Therapeutic antibodies have shown little efficacy in the treatment of pancreatic ductal adenocarcinomas (PDAC). Tumor desmoplasia, hypovascularity, and poor perfusion result in insufficient tumor cell exposure, contributing to treatment failure. Smoothened inhibitors of hedgehog signaling (sHHi) increase PDAC tumor permeability, perfusion, and drug delivery, and provide a tool to develop a quantitative, mechanistic understanding as to how the temporal dynamics of tumor priming can impact intratumor distribution of monoclonal antibodies (mAb). A linked pharmacokinetic (PK)/pharmacodynamic (PD) model was developed to integrate the plasma and tumor PK of a sHHi priming agent with its effects upon downstream stromal biomarkers Gli1, hyaluronic acid, and interstitial fluid pressure in PDAC patient-derived xenograft (PDX) tumors. In parallel, in situ tumor concentrations of cetuximab (CTX: anti-epidermal growth factor receptor; EGFR) were quantified as a marker for tumor delivery of mAb or antibody-drug conjugates. A minimal, physiologically-based pharmacokinetic (mPBPK) model was constructed to link sHHi effects upon mechanistic effectors of tumor barrier compromise with the intratumor distribution of CTX, and CTX occupancy of EGFR in tumors. Integration of the mPBPK model of mAb deposition and intratumor distribution with the PK/PD model of tumor responses to priming not only identified physiological parameters that are critical for tumor antibody distribution, but also provides insight into dosing regimens that could achieve maximal tumor disposition of therapeutic antibodies under conditions of transient PDAC tumor permeability barrier compromise that mechanistically-diverse tumor priming strategies may achieve.(c) 2023 American Pharmacists Association. Published by Elsevier Inc. All rights reserved.

Antibody-drug conjugates (ADCs) have attracted great attention in recent years in the wake of an accelerated FDA approval rate and several large-scale acquisitions. To date, there are ten ADC drugs on the market and more than 70 in various stages of clinical trials. Yet, due to the complicated nature of ADC molecules, considerations need to cover many aspects for the success of ADCs, including target specificity, linker-payload stability, tumor permeability, and clearance rate. This topical review summarizes and discusses current methods used to increase stability and homogeneity of ADCs of cysteine conjugation. We believe that they will lead to improvement of efficacy and pharmacokinetics (PK) of ADC drugs.

BACKGROUND:Antibody-drug conjugate (ADC) construction poses numerous challenges that limit clinical progress. In particular, common bioconjugation methods afford minimal control over the site of drug coupling to antibodies. Here, such difficulties are overcome through re-bridging of the inter-chain disulfides of cetuximab (CTX) with auristatin-bearing pyridazinediones, to yield a highly refined anti-epidermal growth factor receptor (EGFR) ADC.METHODS:In vitro and in vivo assessment of ADC activity was performed in KRAS mutant pancreatic cancer (PaCa) models with known resistance to CTX therapy. Computational modelling was employed for quantitative prediction of tumour response to various ADC dosing regimens.RESULTS:Site-selective coupling of an auristatin to CTX yielded an ADC with an average drug:antibody ratio (DAR) of 3.9, which elicited concentration- and EGFR-dependent cytotoxicity at sub-nanomolar potency in vitro. In human xenografts, the ADC inhibited tumour growth and prolonged survival, with no overt signs of toxicity. Key insights into factors governing ADC efficacy were obtained through a robust mathematical framework, including target-mediated dispositional effects relating to antigen density on tumour cells.CONCLUSIONS:Together, our findings offer renewed hope for CTX in PaCa therapy, demonstrating that it may be reformatted as a next-generation ADC and combined with a predictive modelling tool to guide successful translation.

Kadcyla® (T-DM1), an antibody-drug conjugates (ADCs) for HER2+ breast cancer treatment, has been approved by the Food and Drug Administration (FDA) in 2013. An ADC of random lysine conjugation, it has difficulties in DAR control and unsatisfactory PK due to uneven DAR distribution. It also gives rise to aggregation during conjugation because of the hydrophobicity nature of the cytotoxin, DM1. The linker-drug in T-DM1, SMCC-DM1 is hydrophobic and requires certain percentage of organic solvent such as DMA in the conjugation solution, limiting the manufacturing process in an organic-solvent-compatible device and adding extra costs. To address these problems, a site-specific conjugation method was developed involving full reduction of antibody and full conjugation with the bridge-like conjugator-drug, based on the work of Caddick and co-workers, to obtain a site-directed antibody-drug conjugate with DAR 4. The bridge-like conjugator was assembled with SMCC-DM1 and different lengths of hydrophilic polyethylene glycol (PEG) moiety. By applying PEG moiety in the side chain of the linker-drug, the organic solvent used in the conjugation can be reduced. When the PEG length is about 26 units, organic solvent is no longer needed in the conjugation. Reducing the amount of organic solvent in conjugation could also diminish the aggregation occurrence during the conjugation. Moreover, the conjugation configuration with the designed conjugator was also discussed in the article. The binding affinity of the resulting ADCs did not show significant decrease and the cell based assay and animal study have shown the comparable results with T-DM1.