The novel calicheamicin-conjugated CD22 antibody inotuzumab ozogamicin (CMC-544) effectively kills primary pediatric acute lymphoblastic leukemia cells

Abstract

We investigated whether the newly developed antibody (Ab) -targeted therapy inotuzumab ozogamicin (CMC-544), consisting of a humanized CD22 Ab linked to calicheamicin, is effective in pediatric primary B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells in vitro, and analyzed which parameters determine its efficacy. CMC-544 induced dose-dependent cell kill in the majority of BCP-ALL cells, although IC 50 values varied substantially (median 4.8 ng/ml, range 0.1-1000 ng/ml at 48 h). The efficacy of CMC-544 was highly dependent on calicheamicin sensitivity and CD22/CMC-544 internalization capacity of BCP-ALL cells, but hardly on basal and renewed CD22 expression. Although CD22 expression was essential for uptake of CMC-544, a repetitive loop of CD22 saturation, CD22/CMC-544 internalization and renewed CD22 expression was not required to achieve intracellular threshold levels of calicheamicin sufficient for efficient CMC-544-induced apoptosis in BCP-ALL cells. This is in contrast to studies with the comparable CD33 immunotoxin gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia (AML) patients, in which complete and prolonged CD33 saturation was required for apoptosis induction. These data suggest that CMC-544 treatment may result in higher response rates in ALL compared with response rates obtained in AML with Mylotarg, and that therefore clinical studies in ALL, preferably with multiple low CMC-544 dosages, are warranted.

A Reevaluation of CD22 Expression in Human Lung Cancer

“…Because of its restriction to the B cell lineage and its rapid internalization following antibody-mediated cross-linking, CD22 is an attractive therapeutic target for treating B cell malignancies and autoimmune diseases involving dysregulated B cells (14–22). …”

“…Over the last two decades, we and others have tested monoclonal antibodies (MAbs) and immunoconjugates directed against CD22 in mouse xenograft models of human B cell lymphomas and leukemias (14–22). In Phase I and II clinical trials in humans, side effects have been tolerable and efficacy has been encouraging (23–28).…”

The Next Generation of Antibody Drug Conjugates

“…13,14 In addition to its consistent expression in B-cell cancers, CD22 is rapidly internalized by endocytosis with a half-life of less than 1 hour upon ligand-or anti-CD22 mAb binding and it is not shed into the extracellular environment. 15,16 All together, these properties make CD22 a good antigen for targeting with ADC therapies. 12 IO differs from the currently approved ADCs (T-DM1 and BV) in at least two ways, First, IO is comprised of an IgG4 mAb containing no effector functions, unlike T-DM1 and BV, which contain IgG1 scaffolds.…”

Efficacy of a CD22-targeted antibody-saporin conjugate in a xenograft model of precursor-B cell acute lymphoblastic leukemia

“…The next generation of antibody-based therapy involves the use of mAbs directly conjugated to potent cytotoxic agents for specific intracellular delivery. In ALL, ADCs have demonstrated remarkable pre-clinical and clinical efficacy and may at some point, obviate the need for systemic chemotherapy or reduce the necessary dose [7][8][9].…”