Antitumor activity of L-asparaginase from Erwinia carotovora against different human and animal leukemic and solid tumor cell lines

The dose- and time-dependent antitumor and cytotoxic effects of L-asparaginases from Erwinia carotovora (ECAR LANS) and Escherichia coli (MEDAC) have been investigated using human leukemic cells and human and animal solid tumor cells. These included human T-cell acute lymphoblastic leukemia cell lines (Jurkat, Jurkat/A4, Molt-4), human chronic myeloid leukemia K562 cells, human promyelocytic leukemia HL-60, and also human solid tumor cells (prostate carcinoma LnCap, breast adenocarcinoma MCF7, ovarian adenocarcinoma SCOV-3 and carcinoma CaOV, hepatocarcinoma Hep G2, fibrosarcoma HT-1080) and animal solid tumor cells (rat Gasser’s ganglion neurinoma cells GGNC-1, mouse glioblastoma EPNT-5). We investigated sensitivity of tumor cells (seeded at different density) to L-asparaginases, as well the effect of L-asparaginases on cell growth rate, protein and DNA synthesis in the presence of various cytostatics. Cell cycle analysis by flow cytofluorimetry and detection of apoptotic cells before and after treatment with L-asparaginases indicate that ECAR LANS L-asparaginase suppressed growth of all tested solid tumor cells. Evaluation of leukemic cell number after treatment with L-asparaginases for 24, 48 and 72 h demonstrated that asparagine deficiency did not kill cells but stopped normal cell division. The cytofluorometric study of solid and leukemic cells revealed that except HL-60 cells the treatment with L-asparaginase for 72 h did not change cell cycle phase distribution and did not increase the number of apoptotic cells. Combined treatment of cells using a combination of L-asparaginase and doxorubicin significantly increased the number of apoptotic cells up to 60% (MCF-7 cells), 40% (Jurkat cells) and even 99% (HL-60). High levels of DNA and protein synthesis rates in asparaginase-treated tumor cells suggest lack of massive entry of tumor cells to apoptosis. This conclusion is based on the fact of sensitivity of multi-resistant Jurkat/A4 cells to L-asparaginases (it is nearly impossible to induce apoptosis in these cells). Since ECAR LANS did not influence growth of normal human fibroblasts it appears that the enzyme cytotoxicity is associated only asparagine deficiency.