Prognostic value of TrkA protein detection by monoclonal antibody 5C3 in neuroblastoma

The effects of nerve growth factor, a neurotrophin mediating growth and differentiation of neural crest-derived cells, are mediated by the receptor TrkA. TrkA mRNA expression has been associated with a good prognosis in human neuroblastoma (NB). We describe the use of monoclonal antibody 5C3 in detecting TrkA expression by immunohistochemistry in NB and other malignant tumors. A murine anti-TrkA IgG1 monoclonal antibody, 5C3, was generated against the extracellular domain of human p140(TrkA). 5C3 detected a 140-kDa band on Western blots. 5C3 was optimized for immunostaining and used to detect p140(TrkA) on 113 frozen NB samples and 42 samples from nine other malignancies. MOPC21 IgG1 antibody was used as a control. Results by immunohistochemistry were compared to TrkA expression assessed by reverse transcription-PCR and Western analysis. The prognostic value of TrkA expression by these methods was evaluated and compared to other known prognostic variables, including stage, age, and MYCN copy number. TrkA expression was detected by immunohistochemistry in 73 of the 113 NB tumor specimens and strongly correlated with nonmetastatic disease. TrkA expression was specific for NB among small round blue cell tumors. Both TrkA expression by immunohistochemistry and localized/4s disease correlated with survival. Tumors from 55 of 60 patients with localized/4s NB exhibited homogeneous or a mixed pattern of TrkA immunohistochemistry, whereas only 18 of 53 patients with stage 4 NB were immunoreactive. Detection of TrkA by reverse transcription-PCR and Western analysis was much more sensitive and no longer correlated with survival. 5C3 enables rapid detection of p140(TrkA) by immuno-histochemistry and identifies patients more likely to have localized NB with a favorable clinical outcome. Lack of TrkA expression is correlated with metastatic, malignant NB. A subset of patients with NB, however, died of aggressive metastatic disease despite TrkA expression. As a mimic of nerve growth factor, 5C3 may be useful in the study of TrkA-expressing tumors.