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

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 site-specifically conjugated with a potent antitubulin cytotoxic drug-linker, 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 antitumor 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.

ARX788, a Site-specific Anti-HER2 Antibody-Drug Conjugate, Demonstrates Potent and Selective Activity in HER2-low and T-DM1-resistant Breast and Gastric Cancers.

First-generation antibody-drug conjugates (ADC) are heterogeneous mixtures that have shown clinical benefit, but generally exhibited safety issues and a narrow therapeutic window due, in part, to off-target toxicity caused by ADC instability. ARX788 is a next-generation, site-specific anti-HER2 ADC that utilizes a unique nonnatural amino acid-enabled conjugation technology and a noncleavable Amberstatin (AS269) drug-linker to generate a homogeneous ADC with a drug-to-antibody ratio of 1.9. ARX788 exhibits high serum stability in mice and a relatively long ADC half-life of 12.5 days. When compared in vitro against T-DM1 across a panel of cancer cell lines, ARX788 showed superior activity in the lower HER2-expressing cell lines and no activity in normal cardiomyocyte cells. Similarly, ARX788 significantly inhibited tumor growth, and generally outperformed T-DM1 in HER2-high and HER2-low expression xenograft models. Breast and gastric cancer patient-derived xenograft studies confirmed strong antitumor activity of ARX788 in HER2-positive and HER2-low expression tumors, as well as in a T-DM1-resistant model. The encouraging preclinical data support the further development of ARX788 for treatment of patients with HER2-positive breast and gastric cancer, including those who have developed T-DM1 resistance, and patients with HER2-low expression tumors who are currently ineligible to receive HER2-targeted therapy.

Total Synthesis of (R)-Dihydroactinidiolide and (R)-Actinidiolide Using Asymmetric Catalytic Hetero-Diels-Alder Methodology.

The total synthesis of the naturally occurring bicyclic lactones (R)-dihydroactinidiolide and (R)-actinidiolide is presented. The key step in the syntheses is the copper(II)-bisoxazoline-catalyzed hetero-Diels-Alder reaction of a cyclic diene with ethyl glyoxylate giving the hetero-Diels-Alder product in high yield and with very high regio-, diastereo-, and enantioselectivity. The total syntheses proceed via an intermediate, which also has the potential for a series of other natural products. The structure of the key intermediate is confirmed by X-ray analysis.

Catalytic Approach for the Formation of Optically Active Allyl alpha-Amino Acids by Addition of Allylic Metal Compounds to alpha-Imino Esters.

A new catalytic enantioselective approach for the formation of allyl alpha-amino acid derivatives by reaction of N-tosyl alpha-imino esters with allyl stannanes and silanes catalyzed by chiral copper(I) complexes has been developed. A series of different BINAP and phosphine-oxazoline (P,N) ligands have, in combination with various Lewis acids, been tested as chiral catalysts for allylation of N-tosyl alpha-imino esters. It has been found that both type of ligands, in combination with copper(I) salts, give highly valuable unsaturated alpha-amino acid derivatives. The reaction has been investigated for different allyl stannanes and silanes, and it has been found that tri-n-butyl allyl stannane gives the best results of the simple allyl compounds tested, leading to gamma,delta-unsaturated alpha-amino acid derivatives in up to 94% yield and with up to 83% ee, which can be improved to be >95% ee by recrystallization. The reaction has also been investigated using different acyclic and cyclic allyl stannanes leading to various types of unsaturated alpha-amino acid derivatives in very high yield (up to 95%) and with up to 98% ee. The stereochemistry and absolute configurations of the allyl alpha-amino acid derivatives have been determined by X-ray analysis, and it is suggested that the reaction takes place as an ene-like reaction.

Chiral CO(2)-Synthons via Catalytic Asymmetric Hetero-Diels-Alder Reactions of Ketomalonate and Dienes.

A catalytic enantioselective approach for the formation of chiral CO(2)-synthons is presented. The described methodology is based on the reaction of dienes with diethyl ketomalonate using C(2)-symmetric bisoxazolines as the chiral ligands and copper(II) and zinc(II) as the Lewis acids. For cyclic dienes the reaction proceeds in good yield and with up to 93% ee for 1,3-cyclohexadiene, while for cyclopentadiene the reaction also proceeds well at low temperature, but increasing the temperature leads to a retro-Diels-Alder reaction. The reaction has been studied under different conditions and for various dienes, and it has been found that for activated dienes both the hetero-Diels-Alder and Mukaiyama aldol products are isolated. The compound formed by the enantioselective hetero-Diels-Alder reaction of 1,3-cyclohexadiene with ketomalonate has been converted to both the CO(2)-synthon formed in principle from the [2+4] cycloaddition reaction of CO(2) and 1,3-cyclohexadiene, and attractive optically active 1,4-disubstituted cyclohexene diols. The absolute configuration of the hetero-Diels-Alder adduct has been assigned on the basis of the structure of (1S)-camphanic ester of a 1,4-disubstituted cyclohexene diol which gave suitable crystals for X-ray analysis. The reactions have also been analyzed from a theoretical point of view. First, the [2+4] cycloaddition reaction of CO(2) with 1,3-cyclohexadiene has been investigated, and then the relative stability of the two major isomers of bidentate ketomalonate coordinated to a copper(II) or zinc(II) Lewis acid dication was investigated applying density functional theory calculations. Finally, the energetics of the [2+4] hetero-Diels-Alder addition mechanisms typical of the reaction with normal dienes catalyzed by C(2)-symmetric bisoxazoline-zinc(II) complexes using semiempirical calculations are presented.

Catalytic Enantioselective Aza Diels-Alder Reactions of Imino Dienophiles.

1 mol% of catalyst is sufficient: The hetero Diels-Alder reaction of α-imino esters 1 with activated conjugated dienes 2 (R=H, Me) needs only 1 mol% of a 2,2'-bis(diarylphosphanyl)-1,1'-binaphthyl (BINAP) copper(I) complex as the catalyst to generate the adducts 3 in good yields and with enantioselectivities up to 96%. The reaction can also be carried out on gram scale! Tos=H3 CC6 H4 SO2 ; TMS=Me3 Si.

Synthesis and biological activity of new 5-O-sugar modified ketolide and 2-fluoro-ketolide antibiotics.

A series of new triazole-containing ketolides and 2-fluoro-ketolides in which the 5-O-desosamine was replaced by unnatural sugars were synthesized and evaluated against relevant macrolide-sensitive and macrolide-resistant respiratory pathogens. Excellent in vitro antibacterial activities were demonstrated for ketolide analogues having the 6'-OBz-3'-dimethylamino-glucose and 6'-OBz-4'-deoxy-3'-dimethylamino-glucose substituents.

Structure-activity relationships of bivalent aminoglycosides and evaluation of their microbiological activities.

A library of 4,5- and 4,6-linked bivalent aminoglycoside (AMG) antibiotics consisting of neamine and nebramine pharmacophores have been synthesized. We probed the effect of the linker on antibiotic activity with a series of selected synthetic analogues with varied length and substituents. A number of compounds demonstrated in vitro activity against several bacterial strains and showed activity against drug resistant strains of Pseudomonas aeruginosa. Among the compounds prepared, analogues 12a-d were novel 4,6-linked AMGs containing the nebramine pharmacophore. In addition the lead compound OPT-11 possessed an ED(50) of

New catalysts for the asymmetric hydrosilylation of ketones discovered by mass spectrometry screening.

A method for determining enantiomeric excess by mass spectrometry was employed to screen a family of chiral phosphite P,N-ligands for activity in the rhodium-catalyzed asymmetric hydrosilylation of ketones. The identification of an effective set of ligands was followed by preliminary studies of the reaction scope and mechanism. Asymmetric induction of 84-88% ee for larger-scale reactions was observed, which is close to the level of the best alternative catalysts previously discovered. The screening method was shown to be applicable to a variety of substrates without the need for special optimization.

Glyco-optimization of aminoglycosides: new aminoglycosides as novel anti-infective agents.

Glyco-optimization (OPopS) of aminoglycosides has been performed by replacing the existing sugar moiety with a variety of sugar derivatives. Glycosylation of the 6-position of nebramine provided a library of novel 4,6-linked aminoglycosides (AMGs). Among them, compounds 8b,g,i,l, and 8u with 2"-amino, 2",3"-diamino, 2",4"-diamino, 3",4"-diamino, 3"-amino groups, respectively, showed significant antimicrobial activity against Gram-(+) and -(-) bacteria. Several were particularly potent against Pseudomonus aeruginosa with MICs in the 1-2 microg/mL range.