Amonafide-based HO-responsive theranostic prodrugs: Exploring the correlation between HO level and anticancer efficacy.

Leveraging the elevated hydrogen peroxide (HO) levels in cancer cells, HO-activated prodrugs have emerged as promising candidates for anticancer therapy. Notably, the efficacy of these prodrugs is influenced by the varying HO levels across different cancer cell types. In this context, we have developed a novel HO-activated prodrug, PBE-AMF, which incorporates a phenylboronic ester (PBE) motif. Upon HO exposure, PBE-AMF liberates the fluorescent and cytotoxic molecule amonafide (AMF), functioning as a theranostic agent. Our studies with PBE-AMF have demonstrated a positive correlation between intracellular HO concentration and anticancer activity. The breast cancer cell line MDA-MB-231, characterized by high HO content, showed the greatest susceptibility to this prodrug. Subsequently, we replaced the PBE structure with phenylboronic acid (PBA) to obtain the prodrug PBA-AMF, which exhibited enhanced stability, aqueous solubility, and tumor cell selectivity. This selectivity is attributed to its affinity for sialic acid, which is overexpressed on the surfaces of cancer cells. In vitro assays confirmed that PBA-AMF potently and selectively inhibited the proliferation of MDA-MB-231 cells, while sparing non-cancerous MCF-10A cells. Mechanistic investigations indicated that PBA-AMF impedes tumor proliferation by inhibiting DNA synthesis, reducing ATP levels, inducing apoptosis, and arresting the cell cycle. Our work broadens the range of small molecule HO-activated anticancer theranostic prodrugs, which are currently limited in number. We anticipate that the applications of PBA-AMF will extend to a wider spectrum of tumors and other diseases associated with increased HO levels, thereby offering new horizons in cancer diagnostics and treatment.