7 research outputs found
Understanding How the Stability of the Thiol-Maleimide Linkage Impacts the Pharmacokinetics of Lysine-Linked Antibody–Maytansinoid Conjugates
Antibody-drug
conjugates (ADCs) have become a widely investigated
modality for cancer therapy, in part due to the clinical findings
with ado-trastuzumab emtansine (Kadcyla). Ado-trastuzumab emtansine
utilizes the Ab-SMCC-DM1 format, in which the thiol-functionalized
maytansinoid cytotoxic agent, DM1, is linked to the antibody (Ab)
via the maleimide moiety of the heterobifunctional SMCC linker. The
pharmacokinetic (PK) data for ado-trastuzumab emtansine point to a
faster clearance for the ADC than for total antibody. Cytotoxic agent
release in plasma has been reported with nonmaytansinoid, cysteine-linked
ADCs via thiol-maleimide exchange, for example, brentuximab vedotin.
For Ab-SMCC-DM1 ADCs, however, the main catabolite reported is lysine-SMCC-DM1,
the expected product of intracellular antibody proteolysis. To understand
these observations better, we conducted a series of studies to examine
the stability of the thiol-maleimide linkage, utilizing the EGFR-targeting
conjugate, J2898A-SMCC-DM1, and comparing it with a control ADC made
with a noncleavable linker that lacked a thiol-maleimide adduct (J2898A-(CH<sub>2</sub>)<sub>3</sub>-DM). We employed radiolabeled ADCs to directly
measure both the antibody and the ADC components in plasma. The PK
properties of the conjugated antibody moiety of the two conjugates,
J2898A-SMCC-DM1 and J2898A-(CH<sub>2</sub>)<sub>3</sub>-DM (each with
an average of 3.0 to 3.4 maytansinoid molecules per antibody), appear
to be similar to that of the unconjugated antibody. Clearance values
of the intact conjugates were slightly faster than those of the Ab
components. Furthermore, J2898A-SMCC-DM1 clears slightly faster than
J2898A-(CH<sub>2</sub>)<sub>3</sub>-DM, suggesting that there is a
fraction of maytansinoid loss from the SMCC-DM1 ADC, possibly through
a thiol-maleimide dependent mechanism. Experiments on ex vivo stability
confirm that some loss of maytansinoid from Ab-SMCC-DM1 conjugates
can occur via thiol elimination, but at a slower rate than the corresponding
rate of loss reported for thiol-maleimide links formed at thiols derived
by reduction of endogenous cysteine residues in antibodies, consistent
with expected differences in thiol-maleimide stability related to
thiol p<i>K</i><sub>a</sub>. These findings inform the design
strategy for future ADCs