Epigenetic drugs in somatostatin type 2 receptor radionuclide theranostics and radiation transcriptomics in mouse pheochromocytoma models

Combined PET Radiotracer Approach Reveals Insights into Stromal Cell-Induced Metabolic Changes in Pancreatic Cancer In Vitro and In Vivo

Background/Objective Pancreatic stellate cells (PSCs) in pancreatic adenocarcinoma (PDAC) are producing extracellular matrix, which promotes the formation of a dense fibrotic microenvironment. This makes PDAC a highly heterogeneous tumor-stroma-driven entity, associated with reduced perfusion, limited oxygen supply, high interstitial fluid pressure, and limited bioavailability of therapeutic agents. Methods In this study, spheroid and tumor xenograft models of human PSCs and PanC-1 cells were characterized radiopharmacologically using a combined positron emission tomography (PET) radiotracer approach. [18F]FDG, [18F]FMISO, and [18F]FAPI-74 were employed to monitor metabolic activity, hypoxic metabolic state, and functional expression of fibroblast activation protein alpha (FAPα), a marker of activated PSCs. Results In vitro, PanC-1 and multi-cellular tumor spheroids demonstrated comparable glucose uptake and hypoxia, whereas FAPα expression was significantly higher in PSC spheroids. In vivo, glucose uptake as well as the transition to hypoxia were comparable in PanC-1 and multi-cellular xenograft models. In mice injected with PSCs, FAPα expression decreased over a period of four weeks post-injection, which was attributed to the successive death of PSCs. In contrast, FAPα expression increased in both PanC-1 and multi-cellular xenograft models over time due to invasion of mouse fibroblasts. Conclusion The presented models are suitable for subsequently characterizing stromal cell-induced metabolic changes in tumors using noninvasive molecular imaging techniques.

Somatostatin receptor subtype 2A expression and genetics in 184 paragangliomas: a single center retrospective observational study

PURPOSE

Adrenal and extra-adrenal paragangliomas (PGLs) are a group of neuroendocrine tumors (NETs) with strong heterogeneity, which often express somatostatin receptor subtype 2 A (SSTR2A). However, the association between SSTR2A expression and genetic status of PGLs remains unclear. The purpose of the study was to identify whether various pathogenic variants (PVs) had an impact on SSTR2A expression in PGLs.

METHODS

This retrospective study included 184 patients with pathologically confirmed PGLs. The immunohistochemical expression of SSTR2A were studied in 184 tumors and PVs were tested in 159 tumor samples. Clinical and genetic data were compared in SSTR2A positive and negative PGLs.

RESULTS

SSTR2A was positive in 63.6% (117/184) of all tumors. PGLs with negative SSTR2A were more likely to be extra-adrenal (37.0% vs 18.0%; P = 0.005) and exhibited a considerably greater proportion of PVs (75.4% vs. 49.0%; P = 0.001) than those with positive SSTR2A. Compared to those without PVs, a higher proportion of PGLs with PVs in cluster 1B (P = 0.004) and cluster 2 (P = 0.004) genes, especially VHL (P = 0.009), FGFR1 (P = 0.010) and HRAS (P = 0.007), were SSTR2A negative. SSTR2A was positive in all tumors (4/4) with SDHx PVs and in 87.5% (7/8) of metastatic PGLs.

CONCLUSIONS

SSTR2A negativity was correlated with extra-adrenal tumor location and PVs in cluster 1B and cluster 2 genes such as VHL, FGFR1 and HRAS. Immunohistochemistry of SSTR2A should be taken into consideration in the personalized management of PGLs.

Improving susceptibility of neuroendocrine tumors to radionuclide therapies: personalized approaches towards complementary treatments

Radionuclide therapies are an important tool for the management of patients with neuroendocrine neoplasms (NENs). Especially [131I]MIBG and [177Lu]Lu-DOTA-TATE are routinely used for the treatment of a subset of NENs, including pheochromocytomas, paragangliomas and gastroenteropancreatic tumors. Some patients suffering from other forms of NENs, such as medullary thyroid carcinoma or neuroblastoma, were shown to respond to radionuclide therapy; however, no general recommendations exist. Although [131I]MIBG and [177Lu]Lu-DOTA-TATE can delay disease progression and improve quality of life, complete remissions are achieved rarely. Hence, better individually tailored combination regimes are required. This review summarizes currently applied radionuclide therapies in the context of NENs and informs about recent advances in the development of theranostic agents that might enable targeting subgroups of NENs that previously did not respond to [131I]MIBG or [177Lu]Lu-DOTA-TATE. Moreover, molecular pathways involved in NEN tumorigenesis and progression that mediate features of radioresistance and are particularly related to the stemness of cancer cells are discussed. Pharmacological inhibition of such pathways might result in radiosensitization or general complementary antitumor effects in patients with certain genetic, transcriptomic, or metabolic characteristics. Finally, we provide an overview of approved targeted agents that might be beneficial in combination with radionuclide therapies in the context of a personalized molecular profiling approach.

Metastatic Pheochromocytoma and Paraganglioma: Somatostatin Receptor 2 Expression, Genetics, and Therapeutic Responses

CONTEXT

Pheochromocytomas and paragangliomas (PPGLs) with pathogenic mutations in the succinate dehydrogenase subunit B (SDHB) are associated with a high metastatic risk. Somatostatin receptor 2 (SSTR2)-dependent imaging is the most sensitive imaging modality for SDHB-related PPGLs, suggesting that SSTR2 expression is a significant cell surface therapeutic biomarker of such tumors.

OBJECTIVE

Exploration of the relationship between SSTR2 immunoreactivity and SDHB immunoreactivity, mutational status, and clinical behavior of PPGLs. Evaluation of SSTR-based therapies in metastatic PPGLs.

METHODS

Retrospective analysis of a multicenter cohort of PPGLs at 6 specialized Endocrine Tumor Centers in Germany, The Netherlands, and Switzerland. Patients with PPGLs participating in the ENSAT registry were included. Clinical data were extracted from medical records, and immunohistochemistry (IHC) for SDHB and SSTR2 was performed in patients with available tumor tissue. Immunoreactivity of SSTR2 was investigated using Volante scores. The main outcome measure was the association of SSTR2 IHC positivity with genetic and clinical-pathological features of PPGLs.

RESULTS

Of 202 patients with PPGLs, 50% were SSTR2 positive. SSTR2 positivity was significantly associated with SDHB- and SDHx-related PPGLs, with the strongest SSTR2 staining intensity in SDHB-related PPGLs (P = .01). Moreover, SSTR2 expression was significantly associated with metastatic disease independent of SDHB/SDHx mutation status (P < .001). In metastatic PPGLs, the disease control rate with first-line SSTR-based radionuclide therapy was 67% (n = 22, n = 11 SDHx), and with first-line "cold" somatostatin analogs 100% (n = 6, n = 3 SDHx).

CONCLUSION

SSTR2 expression was independently associated with SDHB/SDHx mutations and metastatic disease. We confirm a high disease control rate of somatostatin receptor-based therapies in metastatic PPGLs.

Up-Regulation of PSMA Expression In Vitro as Potential Application in Prostate Cancer Therapy

Possibilities to improve the therapeutic efficacy of Lu-177-PSMA-617 radionuclide therapy by modulation of target expression are being investigated. Knowledge on regulatory factors that promote prostate cancer (PCa) progression may contribute to targeting prostate cancer more effectively. We aimed at the stimulation of PCa cell lines using the substances 5-aza-2'-deoxycitidine (5-aza-dC) and valproic acid (VPA) to achieve increased prostate-specific membrane antigen (PSMA) expression. PC3, PC3-PSMA, and LNCaP cells were incubated with varying concentrations of 5-aza-dC and VPA to investigate the cell-bound activity of Lu-177-PSMA-617. Stimulation effects on both the genetically modified cell line PC3-PSMA and the endogenously PSMA-expressing LNCaP cells were demonstrated by increased cellular uptake of the radioligand. For PC3-PSMA cells, the fraction of cell-bound radioactivity was enhanced by about 20-fold compared to that of the unstimulated cells. Our study reveals an increased radioligand uptake mediated by stimulation for both PC3-PSMA and LNCaP cell lines. In perspective of an enhanced PSMA expression, the present study might contribute to advanced radionuclide therapy approaches that improve the therapeutic efficacy, as well as combined treatment options.