Impact of Drug Conjugation on Pharmacokinetics and Tissue Distribution of Anti-STEAP1 Antibody–Drug Conjugates in Rats

Abstract

Antibody-drug conjugates (ADCs) are designed to combine the exquisite specificity of antibodies to target tumor antigens with the cytotoxic potency of chemotherapeutic drugs. In addition to the general chemical stability of the linker, a thorough understanding of the relationship between ADC composition and biological disposition is necessary to ensure that the therapeutic window is not compromised by altered pharmacokinetics (PK), tissue distribution, and/or potential organ toxicity. The six-transmembrane epithelial antigen of prostate 1 (STEAP1) is being pursued as a tumor antigen target. To assess the role of ADC composition in PK, we evaluated plasma and tissue PK profiles in rats, following a single dose, of a humanized anti-STEAP1 IgG1 antibody, a thio-anti-STEAP1 (ThioMab) variant, and two corresponding thioether-linked monomethylauristatin E (MMAE) drug conjugates modified through interchain disulfide cysteine residues (ADC) and engineered cysteines (TDC), respectively. Plasma PK of total antibody measured by enzyme-linked immunosorbent assay (ELISA) revealed ∼45% faster clearance for the ADC relative to the parent antibody, but no apparent difference in clearance between the TDC and unconjugated parent ThioMab. Total antibody clearances of the two unconjugated antibodies were similar, suggesting minimal effects on PK from cysteine mutation. An ELISA specific for MMAE-conjugated antibody indicated that the ADC cleared more rapidly than the TDC, but total antibody ELISA showed comparable clearance for the two drug conjugates. Furthermore, consistent with relative drug load, the ADC had a greater magnitude of drug deconjugation than the TDC in terms of free plasma MMAE levels. Antibody conjugation had a noticeable, albeit minor, impact on tissue distribution with a general trend toward increased hepatic uptake and reduced levels in other highly vascularized organs. Liver uptakes of ADC and TDC at 5 days postinjection were 2-fold and 1.3-fold higher, respectively, relative to the unmodified antibodies. Taken together, these results indicate that the degree of overall structural modification in anti-STEAP1-MMAE conjugates has a corresponding level of impact on both PK and tissue distribution.

Synthesis of site-specific antibody-drug conjugates using unnatural amino acids

“…Pharmacokinetic parameters were calculated by noncompartment modeling, and also did not show significant differences in clearance rates for IgG-nAF and IgG at 0.31 ± 0.03 mL/h/kg and 0.3 ± 0.11 mL/h/kg, respectively (Table S2). Thus, our site-specific ADCs have pharmacokinetics similar to the unconjugated antibody, and improved relative to many nonspecifically conjugated ADCs (38,39). It is likely that nonspecific conjugates of hydrophobic drugs lead to a population of antibodies with reduced solubility.…”

“…Next, we examined the pharmacokinetics of anti-Her2-IgG(HC-A121X)-nAF in rodents because most ADCs have reduced half-lives compared with the native antibody (20,38,39). A single dose of 1 mg/kg anti-Her2-IgG-nAF in PBS was injected intravenously in five rats, and serum was collected at regular intervals for 14 d and analyzed by ELISA using antihuman κ-antibody.…”

Differential Effects of Predosing on Tumor and Tissue Uptake of an111In-Labeled Anti-TENB2 Antibody–Drug Conjugate

“…Anti-TENB2-MMAE was labeled with DOTA for 111 In complexation by random modification of lysine residues as previously described (19). We observed 2.9 and 3.1 DOTA units, respectively, by reduced and intact liquid chromatography mass spectrometry.…”

STEAP1 is overexpressed in cancers: A promising therapeutic target

“…Active immunization against STEAP1 using DNA prime/modified vaccinia virus Ankara boost strategy inhibits prostate cancer progression in a murine model [6]. The immunogenicity of STEAP1 has led to the development of anti-STEAP1 antibody-drug conjugates to combine the specificity of anti-STEAP1 antibody to the cytotoxic potency of chemotherapeutic drugs [37].…”

“…STEAP1 overexpression could promote proliferation, invasiveness, tumorigenicity, and metastasis through ROS-levels upregulation in cancer. A recent study reported the interest of antibody-drug conjugates as promising therapeutic approach combining the STEAP1 antigen targeting specificity of monoclonal antibodies with the cytotoxic potency of chemotherapeutic drugs [37].…”