camptothecin

Overview

Camptothecin (CPT) is a naturally occurring cytotoxic monoterpene indole alkaloid first isolated from the bark and wood of Camptotheca acuminata (the "happy tree"), a deciduous tree native to southern China. Its core mechanism of action centers on the inhibition of topoisomerase I (Top1), an enzyme essential for relieving torsional stress in DNA during replication and transcription. Camptothecin stabilizes the transient Top1–DNA cleavage complex, preventing DNA re-ligation and causing irreversible strand breaks that ultimately trigger apoptosis in rapidly dividing cancer cells. Due to its potent antiproliferative activity, CPT has served as the chemical scaffold for several clinically approved derivatives, including irinotecan, topotecan, and the more recent exatecan, which retain the core lactone pharmacophore while addressing the pharmacokinetic limitations of the parent compound.

Beyond its direct clinical use, camptothecin occupies a central role in contemporary oncology drug development as a payload in antibody-drug conjugates (ADCs). Its high cytotoxic potency at picomolar concentrations makes it an attractive warhead when precision tumor targeting is required. The compound's reactivity, limited aqueous solubility, and narrow therapeutic window have driven sustained innovation in prodrug design, linker chemistry, and nanoparticle-based delivery systems, establishing CPT as one of the most intensively engineered small molecules in translational cancer research.

Focus of Latest Publications

Recent publications have focused on camptothecin as a cytotoxic payload in stimulus-responsive delivery systems designed to improve selectivity, reduce systemic toxicity, and enable imaging-guided therapy. Several studies coupled camptothecin to nanostructures or prodrug platforms that respond to tumor- or disease-associated microenvironmental cues, including acidic pH, γ-glutamyl transpeptidase, glutathione, hypochlorous acid, and reactive oxygen species. Across these reports, camptothecin was used to test whether controlled release could preserve antitumor activity while improving solubility, stability, and tissue specificity.

In one study, camptothecin was incorporated into an HOCl-activated acyl hydrazide prodrug platform, where the camptothecin conjugate DHU-OH-6 showed improved aqueous solubility and reduced intrinsic cytotoxicity relative to free camptothecin, while retaining efficient HOCl-triggered release of the active drug. The same platform enabled fluorescence imaging of exogenous and endogenous HOCl and supported fluorescence-guided therapy in an imiquimod-induced psoriasis mouse model, where it alleviated skin lesions and reduced systemic toxicity compared with free camptothecin. Another report described a tandem-responsive dendritic dot in which camptothecin was covalently conjugated to a Cy5-containing polylysine dendrimer; sequential activation by acidic pH and γ-glutamyl transpeptidase exposed amines that promoted camptothecin release and turned on fluorescence, resulting in enhanced cellular transcytosis and potent antitumor activity in vitro and in vivo against hepatocellular carcinoma.

Additional work developed a γ-glutamyl transferase/glutathione cascade-responsive unimolecular nanoprodrug in which camptothecin was linked through glutathione-cleavable moieties and decorated with a γ-glutamyl transferase-responsive surface group to improve uptake and tumor selectivity. This system was reported to show satisfactory cancer/normal cell selectivity, safety, and anticancer efficacy in vitro and in vivo. A separate ROS/pH dual-responsive nanosystem, CPT@EZ@HP, encapsulated camptothecin within Zn2+-epigallocatechin gallate metal-phenolic coordination structures and used phenylboronic acid-conjugated hyaluronic acid for CD44-targeting and ROS responsiveness; in liver fibrosis models, it targeted activated hepatic stellate cells, scavenged ROS, promoted macrophage polarization toward the M2 phenotype, and released camptothecin under acidic conditions to inhibit HIF-1α-mediated glycolysis and suppress fibrotic progression.

Camptothecin also appeared in broader oncology prodrug and ADC design efforts. A Tyrosinase-responsive prodrug strategy introduced a Tyrosinase-specific recognition unit into camptothecin and doxorubicin constructs, but only the doxorubicin prodrug showed efficient Tyrosinase activation and improved melanoma selectivity, indicating that the camptothecin version did not exhibit similar activity under the reported conditions. In parallel, discovery chemistry efforts on camptothecin-based linker-payloads for antibody-drug conjugates identified novel N-linked camptothecin derivatives with favorable biophysical properties, in vitro potency, and strong target-mediated in vivo efficacy. Collectively, these publications emphasize camptothecin’s continued role as a benchmark topoisomerase I-targeting payload and as a scaffold for engineering responsive prodrugs and conjugates with improved therapeutic performance.