Doxorubicin (DOX) and mitoxantrone (MTX) are two chemotherapeutic drugs, inhibitors of topoisomerase II that are used against several types of cancer. Regardless of their efficacy in cancer treatment, these drugs can cause long-term toxicity in several organs. The chemotherapy-induced cognitive impairment or ‘chemobrain’ has been widely demonstrated in neuropsychological testing in cancer patients, even several years after treatment. Nonetheless, the underlying mechanisms of chemobrain are still not fully understood. Our work aimed to evaluate the effects of clinically relevant cumulative doses of DOX or MTX on the brain of male CD-1 mice at 3 different ages [juvenile (4 weeks), adult (3 months) and old (18-20 months)]. Mice received intraperitoneal injections of the drugs or a saline solution (control groups), twice a week, for 3 weeks. Between different aged groups, MTX-groups received a total cumulative dose of MTX 6 mg/kg. Regarding DOX, infant and adults received a cumulative dose of DOX 18 mg/kg, while the old group received a total cumulative dose of DOX 9 mg/kg. During the entire experimental procedure mice well-being was monitored, as well as food and water consumption. Mice were euthanized one week (adults and old mice) or seventeen days (juvenile mice) after the last injection and several determinations were done.

Concerning the brain’s redox status, total glutathione (GSHt), reduced glutathione (GSH) and GSH/oxidized glutathione (GSSG) ratio decreased in DOX adults, but in DOX infant brains despite receiving an equal cumulative dose no changes were seen. Nevertheless, DOX increased brain ATP levels in juvenile mice. MTX did not cause significant changes neither in glutathione nor in ATP brain levels in the groups tested. An extra experimental procedure was done with adult mice, where the left brain hemisphere was fixated in 4% paraformaldehyde, mounted in a vibratome and sectioned in the coronal plane throughout its extent. A systematic random sampling of the coronal sections was done at 480 µm interval. The sections obtained are being used for immunofluorescent detection of phosphorylated Tau, glial fibrillary acidic protein, BAX and p53 proteins in the hippocampus formation.

In conclusion, our work showed that DOX and MTX differentially impact the brain and that DOX evoked damage might be dependent on animals’ age.

Ackowledgments:

ARM and VMC acknowledge Fundação da Ciência e Tecnologia (FCT) for their grants (SFRH/BD/129359/2017 and SFRH/BPD/110001/2015). Work supported by FEDER funds through the Operational Programme for Competitiveness Factors – COMPETE and by national funds by the FCT within the project “PTDC/DTP-FTO/1489/2014 – POCI-01-0145-FEDER-016537”.