Biological evaluation of complexes of cyclopentadienyl M(CO)3+ (M = Re, 99mTc) with high blood–brain barrier penetration potential as brain cancer agents

To address the major medical need for effective chemotherapeutics/diagnostics for brain cancer, in this work three cyclopentadienyl M(CO)3+ (M = Re, 99mTc) complexes, which cross the blood-brain barrier (BBB) in high % and are designed to mimic the anticancer agent 2-phenylbenzothiazole, are in vitro and in vivo evaluated for anticancer action. The study includes cytotoxicity and uptake studies in cancer and healthy neuronal cell lines, mechanistic investigation of potential anticancer pathways, and biodistribution studies in mice bearing glioblastoma xenografts. The stable Re complexes exhibit selective uptake and significant antiproliferative effect, particularly against U-251 MG glioblastoma cells, with no significant toxicity in healthy neurons, demonstrating the suitability of this type of complexes to serve as selective therapeutic/imaging agents for brain cancer. Furthermore, they result in the generation of elevated Reactive Oxygen Species (ROS) levels, and lead to significant G2/M arrest followed by apoptosis. Biodistribution studies in U-251 MG xenograft bearing mice with the radioactive 99mTc complex that exhibits the highest BBB penetration, show retention at the tumor-site offering a diagnostic prospect and, in addition, indicating the capability of the Re analogue to accumulate at the tumor site for therapeutic action. Overall, the complexes demonstrate significant anticancer properties that, combined with their high BBB penetration potential, render them strong candidates for further evaluation as brain cancer agents.