Precision Chemoradiotherapy for HER2 Tumors Using Antibody Conjugates of an Auristatin Derivative with Reduced Cell Permeability

Abstract

The most successful therapeutic strategies for locally advanced cancers continue to combine decades-old classical radiosensitizing chemotherapies with radiotherapy. Molecular targeted radiosensitizers offer the potential to improve the therapeutic ratio by increasing tumor-specific kill while minimizing drug delivery and toxicity to surrounding normal tissue. Auristatins are a potent class of anti-tubulins that sensitize cells to ionizing radiation damage and are chemically amenable to antibody conjugation. To achieve tumor-selective radiosensitization, we synthesized and tested anti-HER2 antibody-drug conjugates of two auristatin derivatives with ionizing radiation. Monomethyl auristatin E (MMAE) and monomethyl auristatin F (MMAF) were attached to the anti-HER2 antibodies trastuzumab and pertuzumab through a cleavable linker. While MMAE is cell permeable, MMAF has limited cell permeability as free drug resulting in diminished cytotoxicity and radiosensitization. However, when attached to trastuzumab or pertuzumab, MMAF was as efficacious as MMAE in blocking HER2-expressing tumor cells in G 2-M. Moreover, MMAF anti-HER2 conjugates selectively killed and radiosensitized HER2-rich tumor cells. Importantly, when conjugated to targeting antibody, MMAF had the advantage of decreased bystander and off-target effects compared with MMAE. In murine xenograft models, MMAF anti-HER2 antibody conjugates had less drug accumulated in the normal tissue surrounding tumors compared with MMAE. Therapeutically, systemically injected MMAF anti-HER2 conjugates combined with focal ionizing radiation increased tumor control and improved survival of mice with HER2-rich tumor xenografts. In summary, our results demonstrate the potential of cellimpermeable radiosensitizing warheads to improve the therapeutic ratio of radiotherapy by leveraging antibody-drug conjugate technology.

A poly-ADP-ribose polymer-based antibody-drug conjugate

“… 30 – 32 Conjugation of MMAF with several antibodies resulted in ADCs with potent anti-tumor activities. 33 – 36 The free carboxyl group of MMAF also facilitates synthesis of drug-linker conjugates with high potency. 37 Trastuzumab and MMAF were selected as a model targeting antibody and cytotoxic payload for synthesizing the PAR polymer-based ADC.…”

CD19-Targeted Immunotherapies for Diffuse Large B-Cell Lymphoma

“…As a tubulin-binding molecule, dolastatin exerts its cytotoxic effect through the inhibition of microtubule assembly and tubulin-dependent GTP hydrolysis, leading to cell cycle arrest and apoptosis ( 21 ). MMAF differs from another auristatin derivative, monomethyl auristatin E (MMAE), for a C-terminal modification which is aimed to limit membrane permeability and reduce bystander and off-target toxicity ( 22 ). A phase 1 study (NCT01786135) demonstrated the safety of SGN-CD19A in the clinical setting of R/R B-cell NHL, with 30% of evaluable patients achieving a complete response ( 23 ).…”

A FZD7-specific Antibody–Drug Conjugate Induces Ovarian Tumor Regression in Preclinical Models

“…F7-ADC consists of F7-Ab conjugated to the antimitotic drug, monomethyl auristatin E (MMAE), by cleavable MC-VC-PABC linkers (Figure 2A). An average of four MMAE molecules were conjugated to cysteine residues in the antibody hinge region, following reduction of disulfides (41,42). For non-invasive F7-ADC tracking, we also conjugated a Cy5 fluorophore to a hinge region disulfide via a non-cleavable maleimide linker.…”

“…F7-Ab-MMAE drug conjugate was synthesized using methods previously described (41,42). A solution (2 mL, 10.2 mg/mL) of F7-Ab was treated with sodium bicine buffer (200 μL, 1M pH 8.3) and sodium diethylenetriaminepentaacetic acid (20 μL, 100 mM pH 7).…”