Objective To analyze and evaluate the characteristics of enzyme kinetics of CTX-M-14 type extended-spectrum β-lactamase(ESBL) with Pro167 residue substitution. Methods By molecular cloning and PCR techniques, CTX-M-14 gene was directionally cloned into plasmid pET28a( + ) from a clinical E. coli isolate and formed an expression vector to transform competent E. coli BL21 (DE3 ). Prol67 residue substitutions of P167G, P167Q, P167S and P167T were introduced to CTX-M-14 by site-directed muta-genesis based on overlap extension PCR with the former recombinant plasmid as PCR template, respectively.The wild-type CTX-M-14, recombinant CTX-M-14 protein and its variants were expressed and purified, then their steady-state kinetic parameters (Kcat, Km and Kcat/Km ) against β-lactam antibiotics were determined.Results The kinetic parameters of wild-type and recombinant CTX-M-14 had no statistically significant differences (P>0.1). The 1/Km, Kcat and Kcat/Km values of P167S variant against ceftazidime were 16-fold, 2.87-fold and 43.6-fold higher than those of recombinant CTX-M-14, respectively, and the Kcat/Km value of P167S variant against penicillin, ampicillin, cefazolin, cefuroxime, ceftriaxone, cefotaxime decreased( < 0.05). Compared with the kinetic parameters of recombinant CTX-M-14, the kinetic parameters of P167T variant against ceftazidime had no significant change, but the Kcat values of P167Q and P167G variants decreased dramatically(P<0.01). Conclusion There was no difference between the enzyme activities of wild-type and recombinant CTX-M-14. P167S variant could not only promote the enzyme affinity of CTX-M-14 to ceftazidime but also improve the conversion rate of enzyme-substrate complex in the ceftazidime hydrolysis. The comparison of the kinetic parameters of CTX-M-14 and its variants with Pro167 residue substitution showed that the increased activity of CTX-M ESBL variants against ceftazidime could not be simply explained with the enlarged cavity in active site that may be caused by the replacement of Pro167 residue by smaller amino acids.

BACKGROUNDThe aim of this research was to investigate the impact of post-transplantation adjuvant chemotherapy in the prevention of tumor recurrence and metastasis for hepatocellular carcinoma (HCC) exceeding Milan criteria after liver transplantation.

METHODSA total of 117 patients with HCC exceeding the Milan criteria who had undergone orthotopic liver transplantation (OLT) from August 2002 to February 2009 were enrolled and retrospectively analyzed. The patients were divided into four groups according to chemotherapy regimens and the impact of different chemotherapy regimens on survival, disease-free survival, and adverse effects were compared.

RESULTSOne year survival rates for the gemicitabine, conventional chemotherapy, oxaliplatin plus capecitabine and the best supportive care (BSC) group were 87.5%, 84.2%, 81.6%, and 67.5%. The 3-year survival rates were 48.1%, 25.9%, 31.6%, and 33.7%, respectively for the four groups. One year disease free survival rates for the four groups were 69.8%, 47.4%, 53.8%, and 45.7% respectively. And 3-year disease free survival rates were 43.2%, 23.7%, 23.6%, and 25.1% for the four groups. Stratification analysis showed that the gemcitabine regimen and conventional chemotherapy could significantly improve the survival rate and disease free survival rate for HCC patients who had major vascular invasion and/or microvascular invasion after liver transplantation compared with BSC group.

CONCLUSIONSFor HCC patients beyond Milan criteria, especially who had vascular invasion and/or micorvascular invasion, post-transplantation adjuvant chemotherapy can significantly improve survival. Gemcitabine is a proper regimen for postoperative adjuvant chemotherapy. Conventional chemotherapy can also benefit patients, but the adverse effects are not satisfactory.

Antineoplastic Agents ; adverse effects ; therapeutic use ; Carcinoma, Hepatocellular ; drug therapy ; surgery ; Chemotherapy, Adjuvant ; methods ; Deoxycytidine ; adverse effects ; analogs & derivatives ; therapeutic use ; Doxorubicin ; adverse effects ; therapeutic use ; Female ; Humans ; Liver Neoplasms ; drug therapy ; surgery ; Liver Transplantation ; Male