This year we have continued to identify novel mAbs in several formats as Fabs, scFvs and eAds against cancer-related proteins. These mAbs were tested for their activity against cancer cells in vitro and used for development of novel approaches for multispecific targeting. We have also developed several libraries of eAds which can be used as a source of binders to various targets. The major accomplishments are summarized below. 1) We have previously proposed to use isolated CH2 domains as scaffolds for construction of libraries containing diverse binders and generated such libraries by using random mutagenesis for diversification. However, native isolated CH2 is not very stable and the generation of many mutations could lead to an increase in immunogenicity. Previously we also demonstrated that engineering an additional disulfide bond and removing seven N-terminal residues results in an eAd (m01s) with highly increased stability. We and others have also previously shown that grafting of the heavy chain complementarity region 3 (CDR-H3 (H3)) onto cognate positions of the variable domain leads to highly diversified libraries from which a number of binders to various antigens have been selected. However, grafting of H3s to non-cognate positions in constant domains results in additional residues at the junctions of H3s and the CH2 framework. We developed a new method based on multi-step PCR that allows the precise replacement of loop FG (no changes in its flanking sequences) by human H3s from another library. Using this method and limited mutagenesis of loops BC and DE we generated an eAd phage library. Panning of this library against an HIV-1 gp41 MPER peptide resulted in selection of a binder, m2a1, which neutralized HIV-1 isolates from different clades with modest activity and retained the m01s capability of binding to the human neonatal Fc receptor (hFcRn). This result provides for the first time a proof of concept that CH2-based antigen binders that also mimic to certain extent other functions of full-size antibodies (binding to FcRn) can be generated that also mimic to certain extent other functions of full-size antibodies (binding to FcRn);we have previously hypothesized that such binders can be made and coined the term nAbs. Further studies in animal models and in humans will show how useful nAbs could be as therapeutics and diagnostics.2) Therapeutic mAbs have several advantages over small molecule drugs and small proteins and peptides, including a long serum half-life. The long serum half-life of IgG is due, in part, to its molecular weight (150kDa) and its ability to bind FcRn. Both the CH2 and CH3 domains of Fc are involved in FcRn binding. Antibody fragments and antibody-like scaffolds have improved penetration into tissues due to their small size, yet suffer from a short serum half-life of less than one hour. The human CH2 domain (CH2D) of IgG1 retains a portion of the FcRn binding site, is amenable to modification for target binding, and may represent the smallest antibody-like scaffold retaining a relatively long serum half-life. We generated a dimeric CH2D (dCH2D) and determined its pharmacokinetics (PK), as well as the PK of wild-type monomeric CH2D (mCH2D) and a short stabilized CH2D variant (ssCH2D) in normal B6 mice, human FcRn transgenic mice and cynomolgus macaques. The elimination half-life of dCH2D was 9.9, 10.4 and 11.2 hours, and that of ssCH2D was 13.1, 9.9 and 11.4 hours, in B6 mice, hFcRn mice and cynomolgus macaques, respectively. These half-lives were slightly longer than that of mCH2D (6.9 and 8.8 hours) in B6 and hFcRn mice, respectively. These data demonstrate that engineered CH2D-based variants have relatively long serum half-lives, making them a unique scaffold suitable for development of targeted therapeutics.3) We are also improving CH2-based scaffolds for binding to human neonatal Fc receptor (FcRn) with the specific aim to generate nAbs that can bind specifically to a cancer-related protein and simultaneously to the FcRn. Changes in the affinity of IgGs to FcRn lead to changes in the half-life of engineered IgGs and Fc fusion proteins. Longer half-life of therapeutic antibodies means lower dose and longer interval between administering. For some diagnostic agents including imaging or radio-labeled agents a shorter half life in circulation results in lower non-specific binding and decreased side effects. Fc engineered to bind antigens but preserve interactions with FcRn and Fc fused with monomeric proteins currently are being developed as candidate therapeutics with prolonged half-lives;in these and other cases, Fc is a dimer of two CH2-CH3 chains. To further reduce the size of Fc but preserve FcRn binding, we generated three human soluble monomeric IgG1 Fcs (mFcs) by using a combination of structure-based rational protein design combined with multiple screening strategies. These mFcs were highly soluble and retained binding to human FcRn comparable with that of Fc. These results provide direct experimental evidence that efficient binding to human FcRn does not require human Fc dimerization. The newly identified mFcs are promising for the development of mFc fusion proteins and for novel types of mFc-based therapeutic antibodies of small size and long half-lives.4) We have hypothesized that mAbs targeting two or more nonoverlapping epitopes on the same ligand could form oligomeric antibody-ligand complexes that can bind to cells expressing Fc gamma receptors (Fc?Rs) with high avidity leading to their fast and irreversible removal from the circulation. Insulin-like growth factor II (IGF-II) is an example of such ligands and an important target for human cancer therapy. We identified two mAbs, m610.27 and m630.3, which bound to nonoverlapping epitopes on IGF-II with nanomolar affinity, and generated a bispecific antibody, m660. m660 inhibited the interaction of human IGF-II (hIGF-II) with the human breast cancer cell line MCF-7, hIGF-II-mediated IGF receptor type I and insulin receptor phosphorylation, and cell growth. In the presence of hIGF-II, large complexes of m660 were formed that bound to Fc?RII-expressing BJAB cells much more efficiently than the monospecific antibody-hIGF-II complexes and were presumably phagocytosed by phorbol 12-myristate 13-acetate-stimulated macrophage-like U937 cells. A mixture of m610.27 and m630.3 exhibited similar properties. To our knowledge, these mAbs are the first reported to target nonoverlapping epitopes on a cancer-related ligand and could represent a novel class of candidate therapeutics against cancers. This approach could also be used to irreversibly eliminate other disease-related soluble ligands. 5) The type 1 insulin-like growth factor receptor (IGF1R) and its ligands (IGF-I and IGF-II) have been implicated in a variety of physiologic processes and in diseases such as cancer. In addition to IGF1R, IGF-II also activates the insulin receptor (IR) isoform A, and therefore, antibodies against IGF-II can inhibit cell proliferation mediated by the signaling through both IGF1R and IR triggered by IGF-II. We identified a new human monoclonal antibody (mAb), m708.2, which binds to IGF-I and IGF-II but not to insulin. m708.2 potently inhibited signal transduction mediated by the interaction of IGF-I or IGF-II with the IGF1R and IGF-II with the IR. It also inhibited the growth of the breast cancer cell line MCF-7. An affinity-matured derivative of m708.2, m708.5, bound to IGF-I with equilibrium dissociation constant, K(D) = 200 pM and to IGF-II with K(D) = 60 pM. m708.5 inhibited signal transduction mediated by IGF-I and IGF-II and cancer cell growth more potently than m708.2. These results suggest that m708.5 could have potential as a candidate therapeutic for cancers driven by the IGF-I and IGF-II interactions with IGF1R and IR.
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