Abstract LB-20: PEGylated TRAIL/Apo2L shows greatly improved circulating half life and improved anti-tumor efficacy in xenograft models for colon and pancreatic cancer

PURPOSE TRAIL/Apo2L is a death receptor (DR) agonist, inducing apoptosis through the extrinsic pathway in tumor cells expressing DR4 or DR5. Agonistic antibodies or the naked ligand have been tested in the clinic to treat solid tumors. Owing to its extremely short serum half life, TRAIL must be administered by daily IV infusions. Attaching polyethylene glycol (PEG) to the ligand could afford a longer half life and systemic exposure, thus requiring fewer hospital visits for the patient. However, as TRAIL is a functional homotrimer with complex ligand-receptor interactions, non-specific PEGylation will likely result in diminished potency. Using Ambrx9s proprietary site specific PEGylation, we evaluated the potency and circulating half life of several PEGylated TRAIL variants. METHODS Using Ambrx proprietary technology, PEG can be attached at a precise location so as not to interfere with receptor binding by engineering insertion of a non-natural amino acid, pAF, which provides a site-specific reactive moiety for attaching other molecules. Several trimeric-PEG-TRAIL analogs were generated and tested for anti-proliferation in vitro and for pharmacokinetic (PK) parameters in the rat. Finally, a PEG-TRAIL analog was tested for anti-tumor activity in pancreatic and colon cancer xenograft model. RESULTS PEGs of varying length (3k, 5k, 10k, and 20k) were attached to site-specifically incorporated pAf to yield one, two or three PEGs per trimeric molecule. One selected PEG analog showed only minimal loss of anti-proliferative activity when tested against a panel of cell lines including representatives from colon, pancreatic, lung and lymphoma cancers. The rat serum half life and AUC of PEG-TRAIL was approximately 6 and 21 fold better as compared to wild type (wt) TRAIL. Administering PEG-TRAIL qdx1 resulted in identical efficacy in pancreatic and colon xenografts as wt TRAIL administered qdx5. Finally, PEG-TRAIL was dramatically more efficacious than Mapatumumab at 1/5 the dose or wt TRAIL at equivalent dose, but had similar efficacy to Lexatumumab. Thus, site specific PEGylation of TRAIL homotrimer produces a drug that maintains in vivo potency and allows intermittent rather than daily dosing. CONCLUSIONS Modifying TRAIL by attaching a single PEG moiety to the homo-trimeric molecule increases rat serum half life compared to wild type TRAIL without decreasing agonistic potency or anti-tumor efficacy in xenograft animal models. There is potential for administering PEGylated TRAIL to patients with pancreatic or colon cancer with a once weekly instead of a daily dosing regimen. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-20. doi:10.1158/1538-7445.AM2011-LB-20