Environmental degradation of human metabolites of cyclophosphamide leads to toxic and non-biodegradable transformation products

• Published in: The Science of the total environment Vol. 857; p. 159454
• Main Authors: Suk, Morten, Kümmerer, Klaus
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.01.2023
• Subjects: Antineoplastic drugs; Biodegradation; Cyclophosphamide; Degradation products; Metabolites; Nitrogen mustards; Biodegradation; Antineoplastic drugs; Cyclophosphamide; Degradation products; Nitrogen mustards; Metabolites
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.159454

The present study assessed the ready biodegradability of the prodrug cyclophosphamide (CPA) and its stable human metabolites in the closed bottle test (CBT). The results of the CBT showed that only the main human metabolite, carboxyphosphamide (CXP), was biodegradable to a certain extent (23 ± 2.4 % ThODNH3). All other metabolites showed neither biodegradation under these conditions nor were any toxic effects on the inoculum observed. Yet, HRMSn results revealed partial primary elimination of all human metabolites and formation of 25 new transformation products. Abiotic degradation via SNi and SN2 reactions was proposed as the main degradation pathway during the CBT. The main degradation products were assigned as 3-(2-chloroethyl)oxazolidin-2-one (COAZ), cytotoxic N-2-chloroethylaziridine (CEZ) and nor‑nitrogen mustard (NNM), an analogue of the chemical warfare agent HN2. While the acute ecotoxicity of the detected products is widely unknown, many have already been reported in medical literature to be either mutagenic, genotoxic, cytotoxic or carcinogenic and may therefore cause a greater risk than their precursors. QSAR models predicted that 16 of them are mutagenic and genotoxic, thus classifying the majority of the chemicals as potential environmental hazards. The central intermediates during the degradation process were proposed as CEZ and its corresponding aziridinium ion. However, other degradation products may occur depending on the type and strength of nucleophiles present in the matrices. Overall, the results demonstrated the importance to include human metabolites in the evaluation of the environmental fate of pharmaceuticals and their risk assessment especially when investigating prodrugs. The results underline the importance of identifying possible degradation products of metabolites, as they can be more toxic than related parent compounds and metabolites and can cause a greater risk to the environment and humans. [Display omitted] •Investigation of ready biodegradability of the human metabolites of CPA in the CBT•The main human metabolite of CPA, CXP, showed partial biodegradation.•Structural elucidation of 25 degradation products by HRMSn•Abiotic elimination via SNi and SN2 reaction mechanism is the main degradation pathway.•Identification of COAZ, the cytotoxic NNM and CEZ as major degradation products