MDM2 and neoplasm: Thus, we hypothesized that treatment of tumor cells with high concentrations of SP-141 for shorter periods (e.g., <4 h) might induce MDM2 expression as a consequence of p53 activation, whereas low concentrations of SP-141 (≤1 μM) and longer incubation times (≥20 h) appear to promote MDM2 degradation in vitro.