No abstract

Overexpression of both cellular Src (c-Src) and the epidermal growth factor receptor (EGFR) occurs in many of the same human tumors, suggesting that they may functionally interact and contribute to the progression of cancer. Indeed, in murine fibroblasts, overexpression of c-Src has been shown to potentiate the mitogenic and tumorigenic capacity of the overexpressed EGFR. Potentiation correlated with the ability of c-Src to physically associate with the activated EGFR and the appearance of two unique in vivo phosphorylations on the receptor (Tyr-845 and Tyr-1101). Using stable cell lines of C3H10T 1 ⁄2 murine fibroblasts that contain kinase-deficient (K؊) c-Src and overexpressed wildtype EGFR, we show that the kinase activity of c-Src is required for both the biological synergy with the receptor and the phosphorylations on the receptor, but not for the association of c-Src with the receptor. In transient transfection assays, not only epidermal growth factor but also serum-and lysophosphatidic acid-induced DNA synthesis was ablated in a dominant-negative fashion by a Y845F mutant of the EGFR, indicating that c-Src-induced phosphorylation of Y845 is critical for the mitogenic response to both the EGFR and a G protein-coupled receptor (lysophosphatidic acid receptor). Unexpectedly, the Y845F mutant EGFR was found to retain its full kinase activity and its ability to activate the adapter protein SHC and extracellular signal-regulated kinase ERK2 in response to EGF, demonstrating that the mitogenic pathway involving phosphorylation of Y845 is independent of ERK2-activation. The application of these findings to the development of novel therapeutics for human cancers that overexpress c-Src and EGFR is discussed.Considerable evidence has accumulated in recent years to suggest that cellular Src (c-Src) and members of the epidermal growth factor (EGF) receptor (EGFR) family are critical elements in the etiology of multiple human cancers. Both kinases are found overexpressed in many of the same types of tumors, including glioblastomas and carcinomas of the colon, breast, and lung (1-4), raising the question of whether they functionally interact to promote the growth of these malignancies. In breast cancer, overexpression of EGFR family members is estimated to occur in 60% or more of the cases (5), and overexpression of the family member HER2͞NEU, has been associated with a poor prognosis for the disease (6). Recent reports have also described overexpression of c-Src in a significant majority of patients with breast cancer, a frequency that approaches 100% (1). Studies to assess the oncogenic potential of each kinase have shown that the EGFR is tumorigenic when overexpressed in cultured fibroblasts and activated by ligand (7,8), but overexpression of c-Src alone is insufficient for malignant transformation (9, 10).A possible role for c-Src in tumorigenesis was revealed when it was demonstrated in C3H10T 1 ⁄2 murine fibroblasts that co-overexpression of c-Src and the EGFR resulted in a synergistic increase in EGF-ind...

No abstract

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.

Abegrin TM (MEDI-522 or Vitaxin TM ), a humanized monoclonal antibody against human integrin A v B 3 , is in clinical trials for cancer therapy. In vivo imaging using Abegrin TM

No abstract

Axin and the adenomatous polyposis coli protein (APC) interact to down-regulate the proto-oncogene ␤-catenin. We show that transposition of an axin-binding site can confer ␤-catenin regulatory activity to a fragment of APC normally lacking this activity. The fragment containing the axin-binding site also underwent hyperphosphorylation when coexpressed with axin. The phosphorylation did not require glycogen synthase kinase 3␤ but instead required casein kinase 1⑀, which bound directly to axin. Mutation of conserved serine residues in the ␤-catenin regulatory motifs of APC interfered with both axin-dependent phosphorylation and phosphorylation by CKI⑀ and impaired the ability of APC to regulate ␤-catenin. These results suggest that the axin-dependent phosphorylation of APC is mediated in part by CKI⑀ and is involved in the regulation of APC function.Mutations that interfere with the ability of cells to regulate ␤-catenin have been identified in a wide variety of human cancers (reviewed in Ref. 1). In some cases the mutations occur in the ␤-catenin gene (CTNNb1) itself, affecting specific amino acids that are integral to the ubiquitin-dependent targeted degradation of the protein. In other cases, proteins that facilitate the process of ␤-catenin degradation are instead mutated, and the wild type ␤-catenin protein assumes a prolonged halflife. In either scenario the outcome is aberrant transcription of genes that are activated by ␤-catenin signaling. Two of the proteins that facilitate the turnover of ␤-catenin are axin and the adenomatous polyposis coli (APC) 1 protein, both of which bind directly to ␤-catenin (2-6). The APC tumor suppressor was identified as the gene responsible for a heritable predisposition to colorectal cancer, referred to as familial polyposis coli, and is also mutated in most sporadic colorectal cancers (7-10). Axin was shown to regulate negatively wnt-1 signaling, and its direct association with APC, ␤-catenin, and glycogen synthase kinase 3␤ (GSK3␤) is consistent with its involvement in the wnt-1 pathway (2,(11)(12)(13)(14). Recently, mutations that inactivate axin were identified in a subset of human hepatocellular cancers and cancer cell lines (15). Thus, APC and axin function in concert to regulate ␤-catenin, and the inactivation of either of these genes, or the mutational activation of ␤-catenin, contributes to the oncogenic state of transformed cells.A multiprotein complex consisting minimally of APC, Dishevelled, GSK3␤, and protein phosphatase PP2A, all of which bind directly to independent sites on axin (16), regulates the stability of ␤-catenin. ␤-Catenin binds directly to both APC and axin, and its phosphorylation by GSK3␤ leads to its recognition by a ubiquitin-protein isopeptide ligase containing the F box protein ␤-TRCP (17-20). In vitro reconstitution experiments have demonstrated that the association of axin with APC enhances the binding of ␤-catenin to axin and consequently facilitates the phosphorylation of ␤-catenin by GSK3␤ (21). APC is also phosphorylated by GSK3␤, which ...

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]