MANAGEMENT OF ENDOCRINE DISEASE: Personalized medicine in the treatment of acromegaly

Precision medicine in the treatment of acromegaly

Acromegaly is a chronic disorder usually diagnosed late in the disease evolution, leading to substantial morbidity and mortality related to this long period of undiagnosed state as well as the difficulty in achieving normalization of GH hypersecretion and controlling tumor mass. First generation somatostatin analogues (SSA) are accepted as the first-line medical therapy or as second-line therapy in patients undergoing unsuccessful surgery. However, because a high percentage of patients experience SSA treatment failure, the inclusion of biomarkers associated with a successful or non-successful response to these drug (as well as to all classes of medical therapy) is necessary to better guide the choice of treatment, potentially allowing for a quicker achievement of disease control. The current treatment algorithms for acromegaly are based upon a "trial and error" approach with additional treatment options provided when disease is not controlled. In many other diseases, their therapeutic algorithms have been evolving towards personalizing treatment with medication that best matches individual disease characteristics, using biomarkers that identify therapeutic response, thus allowing the personalization of the therapy. It is time to introduce this approach to acromegaly treatment algorithms. This paper reviews the potential tools for doing so.

cAMP/PKA-induced filamin A (FLNA) phosphorylation inhibits SST2 signal transduction in GH-secreting pituitary tumor cells

An efficient intracellular response to somatostatin analogs (SSA) in pituitary tumors requires filamin A (FLNA). Since cAMP pathway plays an important role in GH-secreting pituitary tumors pathogenesis and FLNA is phosphorylated by PKA on S2152, aim of this study was to investigate in tumoral somatotrophs the impact of cAMP pathway activation and SSA stimulation on FLNA phosphorylation and the consequences on SST2 function. We found a PKA-mediated increase (2-fold) and SST2 agonist-induced decrease (-50%) of FLNA phosphorylation in GH3, GH4C1 and primary somatotroph tumor cells. This modification regulates FLNA function. Indeed, phosphomimetic S2152D FLNA mutant, but not phosphodeficient S2152A, abolished the known SSA antitumoral effects, namely: 1) inhibition of cell proliferation, reduction of cyclin D3 and increase of p27; 2) increase of cell apoptosis; 3) inhibition of cell migration via RhoA activation and cofilin phosphorylation. Coimmunoprecipitation and immunofluorescence assays showed that S2152A FLNA was recruited to activated SST2, whereas S2152D FLNA constitutively bound SST2 on the plasma membrane, but prevented G_αi proteins recruitment to SST2. In conclusion, we demonstrated that FLNA phosphorylation, promoted by cAMP pathway activation and inhibited by SSA, prevented SST2 signaling in GH-secreting tumoral pituitary cells.