ALBERT

Description: Previously we have demonstrated that multiple myeloma cell lines and primary cells express CD52, the antigenic target of Campath-1H, and that they undergo apoptosis following treatment with alemtuzumab in-vitro (Gasparetto et al. ASH #3210,2002). Based on these observations, we initiated a clinical trial where patients with advanced, multiply relapsed MM were treated with subcutaneous (sc) alemtuzumab as a single agent. Nine patients (6 men/4 women, age range 45–69 yrs) were initially treated with the standard dose of 30mg sc three times per week for up to 12 weeks. All patients had at least 4 lines of prior therapy and 8/9 patients had undergone high dose chemotherapy followed by autologous peripheral blood stem cell transplant. Treatment related toxicities included pancytopenia in all patients with grade IV neutropenia in the first four patients, necessitating withdrawal from study. Subsequently, all patients were treated with G-CSF and aggressive transfusion support and no further patients were removed from study due to cytopenias. All patients were prophylaxed with Famvir, Fluconazole and Septra and no opportunistic infections were noted during treatment. Two patients developed acute renal insufficiency that reversed when alemtuzumab was discontinued. One patient completed the entire 12 weeks of treatment. One patient had a PR with a 40% reduction in M-protein after two months of treatment, which reversed once Campath-1H was discontinued. Pharmacokinetic studies of one patient demonstrated that it required 8–10 weeks of treatment using the sc protocol to achieve serum levels of alemtuzumab of 1ug/ml, the level considered to be tumoricidal in-vivo. Based on this observation, the treatment protocol was modified so that the initial week of escalating doses was given IV to achieve more rapid therapeutic levels. Following this, sc alemtuzumab was given as above. One patient with non-secretory multiple myeloma with relapsed disease following 5 prior lines of therapy has been treated with this modified protocol. Treatment with alemtuzumab and growth factor support in this patient has been well tolerated except for the development of RSV pneumonia. At 4 weeks, a PET scan demonstrated a significant overall decrease in metabolic activity in multiple bony areas consistent with a response to treatment. These initial results suggests that alemtuzumab is associated with significant toxicities in patients with advanced multiple myeloma including pancytopenia, infections and possibly renal insufficiency but all of these were reversible and have been minimized with aggressive prophylactic therapy. Alemtuzumab does appear to have modest activity against MM in this heavily pre-treated group suggesting that it should be explored in combination with other agents and at earlier stages of disease.

Description: Abstract 2681 Background: Despite recent advances, the 5 year overall survival for patients with high risk diffuse large B cell lymphoma (DLBCL) is approximately 50% and there is still no known cure for patients with mantle cell lymphoma (MCL). This phase II study of multimodal dose dense therapy evaluated 2 courses of dose intense chemotherapy followed by radioimmunotherapy (RIT) consolidation in patients with previously untreated, mantle cell or high/high intermediate (int) risk aggressive B cell lymphoma. Aim: To evaluate the efficacy and safety of dose intense/dose dense, multimodal chemo-immunotherapy combined with RIT. Methods: Patients with untreated MCL or high int/high risk DLBCL were enrolled. Treatment regimen involved 3 phases of therapy: induction 1, induction 2 and consolidation with RIT (Table 1). Induction 2 occurred approximately 5 weeks after induction 1 and RIT was given 12–24 weeks after rituximab was completed. Patients were evaluated after each treatment phase and those with stable disease (SD) or better and blood count recovery could proceed to the next phase of therapy. Results: Thirty nine patients (pts) with high/high int risk DLBCL (n=25) or MCL (n=14) were enrolled. The median age was 60 years (range 21–80). Toxicity: Common, anticipated toxicities in the induction phases were thrombocytopenia, neutropenia, nausea, fatigue, and anemia. During Ind1 (n=39), grade (gr) III mucositis occurred in 13 pts (33%) and febrile neutropenia (FN) in 31 (79%). Three pts did not proceed to Ind2 due to death (1 candidemia, 1 septic knee prosthesis, 1 from complications of colectomy for prolonged diverticulitis after count recovery) and 2 withdrew to pursue less intense chemotherapy. During Ind2 (n=34) gr III mucositis occurred in 12pts (35%) and FN in 24 (67%). Two pts had gr III/IV cerebellar toxicity that was disabling in 1 pt. Of the 34 pts who received the Ind2, 9 did not receive RIT due to progressive disease (PD) (4), prolonged cytopenias (4), or diagnosis of pancreatic cancer (1). Twenty five pts received RIT and 3 (12%) had FN, 20 (80%) had gr III/IV neutropenia, 23 (92%) had gr III/IV thrombocytopenia, 1 pt died from bacteremia. Two pts developed myelodysplasia 21 and 48 months after starting therapy. Response: Pts were evaluated for response after Ind1, Ind2 and RIT. 38/39 pts were evaluable for response, with 1 pt withdrawing prior to assessment. The pts who died prior to response evaluation were counted as non-responders. The best overall response rate (ORR) was 95% (36/38) with a complete response rate (CR) of 84% (32/38). See tables 2 and 3 for more detailed response data by phase of treatment and disease type. After a median follow up of 17.2 months, 30 pts (77%) are alive (see figure). The median overall survival for MCL has not been reached and is 36.5 months for DLBCL. Deaths were from Hodgkin lymphoma (1), infection (3), DLBCL (2), complications of surgery (1), MCL (2). The median progression free survival is 36.5 months with 11/14 (79%) MCL and 14/25 (56%) DLBCL pts alive and in continued CR. Conclusion: The combination of dose dense, dose intense chemotherapy, monoclonal antibody, and RIT demonstrates considerable efficacy, despite expected toxicity, in high risk DLBCL and MCL pts. The response rates seen in this study are higher than expected from standard R-CHOP in this pt population. Further follow up to determine impact on OS and long term complications will be required to confirm these promising outcomes. Disclosures: Beaven: Glaxo Smith Kline: Family Member Employed by GSK. Off Label Use: Tositumomab is approved for use in relapsed/refractory low grade CD20 positive NHL. It is not FDA approved for first line use in diffuse large B cell lymphoma or mantle cell lymphoma. Neither cytarabine nor etoposide are approved for use in non-Hodgkin lymphoma. Rizzieri:Glaxo Smith Kline: Speakers Bureau. Moore:Glaxo Smith Kline: Speakers Bureau.

Description: High-dose therapy plus autologous stem cell transplant (ASCT) is the standard of care for patients with multiple myeloma (MM) aged ≤65 years. Melphalan–prednisone (MP)-based therapy is the standard for non-ASCT candidates but is not typically used for transplant-eligible patients as prolonged therapy with melphalan can adversely affect stem cell collection. The phase 3 VISTA study demonstrated the superior efficacy of bortezomib plus MP (VMP) versus MP in previously untreated MM patients ineligible for ASCT. In this phase 2 study, we evaluated the efficacy of a shorter course of VMP on a different treatment schedule as induction therapy prior to ASCT or as frontline therapy in non- ASCT candidates. Patients aged ≥18 years with previously untreated MM received up to six 28-day cycles of bortezomib 1.3 mg/m2 IV, days 1, 4, 8, and 11, plus oral melphalan 6 mg/m2 and oral prednisone 60 mg/m2, days 1–7. After 2–6 cycles, ASCT-eligible patients could proceed to stem cell mobilization (G-CSF 10 mg/kg/day ± GM-CSF 250 mg/m2/ day or cyclophosphamide 4 g/m2 + GM-CSF) and conditioning with melphalan 200 mg/ m2 (140 mg/m2 if aged 〉65 years). Response was assessed every two cycles and post- ASCT by International Uniform Response Criteria. The primary end point was complete response (CR) rate to VMP. A total of 45 patients were enrolled; 27 were male. Median age was 63 years (range 33–75). MM subtype was 67% IgG, 16% IgA, and 9% each κ- and λ- light-chain; 37% of patients had ISS Stage III MM, 22% had ECOG performance status 〉1, and 70% had ≥40% plasma cells in bone marrow. In total, 20 patients proceeded to ASCT. Median duration of VMP was 4 cycles in both non-ASCT (range 1–6) and ASCT (range 2–6) patients. Response rate (best response) to VMP was 95% (42 of 44 evaluable patients), including 9% stringent CR (sCR), 9% CR (18% ≥CR [95% CI: 7%, 30%]), 27% very good partial response (VGPR), and 50% partial response (PR). Best response was achieved after cycle 2 in 10 patients, cycle 4 in 25 patients, and cycle 6 in 7 patients. All 20 ASCT patients had successful stem cell mobilization; median yield of CD34+ cells/ kg was 5.6 x 106 (range 2.3–12.2 x 106), in a median of 2 collection days. Post-transplant responses were 10% sCR, 20% CR, 55% VGPR, and 5% PR; the remaining 2 patients need further follow-up for response assessment. Response improved post-VMP to post-ASCT in 10 patients (6 PR to VGPR, 2 PR to CR, 2 VGPR to CR). After median follow-up of 14.0 months (range 7.4–47.7) and 14.6 months (range 8.2–42.9) in non-ASCT and ASCT patients, respectively, both median time to progression and progression-free survival were 19.8 months (95% CI: 14.3 months, not estimable [NE]) in non-ASCT patients and 27.9 months (95% CI: 14.6 months, NE) in ASCT patients. A total of 7 patients (5 non- ASCT, 2 ASCT) have died; 1-year survival rate was 82% (95% CI: 59%, 93%) in non- ASCT patients and 95% (95% CI: 69%, 99%) in ASCT patients. Most common grade 3/4 adverse events in all 45 patients during VMP therapy included peripheral neuropathy (24%), thrombocytopenia (20%), neutropenia (18%), and infection (9%). Only 1 patient had deep-vein thrombosis. In conclusion, VMP represents a highly effective therapy for previously untreated MM, with 45% of patients achieving VGPR or better, including 18% sCR/CR. Toxicities were predictable and generally manageable. Short-course VMP therapy did not negatively impact stem cell mobilization, supporting its use as induction therapy prior to ASCT. Very high post-transplant response rates were seen, with 85% of patients achieving ≥VGPR, including 30% sCR/CR. Since achievement of CR/VGPR is associated with improved long-term outcomes in MM, the preliminary outcome data presented here appear promising; however, longer follow-up is required.

Description: Survival of CLL cells requires sustained activation of the anti-apoptotic PI-3-kinase/Akt pathway, and many therapies for CLL cause leukemia cell death by triggering apoptosis. Blood lipoprotein particles are either pro- or anti-apoptotic. High density lipoprotein (HDL) particles are anti-apoptotic through sphingosine-1-phosphate receptor 3 (S1P3)-mediated activation of the PI-3-K/Akt pathway. We have noted that apoE4-very low density lipoprotein (VLDL) (but not apoE2- or apoE3-VLDL) particles increase apoptosis of endothelial cells by recruiting the phosphoinositol phosphatase SHIP-2 to the plasma membrane, thereby directly inhibiting the anti-apoptotic activity of HDL (DeKroon R, et al., Circ Res99:829–836, 2006). Since apoE4-VLDL increases apoptosis of certain cells, and since increased leukemia cell apoptosis favors longer survival in CLL, we hypothesized that APOE4 genotype would beneficially influence the clinical course of CLL. Of the 193 CLL patients (50 women and 133 men) studied, 29% had an APOE4 genotype. In the entire group, survival of men and women was not statistically different. However, women (but not men) with an APOE4 genotype had markedly longer survival than non-APOE4 patients (median 〉25 yr vs. 14.0 yr; p = 0.02) (Figure). Figure Figure Men and women had the same time-to-treatment (treatment-free survival) irrespective of APOE genotype. VLDL is metabolized to LDL by the actions of LPL. Patients had shorter survival and time-to-treatment if their CLL cell lipoprotein lipase (LPL) mRNA levels were high (p = 0.002). In analyzing APOE genotype and LPL levels in the same patients, we demonstrated that APOE4 was a more important determinant of survival than was the LPL level (p = 0.0007). The beneficial effect of APOE4 in CLL survival is likely mediated through allele-specific influences of APOE4 on serum lipoproteins increasing leukemia cell apoptosis. The frequency of the APOE alleles in the CLL patient population was not significantly different than that of a control population (16 and 13%, respectively). APOE genotype therefore does not appear to affect susceptibility to CLL, but influences the clinical course of disease, particularly after therapy is initiated. In contrast, APOE genotype does influence susceptibility to other diseases, most notably Alzheimer’s disease in which APOE4 markedly increases risk. The beneficial impact of APOE4 in CLL and its deleterious impact on Alzheimer’s disease expression may relate to a common mechanism of APOE4 in enhancing apoptotic cell death. APOE genotyping of patients with CLL may provide important clinical prognostic information, particularly in women. Most importantly, the allele-specific influence of APOE on disease progression may provide important new insights into the mechanisms of disease and response to therapy, and lead to new agents for treatment.

Description: The failure to overcome drug resistance leads to a high rate of relapse in elderly patients with acute myeloid leukemia. We evaluated, in a Phase I study the feasibility of a dose dense regimen of HiDAC, and MylotargTM therapy for newly diagnosed elderly (≥60 years) patients with AML in terms of toxicity with two cycles of this regimen as the sole induction and consolidation therapy. HiDAC was administered in a dose escalation pattern: 3000mg/m2 intravenously given for 6, and 9 doses, and MylotargTM was administered at a dose of 6mg/m2 intravenously on days 1 and 8 of each cycle. Patients without unacceptable toxicity, defined as failure to recover counts to a minimum of ANC ≥ 500/ μl, platelets ≥ 30K and hematocrit ≥ 25%, received a second cycle of therapy, though not before day 28 following day 1 of induction. In addition, death within the first 30 days of induction (not related to disease progression) and life-threatening non-hematologic toxicity (such as cardiac or pulmonary arrest) was also considered dose-limiting. Patients with persistent disease but at least a 50% decrease in the marrow or peripheral blood blast count, or those with low blood counts and patients achieving CR without platelet recovery (CRp) at the 4–6 week examination received cycle 2 with a de-escalation of the Mylotarg dose (from 6 mg/m2 to 4 mg/m2). All patients received G-CSF 5mcg/kg/day subcutaneously from days 11–14. Eight patients (five male, three female) with a median age of 68 years (range 60–74) were enrolled. In cohort one (6 doses of HiDAC), four of six patients were able to complete both cycles of therapy and two of these have achieved CR. Two of the six patients achieved CRp with persistent thrombocytopenia and thus received a second cycle of chemotherapy off protocol. One patient in this cohort had progressive disease and persistent pancytopenia requiring transfusions and subsequently received chemotherapy using Etoposide and Cyclophosphamide. Five out of six patients are alive and remain disease free. In cohort two (9 doses of HiDAC), two patients have been enrolled thus far. One patient developed neurotoxicity after six doses of HiDAC and thus completed both cycles of therapy with six doses of HiDAC along with protocol dose of MylotargTM. The other patient was able to get all nine doses of HiDAC and both patients have achieved a CR. No unexpected hematologic toxicity was observed. All patients developed grade IV thrombocytopenia requiring platelet transfusions. One patient in cohort one died after developing aspergillus infection and multiorgan failure before he could be evaluated for response. Two patients in cohort one developed uncomplicated gram-positive bacteremia requiring antibiotics. In cohort two, one patient developed neurotoxicity and the other developed uncomplicated gram-positive bacteremia. At the time of submission of this abstract seven out of eight patients are alive with four CR and two CRp. No veno-occlusive disease was seen in these eight patients treated with two cycles of HiDAC and MylotargTM back to back. The high rate of CR and relatively good tolerance of this regimen remains encouraging.

Description: We report a phase 1 study of pharmacokinetics, dosimetry, toxicity, and response of 131I anti-tenascin chimeric 81C6 for the treatment of lymphoma. Nine patients received a dosimetric dose of 370 MBq (10 mCi). Three patients received an administered activity of 1480 MBq (40 mCi), and 2 developed hematologic toxicity that required stem cell infusion. Six patients received an administered activity of 1110 MBq (30 mCi), and 2 developed toxicity that required stem cell infusion. The clearance of whole-body activity was monoexponential with a mean effective half-life of 110 hours (range, 90-136 hours) and a mean effective whole-body residence time of 159 hours (range, 130-196 hours). There was rapid uptake within the viscera; however, tumor uptake was slower. Activity in normal viscera decreased proportional to the whole body; however, tumor sites presented a slow clearance (T1/2, 86-191 hours). The mean absorbed dose to whole-body was 67 cGy (range, 51-89 hours), whereas the dose to tumor sites was 963 cGy (range, 363-1517 cGy). Despite lack of a “blocking” antibody, 1 of 9 patients attained a complete remission and 1 a partial remission. These data demonstrate this radiopharmaceutical to be an encouraging agent for the treatment of lymphoma particularly if methods to protect the normal viscera are developed.

Description: Background: Although complete remission rates for AML are near 70% with combination induction and consolidation chemotherapy, most patients will relapse and die from the disease or treatment complications. New agents with unique mechanisms are needed. One such class of therapeutics are fusion proteins consisting of protein synthesis inactivating peptide toxins fused to tumor cell selective ligands. DT388-IL3 is one such fusion protein. Rationale: In preclinical studies, DT388-IL3 was cytotoxic to the IL3 receptor expressing leukemia cell lines but not toxic to IL3 receptor negative cell lines. This agent was less toxic to normal progenitors and not toxic to early hematopoietic stem cells. The majority of AML progenitors overexpress IL3 receptors. Animal model work in mice bearing human leukemia cells has demonstrated anti-leukemia efficacy which is dose dependent with this agent. Toxicities in monkeys include vascular leak syndrome and pancytopenia observed only at the highest doses. The MTD in monkeys was estimated at 60mcg/kg/day. We report preliminary data on the use of DT388-IL3 fusion protein in humans from an ongoing phase I trial. Pharmacokinetics; clinical and immune response to this novel fusion protein are also being followed. Patients and Methods: Patients with refractory AML were eligible. The first dose level was qd M-W-F X six doses of DT388-IL3 at 4mcg/kg/day with dose escalation planned for subsequent patients. Patients with progression of disease or unacceptable study drug toxicity were to be removed from the study. Toxicity was graded according to NCI CTCAE version 3.0. Three patients have been treated with DT388-IL3. Serum samples were collected and will be assayed for anti-DT388-IL3 antibodies prior to and after treatment. Blood samples were obtained to measure circulating levels of active DT388-IL3 and its half life. Patient blasts were also collected prior to treatment for later analysis of expression of IL3 receptors. Result: Two patients tolerated the treatment schedule(of six doses) without any significant toxicities. Mild fever, headaches, nausea were noted. Both of these patients had progression of disease-one during treatment and one on day 15 bone marrow biospy. The above mentioned patients died secondary to disease complications at 2 weeks and 18 weeks after their last dose of the study agent respectively. DT388-IL3 levels on these two patients post infusion were below the the reliable detectable limits of the assay. The third patient became febrile and hypotensive after the first dose. The hypotension persisted and she did not receive any further doses. This patient is alive 5 weeks later with supportive care alone. DT388-IL3 levels following this patient’s dose are as follows: 2min post infusion 34.3ng/ml, 30min post infusion 1.9ng/ml, 60min post infusion 0.075ng/ml, 120min post infusion 0.003ng/ml, 240min post infusion undetectable. Conclusion: Preclinical/animal studies suggest that DT388-IL3 has anti-leukemia efficacy. Preliminary data from our ongoing phase I trial reveals minimal study agent related toxicity and no life threatening complications at this first dose level. Dose escalation is planned as per protocol.

Description: Background and Significance : Chronic lymphocytic leukemia (CLL) is the most heritable hematologic malignancy; however, no common CLL predisposition genes are known. Monoclonal B lymphocytosis (MBL) is a hematologic syndrome characterized by small accumulations of B lymphocytes in the peripheral blood. MBL has a CLL-like immunophenotype, may progress to overt CLL, and is over represented in CLL families. Therefore, MBL observed in the context of familial CLL may be a marker of inherited risk for development of CLL. Detailed characterization of family-associated MBL may also provide mechanistic insights into the pathogenesis of familial CLL. Our strategy was to detail the biologic characteristics of CLL in family-associated MBL. Methods : Persons with MBL were identified by flow cytometric screening of peripheral blood from unaffected members of CLL kindreds ascertained by Genetic Epidemiology of CLL Consortium (GEC) sites. Flow cytometry was used to determine the surface immunophenotype including CD38 and intracellular ZAP-70. We defined MBL as populations of CD19+, CD5+, CD20lo, CD23+ B cells that comprised at least 2% of the CD19+ peripheral B cell compartment and did not exceed 5.0 × 109 MBL cells/L. RNA and genomic DNA from single MBL cells isolated by flow cytometric sorting were analyzed using PCR to determine immunoglobulin heavy and light chain sequences. MBL cells were sorted in bulk for FISH for loci associated with clinical CLL. Results : Twenty-two out of 190 (12%) unaffected family members were found to have MBL. We observed significant variability in the size of the MBL clone as a percentage of the CD19+ B cell compartment (mean 32%; range 2%–97%). Nonetheless, the absolute size of the MBL clone was small, 15 of 17 individuals had 〈 200 × 106 MBL cells/L. CD38 expression (defined as CD38 surface expression in ≥30% of MBL cells) was observed in 8 of 18 subjects tested. ZAP-70 (defined as intracellular expression in ≥ 20% of MBL cells) was expressed in 4 of 12 participants. Among 12 subjects tested, 5 MBL expressed both surface IgD and IgM, 3 expressed IgD only, 2 expressed IgM only, and 2 did not express IgD or IgM. Analysis of immunoglobulin heavy and light chains has been completed in 8 individuals. Both immunoglobulin heavy chain variable (IgVH) region mutated (n = 12) and unmutated (n = 4) sequences were observed. Four of 8 individuals had 2 or more unrelated MBL clones (range 2–5), including one individual with both unmutated and mutated clones. Among the 16 MBL clones identified in these 8 subjects, VH3 or VH4 rearrangements were observed in all MBL clones. The most commonly rearranged IgVH genes were 3–07 (3 MBL clones), 3–15 (3), and 4–34 (3). No VH1 family gene rearrangements were observed. In one individual, a VH3–07 MBL clone showed intraclonal diversification suggestive of antigen driven immunoglobulin sequence changes. Twenty productive light chain rearrangements were identified among the 16 MBL clones, with 11 Vλ and 9 Vκ genes used. We observed 6 productive rearrangements of Vλ1–51. MBL cells were bulk sorted for FISH from 9 subjects. Mono or biallelic deletion of 13q14.3 was observed in 5 subjects, the other 4 were normal. Conclusions : Our findings confirm that MBL is commonly observed among the unaffected family members from CLL kindreds. We found that some MBL clones express ZAP-70, CD38 or have unmutated IgVH genes and thus are similar to clinical CLL. The clinical outcome of these MBL clones in relation to our baseline prognostic characterization will be of interest. Small MBL clones are commonly oligoclonal. Importantly, although the immunoglobulin heavy and light chain genes rearranged in these MBL clones are all commonly used in CLL, the absence of VH1 and abundance of Vλ1–51 rearrangements do suggests differences in BCR usage between CLL and MBL. Further investigation of family associated MBL may clarify the genetics and immunobiology of familial CLL.

Description: Abstract 1241 Poster Board I-263 Background and Significance Monoclonal B lymphocytosis (MBL) is a hematologic syndrome characterized by accumulations of clonal B lymphocytes in the peripheral blood. Most MBL have a CLL-like immunophenotype, though other, less common phenotypes are observed. Although some MBL, particularly those with MBL cell counts 〉1.9 × 109 / L, progress to CLL, “low count” MBL (

Description: Abstract 4190 Background and Significance: Myeloid Cell Leukemia-1 (Mcl-1) is an anti-apoptotic protein that is elevated in fludarabine-resistant CLL patients. Expression levels of Mcl-1 correlate with time to first treatment and overall survival in CLL patients. Furthermore, elevated levels of Mcl-1 have also been reported in B-cell lymphomas. The regulation of Mcl-1 stability occurs through phosphorylation of several serine and threonine residues catalyzed by constitutively activated kinases. The tumor suppressor protein phosphatase 2A (PP2A) is important in deactivation of several kinases: Akt, the mitogen activated protein kinases (MAPK) p38, JNK, ERK, and NFkB (through IkK). We have discovered novel peptides that antagonize the SET oncoprotein, a potent physiological inhibitor of PP2A, and increase cellular PP2A activity. Importantly, we note that SET is overexpressed in CLL and B-cell lymphoma cells and that treatment of these cells with SET antagonist peptides is cytotoxic for the malignant cells both in vitro and in vivo. We show here that activation of PP2A by antagonism of SET results in reduced Mcl-1 levels and induction of apoptosis in CLL and B-cell lymphoma cells. Methods: Patients were from the Duke University and V.A. Medical Centers, and normal controls were from the community. Blood CLL cells and control normal B-cells were purified using negative selection with antibodies. The human Ramos and Raji B-cell lymphoma cell lines were from ATCC. We determined cytotoxicity using the MTS colorimetric assay. SET antagonist peptides were prepared by chemical synthesis. Western blotting and immunoprecipitation were performed with antibodies to SET, Mcl-1, PP2Ac, c-Myc, Axin, Pin-1, GSK3beta, Bcl-2, Bcl-XL and beta-actin. Apoptosis assays were performed with the annexin-V/propidium iodide staining method. Results: We previously demonstrated SET overexpression in CLL cells and that SET antagonist peptides activate PP2A and are cytotoxic for malignant B-cells. Using freshly-isolated CLL cells and Raji and Ramos cell lines, cytotoxicity of the SET antagonist peptide COG449 was evaluated. We found the concentrations for 50% cytotoxicity (ED50) to be 77 nM for CLL cells, 125 nM for Ramos cells, 250 nM for Raji cells, and 〉10,000 nM for normal B-cells. Annexin-V staining indicated that apoptosis was induced at concentrations comparable to the ED50s for cytotoxicity of the compounds tested. COG449 treatment of NOD/SCID mice bearing tumors after xenografting with Ramos cells resulted in reduced tumor growth. After treatment for 8 days, there was a 61% reduction in final tumor mass at harvest on day 19 (p