Heparin binding epidermal growth factor like growth factor (HB) is a promising target for human cancer therapy.

Abstract

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[Introduction]We have demonstrated that HB plays a pivotal role in tumorgenicity in ovarian cancer. To explore the possibility that HB can be recognized as a target molecule for other cancers, we investigated the primacy of HB expression among EGFR ligands and antitumor effects of a specific inhibitor against HB, CRM197, on nude mice in a variety of human cancer cells.[Method]Human Ovarian cancer (5 cell lines), cervical adenocarcinoma (2 cell lines), endometrial cancer (3 cell lines), breast cancer (4 cell lines),gastric cancer (2 cell lines), lung cancer (5 cell lines), and malignant melanoma (3 cell lines) were used. Each mRNA expression level of seven EGFR ligands, including HB, EGF, amphiregulin, TGF alpha, epiregulin, betacellulin, epigen, EGFR, and GAPDH was examined by real-time quantitative PCR. To determine the mRNA expression levels of EGFR ligands and EGFR, we used the mRNA expression index (EI), which is a relative mRNA expression level standardized by GAPDH. The mRNA EI was calculated as follows: mRNA EI = (copy numbers of each EGFR ligand or EGFR mRNA/copy numbers of GAPDH mRNA) × 10⁵ arbitrary units. To assess the antitumor effect of CRM 197, CRM 197 was injected intraperitoneally into tumor-bearing mice every week (50mg/kg/week ), when each human cancer cell (5×10⁶cells) was subcutaneously inoculated on nude mice at 5 weeks of age and each tumor volume was over 70 mm³. Each tumor volume was estimated from two dimensional tumor measurements,tumor volume(mm³) = length ×width²/2. The values for each EGFR ligands and tumor volume were analyzed using Mann-Whitney U test. P<0.05 was considered statistically significant.[Result]Expression indices of HB showed more than 5∼10 times, compared with the expression of other EGFR ligands in all the cells except for lung cancer cells. The predominant expression of EGFR ligand in common was not found only in lung cancer cells. However, the second highest expressed molecule among EGFR ligands was not always identical in all the cancer cells. Expression of EGFR was detected in all the cancer cells. In 3 cell lines of ovarian cancers, one cell line of breast cancer, 3 cell lines of gastric cancer, and one cell line of malignant melanoma, a tumor formation was confirmed on nude mice after inoculation of cells. In the administration of CRM197, the tumor volume on treated mice was significantly reduced, compared to that on untreated mice in ovarian (3 cell lines), breast (one cell line), gastric (3 cell lines) cancer, and malignant melanoma (one cell line). However, there was no significant difference in the tumor volume between the treatment and untreatment of CRM197 in both lung cancer cells. Taken together, these results suggested that HB may be involved in tumor formation of many human cancers.[Conclusion]HB is recognized as a promising target molecule for a variety of human cancers, and CRM 197 is a possibly useful tool for cancer therapy.