Expression of somatostatin receptor subtype 2 and subtype 5 in thyroid malignancies

Octreotide and Octreotide-derived delivery systems

Pharmaceutical peptide Octreotide is a somatostatin analog with targeting and therapeutic abilities. Over the last decades, Octreotide has been developed and approved to treat acromegaly and neuroendocrine tumours, and Octreotide-based radioactive conjugates have been leveraged clinically to detect small neuroendocrine tumour sites. Meanwhile, variety of Octreotide-derived delivery strategies have been proposed and explored for tumour targeted therapeutics or diagnostics in preclinical or clinical settings. In this review, we especially focus on the preclinical development and applications of Octreotide-derived drug delivery systems, diagnostic nanosystems, therapeutic nanosystems and multifunctional nanosystems, we also briefly discuss challenges and prospects of these Octreotide-derived delivery systems.

Comparative evaluation of somatostatin and CXCR4 receptor expression in different types of thyroid carcinoma using well-characterised monoclonal antibodies

Background

Papillary and follicular thyroid carcinomas can be treated surgically and with radioiodine therapy, whereas therapeutic options for advanced stage IV medullary and for anaplastic tumours are limited. Recently, somatostatin receptors (SSTs) and the chemokine receptor CXCR4 have been evaluated for the treatment of thyroid carcinomas, however, with contradictory results.

Methods

The expression of the five SSTs and of CXCR4 was assessed in 90 samples from 56 patients with follicular, papillary, medullary, or anaplastic thyroid carcinoma by means of immunohistochemistry using well-characterised monoclonal antibodies. The stainings were evaluated using the Immunoreactivity Score (IRS) and correlated to clinical data. In order to further substantiate the immunohistochemistry results, in serial sections of a subset of the samples receptor expression was additionally examined at the mRNA level using qRT-PCR.

Results

Overall, SST and CXCR4 protein expression was low in all four entities. In single cases, however, very high IRS values for SST2 and CXCR4 were observed. SST2 was the most frequently expressed receptor, found in 38% of cases, followed by SST5 and SST4, found in 14 and 9% of tumours, respectively. SST1 and SST3 could not be detected to any significant extent. CXCR4 was present in 12.5% of medullary and 25% of anaplastic carcinomas. Expression SST3, SST4, SST5 and CXCR4 was positively correlated with expression of the proliferation marker Ki-67. Additionally, a negative interrelationship between SST4 or SST5 expression and patient survival and a positive association between SST3 expression and tumour diameter were observed. qRT-PCR revealed a similar receptor expression pattern to that seen at the protein level. However, probably due to the low overall expression, no correlation was found for the SSTs or the CXCR4 between the IRS and the mRNA values.

Conclusions

SST- or CXCR4-based diagnostics or therapy in thyroid carcinomas should not be considered in general but may be feasible in single cases with high levels of expression of these receptors.

Evaluation of preclinical efficacy of everolimus and pasireotide in thyroid cancer cell lines and xenograft models

BACKGROUND

Signaling through mTOR and somatostatin pathway is implicated in thyroid cancer development.

METHOD

We evaluated everolimus, an mTOR inhibitor and pasireotide, a multi receptor somatostatin analogue as potential therapy of thyroid cancer focusing on the in vitro and in vivo efficacy, as well as possible mechanism to explain any observed interaction.

RESULTS

Both everolimus and pasireotide inhibit the growth of thyroid cancer cell lines in vitro with varied efficacy that correlates with tumor origin and somatostatin receptor (SSTR) expression profile of the cell lines. In vitro activity of everolimus show positive correlation with the expression of SSTR types 1, 4 and 5 (CC: 0.9; 0.85, 0.87) while pasireotide activity show negative correlation with SSTR2 (CC: -0.87). Although there is greater modulation of pS6 when pasireotide is combined with everolimus, there is no significant abrogation of the expected feedback upregulation of AKT induced by everolimus. Also, the combination is not significantly better than each agent alone in short and long term in vitro assays. Continuous administration of everolimus at a low dose as opposed to high intermittent dosing schedule has greater antitumor efficacy against thyroid cancer xenografts in vivo. Pasireotide LAR has modest in vivo efficacy and the combination of everolimus and pasireotide LAR achieve greater tumor growth inhibition than each agent alone in TPC-1 xenograft model of thyroid cancer (p = 0.048).

CONCLUSION

Our findings provide support for the clinical evaluation of everolimus and pasireotide in thyroid cancer and other neuroendocrine tumors.

Characterization of somatostatin receptors (SSTRs) expression and antiproliferative effect of somatostatin analogues in aggressive thyroid cancers

BACKGROUND

Certain human carcinomas have demonstrated a distinct expression of somatostatin receptors. Data on somatostatin receptor expression in follicular thyroid cancer and anaplastic thyroid cancer has been limited and conflicting. This study seeks to characterize somatostatin receptor expression in follicular thyroid cancer and anaplastic thyroid cancer and to assess the effects of somatostatin analogues.

METHODS

Anaplastic thyroid cancer (Hth7 and 8505C) and follicular thyroid cancer (FTC-236) (Sigma-Aldrich, St. Louis, MO) cells were cultured. Capillary immunoblotting and reverse transcription polymerase chain reaction (RT-PCR) were used to determine the basal expression of protein and mRNA of SSTR1-SSTR5. Cells were treated with the somatostatin analogues octreotide, pasireotride (SOM230), and KE-108 for 48h. IC₅₀ was determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and cell proliferation was measured by viable cell count. Presence of SSTR2 was assessed by immunohistochemistry.

RESULTS

Immunoblotting analysis demonstrated that most cell lines expressed SSTR1-SSTR3 and SSTR5 in varying degrees. Reverse transcription polymerase chain reaction analysis showed that mRNA expression for SSTR2 and SSTR3 correlated with protein expression. MTT assays showed that KE-108 and SOM230 were able to inhibit cell proliferation. Tissue microarray (TMA) showed that SSTR2 was highly expressed in human tissues of aggressive thyroid carcinomas.

CONCLUSION

Follicular thyroid cancer and anaplastic thyroid cancer express SSTR1-3 and SSTR5 in distinct fashions both at a message and protein level. Our results suggest that somatostatin receptors are still a relevant and promising drug target against non-medullary thyroid cancers.

Somatostatin receptor expression in lymphomas: a source of false diagnosis of neuroendocrine tumor at 68Ga-DOTANOC PET/CT imaging

BACKGROUND

⁶⁸Ga-DOTANOC PET/CT is routinely used to image neuroendocrine tumors (NETs). A case of lymphoma initially thought to be NET based on a positive ⁶⁸Ga-DOTANOC PET/CT was recently seen at our institution. This prompted us to determine prospectively somatostatin receptor (SSTR) status in patients with lymphoma by immunohistochemical analysis of SSTR subtypes 2, 3 and 5 (SSTR_2,3,5) and ⁶⁸Ga-DOTANOC PET/CT imaging.

MATERIAL AND METHODS

Twenty-one patients with newly diagnosed lymphoma were referred to ⁶⁸Ga-DOTANOC and FDG PET/CT prior to any treatment. Tracer uptake was evaluated visually by two nuclear medicine specialists. Maximum standardized uptake values (SUVmax) were determined from 14 nodal and two extranodal regions with highest uptake in each patient. Lesions were then graded with Deauville score (1-5) on FDG PET/CT and modified Krenning score (0-4) on ⁶⁸Ga-DOTANOC PET/CT, respectively. SSTR_2,3,5 status was analyzed from routine biopsies of lymphomatous tissue and matched to corresponding PET/CT findings.

RESULTS

About 20/21 patients had FDG-positive lymphoma (Deauville score ≥3). Uptake of ⁶⁸Ga-DOTANOC was regarded as positive if Krenning score was ≥2 and resulted in 13/21 (62%) patients having ⁶⁸Ga-DOTANOC-positive lymphomas. The highest uptake of ⁶⁸Ga-DOTANOC was seen in Hodgkin's lymphoma of nodular sclerosis subtype and in diffuse large B-cell lymphoma (SUVmax median 9.8 and 9.7, respectively). Both cases showed strong SSTR₂ immunopositivity in tumor cells. Some patients had SSTR₂ immunopositivity predominantly in endothelial and dendritic cells and follicular centers of lymph nodes contributing to a positive PET/CT with probably low tumor-specific uptake. SSTR₃ and SSTR₅ were negative in most lymphoma subtypes.

CONCLUSIONS

According to this pilot study, ⁶⁸Ga-DOTANOC PET/CT is positive in some lymphoma subtypes which express SSTRs. These tumors present a potential risk of being misinterpreted as NETs if a representative tumor sample is not available. Lymphomas with high expression of SSTRs may be amenable to treatments targeting these receptors.

Nodular Thyroid Disease and Thyroid Cancer in the Era of Precision Medicine

The management of thyroid nodules, one of the main clinical challenges in endocrine clinical practice, is usually straightforward. Although the most important concern is ruling out malignancy, there are grey areas where uncertainty is frequently present: the nodules labelled as indeterminate by cytology and the extent of therapy when thyroid cancer is diagnosed pathologically. There is evidence that the current available precision medicine tools (from all the "-omics" to molecular analysis, fine-tuning imaging or artificial intelligence) may help to fill present gaps in the future. We present here a commentary on some of the current challenges faced by endocrinologists in the field of thyroid nodules and cancer, and illustrate how precision medicine may improve their diagnostic and therapeutic capabilities in the future.