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Metals and metal-based compounds continue to have pharmacological and toxicological relevance. The prevalence of heavy metal exposure and its impact on health has exponentially increased scientific investigation since the 1960s and reached an all-time high in 2021. The concentrations of heavy metals in drinking water, air pollution, and occupational exposure exceeds regulatory limits worldwide and remain an issue for arsenic, cadmium, mercury, chromium, lead, and other metals. Novel methods to quantify environmental exposure and analyze pathological development continue to be in high demand1,2,3.
Conversely, the medical field has harnessed the physiochemical properties of various metals for clinical treatment. Metal-based drugs or metallodrugs have a rich history of medicinal purposes and have shown activity against a range of diseases, with the highest success as chemotherapeutics4. The most famous of metallodrugs, cisplatin, is a Pt-based anticancer drug deemed by the World Health Organization (WHO) as one of the world's essential drugs5. In 2010, cisplatin and its Pt derivatives had up to a 90% success rate in several cancers and were used in approximately 50% of chemotherapy regimens6,7,8. Although Pt-based chemotherapeutics have had irrefutable success, the dose-limiting toxicity has set in motion investigations of alternative metal-based drugs with refined biological delivery and activity. Of these alternatives, Ru-based compounds have become the most popular9,10,11,12.
Novel models and methodology are required to keep pace with the rate of need for metal pharmaco- and toxicokinetic studies. The zebrafish model lies at the intersection of complexity and throughput, being a high-fecundity vertebrate with 70% conserved gene homology13. This model has been an asset in pharmacology and toxicology, with extensive screenings for various compounds for lead discovery, target identification, and mechanistic activity14,15,16,17. However, high-throughput screening of chemicals typically relies on waterborne exposures. Given that uptake can be variable based on the physicochemical properties of the compound in solution (i.e., photodegradation, solubility), this can be a major limitation of correlating dose delivery and response.
To overcome this limitation for comparison of dose to higher vertebrates, a methodology was designed to analyze trace metal concentrations in zebrafish larval tissue. Here, dose-response curves of lethal and sublethal endpoints were evaluated for cisplatin and novel Ru-based anticancer compounds. Lethality and delayed hatching were evaluated for nominal concentrations of 0, 3.75, 7.5, 15, 30, and 60 mg/L cisplatin. Pt accumulation in organism tissue was determined by ICPMS analysis, and organism uptake of respective doses were 0.05, 8.7, 23.5, 59.9, 193.2, and 461.9 ng (Pt) per organism. Additionally, zebrafish larvae were exposed to 0, 3.1, 6.2, 9.2, 12.4 mg/L of PMC79. These concentrations were analytically determined to contain 0, 0.17, 0.44, 0.66, and 0.76 mg/L of Ru. This protocol also allowed for the distinguishment of concentrations of Pt sequestered in the chorion of the larvae compared with the zebrafish tissue. This methodology was able to provide reliable, robust data for comparisons of pharmaco- and toxicokinetic activity between a well-established chemotherapeutic and a novel compound. This method can be applied to a wide range of metals and metal-based compounds.