A sensitive double antibodies sandwich ELISA for the diagnosis and therapeutic evaluation of cervical cancer.

Background: Vascular endothelial growth factor (VEGF) is a highly specific factor for tumors growth. However, the study on the mechanism of VEGF in cervical cancer, and the correlation between the expression level of VEGF and the therapeutic evaluation, prognosis of cervical cancer is not clear till now.

Methods: In this study, RT-qPCR and IHC were used to evaluate the abnormal expression of VEGF in cervical cancer. The survival plots of the VEGF expression related to OS were observed by using the KM plotter. The mAbs against VEGF were screened and identified by ELISA addicted test, indirect ELISA, Western-blot, and dot-ELISA. We designed and prepared the overlapping truncations (V1, V2, V3) of VEGF to identify the B cell epitopes. Then, the epitopes recognized by anti-VEGF mAbs were mapped and displayed on a 3D structure of VEGF by using the PyMOL software. The highly specific and sensitive sandwich ELISA was established to detect the total VEGF quantification in 206 clinical sera samples, thus to evaluate the changes of VEGF before and after chemoradiotherapy in cervical cancer patients.

Results: The VEGF was high expressed in cervical cancer tissues and cells, resulting a poor prognosis of cervical cancer. The mAbs 2E5 and 6D9 were selected with the titer of 1:256000 and 1:128000 respectively. The mAbs both had strong ability to combine with VEGF protein within 15 min and were identified as subclass IgG1 with κ-type light chains. 2E5 bound to V1 and V2, recognizing the N-terminal (1-121 aa) of VEGF, however 6D9 bound to V3, recognizing the C-terminal (116-174 aa) of VEGF. The 206 clinical samples were tested with the established VEGF-DAS-ELISA and calculated according to the equation (y = 0.0042088× + 0.105109, R = 0.998). The results indicated that the expression levels of VEGF in cervical cancer samples were positively higher than those in normal samples. Importantly, we found the expression level of sera VEGF in cervical cancer patients decreased significantly after chemoradiotherapy. Therefore, the variable of VEGF levels in cervical cancer patients before and after treatment can be used as a new indicator of efficacy evaluation to guide the clinical treatment of cervical cancer.

Conclusion: A sensitive DAS-ELISA was established successfully, using which we can track the VEGF to evaluate the efficacy and estimate prognosis of cervical cancer. It is helpful for the diagnosis, therapeutic evaluation and prognosis of cervical cancer.