The receptor for insulin-like growth factor 1 (IGF-1) mediates multiple cellular responses, including stimulation of both proliferative and anti-apoptotic pathways. We have examined the role of cross talk between the IGF-1 receptor (IGF-1R) and the epidermal growth factor receptor (EGFR) in mediating responses to IGF-1. In COS-7 cells, IGF-1 stimulation causes tyrosine phosphorylation of the IGF-1R ␤ subunit, the EGFR, insulin receptor substrate-1 (IRS-1), and the Shc adapter protein. Shc immunoprecipitates performed after IGF-1 stimulation contain coprecipitated EGFR, suggesting that IGF-1R activation induces the assembly of EGFR⅐Shc complexes. Tyrphostin AG1478, an inhibitor of the EGFR kinase, markedly attenuates IGF-1-stimulated phosphorylation of EGFR, Shc, and ERK1/2 but has no effect on phosphorylation of IGF-1R, IRS-1, and protein kinase B (Akt). Cross talk between IGF-1 and EGF receptors is mediated through an autocrine mechanism involving matrix metalloprotease-dependent release of heparin-binding EGF (HB-EGF), because IGF-1-mediated ERK activation is inhibited both by [Glu 52 ]Diphtheria toxin, a specific inhibitor of HB-EGF, and the metalloprotease inhibitor 1,10-phenanthroline. These data demonstrate that IGF-1 stimulation of the IRS-1/PI3K/Akt pathway and the EGFR/Shc/ERK1/2 pathway occurs by distinct mechanisms and suggest that IGF-1-mediated "transactivation" of EGFR accounts for the majority of IGF-1-stimulated Shc phosphorylation and subsequent activation of the ERK cascade.The insulin receptor family is comprised of three members, the insulin receptor, the insulin-like growth factor-1 receptor (IGF-1R), 1 and the insulin receptor-related receptor, an orphan whose endogenous ligand is unknown. The three receptors share a common topology, each composed of two entirely extracellular ␣ subunits containing the ligand-binding domain, and two ␤ subunits that contain a single transmembrane domain and an intracellular domain possessing intrinsic ligand-stimulated tyrosine kinase activity. Like classical receptor tyrosine kinases, such as epidermal growth factor receptor (EGFR), stimulation of insulin receptors leads both to receptor autophosphorylation and to the recruitment and activation of signaling proteins that contain specific phosphotyrosine-binding Src-homology 2 (SH2) domains.In the case of EGFR, phosphorylation of tyrosine residues within the intracellular domain provides docking sites for SH2 domain proteins, including the Ras guanine nucleotide exchange factor complex Grb2⅐mSos, Ras-GTPase-activating protein, phospholipase C␥, the p85⅐p110␣ phosphatidylinositol 3-kinase (PI3K) complex, and the nonreceptor tyrosine kinases c-Src and c-Fyn, as well as for adapter proteins such as Shc and Gab1. Thus the phosphorylated EGFR serves as a scaffold for the assembly, at the plasma membrane, of a multienzymesignaling complex that mediates the intracellular response to EGF (1). Unlike the EGF receptor, autophosphorylated insulin family receptors do not signal via the direct recruitment of these s...

Ipilimumab therapy resulted in clinically meaningful responses in advanced melanoma patients, and the results support further investigations of ipilimumab in combination with DTIC.

MDX-060 was well tolerated at doses up to 15 mg/kg. MDX-060 has limited activity as a single agent, but the minimal toxicity observed and the significant proportion of patients with stable disease suggests that further study of MDX-060 in combination with other therapies is warranted.

The murine Ly-6A/E gene is transcriptionaly induced in cells exposed to interferon a/P or y (IFN-a/13 or IFN-y). Analysis of the 5' flanking sequence using reporter plasmids that contain upstream elements of the Ly-6E gene has previously identified an 850-base-pair IFN-responsive region that lacked an IFN-a-stimulated response element (ISRE), the element present and required for an IFN-a response of a number of genes. Analysis by deletion and stable transfection of the IFN-responsive region ofthe Ly-6E promoter has defined an 80-base-pair region containing an IFN-y activation site (GAS) but no ISRE that alows IFN-y and IFN-a inducibility of the Ly-6E gene. As tested by specific antiserum, a 91-kDa protein known to be activated in IFN-a-or IFN-'treated cells binds to-the GAS element from the Ly-6E promoter. The 91-kDa protein exists as an inactive cytoplasmic precursor and depends on tyrosine phosphorylation for its activation. Thus the same 91-kDa protein appears to act in the signal transduction pathways of both types of IFN for the Ly-6-A/E gene.

␤-Arrestins can act as adapter molecules, coupling Gprotein-coupled receptors to proteins involved in mitogenic as well as endocytic pathways. We have previously identified c-SRC as a molecule that is rapidly recruited to the ␤2-adrenergic receptor in a ␤-arrestin1-dependent manner. Recruitment of c-SRC to the receptor appears to be involved in pathways leading to receptor internalization and mitogen-activated protein kinase activation. This recruitment of c-SRC to the receptor involves an interaction between the amino-terminal proline-rich region of ␤-arrestin1 and the Src homology 3 (SH3) domain of c-SRC, but deletion of the proline-rich domain does not totally ablate the interaction. We have found that a major interaction also exists between ␤-arrestin1 and the catalytic or kinase domain (SH1) of c-SRC. We therefore hypothesized that a catalytically inactive mutant of the isolated catalytic subunit, SH1(kinase dead) (SH1(KD)), would specifically block those cellular actions of c-SRC that are mediated by ␤-arrestin1 recruitment to the G-protein-coupled receptor. In contrast, the majority of cellular phosphorylations catalyzed by c-SRC, which do not involve interaction with the SH1 domain, would be predicted to be unaffected. The SH1(KD) mutant did indeed block ␤2-adrenergic receptor internalization and receptor-stimulated tyrosine phosphorylation of dynamin, actions previously shown to be c-SRC-dependent. In contrast, SAM-68 and whole cell tyrosine phosphorylation by c-SRC was unaffected, indicating that the SH1(KD) mutant did not inhibit c-SRC tyrosine kinase activity in general. These results not only clarify the nature of the ␤-arrestin1/c-SRC interaction but also implicate ␤-arrestin1 as an important mediator of receptor internalization by recruiting tyrosine kinase activity to the cell surface to phosphorylate key endocytic intermediates, such as dynamin.

Purpose: The incidence of non-Hodgkin's lymphoma (NHL), the fifth most common malignancy in the United States, has increased over 70% in the last 30 years. Fifty percent to 75% of patients with low-grade or follicular NHL respond to rituximab therapy. However, responses are generally of limited duration, and complete responses are rare. Preclinical work suggests that human recombinant interleukin-2 (rIL-2; aldesleukin, Proleukin) enhances rituximab efficacy. Antibody-dependent cellular cytotoxicity (ADCC) is an important mechanism of action of rituximab. rIL-2 induces expansion and activation of Fc receptor (FcR)^bearing cells, thereby enhancing ADCC. Therefore, a large, multicenter phase 2 trial to assess the effects of rIL-2 on rituximab therapy in patients with rituxumab-refractory low-grade NHL was conducted. Experimental Design: The combination of rituximab and rIL-2 was studied in 57 patients with rituximab-refractory low-grade NHL (i.e., patients must have received a single-agent course of rituximab and showed no tumor response, or had a response lasting <6 months). I. V. rituximab was given at 375 mg/m 2 (weeks 1-4). S.C. rIL-2 was given thrice a week at 14 MIU (weeks 2-5) and at 10 MIU (weeks 6-9). Results: Rituximab plus rIL-2 combination therapy was safe and generally well tolerated, but responses were low. Fifty-seven patients were enrolled with 54 evaluable for response; however, only five responses (one complete and four partial) were observed. Correlative data indicate that rIL-2 expanded FcR-bearing cells and enhanced ADCC. However, other factors, such as FcgR polymorphisms in patients refractory to single-agent rituxumab and heterogeneous tumor biology, may have influenced the lack of clinical efficacy seen with this combination therapy. Conclusions: rIL-2 expands FcR-bearing cellular subsets in vivo and enhances in vitro ADCC of rituxumab. However, these findings do not directly translate into meaningful clinical benefit for patients with rituxumab-refractory NHL.

Cloretazine has significant activity and modest extramedullary toxicity in elderly patients with AML or high-risk MDS. Response rates remain consistent despite increasing age and comorbidity.

No abstract