Abstract B5: Preclinical characterization of a novel orally-available MDM2 inhibitor DS-3032b: Anti-tumor profile and predictive biomarkers for sensitivity

Synthesis and biological evaluation of 4-imidazolidinone-containing compounds as potent inhibitors of the MDM2/p53 interaction

Inhibition of MDM2/p53 interaction with small-molecule inhibitors stabilizes p53 from MDM2 mediated degradation, which is a promising strategy for the treatment of cancer. In this report, a novel series of 4-imidazolidinone-containing compounds have been synthesized and tested in MDM2/p53 and MDM4/p53 FP binding assays. Upon SAR studies, compounds 2 (TB114) and 22 were identified as the most potent inhibitors of MDM2/p53 but not MDM4/p53 interactions. Both 2 and 22 exhibited strong antiproliferative activities in HCT-116 and MOLM-13 cell lines harboring wild type p53. Mechanistic studies show that 2 and 22 dose-dependently activated p53 and its target genes and induced apoptosis in cells based on the Western blot, qPCR, and flow cytometry assays. In addition, the antiproliferative activities of 2 and 22 were dependent on wild type p53, while they were not toxic to HEK-293 kidney cells. Furthermore, the on-target activities of 2 were general and applicable to other cancer cell lines with wild type p53. These attributes make 2 a good candidate for future optimization to discover a potential treatment of wild-type p53 cancer.

Design, Synthesis, Chemical and Biochemical Insights Into Novel Hybrid Spirooxindole-Based p53-MDM2 Inhibitors With Potential Bcl2 Signaling Attenuation

The tumor resistance to p53 activators posed a clinical challenge. Combination studies disclosed that concomitant administration of Bcl2 inhibitors can sensitize the tumor cells and induce apoptosis. In this study, we utilized a rapid synthetic route to synthesize two novel hybrid spirooxindole-based p53-MDM2 inhibitors endowed with Bcl2 signaling attenuation. The adducts mimic the thematic features of the chemically stable potent spiro [3H-indole-3,2'-pyrrolidin]-2(1H)-ones p53-MDM2 inhibitors, while installing a pyrrole ring via a carbonyl spacer inspired by the natural marine or synthetic products that efficiently inhibit Bcl2 family functions. A chemical insight into the two synthesized spirooxindoles including single crystal x-ray diffraction analysis unambiguously confirmed their structures. The synthesized spirooxindoles 2a and 2b were preliminarily tested for cytotoxic activities against normal cells, MDA-MB 231, HepG-2, and Caco-2 via MTT assay. 2b was superior to 5-fluorouracil. Mechanistically, 2b induced apoptosis-dependent anticancer effect (43%) higher than that of 5-fluorouracil (34.95%) in three studied cancer cell lines, activated p53 (47%), downregulated the Bcl2 gene (1.25-fold), and upregulated p21 (2-fold) in the treated cancer cells. Docking simulations declared the possible binding modes of the synthesized compounds within MDM2.

Dispirooxindoles Based on 2-Selenoxo-Imidazolidin-4-Ones: Synthesis, Cytotoxicity and ROS Generation Ability

A regio- and diastereoselective synthesis of two types of dispiro derivatives of 2-selenoxoimidazolidin-4-ones, differing in the position of the nitrogen atom in the central pyrrolidine ring of the spiro-fused system-namely, 2-selenoxodispiro[imidazolidine-4,3'-pyrrolidine-2',3″-indoline]-2″,5-diones (5a-h) and 2-senenoxodispiro[imidazolidine-4,3'-pyrrolidine-4',3″-indoline]-2″,5-diones (6a-m)-were developed based on a 1,3-dipolar cycloaddition of azomethine ylides generated from isatin and sarcosine or formaldehyde and sarcosine to 5-arylidene or 5-indolidene-2-selenoxo-tetrahydro-4H-imidazole-4-ones. Selenium-containing dispiro indolinones generally exhibit cytotoxic activity near to the activity of the corresponding oxygen and sulfur-containing derivatives. Compounds 5b, 5c, and 5e demonstrated considerable in vitro cytotoxicity in the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) test (concentration of compounds that caused 50% death of cells (CC₅₀) 7.6-8.7 μM) against the A549 cancer cell line with the VA13/A549 selectivity index 5.2-6.9; some compounds (5 and 6) increased the level of intracellular reactive oxygen species (ROS) in the experiment on A549 and PC3 cells using platinized carbon nanoelectrode. The tests for p53 activation for compounds 5 and 6 on the transcriptional reporter suggest that the investigated compounds can only have an indirect p53-dependent mechanism of action. For the compounds 5b, 6b, and 6l, the ROS generation may be one of the significant mechanisms of their cytotoxic action.

The past, present and future of potential small-molecule drugs targeting p53-MDM2/MDMX for cancer therapy

The p53 gene, a well-known tumor suppressor gene, plays a crucial role in cell cycle regulation, DNA repair, cell differentiation, and apoptosis. MDM2 exerts p53-dependent activity mainly by binding to p53 protein to form MDM2-p53 negative feedback loop. In addition, MDM2 is involved in a number of pathways that regulate cell proliferation and apoptosis, playing a p53-independent role. The p53 binding domain of MDMX bind to p53 transcriptional activation domain, inhibiting the transcriptional activity of p53 on its downstream genes, but does not mediate the degradation of p53. The anti-tumor effect is exerted by inhibiting the interaction between the MDM2/MDMX protein and the p53 protein by a small-molecule or by restoring the activity of the p53 protein. This review describes in the structural features, biological functions and mechanisms of p53-MDM2/MDMX, and summarizes small-molecule targeting p53-MDM2/MDMX.

Targeted Synthesis of Complex Spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-ones by Intramolecular Cyclization of Azomethine Ylides: Highly Potent MDM2-p53 Inhibitors

Mouse double minute 2 (MDM2) is a main and direct inhibitor of the crucial tumor suppressor p53. Reports from initial clinical trials showed that blocking this interaction with a small-molecule inhibitor can have great value in the treatment of cancer for patients with p53 wild-type tumors; however, it also revealed dose-limiting hematological toxicities and drug-induced resistance as main issues. To overcome the former, an inhibitor with superior potency and pharmacokinetic properties to ultimately achieve full efficacy with less-frequent dosing schedules is required. Toward this aim, we optimized our recently reported spiro-oxindole inhibitors by focusing on the crucial interaction with the amino acid side chain of His96MDM2 . The designed molecules required the targeted synthesis of structurally complex spiro[indole-3,2'-pyrrolo[2,3-c]pyrrole]-2,4'-diones for which we developed an unprecedented intramolecular azomethine ylide cycloaddition and investigated the results by computational methods. One of the new compounds showed superior cellular potency over previously reported BI-0252. This finding is a significant step toward an inhibitor suitable to potentially mitigate hematological on-target adverse effects.

Discovery of Novel Spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-one Compounds as Chemically Stable and Orally Active Inhibitors of the MDM2-p53 Interaction

Scaffold modification based on Wang's pioneering MDM2-p53 inhibitors led to novel, chemically stable spiro-oxindole compounds bearing a spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-one scaffold that are not prone to epimerization as observed for the initial spiro[3H-indole-3,3'-pyrrolidin]-2(1H)-one scaffold. Further structure-based optimization inspired by natural product architectures led to a complex fused ring system ideally suited to bind to the MDM2 protein and to interrupt its protein-protein interaction (PPI) with TP53. The compounds are highly selective and show in vivo efficacy in a SJSA-1 xenograft model even when given as a single dose as demonstrated for 4-[(3S,3'S,3'aS,5'R,6'aS)-6-chloro-3'-(3-chloro-2-fluorophenyl)-1'-(cyclopropylmethyl)-2-oxo-1,2,3',3'a,4',5',6',6'a-octahydro-1'H-spiro[indole-3,2'-pyrrolo[3,2-b]pyrrole]-5'-yl]benzoic acid (BI-0252).