Epidermal growth factor receptor expression affects the efficacy of the combined application of saponin and a targeted toxin on human cervical carcinoma cells.

Cervical cancer is the second most common cancer in women worldwide. Targeting the epidermal growth factor receptor (EGFR) is a very promising approach since it is overexpressed in about 90% of cervical tumors. Here, we quantified the toxic effect of SE, a targeted toxin consisting of epidermal growth factor (EGF) as targeting moiety and the plant toxin saporin-3, on 3 common human cervical carcinoma cell lines (HeLa, CaSki and SiHa) and recently established lines (PHCC1 and PHCC2) from 2 different individuals. A human melanocytic and a mouse cell line served as negative control. Additionally, we combined SE with saponinum album, a saponin composite from Gypsophila paniculata, which exhibited synergistic properties in previous studies. The cell lines, except for SiHa cells, revealed high sensitivity to SE with 50% cell survival in the range of 5-24.5 nM. The combination with saponin resulted in a remarkable enhancement of cytotoxicity with enhancement factors ranging from 9,000-fold to 2,500,000-fold. The cytotoxicity of SE was clearly target receptor specific since free EGF blocks the effect and saporin-3 alone was considerably less toxic. For all cervical carcinoma cell lines, we evinced a clear correlation between EGFR expression and SE sensitivity. Our data indicate a potential use of targeted toxins for the treatment of cervical cancer. In particular, the combination with saponins is a promising approach since efficacy is drastically improved.

A lysine-free mutant of epidermal growth factor as targeting moiety of a targeted toxin.

AIMS: Elevated levels of epidermal growth factor (EGF) receptor are observed on several human tumors, e.g. cervical carcinoma and mamma carcinomas. The natural ligand EGF is an alternative to established antibodies and tyrosine kinase inhibitors for targeting EGF receptor-overexpressing tumor cells for therapy. Conjugations of compounds to EGF lack the necessary homogeneity for an intended application, since several amino acids may react with the chemical linker. MAIN METHODS: We designed an EGF variant (EGF(RR)) in which the two lysines were substituted with arginine (K28R and K48R). EGF(RR) was fused to the protein toxin saporin to obtain a model protein for detailed analyses on EGF receptor binding and on both the enzymatic activity of saporin and the cytotoxicity of the fusion protein. KEY FINDINGS: The mutation decreased the enzymatic activity of saporin 2.3-fold and the binding of EGF(RR) retained its specificity for EGF receptor while increasing the Kd 5.5-fold. In spite of these differences the cytotoxicity of the fusion protein was unchanged in comparison to a fusion protein with EGF both when applied alone and in combination with cytotoxicity augmenting saponin. SIGNIFICANCE: We conclude that EGF(RR) retained its ability to bind with high specificity to EGF receptor and is thus suitable for a number of chemical linkage applications such as targeting drugs or dyes to EGF receptor-expressing cells.