Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk

Abstract

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to a toxin, gemtuzumab ozogamicin (GO), is used for the treatment of AML (Mylotarg). Therefore, we investigated whether the response of AML cells to GO treatment also depends on Syk expression. Forty primary AML samples (25 Syk-positive and 15 Syk-negative) were tested for their response to the anti-proliferative effects of GO and unmodified anti-CD33 mAb. A correlation between Syk expression and the response of leukemia cells to GO and anti-CD33 mAb was found. 'Blocking' of Syk by small interfering RNA resulted in unresponsiveness of AML cells to both GO and anti-CD33 mAb-mediated cytotoxicity. Syk upregulation by the demethylating agent 5-azacytidine (5-aza) induced re-expression of Syk in some cases, resulting in enhanced GO and anti-CD33-mediated inhibition of leukemia cell growth. Thus, the cytotoxicity of both GO and anti-CD33 in primary AML samples was associated with Syk expression. 5-Aza restored Syk and increased the sensitivity of originally Syk-negative, non-responsive cells to CD33 ligation to levels of Syk-positive cells. These data have clinical significance for predicting response to GO and designing clinical trials.

Analysis of factors that affect in vitro chemosensitivity of leukaemic stem and progenitor cells to gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukaemia

“…33 Likewise, there is the potential of combining Mylotarg with CD33 modulators and assessing which patients may (or not) benefit from such a regimen. For example, the hypomethylating agent 5-azacytidine is known to increase CD33 expression sensitizing cells to Mylotarg treatment, 34 and our laboratory data strongly support the use of 5-azacytidine in combination with Mylotarg to achieve better cell kill. 35 The result of multivariate analysis suggests that LSPC burden and FLT3 status are the main predictors of Mylotarg response in our cohort of patients.…”

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

“…This is in contrast to GO, where expression of the protein kinase Syk was essential for efficacy of GO in AML cells, suggesting that CD33 signaling contributed to GO-induced cell death. 36 For future clinical trials with CMC-544, preferably CD22-positive patients should be included, but our data suggest that the level of CD22 expression does not need to be taken into account (although high CD22 expression on ALL cells will enhance/facilitate CMC-544-induced cell death). However, given the CD22-independent uptake of CMC-544, it may be interesting to evaluate the in vivo efficacy of CMC-544 in CD22-negative ALL patients as well.…”

Syk Interacts with and Phosphorylates Nucleolin To Stabilize Bcl-xL mRNA and Promote Cell Survival

“…In certain malignancies of B-cell origin, it is tonic signaling from the BCR that is proposed to activate Syk to promote cell survival (4,7,8). Interestingly, the repertoire of cells in which Syk functions as a prosurvival factor extends to tumors of B-cell origin that have not yet rearranged immunoglobulin genes, hematological malignancies not of B-cell origin, and nonhematological cancers, such as retinoblastoma and certain carcinomas of the lung and pancreas (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Whether ITAM-bearing receptors other than the BCR are involved in sending tonic signals via Syk in these cell types is as yet unclear.…”

“…Constitutively active Syk has been reported to promote the survival of non-Hodgkin's lymphoma, acute lymphoblastic leukemia, chronic lymphocytic leukemia, and Epstein-Barr virus-associated B-cell lymphoma (3)(4)(5)(6)(7)(8)(9)(10)(11). The inhibition of Syk also promotes the differentiation of acute myeloid leukemia (AML) and attenuates the growth of AML cell lines and primary blasts (12,13). The formation of a Tel-Syk fusion protein that results from a chromosomal translocation results in a myeloid proliferative disorder, while Itk-Syk fusion proteins are found in some T-cell lymphomas (14,15).…”