Adapting pharmacokinetic properties of a humanized anti-interleukin-8 antibody for therapeutic applications using site-specific pegylation

A neutralizing anti-interleukin-(IL-)8 monoclonal antibody was humanized by grafting the complementary determining regions onto the human IgG framework. Subsequent alanine scanning mutagenesis and phage display enabled the production of an affinity matured antibody with a >100-fold improvement in IL-8 binding. Antibody fragments can be efficiently produced in Escherichia coli but have the limitation of rapid clearance rates in vivo. The Fab' fragment of the antibody was therefore modified with polyethylene glycol (PEG) in order to obtain a more desirable pharmacokinetic profile. PEG (5-40 kDa) was site-specifically conjugated to the Fab' via the single free cysteine residue in the hinge region. In vitro binding and bioassays showed little or no loss of activity. The pharmacokinetic profiles of the 20 kDa, 30 kDa, 40 kDa, and 40 kDa branched PEG-Fab' molecules were evaluated in rabbits. Relative to the native Fab', the clearance rates of the PEGylated molecules were decreased by 44-175-fold. In a rabbit ear model of ischemia/reperfusion injury, all PEGylated Fab' molecules were as efficacious in reducing oedema as the original monoclonal antibody. These studies demonstrate that it is possible to customize the pharmacokinetic properties of a Fab' while retaining its antigen binding activity.

An investigation of angiotensin II agonist and antagonist analogues with 5,5-dimethylthiazolidine-4-carboxylic acid and other constrained amino acids

To probe the receptor-bound conformational requirements of angiotensin II (ANG II) octapeptide agonists and antagonists, the synthesis and biological activities of [Sar1]ANG II agonist and [Sar1,X8]ANG II antagonist analogues (X8 = Ile, D-Phe, or Aib) bearing conformational constraints in positions 3, 5, and 7 were investigated and compared with previous literature efforts. The conformational constraints that were examined include Pro, Dtc (5,5-dimethylthiazolidine-4-carboxylic acid), Aib, Cle, (NMe)Ala, (NMe)Ile, and the lactam modification, L,L-lactam-Phe, previously described by Freidinger et al. (J. Org. Chem. 1982, 47, 104-109). Both [Sar1,(NMe)Ala3 and Pro3]ANG II retained agonist activity, while only [Sar1,(NMe)Ala3,Ile8]ANG II retained antagonist activity. [Sar1,Dtc5]ANG II displayed superior agonist activity, while both [Sar1,Dtc5 and Cle5,Ile8] ANG II displayed superior antagonist activity. In contrast to position 5, Dtc7 substitution for Pro7 of either [Sar1]ANG II or [Sar1,Ile8]ANG II gave analogues with reduced activities. These results are consistent with the hypothesis that conformations of [Sar1]ANG II and [Sar1,Ile8]ANG II containing a C7 conformation in position 7 are preferred for both ANG II agonist and antagonist activity. Incorporation of the L,L-lactam-Phe modification into [Sar1]ANG II gives a pure ANG II antagonist (pA2 8.3), comparable to saralasin (pA2 8.6). In positions 3, 5, and 7 the conformational requirements for the ANG II agonist [Sar1]ANG II and the ANG II antagonist [Sar1,Ile8]ANG II may be different. Individual substitution of (NMe)Ala3, Dtc5, D-Phe8 and Aib8 [[Sar1,Aib8]ANG II: Khosla et al. J. Med. Chem. 1977, 20, 1051-1055] into [Sar1,Ile8]ANG II gives analogues that retain antagonist activity. Multiple substitutions of these types of residues into [Sar1,Ile8]ANG II gives analogue 45 [Sar1,(NMe)Ala3,Dtc5,Aib8]ANG II, 46 [Sar1(NMe)Ala3,D-Phe8]AII, and 47 [Sar1,Dtc5,D-Phe8]AII, which display considerably reduced antagonist activity. In ANG II antagonists the construction of highly constrained analogues may not be possible by the additive substitution of "preferred" constrained amino acids into a single analogue.

Epitopes of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins recognized by antibodies in the sera of HIV-1-infected individuals

Sera from human immunodeficiency virus (HIV)-infected study subjects and controls were analyzed by enzyme-linked immunosorbent assay using 10 synthetic peptides to identify epitopes of HIV envelope glycoproteins (ENVgp) that were recognized by antibodies. Two epitopes of HIV ENVgp, ENVP466 (amino acids 466-481) and ENVP497 (amino acids 497-509), were recognized by antibodies in the sera of most HIV-infected individuals. The frequency of individuals with detectable serum antibodies to these two epitopes was not associated with the stage of HIV disease. Purified antibodies to ENV497 had only very weak neutralizing activity against infectious HIV. These data suggest that a particular dominant type of antibody response to HIV's ENVgp has minimal protective effects. These and other studies to identify and stimulate immune responses to selected epitopes of HIV antigens may be useful in the design of vaccines to prevent or treat HIV infections.

The role of position 4 in angiotensin II antagonism: a structure-activity study

A number of [Sar1,(pX)Phe4]-ANG II and [Sar1,(pX)Phe4,Ile8]-ANG II analogues were prepared. A good correlation between pX structure in [Sar1,(pX)Phe4]-ANG II and antagonist activity could not be found. However, the data suggest a general trend: Position 4 para substituents that are hydrophilic and capable of donating a hydrogen atom in a hydrogen bond promote agonist activity, while para substituents that are hydrophobic and incapable of donating a hydrogen atom promote antagonist activity. These properties were found to be optimal in the p-chloro substituent. The resulting analogue [Sar1,(pCl)Phe4]-ANG II is a potent ANG II antagonist in vivo. The pX substituents that promote antagonist activity in the [Sar1,(pX)Phe4]-ANG II series were unfavorable in [Sar1,(pX)Phe4,Ile8]-ANG II analogues. ANG II analogues that are antagonists by virtue of an alteration in position 8 require a position 4 agonist side chain. Concurrent modifications of positions 4 and 8 do not give rise to potent antagonists with reduced partial agonist activity.

Potent angiotensin II antagonists with non-beta-branched amino acids in position 5

Amino acids with lipophilic side chains that contain more than one functional group on the beta-carbon, i.e. a beta-branched hydrocarbon moiety, are required in position 5 of angiotensin II (AII) analogue with potent agonist activity. This requirement for agonist activity does not follow for AII analogues with potent antagonist activity. Straight-chain amino acids may be substituted into position 5 of [Sar1,X5,Ile8]AII with retention or enhancement of antagonist activity, e.g. (X5,pA2 rabbit aorta) Phe, 9.15; Tyr, 9.6; His, 9.0; Glu,9.0; Nle, 8.85, compared to Ile, 9.1. beta-Branched side chains can still enhance the antagonist activities of [Sar1,X5,Ile8]AII analogues, e.g. X5 = (beta Me)Phe, pA2 = 9.3. An X-ray crystal structure of the Boc-(beta Me)Phe DCHA salt, prepared for the synthesis of [Sar1,-(beta Me)Phe5, Ile8]AII, revealed an S,S configuration of alpha- and beta-carbon atoms. Contrary to previous literature reports, chemical nonequivalence of the deta-protons of Pro was observed in the 1H NMR spectra of [Sar1,X5,Ile8]AII analogues bearing both beta-branched X5 side chains (X5 = Ile) and non-beta-branched X5 side chains (X5 = Ala, His).

The importance of residues 2 (arginine) and 6 (histidine) in high-affinity angiotensin II antagonists

The structure-antagonist activity relationship is described for analogues of [Sar1,Ile8]angiotensin II substituted in position 2 (arginine) and position 6 (histidine). An extreme sensitivity of potency to alterations in these positions was observed, suggesting that both residues are important for binding. Evidence is presented suggesting that the position 6 histidine side chain in angiotensin II (AII) is not involved in receptor stimulation. The structure-activity relationship is also explored for both [des-Asp1] AII (AIII) and [des-Asp1,Ile8]AII analogues substituted in position 2 (arginine). The substitution of D-N-methylalanine, D-(NMe)Ala, into position 2 of both [des-Asp1]AII and [des-Asp1,Ile8]AII gives analogues 39 and 40 that appear to be more potent than the native [Arg2]peptides and that are the most potent AIII agonists and antagonists described to date.

Effects of D-amino acid substitution on antagonist activities of angiotensin II analogues

The synthesis and biological activities of angiotensin II (AII) analogues are described and compared to the literature. D-Amino acid substitution was employed to search for novel AII antagonists that would also display reduced partial agonist activity. Substitution of D-amino acids into the interior positions 2-7 of [Sar1,Ile8]-AII gave rise to inactive compounds or weak antagonists. Substitution of D-amino acids into position 8 gave rise to potent antagonists in vivo including [Sar1,D-Phe8]-AII 8, [Sar1,D-(alpha Me)Phe8]-AII (35), [Sar1,D-Trp8]-AII (32), [Sar1,D-Phg8]-AII (29), [Sar1,D-Peg8]-AII (30), and [Sar1,D-Phe8]-AII-NH2 (31). The structural requirements for D-AA8 analogues (antagonists) showed similarities with those of L-AA8 analogues (agonists). The latter three analogues, 29-31, were considerably more potent in vivo than their in vitro affinities would indicate, suggesting that these analogues may resist carboxypeptidase-like degradation. While partial agonist activity was not removed by D-AA8 substitution, [Sar1,D-Phe8]-AII-NH2 (31) displays lower partial agonist activity than [Sar1,Ile8]-AII. A receptor model is presented that highlights the difference between [L-AA8]-AII analogue agonist activity and [D-AA8]-AII analogue antagonist activity.