## 1 Introduction  
Metal-organic frameworks (MOFs) are coordination networks with an open framework made of organic linkers and inorganic nodes containing potential voids [1; 2; 3]. They can interact with drugs in various ways, such as hydrogen bonding, van der Waals forces, aggregation, and encapsulation [4; 5; 6; 7]. Unlike conventional drug delivery systems, such as micelles, liposomes, inorganic carriers, and polymers, MOFs have advantages with compositional tunability, which can be useful for engineering interaction with the drugs and their encapsulation [8; 9; 10; 11; 12]. By changing either the organic linker or the metal ion or both, MOFs can be tailored for specific drug release properties at the tumour site [13]. Many studies have explored the use of MOFs for cancer treatment, showing their potential in drug delivery, imaging, and therapy. These studies demonstrate the versatility of MOFs in overcoming the limitations of conventional cancer treatments and provide a basis for further progress in the field of oncology [14,15]. MOFs can be developed using synthetic and natural compounds, employing chemical and physical approaches [16,17]. These MOFs can be endowed with different chemical and physical properties and evaluated for targeted drug delivery in various diseases at the subcellular level [18,19]. Zr-based MOFs are promising materials for biomedical applications such as drug delivery and bio-imaging because of their tunable surface properties, low toxicity, and structural stability in physiological conditions [20]. For instance, Zr-based MOFs have been shown to effectively encapsulate water-soluble azo compounds, exhibiting anticancer effects, especially in the hypoxic conditions of pancreatic cancer [21]. Two separate studies explored the accumulation of the radiotracer \({}^{89}\)Zr-rastuzumab in lesions of metastatic breast cancer patients [22, 23, 24] and the use of Zr(IV) ions in the synthesis of nanoscale porphyrin MOFs for the targeted delivery of doxorubicin in liver cancer metastasis in mice [25]. Zr-based MOFs, such as UiO-66 and UiO-66-NH\({}_{2}\) (UiO stands for University of Oslo), are highly stable and can operate at various pH, temperature, aqueous, and physiological conditions [20,26]. UiO-66 (zirconium benzene-1,4-dicarboxylate) is a porous MOF composed of zirconium oxide and hydroxo nodes (ZrO, Zr\({}_{6}\)O\({}_{4}\)(OH)\({}_{4}\)) and benzene-1,4-dicarboxylate (BDC) linkers [26,27]. UiO-66-NH\({}_{2}\) is an analogue of UiO-66 with an amine-functionalised benzenedicarboxylate linker which enables the MOF to interact with drugs or biomolecules by supramolecular interactions, such as hydrogen bonding, for controlled delivery applications [27]. These MOFs exhibit resistance to aqueous and acidic conditions, coupled with robust stability under extreme pressures, reaching up to 10,000 kg cm\({}^{-2}\), and elevated temperatures, as high as 540 \({}^{\circ}\)C [28]. Importantly, both UiO-66 and UiO-66-NH\({}_{2}\) demonstrate hydrolytic stability, which can be attributed to varying pKa values originating from the presence of oxo-hydroxy groups within the Zr cluster [29]. UiO-66 and UiO-66-NH\({}_{2}\) have demonstrated successful applications in delivering various anticancer drugs across different cancer cell lines [30, 31, 32]. Mitoxantrone (MTX, Figure 1) is a chemotherapeutic agent used to treat different kinds of cancers, especially breast cancer that has spread to other parts of the body [33, 34, 35, 36, 37]. However, MTX can also cause serious side effects, such as cardiotoxicity, myelosuppression, and other debilitating side effects. MTX operates by instigating double-strand DNA breaks through the formation of covalent complexes with topoisomerase II, facilitated by its intercalation within the DNA structure [38,39]. One way to improve the effectiveness and delivery of MTX is to use nanocarriers that can carry drugs inside them. These particles can be designed to have specific properties, such as size, shape, and biocompatibility.