ALBERT

Description: SGN-40 is a humanized monoclonal antibody against CD40, a TNF receptor family member expressed in non-Hodgkin lymphoma (NHL), multiple myeloma, and several carcinomas. SGN-40 is cytotoxic to NHL cell lines via activation of proapoptotic signal transduction pathways and mediates antibody dependent cellular cytotoxicity (ADCC) effector function activity. In this study we examined the anti-tumor activity of SGN-40 in combination with the anti-CD20 antibody, rituximab, in lymphoma cell line models. Cell proliferation data (3H-thymidine incorporation assay) was generated for SGN-40 and rituximab alone and in combination for three NHL cell lines (Ramos, RL, and SU-DHL-4) and combination index (CI) analyses performed. SGN-40 was reproducibly synergistic with rituximab in Ramos cells and additive in the RL and SU-DHL-4 cell lines in this assay. This suggested that different anti-proliferative signaling events are activated by these antibodies, which produce a greater anti-tumor effect when combined. To better understand the combined activity of SGN-40 and rituximab, the signal transduction pathways activated by each antibody were examined. In Ramos cells SGN-40 signaling caused the degradation of pro-survival BCL-6 oncoprotein and upregulation of TAp63α, a proapoptic p53 family member, while only BCL-6 degradation was triggered in the RL and SU-DHL-4 cell lines. In contrast, rituximab signaling degraded BCL-6 protein in only one cell line (SU-DHL-4), and did not upregulate TAp63α expression in any of the cell lines examined. To further define the combined activity of SGN-40 with rituximab the effector function activity of both antibodies were examined in vitro. ADCC assays in the WIL2-S and Raji cell lines both showed a greater percent cell lysis in the presence of both SGN-40 and rituximab compared to either drug alone. Next, the SGN-40 and rituximab were tested in subcutaneous mouse models of NHL to evaluate this combination in vivo. In a Ramos model, SGN-40 and rituximab (dosed at 4.0mg/kg, q4dx4, ip) had significantly greater anti-tumor response when combined compared to the equivalent dose of either antibody alone. The anti-tumor response achieved with dual dosing of SGN-40 and rituximab was greater than the response expected if the combination was additive. Our data suggests that the improved efficacy of SGN-40, rituximab combination therapy in vivo is due to distinct apoptotic signaling pathways activated by these two antibodies in addition to augmented effector function activity. The combination of SGN-40 and rituximab is currently being studied in clinical trials of NHL.

Description: Despite major advances in the treatment of non-Hodgkin lymphoma (NHL), including the use of chemotherapeutic agents and the anti-CD20 antibody rituximab, the majority of patients eventually relapse, and salvage treatments with non–cross-resistant compounds are needed to further improve patient survival. Here, we evaluated the antitumor effects of the microtubule destabilizing agent monomethyl auristatin E (MMAE) conjugated to the humanized anti-CD19 antibody hBU12 via a protease-sensitive valine-citrulline (vc) dipeptide linker. hBU12-vcMMAE induced potent tumor cell killing against rituximab-sensitive and -resistant NHL cell lines. CD19 can form heterodimers with CD21, and high levels of CD21 were reported to interfere negatively with the activity of CD19-targeted therapeutics. However, we observed comparable internalization, intracellular trafficking, and drug release in CD21low and CD21high, rituximab-sensitive and -refractory lymphomas treated with hBU12-vcMMAE. Furthermore, high rates of durable regressions in mice implanted with these tumors were observed, suggesting that both rituximab resistance and CD21 expression levels do not impact on the activity of hBU12-vcMMAE. Combined, our data suggest that hBU12-vcMMAE may represent a promising addition to the treatment options for rituximab refractory NHL and other hematologic malignancies, including acute lymphoblastic leukemia.

Description: Antigens expressed on malignant cells in the absence of significant expression on normal tissues are highly desirable targets for therapeutic antibodies. CD70 is a TNF superfamily member whose normal expression is restricted to activated lymphocytes but is aberrantly expressed in hematologic malignancies and solid tumors including non-Hodgkin’s lymphoma (NHL), Hodgkin’s disease, multiple myeloma (MM), Waldenstrom’s macroglobulinemia, renal cell carcinoma, glioblastoma, and nasopharyngeal carcinoma. To target CD70-expressing hematologic malignancies, we have engineered a humanized IgG1 anti-CD70 antibody that mediates lysis of tumor targets via ADCC and CDC and facilitates antibody dependent cellular phagocytosis in vitro. In vivo, administration of SGN-70 prolonged survival of SCID mice bearing CD70+ disseminated human NHL or MM xenografts. Intravenous injection of the CD70+ MM cell line MM.1S resulted in disease as measured by onset of paralysis, presence of CD138+ MM cells in the bone marrow, and increasing levels of circulating human Ig lambda light chain. SGN-70 treatment of MM.1S-bearing mice significantly delayed onset of paralysis and reduced the monoclonal protein levels detected in serum approximately 4-fold compared to untreated or non-binding antibody control-treated mice. Whereas myeloma cells comprised 32±6.4 % of mononuclear cells in the long bone marrow of control mice, SGN-70 treatment reduced the myeloma cell fraction to 4.9±1.9% of mononuclear cells recovered. SGN-70 treatment also significantly extended the survival of mice bearing disseminated Raji tumors (NHL) compared to control mice. Survival benefit was absent when mice received an Fc-modified antibody deficient in effector functions, confirming that the activity of SGN-70 in these models was dependent upon Fc-FcγR interaction with host immune cells. Together, these data demonstrate that SGN-70 possesses effector cell-mediated antitumor activity and provides rationale for clinical study of SGN-70 in CD70+ hematologic malignancies.

Description: SGN-30, a chimeric monoclonal antibody with apoptotic-signaling activity against CD30-positive malignancies, is currently in Phase II clinical evaluation against anaplastic large cell lymphoma and Hodgkin’s disease (HD). Mechanisms underlying SGN-30’s anti-tumor activity were evaluated using cDNA array analysis of SGN-30-treated L540 HD cells. Changes in expression of growth and apoptotic related genes including cyclin D2 and p21CIP1/WAF1 followed treatment of L540 and L540cy cells with SGN-30. Intra-cellular staining showed increases in both activated caspase-3 and p21CIP1/WAF1 in L540cy. These alterations coincided with increased Annexin V/PI staining. In addition to directly inducing apoptosis, SGN-30 mediated alterations in gene expression and could sensitize cells to standard chemotherapeutics. To evaluate this potential, L540cy cells were treated for 24 h with SGN-30 followed by exposure to a panel of chemotherapeutics commonly used in HD therapy and the combinations quantified by the Combination Effects method. Most of the chemotherapies examined were at least additive or better in combination with SGN-30, with bleomycin producing the strongest synergistic response. In vitro data were confirmed by the significantly increased efficacy of SGN-30 and bleomycin against established L540cy HD tumor xenografts in SCID mice. Results suggest that in addition to direct cell killing, SGN-30 binding to CD30 on HD tumor cells effects both growth arrest and drug sensitization by altering gene expression of cell cycle and apoptotic-related genes. Importantly, tumor cell sensitization to established chemotherapies, in particular DNA damaging agents used to treat HD, suggests that SGN-30 could improve the outcome of current drug-based therapies for treating HD.

Description: CD40 is a TNF receptor family member that is expressed on B cells and by a wide variety of transformed cells including non-Hodgkin’s lymphoma (NHL), multiple myeloma, and various solid tumors. The humanized anti-CD40 antibody, SGN-40, is a partial agonist that induces apoptosis as well as mediates ADCC against CD40+ NHL B cell lines, contributing to in vivo antitumor activity observed in human lymphoma xenograft models. The current study demonstrates the ability of SGN-40 to initiate multiple signaling cascades upon ligation of CD40 on NHL cell lines. SGN-40 was shown to activate the stress-induced p38 MAP kinase and pro-survival pathways including NF-κB, p42/44 MAP kinase and, to a lesser extent, AKT. Consistent with the apoptosis-inducing activity of SGN-40, cleavage of caspase-3 and its downstream substrate poly (ADP-ribose) polymerase was detected in NHL cell lines. SGN-40 signaling was qualitatively similar to that mediated by trimeric recombinant human CD40 ligand (rhCD40L). However, the overall magnitude of signaling was lower with SGN-40 compared to rhCD40L, consistent with the partial agonistic properties of SGN-40. In addition, constitutive phospho-AKT levels, a key pro-survival signal, were found to be very low in most high-grade lymphoma cell lines and primary NHL specimens, in contrast to the high levels reported in carcinomas. Low AKT activity may bias lymphoma cells toward apoptosis in response to SGN-40 signaling. To augment SGN-40-induced cell killing, in vitro combination studies with chemotherapeutics have been performed using the Ramos, RL, and HT NHL lines. We now report that SGN-40 has additive activity when combined with cisplatin, melphalan, or mitoxantrone and is synergistic with bleomycin. Furthermore, in vivo activity of combination therapy has been demonstrated in a subcutaneous Ramos lymphoma xenograft model. While tumor growth was delayed by either CHOP (cyclophosphamide, adriamycin, vincristine, prednisone) or SGN-40 alone, the combination of SGN-40 and CHOP was significantly more active. Our results suggest that SGN-40 can be combined with standard lymphoma therapies resulting in improved therapeutic efficacy, and provide a rationale for combination clinical trials involving SGN-40. The molecular mechanisms through which standard chemotherapeutic agents enhance SGN-40-mediated cell killing in target lymphoma B cells are currently being investigated.

Description: SGN-40 is a humanized antibody targeting CD40, a TNF receptor family member expressed on normal B cells, non-Hodgkin’s lymphoma (NHL), multiple myeloma, and a variety of carcinomas. Previous studies have shown that SGN-40 triggers proapoptotic signal transduction, mediates effector function (ADCC), and has in vivo antitumor activity in CD40+ lymphoma xenograft models. We now report in vivo efficacy data for SGN-40 in combination with the anti-CD20 monoclonal antibody, rituximab, and approved chemotherapy regimens for the treatment of NHL. The growth of subcutaneous Ramos tumors in SCID mice was delayed following SGN-40 or rituximab treatment. However, the combination of SGN-40 + rituximab (S-R) significantly improved efficacy over either antibody alone. SGN-40 was then tested with ICE (ifosfamide, carboplatin, etoposide) chemotherapy with or without rituximab (S-R-ICE and S-ICE). These studies demonstrated that both S-R-ICE and S-ICE treated mice had lower tumor burden than R-ICE or SGN-40 treated animals. Additionally, the effect of SGN-40 in combination with CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) chemotherapy with or without rituximab (S-R-CHOP and S-CHOP) was examined. S-R-CHOP and S-CHOP therapies showed a significant delay in tumor growth compared with R-CHOP or SGN-40 alone. Furthermore, the efficacy observed in S-R-ICE and S-R-CHOP treatments exceeded the S-R combination, suggesting that SGN-40 chemosensitizes lymphoma cells by a signaling mechanism in addition to augmenting ADCC when combined with rituximab. To better understand the chemosensitization effect of SGN-40 in xenograft models, signal transduction events triggered by SGN-40 were examined in vitro. SGN-40 treatment caused the sustained degradation of the BCL-6 protooncogene in several lymphoma cell lines, following prolonged MAP Kinase pathway activation. BCL-6 is implicated in lymphomagenesis of germinal center derived lymphomas, and is proteasomally degraded after phosphorylation by ERK1/2 MAPK. Immunohistochemical analyses of Ramos tumors harvested from mice following treatment with SGN-40 or S-CHOP revealed elevated numbers of apoptotic cells versus untreated tumors. A distinct downregulation of BCL-6 staining in Ramos tumor cells was also observed in SGN-40 and S-CHOP treated animals, correlating with increased cell death. Finally, in some NHL lines SGN-40 upregulated the p53 family member TAp63alpha, a chemo-sensitizing transcription factor capable of inducing apoptosis when overexpressed. When combined with cytotoxic agents, SGN-40 caused a greater induction of TAp63alpha compared with chemotherapy alone, a potential mechanism underlying the improved antitumor activity seen in combination studies. Collectively, these data suggest that SGN-40 signaling occurs at the tumor site, likely contributing directly to tumor cell killing and chemosensitization. These preclinical studies support our earlier work suggesting that addition of SGN-40 to standard therapeutic regimens may improve the outcome for patients with NHL.