Preclinical characterization of SGN-70, a humanized antibody directed against CD70.

PURPOSE: CD70 (CD27L) is a member of the tumor necrosis factor family aberrantly expressed on a number of hematologic malignancies and some carcinomas. CD70 expression on malignant cells coupled with its highly restricted expression on normal cells makes CD70 an attractive target for monoclonal antibody (mAb)-based therapies. We developed a humanized anti-CD70 antibody, SGN-70, and herein describe the antitumor activities of this mAb. EXPERIMENTAL DESIGN: CD70 expression on primary tumors was evaluated by immunohistochemical staining of Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma, and renal cell carcinoma tissue microarrays. The CD70-binding and cytotoxic activities of SGN-70 were tested in vitro using a number of cell-based assays. The in vivo antitumor properties of SGN-70 were tested in severe combined immunodeficient mice bearing disseminated lymphoma and multiple myeloma xenografts. Mechanism-of-action studies were conducted using SGN-70v, a variant mAb with equivalent target-binding activity but impaired Fcgamma receptor binding compared with SGN-70. RESULTS: Immunohistochemical analysis identified CD70 expression on approximately 40% of multiple myeloma isolates and confirmed CD70 expression on a high percentage of Hodgkin lymphoma Reed-Sternberg cells, non-Hodgkin lymphoma, and renal cell carcinoma tumors. SGN-70 lysed CD70+ tumor cells via Fc-dependent functions, including antibody-dependent cellular cytotoxicity and phagocytosis and complement fixation. In vivo, SGN-70 treatment significantly decreased tumor burden and prolonged survival of tumor-bearing mice. CONCLUSIONS: SGN-70 is a novel humanized IgG1 mAb undergoing clinical development for the treatment of CD70+ cancers. SGN-70 possesses Fc-dependent antibody effector functions and mediates antitumor activity in vivo.

Novel peptide linkers for highly potent antibody-auristatin conjugate.

Auristatins are highly potent antimitotic agents that have received considerable attention because of their activities when targeted to tumor cells in the form of antibody-drug conjugates (ADCs). Our lead agent, SGN-35, consists of the cAC10 antibody linked to the N-terminal amino acid of monomethylauristatin E (MMAE) via a valine-citrulline p-aminobenzylcarbamate (val-cit-PABC) linker that is cleaved by intracellular proteases such as cathepsin B. More recently, we developed an auristatin F (AF) derivative monomethylauristatin F (MMAF), which unlike MMAE contains the amino acid phenylalanine at the C-terminal position. Because of the negatively charged C-terminal residue, the potency of AF and MMAF is impaired. However, their ability to kill target cells is greatly enhanced through facilitated cellular uptake by internalizing mAbs. Here, we explore the effects of linker technology on AF-based ADC potency, activity, and tolerability by generating a diverse set of dipeptide linkers between the C-terminal residue and the mAb carrier. The resulting ADCs differed widely in activity, with some having significantly improved therapeutic indices compared to the original mAb-Val-Cit-PABC-MMAF conjugate. The therapeutic index was increased yet further by generating dipeptide-based ADCs utilizing new auristatins with methionine or tryptophan as the C-terminal drug residue. These results demonstrate that manipulation of the C-terminal peptide sequence used to attach auristatins to the mAb carrier can lead to highly potent and specific conjugates with greatly improved therapeutic windows.

Anti-leukemic activity of lintuzumab (SGN-33) in preclinical models of acute myeloid leukemia.

Despite therapeutic advances, the long-term survival rates for acute myeloid leukemia (AML) are estimated to be 10% or less, pointing to the need for better treatment options. AML cells express the myeloid marker CD33, making it amenable to CD33-targeted therapy. Thus, the in vitro and in vivo anti-tumor activities of lintuzumab (SGN-33), a humanized monoclonal anti-CD33 antibody undergoing clinical evaluation, were investigated. In vitro assays were used to assess the ability of lintuzumab to mediate effector functions and to decrease the production of growth factors from AML cells. SCID mice models of disseminated AML with the multi-drug resistance (MDR)-negative HL60 and the MDR(+), HEL9217 and TF1-alpha, cell lines were developed and applied to examine the in vivo antitumor activity. In vitro, lintuzumab significantly reduced the production of TNFalpha-induced pro-inflammatory cytokines and chemokines by AML cells. Lintuzumab promoted tumor cell killing through antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) activities against MDR(-) and MDR(+) AML cell lines and primary AML patient samples. At doses from 3 to 30 mg/kg, lintuzumab significantly enhanced survival and reduced tumor burden in vivo, regardless of MDR status. Survival of the mice was dependent upon the activity of resident macrophages and neutrophils. The results suggest that lintuzumab may exert its therapeutic effects by modulating the cytokine milieu in the tumor microenvironment and through effector mediated cell killing. Given that lintuzumab induced meaningful responses in a phase 1 clinical trial, the preclinical antitumor activities defined in this study may underlie its observed therapeutic efficacy in AML patients.