[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.

[Alkylating agents]

With the approval of mechlorethamine by the FDA in 1949 for the treatment of hematologic malignancies, alkylating agents are the oldest class of anticancer agents. Even though their clinical use is far beyond the use of new targeted therapies, they still occupy a major place in specific indications and sometimes represent the unique option for the treatment of refractory diseases. Here, we are reviewing the major classes of alkylating agents and their mechanism of action, with a particular emphasis for the new generations of alkylating agents. As for most of the chemotherapeutic agents used in the clinic, these compounds are derived from natural sources. With a complex but original mechanism of action, they represent new interesting alternatives for the clinicians, especially for tumors that are resistant to conventional DNA damaging agents. We also briefly describe the different strategies that have been or are currently developed to potentiate the use of classical alkylating agents, especially the inhibition of pathways that are involved in the repair of DNA lesions induced by these agents. In this line, the development of PARP inhibitors is a striking example of the recent regain of interest towards the "old" alkylating agents.