develop a small molecule GRK6 inhibitor as an MM therapeutic. From a focused library of known kinase inhibitors, we identified two hits with moderate biochemical potencies against GRK6. From these hits, we developed potent (IC 50 < 10 nM) analogues with selectivity against off-target kinases. Further optimization led to the discovery of an analogue ( 18 ) with an IC 50 value of 6 nM against GRK6 and selectivity against a panel of 85 kinases. Compound 18 has potent cellular target engagement and antiproliferative activity against MM cells and is synergistic with bortezomib. In summary, we demonstrate that targeting GRK6 with small molecule inhibitors represents a promising approach for MM and identify 18 as a novel, potent, and selective GRK6 inhibitor.

Autologous stem cell transplant (ASCT) is a feasible treatment option for multiple myeloma (MM) patients with renal insufficiency; however, these patients tend to experience higher rates of drug toxicity and transplant-related mortality (TRM) during ASCT. Recent adoption of bortezomib-based induction regimens and dose reduction of melphalan during conditioning may improve outcomes in this population. In this single center retrospective study, we compared the toxicity and survival outcomes of 96 MM patients with renal insufficiency undergoing ASCT between two eras: 1998-2007 and 2008-2016. The proportion of dialysis dependent patients was similar in both groups (49 and 45%). We found no TRM in those transplanted more recently as compared with 13% in the older era of ASCT. There were significantly more high grade (grades 3-4) toxicities in the older era of ASCT including high grade electrolyte abnormalities, mucositis, delirium, and bleeding. Patients transplanted more recently had significantly higher overall response rate (ORR) as well as deeper responses to ASCT (≥VGPR in 79% vs 39%). Progression-free survival (PFS) was prolonged by 26 months in the more recent era compared with the older era. Overall, improvements in treatment regimens have resulted in reduced TRM and toxicities for patients with renal insufficiency undergoing ASCT.

Introduction: The combination of lenalidomide and dexamethasone (Len-Dex) is an established regimen for patients with relapsed or refractory myeloma. To prolong the benefit of this effective regimen, the Myeloma Program at Princess Margaret Cancer Centre has routinely added a third agent, oral cyclophosphamide (Cy) given weekly, to Len-Dex at disease progression., Patients and Methods: In the present report, we describe the cases of 53 patients who had received Len-Dex-Cy for a minimum of 4 weeks from January 2007 to December 2014 after progression with Len-Dex alone. The dose of added Cy ranged from 250 to 500 mg weekly. The median number of previous regimens, including Len-Dex, was 2 (range, 2-4); 80% of patients had undergone previous autologous stem cell transplantation., Results: The overall rate of response equal to or greater than a partial response was 34%, and clinical benefit (stable disease or better) was observed in 87% of the patients. The median duration of Len-Dex-Cy therapy was 6.9 months (range, 0.9-55.1 months). The median progression-free survival was 6.1 months (range, 4.2-8.1 months) from the addition of Cy and 24.1 months (range, 15.9-32.0 months) from start of Len-Dex., Conclusion: The addition of Cy for patients with myeloma developing progression with Len-Dex was an inexpensive option with manageable toxicity that resulted in a clinically meaningful extension of disease control., (Copyright © 2018. Published by Elsevier Inc.)

Background: Translocation t(4;14) has traditionally been classified as a high-risk cytogenetic feature in patients with multiple myeloma with shortened progression-free (PFS) and overall survival (OS) despite initial response to treatment. Recent data have shown an improved long-term survival in these patients treated with novel agents, such as bortezomib., Patients and Methods: We conducted a retrospective study on our patients with t(4;14) multiple myeloma treated with bortezomib-based induction between July 1, 2006 and June 30, 2014 to assess the real-world outcomes of these patients in a tertiary center., Results: Among the 75 patients analyzed, the median PFS was 33.5 months, and the median OS was 69.6 months after a median follow-up of 41 months. Even in the era of novel agents, patients who received frontline autologous stem cell transplant had a better PFS than those who received chemotherapy alone (median PFS, 24.2 months vs. 41.5 months; P = .01). Hypercalcemia at the time of presentation was found to be a significant predictor of progression (hazard ratio [HR], 10.1; 95% confidence interval [CI], 4.0-26.0) and death (HR, 9.4; 95% CI, 3.2-27.8), and co-harboring of del(17p) by fluorescent in situ hybridization with t(4;14) was associated with a significantly inferior OS (HR, 4.0; 95% CI, 1.4-11.4)., Conclusion: Even in the era of novel agents, t(4;14) remains a negative prognostic marker. Frontline autologous stem cell transplant remains as an essential tool when treating these high-risk patients, but further prospective randomized studies are needed to determine the most effective strategy for this patient group., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Introduction: Cyclophosphamide, bortezomib, and prednisone (CyBorP) is a highly effective, well-tolerated regimen in relapsed/refractory multiple myeloma. CyBorP, originally developed at our center to include weekly bortezomib (Bor) and alternate-day prednisone (P), was recently modified so that weekly dexamethasone (D) replaced prednisone., Patients and Methods: To assess the effectiveness and tolerability of CyBorP/D in real-world practice, we identified 96 relapsed/refractory patients who received ≥ 1 28-day cycle of CyBorP/D, consisting of cyclophosphamide 300 mg/m(2) (days 1, 8, 15, and 22), Bor 1.0 to 1.5 mg/m(2) (days 1, 8, and 15), and either P 50 to 100 mg on alternate days or D 20 to 40 mg weekly between 2007 and 2013., Results: Sixty-six (69%) patients achieved ≥ partial response: 16 with clinical complete response and 25 with very good partial response; 22 others had stable disease. Progression-free and overall survival for all patients were 16.2 months (95% confidence interval [CI], 7.7-20.1 months) and 26.3 months (95% CI, 21.6-81.2 months), respectively. Although 26 patients had prior Bor exposure, there was no difference in progression-free or overall survival versus Bor-naive patients., Conclusion: Toxicities with CyBorP/D were generally mild and manageable. New onset peripheral neuropathy was seen in 13 cases; 9 of 26 patients with pre-existing peripheral neuropathy developed worsening symptoms. No second primary malignancies were observed., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The molecular target(s) cooperating with proteasome inhibition in multiple myeloma (MM) remain unknown. We therefore measured proliferation in MM cells transfected with 13 984 small interfering RNAs in the absence or presence of increasing concentrations of bortezomib. We identified 37 genes, which when silenced, are not directly cytotoxic but do synergistically potentiate the growth inhibitory effects of bortezomib. To focus on bortezomib sensitizers, genes that also sensitized MM to melphalan were excluded. When suppressed, the strongest bortezomib sensitizers were the proteasome subunits PSMA5, PSMB2, PSMB3, and PSMB7 providing internal validation, but others included BAZ1B, CDK5, CDC42SE2, MDM4, NME7, RAB8B, TFE3, TNFAIP3, TNK1, TOP1, VAMP2, and YY1. The strongest hit CDK5 also featured prominently in pathway analysis of primary screen data. Cyclin-dependent kinase 5 (CDK5) is expressed at high levels in MM and neural tissues with relatively low expression in other organs. Viral shRNA knockdown of CDK5 consistently sensitized 5 genetically variable MM cell lines to proteasome inhibitors (bortezomib and carfilzomib). Small-molecule CDK5 inhibitors were demonstrated to synergize with bortezomib to induce cytotoxicity of primary myeloma cells and myeloma cell lines. CDK5 regulation of proteasome subunit PSMB5 was identified as a probable route to sensitization.

A paucity of validated kinase targets in human multiple myeloma has delayed clinical deployment of kinase inhibitors in treatment strategies. We therefore conducted a kinome-wide small interfering RNA (siRNA) lethality study in myeloma tumor lines bearing common t(4;14), t(14;16), and t(11;14) translocations to identify critically vulnerable kinases in myeloma tumor cells without regard to preconceived mechanistic notions. Fifteen kinases were repeatedly vulnerable in myeloma cells, including AKT1, AK3L1, AURKA, AURKB, CDC2L1, CDK5R2, FES, FLT4, GAK, GRK6, HK1, PKN1, PLK1, SMG1, and TNK2. Whereas several kinases (PLK1, HK1) were equally vulnerable in epithelial cells, others and particularly G protein-coupled receptor kinase, GRK6, appeared selectively vulnerable in myeloma. GRK6 inhibition was lethal to 6 of 7 myeloma tumor lines but was tolerated in 7 of 7 human cell lines. GRK6 exhibits lymphoid-restricted expression, and from coimmunoprecipitation studies we demonstrate that expression in myeloma cells is regulated via direct association with the heat shock protein 90 (HSP90) chaperone. GRK6 silencing causes suppression of signal transducer and activator of transcription 3 (STAT3) phosphorylation associated with reduction in MCL1 levels and phosphorylation, illustrating a potent mechanism for the cytotoxicity of GRK6 inhibition in multiple myeloma (MM) tumor cells. As mice that lack GRK6 are healthy, inhibition of GRK6 represents a uniquely targeted novel therapeutic strategy in human multiple myeloma.

As multiple myeloma tumors universally dysregulate cyclin D genes we conducted high-throughput chemical library screens for compounds that induce suppression of cyclin D2 promoter transcription. The top-ranked compound was a natural triterpenoid, pristimerin. Strikingly, the early transcriptional response of cells treated with pristimerin closely resembles cellular responses elicited by proteosome inhibitors, with rapid induction of heat shock proteins, activating transcription factor 3 (ATF3), and CHOP. Enzymatic assays and immunoblotting confirm that pristimerin rapidly (< 90 minutes) and specifically inhibits chymotrypsin-like proteosome activity at low concentrations (< 100 nM) and causes accumulation of cellular ubiquitinated proteins. Notably, cytotoxic triterpenoids including pristimerin inhibit NF-kappaB activation via inhibition of IKK alpha or IKK beta, whereas proteosome inhibitors instead suppress NF-kappaB function by impairing degradation of ubiquitinated I kappaB. By inhibiting both IKK and the proteosome, pristimerin causes overt suppression of constitutive NF-kappaB activity in myeloma cells that may mediate its suppression of cyclin D. Multiple myeloma is exquisitely sensitive to proteosome or NF-kappaB pathway inhibition. Consistent with this, pristimerin is potently and selectively lethal to primary myeloma cells (IC(50) < 100 nM), inhibits xenografted plasmacytoma tumors in mice, and is synergistically cytotoxic with bortezomib--providing the rationale for pharmaceutical development of triterpenoid dual-function proteosome/NF-kappaB inhibitors as therapeutics for human multiple myeloma and related malignancies.

D-cyclins are regulators of cell division that act in a complex with cyclin-dependent kinases to commit cells to a program of DNA replication. D-cyclins are overexpressed in many tumors, including multiple myeloma and leukemia, and contribute to disease progression and chemoresistance. To better understand the role and impact of D-cyclins in hematologic malignancies, we conducted a high throughput screen for inhibitors of the cyclin D2 promoter and identified the drug cyproheptadine. In myeloma and leukemia cells, cyproheptadine decreased expression of cyclins D1, D2, and D3 and arrested these cells in the G(0)/G(1) phase. After D-cyclin suppression, cyproheptadine induced apoptosis in myeloma and leukemia cell lines and primary patient samples preferentially over normal hematopoietic cells. In mouse models of myeloma and leukemia, cyproheptadine inhibited tumor growth without significant toxicity. Cyproheptadine-induced apoptosis was preceded by activation of the mitochondrial pathway of caspase activation and was independent of the drug's known activity as an H1 histamine and serotonin receptor antagonist. Thus, cyproheptadine represents a lead for a novel therapeutic agent for the treatment of malignancy. Because the drug is well tolerated and already approved in multiple countries for clinical use as an antihistamine and appetite stimulant, it could be moved directly into clinical trials for cancer.

Knockout and transgenic studies in mice demonstrate that normal somatic tissues redundantly express 3 cyclin D proteins, whereas tumor cells seem dependent on a single overexpressed cyclin D. Thus, selective suppression of the individual cyclin D deregulated in a tumor represents a biologically valid approach to targeted cancer therapy. In multiple myeloma, overexpression of 1 of the cyclin D proteins is a ubiquitous feature, unifying at least 7 different initiating genetic events. We demonstrate here that RNAi of genes encoding cyclin D1 and cyclin D2 (CCND1 and CCND2, respectively) inhibits proliferation and is progressively cytotoxic in human myeloma cells. By screening a chemical library using a cell-based assay for inhibition of CCND2 trans-activation, we identified the plant cytokinin kinetin riboside as an inhibitor of CCND2 trans-activation. Kinetin riboside induced marked suppression of CCND2 transcription and rapidly suppressed cyclin D1 and D2 protein expression in primary myeloma cells and tumor lines, causing cell-cycle arrest, tumor cell-selective apoptosis, and inhibition of myeloma growth in xenografted mice. Mechanistically, kinetin riboside upregulated expression of transcription repressor isoforms of cAMP-response element modulator (CREM) and blocked both trans-activation of CCND2 by various myeloma oncogenes and cis-activation of translocated CCND1, suggesting induction of an overriding repressor activity that blocks multiple oncogenic pathways targeting cyclin D genes. These data support targeted repression of cyclin D genes as a therapeutic strategy for human malignancies.