A. Janssen1, Z. Sun1, Z. Aburjania1, H. Jin1, R. Jaskula-Sztul1, H. Chen1 1University Of Alabama at Birmingham,Department Of Surgery,Birmingham, Alabama, USA
Introduction: Medullary Thyroid Cancers (MTC) are neuroendocrine tumors (NETs) that arise from calcitonin-producing C-cells of the thyroid gland. Although MTCs are slow growing, they are frequently metastatic at the time of discovery and not amenable to curative surgery. They also secrete excessive hormones, often causing debilitating symptoms such as facial flushing and diarrhea. Somatostatin receptors (SSTRs) are a family of five G protein-coupled receptors that are overexpressed in 85% of NETs. SSTRs participate in modulation of neurotransmission, inhibition of hormone secretion, and inhibition of cell proliferation. Somatostatin (SST) analogs have been used for treatment and imaging studies in NETs, but have not shown to be very practical in MTCs due to low or lack of SSTR expression. Herein, we describe the novel use of a class of drugs known as histone deacetylase inhibitors (HDACi) that have the unique ability to up regulate expression of SSTRs on MTCs, and are able to induce expression in patients with no phenotypic expression of SSTRs. The use of HDACi will further advance SST analog therapies and imaging studies in NETs.
Methods: We used Quantitative real time PCR (Q-PCR) to evaluate basal expression of SSTR1 to SSTR5 on two MTC cell lines– MZ and TT– against a positive control pulmonary fibroblast cell WI-38. Time dependent induction of SSTRs was then evaluated with Q-PCR for MZ and TT cells treated with a potent HDACi Thilandepsin-A (TDP-A) at 12, 24, and 48 hours. Furthermore, we assessed dose dependent induction for SSTR1-5 on MZ and TT at 48 hours with four separate HDACi– FK228, SAHA, TDP-A and VPA– using Q-PCR and Western Blot analysis for all treatments.
Results: Basal expression for both cell lines showed an increased expression in one or more SSTRs. MZ cells showed increased expression in SSTR2, SSTR4 and SSTR5, with very low expression of SSTR1. TT cells showed a significant expression of SSTR1 and SSTR2 with no basal expression of SSTR4. After Treatment with all four HDACi, MZ cells showed an eight- to fourteen-fold increase in message for SSTR1 and a two-fold increase in SSTR2. TT cells showed increased expression of SSTR2, SSTR3 and SSTR5. More importantly, TT cells had no basal expression of SSTR4, but treatment showed to induce expression of SSTR4.
Conclusion: We demonstrated that four tested HDACi increased message and protein levels of SSTRs in MTC cells in a time and dose dependent manner. We also showed that HDACi have the capability to induce expression of SSTRs even if there is no basal expression. This novel finding provides an avenue to improve SST analog therapies and imaging studies for MTCs.