Background Pathological forms of TAR DNA-binding protein 43 (TDP-43) are present in motor neurons of almost all amyotrophic lateral sclerosis (ALS) patients, and mutations in TDP-43 are also present in ALS. Loss and gain of TDP-43 functions are implicated in pathogenesis, but the mechanisms are unclear. While the RNA functions of TDP-43 have been widely investigated, its DNA binding roles remain unclear. However, recent studies have implicated a role for TDP-43 in the DNA damage response. Methods We used NSC-34 motor neuron-like cells and primary cortical neurons expressing wildtype TDP-43 or TDP-43 ALS associated mutants (A315T, Q331K), in which DNA damage was induced by etoposide or H2O2 treatment. We investigated the consequences of depletion of TDP-43 on DNA repair using small interfering RNAs. Specific non homologous end joining (NHEJ) reporters (EJ5GFP and EJ2GFP) and cells lacking DNA-dependent serine/threonine protein kinase (DNA-PK) were used to investigate the role of TDP-43 in DNA repair. To investigate the recruitment of TDP-43 to sites of DNA damage we used single molecule super-resolution microscopy and a co-immunoprecipitation assay. We also investigated DNA damage in an ALS transgenic mouse model, in which TDP-43 accumulates pathologically in the cytoplasm. We also examined fibroblasts derived from ALS patients bearing the TDP-43 M337V mutation for evidence of DNA damage. Results We demonstrate that wildtype TDP-43 is recruited to sites of DNA damage where it participates in classical NHEJ DNA repair. However, ALS-associated TDP-43 mutants lose this activity, which induces DNA damage. Furthermore, DNA damage is present in mice displaying TDP-43 pathology, implying an active role in neurodegeneration. Additionally, DNA damage triggers features typical of TDP-43 pathology; cytoplasmic mis-localisation and stress granule formation. Similarly, inhibition of NHEJ induces TDP-43 mis-localisation to the cytoplasm. Conclusions This study reveals that TDP-43 functions in DNA repair, but loss of this function triggers DNA damage and is associated with key pathological features of ALS.

Mitoxantrone was efficiently encapsulated within cucurbit[8]uril in a 2:1 complex where the two mitoxantrone molecules were symmetrically located through both portals of a cucurbit[8]uril cage. The novel complex facilitates increased mitoxantrone uptake in mouse breast cancer cells and decreases the toxicity of the drug in healthy mice. In an orthotopic mouse model of metastatic breast cancer the complex still maintains anticancer activity compared to the free drug, yet provides a statistically significant increase in the survival of these mice compared to conventional mitoxantrone treatment. This new low toxicity formulation offers the possibility to increase mitoxantrone dose and thus maximize efficacy while managing the dose limiting side effects.

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Anthracyclines are a clinically important class of antineoplastic agents used to treat a wide variety of solid and blood cancers. The first described anthracycline, daunorubicin, was first isolated from a strain of Streptomyces peucetius in the early 1960s. Clinically the most widely used are doxorubicin, daunorubicin and their semisynthetic derivatives epirubicin and idarubicin. They primarily act by intercalating with DNA and inhibiting topoisomerase II, resulting in DNA breaks and abrogated DNA synthesis. The most serious side effect of anthracycline use is cumulative dose-dependent cardiotoxicity, limiting recommended maximum lifetime treatment to 400-450 mg/m2. Several liposomal formulations of doxorubicin are in use, having the benefits of prolonging retention rate while reducing peak plasma concentration of free drug. Several clinical trials of anthracycline-loaded nanoparticles are currently underway.

Chemotherapy remains as the mainstay systemic therapy for triple negative breast cancer patients since targeted therapies are not suitable for this breast cancer subtype. Among the chemotherapies for triple negative breast cancer, doxorubicin is known to be effective but its use is hampered by a risk of developing doxorubicin-mediated cardiomyopathy. Doxorubicin causes cardiotoxicity primarily through topoisomerase-IIβ poisoning, resulting in cardiomyocyte apoptosis. Notably, cardioprotection has been reported after combination treatment of doxorubicin with an acyloxyalkyl ester, AN-7 in an in vivo model. As an acyloxyalkyl ester, AN-7 also releases formaldehyde upon esterase hydrolysis. Therefore, the aim of this study was to elucidate the mechanism of cardioprotection conferred by the co-treatment of doxorubicin with formaldehyde-releasing prodrugs in BALB/c mice bearing mammary 4T1.2 tumours. Both experimental and clinically available formaldehyde-releasing prodrugs were investigated in this triple negative breast cancer model. Cardiac damage was induced with a single dose of doxorubicin at 16 mg/kg in mammary tumour-bearing mice. Combined treatment of doxorubicin and formaldehyde-releasing prodrugs significantly reduced γH2AX foci (a marker for topoisomerase-IIβ poisoning) and protected the heart from doxorubicin-induced myocardial apoptosis. To investigate if the combination treatments were cardioprotective due to alteration in doxorubicin biodistribution, the initial response to the first dose of doxorubicin was investigated by treating tumour-bearing mice with 4 mg/kg 14C-doxorubicin. Addition of formaldehyde-releasing prodrugs enhanced formation of formaldehyde-mediated doxorubicin-DNA adducts in the hearts, independent of doxorubicin biodistribution in the heart, blood and tumours. This doxorubicin-DNA adduct forming treatment was associated with a novel cardiac transcriptomic profile as compared to doxorubicin single agent treatment, as assessed by RNA-sequencing. These combination treatments also maintained doxorubicin antitumour efficacy with respect to inducing dsDNA breaks, promoting apoptosis and inhibiting mammary tumour proliferation. The switch in doxorubicin action from cardiac topoisomerase-IIβ poisoning to doxorubicin-DNA adduct formation protects the heart from doxorubicin-mediated cardiac damage. Hence, the combination treatment of doxorubicin and formaldehyde-releasing prodrugs may be a promising cardioprotective therapy that does not compromise doxorubicin activity against mammary tumours. Citation Format: Alison Cheong, Sean McGrath, Tina Robinson, Ruqaya Maliki, Alex Spurling, Ada Rephaeli, Abraham Nudelman, Don R. Phillips, Belinda S. Parker, Salvatore Pepe, Suzanne M. Cutts. A switch in mechanism of action attenuates doxorubicin-mediated cardiotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 992.