Antibody-drug conjugate (ADC) which delivers cytotoxic drugs specifically into targeted cells through internalization and lysosomal trafficking has emerged as an effective cancer therapy. We show that a bivalent biparatopic antibody targeting two non-overlapping epitopes on HER2 can induce HER2 receptor clustering, which in turn promotes robust internalization, lysosomal trafficking, and degradation. When conjugated with a tubulysin-based microtubule inhibitor, the biparatopic ADC demonstrates superior anti-tumor activity over ado-trastuzumab emtansine (T-DM1) in tumor models representing various patient subpopulations, including T-DM1 eligible, T-DM1 ineligible, and T-DM1 relapsed/refractory. Our findings indicate that this biparatopic ADC has promising potential as an effective therapy for metastatic breast cancer and a broader patient population may benefit from this unique HER2-targeting ADC.

Since the first approval of gemtuzumab ozogamicin (Mylotarg; Pfizer; CD33 targeted), two additional antibodydrug conjugates (ADC), brentuximab vedotin (Adcetris; Seattle Genetics, Inc.; CD30 targeted) and inotuzumab ozogamicin (Besponsa; Pfizer; CD22 targeted), have been approved for hematologic cancers and 1 ADC, trastuzumab emtansine (Kadcyla; Genentech; HER2 targeted), has been approved to treat breast cancer. Despite a clear clinical benefit being demonstrated for all 4 approved ADCs, the toxicity profiles are comparable with those of standard-of-care chemotherapeutics, with dose-limiting toxicities associated with the mecha-nism of activity of the cytotoxic warhead. However, the enthusiasm to develop ADCs has not been dampened; approximately 80 ADCs are in clinical development in nearly 600 clinical trials, and 2 to 3 novel ADCs are likely to be approved within the next few years. While the promise of a more targeted chemotherapy with less toxicity has not yet been realized with ADCs, improvements in technology combined with a wealth of clinical data are helping to shape the future development of ADCs. In this review, we discuss the clinical and translational strategies associated with improving the therapeutic index for ADCs.

Abstract. S100/~ produced in Escherichia coli from a synthetic gene (Van Eldik, L. J., J. L. Staecker, and E Winningham-Major. 1988. J. Biol. Chem. 263:7830-7837) stimulates neurite outgrowth and enhances cell maintenance in cultures of embryonic chick cerebral cortex neurons. In control experiments, the neurite extension activity is reduced by preincubation with antibodies made against bovine brain S100/L When either of the two cysteines in S100/3 are altered by site-directed mutagenesis, the resultant proteins maintain the overall biochemical properties of S100/~, but lose both the neurite extension and neuronal survival activities. However, another S100/3 mutant, in which the relative position of one of the two cysteines was changed, had neurotrophic activity similar to that of the unmodified protein. These and other results indicate that (a) specific neurite extension activity and neuronal survival activity are two related activities inherent to the S100/3 molecule; (b) a disulfide-linked form of S100/~ is required for full biological activity, and (c) the relative position of the cysteines can be modified. These data suggest potential in vivo roles for S100/~ in the development and maintenance of neuronal function in the central nervous system, and demonstrate the feasibility of the longer term development of selective pharmacological agents based on the S100/~ structure.T HE early development of the vertebrate nervous system involves a complex set of events, including neuronal and glial cell proliferation, migration and differentiation; neurite outgrowth and guidance; and establishment of appropriate synapses. This program of development is further complicated by interactions among different components of the nervous system. For example, specific extracellulax signals function as neurotrophic factors by stimulating neurite outgrowth and/or enhancing neuronal survival. Identification and characterization of factors that have neurotrophic activity are important steps in understanding the moleculax mechanisms by which neuronal development and axonal growth are controlled. Many types of neurotrophic factors have been described, including ions, hormones, extracellulax matrix proteins, cell-cell adhesion proteins, growth factors, and oncogenes (for reviews, see Greene, 1982;Berg, 1984; Thoenen et ai., 1987;Walicke, 1989). One of the best characterized neurotrophic factors is nerve growth factor

The EphA2 receptor tyrosine kinase is selectively expressed on the surface of many different human tumors. We have previously shown that tumor cells can be targeted by EphA2 monoclonal antibodies and that these antibodies function, in part, by inducing EphA2 internalization and degradation. In this report, we describe the isolation and characterization of a fully human monoclonal antibody (1C1) that selectively binds both the human and rodent EphA2 receptor. After cell binding, the antibody induces rapid tyrosine phosphorylation, internalization, and degradation of the EphA2 receptor. Because monoclonal antibodies that selectively bind tumor cells and internalize provide a vehicle for targeted delivery of cytotoxics, 1C1 was conjugated to the microtubule inhibitor monomethylauristatin phenylalanine using a stable maleimidocaproyl linker. The anti-EphA2 antibody-drug conjugate [1C1-maleimidocaproyl-MMAF (mcMMAF)] stimulated the activation of caspase-3/caspase-7 and the death of EphA2-expressing cells with IC 50 values as low as 3 ng/mL. Similarly, the conjugate induced degradation of the EphA2 receptor and inhibited tumor growth in vivo. Administration of 1C1-mcMMAF at doses as low as 1 mg/kg once weekly resulted in significant growth inhibition of EphA2-expressing tumors without any observable adverse effects in mouse xenograft and rat syngeneic tumor models. Our data support the use of an antibody-drug conjugate approach to selectively target and inhibit the growth of EphA2-expressing tumors. [Cancer Res 2008;68(22):9367-74]

Insulin-like growth factors (IGF), IGF-I and IGF-II, are small polypeptides involved in regulating cell proliferation, survival, differentiation, and transformation.