ALBERT

Description: Abstract 2945 Background: Despite recent advances of therapeutic strategies, multiple myeloma (MM) still remains mostly incurable due to its drug resistance by both various cell intrinsic molecular abnormalities and the supports of myeloma microenvironment factors. The search for new therapeutic target molecule upon which various MM-promoting signalings converge is essential for the development of more effective therapy for MM. RSK2 is a member of the 90 kDa ribosomal S6 kinases (RSKs) family of serine (Ser) /threonine (Thr) kinases and lies downstream of RAS/ERK-1/2 signaling cascade. In MM, it has been shown that RSK2 mediates signaling initiated by FGFR3 activation for cell survival, but the functional role and the value as the therapeutic target of RSK2 have not been clearly defined. In this study, we precisely studied the association with RSK2 activation and chromosomal status, especially focusing on RSK2Ser227, which is responsible for downstream signaling phosphorylation, and the value of RSK2 as the therapeutic target in MM. Methods: Twelve human myeloma-derived cell lines and primary MM cells were utilized in this study. The use of human samples was approved by the ethical review board of our institute. Cell killing assay was performed using flow cytometry. Growth inhibitory assay was performed with modified MTT assay. Protein levels were examined by Western blotting. BI-D1870, a RSK2 inhibitor, was purchased from Symansis Limited (Auckland, New Zealand). RNA interference for RSK2 was performed by transfection of small interfering RNA (siRNA) into NCI-H929 cells by means of CLB-Transfection Kit (Lonza, Swiss) with protocol 9. Drug combination assays were evaluated with CalcuSyn software (Biosoft, Cambridge, UK). Results: RSK2Ser227 was shown to be phosphorylated in all 12 MM cell lines and 6 of 9 primary MM cells. t(4;14) involving IgH/FGFR3 was detected only in 7 cell lines and high FGFR3 expression was identified only in 6 cell lines. RSK2Ser227 was phosphorylated even in the absence of ERK1/2 or RSK2Tyr529 phosphorylation in several MM cell lines, indicating that their activation was not mandatory to RSK2Ser227 phosphorylation. Our study also did not show any positive relationship between RSK2Ser227 phosphorylation and other so-called “high-risk” cytogenetic abnormalities, such as 13q-, t(11;14), t(8;14), t(14;16), 1q21+, or 17p-. Treatment with BI-D1870 (RSK2 inhibitor) resulted in complete dephosphorylation of RSK2Ser227, but not RSK2Tyr529. The phosphorylation status of ERK1/2, or related signaling kinases, such as AKT, p38 MAPK, or JNK was also not affected. BI-D1870 showed dose-dependent growth inhibition effect in 6 MM-derived cell lines by inducing apoptosis. At molecular level, Mcl-1, p21WAF1/CIP1, cyclin D2 and c-Myc was significantly down-regulated and Bim was up-regulated by BI-D1870 intervention in NCI-H929 cell. BI-D1870 didn't modulate expression level of IRF-4. These change were also observed in other MM cell lines (KMS-34, AMO-1). To exclude the possibility that above BI-D1870 induced changes in protein expression and cell death are due to its off-target effects, we performed gene knockdown experiments of RSK2. Transient gene knockdown of RSK2 by means of RNAi caused downregulation of cyclin D2, p21WAF1/CIP1, c-Myc, while it induced cell death in NCI-H929 cells. In contrast, Bim expression was not altered by RSK2 knockdown. Lenalidomide (LEN) is the most powerful currently available IMiD for MM treatment. While cell death induction by LEN (100μM) was partly prevented by IL-6 (50ng/ml) in NCI-H929 cells, co-administration of BI-D1870 (0.2 μM, at the degree of low concentration not to affect cell viability when used solely) overcame the resistance to LEN induced by IL-6. KMS-11/BTZ were highly resistant to bortezomib (BTZ)-induced cell death, by contrast, it showed the similar sensitivities to BI-D1870-induced cell death when compared with their parental cells. And more, BI-D1870 showed synergistic or additive effects with upcoming new anti-MM agents, such as RAD001, MS-275 and ABT-263 in MM cell lines. Conclusions: RSK2, especially RSK2Ser227, may be a universal therapeutic target for MMs with diverse molecular signatures. Disclosures: Iida: Janssen Pharmaceutical K.K.: Honoraria.

Description: Abstract 3772 Poster Board III-708 [Purpose] Bortezomib (BTZ), a proteasome inhibitor, has been introduced into the treatment of multiple myeloma (MM). It shows remarkable response against both relapsed/refractory and newly diagnosed MM. However, it is often encountered that BTZ treatment achieves very short duration of response and permits early drug resistance. Therefore, understanding the mechanisms underlying this drug resistance is necessary to develop novel treatments to overcome this problem. [Materials & Methods] We established two stable BTZ-resistant MM cell lines, KMS-11/BTZ and OPM-2/BTZ, whose IC50 values were respectively 24.7- and 16.6-fold higher than their parental cell lines, under continuous exposure to BTZ. Using these resistant cells, we investigated on their proteasome activity, the alteration of proteasome β5 subunit (PSMB5) gene, misfolded protein accumulation, endoplasmic reticulum (ER) stress, and apoptosis signals including BH3 only proteins in comparison with their parental cells at clinically achievable concentration of BTZ treatment. [Results & Discussion] No activation of caspase -3,-8, and -9 and BH3 only protein, Noxa, which were initially up-regulated in BTZ-treated cells, were noted in BTZ-resistant cells even in the presence of BTZ. These results indicate avoidance of fatal intracellular stress may block transcriptional activation of Noxa in resistant cells at an early phase after BTZ exposure. In gel shift assay detecting NF-kB-DNA complexes, BTZ-resistant cells maintained constitutive NF-kB activation, whereas their parental cells lost its activity in the presence of BTZ. In addition, cellular proteasome activities including chymotrypsin-like and caspase-like activity were markedly inhibited by BTZ treatment in parental cells, and moderately also in BTZ-resistant cells, when detected by fluorogenic substrates specific for each proteasome activity. While time-dependent accumulation of ubiquitinated proteins was prevented only in BTZ-resistant cells, but not in their parental cells after BTZ exposure. Resistance was partly explained by the presence of a unique point mutation, G322A, in the gene encoding PSMB5 in both BTZ-resistant cell lines, which substituted Thr for Ala at the codon 49 in amino acid level. This constitution has been reported to gives rise to the conformational change of BTZ-binding pocket in β5 subunit, which results in partial disruption of the contact between BTZ and chymotrypsin-like active site. Furthermore, BTZ-resistant and parental MM cells had nearly equal expression of cytoplasmic and ER chaperons, however, only BTZ-resistant cells could prevent misfolded protein accumulation and therefore avoid fatal ER stress represented as activation of CHOP and of caspase-4, -12 after BTZ treatment. [Conclusion] Two kinds of stable BTZ-resistant MM cell lines were established, which acquired the unique point mutation (G322A) in BTZ-binding pocket of PSMB5, prevented the accumulation of misfolded proteins probably via reduced affinity of 26S proteasome to BTZ and avoided the development of catastrophic ER stress unlike their parental cells. These cell lines will provide better understanding of the underlying mechanisms of the BTZ-resistance, and will lead to the development of novel treatment strategies for overcoming BTZ-resistance in the patients with MM. Disclosures: Iida: JANSSEN PHARMACEUTICAL: Honoraria; KYOWA KIRIN: Research Funding. Nakashima:KYOWA KIRIN: Employment. Miyazaki:KYOWA KIRIN: Employment. Shiotsu:KYOWA KIRIN: Employment.

Description: Background : HSP90 plays an important role in chaperoning key proteins implicated in malignant disease and is a promising therapeutic target. We now report the in vitro and in vivo activity of a novel HSP90 inhibitor of non-ansamycin, non-purine analogue class, KW-2478, (Kyowa Hakko Kirin) in B-cell malignancies including multiple myeloma (MM), B-cell lymphoma (BCL) and mantle cell lymphoma (MCL) cells, and in primary tumour cells from MM and BCL patients. Procedures: The binding affinity of KW-2478 to HSP90 was examined using immobilised human HSP90a and a biotinylated HSP90 binding agent, radicicol (bRD). The effect of KW-2478 on cell viability, cell growth and apoptosis induction were evaluated in cell lines, with KW-2478 induced changes in major HSP90 client proteins studied by Western blotting analysis. The in vivo anti-tumour activity of KW-2478 was evaluated in a human MM xenograft mouse model,. Primary MM cells were studied using a co-culture system with the HS-5 bone marrow stromal cell line (BMSCs), while primary BCL samples were cultured on CHO cells stably transfected to produce CD40L. Results: KW-2478 inhibited the binding of bRD to HSP90α in concentration-dependent manner with an IC50 value of 3.8 nM. KW-2478 clearly inhibited cancer cell growth in all cell lines, with EC50 values from 101–252 nM in BCL, 81.4–91.4 nM in MCL and 120–622 nM in MM. The drug also exhibited potent growth inhibitory activity in primary CLL (n=3) and NHL (n=2) cells with EC50 values of 40–170 nM and 200–400 nM, respectively. In 2 of 4 human primary myeloma cells, KW-2478 at 2 μM inhibited cell growth by at least 50%. The presence of BMSCs did not affect drug activity against primary MM cells and importantly there was little or no effect on cell number or viability of normal BMSCs at up to 20 μM KW-2478. Exposure of MM and BCL cell lines to KW-2478 for 24 hours resulted in the degradation of HSP90 client proteins (IGF-1Rβ and Raf-1) and the induction of HSP70. KW-2478 also induced PARP cleavage and dephosphorylated Erk1/2 in NCI-H929 cells. Further studies in selected cell lines showed that exposure to 1 μM KW-2478 or lower resulted in the depletion of p53 and Akt proteins, a reduction in nuclear NFKB, and the cleavage of caspase-3. In the NCI-H929 xenograft model, KW-2478 (qd×5, i.v.) showed a statistically significant suppression of tumour growth at the doses of 25, 50, 100 and 200 mg/kg. Moreover, tumour regressions were observed at doses of 100 and 200 mg/kg, with a significant decrease in serum M protein concentration at doses of 50, 100 and 200 mg/kg. No severe KW-2478 toxicity was observed as assessed by treatment-related mortality and body weight change. Conclusions: The novel HSP90 inhibitor KW-2478 showed a potent anti-tumour activity both in vitro and in vivo, including activity in primary patient samples. The agent retained its activity in primary myeloma cells in the presence of BMSCs, suggesting that KW-2478 can overcome the protective effect of the bone marrow microenvironment. Additional pharmacokinetic and safety data support the further development of KW-2478 and the drug is currently undergoing clinical evaluation in a phase I trial.

Description: Constitutive activation of FLT3 kinase is associated with poor prognosis in AML and is present in 30–40% of AML patients. KW-2449 is a multi-kinase inhibitor against FLT3, FGFR1, Abl and Abl-T315, tyrosine kinases with IC50 values of 0.007, 0.036, 0.014 and 0.004 μmol/L, respectively. While it has inhibitory activity against c-Src, JAK2 and c-Kit tyrosine kinases with IC50 values between 0.15–0.40 μmol/L, it has little effect on kinase activity of PDGFR, Fms, IGF1R, and EGFR at a concentration of 1.0 μmol/L. KW-2449 uniquely inhibits Aurora A serine threonine kinase with IC50 of 0.048 μmol/L. Since KW-2449 possesses potent FLT3 as well as Aurora inhibition activity, we studied its possible mode of actions for anti-leukemic effects in both in FLT3 constitutively activated and FLT3 wild type leukemia cell lines. In FLT3-ITD (+) MOLM-13 cells, the exposure of KW-2449 induced a concentration-dependent reduction of phosphorylated FLT3 (P-FLT3) and STAT5 (P-STAT5), a key downstream signal molecules of FLT3. In MOLM-13 cells, KW-2449 also induced G1 arrest and apoptosis over the GI50 value (0.01 - 0.02 μmol/L). In addition, KW-2449 showed potent growth inhibitory activity against 32D cells transfected with FLT3-ITD, FLT3-D835Y or WTFLT3 plus FL, with GI50 values below 0.05 μmol/L. It also inhibited the growth of FLT3 wild type human leukemia RS4;11 cells giving the GI50 value of 0.23 μmol/L. Exposure of RS4;11 cells to KW-2449 also induced the reduction of phosphorylated Histone H3 which is a key downstream signal for Aurora kinase, as well as G2/M arrest and apoptosis over the GI50 value. These data provide additional evidence that Aurora inhibition may play a critical role in the anti-proliferative effects of KW-2449 in FLT3 wild type leukemia. To assess the anti-leukemia activity of KW-2449 in vivo, the SCID mice subcutaneously inoculated with MOLM-13 leukemia were treated with oral KW-2449 bid for 14 days. Dose- dependent tumor growth inhibitory activity was observed at doses ranging from 2.5 to 20 mg/kg. Treatment with 20 mg/kg bid induced complete remission of inoculated tumour in all mice in the cohort without causing significant body weight loss. A PK/PD study using this model revealed significant decreases of P-FLT3 and P-STAT5 in tumors 4 to 8 hours after KW-2449 treatment at 20 mg/kg. In addition, oral administration of 20 mg/kg of KW-2449 showed the survival-prolongation effect in two xenograft models in which the mice were intravenously inoculated with MOLM-13 or 32D/FLT3-D835Y. Furthermore, anti-proliferative activity of KW-2449 was examined in primary samples from AML patients with FLT3 mutation or wildtype. The concentration-dependent growth inhibitory effects that were correlated with P-FLT3 and P-STAT5 reduction were observed in the primary leukemia cells with FLT3 activating mutation. Since KW-2449 shows a potent and unique kinase inhibition profile, it is expected that it could be effective not only in the treatment of AML with FLT3 mutations, but also in FLT3 wild-type AML, imatinib-resistant chronic myeloid leukemia (CML), ALL, and other hematological malignancies. KW-2449 is being investigated in a Phase I, open label, single agent, dose-escalation, multi-center study in patients with relapsed and refractory AML, MDS, CML and ALL.

Description: KW-2449, a multikinase inhibitor of FLT3, ABL, ABL-T315I, and Aurora kinase, is under investigation to treat leukemia patients. In this study, we examined its possible modes of action for antileukemic effects on FLT3-activated, FLT3 wild-type, or imatinib-resistant leukemia cells. KW-2449 showed the potent growth inhibitory effects on leukemia cells with FLT3 mutations by inhibition of the FLT3 kinase, resulting in the down-regulation of phosphorylated-FLT3/STAT5, G1 arrest, and apoptosis. Oral administration of KW-2449 showed dose-dependent and significant tumor growth inhibition in FLT3-mutated xenograft model with minimum bone marrow suppression. In FLT3 wild-type human leukemia, it induced the reduction of phosphorylated histone H3, G2/M arrest, and apoptosis. In imatinib-resistant leukemia, KW-2449 contributed to release of the resistance by the simultaneous down-regulation of BCR/ABL and Aurora kinases. Furthermore, the antiproliferative activity of KW-2449 was confirmed in primary samples from AML and imatinib-resistant patients. The inhibitory activity of KW-2449 is not affected by the presence of human plasma protein, such as α1-acid glycoprotein. These results indicate KW-2449 has potent growth inhibitory activity against various types of leukemia by several mechanisms of action. Our studies indicate KW-2449 has significant activity and warrants clinical study in leukemia patients with FLT3 mutations as well as imatinib-resistant mutations.

Description: Abstract 1839 The implementation of hematopoietic stem cell transplantation and new agents such as bortezomib, thalidomide, and lenalidomide (Len) has dramatically improved survival in patients with multiple myeloma (MM). However, most MM patients eventually relapse after achieving of complete response. The existence of cancer stem cells is suggested to cause the relapse and considered as an important therapeutic target. We have demonstrated that HM1.24 (CD317) is selectively over-expressed on neoplastic plasma cells and that a defucosylated humanized monoclonal antibody (mAb) specific to HM1.24 (YB-AHM) is able to induce potent antibody-dependent cellular cytotoxicity (ADCC) against human MM cells in the presence of human effector cells. On the other hand, Len, an immunomodulatory drug, has been shown to activate NK cells to enhance their ADCC activity. Recently, we have reported that “side population (SP)” cells expelling a Hoechst 33342 dye represent a fraction with cancer stem cell-like property in MM cells. Moreover, we have found that MM cancer stem-like cells over-express pluripotency-associated transcription factors such as Sox2 and Nanog, and that these factors are useful for evaluating the potential of MM cancer stem-like cells. Here, we evaluated the efficacy of the combinatory therapy of YB-AHM and Len on MM cancer stem-like cells. We first examined the expression levels of the target molecule, HM1.24 on SP fraction of MM cells. Although SP cells expressed higher levels of ABC transporter ABCG2 compared with main population (MP) cells, HM1.24 was highly expressed in both SP and MP fractions in MM cells. We next examined the inhibitory effect of YB-AHM and Len on clonogenic activity of MM cell lines. RPMI 8226, U266, and OPM-2 cells were pre-incubated with YB-AHM (0.1 μg/ml) and Len (3 μM)-stimulated peripheral blood mononuclear cells (PBMCs) at an effector/target (E/T) ratio of 10 for 4 hours, and then were cultured into H4034 methylcellulose medium. Colony formation of MM cells was examined after 14 days. Treatment with YB-AHM and Len-stimulated PBMCs significantly suppressed the colony formation of MM cell lines compared with the no-treatment group (4±5 vs 62±2 colonies/well in RPMI 8226, p

Description: Abstract 1342 In mature lymphoid malignancies including T-cell lymphoma and multiple myeloma (MM), aberrant acetylation status has been strongly linked to their tumorigenesis. Thus, the modulation of acetylation through targeting histone deacetylases (HDACs) is considered to be a viable therapeutic strategy. Vorinostat (SAHA) is the first HDAC inhibitor approved by the FDA for the patients with cutaneous T-cell lymphoma (CTCL). Anti-tumor activity of SAHA against CTCL, adult T-cell leukemia/lymphoma (ATLL), and MM cell lines was examined. Most of these cells were found to be sensitive to this drug at IC50 of less than 1–2uM. For further clarification of its mechanism of action, we established five SAHA-resistant cell lines consisting of 3 CTCL and 2 MM using dose stepwise increase method over six months. IC50 of the SAHA-resistant cells was 4-to 14-fold higher than that of their parental cells. These cell lines also showed cross-resistance of 2.8- to 17.5-fold against another pan-HDAC inhibitor, panobinostat (LBH589). Regarding HDAC activity, it was greatly inhibited by SAHA in parental cells, whereas it was only partly inhibited in SAHA-resistant cells. That is, SAHA-resistant cells have lost apart of the HDAC inhibiting function caused by SAHA. Moreover, SAHA-resistant cells showed higher anti-apoptosis ability when exposed with SAHA than their parental cells with acetylation status of histone H3 being remained low. Next, we performed microarray analysis to compare expression levels of various HDACs and other related genes between parental and SAHA-resistant cells. Results indicated that the expression level of HDAC3 being obviously low in resistant cells among various HDACs, which was also confirmed by real-time PCR. In line with mRNA analysis, protein level of HDAC3 was also decreased in SAHA-resistant cells compared with their parental cells, while other HDAC expression remained unchanged. We assumed that HDAC3 could be a main target of SAHA. To examine this possibility, we established both HDAC3 knocked-down and over-expressing cell lines, and examined the sensitivity of these cells to SAHA. HDAC3 knocked-down cells showed obviously SAHA-resistant feature in MTS assay, however, HDAC3 over-expressing cells showed higher sensitivity to SAHA. Knocking out other HDACs (1, 2 and 8) in parental cell lines did not change the sensitivity to SAHA. Thus, our results suggest that SAHA induced apoptosis depends on the inhibition of HDAC3. To search for other possible mechanisms, we screened for the mutations in HDAC2, 3, 4 and 8, but did not find them. Finally, we supposed that HDAC3 expression was epigenetically silenced by promoter methylation in SAHA resistant cells, and attempted to restore HDAC3 expression in the presence of 5-azacytidine, a DNA demethylase. We incubated SAHA-resistant cells with non-toxic levels of 5-azacytidine (4uM) for 9 days, and confirmed that HDAC3 expression was restored during 6–9 days after exposure. When HDAC3 expression being restored, the resistant cells showed higher sensitivity to SAHA. It suggests that hyper-methylation of promoter sequences of HDAC3 contributed to the mechanism of SAHA-resistance. From these results, we conclude that anti-tumor effect of HDAC inhibitors depends on the expression level of HDCA3 in mature lymphoid malignancies, and HDAC3 might provide a useful biomarker for identifying favorable response to HDAC inhibitors, and the overcoming the resistance of HDAC inhibitors. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 5034 Introduction: The IRE1α-XBP1 pathway, a key component of the endoplasmic reticulum (ER) stress response, is considered to be a critical regulator for survival of multiple myeloma (MM) cells. Because of the production of abundant immunoglobulins and cytokines, MM cells need to survive under chronic ER stress. In addition, MM cells are located in the bone marrow milieu, which is usually considered hypoxic compared to other organs. Therefore, MM cells need to possess mechanisms to protect against ER stress. Among the unfolded protein responses in MM cells, the IRE1α-XBP1 pathway has been implicated in the proliferation and survival of MM cells to a greater extent than in those of monoclonal gammopathy of undetermined significance or normal plasma cells. It has been reported to be a prognostic factor and could be a target for immunotherapy or chemotherapy. Based on previous reports, it is proposed that an inhibitor of IRE1α-XBP1 activation should be a potent therapeutic agent for MM. Therefore, the availability of small molecule inhibitors targeting this pathway would offer a new therapeutic strategy for MM. Here, we screened small molecule inhibitors of ER stress-induced XBP1 activation, and identified toyocamycin from a culture broth of an Actinomycete strain. Materials & Methods: First, we evaluated the mechanism of toyocamycin-induced inhibition of IREα activity, with focused on its kinase activity, endonuclease activity, and other unfolded protein responses. Next, the activity of toyocamycin was evaluated on MM cell lines and other tumor cells about IRE1α activity and cytotoxicity. Similarly, 9 primary MM cells were tested. Finally, the in vivo efficacy of toyocamycin was evaluated in a human MM xenograft model. Results & Discussion: Toyocamycin was shown to suppress thapsigargin-, tunicamycin- and 2-deoxyglucose-induced XBP1 mRNA splicing in HeLa cells without affecting ATF6 and PERK activation. Furthermore, although toyocamycin was unable to inhibit IRE1 a phosphorylation, it prevented IRE1α-induced XBP1 mRNA cleavage in vitro. Thus, toyocamycin is an inhibitor of IRE1α-induced XBP1 mRNA cleavage. Next, we examined the effect of toyocamycin on MM cells. Most MM cell lines have activated XBP1 protein expression, represented as the overexpression of spliced XBP1 isoform, whereas non-MM cells including other hematological and solid tumor cells have little activation of XBP1. Toyocamycin inhibited constitutive activation of XBP1 in MM cell lines without affecting IRE1α phosphorylation. This inhibition occurred within 6 hours after exposure to 30 nM toyocamycin. We then evaluated the growth inhibitory effect of toyocamycin on 7 MM cell lines with high spliced-XBP1 expression, 3 MM cell lines with low spliced-XBP1 expression, and 4 non-MM cell lines as assessed by MTS assay. All MM cells with high spliced-XBP1 expression showed remarkable decline in cellular viability at 30 nM or higher concentrations of toyocamycin than other MM cells with low spliced-XBP1 expression, and non-MM cell lines showed little reduction in cellular viability. MM cell lines expressing high spliced-XBP1 showed robust dose-dependent apoptosis after exposure to various concentrations of toyocamycin for 24 hours, as assessed by the number of Annexin V-positive cells. Toyocamycin also induces marked apoptosis on two bortezomib (BTZ)-resistant MM cells at nM concentration. It also inhibited constitutive activation of XBP1 expression in primary MM cells derived from patients, showing dose-dependent reduced viability without any cytotoxicity to PBMCs from healthy donors. Toyocamycin also showed synergistic effects with bortezomib, and induced apoptosis of primary MM cells from patients including bortezomib-resistant cases at nano-molar levels in a dose-dependent manner. It also inhibited growth of xenografts in an in vivo model of human MM, and showed enhanced growth inhibition when combined with bortezomib. Taken together, we found that adenosine analog toyocamycin has a potent IRE1α-XBP1 inhibitory effect on MM cells with excessive ER-stress. It triggers dose-dependent apoptosis in MM cells. These results suggest toyocamycin can be a lead compound for developing novel anti-MM therapy, and also provide a preclinical rationale for conducting clinical trials using toyocamycin or other adenosine analog alone or in combination with BTZ for treating MM. Disclosures: No relevant conflicts of interest to declare.

Description: Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimericbcr-abl gene giving rise to a p210Bcr-Ablprotein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G1 phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210Bcr-Abl, Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and HA showed transient depletion of these proteins. KF58333 also down-regulated the level of cell cycle–dependent kinases 4 and 6 and up-regulated cell cycle–dependent kinase inhibitor p27Kip1protein without an effect on the level of Erk and Hsp90 proteins. Immunoprecipitation analysis showed that p210Bcr-Abl formed multiple complexes with Hsp90, some containing p23 and others Hsp70; KF58333 treatment dissociated p210Bcr-Abl from Hsp90/p23 chaperone complexes. Furthermore, KF58333 induced apoptosis in K562 cells and administration of KF58333 prolonged the survival time of SCID mice inoculated with K562 cells. These results suggest that KF58333 may have therapeutic potential for the treatment of CML that involves abnormal cellular proliferation induced by p210Bcr-Abl.

Description: BIW-8962 is a humanized anti-ganglioside GM2 (GM2) monoclonal antibody, produced by Poteligent technology to enhance ADCC activity. GM2 is expressed on many cancer cells including multiple myeloma (MM), small cell lung cancer and glioma cells. In this study, we evaluated the anti-myeloma activity of BIW-8962 in preclinical myeloma models both in vitro and in vivo. Expression of GM2 was analyzed in 15 human MM cell lines by FCM. Eleven out of 15 MM cell lines had positive surface expression of GM2. GM2 as a potential target was then verified in primary MM samples obtained from patients. Eleven out of 15 samples were positive for GM2. We then used two GM2 positive MM cell lines (U266B1 and KMS-11) and evaluated ADCC and CDC activity of BIW-8962 in vitro. BIW-8962 exhibited a potent ADCC and less potent CDC activity. In vivo anti-tumor activity of BIW-8962 was then examined using the standard subcutaneous xenograft model; KMS-11 was inoculated in the flank of SCID mice. BIW-8962 (intravenously administered biweekly for 3 weeks) exhibited a potent anti-tumor activity from as low a dose level as 0.1 mg/kg. Furthermore, in a more clinically relevant model, in which OPM-2/GFP (GM2 positive MM cell line) cells were intravenously inoculated into SCID mice with preferentially tumor growth within the bone marrow microenvironment, BIW-8962 (intravenously administered biweekly for 4 weeks, 10 mg/kg) suppressed OPM-2/GFP cell growth and serum M protein elevation, demonstrating in vivo anti-myeloma effect of BIW-8962. Our preclinical investigations rationalize clinical evaluation of BIW-8962 in patients with MM. Currently BIW-8962 is being investigated in a Phase 1 study in patients with multiple myeloma.