David J. Panka

Canstatin, a Novel Matrix-derived Inhibitor of Angiogenesis and Tumor Growth

We isolated and identified an endogenous 24-kDa human basement membrane-derived inhibitor of angiogenesis and tumor growth, termed canstatin. Canstatin, a fragment of the α2 chain of type IV collagen, was produced as a recombinant molecule inEscherichia coli and 293 embryonic kidneys cells. Canstatin significantly inhibited human endothelial cell migration and murine endothelial cell tube formation. Additionally, canstatin potently inhibited 10% fetal bovine serum-stimulated endothelial cell proliferation and induced apoptosis, with no inhibition of proliferation or apoptosis observed on non-endothelial cells. Inhibition of endothelial proliferation was not concomitant with a change in extracellular signal-regulated kinase activation. We demonstrate that apoptosis induced by canstatin was associated with a down-regulation of the anti-apoptotic protein, FLIP. Canstatin also suppressed in vivo growth of large and small size tumors in two human xenograft mouse models with histology revealing decreased CD31-positive vasculature. Collectively, these results suggest that canstatin is a powerful therapeutic molecule for suppressing angiogenesis.

Phosphatidylinositol 3-Kinase/Akt Activity Regulates c-FLIP Expression in Tumor Cells

The caspase-8 homologue FLICE-inhibitory protein (FLIP) functions as a caspase-8 dominant negative, blocking apoptosis induced by the oligomerization of the adapter protein FADD/MORT-1. FLIP expression correlates with resistance to apoptosis induced by various members of the tumor necrosis factor family such as TRAIL. Furthermore, forced expression of FLIP renders cells resistant to Fas-mediated apoptosis. Although FLIP expression is regulated primarily by MEK1 activity in activated T cells, the oncogenic signaling pathways that regulate FLIP expression in tumor cells are largely unknown. In this report, we examined the roles of the MAP kinase and phosphatidylinositol (PI) 3-kinase signaling pathways in the regulation of FLIP expression in tumor cells. We observed that the MEK1 inhibitor PD98059 reduced FLIP levels in only 2 of 11 tumor cell lines tested. In contrast, disruption of the PI 3-kinase pathway with the specific inhibitor LY294002 reduced Akt (protein kinase B) phosphorylation and the levels of FLIP protein and mRNA in all cell lines evaluated. The introduction of a dominant negative Akt adenoviral construct also consistently reduced FLIP expression as well as the phosphorylation of the Akt target glycogen synthase kinase-3. In addition, infection of the same cell lines with a constitutively active Akt adenovirus increased FLIP expression and the phosphorylation of GSK-3. These data add FLIP to the growing list of apoptosis inhibitors in which expression or function is regulated by the PI 3-kinase-Akt pathway.

The Raf Inhibitor BAY 43-9006 (Sorafenib) Induces Caspase-Independent Apoptosis in Melanoma Cells

Mitogen-activated protein kinase (MAPK) is activated in the majority of melanomas, and its activity is essential for cell survival. In this report, we examined the effects of a novel raf inhibitor BAY 43-9006 on melanoma cell viability and intracellular signaling and found that it induces apoptosis through a caspase-independent mechanism. At concentrations that suppress extracellular signal-regulated kinase (ERK) phosphorylation, BAY 43-9006 dephosphorylates Bad on Ser(75) and Ser(99), activates Bak and Bax, and reduces the mitochondrial transmembrane potential. BAY 43-9006 (sorafenib) down-modulates the levels of Bcl-2 and Bcl-X(L) in a MAPK-independent manner in A2058 and SKMEL5 melanoma cells but not in the more resistant A375 cells. Of the three lines tested, only A375 cells were rescued from BAY 43-9006-induced apoptosis by knocking down Bad. BAY 43-9006 induced poly(ADP-ribose) polymerase cleavage and the mitochondrial release of cytochrome c and SMAC. However, the pan-caspase inhibitor Z-VAD-fmk had only a modest protective effect against the drug, suggesting that BAY 43-9006-induced apoptosis is largely caspase independent. BAY 43-9006 but not the MAP/ERK kinase inhibitors PD98059 or U0126 induced the nuclear translocation of apoptosis-inducing factor (AIF) in A2058 and SKMEL5 cells, and the introduction of a small interfering RNA (siRNA) for AIF partially protected these cells from BAY 43-9006-induced apoptosis. The AIF siRNA had little effect in A375 cells, in which drug-induced AIF release was negligible. These data indicate that in sensitive cell lines, BAY 43-9006-induced apoptosis is independent of Bad dephosphorylation and caspase activation and largely mediated through the nuclear translocation of AIF.

The Efficacy of the Novel Dual PI3-Kinase/mTOR Inhibitor NVP-BEZ235 Compared with Rapamycin in Renal Cell Carcinoma

Purpose: Inhibitors of TORC1 have been shown to be active in patients with metastatic renal cell carcinoma (RCC). As the phosphatidylinositol 3-kinase (PI3K) pathway activates numerous other kinases, transcription factors, and proteins associated with cell growth and survival besides mammalian target of rapamycin (mTOR), disruption of this pathway upstream of mTOR may be more effective than inhibition of TORC1 alone. Experimental Design: To investigate this possibility, the dual PI3K/mTOR inhibitor NVP-BEZ235 was compared with rapamycin in RCC cell lines and xenografts generated from 786-O and A498 cells. Results: Treatment of RCC cell lines with NVP-BEZ235 in vitro resulted in the nuclear translocation of p27, greater reduction in tumor cell proliferation, and more complete suppression of Akt, Mnk-1, eIF4E, and 4EBP-1 phosphorylation and cyclin D1 and hypoxia-inducible factor 2α (HIF2α) expression than that achieved with rapamycin. The reduction of HIF2α levels correlated with reduced HIF activity as determined by luciferase assay. NVP-BEZ235 induced growth arrest in both the 786-O and A498 xenografts that was associated with inhibition of Akt and S6 phosphorylation as well as the induction of apoptosis and reduction in markers of tumor cell proliferation. In contrast, rapamycin induced only minimal growth retardation. Conclusion: Dual inhibition of PI3K/mTOR with NVP-BEZ235 induced growth arrest in RCC cell lines both in vitro and in vivo more effectively than inhibition of TORC1 alone. These results provide the rationale for the clinical assessment of agents such as NVP-BEZ235 in patients with advanced RCC. Clin Cancer Res; 16(14); 3628–38. ©2010 AACR.

Anatomy of autoantibody production: Dominant localization of antibody-producing cells to T cell zones in fas-deficient mice

The goal of this study was to examine the in vivo site of autoantibody production in normal and autoimmune-prone mice. B cells were identified in tissue sections with IgM- and IgG2a-specific riboprobes that readily distinguished resting cells from antibody-forming cells (AFC). In normal mice, the few identifiable IgG2a-secreting cells were found in the red pulp. By contrast, in Ipr mice exceedingly high numbers of IgG2a and autoantibody-producing cells were found deep within the T cell-rich periarteriolar lymphoid sheaths (PALS). This unusual anatomic location of autoantibody-secreting B cells is unique to Fas dysregulated strains, since IgG2-producing cells in MRL/+ and (SWR x NZB)F1 mice were found predominantly in the red pulp or outer PALS, similar to normal mice. Furthermore, analysis of spleens from Ipr and non-Ipr anti-DNA immunoglobulin transgenic mice revealed dramatic accumulation of Tg+ cells in the inner PALS only in Ipr mice. These data suggest that in the absence of Fas, autoreactive B cells accumulate in T cell-rich zones, and this anatomic feature may contribute to autoantibody production.

Canstatin inhibits Akt activation and induces Fas-dependent apoptosis in endothelial cells

Canstatin, a 24-kDa peptide derived from the C-terminal globular non-collagenous (NC1) domain of the α2 chain of type IV collagen, was previously shown to induce apoptosis in cultured endothelial cells and to inhibit angiogenesis in vitro and in vivo. In this report, we demonstrate that canstatin inhibits the phosphorylation of Akt, focal adhesion kinase, mammalian target of rapamycin, eukaryotic initiation factor-4E-binding protein-1, and ribosomal S6 kinase in cultured human umbilical vein endothelial cells. It also induces Fas ligand expression, activates procaspases 8 and 9 cleavage, reduces mitochondrial membrane potential, and increases cell death (as determined by propidium iodide staining). Canstatin-induced activation of procaspases 8 and 9 as well as the induced reduction in mitochondrial membrane potential and cell viability were attenuated by the forced expression of FLICE-inhibitory protein. Canstatin-induced procaspase 8 activation and cell death were also inhibited by a neutralizing anti-Fas antibody. Collectively, these data indicate that canstatin-induced apoptosis is associated with phosphatidylinositol 3-kinase/Akt inhibition and is dependent upon signaling events transduced through membrane death receptors.

Targeting the Mitogen-Activated Protein Kinase Pathway in the Treatment of Malignant Melanoma

The mitogen-activated protein kinase (MAPK; i.e., Ras–Raf–Erk) pathway is an attractive target for therapeutic intervention in melanoma due to its integral role in the regulation of proliferation, invasiveness, and survival and the recent availability of pharmaceutical agents that inhibit the various kinases and GTPases that comprise the pathway. Genetic studies have identified activating mutations in either B-raf or N-ras in most cutaneous melanomas. Other studies have delineated the contribution of autocrine growth factors (e.g., hepatocyte growth factor and fibroblast growth factor) to MAPK activation in melanoma. Still, others have emphasized the consequences of the down-modulation of endogenous raf inhibitors, such as Sprouty family members (e.g., SPRY2) and raf-1 kinase inhibitory protein, in the regulation of the pathway. The diversity of molecular mechanisms used by melanoma cells to ensure the activity of the MAPK pathway attests to its importance in the evolution of the disease and the likelihood that inhibitors of the pathway may prove to be highly effective in melanoma treatment. MAPK inhibition has been shown to result in the dephosphorylation of the proapoptotic Bcl-2 family members Bad and Bim. This process in turn leads to caspase activation and, ultimately, the demise of melanoma cells through the induction of apoptosis. Several recent studies have identified non–mitogen-activated protein/extracellular signal-regulated kinase kinase–binding partners of raf and suggested that the prosurvival effects of raf and the lethality of raf inhibition are mediated through these alternative targets, independent of the MAPK pathway. Other studies have suggested that endothelial cells are the primary targets of raf inhibitors in vivo and that the antitumor effect of these agents are largely attributable to angiogenesis inhibition. This article reviews the genetic and biochemical factors contributing to MAPK activation in melanoma, the mechanisms by which inhibition of the pathway might prove deleterious to tumor cells, and the potential of MAPK inhibitors in the treatment of the disease.

Correlation of NRAS Mutations with Clinical Response to High Dose IL-2 in Patients with Advanced Melanoma

The purpose of this study is to identify clinical and molecular characteristics of melanoma patients that predict response to high-dose interleukin-2 (HD IL-2) to improve patient selection for this approved but toxic therapy. We reviewed the records of 208 patients with unresectable stage III/IV melanoma treated with HD IL-2 at the University of Texas M.D. Anderson Cancer Center (n=100) and the Beth Israel Deaconess Medical Center (n=108) between 2003 and 2009. The BRAF and NRAS mutation status of the tumors was determined for patients with available tissue samples and the mutation status and clinical characteristics were compared with clinical outcomes. Pretreatment serum lactate dehydrogenase levels were available for most patients (n=194). Tissue was available for mutational analysis on a subset of patients (n=103) and the prevalence of mutations was as follows: BRAF 60%, NRAS 15%, WT/WT 25%. In the subset of patients for which mutational analysis was available, there was a significant difference in the response rate based on the mutation status: NRAS 47%, BRAF 23%, and WT/WT 12% (P=0.05). Patients with NRAS mutations had nonstatistically longer overall survival (5.3 vs. 2.4 y, P=0.30) and progression-free survival (214 vs. 70 d, P=0.13). Patients with an elevated lactate dehydrogenase level had a decreased progression-free survival (46 vs. 76 d, P<0.0001), decreased overall survival (0.56 vs. 1.97 y, P<0.0001), and trended toward a decreased response rate (7% vs. 21%, P=0.08). NRAS mutational status is a new candidate biomarkers for selecting patients with melanoma for HD IL-2 treatment.

Three Phase II Cytokine Working Group Trials of gp100 (210M) Peptide Plus High-Dose Interleukin-2 in Patients With HLA-A2–Positive Advanced Melanoma

PURPOSE High-dose interleukin-2 (IL-2) induces responses in 15% to 20% of patients with advanced melanoma; 5% to 8% are durable complete responses (CRs). The HLA-A2-restricted, modified gp100 peptide (210M) induces T-cell immunity in vivo and has little antitumor activity but, combined with high-dose IL-2, reportedly has a 42% (13 of 31 patients) response rate (RR). We evaluated 210M with one of three different IL-2 schedules to determine whether a basis exists for a phase III trial. PATIENTS AND METHODS In three separate phase II trials, patients with melanoma received 210M subcutaneously during weeks 1, 4, 7, and 10 and standard high-dose IL-2 during weeks 1 and 3 (trial 1), weeks 7 and 9 (trial 2), or weeks 1, 4, 7, and 10 (trial 3). Immune assays were performed on peripheral-blood mononuclear cells collected before and after treatment. RESULTS From 1998 to 2003, 131 patients with HLA-A2-positive were enrolled. With 60-month median follow-up time, the overall RR for 121 assessable patients was 16.5% (95% CI, 10% to 26%); the RRs were 23.8% in trial 1 (42 patients), 12.5% in trial 2 (40 patients), and 12.8% in trial 3 (39 patients). There were 11 CRs (9%) and nine partial responses (7%), with 11 patients (9%) progression free at >or= 30 months. Immune studies including assays of CD3-zeta expression and numbers of CD4(+)/CD25(+)/FoxP3(+) regulatory T cells, CD15(+)/CD11b(+)/CD14(-) immature myeloid-derived cells, and CD8(+)gp100 tetramer-positive cells in the blood did not correlate with clinical benefit. CONCLUSION The results again demonstrate efficacy of high-dose IL-2 in advanced melanoma but did not demonstrate the promising clinical activity reported with vaccine and high-dose IL-2 in any of three phase II trials.

Resistance of Renal Cell Carcinoma to Sorafenib Is Mediated by Potentially Reversible Gene Expression

Purpose Resistance to antiangiogenic therapy is an important clinical problem. We examined whether resistance occurs at least in part via reversible, physiologic changes in the tumor, or results solely from stable genetic changes in resistant tumor cells. Experimental Design Mice bearing two human RCC xenografts were treated with sorafenib until they acquired resistance. Resistant 786-O cells were harvested and reimplanted into naïve mice. Mice bearing resistant A498 cells were subjected to a 1 week treatment break. Sorafenib was then again administered to both sets of mice. Tumor growth patterns, gene expression, viability, blood vessel density, and perfusion were serially assessed in treated vs control mice. Results Despite prior resistance, reimplanted 786-O tumors maintained their ability to stabilize on sorafenib in sequential reimplantation steps. A transcriptome profile of the tumors revealed that the gene expression profile of tumors upon reimplantation reapproximated that of the untreated tumors and was distinct from tumors exhibiting resistance to sorafenib. In A498 tumors, revascularization was noted with resistance and cessation of sorafenib therapy and tumor perfusion was reduced and tumor cell necrosis enhanced with re-exposure to sorafenib. Conclusions In two RCC cell lines, resistance to sorafenib appears to be reversible. These results support the hypothesis that resistance to VEGF pathway therapy is not solely the result of a permanent genetic change in the tumor or selection of resistant clones, but rather is due to a great extent to reversible changes that likely occur in the tumor and/or its microenvironment.