The oncogenic activation of the rearranged during transfection (RET) proto-oncogene has a main role in the pathogenesis of medullary thyroid cancer (MTC). Several lines of evidence suggest that RET function could be influenced by cyclic AMP (cAMP)-dependent protein kinase A (PKA) activity. We evaluated the in vitro anti-tumor activity of 8-chloroadenosine-3′,5′-cyclic monophosphate (8-Cl-cAMP) and PKA type I-selective cAMP analogs [equimolar combination of the 8-piperidinoadenosine-3′,5′-cyclic monophosphate (8-PIP-cAMP) and 8-hexylaminoadenosine-3′,5′-cyclic monophosphate (8-HA-cAMP) in MTC cell lines (TT and MZ-CRC-1)]. 8-Cl-cAMP and the PKA I-selective cAMP analogs showed a potent anti-proliferative effect in both cell lines. In detail, 8-Cl-cAMP blocked significantly the transition of TT cell population from G2/M to G0/G1 phase and from G0/G1 to S phase and of MZ-CRC-1 cells from G0/G1 to S phase. Moreover, 8-Cl-cAMP induced apoptosis in both cell lines, as demonstrated by FACS analysis for annexin V-FITC/propidium iodide, the activation of caspase-3 and PARP cleavage. On the other hand, the only effect induced by PKA I-selective cAMP analogs was a delay in G0/G1-S and S-G2/M progression in TT and MZ-CRC-1 cells, respectively. In conclusion, these data demonstrate that cAMP analogs, particularly 8-Cl-cAMP, significantly suppress in vitro MTC proliferation and provide rationale for a potential clinical use of cAMP analogs in the treatment of advanced MTC.

Apoptosis, cAMP analogs, cAMP-dependent protein kinase A (PKA) pathway, Cell cycle, Medullary thyroid cancer
This work was partially supported by the Italian Ministry of Education, Research and University (FIRB RBAP11884 M) and by Rusconi Foundation,
Department of Internal Medicine

Dicitore, A, Grassi, E.S, Caraglia, M, Borghi, A.M, Gaudenzi, G, Hofland, L.J, … Vitale, G. (2016). The cAMP analogs have potent anti-proliferative effects on medullary thyroid cancer cell lines. Endocrine, 51(1), 101–112. doi:10.1007/s12020-015-0597-7