Epigenetic-Like Stimulation of Receptor Expression in SSTR2 Transfected HEK293 Cells as a New Therapeutic Strategy

Abstract

The aim of the study was to increase the uptake of the SSTR2-targeted radioligand Lu-177-DOTATATE using the DNA methyltransferase inhibitor (DNMTi) 5-aza-2′-deoxycytidine (5-aza-dC) and the histone deacetylase inhibitor (HDACi) valproic acid (VPA). The HEKsst2 and PC3 cells were incubated with variable concentrations of 5-aza-dC and VPA to investigate the uptake of Lu-177-DOTATATE. Cell survival, subsequent to external X-rays (0.6 or 1.2 Gy) and a 24 h incubation with 57.5 or 136 kBq/mL Lu-177-DOTATATE, was investigated via colony formation assay to examine the effect of the epidrugs. In the case of stimulated HEKsst2 cells, the uptake of Lu-177-DOTATATE increased by a factor of 28 in comparison to the unstimulated cells. Further, stimulated HEKsst2 cells demonstrated lower survival fractions (factor 4). The survival fractions of the PC3 cells remained almost unchanged. VPA and 5-aza-dC did not induce changes to the intrinsic radiosensitivity of the cells after X-ray irradiation. Clear stimulatory effects on HEKsst2 cells were demonstrated by increased cell uptake of the radioligand and enhanced SST2 receptor quantity. In conclusion, the investigated approach is suitable to stimulate the somatostatin receptor expression and thus the uptake of Lu-177-DOTATATE, enabling a more efficient treatment for patients with poor response to peptide radionuclide therapy (PRRT).

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

“…Specific transcriptional responses of tumors to the combination of epigenetic treatment and PRRT can be attributed to two separate effects; first, to direct effects of the epigenetic drugs that occurred immediately after pre-treatment and persisted throughout the PRRT phase, and second, to indirect effects of the epigenetic drugs that occurred first during PRRT as a result of increased [ 177 Lu]Lu-DOTA-TATE uptake. Since a recent study showed that epigenetic treatment with VPA and DAC did not sensitize HEK293 and PC3 cells to X-ray irradiation in vitro 27 , we suspect the observed additional treatment effects to result from increased [ 177 Lu]Lu-DOTA-TATE uptake and higher radiation doses absorbed by the tumors. On the other hand, there is literature supporting the radiosensitizing effects of HDAC inhibitors in neuroendocrine tumor cell lines 19 , 26 .…”

“…modulating heterochromatin and euchromatin accessibility, respectively. Successful up-regulation of SSTR2 was demonstrated in various neuroendocrine tumor cell lines and tumor models through attenuation of DNA methylation by treatment with DNA-N-methyltransferase (DNMT) inhibitors and via increase in histone acetylation levels by treatment with histone deacetylase (HDAC) inhibitors [16][17][18][19][20][21][22][23][24][25][26][27]. It was proposed that SSTR2 expression is regulated by DNA methylation of a CpG island within the SSTR2 promoter [20].…”

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

“…This original basic (preclinical) research article (Kotzerke et al 2022 ) aimed at enhancing the uptake of the recently approved SST 2 -targeting peptide radioligand [ 177 Lu]Lu-DOTA-TATE by neoadjuvant use of so called epigenetic modifiers (“epidrugs”), i.e. the DNA methyltransferase inhibitor (DNMTi) 5-aza-2’-deoxycytidine (5-aza-dC) and the histone deacetylase inhibitor (HDACi) valproic acid (VPA), a putative radiosensitizer.…”

“…Non-stimulated HEKsst2 and HEK cells are shown as a reference (40× magnification). The figure is reproduced with permission from Kotzerke et al ( 2022 ) …”

Aberrant Methylation of Somatostatin Receptor 2 Gene Is Initiated in Aged Gastric Mucosa Infected with Helicobacter pylori and Consequential Gene Silencing Is Associated with Establishment of Inflammatory Microenvironment In Vitro Study

“…However, it is still not clear in detail how SSTR2 contributes to gastric carcinogenesis. On the other hand, recent studies have suggested that SSTR2 may be a therapeutic target in nasopharyngeal carcinoma associated with infection by the Epstein–Barr virus [ 14 ] and that the increased SSTR2 expression induced by the epidrugs, such as the DNA methyltransferase inhibitor and the histone deacetylase inhibitor, may improve treatment strategies for patients with neuroendocrine tumors [ 15 ].…”