CRM1 inhibition induces tumor cell cytotoxicity and impairs osteoclastogenesis in multiple myeloma: molecular mechanisms and therapeutic implications

The key nuclear export protein CRM1/XPO1 may represent a promising novel therapeutic target in human multiple myeloma (MM). Here we showed that chromosome region maintenance 1 (CRM1) is highly expressed in patients with MM, plasma cell leukemia cells and increased in patient cells resistant to bortezomib treatment. CRM1 expression also correlates with increased lytic bone and shorter survival. Importantly, CRM1 knockdown inhibits MM cell viability. Novel, oral, irreversible selective inhibitors of nuclear export (SINEs) targeting CRM1 (KPT-185, KPT-330) induce cytotoxicity against MM cells (ED50<200 nM), alone and cocultured with bone marrow stromal cells (BMSCs) or osteoclasts (OC). SINEs trigger nuclear accumulation of multiple CRM1 cargo tumor suppressor proteins followed by growth arrest and apoptosis in MM cells. They further block c-myc, Mcl-1, and nuclear factor κB (NF-κB) activity. SINEs induce proteasome-dependent CRM1 protein degradation; concurrently, they upregulate CRM1, p53-targeted, apoptosis-related, anti-inflammatory and stress-related gene transcripts in MM cells. In SCID mice with diffuse human MM bone lesions, SINEs show strong anti-MM activity, inhibit MM-induced bone lysis and prolong survival. Moreover, SINEs directly impair osteoclastogenesis and bone resorption via blockade of RANKL-induced NF-κB and NFATc1, with minimal impact on osteoblasts and BMSCs. These results support clinical development of SINE CRM1 antagonists to improve patient outcome in MM.

Diagnostic and prognostic use of FDG-PET scans in Waldenstrom's macroglobulinemia

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Background: Waldenstrom's macroglobulinemia (WM) is a rare lymphoplasmacytic lymphoma. More sensitive tools of tumor burden and prognosis are needed in these patients (pts). The use of FDG-PET has not been previously studied in WM but has proved an effective diagnostic and prognostic tool effective in low-grade lymphomas. Therefore the objective of this study was to determine whether FDG-PET was an effective tool in evaluating pts with WM. Methods: We included all pts enrolled on a prospective phase II clinical trial of bortezomib and rituximab for pts with upfront or relapsed/refractory (RR) WM. All pts were CD20 positive with histologically confirmed disease and underwent staging evaluation by FDG-PET in combination with CT scan before and after therapy. Patients received 6 cycles of bortezomib IV weekly at 1.6mg/m2 on days 1, 8, 15q28 and rituximab at 375 mg/m2 on days 1, 8, 15 and 22 in cycles 1 and 4. Correlation was made with the international prognostic scoring system for WM and monoclonal protein response rate. Results: 53 pts were included, of which 35 were RR and 18 pts were upfront. Median age was 63 years (range 42–81), 64% were male. Before therapy, 34 pts (64.2%) had positive FDG-PET findings with a median IgM of 2825, Beta 2 microglobulin of 3.6, and Age of 61. 36 pts showed a minor response or greater with a correlation to negative PETs after therapy. Conclusions: Over 60% of WM pts demonstrated FDG-avid disease when using FDG-PET scans, with the majority showing negative disease after therapy. This correlates with the 67.9% response rate. Positive PET images were inversely correlated to IgM level and directly related to elevated Beta-2 microglobulin and age. Significantly PET positive individuals may demonstrate a poorer prognosis. FDG-PET scans may prove an effective tool in the diagnosis and prognosis in WM.

[Table: see text]

Lenalidomide, bortezomib, and dexamethasone in relapsed/refractory multiple myeloma (MM): Encouraging outcomes and tolerability in a phase II study

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Background: Lenalidomide (Revlimid, Len), bortezomib (VELCADE, Bz; maximum tolerated dose [MTD] 15 mg/1.0 mg/m2) ± dexamethasone (Dex; 20–40 mg; RVD) was well tolerated in a phase I study in relapsed/refractory MM patients (pts), with 58% ≥MR. This multicenter phase 2 study evaluated RVD efficacy and safety at the MTD. Methods: Patients received up to eight 21-day cycles of Len 15 mg (days 1–14), Bz 1.0 mg/m2 (days 1, 4, 8, 11), and Dex 40/20 mg (cycles 1–4/5–8, days of/after Bz dosing). After cycle 8, patients with stable/responding disease received maintenance (Len, days 1–14; Bz, days 1, 8; doses per end of cycle 8; Dex 10 mg, days 1, 2, 8, 9) until progression or unacceptable toxicity. Pts with significant peripheral neuropathy were excluded. Results: Among 64 pts, 38 (59%) had relapsed and 26 (41%) refractory/relapsed MM. Median number of prior therapies was two, including Len (8%), Bz (55%), Dex (92%), thalidomide (77%), and stem cell transplant (SCT, 36%). Forty-one pts (64%) completed 8 cycles, 33 continue on maintenance, 22 discontinued early (11 due to progressive disease). Toxicities were manageable, primarily grade (G) 1/2 myelosuppression; 2 developed DVT on aspirin, 2 G3 atrial fibrillation, 1 G3 peripheral neuropathy. One pt died on-study (fungal pneumonia, possibly due to Dex). Overall response rate (62 evaluable patients) was 84% ≥MR, including 21% CR/nCR, 68% ≥PR, which was independent of high-risk features and prior treatment ( Table ). Median duration of response is 24 weeks (range 6–81). Time-to-events data including median time to progression, progression-free survival, and 1-year survival rates will be presented. Conclusions: RVD is active and well tolerated in pts with relapsed/refractory MM, including pts who have received prior Len, Bz, thalidomide, and SCT. Durable responses have been observed and appear independent of adverse cytogenetics and other recognized risk factors.

[Table: see text]

[Table: see text]

MicroRNAs 15a and 16–1 regulates tumor proliferation in multiple myeloma

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Background: MicroRNAs (miRNAs) are non-coding RNAs that act as negative regulators of gene expression. They have been described to play roles in solid tumors and hematologic malignancies. However the role of miRNAs in multiple myeloma (MM) has not been yet fully described. Methods: We performed miRNA-profiling of primary bone marrow-derived CD138+ MM cells, compared to their normal cellular counterparts and validated data by qRT-PCR. In vitro and in vivo functional studies were performed on miRNA-15a- and -16–1-precursors-transfected MM cells. Effect of miRNA-15a and -16–1 on signaling cascades have been evaluated by western blot and immunofluorescence. NF-kB activity has been studied using the Active Motif TransAM kit. In vivo MM cell growth has been evaluated by either using an in vivo imaging model or bioluminescence. Angiogenesis has been studied both in vitro and in vivo using the chorioallantoic membrane model. Results: We identified a MM-specific miRNA signature characterized by down-expression of miRNA-15a, -16–1 and over-expression of miRNA-222/-221/-382/-181a/-181b (P<0.01). Data were confirmed by qRT-PCR on matched samples. Predicted targets for the decreased miRNAs in MM patients included pro-angiogenic cytokines, oncogenes, cell cycle regulators, NFkB activators. Conversely, predicted targets for the increased miRNAs included cell cycle inhibitors, suppressors of cytokine signaling, and pro-apoptotic factors. We demonstrated that miRNA-15a and - 16–1 regulate proliferation and growth of MM cells. Indeed, transfected cells showed decreased DNA synthesis; decreased cyclinD1/cyclinD3/CDC25a/pRb protein expression; phase G1 cell cycle arrest. Moreover, transfected cells showed inhibition of NFkB pathway as shown by reduced p65-/p50-/p52-NFkB activities; downregulation of p-p65/p50/p52 nuclear protein level; upregulation of cttosolic phospho-IkB; and inhibited translocation of p-p65 from the cytolplasm to the nucleus. Similarly, inhibition of MM cell growth was confirmed in vivo; and anti-angiogenic properties of miRNA-15a and -16–1 were demonstrated both in vitro and in vivo. Conclusions: These data indicate that miRNAs play a pivotal role in the biology of MM; providing the basis for the development of new miRNA-based targeted therapies in this disease.

No significant financial relationships to disclose.

A novel Bcl-2/Bcl-X(L)/Bcl-w inhibitor ABT-737 as therapy in multiple myeloma

Bcl-2 or Bcl-X(L) confers resistance to chemotherapy in multiple myeloma (MM). Here we characterized the effects of ABT-737, a potent small-molecule inhibitor of antiapoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w with markedly higher affinity than previously reported compounds, on human MM cells. ABT-737 induces apoptosis in MM cells, including those resistant to conventional therapy. Examination of purified patient MM cells demonstrated similar results, without significant toxicity against normal peripheral blood mononuclear cells and MM bone marrow stromal cells. Importantly, ABT-737 decreases the viability of bortezomib-, dexamethasone-(Dex) and thalidomide-refractory patient MM cells. Additionally, ABT-737 abrogates MM cell growth triggered by interleukin-6 or insulin-like growth factor-1. Mechanistic studies show that ABT-737-induced apoptosis is associated with activation of caspase-8, caspase-9 and caspase-3, followed by poly(ADP-ribose) polymerase cleavage. Combining ABT-737 with proteasome inhibitor bortezomib, melphalan or dexamethasone induces additive anti-MM activity. Taken together, our study provides the rationale for clinical protocols evaluating ABT-737, alone and together with botezomib, mephalan or dexamethasone, to enhance MM cell killing, overcome drug resistance conferred by Bcl-2 and improve patient outcome in MM.

Sildenafil citrate suppresses disease progression in patients with Waldenstrom’s macroglobulinemia

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Background: Responses to sildenafil citrate (Viagra), a phosphodiesterase-5 inhibitor used to treat erectile dysfunction, have been observed in patients with Waldenstrom’s Macroglobulinemia (WM). Moreover, sildenafil citrate induces apoptosis of WM lymphoplasmacytic cells (Clin Lymphoma 5:205, 2004). We therefore conducted a prospective phase II study of sildenafil citrate in patients with slowly progressing WM who did not meet consensus eligibility for active therapy (Semin Oncol 2003; 30:116). Intended therapy was as follows: Week 1 25 mg po qD Week 2 50 mg po qD Week 3 75 mg po qD Week 4, then Months 2–24 100mg po qD or Maximum Tolerated Dose Methods: Thirty patients were enrolled, 18 of whom were previously untreated. All patients demonstrated progressing disease prior to enrollment. Median age was 66 (range 43–85 yrs), baseline BM involvement was 30% (range 5–90%), serum IgM was 3,640 (range 790–6,720 mg/dL), hematocrit was 37.1% (range 32.7–58.5%), and B2M was 2.3 (range 1.5–8.9 mg/dL). Patients were evaluable for response after 3 months of therapy. Results: At a median of 3 months, serum IgM levels declined in 19/30 (63%) patients from a median of 3,640 (range 790–6,720 mg/dL) to 2,965 (range 1,170–6,110 mg/dL). 5/30 patients (17%) demonstrated at least a minor response (≥25% IgM decrease). Two patients were taken off study for non-response to therapy. Toxicities were mild and included headaches, sinus congestion, facial flushing, dyspepsia, and generally resolved on their own with prolonged sildenafil citrate usage. Only two patients required dose modification to 25 mg and 75 mg po qD, respectively. Corollary studies to determine putative mechanisms of action for sildenafil citrate in WM were also performed and will be updated at the meeting. Conclusions: This prospective clinical trial provides preliminary evidence for activity of sildenafil citrate in patients with advancing WM. With minimal toxicity, sildenafil citrate appears to have suppressed disease progression in more than half of patients and has resulted in objective responses, thus warranting further investigation in WM and possibly other B-cell disorders.

No significant financial relationships to disclose.

Effects of chronic wound fluid on the structure and biological activity of becaplermin (rhPDGF-BB) and becaplermin gel

In this study, the effects of chronic wound fluid on the structure and biological activity of becaplermin (recombinant human platelet-derived growth factor-BB [rhPDGF-BB]) were evaluated. Wound fluid was collected from 12 subjects with diabetic ulcers or pressure ulcers. Wound fluid +/- becaplermin was added to cell cultures before- and after incubation for 12 hours at 37 degrees C or after 12 hours' topical treatment. Biological activity, concentration, and immunogenicity were determined by [3H]thymidine incorporation into quiescent human foreskin fibroblasts, enzyme-linked immunosorbent assay (ELISA), and Western blot analysis, respectively. No PDGF-BB or mitogenic activity was detected in chronic wound fluid alone. Mitogenic activity was present in post-treatment samples from becaplermin-treated subjects but not placebo-treated subjects. Exposure to chronic wound fluid for 12 hours did not alter the amount, banding pattern, or mitogenic activity of becaplermin. Biologically active becaplermin remains in wound fluid 12 hours after topical application of becaplermin gel.

The mechanism of anti-CD3 monoclonal antibodies. Mediation of cytolysis by inter-T cell bridging

OKT3, an anti-CD3 MAB, depletes T cells in vivo and is among the most potent inhibitors of acute allograft rejection. The mechanism of this inhibition is unknown. The present studies investigate whether anti-CD3 antibodies have the ability to crosslink CD3 on two different cells and induce TCR-dependent antibody-bridged cell-mediated cytolysis (TCR-ABCMC) between T cells. Two different anti-CD3 antibodies (OKT3 and CD3,3) and OKT3 F(ab')2 were all highly effective in inducing cytolysis of CD8+ and CD4+ T cells by CD8+ T cells, and CD8+ T cells by CD4+ T cells. Monovalent OKT3 Fab was 25-125-fold less potent than OKT3 F(ab')2. Monovalent CD3,X was totally ineffective. The necessity for intercellular bridging was evidenced by the observation that an anti-CD3:anti-CD4 (CD3,4) bispecific MAB (BSMAB) was effective in mediating lysis of CD4+ but not CD8+ T cells by CD8+ T cells. These studies indicate that neither FcR-mediated ADCC nor complement fixation is necessary for bivalent anti-CD3 MAB to lyse T cells. Inter-T cell TCR-ABCMC may be particularly effective in inflammatory tissues, such as rejecting allografts and autoimmune diseases, in which numerous cytolytic T lymphocytes are present in close association with other T cells.

Specific inhibition of OKT8 binding to peripheral blood mononuclear cells by jacalin

Human T-specific monoclonal antibodies were used to study the interactions between the binding of jacalin to peripheral blood mononuclear cells (PBMC) and the immunoregulatory molecules displayed at the surface of T cells. Jacalin inhibits the binding of OKT8 (anti-CD8) to both fresh PBMC and jacalin-induced T cell blasts. In both cases the binding of anti-CD3 (OKT3) or anti-CD4 (OKT4) was not affected by the lectin. The effect of jacalin on OKT8 binding is abolished by 1-O-alpha-D-methylgalactopyranoside, suggesting its mediation by the lectin saccharide combining sites. Preincubation experiments indicated that the inhibitory effect of jacalin is due to a competition between the lectin and the monoclonal antibody. The effect of the lectin could also be reversed by increasing concentrations of the monoclonal antibody. Taken together this data demonstrates a specific inhibition of OKT8 (anti-CD8) binding by jacalin. This effect is mediated by the binding of the lectin to structures on the cell surface, perhaps the CD8 antigen. The data also points to the discovery of a new mitogen that could be useful for studying the physiological role of CD8 on T cell responses.

B-cell activation and immunoregulation in end-stage renal disease patients receiving hemodialysis

B-lymphocyte functions were studied in peripheral blood mononuclear cells of end-stage renal disease patients undergoing intermittent hemodialysis for longer than two years. T-cell-dependent B lymphocyte proliferation after pokeweed mitogen stimulation was low in half of the hemodialyzed patients. T cell-independent B cell response to Staphylococcus aureus, Cowan I, was also significantly reduced. Spontaneous production of immunoglobulin in cultures of peripheral blood mononuclear cells of uremic patients was comparable with that of healthy controls, but pokeweed mitogen-stimulated antibody secretion was significantly reduced with cells from patients undergoing hemodialysis. Helper T-cell functions in B-cell activation were also qualitatively deficient in uremic patients. It is concluded that B-cell activation and immunoregulation is defective in patients undergoing long-term hemodialysis.

Suppressor cells in end-stage renal disease. Functional assays and monoclonal antibody analysis

Suppressor cell activity after concanavalin A induction was studied in peripheral blood mononuclear cells of patients undergoing long-term hemodialysis. Suppression both of the mixed lymphocyte reaction and of allogeneic cells stimulated with phytohemagglutinin was significantly higher with peripheral blood mononuclear cells from patients undergoing hemodialysis than with cells from control subjects. Expression of the Ia antigen on T lymphocytes (associated with immunologic activation) was studied by staining with monoclonal antibodies and two-color fluorescence analysis in a computer-linked cytofluorograph. In unstimulated cells, there was no significant difference between the patients and control subjects. After concanavalin A induction, the percentage of T4, and particularly of T8, cells expressing the Ia antigen was significantly higher in the group undergoing hemodialysis. The functional suppression seen after concanavalin A induction in the mixed lymphocyte reaction was significantly reduced by treatment with OKT8 monoclonal antibody and complement; in phytohemagglutinin cultures, both OKT8 and OKIa*1 antibodies were effective. The reduced in vitro response of uremic lymphocytes may thus be a consequence of increased suppressor activity associated with the T8-positive, Ia-positive subset of T cells.

T cell subsets and cellular immunity in end-stage renal disease

The T lymphocyte population was studied by immunofluorescent staining with monoclonal antibodies and laser flow cytometry in the blood of 50 patients with end-stage renal disease undergoing long-term maintenance intermittent hemodialysis. The absolute number of T cells was lower in patients receiving dialysis for more than one year (p less than 0.001), as was the absolute count of helper T cells (p less than 0.005). In patients under 30 years of age, the absolute number of helper T cells was markedly reduced, whereas the number of suppressor/cytotoxic T lymphocytes was not changed. In patients between the ages of 30 and 60 years, both helper and suppressor cells were significantly reduced. In patients over 60 years of age, only the number of helper T cells was reduced. The in vitro response of patients' lymphocytes was reduced both in the mixed lymphocyte reaction (p less than 0.01) and after phytohemagglutinin stimulation (p less than 0.001). Natural killer cytotoxicity of patients' peripheral blood mononuclear cells, however, was unaffected.