EGF-SubA Is Cytotoxic to Laryngeal SCC Cells

Abstract

Objective: 1) Examine the effect and mechanism of action of EGF-SubA on laryngeal (LSCC) cells. EGF-SubA is a novel cytotoxic drug that promotes cleavage of GRP-78, a key component of the unfolded protein response. 2) Examine the interaction of EGF-SubA with clinically relevant modalities: cisplatin and gamma radiation in LSCC cells.

Method: In vitro cytotoxicity was determined for a panel of 7 LSCC lines of varying p53 status using MTT assays. For studies of EGF-SubA combined with cisplatin or gamma radiation, apoptosis was also determined by flow cytometry. Clonogenic assays were used to determine the effect of combining EGF-SubA with gamma radiation.

Results: EGF-SubA is cytotoxic to LSCC (laryngeal squamous cell carcinoma) cells at picoMolar concentrations, regardless of p53 status in lines derived from primary tumor sites and from metastases. The cytotoxic effects of EGF-SubA are not rapid and do not depend upon apoptosis. EGF-SubA acted as a radiosensitizing agent when used in combination with gamma radiation producing a 30% reduction in the surviving fraction at 2Gy. Furthermore, EGF-SubA evoked at least an additive cytotoxic effect when used in combination with cisplatin. Flow cytometry demonstrated that in contrast to EGF-SubA alone, both combined treatments induced apoptosis.

Conclusion: In vitro EGF-SubA is highly cytotoxic to LSCC cells at picoMolar concentrations, and while the mechanism of cell death of EGF-SubA alone is unclear, combinations of EGF-SubA with genotoxic agents potently induce apoptosis.