[Dbait: An innovative concept to inhibit DNA repair and treat cancer]

The ability of cancer cells to recognize damage and initiate DNA repair is an important mechanism for therapeutic resistance. The use of inhibitors of DNA damage repair or signaling pathways appears to provide a unique opportunity for targeting genetic differences between tumor and normal cells. In this review, we firstly describe the main DNA lesions induced by the different treatments and the pathways involved in their repair. Then we review the mechanism of action and applications of an innovative DNA repair inhibitor: Dbait (and its clinical form DT01). Dbait/DT01 consists of 32 bp deoxyribonucleotides forming an intramolecular DNA double helix that mimics DNA lesions. They act as a bait for DNA damage signaling enzymes, the polyadenyl-ribose polymerase (PARP), and the DNA-dependent kinase (DNA-PK), inducing a "false" DNA damage signal and ultimately inhibiting recruitment at the damage site of many proteins involved in double-strand break and single-strand break repair pathways. Preclinical studies have demonstrated the capacity of Dbait/DT01 to improve the efficiency of (i) chemotherapy in colorectal cancer or hepatocellular carcinoma models, (ii) radiofrequency ablative in colorectal cancer liver metastases models, and (iii) radiotherapy in xenografted mice with head & neck squamous cell carcinoma, glioblastoma and melanoma. Following this good preclinical results, we performed a first-in-human phase 1-2a study evaluating the safety and efficacy of the combination of DT01 with radiotherapy for the treatment of skin metastases of melanoma. Twenty-three patients were included. No dose-limiting toxicity was observed. An objective response was observed in 59% lesions, including 30% complete responses. This first promising clinical efficacy provides future potential interesting clinical development of Dbait/DT01 with various anticancer treatments.

[Triple-negative breast cancer: histoclinical and molecular features, therapeutic management and perspectives]

Triple-negative breast cancer (TNBC), as defined by the absence of estrogen and progesterone receptor expression, as well as the lack of HER2 overexpression/amplification, corresponds to 15% of breast cancer and represents an aggressive form of the disease. TNBC are frequently confounded with basal subtype in the molecular classification of breast cancer and also share some similarities with BRCA1-mutated tumors. Epidemiological and clinical characteristics are distinct from other subtypes, including a younger age at diagnosis, a higher risk of relapse in spite of increased chemosensitivity, and a higher incidence of lung and brain metastatic relapses. Conventional cytotoxics remain the mainstay of current systemic management but recent evaluation of more targeted therapeutics, including specific cytotoxics (such as the use of platinum salts), PARP and EGFR inhibition, and antiangiogenics have been performed, providing contrasted but rather disappointing results. Recent data indicate that TNBC represent a heterogeneous entity composed of multiple and distinct molecular subtypes, which should deserve specific targeted therapeutics.

A DNA repair BRCA1 estrogen receptor and targeted therapy in breast cancer

BRCA1 is a key mediator of DNA repair pathways and participates in the maintenance of the genomic integrity of cells. The control of DNA damage repair mechanisms by BRCA1 is of great interest since molecular defects in this pathway may reflect a predictive value in terms of a cell’s sensitivity to DNA damaging agents or anticancer drugs. BRCA1 has been found to exhibit a hormone-dependent pattern of expression in breast cells. Wild-type BRCA1 is required for the inhibition of the growth of breast tumor cells in response to the pure steroidal ERα antagonist fulvestrant. Also a loss of BRCA1-mediated transcriptional activation of ERα expression results in increased resistance to ERα antagonists. Platinum-based drugs, poly(ADP-ribose) polymerase (PARP) inhibitors, and their combination are currently included in chemotherapy regimens for breast cancer. Preclinical and clinical studies in a BRCA1-defective setting have recently indicated a rationale for the use of these compounds against hereditary breast cancers. Initial findings indicate that neoadjuvant use of cisplatin results in high rates of complete pathological response in patients with breast cancer who have BRCA1 mutations. Cisplatin produces a better response in triple-negative breast cancer (TNBC) than in non-TNBC diseases in both the neoadjuvant and adjuvant settings. This implies that TNBC cells may harbor a dysfunctional BRCA1 repair pathway.