title: Purification and Characterization of Glutaminase Free Asparaginase from Enterobacter cloacae: In-Vitro Evaluation of Cytotoxic Potential against Human Myeloid Leukemia HL-60 Cells.
abstract: Asparaginase is an important antileukemic agent extensively used worldwide but the intrinsic glutaminase activity of this enzymatic drug is responsible for serious life threatening side effects. Hence, glutaminase free asparaginase is much needed for upgradation of therapeutic index of asparaginase therapy. In the present study, glutaminase free asparaginase produced from Enterobacter cloacae was purified to apparent homogeneity. The purified enzyme was found to be homodimer of approximately 106 kDa with monomeric size of approximately 52 kDa and pI 4.5. Purified enzyme showed optimum activity between pH 7-8 and temperature 35-40°C, which is close to the internal environment of human body. Monovalent cations such as Na+ and K+ enhanced asparaginase activity whereas divalent and trivalent cations, Ca2+, Mg2+, Zn2+, Mn2+, and Fe3+ inhibited the enzyme activity. Kinetic parameters Km, Vmax and Kcat of purified enzyme were found to be 1.58×10-3 M, 2.22 IU μg-1 and 5.3 × 104 S-1, respectively. Purified enzyme showed prolonged in vitro serum (T1/2 = ~ 39 h) and trypsin (T1/2 = ~ 32 min) half life, which is therapeutically remarkable feature. The cytotoxic activity of enzyme was examined against a panel of human cancer cell lines, HL-60, MOLT-4, MDA-MB-231 and T47D, and highest cytotoxicity observed against HL-60 cells (IC50 ~ 3.1 IU ml-1), which was comparable to commercial asparaginase. Cell and nuclear morphological studies of HL-60 cells showed that on treatment with purified asparaginase symptoms of apoptosis were increased in dose dependent manner. Cell cycle progression analysis indicates that enzyme induces apoptosis by cell cycle arrest in G0/G1 phase. Mitochondrial membrane potential loss showed that enzyme also triggers the mitochondrial pathway of apoptosis. Furthermore, the enzyme was found to be nontoxic for human noncancerous cells FR-2 and nonhemolytic for human erythrocytes.
authors.affiliation: Bacteriology Laboratory, Department of P. G. Studies and Research in Biological Science, Rani Durgavati University, Jabalpur, Madhya Pradesh, India.
authors.forename: Islam
authors.initials: I
authors.lastname: Husain
authors.affiliation: Bacteriology Laboratory, Department of P. G. Studies and Research in Biological Science, Rani Durgavati University, Jabalpur, Madhya Pradesh, India.
authors.forename: Anjana
authors.initials: A
authors.lastname: Sharma
authors.affiliation: Cancer Pharmacology Division, Indian Institute of Integrative Medicine, Jammu, India.
authors.forename: Suresh
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Cancer Pharmacology Division, Indian Institute of Integrative Medicine, Jammu, India.
authors.forename: Fayaz
authors.initials: F
authors.lastname: Malik
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001215:Asparaginase / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D016972:Enterobacter cloacae / Q000201:enzymology*; D004789:Enzyme Activation; D004795:Enzyme Stability; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D018922:HL-60 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008970:Molecular Weight; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D000970:Antineoplastic Agents; D001426:Bacterial Proteins; D001215:Asparaginase