The Skaggs Institute
for Chemical Biology

Scientific Report 2007

Selective Therapies With Monoclonal Aldolase Antibody Conjugates

S.C. Sinha, R.A. Lerner, Z. Chen, Z.-Z. Huang, R. Goswami

Our long-term goals include development of selective chemotherapy for the treatment of cancer. We have developed 2 antibody conjugates, 1 catalytic and 1 noncatalytic, composed of the aldolase monoclonal antibody 38C2 and small-molecule inhibitors. The catalytic construct is a classical conjugate of small molecules to 38C2 through the surface lysine residues or the sulfide functional groups obtained by reducing the disulfide bridge in the antibody hinge region. In the noncatalytic construct, the small molecules conjugate in the 38C2 binding sites and redirect the antibody to cells. Formation of the constructs was verified by using mass spectrometry; both constructs had approximately 2 molecules of a small molecule. In flow cytometry assays, both constructs bound cells expressing integrin α_vβ₃ with high affinity.

Because integrin α_vβ₃ is expressed on numerous primary and metastatic tumor cells and in tumor vasculature, the resulting antibody constructs are expected to be highly useful in cancer therapy. In MDA-MB-231 cells in a mouse model of breast cancer metastasis, the efficacy of the nontargeting constructs was promising. In vitro, the catalytic 38C2 construct activated doxorubicin prodrugs and was cytotoxic to MDA-MB-231 cells. For studies with the catalytic construct, we also designed a series of doxorubicin prodrugs (Fig. 1), and evaluated them in vitro. Our selective chemotherapy studies are carried out in collaboration with C.F. Barbas, Skaggs Institute, and B. Felding-Habermann, Scripps Research.

Fig. 1. Structure of integrin-targeting compounds for 38C2-construct formation, doxorubicin prodrugs, and 27-hydroxybullatacin.

We are also developing peptidomimetic inhibitors, cytotoxic natural products, and their conjugates, which can be combined with the aldolase antibody 38C2–based technology to further improve the efficacy of the compounds by a combination therapy. These compounds include protease inhibitors and anticancer adjacent bis-tetrahydrofuran annonaceous acetogenins. Numerous proteases are overexpressed in several cancer cell lines and are highly implicated in tumor growth and metastases. Inhibition of such proteases has potential application in cancer therapy. In collaboration with C. Liu, Scripps Research, we are developing inhibitors of legumain protease, which is highly expressed in a number of cancer cell lines, including prostate and breast cancer cells.

Annonaceous acetogenins are among the most cytotoxic compounds. Each acetogenin can have as many as 64 stereoisomers because of the bis-tetrahydrofuran fragment alone flanked by a hydroxy function on each side. In order to understand the structure-activity relationship of these compounds and carry out comprehensive biological studies, total synthesis of all 64 stereoisomers is required. This synthesis has been the focus of research for several years, not only by us but also by many others. However, despite a continued effort, synthesis of all 64 stereoisomers of asimicin or bullatacin, which are among the most cytotoxic adjacent bis-tetrahydrofuran acetogenins, has not yet been achieved. We have now prepared 8 adjacent bis-tetrahydrofuran acetogenins via 2 bis-tetrahydrofuran precursors. We have also prepared 27-hydroxybullatacin, which is highly active against pancreatic cancer cells, and the 15-epimer of 27-hydroxybullatacin (Fig. 1). Biological evaluations of these compounds will be done in collaboration with F. Valeriote, Henry Ford Health System, Detroit, Michigan.

Publications

Abraham, S., Guo, F., Li, L.-S., Rader, C., Liu, C., Barbas, C.F. III, Lerner, R.A. Sinha, S.C. Synthesis of the next-generation therapeutic antibodies that combine cell targeting and antibody-catalyzed prodrug activation. Proc. Natl. Acad. Sci.
U. S. A. 104:5584, 2007.

Das, S., Abraham, S., Sinha, S.C. Studies toward the total synthesis of sorangiolides and their analogs: a convergent stereoselective synthesis of the macrocyclic lactone precursors. Org. Lett. 9:2273, 2007.

Lo, H.C., Han, H., D'Souza, L.J., Sinha, S.C., Keinan, E. Rhenium(VII) oxide-catalyzed heteroacylative ring-opening dimerization of tetrahydrofuran. J. Am. Chem. Soc. 129:1246, 2007.

Sinha, S.C., Das, S., Li, L.-S., Lerner, R.A., Barbas, C.F. III. Preparation of integrin α_vβ₃-targeting Ab 38C2 constructs. Nat. Protoc. 2:449, 2007.