Synthesis and Preclinical Evaluation of Radiolabeled [103Ru]BOLD-100

Metal-based molecules in the treatment of cancer: From bench to bedside

Cancer remains one of the leading causes of death in the world, with more than 9 million deaths in 2022, a number that continues to rise. This highlights the urgent need for the development of new drugs, with enhanced antitumor capabilities and fewer side effects. Metal-based drugs have been used in clinical practice since the late 1970s, beginning with the introduction of cisplatin. Later, two additional platinum-based molecules, carboplatin, and oxaliplatin, were introduced, and all three continue to be widely used in the treatment of various cancers. However, despite their significant anticancer activity, the undesirable side effects of these drugs have motivated the scientific community to explore other metal-based complexes with greater anticancer potential and fewer adverse effects. In this context, metals such as ruthenium, copper, gold, zinc, palladium, or iridium, present promising alternatives for the development of new anticancer agents. Unfortunately, although thousands of metal-based drugs have been synthesized and tested both in vitro and in animal models, only a few ruthenium-based drugs have entered clinical trials in recent years. Meanwhile, many other molecules with comparable or even greater anticancer potential have not advanced beyond the laboratory stage. In this review, we will revisit the mechanisms of action and anticancer activities of established platinum-based drugs and explore their use in recent clinical trials. Additionally, we will examine the development of potential new metal-based drugs that could one day contribute to cancer treatment worldwide.

From Concept to Cure: The Road Ahead for Ruthenium-Based Anticancer Drugs

The evolution of chemotherapy, especially the dawn of metal-based drugs, represents a transformative era in cancer treatment. From the serendipitous discovery of mustard gas's cytotoxic effects to the sophisticated development of targeted therapies, chemotherapy has significantly refined. Central to this progression is the incorporation of metal-based compounds, such as platinum (Pt), ruthenium (Ru), and gold (Au), which offer unique mechanisms of action, distinguishing them from organic therapeutics. Among these, Ru complexes, exemplified by BOLD-100 and TLD1433, have shown exceptional promise due to their selective activity, lower propensity for resistance, and the ability to target spescific cellular pathways. This paper explores the journey of such Ru candidates, focusing on the mechanisms, efficacy, and clinical potential of these Ru-based drugs, which stand at the forefront of current research, aiming to provide more targeted, less toxic, and highly effective cancer treatments.

Synthesis and preclinical evaluation of BOLD-100 radiolabeled with ruthenium-97 and ruthenium-103

BOLD-100 (formerly IT-139, KP1339), a well-established chemotherapeutic agent, is currently being investigated in clinical trials for the treatment of gastric, pancreatic, colorectal, and bile duct cancer. Despite numerous studies, the exact mode of action is still the subject of discussions. Radiolabeled BOLD-100 could be a powerful tool to clarify pharmacokinetic pathways of the compound and to predict therapy responses in patients using nuclear molecular imaging prior to the therapy. In this study, the radiosyntheses of carrier-added (c.a.) [97/103Ru]BOLD-100 were performed with the two ruthenium isotopes ruthenium-103 (103Ru; β-, γ) and ruthenium-97 (97Ru; EC, γ), of which in particular the latter isotope is suitable for imaging by single-photon emission computed tomography (SPECT). To identify the best tumor-to-background ratio for diagnostic imaging, biodistribution studies were performed with two different injected doses of c.a. [103Ru]BOLD-100 (3 and 30 mg kg-1) in Balb/c mice bearing CT26 allografts over a time period of 72 h. Additionally, ex vivo autoradiography of the tumors (24 h p.i.) was conducted. Our results indicate that the higher injected dose (30 mg kg-1) leads to more unspecific accumulation of the compound in non-targeted tissue, which is likely due to an overload of the albumin transport system. It was also shown that lower amounts of injected c.a. [103Ru]BOLD-100 resulted in a relatively higher tumor uptake and, therefore, a better tumor-to-background ratio, which are encouraging results for future imaging studies using c.a. [97Ru]BOLD-100.