A general approach to site-specific antibody drug conjugates.

Using an expanded genetic code, antibodies with site-specifically incorporated nonnative amino acids were produced in stable cell lines derived from a CHO cell line with titers over 1 g/L. Using anti-5T4 and anti-Her2 antibodies as model systems, site-specific antibody drug conjugates (NDCs) were produced, via oxime bond formation between ketones on the side chain of the incorporated nonnative amino acid and hydroxylamine functionalized monomethyl auristatin D with either protease-cleavable or noncleavable linkers. When noncleavable linkers were used, these conjugates were highly stable and displayed improved in vitro efficacy as well as in vivo efficacy and pharmacokinetic stability in rodent models relative to conventional antibody drug conjugates conjugated through either engineered surface-exposed or reduced interchain disulfide bond cysteine residues. The advantages of the oxime-bonded, site-specific NDCs were even more apparent when low-antigen-expressing (2+) target cell lines were used in the comparative studies. NDCs generated with protease-cleavable linkers demonstrated that the site of conjugation had a significant impact on the stability of these rationally designed prodrug linkers. In a single-dose rat toxicology study, a site-specific anti-Her2 NDC was well tolerated at dose levels up to 90 mg/kg. These experiments support the notion that chemically defined antibody conjugates can be synthesized in commercially relevant yields and can lead to antibody drug conjugates with improved properties relative to the heterogeneous conjugates formed by nonspecific chemical modification.

Site-specific antibody-polymer conjugates for siRNA delivery.

We describe here the development of site-specific antibody-polymer conjugates (APCs) for the selective delivery of small interference RNAs (siRNAs) to target cells. APCs were synthesized in good yields by conjugating an aminooxy-derivatized cationic block copolymer to an anti-HER2 Fab or full-length IgG by means of genetically encoded p-acetyl phenylalanine (pAcF). The APCs all showed binding affinity comparable to that of HER2 as their native counterparts and no significant cellular cytotoxicity. Mutant S202-pAcF Fab and Q389-pAcF IgG polymer conjugates specifically delivered siRNAs to HER2(+) cells and mediated potent gene silencing at both the mRNA and protein levels. However, a mutant A121-pAcF IgG polymer conjugate, despite its high binding affinity to HER2 antigen, did not induce a significant RNA interference response in HER2(+) cells, presumably due to steric interference with antigen binding and internalization. These results highlight the importance of conjugation site on the activity of antibody-polymer-based therapeutics and suggest that such chemically defined APCs may afford a useful targeted delivery platform for siRNAs or other nucleic acid-based therapies.

Improvement in oncology practice performance through voluntary participation in the Quality Oncology Practice Initiative.

PURPOSE: The Quality Oncology Practice Initiative (QOPI) became available to all American Society of Clinical Oncology member physicians in 2006 as a voluntary medical oncology practice-based quality measurement and improvement project. QOPI assesses practice performance for a series of evidence- and consensus-based process measures, relying on practices to complete structured chart reviews and submit data via a secure Web-based portal. METHODS: This analysis focused on the 71 practices that participated in both the March and September 2006 data collections (7,624 charts abstracted in March and 10,240 in September). Among 33 measures common to both collections, five measures were closely correlated, and 28 are included in the final analysis. Composite scores were created for six different domains of care. Statistical significance was tested on both absolute changes and relative changes (relative failure reduction) of quality measures from baseline to follow-up and between the lower quartile and all other quartiles. RESULTS: Practice performance on individual measures varied between 18.8% and 98.6%. Mean overall performance as measured by a composite score increased from 78.7% in March to 82.3% in September (P < .05). Improvement was most marked among practices originally performing in the bottom quartile. Using a composite score, the absolute and relative performance for the bottom quartile improved by 27% and 35%, respectively, statistically superior to that of all others. CONCLUSION: Practices that participated in QOPI demonstrated improved performance in self-reported process measures, with the greatest improvement demonstrated in initially low-performing practices.