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 overexpression of CEACAM6 in Detroit 562 cells was accompanied by a profound and significant decrease in the apoptotic index of tumour cells in vivo in comparison to control tumours. These data indicate the enhanced tumour growth observed in the CEACAM6 over expressing cells was predominantly attributable to a decrease in caspase 3 dependent cell death in vivo. These effects were natural product library not observed in vitro and suggest that CEACAM6 mediated alterations in tumour proliferation and apoptosis are regulated by factors particular for the microenvironment in which the tumours reside in vivo. Differences in in vitro and in vivo apoptotic responses will not be unexpected. We have previously reported that agents including histone deacetylase inhibitors exhibit substantial cytotoxic effects on SCC cells in vitro however fail to induce cytotoxicity against SCC cells in xenotransplant models or human subjects.
In addition, a recent study reported that stromal elements are able to modify tumour cell sensitivity to natural product library cytotoxic drugs. Next, we investigated no matter if decreasing CEACAM6 expression would also have the ability to modulate tumour initiation and growth in the Detroit 562 cell line. Efficiency of knock down of CEACAM6 was achieved making use of 2 miR RNAi sequences, miR CEA and miR CEA Dux, and was measured by rt PCR. CEA BIX01294 Dux sequence had the greatest knock down with the 2 sequences, with 96.98% knock down at the mRNA level. Employing the CEA Dux sequence, the knock down of CEACAM6 was confirmed at the protein level. BrdU and Annexin V assay analysis indicated that knock down of CEACAM6 in the Detroit 562 cells had no significant effect on the proliferative potential or basal levels of cell death in comparison to control cells.
This would suggest that the modest Erythropoietin effects of overexpression of CEACAM6 on proliferation and apoptosis observed in an in vitro setting may possibly be an artefact of overexpression. Next, we examined the capacity of CEACAM6 Dux transduced or control transduced cells to establish tumours inside a xenotransplant model. CEACAM6 knockdown cells took longer to establish and grow than control cells. Immunohistochemistry confirmed that knock down of Ceacam6 persisted towards the termination with the study in xenotransplanted tumours. These data indicate that CEACAM6 expression was decreased, but not totally ablated, in the CEACAM6 knock down tumours when in comparison to control tumours.
Combined, the overexpression and knockdown studies show that CEACAM6 can enhance the tumourogenesity of HNSCC cells. In addition, we show that CEACAM6 overexpression enhances tumourogenesity by inhibiting apoptosis. BIX01294 We have shown that CEACAM6 can improve tumour initiating activity and inhibit apoptosis. Therefore, we were enthusiastic about no matter if the antiapoptotic effects of CEACAM6 could extend towards the suppression of cytotoxic activity of a PI3K/AKT/mTOR inhibitor, BGT226. Human SCC often harbor defects in survival pathways including the PTEN/PI3K/AKT/mTOR pathway which natural product library can attenuate responses to chemotherapeutics. In addition, it has been previously reported that CEACAM6 can inhibit cytotoxicity induced by a standard chemotherapeutic, gemcitabine, in pancreatic cancer cells.
Anticancer treatment options are increasingly relying on the use of targeted therapies and we've previously shown that targeting the PI3K/AKT/ mTOR pathways in HNSCC shows considerable anticancer activity in xenotransplant models of HNSCC. We compared the sensitivity of Detroit BIX01294 562 cells towards the PI3K/AKT inhibitor, BGT226, using the sensitivity of Detroit 562 cells in which CEACAM6 is overexpressed or knocked down by stable expression of an shRNA . Figure 6 shows natural product library that inhibition of CEACAM6 enhances sensitivity of SCC cells to BGT226. Overexpression of CEACAM6 reduces the sensitivity and maximal response to BGT226 . In addition, we show that overexpression of CEACAM6 causes an induction of AKT whilst knockdown of CEACAM6 causes a reduction in total and phospho S473 AKT.
These data indicate that CEACAM6 is really a modulator with the constitutive PI3K/AKT survival pathway in SCC cells BIX01294 and is able to modulate the cytotoxic response to pharmacological inhibitors with the PI3K/AKT pathway. Lastly, we had previously reported that SCC cells when grown, inside a xenotransplant model, display initial transient sensitivity to BGT226 followed by the expansion of BGT226 resistant cells. We now report that 4 weeks of everyday therapy with BGT226 of mice bearing tumours derived from Detroit 562 cells selectively ablates CEACAM6 good foci in the tumours. Discussion In this study we report, for the first time, on the function of CEACAM6 in HNSCC. Prior work with keratinocytes and keratinocyte derived SCC cells has shown that CEACAM6 is selectively expressed in differentiated keratinocytes and is extremely expressed inside a tumourigenic clonal variant with the Detroit 562 HNSCC cell line. In addition, other workers have reported that i CEACAM6 overexpression occurs in selection of epithelial malignancies, ii that CEACAM6 overexpression is associated with improved metasta