Cancer currently represents the second leading cause of death worldwide. According to the World Health Organization, in 2020, about 10 million people died from the disease and, for 2040, 19.3 million new cases are expected being 3 million of Breast Cancer (BC) [1]. BC treatment requires multidisciplinary efforts to overcome the heterogeneity of these tumors. Molecularly, they are categorized according to the activation of human epidermal growth factor 2 (HER2, encoded by ERBB2), expression of hormone receptors (estrogen receptor – ER and progesterone receptor – PR), and/or mutations in BRCA1/2 (Breast Cancer Type 1 and 2) tumor suppressors. Thus, there are luminal A (ER+ and HER2-); luminal B-like HER2- (ER+ and/or PR+, Ki67 > 14%); luminal B-like HER2+ (ER+ and/or PR+, HER2+); HER2-enriched (ER-, PR- and HER2+); and triple-negative (TN) breast cancers (ER-, PR- and HER2-) [2,3].

Locoregional therapy strategies (surgery and radiotherapy) and systemic therapy (hormone therapy, targeted therapy and chemotherapy) are adopted according to the histological and molecular characteristics, in a neoadjuvant or adjuvant regimen [3]. Patients with a high histological grade and increased risk of recurrence are commonly treated with chemotherapy [4] with a reduction in lesion size and a complete pathological response at the beginning of the treatment. However, the low selectivity, the activation of multiple drug resistance (MDR) mechanisms, the appearance of dormant and tolerant clones, and remodeling of the tumor microenvironment (TME) can compromise the successful of the strategy adopted [5].

In this context, the synthesis of new therapeutic agents based on cationic complexes emerges as a promising alternative in the development of novel chemotherapeutic agents. Copper is an essential micronutrient capable of existing in two distinct redox states: oxidized Cu(II) or reduced Cu(I), which allows its participation in redox reactions and transduction of cellular signals. Cu(II) acts as a Lewis acid and is an intermediate acid on the Person scale, being complexed with different ligands and atom donors [6]. In addition, copper is an important structural component and an enzymatic cofactor. Therefore, copper complexes overcome the toxicity of other compounds. In fact, copper uptake occurs naturally by the body, and its influx is even more expressive in tumor cells, since these cells reprogram their metabolism and activate copper-dependent mechanisms, such as angiogenesis, proliferation and invasion [7].

In BC, copper complexes have shown promising results. Previously, Paixão and collaborators synthesized the copper(II) complexes Cu(4-fh)(1,10-phen)(ClO4)2] and [Cu(4-nh)(1,10-phen)(ClO4)2]∙H2O that demonstrated high cytotoxic activity against MDA-MB-231 BCE cells and triggered apoptosis [8]. Another ternary copper(II) complex containing 1,10-phen, [Cu(1,10-phen)(L-tyr)Cl].3H2O, exhibited a remarkable selectivity to MDA-MB-231 BCE lineage. Furthermore, this complex induced cell cycle arrest and apoptosis [9]. Our research group reported the cytotoxicity of two Cu(II) ternary complexes, [Cu(4-fh)(1,10-phen)(ClO4)2] and [Cu(4-nh)(1,10-phen)(ClO4)2]·H2O to MDA-MB-231 cell line. The complex [Cu(4-fh)(1,10-phen)(ClO4)2] showed significant selectivity index and induced DNA damage resulting in cell cycle arrest in G0/G1 and cell death [10].

As firstly proposed by Burnstock in 1972, nucleotides act as autocrine and paracrine messengers, immunomodulating the TME and affecting the physiology of malignant cells [11]. In this context, the presence of adenosine triphosphate (ATP) and adenosine (ADO) is regulated by a hierarchical control system composed by ectonucleotidases, which are ectoenzymes located on the cell surface being responsible for the hydrolysis of extracellular nucleotides [12]. In a previous study, our research group observed that ATP, adenosine diphosphate (ADP) and AMP hydrolysis is higher in MDA-MB-231 lineage compared to MCF7 cells, indicating an orchestrated action of these enzymes in order to establish the concentration of nucleotides that are necessary to maintain the phenotype of triple-negative BC cells [12].

In the present study, we synthesized and evaluated the effects of new copper(II) complexes containing long-chain aliphatic hydrazides and 1,10-phen on a panel of BC cells. We sought to evaluate the biological effects of these complexes on nucleotide hydrolysis in mammary tumor cells, suggesting new mechanisms of action modulated by these copper complexes.