Tools that are highly effective in the treatment of differentiated thyroid cancer (DTC) loose their therapeutic potentials in poorly differentiated tumors. The synthetic analog 8-Cl-cAMP has been known to have an antiproliferative effect in a variety of cancer cells and is tested as antineoplastic agent in clinical trials. The signaling mechanisms that govern the 8-Cl-cAMP-induced growth inhibition are still uncertain and data in thyroid neoplasia are lacking. Therefore, we tested the effects of 8-Cl-cAMP on the growth and apoptotic process in anaplastic (ARO), papillary (NPA) and follicular (WRO) thyroid carcinoma cell lines. Our proliferation data show that growth of ARO, NPA and WRO was inhibited by more than 50% after the treatment with 8-Cl-cAMP in a time- and dose-dependent manners. To test whether apoptosis occurs in 8-Cl-cAMP treated cells, we analyzed cell cycle, DNA fragmentation and caspase activity. We found induction of apoptosis in all the cell lines with different sensitivities. Since MAPKs are involved in the regulation of proliferation and apoptosis, we investigated modification of ERKs, that are preferentially activated in response to mitogens, and p-38 MAPKs, that are activated in response to cell stresses. Following the treatment with 8-Cl-cAMP, no modification of ERK phosphorylation was found while a marked and progressive induction of p38-MAPK phosporylation was seen in all the cell lines. We also evaluated the Akt phosphorylation, as a marker of the PI3K proliferative pathway that as been implicated in thyroid cell proliferation, and we found poor modifications of Akt phosphorylation state after 8-Cl-cAMP treatment.
In conclusion, 8-Cl-cAMP has a potent inhibitory effect on WRO, NPA and ARO cell growth which is accompanied by a pro-apoptotic effect via p38-MAPK. Therefore, 8-Cl-cAMP has a potential to be tested in vivo as a therapeutic agent for poorly DTC.