Single-chain antibody against the common epitope of mutant p53: isolation and intracytosolic expression in mammalian cells

p53 as a target for anti-cancer drug development

Loss of p53 function compromises genetic homeostasis in cells exhibiting deregulated DNA replication and/or DNA damage, and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Progress has recently been made in the clinical use of replication-deficient virus carrying wt-TP53 (Ad5CMV-p53) and/or cancer-selective oncolytic adenoviruses (ONYX-015). These strategies demonstrated clinical activity as monotherapy and were synergistic with traditional chemotherapy agents in the treatment of some types of cancer. In addition, pharmacological methods are under development to either stimulate wild-type p53 protein function, or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3) or single-chain Fv antibody fragments corresponding to defined p53 domains. Here, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

Single chain antibody against the common epitope of mutant p53 restores wild-type activity to mutant p53 protein

Here, we describe the biological activity of ME1, a mouse single chain Fv fragment (scFv) against the common epitope of mutant p53, which is efficiently expressed in mammalian cells. We found that in vivo interaction of the conformational p53 mutant R175H protein with the scFv resulted in the acquisition of wild-type p53 characteristics, manifested in trans-activation of p21, as well as induction of apoptosis. Moreover, antibody binding leads to abrogation of the mutant p53 mediated "gain of function" as estimated by downregulation of EGR-1, a transcriptional target of mutant p53. These findings suggest that the scFv restores wild-type properties to mutant p53.

The tumor suppressor gene TP53: implications for cancer management and therapy

The p53 protein is an inducible transcription factor with multiple anti-proliferative roles in response to genotoxic damage; unprogrammed proliferative stimuli; and deprivation of oxygen, nutrients, or ribonucleotides. Inactivation of the TP53 gene by mutation or deletion is the most common event in human cancer. Loss of p53 function compromises genetic homeostasis in cells exposed to mutagens and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Genetic interventions aiming at expressing wild-type TP53 in cancer cells, either by retroviral or adenoviral transfer, have met limited clinical success. However, recently, the use of a defective adenovirus (ONYX-015) that selectively kills p53-incompetent cells has shown promising effects in pre-clinical and clinical studies. Pharmacological methods are under development to either stimulate wild-type p53 protein function or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3), or single-chain Fv antibody fragments corresponding to defined p53 domains. In addition, detection of mutant TP53 may also serve as a marker for early cancer detection, prediction, and prognosis. In this review, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

Expression and identification of recombinant soluble single-chain variable fragment of monoclonal antibody MC3

AIM: To generate soluble single chain variable fragments (ScFv) of monoclonal antibody MC3 recognizing colorectal and gastric carcinomas.

METHODS: mRNA was isolated from the hybridoma cell line producing MC3 and the DNAs encoding variable domains of heavy and light chains (VH and VL) of the antibody were amplified separately by RT-PCR and assembled into ScFv DNA with a linker DNA.The ScFv DNA was ligated into the phagemid vector pCANTAB5E and the ligated sample was transformed into E. coli TG1.The transformed cells were infected with M13KO7 helper phage to yield recombinant phages. After two rounds of panning with gastric carcinoma cell line AGS highly expressing MC3-binding antigen, the phage clones displaying ScFv fragments of the antibody were selected by ELISA. 4 phage clones showing strong signal in ELISA were used to infect E. coli HB2151 to express soluble ScFvs. The soluble ScFvs were identified by Dot blot and Western blot, and their antigen-binding activity was assayed by ELISA. The VH and VL DNAs of the ScFv DNA derived from phage clone 19 were sequenced.

RESULTS: The VH, VL and ScFv DNAs were about 340 bp, 320 bp and 750 bp respectively. After two rounds of panning to the recombinant phages, 18 antigen-positive phage clones were selected from 30 preselected phage clones by ELISA. All the soluble ScFvs derived from the 4 out of the 18 antigen-positive phage clones were about M_r32000 and concentrated in periplasmatic space under the given culture condition. The soluble ScFvs could bind the antigen, and they shared the same binding site with MC3. The sequences of the VH and VL DNAs of the MC3 ScFv showed that the variable antibody genes belonged to the IgG1 subgroup, κ-type.

CONCLUSION: The soluble ScFv of MC3 is successfully produced, which not only provides a possible novel targeting vehicle for in vivo and in vitro study on associated cancers, but also offers the anuibody a stable genetic source.