Relationship of the CD22 immunotoxin dose and the tumour establishment in a SCID mice model

Fusion toxin BLyS-gelonin inhibits growth of malignant human B cell lines in vitro and in vivo

B lymphocyte stimulator (BLyS) is a member of the TNF superfamily of cytokines. The biological activity of BLyS is mediated by three cell surface receptors: BR3/BAFF-R, TACI and BCMA. The expression of these receptors is highly restricted to B cells, both normal and malignant. A BLyS-gelonin fusion toxin (BLyS-gel) was generated consisting of the recombinant plant-derived toxin gelonin fused to the N-terminus of BLyS and tested against a large and diverse panel of B-NHL cell lines. Interestingly, B-NHL subtypes mantle cell lymphoma (MCL), diffuse large B cell lymphoma (DLBCL) and B cell precursor-acute lymphocytic leukemia (BCP-ALL) were preferentially sensitive to BLyS-gel mediated cytotoxicity, with low picomolar EC₅₀ values. BLyS receptor expression did not guarantee sensitivity to BLyS-gel, even though the construct was internalized by both sensitive and resistant cells. Resistance to BLyS-gel could be overcome by treatment with the endosomotropic drug chloroquine, suggesting BLyS-gel may become trapped within endosomal/lysosomal compartments in resistant cells. BLyS-gel induced cell death was caspase-independent and shown to be at least partially mediated by the “ribotoxic stress response.” This response involves activation of p38 MAPK and JNK/SAPK, and BLyS-gel mediated cytotoxicity was inhibited by the p38/JNK inhibitor SB203580. Finally, BLyS-gel treatment was shown to localize to sites of disease, rapidly reduce tumor burden, and significantly prolong survival in xenograft mouse models of disseminated BCP-ALL, DLBCL, and MCL. Together, these findings suggest BLyS has significant potential as a targeting ligand for the delivery of cytotoxic “payloads” to malignant B cells.

Effect of monensin liposomes on the cytotoxicity of anti-My9-bR immunotoxin

The purpose of the study was to evaluate the utility of monensin liposomes in the enhancement of in-vitro cytotoxicity, apoptosis and in-vivo antitumour activity of anti-My9-bR immunotoxin. Monensin liposomes were prepared and studied for the enhancement of in-vitro cytotoxicity and apoptotic response of anti-My9-bR immunotoxin against both sensitive and resistant human promyelocytic leukemia HL-60 cells by MTS/PES method and acridine orange staining, respectively. Further, the in-vivo cytotoxicity enhancement of anti-My9-bR immunotoxin by monensin liposomes was studied in a survival model of severe combined immunodeficient (SCID) mice bearing intraperitoneal HL-60 tumours. The in-vitro cytotoxicity of anti-My9-bR immunotoxin was enhanced 580 fold and 4.7 fold against sensitive and resistant HL-60 cells, respectively, by monensin liposomes (5 x 10(-8) M). The combination of anti-My9-bR immunotoxin (50ng mL(-1)) with monensin liposomes (5 x 10(-8) M) produced apoptosis in 40% of cells, whereas the apoptotic response was minimal (< 10%) in anti-My9-bR immunotoxin- or monensin liposome (alone)-treated HL-60 (resistant) cells. In SCID mice bearing HL-60 tumours, anti-My9-bR immunotoxin (75 microg kg(-1) administered intravenously every other day for a total of five courses) showed a median survival time of 20 days, which was no different than that of vehicle control- or monensin liposome-treated mice. However, anti-My9-bR immunotoxin (75 microg kg(-1)) in combination with monensin liposomes (4 microg kg(-1) monensin), administered every other day for a total of five courses, was found to prolong the survival of 20% of mice for more than 46 days. Our results indicate that, despite anti-My9-bR immunotoxin being ineffective in the HL-60 tumour model, its combination with monensin liposomes could improve the antitumour response.