Nonclinical Development of Next-generation Site-specific HER2-targeting Antibody–drug Conjugate (ARX788) for Breast Cancer Treatment

Abstract

Conventional antibody-drug conjugates (ADC) utilize native surface-exposed lysines or cysteines on the antibody of interest to conjugate cytotoxic payload. The nonspecific conjugation results in a mixture with variable drug-to-antibody ratios (DAR), conjugation sites, and ADCs that are often unstable in systemic circulation. ARX788 is an ADC consisting of a HER2-targeting antibody sitespecifically conjugated with a potent antitubulin cytotoxic druglinker, AS269. The site-specific conjugation is achieved by first incorporating the nonnatural amino acid, para-acetyl phenylalanine (pAF), into the antibody, followed by covalent conjugation of AS269 to the pAF to form a highly stable oxime bond resulting in a DAR 2 ADC. ARX788 exhibits significant, dose-dependent antitu-mor activity against HER2-expressing breast and gastric xenograft tumors. Pharmacokinetic (PK) studies in multiple species showed the highly stable nature of ARX788 with overlapping PK profiles for the intact ADC and total antibody. Metabolism studies demonstrated that pAF-AS269 was the sole major metabolite of ARX788, with no evidence for the release of free drug often observed in conventional ADCs and responsible for adverse side effects. Furthermore, ARX788 demonstrated a favorable safety profile in monkeys with a highest nonseverely toxic dose of 10 mg/kg, which was well above the efficacious dose level observed in preclinical tumor models, thus supporting clinical development of ARX788.

Azobenzene‐Based Linker Strategy for Selective Activation of Antibody–Drug Conjugates

“…We also realized that the thiosuccinimide linkage in AZO‐ADC‐ 2 was not optimal and could be eliminated by retro‐Michael reactions in vivo, [28] eventually leading to the off‐target of payloads. Combination of this azobenzene‐based linker strategy with site‐specific [29] or “maleimide ring‐opening” conjugation technology [30] is expected to yield an optimised ADC with a satisfactory therapeutic window. In addition, HIC analysis showed that AZO‐ADC‐ 2 eluted about 0.6 min later than the traditional VC‐ADC.…”

HER2+ advanced gastric cancer: Current state and opportunities (Review)

“…A humanized McAb that specifically targets the HER2 protein on cancer cells and a cytotoxic tubulin inhibitor known as AS269 that is conjugated to the McAb const ARX788, a site-specific anti-HER2 antibody-drug combination ( 30 , 103 ) In preclinical studies, ARX788 demonstrated effective anticancer activity in breast cancer and AGC with minimal expression of HER2 and T-DM1 resistance in addition to good safety and antitumor activity in AGC and breast cancer with overexpression of HER2 ( 104 , 105 ). The results of a multicenter dose-expanded phase I clinical trial ( 106 ) showed that ARX788 had good tolerance and antitumor efficacy in patients with HER2 + AGC/GEJ cancer who were non-responsive to trastuzumab.…”

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

“…ARX788 is based in a humanized anti-HER2 antibody that is modified with a nonnatural amino acid ( p -acetyl-phenylalanine, p AcF). The latter binds, through a non-cleavable amberstatin drug-linker (AS269), to the N-terminus of MMAF [ 60 ]. The resulting ADC is highly homogeneous with a DAR of 1.9.…”