Enhancement of radiosensitivity in head and neck cancer cells by ZD1839 ('IRESSA'), a selective epidermal growth factor receptor tyrosine kinase inhibitor.

Overexpression of epidermal growth factor receptor (EGFR) is frequently observed in many solid tumor types, including head and neck squamous cell carcinomas (HNSCC). Recent laboratory experiments have demonstrated that high EGFR levels correlate with increased tumor resistance to radiation. This study investigated the relationship between EGFR expression levels and radiosensitivity in 5 HNSCC cell lines (HSC2, HSC3, HSC4, SCC25, and Ca9-22) and whether treatment with ZD1839 ('Iressa'), a selective EGFR-tyrosine kinase inhibitor (TKI), would improve tumor cell response to radiotherapy. ZD1839 suppressed the growth of HNSCC cell lines in a dose- and time-dependent manner. Radiosensitivity of these HNSCC cell lines, assessed by a clonogenic survival assay, differed greatly and the expression of EGFR varied. EGFR expression levels (EGFR numbers/cell) correlated with increased tumor resistance to radiation (f[x]= 4.54 X, R2 = 0.715; f[x]: EGFR numbers/cell, X: radiosensitivity; D10). Following exposure of the HNSCC cells to 1.0 microM ZD1839 and radiation (0-10 Gy), greater than additive growth inhibitory effects were observed. These results suggest that ZD1839 could enhance tumor radiosensitivity and inhibit tumor growth after radiation, indicating that this combination could have clinical potential in the treatment of patients with head and neck cancer.

Anti-epidermal growth factor receptor monoclonal antibody 225 upregulates p27(KIP1) and p15(INK4B) and induces G1 arrest in oral squamous carcinoma cell lines.

Epidermal growth factor receptor (EGFR) regulates the growth and progression of human oral squamous cell carcinoma (SCC). Recently, the link between EGFR signaling and the cell cycle has been identified. Some reports have described that EGFR-blocking monoclonal antibody 225 (mAb225) induced G1 arrest and inhibited the growth of various cancer cells. The purpose of this study was to evaluate the effect of mAb225 on human oral SCC cell lines. Exposure to mAb225 in culture inhibited the growth of oral SCC cell lines in an EGFR number-independent manner, with the percent inhibition ranging from 13.8 to 76.6%. Flow-cytometric analysis demonstrated that treatment with mAb225 induced cell accumulation in G1 phase, accompanied by a decrease in the percentage of cells in the S phase. Apoptosis was not seen in this study. G1 arrest was accompanied by a decrease in CDK2-, CDK4-, and CDK6-associated histone H1 kinase activities, and an increase in the expression levels of cell cycle inhibitors p27(KIP1) and p15(INK4B). These results suggested that the antiproliferative effect of EGFR blockade by mAb225 in oral SCC may be mediated by p27(KIP1) and p15(INK4B).

Cyclin-dependent kinase inhibitor (roscovitine) suppresses growth and induces apoptosis by regulating Bcl-x in head and neck squamous cell carcinoma cells.

Cyclin-dependent kinases (Cdks) play essential roles in the intracellular controls of the cell cycles. Roscovitine, [2-(R)-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine], is a potent and selective inhibitor of the Cdk2 and Cdc2. We investigated whether this compound was effective against head and neck squamous cell carcinoma (HNSCC) cells. Roscovitine was found to inhibit the growth of all 11 HNSCC cell lines in time- and dose-dependent manner and to diminish the Cdk2 and Cdc2 activities. An induction of apoptosis was observed in all cells, as judged by the cell morphology, along with the appearance of cells with sub-G1 DNA contents, DNA fragmentations, and poly(ADP-ribose) polymerase (PARP) cleavage. In four HNSCC cell lines, apoptosis was induced without antecedent marked cell cycle arrest, and in the other seven cell lines, cell cycle arrest preceded cell death. We also found up-regulation of Bcl-xS in the former cell lines, and in the latter cell lines, the expressions of Bcl-2 and Bcl-xL were induced simultaneously. These results suggest that roscovitine exerts antitumor activities in HNSCC and is associated with induction of Bcl-xS. Roscovitine can be considered to provide a new chemopreventive and chemotherapeutic strategy for the clinical management of HNSCC.

Expression of cell cycle control proteins in normal epithelium, premalignant and malignant lesions of oral cavity.

In this study, we examined the expression of cyclins, cyclin dependent kinase (CDKs) and CDK inhibitors by immunohistochemical analysis in 20 normal mucosa, 42 epithelial dysplasia (ED), and 117 oral squamous cell carcinoma. Neither Cyclin D1 nor CDK2 were detectable in normal tissue and ED. Their presence, however, was detectable in squamous cell carcinoma (SCCs) (Cyclin D1, 35.9%; CDK2, 66.7%). Cyclin E was detectable in 57.1% of severe ED and 62.8% of SCCs. For the CDK inhibitors, these proteins were detectable in all normal mucosa and most of the mild and moderate ED. For severe ED, expression of these proteins was not observed in some cases (p12(DOC-1), 14.3%; p16(INK4A), 28.6%; p27(KIP1), 7.1%). For SCCs, the expression of p12(DOC-1) was lost in 71.8%, p16(INK4A) in 69.2% and p27(KIP1) in 35.9%. These results suggest that elevated expression of cyclin D1, cyclin E, CDK2 and loss of p12(DOC-1), p16(INK4A) and p27(KIP1) may contribute to the multistep nature of oral carcinogenesis.