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CX-5461 Enhances the Efficacy of APR-246 via Induction of DNA Damage and Replication Stress in Triple-Negative Breast Cancer.

ABSTRACT: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer lacking targeted therapy. Here, we evaluated the anti-cancer activity of APR-246, a P53 activator, and CX-5461, a RNA polymerase I inhibitor, in the treatment of TNBC cells. We tested the efficacy of individual and combination therapy of CX-5461 and APR-246 in vitro, using a panel of breast cancer cell lines. Using publicly available breast cancer datasets, we found that components of RNA Pol I are predominately upregulated in basal-like breast cancer, compared to other subtypes, and this upregulation is associated with poor overall and relapse-free survival. Notably, we found that the treatment of breast cancer cells lines with CX-5461 significantly hampered cell proliferation and synergistically enhanced the efficacy of APR-246. The combination treatment significantly induced apoptosis that is associated with cleaved PARP and Caspase 3 along with Annexin V positivity. Likewise, we also found that combination treatment significantly induced DNA damage and replication stress in these cells. Our data provide a novel combination strategy by utilizing APR-246 in combination CX-5461 in killing TNBC cells that can be further developed into more effective therapy in TNBC therapeutic armamentarium.

SUBMITTER: Makhale A

PROVIDER: S-EPMC8198831 | biostudies-literature |

REPOSITORIES: biostudies-literature

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APR-246 Enhances Colorectal Cancer Sensitivity to Radiotherapy.

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Project description:The TP53 tumor suppressor gene is frequently inactivated in human tumors by missense mutations in the DNA binding domain. TP53 mutations lead to protein unfolding, decreased thermostability and loss of DNA binding and transcription factor function. Pharmacological targeting of mutant p53 to restore its tumor suppressor function is a promising strategy for cancer therapy. The mutant p53 reactivating compound APR-246 (PRIMA-1Met) has been successfully tested in a phase I/IIa clinical trial. APR-246 is converted to the reactive electrophile methylene quinuclidinone (MQ), which binds covalently to p53 core domain. We identified cysteine 277 as a prime binding target for MQ in p53. Cys277 is also essential for MQ-mediated thermostabilization of wild-type, R175H and R273H mutant p53, while both Cys124 and Cys277 are required for APR-246-mediated functional restoration of R175H mutant p53 in living tumor cells. These findings may open opportunities for rational design of novel mutant p53-targeting compounds.

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Project description:Two main causes of platinum resistance are mutation in the tumor suppressor gene TP53 and drug-induced increase in intracellular glutathione concentration. Mutations in TP53 occur in about 50% of human tumors. APR-246 (PRIMA-1(MET)) is the first clinical-stage compound that reactivates mutant p53 and induces apoptosis. APR-246 is a prodrug that is converted to the active compound methylene quinuclidinone (MQ), a Michael acceptor that binds to cysteine residues in mutant p53 and restores its wild-type conformation. Here, we show that MQ also binds to cysteine in glutathione, thus decreasing intracellular free glutathione concentration. We also show that treatment with APR-246 completely restores the cisplatin and doxorubicin sensitivity to p53-mutant drug-resistant ovarian cancer cells. We propose that this unique ability of APR-246/MQ to bind to cysteines in both mutant p53 and glutathione has a key role in the resensitization as well as in the outstanding synergistic effects observed with APR-246 in combination with platinum compounds in ovarian cancer cell lines and primary cancer cells. However, MQ binding to cysteines in other targets, for example, thioredoxin reductase, may contribute as well. Strong synergy was also observed with the DNA-damaging drugs doxorubicin and gemcitabine, while additive effects were found with the taxane docetaxel. Our results provide a strong rationale for the ongoing clinical study with APR-246 in combination with platinum-based therapy in patients with p53-mutant recurrent high-grade serous (HGS) ovarian cancer. More than 96% of these patients carry TP53 mutations. Combined treatment with APR-246 and platinum or other DNA-damaging drugs could allow dramatically improved therapy of a wide range of therapy refractory p53 mutant tumors.

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RAD51 ChIP-seq post treatment with CX-5461

Project description:We discovered two small molecule drugs - CX-5461 and CX-3543 - with specific toxicity against BRCA deficiencies in cancer cells and xenograft models. Both CX-5461 and CX-3543 have been previously recognized as RNA pol I inhibitors. CX-5461 is in advanced phase 1 trials for treatment of lymphoma and leukemia through rDNA transcription inhibition in a p53-dependent mechanism. We have discovered a novel activity of CX-5461, as a stabilizer of G-quadruplex DNA sequences inside cells the same as CX-3543. We found that BRCA1 and BRCA2 deficiency markedly increases (one log order) sensitivity to CX-5461 and a related drug CX-3543 in human cancer cell lines and polyclonal patient derived xenograft models, providing a direct therapeutic hypothesis, including PDX tumours resistant to PARP inhibition. We show that in epithelial cells, exposure to CX-5461 and CX-3543 blocks replication forks and induces ssDNA gaps or breaks. The BRCA and NHEJ pathways are required for the repair of CX-5461 and CX-3543 induced DNA damage and failure to do so leads to lethality. RNA pol I inhibition is not a required component of the cell killing mechanism in these tumours, because BRCA2 deficient cells are not more sensitive to BMH-21, a more potent rDNA transcription inhibitor. These data strengthen the concept of G4 targeting as a therapeutic approach, specifically for targeting HR and NHEJ deficient cancers and other tumors deficient for DNA damage repair. Since CX-5461 is already in advanced phase 1 trials for other indications, this has resulted in immediately testable translational implications (Canadian trial, NCT02719977, opened May 2016) as no phase-1 eligible G4 stabilizers have been described to date.

2016-12-06 | GSE90967 | GEO

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