Search

The antibody-drug conjugate, trastuzumab emtansine (Kadcyla), is produced by attachment of the antitubulin drug, DM1, to lysine amines via a heterobifunctional linker, SMCC (succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate). Following the reaction of the N-hydroxysuccinimide activated linker with antibody lysines to produce a linker-modified intermediate (Tmab-MCC), DM1 is added to yield the desired product. In addition to the expected distribution of drug-linked forms (from 0 to 8), mass spectrometry also demonstrates the presence of a second distribution shifted by about +222 Da. This series is consistent with the presence of a population containing a bound linker without DM1 ("unconjugated linker"). Extended characterization of trastuzumab emtansine was performed using capillary isoelectic focusing, CE-SDS, peptide mapping, and LC/MS following (18)O labeling of peptide digests to identify this family of product variants. These studies demonstrate that the presence of these +222 Da species is due to an unexpected reaction of the maleimide moiety in the MCC linker with antibody lysine residues to produce cross-linked species that cannot conjugate to DM1.

Trastuzumab emtansine (Kadcyla) is a recently approved antibody-drug conjugate produced by attachment of the anti-tubulin drug, DM1, to lysine amines via the SMCC linker. The resulting product exhibits a drug load distribution from 0 to 8 drugs per antibody that can be quantified using mass spectrometry. Different statistical models were tested against the experimental data derived from samples produced during process characterization studies to determine best fit. The Poisson distribution gives the best correlation for samples manufactured using the target process conditions (yielding the target average drug to antibody ratio (DAR) of 3.5) as well as those produced under conditions that exceed the allowed manufacturing ranges and yield products with average DAR values that are significantly different from the target (i.e., ≤3.0 or ≥4.0). The Poisson distribution establishes a link between average DAR values and drug load distributions, implying that measurement and control of the former (i.e., via a simple UV spectrophotometric method) could be used to indirectly control the latter in trastuzumab emtansine.

Purpose: Trastuzumab-DM1 (T-DM1) is an antibody-drug conjugate that uses trastuzumab to specifically deliver the maytansinoid antimicrotubule agent DM1 to HER2-positive cells. This first-in-human study of T-DM1 evaluated safety, pharmacokinetics, and preliminary activity of T-DM1 in patients with advanced HER2-positive breast cancer., Patients and Methods: Successive cohorts of patients who had progressed on trastuzumab-based therapy received escalating doses of T-DM1. Outcomes were assessed by standard solid-tumor phase I methods., Results: Twenty-four patients who had received a median of four prior chemotherapeutic agents for metastatic disease received T-DM1 at 0.3 mg/kg to 4.8 mg/kg on an every-3-weeks schedule. Transient thrombocytopenia was dose-limiting at 4.8 mg/kg; the maximum-tolerated dose (MTD) was 3.6 mg/kg. The half-life of T-DM1 at the MTD was 3.5 days, with peak DM1 levels < 10 ng/mL. Clearance at doses < 1.2 mg/kg was faster than at higher doses. Common drug-related adverse events (AEs) included grade < or = 2 thrombocytopenia, elevated transaminases, fatigue, nausea, and anemia. No grade > 1 nausea, vomiting, alopecia, or neuropathy events and no cardiac effects requiring dose modification were reported. The clinical benefit rate (objective response plus stable disease at 6 months) among 15 patients treated at the MTD was 73%, including five objective responses. The confirmed response rate in patients with measurable disease at the MTD (n = 9) was 44%., Conclusion: At the MTD of 3.6 mg/kg every 3 weeks, T-DM1 was associated with mild, reversible toxicity and substantial clinical activity in a heavily pretreated population. Phase II and III trials in patients with advanced HER2-positive breast cancer are under way.

CD22 represents a promising target for antibody-drug conjugate therapy in the context of B cell malignancies since it rapidly internalizes, importing specifically bound antibodies with it. To determine the pharmacokinetic parameters of anti-CD22-MCC-DM1 and MC-MMAF conjugates, various approaches to quantifying total and conjugated antibody were investigated. Although the total antibody assay formats gave similar results for both conjugates, the mouse pharmacokinetic profile for the anti-CD22-MCC-DM1 and MC-MMAF appeared significantly different depending on the conjugated antibody assay format. Since these differences significantly impacted the PK parameters determination, we investigated the effect of the drug/antibody ratio on the total and conjugated antibody quantification using multiple assay formats. Our investigations revealed the limitations of some assay formats to quantify anti-CD22-MCC-DM1 and MC-MMAF with different drug load and in the context of a heterogeneous ADC population highlight the need to carefully plan the assay strategy for the total and conjugated antibody quantification in order to accurately determine the ADC PK parameters.