Abstract C239: BRAK/CXCL14 transgenic mice suppress growth of tumor cell xenografts

Purpose: In searching for a suppressor(s) of tumor progression of head and neck squamous cell carcinoma (HNSCC) in vivo, we found earlier, by the treatment of HNSCC cells with epidermal growth factor, whose receptor is frequently over‐activated in HNSCC, and observation by cDNA microarray analysis followed by reverse‐transcriptase polymerase chain reaction analysis, that the chemokine BRAK/CXCL14 was significantly down regulated. Also, the rate of tumor formation in vivo of BRAK‐expressing vector‐ transfected HNSCC cells in athymic nude mice was significantly lower than that of mock vector‐transfected ones. In addition, tumors formed in vivo by the BRAK‐expressing cells were significantly smaller than those of the mock‐transfected ones, even though the growth rates of both cells in vitro were essentially the same. These results indicate that BRAK/CXCL14 is a chemokine, having suppressive activity toward tumor progression of HNSCC in vivo. In order to confirm further this effect of BRAK/CXCL14, we produced BRAK/CXCL14 transgenic mice and examined the effects of the transgene on the growth of tumor cell xenografts in these animals.

Experimental Procedures: Cytomegalovirus promoter regulated BRAK cDNA was introduced into male pronuclei and 2 line of BRAK transgenic mice were produced on a C57BL/6 background. Blood BRAK levels were determined by ELISA. Lewis lung carcinoma (LLC) cells (1×10⁵ to 3×10⁶/site) were injected subcutaneously into dorso‐lateral region of transgenic (Tg) or wild type C57BL/6 mice. Tumor volume was measured daily by use of slide calipers. Frozen sections of tumor tissues were immunohistochemically stained by anti‐CD31 (endothelial cell marker) or anti‐ ‐smooth muscle cell actin (smooth muscle cell marker).

Results: BRAK/CXCL14 transgenic mice expressed 10 times higher concentrations of BRAK/CXCL14 in their bloodstream than did the wild type ones (1 ng / ml). These mice significantly suppressed the growth of LLC cell xenografts, irrespective of the number of tumor cells injected. Two independently isolated Tg mice lines suppressed tumor cell growth, indicating that the suppression was dependent on higher BRAK/CXCL14 expression and not on destruction of a presumptive tumor promoter gene(s) during the course of introduction of the transgene. Immunohistochemical examination revealed a very restricted staining pattern for anti‐ ‐smooth muscle cell actin in the Tg mice compared with that in wild‐type ones, thus indicating presence of small number of mature blood vessels in tumors of the former.

Conclusion: These mice suppressed growth of LLC cell xenografts, confirming BRAK/CXCL14 to be the first identified suppressor of tumor progression, suppressing not only HNSCC but also tumor cells of another organ origin, i.e., lung. Thus, the expression of BRAK/CXCL14 will be a very promising approach for tumor suppression without side effects, because BRAK/CXCL14 gene is expressed in many normal cells and tissue.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C239.