Pharmacodynamic effects of administration of maytansine conjugated anti-CD22 monoclonal antibodies to cynomolgus monkeys

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Antibody-based B-cell specific therapeutic approaches have revolutionized the treatment of non-Hodgkin's lymphomas (NHL) as well as other hematological malignancies. However, a large variability in clinical response has been observed, and the need to develop effective new treatments remains urgent. A promising approach is the use of antibody-drug conjugates (ADCs), cytotoxic drugs covalently linked to antibodies through specialized chemical linkers for the treatment of NHL. CMC-544, an antibody to a B-cell specific glycoprotein CD22 conjugated to the cytotoxin calicheamicin, has shown clinical activity in patients. In addition, antibodies directed to B-cell targets such as rituximab and epratuzumab are in clinical trials for the treatment of NHL and autoimmune disorders. We have generated10F4v3, an anti-CD22 antibody conjugated to the antimitotic agent maytansine (10F4v3-DM1). DM1 disrupts cellular mitosis through inhibition of tubulin polymerization when internalized into cells. The anti-CD22 DM1 conjugate was shown to have significant potency in preclinical efficacy models of NHL. In order to further characterize this antibody-drug conjugate in preclinical studies, we first evaluated the binding characteristics of the 10F4v3 to peripheral blood B-cells from various geographical sources of cynomolgus monkeys. 10F4v3 bound to peripheral blood B-cells from all cynomolgus monkeys of Indonesian and Mauritian origins, but displayed only limited binding to cynomolgus monkeys of Chinese and Cambodian origins. Therefore, further preclinical evaluation of 10F4v3-DM1 was conducted in Indonesian cynomolgus monkeys to examine the safety, pharmacokinetic, and pharmacodynamic effects in monkeys. B-cells and B-cell subsets were depleted in peripheral blood and lymphoid tissue (spleen, bone marrow) at all doses, with no apparent dose-dependent effects or substantial safety limitations. Based on the nonclinical data, 10F4v3-DM1 exhibits an encouraging pharmacodynamic profile for the potential treatment of non-Hodgkin's lymphoma.

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Evaluation of a gene signature to predict single agent dacetuzumab (SGN-40) activity in patients with DLBCL

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Background: Dacetuzumab (SGN-40) is a humanized IgG1 monoclonal antibody that binds to CD40, mediates effector cell functions, and activates downstream apoptosis signaling pathways. Dacetuzumab has shown single-agent activity in relapsed/refractory DLBCL in phase I and phase II trials, with multiple objective responses and 1/3 of patients demonstrating tumor shrinkage, defined as a decrease in tumor volume (SPD) of at least 10%. We previously reported a 14-gene signature (ASH 2008 #1593) that was strongly associated with dacetuzumab sensitivity in DLBCL cell lines. Here, we report an initial evaluation of the gene signature as a classifier of patients likely to demonstrate tumor shrinkage after dacetuzumab therapy. Methods: The original 14 microarray probes were chosen for high correlation with in vitro dacetuzumab sensitivity (IC25) in 31 NHL cell line models. Matching qRT-PCR probes were developed and confirmed to correlate with the microarray probes in paired cell line samples. In this retrospective analysis, archived paraffin blocks from a 26 patient subset of the phase I and II trials, with a diagnosis of DLBCL and available tumor measurements, were assayed by qRT-PCR. Results: Overall, 42% of patients (11/26) exhibited decreased SPD of at least 10%. Of those who were marker +, 10 out of 13 (78%) had 10% or better decreases in SPD, whereas only 1 of 13 patients who were marker - demonstrated tumor shrinkage (8%). The overall accuracy for predicting tumor shrinkage was 85% (one-sided P=0.002, by permutation test). Among the 14 genes contributing to the multivariate signature, CD22 and VNN2 were the most strongly down-regulated in specimens from patients without at least a 10% decrease in SPD (P=0.14 and P=0.10, respectively), while IGF1R and CTSC were the most strongly up-regulated (P=0.05 and P=0.08, respectively). Conclusions: A 14-gene signature appears to predict tumor shrinkage in DLBCL patients receiving dacetuzumab in single-agent clinical trials (P=0.002). A larger clinical data set will be analyzed to further evaluate the correlation of this gene signature with objective clinical response rates..

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Human semaphorin K1 is glycosylphosphatidylinositol-linked and defines a new subfamily of viral-related semaphorins

The semaphorin family contains a large number of secreted and transmembrane proteins, some of which are known to act as repulsive axon guidance cues during development or to be involved in immune function. We report here on the identification of semaphorin K1 (sema K1), the first semaphorin known to be associated with cell surfaces via a glycosylphosphatidylinositol linkage. Sema K1 is highly homologous to a viral semaphorin and can interact with specific immune cells, suggesting that like its viral counterpart, sema K1 could play an important role in regulating immune function. Sema K1 does not bind to neuropilin-1 or neuropilin-2, the two receptors implicated in mediating the repulsive action of several secreted semaphorins, and thus it likely acts through a novel receptor. In contrast to most previously described semaphorins, sema K1 is only weakly expressed during development but is present at high levels in postnatal and adult tissues, particularly brain and spinal cord.

Hepatocyte growth factor/scatter factor is an axonal chemoattractant and a neurotrophic factor for spinal motor neurons

In the embryonic nervous system, developing axons can be guided to their targets by diffusible factors secreted by their intermediate and final cellular targets. To date only one family of chemoattractants for developing axons has been identified. Grafting and ablation experiments in fish, amphibians, and birds have suggested that spinal motor axons are guided to their targets in the limb in part by a succession of chemoattractants made by the sclerotome and by the limb mesenchyme, two intermediate targets that these axons encounter en route to their target muscles. Here we identify the limb mesenchyme-derived chemoattractant as hepatocyte growth factor/scatter factor (HGF/SF), a diffusible ligand for the c-Met receptor tyrosine kinase, and we also implicate HGF/SF at later stages as a muscle-derived survival factor for motoneurons. These results indicate that, in addition to functioning as a mitogen, a motogen, and a morphogen in nonneural systems, HGF/SF can function as a guidance and survival factor in the developing nervous system.

Physical linkage of a human immunoglobulin heavy chain variable region gene segment to diversity and joining region elements

Antibody genes are assembled from a series of germ-line gene segments that are juxtaposed during the maturation of B lymphocytes. Although diversification of the adult antibody repertoire results in large part from the combinatorial joining of these gene segments, a restricted set of antibody heavy chain variable (VH), diversity (DH), and joining (JH) region gene segments appears preferentially in the human fetal repertoire. We report here that one of these early-expressed VH elements (termed VH6) is the most 3' VH gene segment, positioned 77 kilobases on the 5' side of the JH locus and immediately adjacent to a set of previously described DH sequences. In addition to providing a physical map linking human VH, DH, and JH elements, these results support the view that the programmed development of the antibody VH repertoire is determined in part by the chromosomal position of these gene segments.