Ku86 variant expression and function in multiple myeloma cells is associated with increased sensitivity to DNA damage

A novel BCMA PBD-ADC with ATM/ATR/WEE1 inhibitors or bortezomib induce synergistic lethality in multiple myeloma

To target mechanisms critical for multiple myeloma (MM) plasma cell adaptations to genomic instabilities and further sustain MM cell killing, we here specifically trigger DNA damage response (DDR) in MM cells by a novel BCMA antibody-drug conjugate (ADC) delivering the DNA cross-linking PBD dimer tesirine, MEDI2228. MEDI2228, more effectively than its anti-tubulin MMAF-ADC homolog, induces cytotoxicity against MM cells regardless of drug resistance, BCMA levels, p53 status, and the protection conferred by bone marrow stromal cells and IL-6. Distinctly, prior to apoptosis, MEDI2228 activates DDRs in MM cells via phosphorylation of ATM/ATR kinases, CHK1/2, CDK1/2, and H2AX, associated with expression of DDR-related genes. Significantly, MEDI2228 synergizes with DDR inhibitors (DDRi s) targeting ATM/ATR/WEE1 checkpoints to induce MM cell lethality. Moreover, suboptimal doses of MEDI2228 and bortezomib (btz) synergistically trigger apoptosis of even drug-resistant MM cells partly via modulation of RAD51 and accumulation of impaired DNA. Such combination further induces superior in vivo efficacy than monotherapy via increased nuclear γH2AX-expressing foci, irreversible DNA damages,  and tumor cell death, leading to significantly prolonged host survival. These results indicate leveraging MEDI2228 with DDRi s or btz as novel combination strategies, further supporting ongoing clinical development of MEDI2228 in patients with relapsed and refractory MM.

Ku86 alleviates human umbilical vein endothelial cellular apoptosis and senescence induced by a low dose of ionizing radiation

Objective

The aim of this study was to observe the effect of Ku86 on cellular senescence and apoptosis induced by various doses of ionizing radiation in human umbilical vein endothelial cells (HUVECs).

Methods

Senescence-associated β-galactosidase activity was detected to evaluate cell senescence. Apoptosis was determined by flow cytometry and a caspase enzyme determination kit. p16^Ink4a, Sirt1, superoxide dismutase 2 (SOD2), xanthine oxidase (XOD), and Bcl-2 protein expression levels were measured by western blotting.

Results

Low doses of ionizing radiation induced cellular senescence and apoptosis in a dose-dependent manner. The Ku86 protein was negatively correlated with ionization intensity. After transfection of Ku86 with a vector (pcDNA 3.1), or interference with siRNA (si-Ku86), apoptosis/senescence and related protein expression were observed. Western blot results revealed that this induction of senescence was associated with activated Sirt1 and SOD2, and downregulation of p16^Ink4a and XOD in 0.2 Gy ionizing radiation. The expression levels of apoptosis-associated proteins, such as Bcl-2, cleaved caspase-3, caspase-8, and caspase-9, were significantly altered in both the presence and absence of Ku86 with ionizing radiation (0.2 Gy).

Conclusions

Our study revealed that Ku86 overexpression inhibits HUVEC apoptosis and senescence induced by low doses of ionizing radiation.

A Cyclin-Dependent Kinase Inhibitor, Dinaciclib, Impairs Homologous Recombination and Sensitizes Multiple Myeloma Cells to PARP Inhibition

PARP1/2 are required for single-strand break repair, and their inhibition causes DNA replication fork collapse and double-strand break (DSB) formation. These DSBs are primarily repaired via homologous recombination (HR), a high-fidelity repair pathway. Should HR be deficient, DSBs may be repaired via error-prone nonhomologous end-joining mechanisms, or may persist, ultimately resulting in cell death. The combined disruption of PARP and HR activities thus produces synthetic lethality. Multiple myeloma cells are characterized by chromosomal instability and pervasive DNA damage, implicating aberrant DNA repair. Cyclin-dependent kinases (CDK), upstream modulators of HR, are dysregulated in multiple myeloma. Here, we show that a CDK inhibitor, dinaciclib, impairs HR repair and sensitizes multiple myeloma cells to the PARP1/2 inhibitor ABT-888. Dinaciclib abolishes ABT-888-induced BRCA1 and RAD51 foci and potentiates DNA damage, indicated by increased γH2AX foci. Dinaciclib treatment reduces expression of HR repair genes, including Rad51, and blocks BRCA1 phosphorylation, a modification required for HR repair, thus inhibiting HR repair of chromosome DSBs. Cotreatment with dinaciclib and ABT-888 in vitro resulted in synthetic lethality of multiple myeloma cells, but not normal CD19(+) B cells, and slowed growth of multiple myeloma xenografts in SCID mice almost two-fold. These findings support combining dinaciclib with PARP inhibitors for multiple myeloma therapy. Mol Cancer Ther; 15(2); 241-50. ©2015 AACR.

DNA repair pathways in human multiple myeloma: role in oncogenesis and potential targets for treatment

Every day, cells are faced with thousands of DNA lesions, which have to be repaired to preserve cell survival and function. DNA repair is more or less accurate and could result in genomic instability and cancer. We review here the current knowledge of the links between molecular features, treatment, and DNA repair in multiple myeloma (MM), a disease characterized by the accumulation of malignant plasma cells producing a monoclonal immunoglobulin. Genetic instability and abnormalities are two hallmarks of MM cells and aberrant DNA repair pathways are involved in disease onset, primary translocations in MM cells, and MM progression. Two major drugs currently used to treat MM, the alkylating agent Melphalan and the proteasome inhibitor Bortezomib act directly on DNA repair pathways, which are involved in response to treatment and resistance. A better knowledge of DNA repair pathways in MM could help to target them, thus improving disease treatment.

Adhesion molecules--The lifelines of multiple myeloma cells

Multiple myeloma is an incurable hematological malignancy of terminally differentiated immunoglobulin-producing plasma cells. As a common presentation of the disease, the malignant plasma cells accumulate and proliferate in the bone marrow, where they disrupt normal hematopoiesis and bone physiology. Multiple myeloma cells and the bone marrow microenvironment are linked by a composite network of interactions mediated by soluble factors and adhesion molecules. Integrins and syndecan-1/CD138 are the principal multiple myeloma receptor systems of extracellular matrix components, as well as of surface molecules of stromal cells. CD44 and RHAMM are the major hyaluronan receptors of multiple myeloma cells. The SDF-1/CXCR4 axis is a key factor in the homing of multiple myeloma cells to the bone marrow. The levels of expression and activity of these adhesion molecules are controlled by cytoplasmic operating mechanisms, as well as by extracellular factors including enzymes, growth factors and microenvironmental conditions. Several signaling responses are activated by adhesive interactions of multiple myeloma cells, and their outcomes affect the survival, proliferation and migration of these cells, and in many cases generate a drug-resistant phenotype. Hence, the adhesion systems of multiple myeloma cells are attractive potential therapeutic targets. Several approaches are being developed to disrupt the activities of adhesion molecules in multiple myeloma cells, including small antagonist molecules, direct targeting by immunoconjugates, stimulation of immune responses against these molecules, and signal transduction inhibitors. These potential novel therapeutics may be incorporated into current treatment schemes, or directed against minimal residual malignant cells during remission.

Interactions of the Hdm2/p53 and proteasome pathways may enhance the antitumor activity of bortezomib

PURPOSE

p53 is inactivated in many human malignancies through missense mutations or overexpression of the human homologue of Mdm2 (Hdm2), an E3 ubiquitin ligase that ubiquitinates p53, thereby promoting its proteasomal degradation. The cis-imidazoline nutlin-3 can disrupt the p53-Hdm2 interaction and activate p53, inducing apoptosis in vitro in many malignancies, including multiple myeloma (MM).

EXPERIMENTAL DESIGN

We hypothesized that suppression of Hdm2-mediated p53 ubiquitination may augment sequelae of p53 accumulation caused by proteasomal inhibition. We compared the response of MM cells versus several epithelial cancer models to the proteasome inhibitor bortezomib in combination with nutlin-3.

RESULTS

The combination of sublethal concentrations of bortezomib plus nutlin-3 induced additive cytotoxicity against bortezomib-sensitive MM cell lines. Importantly, however, in breast, prostate, colon, and thyroid (papillary, follicular, anaplastic, and medullary) carcinoma cell lines, this combination triggered synergistic cytotoxicity, and increased expression of p53, p21, Hdm2, Bax, Noxa, PUMA, and cleavage of caspase-3 and poly ADP ribose polymerase. Coculture with bone marrow stromal cells attenuated MM cell sensitivity to nutlin-3 monotherapy and was associated with evidence of suppression of p53 activity in MM cells, whereas combined bortezomib-nutlin-3 treatment maintained cytotoxicity even in the presence of bone marrow stromal cells.

CONCLUSIONS

This differential response of MM versus epithelial carcinomas to combination of nutlin-3 with bortezomib sheds new light on the role of p53 in bortezomib-induced apoptosis. Concurrent Hdm2 inhibition with bortezomib may extend the spectrum of bortezomib applications to malignancies with currently limited sensitivity to single-agent bortezomib or, in the future, to MM patients with decreased clinical responsiveness to bortezomib-based therapy.

Reversal of multidrug resistance by curcumin through FA/BRCA pathway in multiple myeloma cell line MOLP-2/R

Most patients with multiple myeloma (MM) will relapse eventually due to the acquired multidrug resistance (MDR). The objective of this study was to explore the reversal effect of curcumin on the MDR of human MM cell line, MOLP-2/R, and analyze the role of Fanconi anemia (FA)/BRCA pathway in this process. MOLP-2/R was selected by stepwise exposure of parental MOLP-2 cells to increasing concentrations of melphalan. The MTT assay was used to detect the reversal ratio of curcumin. The FANCD2 monoubiquitination expression was detected by western blotting to explore the role of FA/BRCA pathway. Cell cycle, apoptosis, and intracellular drug concentration were analyzed by flow cytometry. The results indicated that combination of melphalan with curcumin had stronger effects on the proliferation inhibition, inducement of apoptosis, G2/M phase arrest, and enhancement of intracellular drug concentration than melphalan alone in MOLP-2/R cells. These effects were accompanied with inhibition of FA/BRCA pathway by down regulation of FANCD2 protein monoubiquitination in a dose-dependent manner. In conclusion, curcumin reversed multidrug resistance of MOLP-2/R through inhibition of FA/BRCA pathway. The possible mechanisms include (1) reduction of DNA damage repair and stimulation of apoptosis of tumor cells through inhibition of FA/BRCA pathway, which is important for DNA repair, and (2) achievement of high concentration in target cells. Curcumin may be a safe reversal agent of multidrug resistance with low-dose DNA cross-linking agents.

Use of Phage Display to Isolate Specific Human Monoclonal Antibody Fragments Against a Potential Target for Multiple Myeloma

Introduction: Multiple myeloma (MM), a malignancy of plasma cells, accounts for 10% of all haematological malignancies and is currently incurable. Although it can be treated, the disease tends to relapse after several years and becomes increasingly resistant to conventional therapy. Investigations into using humoral therapy for MM are now underway with a view that novel therapeutic agents may provide a more targeted therapy for MM. Materials and Methods: Here, phage display, a faster and more efficient method compared to classical hybridoma fusion technology, was used as a proof-of-concept to isolate several single-chain Fragment variables (scFv) against Ku86. Results: Anti-Ku86 polyclonal scFvs biopanning was successful where third round scFvs (A450~1.1) showed a 1/3 increase in binding as compared to the first round scFvs (A450~0.4) with 100ug/mL of antigen (purified human Ku86). Subsequent selection and verification of monoclonal antibodies using third round biopanning revealed 4 good affinity binding clones ranging from A450~0.1 to A450~0.15 on 12.5ug/mL of antigen as compared to low binders (A450~0.07) and these antibodies bind to Ku86 in a specific and dose-dependent manner. Comparative studies were also performed with commercially available murine antibodies and results suggest that 2 of the clones may bind close to the following epitopes aa506-541 and aa1-374. Conclusions: These studies using phage display provide an alternative and viable method to screen for antibodies quickly and results show that good affinity antibodies against Ku86 have been successfully isolated and they can be used for further studies on MM and form the basis for further development as anti-cancer therapeutic agents. Key words: Antibody isolation, Ku86, Phage display, ScFv

Impaired NHEJ function in multiple myeloma

Multiple myeloma (MM) is characterized by multiple chromosomal aberrations. To assess the contribution of DNA repair to this phenotype, ionizing radiation was used to induce DNA double strand breaks in three MM cell lines. Clonogenic survival assays showed U266 (SF4=15.3+6.4%) and RPMI 8226 (SF4=12.6.0+1.7%) were radiation sensitive while OPM2 was resistant (SF4=78.9+4.1%). Addition of the DNA-PK inhibitor NU7026 showed the expected suppression in radiation survival in OPM2 but increased survival in both radiation sensitive cell lines. To examine non-homologous end joining (NHEJ) repair in these lines, the ability of protein extracts to support in vitro DNA repair was measured. Among the three MM cell lines analyzed, RPMI 8226 demonstrated impaired blunt ended DNA ligation using a ligation-mediated PCR technique. In a bacterial based functional assay to rejoin a DNA break within the beta-galactosidase gene, RPMI 8226 demonstrated a 4-fold reduction in rejoining fidelity compared to U266, with OPM2 showing an intermediate capacity. Ionizing radiation induced a robust gamma-H2AX response in OPM2 but only a modest increase in each radiation sensitive cell line perhaps related to the high level of gamma-H2AX in freshly plated cells. Examination of gamma-H2AX foci in RPMI 8226 cells confirmed data from Western blots where a significant number of foci were present in freshly plated untreated cells which diminished over 24h of culture. Based on the clonogenic survival and functional repair assays, all three cell lines exhibited corrupt NHEJ repair. We conclude that suppression of aberrant NHEJ function using the DNA-PK inhibitor NU7026 may facilitate access of DNA ends to an intact homologous recombination repair pathway, paradoxically increasing survival after irradiation. These data provide insight into the deregulation of DNA repair at the site of DNA breaks in MM that may underpin the characteristic genomic instability of this disease.

Ku86 exists as both a full-length and a protease-sensitive natural variant in multiple myeloma cells

Background

Truncated variants of Ku86 protein have previously been detected in 86% to 100% of freshly isolated patient multiple myeloma (MM) cells. Since, the Ku70/Ku86 heterodimer functions as the regulatory subunit of the DNA repair enzyme, DNA-dependent protein kinase, we have been interested in the altered expression and function of Ku86 variant (Ku86v) proteins in genome maintenance of MM.

Results

Although, a number of studies have suggested that truncated forms of Ku proteins could be artificially generated by proteolytic degradation in vitro in human lymphocytes, we now show using whole cell immunoblotting that the RPMI-8226 and SGH-MM5 human MM cell lines consistently express full-length Ku86 as well as a 69-kDa Ku86v; a C-terminus truncated 69-kDa variant Ku86 protein. In contrast, Ku86v proteins were not detected in the freshly isolated lymphocytes as was previously reported. Data also indicates that the Ku86v was not generated as a result of carbohydrate modification but that serine proteases may act on the full-length form of the protein.

Conclusion

These data confirm that MM cells contain bona fide Ku86v proteins that were generated intracellularly by a post-transcriptional mechanism, which required proteolytic processing.

Experimental Study Enhancing the Chemosensitivity of Multiple Myeloma to Melphalan by Using a Tissue-Specific APE1-Silencing RNA Expression Vector

PURPOSE

Because of a developing resistance to chemotherapy agents, multiple myeloma (MM) has been an incurable disease until now. As a means to overcome MM tumor cell resistance and/or sensitize tumor cells to chemotherapeutic treatments currently used, we examined the role of human apurinic/apyrimidinic endonuclease 1 (APE1) in resistance and prognosis in patients with MM.

PATIENTS AND METHODS

Multiple myeloma cells were analyzed by using bone marrow specimens from 32 patients with MM and 10 normal volunteers.

RESULTS

The positive rate of APE1 protein expression was 65.6% in the bone marrow specimens of patients with MM with known clinical outcome. Positive rate of APE1 expression beyond grade 2 in the relapsed/refractory group was significantly higher than that in the untreated group. No positive results of grade > 2 were detected in bone marrow specimens from patients with noncancerous disease. It was also confirmed that the amount of APE1 protein in KM3 cells was positively correlated with the dose and action time of melphalan. Because APE1 was overexpressed in refractory/relapsed MM cells, siRNA-targeted technology was used to decrease APE1 levels in KM3 cells, with protein levels deceasing to 80%-90% within 24 hours and continuing to decease for 72 hours. The best dose and time of inhibiting expression of APE1 protein were 3 mug and 2 days long. A decrease in APE1 levels in siRNA-treated KM3 cells led to enhanced cell sensitization to melphalan.

CONCLUSION

The findings herein present prognostic and therapeutic implications for treating relapsed/refractory MM. The APE1-silencing RNA results demonstrate the feasibility of the therapeutic modulation of APE1 using a variety of molecules and approaches.

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The biology of Ku and its potential oncogenic role in cancer

Ku is a heterodimeric protein made up of two subunits, Ku70 and Ku80. It was originally identified as an autoantigen recognized by the sera of patients with autoimmune diseases. It is a highly versatile regulatory protein that has been implicated in multiple nuclear processes, e.g., DNA repair, telomere maintenance and apoptosis. Accordingly, Ku is thought to play a crucial role in maintenance of chromosomal integrity and cell survival. Recent reports suggest that there is a positive relationship between Ku and the development of cancer, making Ku an important candidate target for anticancer drug development. Specifically, prior studies suggest that a delicate balance exists in Ku expression, as overexpression of Ku proteins promotes oncogenic phenotypes, including hyperproliferation and resistance to apoptosis; whereas deficient or low expression of Ku leads to genomic instability and tumorigenesis. Such observations through various experimental models indicate that Ku may act as either a tumor suppressor or an oncoprotein. Hence, understanding the link between the various functions of Ku and the development of cancer in different cell systems may help in the development of novel anticancer therapeutic agents that target Ku. These studies may also increase our understanding of how Ku autoantibodies are generated in autoimmune diseases.

Expression of DNA repair gene Ku80 in lymphoid neoplasm

OBJECTIVES

Ku, a heterodimer of KU70 and Ku80 that binds to double-strand DNA breaks (DSBs) and activates the catalytic subunit (DNA-PKcs) when DNA is bound, is essential in DSB repair and V(D)J recombination. Ku80 is a putative tumor suppressor gene that might play an important role in drug resistance. Our aim was to determine the role of Ku80 in lymphoid malignancy.

PATIENTS AND METHODS

Competitive reverse transcription-polymerase chain reaction assays were performed and the expression levels of Ku80 were measured in normal peripheral blood mononuclear cells (n = 9) and malignant cells from 25 patients with acute lymphoblastic leukemia (ALL) (14 children, 11 adults), and chronic lymphoproliferative disorders (n = 6). The Ku80 transcripts were sequencing for the possibility of mutation.

RESULTS

No mutation or Ku80 variant at the RNA level was seen in any patient samples or in the Raji or CCRF-CEM cell lines. In Ku80 expression, 8.8-, 1.9-, and 6.2-fold mean increases were seen in adult, pediatric ALL, and chronic lymphoid malignancies compared with the control. The Ku80 was significantly higher in adult than in pediatric ALL (P = 0.02). The amount of Ku80 expression in ALL was moderately correlated with peripheral white blood cell counts, but not with Ki67 labeling index. High Ku80 expressers (higher than the mean of all patients with ALL) tended to respond poorly to therapy: Only 22% of high Ku80 expressers achieved durable complete remission compared to 62% of low expressers.

CONCLUSIONS

Our study suggests that Ku80 might contribute to generally poor prognoses in adult ALL.

Expression of DNA-dependent protein kinase in human granulocytes

Human polymorphonuclear leukocytes (PMN) have been reported to completely lack of DNA-dependent protein kinase (DNA-PK) which is composed of Ku protein and the catalytic subunit DNA-PKcs, needed for nonhomologous end-joining (NHEJ) of DNA double-strand breaks. Promyelocytic HL-60 cells express a variant form of Ku resulting in enhanced radiation sensitivity. This raises the question if low efficiency of NHEJ, instrumental for the cellular repair of oxidative damage, is a normal characteristic of myeloid differentiation. Here we confirmed the complete lack of DNA-PK in PMN protein extracts, and the expression of the truncated Ku86 variant form in HL-60. However, this degradation of DNA-PK was shown to be due to a DNA-PK-degrading protease in PMN and HL-60. In addition, by using a protease-resistant whole cell assay, both Ku86 and DNA-PKcs could be demonstrated in PMN, suggesting the previously reported absence in PMN of DNA-PK to be an artefact. The levels of Ku86 and DNA-PKcs were much reduced in PMN, as compared with that of the lymphocytes, whereas HL-60 displayed a markedly elevated DNA-PK concentration. In conclusion, our findings provide evidence of reduced, not depleted expression of DNA-PK during the mature stages of myeloid differentiation.

Relationship between antiapoptotic molecules and metastatic potency and the involvement of DNA-dependent protein kinase in the chemosensitization of metastatic human cancer cells by epidermal growth factor receptor blockade

The failure to treat metastatic cancer with multidrug resistance is a major problem for successful cancer therapy, and the molecular basis for the association of metastatic phenotype with resistance to therapy is still unclear. In this study, we revealed that various metastatic cancer cells showed consistently higher levels of antiapoptotic proteins, including Bcl-2, nuclear factor-kappaB, MDM2, DNA-dependent protein kinase (DNA-PK), and epidermal growth factor receptor (EGFR), and lower levels of proapoptotic proteins, including Bax and p53 than low metastatic parental cells. This was followed by chemo- and radioresistance in metastatic cancer cells compared with their parental cells. EGFR and DNA-PK activity, which are known to be associated with chemo- and radioresistance, were demonstrated to be mutually regulated by each other. Treatment with PKI166, an EGFR inhibitor, suppressed etoposide-induced activation of DNA-PK in A375SM metastatic melanoma cells. In addition, PKI166 enhanced markedly the chemosensitivities of metastatic cancer cell sublines to various anticancer drugs in comparison with those of low metastatic cancer cells. These results suggest that the activities of DNA-PK and EGFR, which is positively correlated with each other, may contribute to metastatic phenotype as well as therapy resistance, and the EGFR inhibitor enhances the effect of anticancer drugs against therapy-resistant metastatic cancer cells via suppression of stress responses, including activation of DNA-PK.

Critical Role for Hematopoietic Cell Kinase (Hck)-mediated Phosphorylation of Gab1 and Gab2 Docking Proteins in Interleukin 6-induced Proliferation and Survival of Multiple Myeloma Cells

Interleukin-6 (LI-6) is a known growth and survival factor in multiple myeloma via activation of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling cascade. In this report we show that Grb2-associated binder (Gab) family adapter proteins Gab1 and Gab2 are expressed by multiple myeloma cells; and that interleukin-6 induces their tyrosine phosphorylation and association with downstream signaling molecules. We further demonstrate that these events are Src family tyrosine kinase-dependent and specifically identify the role of hematopoietic cell kinase (Hck) as a new Gab family adapter protein kinase. Conversely, inhibition of Src family tyrosine kinases by the pyrazolopyrimidine PP2, as in kinase-inactive Hck mutants, significantly reduces IL-6-triggered activation of extracellular signal-regulated kinase and AKT-1, leading to significant reduction of multiple myeloma cell proliferation and survival. Taken together, these results delineate a key role for Hck-mediated phosphorylation of Gab1 and Gab2 docking proteins in IL-6-induced proliferation and survival of multiple myeloma cells and identify tyrosine kinases and downstream adapter proteins as potential new therapeutic targets in multiple myeloma.

The truncation of Ku86 in human lymphocytes

The Ku heterodimer, which consists of Ku70 and Ku86 subunits, is a major sensor of DNA breaks. A truncated form of Ku86 lacking its C-terminus, termed Ku86 variant, has been detected in extracts from different human cells. Here we report that in human lymphocytes the Ku86 variant is not present in vivo but is generated in vitro upon cell lysis by a trypsin-like protease. The resulting Ku86 variant exists exclusively in complexes with Ku70, which possess strong affinity to DNA double strand termini. In different blood donors the levels of Ku86 variant correlated with the magnitude of radiation induced DNA breaks.

B-cell chronic lymphocytic leukaemia: a polymorphic family unified by genomic features

Human cancer is characterised by complex molecular aberrations which result in a wide variety of clinical manifestations. B-cell chronic lymphocytic leukaemia (B-CLL) is particularly diverse, both in terms of molecular changes and clinical course, and consequently our understanding of the pathology of this disease is generally poor. Furthermore, the heterogeneity of this tumour type coupled with the absence of an obvious genetic "hallmark", such as gain of oncogene function or loss of suppressor-gene function, has led many investigators to question whether B-CLL is a single disease entity. In most cases, B-CLL does not show specific reciprocal chromosomal translocations as found in other haemopoietic malignant diseases. The genomic instability of B-CLL results in numerous different types of chromosomal losses and gains, giving rise to unsettled karyotypes among individuals with this disease. Nevertheless, genetic data imply that B-CLL is a single disease characterised by a common gene-expression profile and by the existence of specific subtypes that may have clinical correlates in patients.

Multistep tumorigenesis of multiple myeloma: its molecular delineation

Multiple myeloma (MM) is an incurable malignant neoplasm affecting terminally differentiated B-cells. It derives from post-germinal center B-cells and develops as a result of multistep tumorigenic events, because approximately one third of all MM cases have a history of preceding monoclonal gammopathy of undetermined significance (MGUS) or smoldering myeloma. MM terminates in the formation of extramedullary invasion or in secondary plasma cell leukemia. To account for this clinical experience, investigators have found that intrinsic chromosomal instability followed by complex chromosomal translocations/deletions plays a crucial role in the development from MGUS to MM. Representative aberrations include chromosomal rearrangements involving 14q32 loci and deletion at the long arm of chromosome 13. Contributing to the progression of MM itself are genomic instability and altered methylation of the specific gene promoters. The former results in activation of specific oncogenes such as RAS and FGFR3 or in inactivation of p53, and the latter results in inactivation of tumor suppressor genes, including p16. An accurate understanding of each of these molecular events should help clarify the development of specific molecular targeting therapies based on the differences in dysfunctional signaling pathways found in the cells of all MM patients.

Essential role of caveolae in interleukin-6- and insulin-like growth factor I-triggered Akt-1-mediated survival of multiple myeloma cells

Caveolae, specialized flask-shaped lipid rafts on the cell surface, are composed of cholesterol, sphingolipids, and structural proteins termed caveolins; functionally, these plasma membrane microdomains have been implicated in signal transduction and transmembrane transport. In the present study, we examined the role of caveolin-1 in multiple myeloma cells. We show for the first time that caveolin-1, which is usually absent in blood cells, is expressed in multiple myeloma cells. Analysis of myeloma cell-derived plasma membrane fractions shows that caveolin-1 is co-localized with interleukin-6 receptor signal transducing chain gp130 and with insulin-like growth factor-I receptor. Cholesterol depletion by beta-cyclodextrin results in the loss of caveola structure in myeloma cells, as shown by transmission electron microscopy, and loss of caveolin-1 function. Interleukin-6 and insulin-like growth factor-I, growth and survival factors in multiple myeloma, induce caveolin-1 phosphorylation, which is abrogated by pre-treatment with beta-cyclodextrin. Importantly, inhibition of caveolin-1 phosphorylation blocks both interleukin-6-induced protein complex formation with caveolin-1 and downstream activation of the phosphatidylinositol 3-kinase/Akt-1 pathway. beta-Cyclodextrin also blocks insulin-like growth factor-I-induced tyrosine phosphorylation of insulin-responsive substrate-1 and downstream activation of the phosphatidylinositol 3-kinase/Akt-1 pathway. Therefore, cholesterol depletion by beta-cyclodextrin abrogates both interleukin-6- and insulin-like growth factor-I-triggered multiple myeloma cell survival via negative regulation of caveolin-1. Taken together, this study identifies caveolin-1 and other structural membrane components as potential new therapeutic targets in multiple myeloma.

An inducible Ku86-degrading serine protease in human cells

The Ku autoantigen has been implicated in a number of cellular functions including growth control, immunoglobulin gene rearrangement and DNA repair. A variant truncated form of Ku86, with an apparent molecular weight of 70 kDa, has been reported to be present in many human cell types. We have previously shown that the amount of variant Ku86 is strongly increased in human peripheral blood mononuclear cells (PBMC) by storage of blood prior to isolation of the PBMC. In this study we report that formation of variant Ku86 in protein extracts is mediated by an inducible trypsin-like serine protease with a higher concentration in the nuclear compartment, as compared with the cytoplasm. However, experiments with SDS-PAGE assay of whole cells yielded no evidence of truncated Ku86, suggesting that the protease is not active in intact cells, but is exerting a marked activity during the protein extraction procedure. Interestingly, the protease level became markedly reduced upon transfer of the cells to growth medium. Protease induction did not correlate with apoptosis, necrotic cell death or with signs of general proteolysis or cytotoxicity. Our findings have methodological implications for the interpretation of experimental Ku86 data, and suggest that this protease may play a role for cellular regulation of Ku function.

Immunomodulatory drug CC-5013 overcomes drug resistance and is well tolerated in patients with relapsed multiple myeloma

Thalidomide (Thal) can overcome drug resistance in multiple myeloma (MM) but is associated with somnolence, constipation, and neuropathy. In previous in vitro studies, we have shown that the potent immunomodulatory derivative of thalidomide (IMiD) CC-5013 induces apoptosis or growth arrest even in resistant MM cell lines and patient cells, decreases binding of MM cells to bone marrow stromal cells (BMSCs), inhibits the production in the BM milieu of cytokines (interleukin-6 [IL-6], vascular endothelial growth factor [VEGF], tumor necrosis factor-alpha [TNF-alpha]) mediating growth and survival of MM cells, blocks angiogenesis, and stimulates host anti-MM natural killer (NK) cell immunity. Moreover, CC-5013 also inhibits tumor growth, decreases angiogenesis, and prolongs host survival in a human plasmacytoma mouse model. In the present study, we carried out a phase 1 CC-5013 dose-escalation (5 mg/d, 10 mg/d, 25 mg/d, and 50 mg/d) study in 27 patients (median age 57 years; range, 40-71 years) with relapsed and refractory relapsed MM. They received a median of 3 prior regimens (range, 2-6 regimens), including autologous stem cell transplantation and Thal in 15 and 16 patients, respectively. In 24 evaluable patients, no dose-limiting toxicity (DLT) was observed in patients treated at any dose level within the first 28 days; however, grade 3 myelosuppression developed after day 28 in all 13 patients treated with 50 mg/d CC-5013. In 12 patients, dose reduction to 25 mg/d was well tolerated and therefore considered the maximal tolerated dose (MTD). Importantly, no significant somnolence, constipation, or neuropathy has been seen in any cohort. Best responses of at least 25% reduction in paraprotein occurred in 17 (71%) of 24 patients (90% confidence interval [CI], 52%-85%), including 11 (46%) patients who had received prior Thal. Stable disease (less than 25% reduction in paraprotein) was observed in an additional 2 (8%) patients. Therefore, 17 (71%) of 24 patients (90% CI, 52%-85%) demonstrated benefit from treatment. Our study therefore provides the basis for the evaluation of CC-5013, either alone or in combination, to treat patients with MM at earlier stages of disease.

Novel biologically based therapeutic strategies in myeloma

Multiple myeloma remains incurable despite advances in conventional chemotherapy and wider applicability of high dose chemotherapy with single and/or tandem autologous peripheral blood stem cell transplantation. Although a complete remission rate of 41% and an event-free survival of 43 months have been reported after tandem transplantation, it is highly unlikely that further improvements in the outcome of multiple myeloma will be achieved by escalating cytotoxic chemotherapy alone. Novel biologically based therapies are therefore urgently required. Targeted therapeutic approaches based on: identification of genetic abnormalities in malignant plasma cells; interrupting growth of myeloma cells; triggering apoptotic signaling cascades in tumor cells; modulating growth and survival of multiple myeloma cells in the bone marrow microenvironment, i.e. angiogenesis and cytokine networks; enhancing allogeneic and autologous antimyeloma immunity; and characterizing newer myeloma antigens for serotherapy are under development. These therapies offer great promise, used alone/or in combination with conventional treatment approaches, to improve the outcome in this disease in newly diagnosed/refractory or relapsed patients with multiple myeloma.

Evidence for replicative repair of DNA double-strand breaks leading to oncogenic translocation and gene amplification

Nonreciprocal translocations and gene amplifications are commonly found in human tumors. Although little is known about the mechanisms leading to such aberrations, tissue culture models predict that they can arise from DNA breakage, followed by cycles of chromatid fusion, asymmetric mitotic breakage, and replication. Mice deficient in both a nonhomologous end joining (NHEJ) DNA repair protein and the p53 tumor suppressor develop lymphomas at an early age harboring amplification of an IgH/c-myc fusion. Here we report that these chromosomal rearrangements are initiated by a recombination activating gene (RAG)-induced DNA cleavage. Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway. Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture. Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

Multiple myeloma

Multiple myeloma (MM) is a malignancy of the plasma cell characterized by migration and localization to the bone marrow where cells then disseminate and facilitate the formation of bone lesions. Unfortunately, while treatment of this disease is effective in palliating the disease, and even prolonging survival, this disease is generally regarded as incurable. Understanding the basic biology of myeloma cells will ultimately lead to more effective treatments by developing target based therapy. In Section I, Dr. Bergsagel discusses the molecular pathogenesis of MM and shares insights regarding specific chromosomal translocations and their role in the genesis and progression of MM. New information regarding FGFR3 as an oncogene as well as how activating mutations may contribute to disease evolution and may be an important target for novel therapeutics of MM is presented. In Section II, Dr. Anderson elaborates on novel therapeutic approaches to MM also targeting fundamental genetic abnormalities in MM cells. Both preclinical and clinical studies of novel agents including PS-341 and IMiDs are highlighted. In Section III, Dr. Harousseau discusses the role of autologous stem cell transplant in MM. He highlights clinical trials addressing the question of conditioning regimens and the impact of tandem transplants. He also addresses the role of allogeneic BMT and the use of attenuated dose conditioning regimens (so called mini-allogeneic transplants) in the treatment of MM. In Section IV, Dr. Dalton provides an overview of the current state of myeloma therapy and summarizes the different and exciting approaches being undertaken to cure this disease.

Isotype class switching and the pathogenesis of multiple myeloma

Translocations at the immunoglobulin heavy chain locus (14q32) are now considered the commonest karyotypic change in multiple myeloma. These translocations are thought to be intimately involved in the pathogenesis of this disease. The heavy chain locus is strongly transcriptionally active in B and plasma cells and transfer of a potential oncogene to 14q32 would result in its dysregulation. Molecular characterization suggests that the majority of these breakpoints cluster in switch regions within the heavy chain locus. Switch regions are normally involved in the regulated process of isotype switching so that in myeloma the rearrangements are believed to be a result of so-called illegitimate (aberrant) switch recombination and are likely to be an early event in myeloma development. A legitimate switch recombination event occurs between two switch regions producing a hybrid switch; this is necessary for class switching to proceed on a productive allele. In this review we describe the process of isotype switching and how illegitimate class switching may be related to the pathogenesis of multiple myeloma.

Nuclear proteins that bind to metal response element a (MREa) in the Wilson disease gene promoter are Ku autoantigens and the Ku-80 subunit is necessary for basal transcription of the WD gene

Wilson disease (WD), an inherited disorder affecting copper metabolism, is characterized by hepatic cirrhosis and neuronal degeneration, which result from toxic levels of copper that accumulate in the liver and brain, respectively. We reported previously that the approximately 1.3-kb promoter of the WD gene contains four metal response elements (MREs). Among the four MREs, MREa plays the most important role in the transcriptional activation of the WD promoter. Electrophoretic mobility shift assays (EMSAs) using synthetic MREa and an oligonucleotide containing the binding site for transcription factor Sp1 revealed the presence of nuclear factors that bind specifically to MREa. Two MREa-binding proteins of 70 and 82 kDa were purified using avidin-biotin affinity chromatography. Amino acid sequences of peptides from each protein were found to be highly homologous to the Ku proteins. Immunoblot analysis and EMSAs showed that the MREa-binding proteins are immunologically related to the Ku proteins. To study further the functional significance of these Ku-related proteins in transcriptional regulation of the WD gene, we performed RNA interference (RNAi) assays using a Ku-80 inverted-repeat gene to inhibit expression of the Ku-80 gene in vivo. Results of the RNAi assays showed that expression of the Ku-80 protein was suppressed in transfected cells, which in turn led to the suppression of the WD gene. In addition, a truncated Ku-80 (DeltaKu-80) mutant inhibited WD promoter activity in HepG2 cells in a dominant-negative manner. We also found that WD promoter activity was decreased in Xrs5 cells, which, unlike the CHO-K1 cells, are defective in the Ku-80 protein. When Ku-80 cDNA was transfected into Xrs5 and CHO cells, WD promoter activity was recovered only in Xrs5 cells. Taken together, our findings suggest that the Ku-80 subunit is required for constitutive expression of the WD gene.

Lack of Ku80 alteration in multiple myeloma

Chromosomal rearrangement involving the immunoglobulin gene locus, as a result of marked chromosomal instability, is the hallmark of human multiple myeloma (MM) cells. Since Ku80 plays a key role in the non-homologous end-joining (NHEJ) system, we investigated whether Ku80 alteration contributes to this genetic instability by examining its status in 16 MM cell lines. Our study demonstrated a lack of Ku80 alterations at the protein, mRNA and gene level in 15 out of the 16 cell lines. Only the U266 cell line carried a missense mutation of Ser335Leu in one allele of the cDNA. Six marrow samples derived from myeloma patients also did not show any aberrant Ku80 protein, in terms of size. Accordingly, Ku80 alteration is unlikely to be involved in MM, in disagreement with a previous study reporting frequent presence of a 69-kD Ku80 variant (Ku86v) with reduced DNA binding activity in MM cells.

Transient association of Ku with nuclear substrates characterized using fluorescence photobleaching

The autoantigen Ku, composed of subunits Ku70 and Ku86, is necessary for repair of DNA double-strand breaks by nonhomologous end joining. Similarly, Ku participates in repair of DNA double-strand breaks that occur during V(D)J recombination, and it is therefore required for the development of B and T lymphocytes. Although previous studies have identified the DNA-binding activities of Ku, little is known concerning its dynamics, such as the mobility of Ku in the nucleus and its rate of association with substrates. To address this question, fluorescence photobleaching experiments were performed using HeLa cells and B cells expressing a green fluorescent protein (GFP) fusion construct of either Ku70 or Ku86. The results show that Ku moves rapidly throughout the nucleus even following irradiation of the cells. However, the rate of diffusion of Ku was approximately 100-fold slower than that predicted from its size. Association of Ku-GFP with a filamentous nuclear structure was also evident, and nuclear extraction experiments suggest that this represents nuclear matrix. A central domain of Ku70 containing its DNA-binding and heterodimerization regions and its nuclear localization signal shows that this alone is sufficient for the observed mobility of Ku70-GFP and its association with nuclear matrix. These data suggest the mobility of Ku is characterized by a transient, high flux association with nuclear substrates that includes both DNA and the nuclear matrix and may represent a mechanism for repair of double-strand breaks using the nuclear matrix as a scaffold.

Translocation of Ku86/Ku70 to the multiple myeloma cell membrane: functional implications

OBJECTIVE

Since the central hallmarks of human multiple myeloma (MM) are abnormalities in immunoglobulin (Ig) gene rearrangement, IgH class switching, and DNA damage repair, and since Ku86 and Ku70 proteins are central to these processes, aberrant Ku function may play a role in MM pathogenesis. Our prior studies demonstrated a 69-kDa Ku86 variant in freshly isolated patient MM cells that confers sensitivity to DNA damage. We also showed that Ku86 on the cell surface of CD40-activated MM cells mediates homotypic tumor cell adhesion, as well as heterotypic adhesion to bone marrow stromal cells. We here define the mechanism and functional significance of CD40-induced Ku translocation from the cytoplasm to the cell membrane in MM cells vs normal B cells.

MATERIALS AND METHODS

We examined Ku86 and Ku70 translocation following CD40 activation in human MM cells vs normal tonsillar B lymphocytes. We then identified the functional sequelae of membrane Ku86 and Ku70 expression on CD40-activated human MM cells.

RESULTS

CD40 activation induces translocation of both Ku86 and Ku70 to the cell surface of MM cells, but not normal tonsillar B cells. Moreover, CD40 activation triggers Ku association with CD40 only in CD40-activated MM cells. Finally, CD40-activated MM cells adhere to fibronectin and are protected against apoptosis triggered by irradiation or doxorubicin; conversely, antibodies to Ku both inhibit tumor cell binding and restore sensitivity to these agents.

CONCLUSION

These results demonstrate functional significance of Ku translocation to the cell membrane of CD40-activated human MM cells. Therefore, targeting Ku86 and Ku70, with blocking peptides for example, might serve as a novel treatment strategy in human MM.

CD40 activation induces p53-dependent vascular endothelial growth factor secretion in human multiple myeloma cells

It was previously demonstrated that p53 status in human multiple myeloma (MM) cells regulates distinct cell cycle responses to CD40 activation. In this study, the production of vascular endothelial growth factor (VEGF) and migration in MM cells triggered by CD40 activation was examined, and the influence of p53 status in regulating this process was determined. Two human MM cell lines that express wild-type p53 at permissive (28 degrees C) and mutant p53 at restrictive (37 degrees C) temperatures were used as a model system. CD40 activation induces a 4-fold (RPMI 8226) and a 6-fold (SV) increase in VEGF transcripts, respectively, under restrictive, but not permissive, temperatures. VEGF expression is significantly induced after CD40 activation in patient MM cells expressing mutant p53. Increased VEGF transcripts result in increased protein and secretion levels, as evidenced by immunoblotting and enzyme-linked immunosorbent assay. In a double-chamber transmigration assay, CD40 activation of MM cells induced a 3-fold (RPMI 8226) and a 5-fold (SV) increase in migration under restrictive, but not permissive, conditions. A 2- to 8-fold induction in migration of patient MM cells expressing mutant p53 was similarly observed. Transduction of MM cells with a luciferase reporter under the control of a human VEGF promoter further indicated that CD40-induced VEGF expression was mediated through a transcriptional control mechanism. Finally, adenovirus-mediated wild-type p53 overexpression down-regulated CD40-induced VEGF expression and transmigration in MM cells expressing mutant p53. These studies demonstrate that CD40 induces VEGF secretion and MM cell migration, suggesting a role for CD40 in regulating MM homing and angiogenesis.

Impaired nonhomologous end-joining provokes soft tissue sarcomas harboring chromosomal translocations, amplifications, and deletions

Although nonhomologous end-joining (NHEJ) deficiency has been shown to accelerate lymphoma formation in mice, its role in suppressing tumors in cells that do not undergo V(D)J recombination is unclear. Utilizing a tumor-prone mouse strain (ink4a/arf(-/-)), we examined the impact of haploinsufficiency of a NHEJ component, DNA ligase IV (Lig4), on murine tumorigenesis. We demonstrate that lig4 heterozygosity promotes the development of soft-tissue sarcomas that possess clonal amplifications, deletions, and translocations. That these genomic alterations are relevant in tumorigenesis is supported by the finding of frequent mdm2 amplification, a known oncogene in human sarcoma. Together, these findings support the view that loss of a single lig4 allele results in NHEJ activity being sufficiently reduced to engender chromosomal aberrations that drive non-lymphoid tumorigenesis.

Inhibition of Ku heterodimer DNA end binding activity during granulocytic differentiation of human promyelocytic cell lines

The heterodimeric Ku protein (composed of the Ku 86 and Ku 70 sub-units) is a nuclear protein which binds to DNA termini without sequence specificity. Ku is the DNA-targeting component of the large catalytic sub-unit of the DNA-dependent protein kinase complex that is required for the repair of DNA double-strand breaks in mammalian cells. We studied the expression and function of Ku/DNA-PK during granulocytic differentiation of two human promyelocytic cell lines, HL60 and NB4, a process associated to decreased radiation resistance. After 3 days exposure to differentiating agents (either all-trans-retinoic acid or DMSO), Ku binding to double stranded (ds)-DNA ends declined dramatically whereas Ku protein levels remain unchanged. The nuclear, but not cytoplasmic, fraction of differentiated HL60 cells extracts exhibited a heat-sensitive inhibitory activity towards DNA binding of recombinant Ku heterodimer. We further demonstrate that immunoprecipitation of Ku is impaired in extracts from differentiated cells by using two antibodies that recognize epitopes within the C-terminus DNA binding domains of Ku 70 and Ku 86 proteins. These results favor the hypothesis of a protein interacting with Ku that would prevent DNA binding of heterodimerized Ku protein by steric hindrance.

Targeted therapy for multiple myeloma

Multiple myeloma (MM) remains incurable with conventional treatment approaches, and novel biologically based therapies are therefore urgently needed. Targeted therapies are either under development or already undergoing clinical evaluation predicated upon: identifying genetic abnormalities in myeloma cells to enhance chemoradiosensitivity; interrupting growth or triggering apoptotic signaling cascades in tumor cells; treating both the tumor cell and its microenvironment; enhancing allogeneic and autologous antimyeloma immunity; and characterizing new myeloma antigens for serotherapy. These therapies, alone or in combination with conventional treatments, offer great promise to improve the outcome for patients with MM.