Effects of the potassium-sparing diuretic amiloride on chemotherapy response in canine osteosarcoma cells

Repurposing Drugs in Small Animal Oncology

Repurposing drugs in oncology consists of using off-label drugs that are licensed for various non-oncological medical conditions to treat cancer. Repurposing drugs has the advantage of using drugs that are already commercialized, with known mechanisms of action, proven safety profiles, and known toxicology, pharmacokinetics and pharmacodynamics, and posology. These drugs are usually cheaper than new anti-cancer drugs and thus more affordable, even in low-income countries. The interest in repurposed anti-cancer drugs has led to numerous in vivo and in vitro studies, with some promising results. Some randomized clinical trials have also been performed in humans, with certain drugs showing some degree of clinical efficacy, but the true clinical benefit for most of these drugs remains unknown. Repurposing drugs in veterinary oncology is a very new concept and only a few studies have been published so far. In this review, we summarize both the benefits and challenges of using repurposed anti-cancer drugs; we report and discuss the most relevant studies that have been previously published in small animal oncology, and we suggest potential drugs that could be clinically investigated for anti-cancer treatment in dogs and cats.

Impact of tumor microenvironment on adoptive T cell transfer activity

Recent advances in immunotherapy have revolutionized the treatment of cancer. The use of adoptive cell therapies (ACT) such as those based on tumor infiltrating lymphocytes (TILs) or genetically modified cells (transgenic TCR lymphocytes or CAR-T cells), has shown impressive results in the treatment of several types of cancers. However, cancer cells can exploit mechanisms to escape from immunosurveillance resulting in many patients not responding to these therapies or respond only transiently. The failure of immunotherapy to achieve long-term tumor control is multifactorial. On the one hand, only a limited percentage of the transferred lymphocytes is capable of circulating through the bloodstream, interacting and crossing the tumor endothelium to infiltrate the tumor. Metabolic competition, excessive glucose consumption, the high level of lactic acid secretion and the extracellular pH acidification, the shortage of essential amino acids, the hypoxic conditions or the accumulation of fatty acids in the tumor microenvironment (TME), greatly hinder the anti-tumor activity of the immune cells in ACT therapy strategies. Therefore, there is a new trend in immunotherapy research that seeks to unravel the fundamental biology that underpins the response to therapy and identifies new approaches to better amplify the efficacy of immunotherapies. In this review we address important aspects that may significantly affect the efficacy of ACT, indicating also the therapeutic alternatives that are currently being implemented to overcome these drawbacks.

Overcoming T cell dysfunction in acidic pH to enhance adoptive T cell transfer immunotherapy

The high metabolic activity and insufficient perfusion of tumors leads to the acidification of the tumor microenvironment (TME) that may inhibit the antitumor T cell activity. We found that pharmacological inhibition of the acid loader chloride/bicarbonate anion exchanger 2 (Ae2), with 4,4’-diisothiocyanatostilbene-2,2’-disulfonicacid (DIDS) enhancedCD4⁺ andCD8⁺ T cell function upon TCR activation in vitro, especially under low pH conditions. In vivo, DIDS administration delayed B16OVA tumor growth in immunocompetent mice as monotherapy or when combined with adoptive T cell transfer of OVA-specificT cells. Notably, genetic Ae2 silencing in OVA-specificT cells improvedCD4⁺/CD8⁺ T cell function in vitro as well as their antitumor activity in vivo. Similarly, genetic modification of OVA-specificT cells to overexpress Hvcn1, a selectiveH⁺ outward current mediator that prevents cell acidification, significantly improved T cell function in vitro, even at low pH conditions. The adoptive transfer of OVA-specificT cells overexpressing Hvcn1 exerted a better antitumor activity in B16OVA tumor-bearingmice. Hvcn1 overexpression also improved the antitumor activity of CAR T cells specific for Glypican 3 (GPC3) in mice bearing PM299L-GPC3tumors. Our results suggest that preventing intracellular acidification by regulating the expression of acidifier ion channels such as Ae2 or alkalinizer channels like Hvcn1 in tumor-specificlymphocytes enhances their antitumor response by making them more resistant to the acidic TME.

The diuretic amiloride attenuates doxorubicin-induced chemobrain in rats: Behavioral and mechanistic study

Cognitive impairment or "chemobrain" is a troublesome adverse effect which had been increasingly reported by cancer patients after doxorubicin (DOX) chemotherapy. Notably, Hypertension, a very common comorbidity in cancer patients, could pose a greater risk for negative cognitive outcomes. Amiloride (AML) is an antihypertensive, potassium-sparing diuretic that has been proven to be neuroprotective in different experimental models; this can be attributed to its ability to inhibit different ion transporters such as Na^+/H⁺ exchanger (NHE), which upon excessive activation can result in intracellular cationic overload, followed by oxidative damage and cellular death. Accordingly, this study was designed to investigate the potential neuroprotective effect of AML against DOX-induced chemobrain and to elucidate possible underlying mechanisms. Briefly, Histopathological examination and neurobehavioral testing (Morris water maze, Y maze and passive avoidance test) showed that AML co-treatment (10 mg/kg/day) markedly attenuated DOX (2 mg/kg/week)-induced neurodegeneration and memory impairment after 4 weeks of treatments. We found that DOX administration up-regulated NHE expression and increased lactic acid content in the hippocampus which were markedly opposed by AML. Moreover, AML mitigated DOX-induced neuroinflammation and decreased hippocampal tumor necrosis factor-α level, nuclear factor kappa-B, and cyclooxygenase-2 expression. Additionally, AML counteracted DOX-induced hippocampal oxidative stress as indicated by normalized malondialdehyde and glutathione levels. Furthermore, AML halted DOX-induced hippocampal apoptosis as evidenced by decreased caspase-3 activity and lower cytochrome c immunoexpression. Our results in addition to the previously reported antitumor effects of AML and its ability to mitigate cancer resistance to DOX therapy could point toward possible new repositioning scenarios of the diuretic AML especially regarding hypertensive cancer patients.

DMF Activates NRF2 to Inhibit the Pro-Invasion Ability of TAMs in Breast Cancer

Tumor-associated macrophages (TAMs) account for more than 50% of the cells in the tumor immune microenvironment of patients with breast cancer. A high TAM density is associated with a poor clinical prognosis. Targeting TAMs is a promising therapeutic strategy because they promote tumor growth, development, and metastasis. In this study, we found that dimethyl formamide (DMF) significantly inhibited the tumor invasion-promoting ability of TAMs in the co-culture system and further showed that DMF functioned by reducing reactive oxygen species (ROS) production in TAMs. The orthotopic 4T1 cell inoculation model and the spontaneous mouse mammary tumor virus-polyoma middle tumor-antigen tumor model were used to evaluate the antitumor effect of DMF. The results showed that DMF significantly inhibited tumor metastasis and increased T-cell infiltration into the tumor microenvironment. Mechanistically, NRF2 activation was necessary for DMF to exert its function, and DMF can play a role in breast cancer as an anticancer drug targeting TAMs.

Sodium homeostasis in the tumour microenvironment

The concentration of sodium ions (Na+) is raised in solid tumours and can be measured at the cellular, tissue and patient levels. At the cellular level, the Na+ gradient across the membrane powers the transport of H+ ions and essential nutrients for normal activity. The maintenance of the Na+ gradient requires a large proportion of the cell's ATP. Na+ is a major contributor to the osmolarity of the tumour microenvironment, which affects cell volume and metabolism as well as immune function. Here, we review evidence indicating that Na+ handling is altered in tumours, explore our current understanding of the mechanisms that may underlie these alterations and consider the potential consequences for cancer progression. Dysregulated Na+ balance in tumours may open opportunities for new imaging biomarkers and re-purposing of drugs for treatment.

Effects of the potassium-sparing diuretic amiloride on chemotherapy response in canine osteosarcoma cells

Background

Osteosarcoma (OSA) is a common bone tumor of mesenchymal origin in dogs. Chemotherapy delays metastasis, yet most dogs die of this disease within 1 year of diagnosis. The high metabolic demand of cancer cells promotes proton pump upregulation, leading to acidification of the tumor microenvironment and chemoresistance. The potassium‐sparing diuretic amiloride is among a class of proton pump inhibitors prescribed for refractory heart failure treatment in dogs.

Objective

We hypothesized that amiloride treatment improves chemotherapy response by reducing acidification in canine OSA cells. Our objective was to assess the in vitro effects of amiloride on cell viability, apoptosis, and metabolism.

Methods

In vitro study. Assessments of cell viability and apoptosis were performed after single agent or combination treatment, along with calculations of pharmacological synergism using the combination index. Protein signaling during apoptosis was evaluated by Western blotting. Metabolic profiling was performed using a Seahorse bioanalyzer.

Results

Amiloride strongly synergized with doxorubicin in combination treatment and exhibited additive or antagonistic effects with carboplatin in canine OSA cells. Combination treatment with doxorubicin significantly upregulated p53‐mitochondrial signaling to activate apoptosis and downregulate Akt phosphorylation. Amiloride‐treated cells further exhibited metabolic switching with reductions in glycolytic capacity and maximal respiration.

Conclusion and Clinical Importance

Amiloride synergized with doxorubicin to potentiate apoptosis in canine OSA cells. These results justify further investigation into repurposing of amiloride as an oncology drug for the treatment of OSA in dogs.