Elsevier

Brain Research

Volume 1760, 1 June 2021, 147397
Brain Research

Cognitive impairment resulting from treatment with docetaxel, doxorubicin, and cyclophosphamide

https://doi.org/10.1016/j.brainres.2021.147397Get rights and content

Highlights

  • TAC significantly compromised the dendritic architecture.

  • TAC downregulation of proteins within key metabolic and signaling pathways associated with cognitive dysfunction.

  • TAC impaired hippocampal dependent behavior.

Abstract

Breast cancer is the most commonly diagnosed cancer among women and it is estimated that about 30% of newly diagnosed cancers in women will be breast cancers. While advancements in treating breast cancer have led to an average 5-year survival rate of 90%, many survivors experience cognitive impairments as a result of chemotherapy treatment. Doxorubicin, cyclophosphamide, and docetaxel (TAC) are commonly administered as breast cancer treatments; however, there are few studies that have tested the cognitive effects of TAC. In the current study, 12-week-old female C57BL/6 mice received 4 weekly intraperitoneal injections of either saline or a combination therapy of doxorubicin and cyclophosphamide followed by 4 weekly docetaxel injections. Four weeks after the last injection, mice were tested for hippocampus-dependent cognitive performance in the Y-maze and the Morris water maze. During Y-maze testing, mice exposed to TAC exhibited impairment. During the water maze assessment, all animals were able to locate the visible and hidden platform locations. However, mice that received the TAC presented with a significant impairment in spatial memory retention on the probe trial days. TAC treatment significantly decreases the dendritic complexity of arborization in the dentate gyrus region of the hippocampus. In addition, comparative proteomic analysis revealed downregulation of proteins within key metabolic and signaling pathways associated with cognitive dysfunction, such as oxidative phosphorylation, ephrin signaling, and calcium signaling.

Introduction

Breast cancer is one of the most commonly diagnosed cancers and the primary cause of mortality due to cancer in women around the world (Miller et al., 2016a, Akram et al., 2017). In developed countries, such as the US, early cancer diagnoses are increasing due to scientific advancements that have improved diagnostic methods. Improved treatment methods have also resulted in an increase of 5-year survival rates up to levels as high as 90% (Akram et al., 2017, Miller et al., 2016a). Despite the advancements in survivorship, there is still much to be understood about the long-term effects that current treatment methods have on the quality of life of survivors. For instance, many breast cancer survivors experience cognitive impairments, such as difficulties in memory, attention, processing speed, and executive function after receiving chemotherapy treatment (Seigers and Fardell, 2011). Due to the untargeted method of administration of chemotherapy patients are at risk for potential side effects in other organ systems unrelated to their cancer, such as the central nervous system. This condition of chemotherapy-induced cognitive impairment, or “chemobrain,” has been of significant interest to researchers, because at present our current understanding of the mechanisms that cause this condition is still limited. In the context of chemobrain one of the most intensively studied regions of the brain, in both animals and humans, is the hippocampus (Inagaki et al., 2007, Dubois et al., 2014, Peukert et al., 2020, Yang and Moon, 2015). The hippocampus is significant due to its strong connection to other brain regions (higher cortical brain structures and limbic system) and its role as a large integrating organ, which encodes and consolidates memory information from multiple brain regions (Schultz and Engelhardt, 2014). Additionally, the hippocampus is connected to the default mode network and thus plays a critical role in memory retrieval and spatial memory retention (Ranganath and Ritchey, 2012, Nadel et al., 2013). There have been numerous studies that have investigated the role of drug treatment-induced structural brain changes within the hippocampus and the implications of these changes have on memory and emotional-related processes (Maguire and Mullally, 2013, Encinas et al., 2011). Chemotherapy in particular has been associated with reduction in hippocampal volume and neurogenesis in addition to cognitive impairment (Inagaki et al., 2007, Dietrich et al., 2006, Janelsins et al., 2010, Christie et al., 2012, McElroy et al.,, Anderson et al., 2020).

The use of chemotherapy to treat breast cancer has a long history dating as far back as the 1940s. Some of the most commonly used chemotherapeutics used to treat breast cancer are doxorubicin, cyclophosphamide, docetaxel, epirubicin, fluorouracil, capecitabine, gemcitabine, paclitaxel, and methotrexate (Lee and Nan, 2012a). Treatment regimens for these chemotherapeutic agents are given both singularly and in combination. The first combination therapy for breast cancer was administered in the 1960s using methotrexate and thioTEPA (Greenspan et al., 1963). Some other common examples of combination therapies are AC (doxorubicin and cyclophosphamide) and CMF (Cyclophosphamide, Methotrexate, and Fluorouracil) (Lee and Nan, 2012). Today, combination therapy has become increasingly more common due to benefits such as lower dosage requirements, decreased likelihood of tumor resistance, and ability to address different molecular targets in carcinogenesis. Despite these benefits, combination therapy also comes with an increased risk of side effects, such as inflammation, neutropenia, and cognitive impairments.

Currently, one of the most common combination therapies for breast cancer is docetaxel, doxorubicin, and cyclophosphamide (TAC). The TAC regimen was first introduced in the late 1990s and was revolutionary because it was the first combination to demonstrate the efficacy of docetaxel in the adjuvant setting (Martin, 2006). Docetaxel is in a class of compounds called taxanes discovered in the 1950s (Guenard, Gueritte-Voegelein, and Potier, 1993). Its mechanism of action is to disrupt microtubule function (Lee and Nan, 2012). Docetaxel can be used to treat breast cancer, prostate cancer, head and neck cancer, and non-small cell lung cancer (Petrylak et al., 2004, Tripathy, 2006, Potter, 2007). Doxorubicin is an anthracycline compound that was discovered by isolating the compound from the bacteria Streptomyces (Lee and Nan, 2012). Its mechanism of action is to inhibit DNA and RNA synthesis by intercalation between base pairs, blocking replication by inhibiting topoisomerase II activity, and creating iron-mediated free oxygen radicals that damage the DNA and cell membranes of cancer cells (Lee and Nan, 2012). Alone, it can be used to treat certain types of thyroid cancers (Gottlieb and Hill, 1974). Finally, cyclophosphamide is an alkylating agent that was derived from mustard gas and approved for medical use in the 1950s (DeVita and Chu, 2008). Its mechanism of action is to crosslink DNA strands at guanine bases, thus preventing DNA from uncoiling during replication (Emadi et al., 2009). The purpose of this study is to investigate the effects of a clinically relevant regimen of TAC on cognition, dendritic structure, and protein regulation within the hippocampus of female mice.

Section snippets

Food consumption & body weight

Food consumption and body weights were tracked during injections, no significant changes in food consumption were identified (F (7,42) = 1.16, P = 1.16; Fig. 1a). For body weight, there were a significant differences between treatment-by-week interaction (F (7,42) = 3.82, P < 0.001; Fig. 1b) however, Holm- Sidak post-hoc analysis did not reveal any significant changes in body weights.

Y maze

In order to assess potential deficits in short term memory and exploratory activity, all animals were subjected

Discussion

In this study, we examined the effects of a TAC regimen on cognition, hippocampal dendritic morphology, and dysregulation of protein pathways. During the Y maze behavioral test, we observed that the TAC group was unable to distinguish the novel arm from the start and familiar arms, indicating that these mice experienced deficits in short-term memory retention when compared to the saline group. In the MWM, we observed a significant deficit in spatial memory retention in the TAC group when

Conclusion

In conclusion, in adult female mice, the effects of TAC were clearly demonstrated with regard to learning and memory through the use of several behavioral assessments. Additionally, we analyzed changes in dendritic morphology and proteomic analysis of the TAC group. These data indicate that TAC induces cognitive dysfunction. In future studies, we would like to further assess the mechanisms underlying cognitive decline, such as oxidative stress. Understanding the relationship between

Animals

Thirty-two 12-week-old CB57BL/6J female mice purchased from Jackson labs were used, with 16 mice per group. 12-week old mice were chosen because they are mature adult age comparatively to humans and this avoided potential health complications with aging due to the long treatment period of 8 weeks. The mice were group housed (n = 5/cage) under a constant 12-hour light: 12-hour dark cycle in a climate-controlled environment. Food and water were provided ad libitum. Mice housed together were the

CRediT authorship contribution statement

Taurean Brown: Conceptualization, Writing - original draft. Taylor McElroy: . Pilar Simmons: . Huddoy Walters: . Fabio Ntagwabira: . Jing Wang: . Stephanie D. Byrum: . Antiño R. Allen: Conceptualization, Resources, Funding acquisition, Writing - original draft.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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