# SiDNA

Signal interfering DNA (siDNA) is a class of short modified double stranded DNA molecules, 8–64 base pairs in length. siDNA molecules are capable of inhibiting DNA repair activities by interfering with multiple repair pathways. These molecules are known to act by mimicking DNA breaks and interfering with recognition and repair of DNA damage induced on chromosomes by irradiation or genotoxic products.

## Dbait

Dbait is a specific siDNA molecule that has been shown to mimic signalling of double-stranded DNA breaks (DSBs) in vivo. Currently, Dbait is the only type of siDNA molecule having been reviewed.

### Mechanism of Action of Dbait

The siDNA family, led by Dbait, consists of 32 base pairs deoxyribonucleotide forming an intramolecular double helix, which mimicks DNA double-strand break lesions. In the event of a double-stranded break in the genome, the cell most commonly repairs the damaged segment via non-homologous end joining (NHEJ). NHEJ involves the ligation of the damaged segments without using a homologous strand as a template, and can lead to frameshift mutations and failure of the cell to properly halt the cell division cycle, which could lead to the cancerization of the cell. Dbait functions primarily by targeting the NHEJ pathway, with the cell detecting the presence of siDNA molecules as double stranded breaks (DSBs). Dbait triggers baited activation of signalling enzymes involved in NHEJ-mediated genome repair to initiate the appropriate cellular response. Dbait is first bound to by Ku protein complexes that trigger the phosphorylation of NHEJ initiation factors such as DNA-PK (DNA-dependent protein kinase) and PARP (polyadenyl-ribose polymerase). DNA-PK overactivation through Dbait in turn triggers the activity of numerous signalling proteins in the NHEJ signalling cascade. DNA-PK hyperactivation induces pan-nuclear phosphorylation of histone H2AX among all the chromatin. H2AX phosphorylation is the signal, which allows double-strand break repair proteins to form DNA repair complexes selectively on DNA double-strand breaks. Dbait-dependent unspecific phosphorylation of H2AX results in inefficient double strand break recognition and repair.

## Possible therapeutic application of Dbait

Most anti-cancer therapies act by induction of DNA damage (chemotherapy and radiation therapy). DNA breaks are the most lethal damage for cells, as double-stranded breaks can lead to loss of entire chromosomal fragments, and even one single double-strand break if unrepaired is sufficient to lead to cell death. Dbait enhances the efficacy of the DNA damaging agents as demonstrated with radiation therapy and/or chemotherapy in multiple in vivo experimental models such as melanoma, glioblastoma and colorectal cancer.
Preclinical proof of concept of the synergic effect of the clinical candidate, DT01, with radiation therapy lead to a first-in-human Phase I, to evaluate the tolerance and efficacy of local DT01 administration in association with RT in patients suffering from in-transit metastases of melanoma. Encouraging results were published in May 2016.
* ↑ Quanz, M; Chassoux D; Berthault N; Agrario C; Sun JS; Dutreix M. (2009). "Hyperactivation of DNA-PK by double-strand break mimicking molecules disorganizes DNA damage response". PLOS ONE. 4 (7): e6298. Bibcode:2009PLoSO...4.6298Q. doi:10.1371/journal.pone.0006298. PMC 2709433. PMID 19621083.
* ↑ Dutreix, M.; Cosset, J. M.; Sun, J. -S. (2010-04-01). "Molecular therapy in support to radiotherapy". Mutation Research/Reviews in Mutation Research. ESF-EMBO Conference: Spatio-Temporal Radiation Biology: Transdisciplinary Advances for Biomedical Applications. 704 (1): 182–189. doi:10.1016/j.mrrev.2010.01.001. ISSN 1383-5742. PMID 20067843.
* ↑ Huang, X; Halicka HD; Darzynkiewicz Z. (2004). "Detection of histone H2AX phosphorylation on Ser-139 is an indicator of DNA damage (DNA double-strand breaks)". Current Protocols in Cytometry. Chapter 7: Unit 7.27. doi:10.1002/0471142956.cy0727s30. PMID 18770804. S2CID 32281084.
* ↑ Quanz, M; Chassoux D; Berthault N; Agrario C; Sun JS; Dutreix M. (2009). "Hyperactivation of DNA-PK by double-strand break mimicking molecules disorganizes DNA damage response". PLOS ONE. 4 (7): e6298. Bibcode:2009PLoSO...4.6298Q. doi:10.1371/journal.pone.0006298. PMC 2709433. PMID 19621083.
* ↑ Quanz M, Berthault N, Roulin C, Roy M, Herbette A, Agrario C, Alberti C, Josserand V, Coll JL, Sastre-Garau X, Cosset JM, Larue L, Sun JS, Dutreix M (2009). "Small-molecule drugs mimicking DNA damage: a new strategy for sensitizing tumors to radiotherapy". Clin. Cancer Res. 15 (4): 1308–16. doi:10.1158/1078-0432.CCR-08-2108. PMID 19190126.
* ↑ Berthault, N; Maury B; Agrario C; Herbette A; Sun JS; Peyrieras N; Dutreix M. (2011). "Comparison of distribution and activity of nanoparticles with short interfering DNA (Dbait) in various living systems". Cancer Gene Ther. 18 (10): 695–706. doi:10.1038/cgt.2011.39. PMC 3176463. PMID 21799529.
* ↑ Coquery N, Pannetier N, Farion R, Herbette A, Azurmendi L, Clarencon D, Bauge S, Josserand V, Rome C, Coll JL, Sun JS, Barbier EL, Dutreix M, Remy CC (2012). "Distribution and radiosensitizing effect of cholesterol-coupled Dbait molecule in rat model of glioblastoma". PLOS ONE. 7 (7): e40567. Bibcode:2012PLoSO...740567C. doi:10.1371/journal.pone.0040567. PMC 3398898. PMID 22815765.
* ↑ Devun, F; Bousquet G; Biau J; Herbette A; Roulin C; Berger F; Sun JS; Robine S; Dutreix M. (2012). "Preclinical study of the DNA repair inhibitor Dbait in combination with chemotherapy in colorectal cancer". J. Gastroenterol. 47 (3): 266–75. doi:10.1007/s00535-011-0483-x. PMID 22068457. S2CID 9579632.
* ↑ Le Tourneau, C; Dreno, B; Kirova, Y; Grob, J J; Jouary, T; Dutriaux, C; Thomas, L; Lebbé, C; Mortier, L (2016-05-24). "First-in-human phase I study of the DNA-repair inhibitor DT01 in combination with radiotherapy in patients with skin metastases from melanoma". British Journal of Cancer. 114 (11): 1199–1205. doi:10.1038/bjc.2016.120. ISSN 0007-0920. PMC 4891504. PMID 27140316.