DNA interstrand cross-link (induced by cyclophosphamide alkylation of guanine)

Cyclophosphamide is a DNA-alkylating chemotherapeutic agent that is metabolically activated to phosphoramide mustard, which forms covalent bonds (alkyl adducts) at the N-7 position of guanine bases in DNA[1][2][6]. The most cytotoxic lesions are interstrand DNA crosslinks, in which two guanine bases on opposite DNA strands are covalently linked, preventing the strands from separating for replication or transcription[1][5]. These crosslinks, if unrepaired, block cell division and lead to programmed cell death (apoptosis)[2][4]. Cyclophosphamide-induced DNA crosslinks are central to the drug's anti-cancer and immunosuppressive effects, but also underlie many of its toxicities in non-cancerous cells, contributing to risks such as myelosuppression and secondary malignancies[4][5]. This entry describes a drug-induced DNA modification/lesion (DNA interstrand cross-link) rather than a canonical molecular target such as a protein, enzyme, or receptor. While this lesion is central to the mechanism of action of cyclophosphamide, it is an *effect* of the drug's interaction with DNA, not the 'target' itself in a conventional sense. The direct molecular target for cyclophosphamide is the guanine base within genomic DNA. Therefore, according to target classification conventions, this entry is marked as 'is_incorrect: true' for a target database, as it represents a biomolecular event or drug effect rather than a discrete, regulatable molecular entity.

Other names

DNA cross-linkInterstrand DNA cross-linkDNA adduct (specifically cyclophosphamide-induced N-7 guanine crosslink)

Cyclophosphamide is metabolized in the liver to form phosphoramide mustard, which alkylates the N-7 position of guanine, resulting in intra- and interstrand DNA crosslinks. These covalent interstrand crosslinks inhibit DNA replication and transcription, leading to cell death if the lesion cannot be repaired. If cross-links cannot be repaired, p53 activation leads to cell cycle arrest and subsequent programmed cell death (apoptosis).