Caelyx

Caelyx is a pegylated liposomal formulation of the anthracycline cytotoxic drug doxorubicin, administered intravenously to treat cancer. The doxorubicin it carries acts inside dividing cells by intercalating into DNA and poisoning topoisomerase II, generating double-strand breaks, and by producing reactive oxygen species that damage DNA, lipids, and proteins; the accumulated damage drives apoptosis through pathways regulated by Bcl-2 family proteins. Enclosing the drug in long-circulating liposomes does not alter this molecular mechanism but changes its distribution: the carrier prolongs circulation, lowers peak free-drug exposure, and favors accumulation in tumors with leaky vasculature, which underlies its reduced cardiotoxicity relative to conventional doxorubicin.

Clinically, Caelyx and related liposomal doxorubicin products are used across solid and hematologic cancers and are frequently combined with other cytotoxics — taxanes such as nab-paclitaxel and docetaxel, along with gemcitabine or oxaliplatin — and with radiotherapy. Much current research treats liposomal doxorubicin as a reference nanomedicine against which newer carriers are measured, including aptamer-functionalized liposomes, hybrid nanogels, functionalized carbon dots, polymeric micelles, and stimulus-responsive lipid nanoparticle, and uses it to probe the delivery barriers that limit chemotherapy: dense extracellular matrix laid down by cancer-associated fibroblasts, elevated interstitial pressure in the tumor microenvironment, and poor penetration into fibrotic tissue such as that of hepatocellular carcinoma. Stromal enzymes including MMP-9 and fibroblast activation protein are exploited to trigger drug release within the tumor, while chitosan-based and nucleoside-transporter-directed carriers aim to make doxorubicin orally absorbable by evading p-glycoprotein efflux and CYP3A4 metabolism. Resistance to doxorubicin, whether free or liposomal, is attributed largely to drug efflux, altered redox homeostasis, and blunted apoptotic signaling.