Antibody-drug conjugates (ADCs) consist of cytotoxic drugs covalently linked to monoclonal antibodies directed to antigens differentially overexpressed in tumor cells. These loaded antibodies are expected to selectively deliver lethal cargoes to tumor cells and provide sustained clinical benefit to pre-selected cancer patients while, at the same time, minimizing systemic toxicity. Although on-target adverse events are not completely avoided and the true efficacy of these innovative agents still requires further clarification, proof-of-concept has already been achieved in clinical settings with immunoconjugates containing calicheamicin, auristatin or maytansine-based cytotoxic payloads. In this present article we review the characteristics of the preceding cytotoxic platforms and their chemical conjugation approaches.

No abstract

No abstract

The contamination of the widely used lifesaving anticoagulant drug heparin in 2007 has drawn renewed attention to the challenges that are associated with the characterization, quality control and standardization of complex biological medicines from natural sources. Heparin is a linear, highly sulfated polysaccharide consisting of alternating glucosamine and uronic acid monosaccharide residues. Heparin has been used successfully as an injectable antithrombotic medicine since the 1930s, and its isolation from animal sources (primarily porcine intestine) as well as its manufacturing processes have not changed substantially since its introduction. The 2007 heparin contamination crisis resulted in several deaths in the United States and hundreds of adverse reactions worldwide, revealing the vulnerability of a complex global supply chain to sophisticated adulteration. This Perspective discusses how the US Food and Drug Administration (FDA), the United States Pharmacopeial Convention (USP) and international stakeholders collaborated to redefine quality expectations for heparin, thus making an important natural product better controlled and less susceptible to economically motivated adulteration.

The present study deals with the conformation in solution of two heparin octasaccharides containing the pentasaccharide sequence GlcN(NAc,6S)-GlcA-GlcN(NS,3,6S)-IdoA(2S)-GlcN(NS,6S) [AGA*IA; where GlcN(NAc,6S) is N-acetylated, 6-O-sulfated alpha-D-glucosamine, GlcN(NS,3,6S) is N,3,6-O-trisulfated alpha-D-glucosamine and IdoA(2S) is 2-O-sulfated IdoA (alpha-L-iduronic acid)] located at different positions in the heparin chain and focuses on establishing geometries of IdoA residues (IdoA(2S) and IdoA) both inside and outside the AGA*IA sequence. AGA*IA constitutes the active site for AT (antithrombin) and is essential for the expression of high anticoagulant and antithrombotic activities. Analysis of NMR parameters [NOEs (nuclear Overhauser effects), transferred NOEs and coupling constants] for the two octasaccharides indicated that between the 1C4 and 2S0 conformations present in dynamic equilibrium in the free state for the IdoA(2S) residue within AGA*IA, AT selects the 2S0 form, as previously shown [Hricovini, Guerrini, Bisio, Torri, Petitou and Casu (2001) Biochem. J. 359, 265-272]. Notably, the 2S0 conformation is also adopted by the non-sulfated IdoA residue preceding AGA*IA that, in the absence of AT, adopts predominantly the 1C4 form. These results further support the concept that heparin-binding proteins influence the conformational equilibrium of iduronic acid residues that are directly or indirectly involved in binding and select one of their equi-energetic conformations for best fitting in the complex. The complete reversal of an iduronic acid conformation preferred in the free state is also demonstrated for the first time. Preliminary docking studies provided information on the octasaccharide binding location agreeing most closely with the experimental data. These results suggest a possible biological role for the non-sulfated IdoA residue preceding AGA*IA, previously thought not to influence the AT-binding properties of the pentasaccharide. Thus, for each AT binding sequence longer than AGA*IA, the interactions with the protein could differ and give to each heparin fragment a specific biological response.

Terminal 1,6-anhydro-aminosugars (1,6-anAS) are typical structural moieties of enoxaparin, a low-molecular-weight heparin (LMWH) widely used for prevention and treatment of thrombotic disorders. In the enoxaparin manufacturing process, these modified amino sugars are formed during the β-eliminative cleavage of heparin. To investigate the effect of terminal anAS on antithrombin (AT) binding and on inhibition of factor Xa (FXa), two octasaccharides containing modified AT-binding pentasaccharide sequences were isolated from enoxaparin. The molecular conformation of the octasaccharides terminating with N-sulfo-1,6-anhydro-D-mannosamine and N-sulfo-1,6-anhydro-D-glucosamine, respectively, has been determined both in the absence and presence of AT by NMR experiments and docking simulations. Reduced overall contacts of the terminal anAS residues with the binding region of AT induce a decrease in affinity for AT as well as lower anti-FXa activity. The anti-FXa measured either in buffer or plasma milieu does not show any significant difference, suggesting that the inhibition of anti-FXa remains specific and biologically relevant.

Summary. Background and objectives: AVE5026 is a novel, hemisynthetic, ultra-low-molecular-weight heparin (ULMWH), which is in clinical development for prevention of venous thromboembolism. Its unique structural features result from the highly selective depolymerization of heparin by the phosphazene base that protects the antithrombin (AT)-binding site from destruction. In the present paper, we describe the chemical and biological characteristics of AVE5026, as well as its effects on experimental thrombosis as compared to those of the low-molecular-weight heparin (LMWH) enoxaparin after a single subcutaneous (s.c.) administration in certain animal models. Method and results: AVE5026 has a higher antifactor Xa (anti-FXa) activity (160 U mg ) as a result of its structure being strongly enriched in specific ATbinding oligosaccharides. In human plasma, potent inhibition of thrombin generation by AVE5026 was closely related to its anti-FXa activity. In a rat venous thrombosis model, AVE5026 showed a dose-dependent antithrombotic activity comparable to that of enoxaparin (ED50-AVE5026 = 1.6 mg kg ). Interestingly, non-occlusive venous thrombosis in rabbits was inhibited by an ED50 of 0.1 mg kg )1 AVE5026, whereas 0.316 mg kg )1 enoxaparin was not active. In a canine model, similarly to enoxaparin (ED50 = 1.3 mg kg ). At equipotent doses, AVE5026 did not affect bleeding parameters, whereas enoxaparin showed increased hemorrhage in rats, rabbits and dogs. Conclusion: These unique structural attributes distinguish AVE5026 from the LMWH class. Based on these data in wellestablished arterial and venous thrombosis models, AVE5026 could represent a valuable alternative in thrombosis prevention with an improved benefit-risk profile as compared to that of enoxaparin.

The 3-O-sulfation of N-sulfated glucosamine is the last event in the biosynthesis of heparin/heparan sulfate, giving rise to the antithrombin-binding pentasaccharide sequence AGA*IA, which is largely associated with the antithrombotic activity of these molecules. The aim of the present study was the structural and biochemical characterization of a previously unreported AGA*IA*-containing octasaccharide isolated from the very-low-molecular-mass heparin semuloparin, in which both glucosamine residues of the pentasaccharide moiety located at the non-reducing end bear 3-O-sulfate groups. Two-dimensional and STD (saturation transfer difference) NMR experiments clearly confirmed its structure and identified its ligand epitope binding to antithrombin. The molecular conformation of the octasaccharide-antithrombin complex has been determined by NMR experiments and docking/energy minimization. The presence of the second 3-O-sulfated glucosamine in the octasaccharide induced more than one order of magnitude increase in affinity to antithrombin compared to the pentasaccharide AGA*IA.