Bromodeoxyuridine (100?mg/kg) was administered by ip injection one hour prior to harvest. by -H2AX foci formation, as compared to LuTate alone. Furthermore, using the AR42J tumour model we demonstrate that this combination of LuTate and talazoparib significantly improved the anti-tumour efficacy of LuTate alone. These findings support the clinical evaluation of the combination of LuTate and PARP inhibition in SSTR2-expressing NET. efficacy of LuTate PRRT. Given the paucity of tractable models of SSTR2-expressing NET has limited the development of novel therapeutic approaches in this setting, the aims of the study were therefore to characterise a panel of cell lines with neuroendocrine features to identify models appropriate for evaluating the anti-tumour activity of combination regimens incorporating SSTR2-targeted PRRT and then employ the model to evaluate the efficacy of the PARP inhibitor, talazoparib in combination with LuTate PRRT. Results Characterisation of cell collection models for SSTR2 expression A panel of tumour cell lines with neuroendocrine features comprising a rat exocrine pancreatic tumour (AR42J)33, human functioning pancreatic carcinoid (BON)34, human medulloblastoma (D341)35, human glioma (U87MG)36, two human neuroblastomas (SK-N-MC37, SK-N-BE(2)38) and an SSTR2 transfected human non-small cell lung malignancy line (H1299-7)39 was initially examined for and expression of SSTR2 mRNA. than but no SSTR2 staining was detected in the U87MG or SK-N-MC tumours. Characterisation of tumour SSTR2 imaging phenotype The tumour models were evaluated Rabbit polyclonal to C-EBP-beta.The protein encoded by this intronless gene is a bZIP transcription factor which can bind as a homodimer to certain DNA regulatory regions. for SSTR2 expression by 68Ga-DOTA-octreotate (GaTate) PET imaging (Fig.?2a, Supplementary Fig.?S1). The PET images showed very high tracer binding in the SSTR2 transfected H1299-7 model with a tumour to background binding ratio (TBR) of 159??14 as determined by semiquantitative analysis. Parbendazole High GaTate binding in D341 (TBR?=?47??6) and AR42J (TBR?=?51??3) tumours was observed while in the SK-N-BE(2) model the TBR was 4-fold lower (TBR?=?13??4). U87MG, BON and SK-N-MC tumours exhibited very low GaTate Parbendazole avidity. Together, these GaTate imaging findings are consistent with the SSTR2 mRNA and protein expression observed GaTate PET imaging phenotype and LuTate response across the tumour panel. (a) Mice bearing subcutaneous tumours were imaged using a small animal PET scanner following administration of GaTate (Images shown in Supp. Physique?1). PET tracer tumour to background uptake ratios were determined and are expressed as mean SEM of at least three impartial tumours. (b) Mice bearing tumours were treated intravenously with saline or 20 MBq LuTate on day 1. Tumour volumes are expressed as mean SEM of 4C8 animals/group. Tumour response to LuTate therapy Cell lines that expressed SSTR2 Parbendazole were implanted into nude mice and once Parbendazole the tumours became well-established the animals were injected intravenously with 20 MBq LuTate and the tumour response evaluated. As seen in Fig.?2b, most tumour models showed similar strong growth kinetics but their response to LuTate varied widely. LuTate treatment of the H1299-7 and AR42J models induced tumour stasis for sixteen and twelve days post dosing, respectively, after which tumour growth rapidly resumed. In contrast, the D341 model, which showed comparable SSTR2 expression and GaTate uptake to that of the AR42J model, was highly sensitive to LuTate with total tumour regression observed for 65 days. The SK-N-BE(2) and BON tumour models which exhibited low SSTR2 expression and GaTate binding were highly resistant to LuTate treatment. Enhancement of DNA damage by combining LuTate with a PARP inhibitor On the basis of its strong tumour growth properties, SSTR2 expression and response to LuTate PRRT, the AR42J collection was then used to explore the ability of a PARP inhibitor to potentiate the effects of LuTate treatment and efficacy of LuTate PRRT in combination with talazoparib We next investigated the anti-tumour effects of LuTate in combination with talazoparib in the AR42J xenograft model observed in our study, however, highlights an important limitation of models for the appropriate assessment of the cellular effects of LuTate. Our results show that while SSTR2 expression is necessary for Parbendazole response to LuTate therapy inactivating mutations.