Targeted internalization and activation of glycosidic switch liposomes by an EphA2 PEG engager increases therapeutic efficacy against lung cancer

Abstract

Glycosidic switch liposome (GSL) technology uses a reversible glucuronide ester to efficiently encapsulate and stably retain potent anticancer drugs in liposomes. Parental drug is generated by enzymatic hydrolysis of the glucuronide switch in the lysosomes of target cells. Here we investigated if bispecific molecules simultaneously targeting polyethylene glycol (PEG) on GSL and an internalizing tumor antigen could increase uptake of GSL into cancer cells and enhance anticancer activity. A bispecific PEG engager (mPEG×EphA2) was generated by fusing a humanized anti-methoxy PEG (mPEG) Fab with an anti-EphA2 single-chain antibody. Mixing GSL with the PEG engager formed αEphA2/GSL, which can target EphA2 on cancer cells to trigger cellular internalization and enzymatic generation of topoisomerase I poison 9-aminocamptothecin (9AC) to kill cancer cells. Mixing mPEG×EphA2 with GSL created αEphA2/GSL targeted liposomes that specifically bind CL1-5 human lung adenocarcinoma cells and increase GSL internalization from 0–62.4% in 60 min. αEphA2/GSL displayed modestly enhanced cellular cytotoxicity in vitro as compared to GSL but targeted GSL increased intratumoral concentrations of 9AC by 8.4 fold at 24 h and the tumor/blood ratios of 9AC for αEphA2/GSL (medium of 9ACtumor/9ACblood ratio = 25.4%) was nearly 6-fold higher than αDNS/GSL (medium of 9ACtumor/9ACblood ratio = 4.4%) at 24 h. Five of seven mice bearing solid CL1-5 tumors were cured by treatment with targeted GSL. The PEG×EphA2 engager increases the uptake and generation of active drug from GSL, resulting in greatly increased therapeutic efficacy against lung cancer. αEphA2/GSL is a promising approach to treat tumors that overexpress EphA2.