Since its discovery over 35 years ago, MDM2 has emerged as an attractive target for the development of cancer therapy. MDM29s activities extend from carcinogenesis to immunity to the response to various cancer therapies. Since the report of the first MDM2 inhibitor more than 30 years ago, various approaches to inhibit MDM2 have been attempted, with hundreds of small-molecule inhibitors evaluated in preclinical studies and numerous molecules tested in clinical trials. Although many MDM2 inhibitors and degraders have been evaluated in clinical trials, there is currently no Food and Drug Administration (FDA)-approved MDM2 inhibitor on the market. Nevertheless, there are several current clinical trials of promising agents that may overcome the past failures, including agents granted FDA orphan drug or fast-track status. We herein summarize the research efforts to discover and develop MDM2 inhibitors, focusing on those that induce MDM2 degradation and exert anticancer activity, regardless of the p53 status of the cancer. We also describe how preclinical and clinical investigations have moved toward combining MDM2 inhibitors with other agents, including immune checkpoint inhibitors. Finally, we discuss the current challenges and future directions to accelerate the clinical application of MDM2 inhibitors. In conclusion, targeting MDM2 remains a promising treatment approach, and targeting MDM2 for protein degradation represents a novel strategy to downregulate MDM2 without the side effects of the existing agents blocking p53-MDM2 binding. Additional preclinical and clinical investigations are needed to finally realize the full potential of MDM2 inhibition in treating cancer and other chronic diseases where MDM2 has been implicated. Significance Statement Overexpression/amplification of the MDM2 oncogene has been detected in various human cancers and is associated with disease progression, treatment resistance, and poor patient outcomes. This article reviews the previous, current, and emerging MDM2-targeted therapies and summarizes the preclinical and clinical studies combining MDM2 inhibitors with chemotherapy and immunotherapy regimens. The findings of these contemporary studies may lead to safer and more effective treatments for patients with cancers overexpressing MDM2.

Overexpression and activation of the murine double minute 2 (MDM2) or nuclear factor of activated T cells 1 (NFAT1) oncoproteins frequently occur in pancreatic cancer. Most MDM2 inhibitors under development target MDM2–p53 binding and have little or no effect on cancers without functional p53, including pancreatic cancer. Some available compounds indirectly inhibit NFAT1 activity by interfering with calcineurin activity, but there are currently no specific inhibitors against NFAT1. Here we performed a high-throughput virtual and cell-based screening to yield a lead compound (MA242) that can directly bind both MDM2 and NFAT1 with high affinity, induce their protein degradation, and inhibit NFAT1-mediated transcription of MDM2. As a result of this binding, MA242 decreased cell proliferation and induced apoptosis in pancreatic cancer cell lines regardless of p53 status. MA242 alone or in combination with gemcitabine inhibited pancreatic tumor growth and metastasis without any host toxicity. Our data indicate that targeting both MDM2 and NFAT1 represents a novel and effective strategy to treat pancreatic cancer. Significance: These findings suggest that pharmacological inhibition of both MDM2 and NFAT1 is a promising strategy for the treatment of pancreatic cancer, even in tumors lacking functional p53. Cancer Res; 78(19); 5656–67. ©2018 AACR.

Overexpression of the MDM2 oncogene and mutations in the p53 tumor suppressor commonly occur in hepatocellular carcinoma (HCC) and are associated with increased mortality due to this disease. Inhibiting MDM2 has been demonstrated to be a valid approach for the treatment of HCC. However, most of the MDM2 inhibitors evaluated to date have been designed to block the MDM2 and p53 binding, and have limited efficacy against tumors with mutant or deficient p53. In the present study, we developed a novel MDM2 inhibitor (termed SP141) that has direct effects on MDM2 and exerts anti-HCC activity independent of the p53 status of the cancer cells. We demonstrate that SP141 inhibits cell growth and prevents cell migration and invasion, independent of p53. Mechanistically, SP141 directly binds the MDM2 protein and promotes MDM2 degradation. The inhibition of MDM2 by SP141 also increases the sensitivity of HCC cells to sorafenib. In addition, in orthotopic and patient-derived xenograft models, SP141 inhibits MDM2 expression and suppresses tumor growth and metastasis, without any host toxicity. Furthermore, the inhibition of MDM2 by SP141 is essential for its anti-HCC activities. These results provide support for the further development of SP141 as a lead candidate for the treatment of HCC.

Prostate cancer remains a major health problem in the USA and worldwide. There is an urgent need to develop novel approaches to preventing primary and metastatic prostate cancer. We have identified 25-OCH₃-protopanaxadiol (GS25), the most active ginsenoside that has been identified so far; it has potent activity against human cancers, including prostate cancer. However, it has not been proven if GS25 could be a safe and effective agent for cancer prevention. In this study, we used the TRAMP model and clearly demonstrated that GS25 inhibited prostate tumorigenesis and metastasis with minimal host toxicity. Mechanistically, GS25 directly bound to the RING domain of MDM2, disrupted MDM2–MDMX binding and induced MDM2 protein degradation, resulting in strong inhibition of prostate cancer cell growth and metastasis, independent of p53 and androgen receptor status. In conclusion, our in vitro and in vivo data support the potential use of GS25 in prevention of primary and metastatic prostate cancer.

The β-catenin and MDM2 oncoproteins are overexpressed and constitutively activated in human pancreatic cancer and contribute to its initiation, progression, and metastasis. The Wnt/β-catenin signaling pathway strongly interacts with the MDM2-p53 signaling pathway, accelerating the tumorigenesis and its development. Therefore, therapies inhibiting both β-catenin and MDM2 are suggested to be ideal treatments for patients with advanced pancreatic cancer. We have recently identified a novel class of β-carboline compounds as the specific and potent MDM2 inhibitors, including a lead compound SP141. In the present study, we utilized SP141 as an exemplary β-carboline compound to characterize β-catenin as a molecular target of the β-carboline compounds and to demonstrate an important role of β-catenin in the anticancer activity of β-carboline. We found that the silencing of either β-catenin or MDM2 largely reduced the anticancer activity of SP141 while the double silencing of both genes almost completely blocked SP141’s activity. SP141 directly bound to β-catenin and inhibited its expression and activity in pancreatic cancer cells in vitro and in vivo. The inhibitory effects of SP141 on β-catenin were mediated by the ubiquitin–proteasome system in an MDM2-independent manner. In conclusion, these results suggest that SP141 exerts its anticancer activity by dually inhibiting β-catenin and MDM2. We envision that β-carboline derivatives can be developed as promising dual inhibitors of β-catenin and MDM2 for the treatment of advanced pancreatic cancer.