Supplementary Material for: The HDM2 (MDM2) Inhibitor NVP-CGM097 Inhibits Tumor Cell Proliferation and Shows Additive Effects with 5-Fluorouracil on the p53-p21-Rb-E2F1 Cascade in the p53wild type Neuroendocrine Tumor Cell Line GOT1

<p><b><i>Background/Aims:</i></b> The tumor suppressor p53 is depleted in many tumor cells by the E3 ubiquitin ligase mouse double minute 2 homolog (MDM2) through MDM2/p53 interaction. A novel target for inhibiting p53 degradation and for causing reexpression of p53<sup>wild type</sup> is inhibition of MDM2. The small molecule NVP-CGM097 is a novel MDM2 inhibitor. We investigated MDM2 inhibition as a target in neuroendocrine tumor cells in vitro. <b><i>Methods:</i></b> Human neuroendocrine tumor cell lines from the pancreas (BON1), lung (NCI-H727), and midgut (GOT1) were incubated with the MDM2 inhibitor NVP-CGM097 (Novartis) at concentrations from 4 to 2,500 nM. <b><i>Results:</i></b> While p53<sup>wild type</sup> GOT1 cells were sensitive to NVP-CGM097, p53<sup>mutated</sup> BON1 and p53<sup>mutated</sup> NCI-H727 cells were resistant to NVP-CGM097. Incubation of GOT1 cells with NVP-CGM097 at 100, 500, and 2,500 nM for 96 h caused a significant decline in cell viability to 84.9 ± 9.2% (<i>p</i> < 0.05), 77.4 ± 6.6% (<i>p</i> < 0.01), and 47.7 ± 9.2% (<i>p</i> < 0.01). In a Western blot analysis of GOT1 cells, NVP-CGM097 caused a dose-dependent increase in the expression of p53 and p21 tumor suppressor proteins and a decrease in phospho-Rb and E2F1. Experiments of co-incubation of NVP-CGM097 with 5-fluorouracil, temozolomide, or everolimus each showed additive antiproliferative effects in GOT1 cells. NVP-CGM097 and 5-fluorouracil increased p53 and p21 expression in an additive manner. <b><i>Conclusions:</i></b> MDM2 inhibition seems a promising novel therapeutic target in neuroendocrine tumors harboring p53<sup>wild type</sup>. Further investigations should examine the potential role of MDM2 inhibitors in neuroendocrine tumor treatment.</p>