MDM2-Recruiting PROTAC Offers Superior, Synergistic Antiproliferative Activity via Simultaneous Degradation of BRD4 and Stabilization of p53

Abstract

While the number of proteins effectively targeted for post-translational degradation by PROTAC has grown steadily, the number of E3 ligases successfully exploited to accomplish this has been limited to the few for which small molecule ligands have been discovered. Although the E3 ligase MDM2 is bound by the nutlin class of small molecule ligands, there are few nutlin-based PROTAC. Since a nutlin-based PROTAC should both knockdown its target protein and upregulate the tumor suppressor, p53, we examined the ability of such a PROTAC to decrease cancer cell viability. A nutlin-based, BRD4-degrading PROTAC, A1874, was able to degrade its target protein by 98% with nanomolar potency. Given the complementary ability of A1874 to stabilize p53, we discovered that the nutlin-based PROTAC was more effective in inhibiting proliferation of many cancer cell lines with wild type p53 than was a corresponding VHL-utilizing PROTAC with similar potency and efficacy to degrade BRD4. This is the first report of a PROTAC in which the E3 ligase ligand and targeting warhead combine to exert a synergistic antiproliferative effect. Our study highlights the untapped potential that may be unlocked by expanding the repertoire of E3 ligases that can be recruited by PROTAC.

Systematic exploration of different E3 ubiquitin ligases: an approach towards potent and selective CDK6 degraders

“…48 For MDM2, the highly potent and selective antagonist idasanutlin (6), 49 was chosen, which has already been successfully incorporated into BRD4-targeting PROTACs. 50 The resulting IAP-and MDM2-based degraders 35 and 37 are depicted in Tables 3 and S5 Previous reports on principles of PROTAC design highlighted the importance of different physiochemical properties to achieve successful degradation. 46,51,52 In order to assess activity determining physicochemical properties, we calculated molecular descriptors, i.e.…”

“…S17, ESI †). Given that any MDM2-based compound might possess additional biological activities by p53/p21 activation, 50,77 CDK4/6 downregulation should be considered as a relevant off-target effect of heterobifunctional MDM2 degraders.…”

A therapeutic patent overview of MDM2/X-targeted therapies (2014–2018)

“…The activity of the disclosed compounds was assessed by a suitable cell-line analysis and the results were categorized in three classes of activity, giving the best result in the category of the degradation of the targeted protein larger the 50% at 1 μM concertation. This simultaneous targeting of the two important cancer-related proteins, namely p53 and BRD4, was recently shown by the Arvinas R&D employees to give much improved results in in vitro cell linebased assays, as compared with a corresponding VHL-utilizing PROTAC with similar potency and efficacy to degrade BRD4 [75].…”

Advances in targeted degradation of endogenous proteins

“…Recently, a potent PROTAC has been developed that connects the MDM2-binder idasanutlin and the bromodomain containing protein 4 (BRD4) inhibitor JQ1. This PROTAC, A1874, degraded BRD4 almost completely in HCT116 cells at 100 nM within 24 h. Additionally, PROTAC treatment led to the stabilization of p53 and had an antiproliferative effect that was synergistic when compared to treatments with either inhibitor alone [68].…”