7-Benzylamino-6-chloro-2-piperazino-4-pyrrolidino-pteridine, a potent inhibitor of cAMP-specific phosphodiesterase, enhancing nuclear protein binding to the CRE consensus sequence in human tumour cells.

The cAMP-specific phosphodiesterase isoenzyme family PDE4 represents the highest cAMP-hydrolysing activity in many human cancer cell lines including the human large cell lung carcinoma cell line LXFL529L. Treatment of LXFL529L cells with the potent PDE4 inhibitor 7-benzylamino-6-chloro-2-piperazino-4-pyrrolidino-pteridine (DC-TA-46) induces dose-dependent growth inhibition. Cells are arrested in the G(1)-phase of the cell cycle and the induction of apoptosis is observed. In this study, we investigated the effect of DC-TA-46 on downstream elements of the cAMP-pathway. DC-TA-46 mediated inhibition of PDE4 activity in LXFL529L cells resulted in an increase of the intracellular cAMP level and significant induction of the activity of protein kinase A (PKA). The regulatory PKA subunit RIalpha was predominantly expressed in LXFL529L cells. In contrast to effects induced by cAMP analogues like 8-Cl-cAMP, the expression of the regulatory subunits of PKA remained unaffected by DC-TA-46. Treatment of LXFL529L cells with DC-TA-46 enhanced the binding of nuclear proteins to the cAMP-responsive element (CRE) consensus sequence TGACGTCA in a time- and dose-dependent manner, indicating the activation of transcription factors by PKA phosphorylation.