Activity of BET-proteolysis targeting chimeric (PROTAC) compounds in triple negative breast cancer

Abstract

Background Triple negative breast cancer (TNBC) is an incurable disease where novel therapeutic strategies are needed. Proteolysis targeting chimeric (PROTAC) are novel compounds that promote protein degradation by binding to an ubiquitin ligase. In this work, we explored the antitumoral activity of two novel BET-PROTACs, MZ1 and ARV-825, in TNBC, ovarian cancer and in a BET inhibitor resistant model. Methods OVCAR3, SKOV3, BT549, MDA-MB-231 cell lines and the JQ1 resistant cell line MDA-MB-231R were evaluated. MTTs, colony-forming assay, three-dimensional cultures in matrigel, flow cytometry, and western blots were performed to explore the anti-proliferative effect and biochemical mechanism of action of MZ1 and ARV-825. In vivo studies included BALB/c nu/nu mice engrafted with MDA-MB-231R cells. Results The BET-PROTACs MZ1 and ARV-825 efficiently downregulated the protein expression levels of the BET protein BRD4, in MDA-MB-231 and MDA-MB-231R. MZ1 and ARV-825 also showed an antiproliferative effect on sensitive and resistant cells. This effect was corroborated in other triple negative (BT549) and ovarian cancer (SKOV3, OVCAR3) cell lines. MZ1 provoked G2/M arrest in MDA-MB-231. In addition, a profound effect on caspase-dependent apoptosis was observed in both sensitive and resistant cells. No synergistic activity was observed when it was combined with docetaxel, cisplatin or olaparib. Finally, in vivo administration of MZ1 rescued tumor growth in a JQ1-resistant xenograft model, reducing the expression levels of BRD4. Conclusions Using both in vitro and in vivo approaches, we describe the profound activity of BET-PROTACs in parental and BETi-resistant TNBC models. This data provides options for further clinical development of these agents in TNBC. Electronic supplementary material The online version of this article (10.1186/s13046-019-1387-5) contains supplementary material, which is available to authorized users.

Targeting non-canonical activation of GLI1 by the SOX2-BRD4 transcriptional complex improves the efficacy of HEDGEHOG pathway inhibition in melanoma

“…Further, BET inhibitors such as JQ1 show a very short half-life, and the concentrations required to mediate single agent activity exceed physiologic safety levels in vivo [ 37 ]. The BRD4 degrader MZ1 potently and rapidly induces preferential removal of BRD4 over BRD2 and BRD3, and has shown high efficacy in ovarian and triple-negative breast cancer in vivo [ 38 ]. The activity of MZ1 is dependent on binding to VHL but is achieved at a sufficiently low concentration not to induce stabilization of the VHL substrate HIF-1α [ 13 ].…”

Major advances in targeted protein degradation: PROTACs, LYTACs, and MADTACs

“…To explore the role of cooperativity in ternary complex formation, the Ciulli group studied PROTAC-induced degradation of the BET protein family (BRD2, BRD3, BRD4) ( 83 ), a protein family extensively studied in the PROTAC field ( 27 , 60 , 73 , 74 , 81 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ). Using SPR and ITC, they found that ternary complexes with positive cooperativity (BRD4 BR2 :PROTAC MZ1:VHL; α = 22) caused more efficient cellular degradation than complexes with negative cooperativity (BRD4 BR2 :PROTAC MP61:VHL; α = 0.2).…”

Significance of Selective Protein Degradation in the Development of Novel Targeted Drugs and Its Implications in Cancer Therapy

“…[ 144 ] BRD4 is a member of the BET protein family, and the PROTAC ARV‐825, which was constructed with the BRD4 inhibitor OTX015 and the CRBN ligand pomalidomide, was shown to selectively degrade BRD4 in Burkitt's lymphoma, triple‐negative breast cancer, multiple myeloma, and cholangiocarcinoma cells. [ 129,145–147 ] Interestingly, ARV‐825 also plays an important role in the treatment of vemurafenib‐resistant melanoma. [ 148 ] Another BRD4‐targeted PROTAC ARV‐771 was synthesized with a BRD4 inhibitor and VHL ligand and experimental results showed rapid degradation of BRD2/3/4 in castration‐resistant prostate cancer.…”