Chapter 23. Recent advances in antibody drug conjugates for cancer therapy

Reversible glycosidic switch for secure delivery of molecular nanocargos

Therapeutic drugs can leak from nanocarriers before reaching their cellular targets. Here we describe the concept of a chemical switch which responds to environmental conditions to alternate between a lipid-soluble state for efficient cargo loading and a water-soluble state for stable retention of cargos inside liposomes. A cue-responsive trigger allows release of the molecular cargo at specific cellular sites. We demonstrate the utility of a specific glycosidic switch for encapsulation of potent anticancer drugs and fluorescent compounds. Stable retention of drugs in liposomes allowed generation of high tumor/blood ratios of parental drug in tumors after enzymatic hydrolysis of the glycosidic switch in the lysosomes of cancer cells. Glycosidic switch liposomes could cure mice bearing human breast cancer tumors without significant weight loss. The chemical switch represents a general method to load and retain cargos inside liposomes, thereby offering new perspectives in engineering safe and effective liposomes for therapy and imaging.

Retention of drugs loaded into liposomes is a major challenge to effective targeted drug delivery. Here, the authors report on the modification of drugs with a glycosidic pH sensitive switch to improve encapsulation and retention of drugs and demonstrate application in an in vivo cancer model.

Effects of Drug Loading on the Antitumor Activity of a Monoclonal Antibody Drug Conjugate

PURPOSE

An antibody-drug conjugate consisting of monomethyl auristatin E (MMAE) conjugated to the anti-CD30 monoclonal antibody (mAb) cAC10, with eight drug moieties per mAb, was previously shown to have potent cytotoxic activity against CD30(+) malignant cells. To determine the effect of drug loading on antibody-drug conjugate therapeutic potential, we assessed cAC10 antibody-drug conjugates containing different drug-mAb ratios in vitro and in vivo.

EXPERIMENTAL DESIGN

Coupling MMAE to the cysteines that comprise the interchain disulfides of cAC10 created an antibody-drug conjugate population, which was purified using hydrophobic interaction chromatography to yield antibody-drug conjugates with two, four, and eight drugs per antibody (E2, E4, and E8, respectively). Antibody-drug conjugate potency was tested in vitro against CD30(+) lines followed by in vivo xenograft models. The maximum-tolerated dose and pharmacokinetic profiles of the antibody-drug conjugates were investigated in mice.

RESULTS

Although antibody-drug conjugate potency in vitro was directly dependent on drug loading (IC(50) values E8<E4<E2), the in vivo antitumor activity of E4 was comparable with E8 at equal mAb doses, although the E4 contained half the amount of MMAE per mAb. E2 was also an active antitumor agent but required higher doses. The maximum-tolerated dose of E2 in mice was at least double that of E4, which in turn was twice that of E8. MMAE loading affected plasma clearance, as E8 cleared 3-fold faster than E4 and 5-fold faster than E2.

CONCLUSIONS

By decreasing drug loading per antibody, the therapeutic index was increased demonstrating that drug loading is a key design parameter for antibody-drug conjugates.

Development of a spectroscopic assay for bifunctional ligand-protein conjugates based on copper

A simple, non-radioactive method for the determination of ligand-to-protein ratio (L/P) for novel ligand-antibody conjugates has been developed based on an exchange equilibrium with the purple Cu(II) complex of arsenazo III. The method requires a UV/Vis spectrometer and has been verified for monoclonal antibody Herceptin conjugates of a variety of ligand modalities, including common macrocyclic compounds NOTA and TETA, and with a new bifunctional tachpyridine (1H-Pyrrole-1-butanamide,N-[4-[[(1alpha,3alpha,5alpha)-3,5-bis[(2-pyridinylmethyl)amino]cyclohexyl](2-pyridinylmethyl)amino]butyl]-2,5-dihydro-2,5-dioxo-(9CI)). The spectroscopically derived values for L/P were verified by titration of the ligand-antibody conjugate with 64Cu. In each case, the value obtained by UV/Vis spectroscopy matches that found by radiolabeling. The method is rapid, taking less than 30 minutes with each ligand in this study.