Towards Imaging Pt Chemoresistance Using Gd(III)-Pt(II) Theranostic MR Contrast Agents

Cisplatin and related Pt(II) chemotherapeutics are indispensable tools for the treatment of various solid tumors. Despite their widespread clinical use in approximately 50 % of chemotherapy regimens, they are hindered by issues with off-target toxicity and chemoresistance, both innate and acquired. To date, there is no effective way to predict the outcome of Pt(II) chemotherapy because the genes associated with resistance are not completely known or understood. Instead, patients undergo weeks to months of potentially harmful therapy before knowing if it is effective. Here we report two Gd(III)-Pt(II) theranostic MR contrast agents that contain cisplatin and carboplatin-based moieties respectively. We used these agents to demonstrate that accumulation differences in Pt(II) sensitive and resistant cells, a dominant factor in chemoresistance, can be imaged by MR. Both theranostic agents bind to DNA, are cytotoxic, and enhance the intracellular T₁-weighted MR contrast of multiple cell lines. Most importantly, the cisplatin-based agent accumulates less in Pt(II) resistant cells in vitro and in vivo, resulting in decreased MR contrast enhancement compared to the parent Pt(II) sensitive cell line. This straightforward method to image a key factor of Pt(II) resistance using MRI is an important first step towards the ultimate goals of predicting response to Pt(II) chemotherapy and monitoring for the onset of chemoresistance – a critical unmet need in medicine that could significantly improve patient outcomes.