Novel synthesis of various orthogonally protected Cα-methyllysine analogues and biological evaluation of a vapreotide analogue containing (S)-α-methyllysine.

Prochiral malonic diesters containing a quaternary carbon center have been successfully transformed into a diverse set of (t)Boc-Fmoc-α(2,2)-methyllysine-OH analogues through chiral malonic half-ester intermediates obtained via enzymatic (Pig Liver Esterase, PLE) hydrolysis. The variety of chiral half-ester intermediates, which vary from 1 to 6 methylene units in the side chain, are achieved in moderate to high optical purity and in good yields. The PLE hydrolysis of malonic diesters with various side chain lengths appears to obey the Jones's PLE model according to the stereochemical configurations of the resulting chiral half-esters. The established synthetic strategy allows the construction of both enantiomers of α(2,2)-methyllysine analogues, and a (S)-ß(2,2)-methyllysine analogue from a common synthon by straightforward manipulation of protecting groups. Two different straightforward and cost effective synthetic strategies are described for the synthesis of α(2,2)-methyllysine analogues. The described strategies should find significant usefulness in preparing novel peptide libraries with unnatural lysine analogues. A Vapreotide analogue incorporating (S)-α(2,2)-methyllysine was prepared. However, the Vapreotide analogue with (S)-α-methyl-α-lysine is found to lose its specific binding to somatostatin receptor subtype 2 (SSTR2).

A prospective evaluation of the effect of chronic proton pump inhibitor use on plasma biomarker levels in humans.

OBJECTIVE: Proton pump inhibitors (PPIs) are used primarily to treat gastroesophageal reflux disease. Proton pump inhibitor-induced achlorhydria increases circulating gastrin and chromogranin A (CGA). Chromogranin is a widely used biomarker for the diagnosis and follow-up for gut-based neuroendocrine tumors (NETs). Proton pump inhibitor-induced increases in CGA or gastrin may falsely suggest the presence of a NET when none exists. Pancreastatin, a fragment of CGA, is also commonly used to diagnose and follow NETs. We hypothesized that chronic PPI use would increase circulating plasma gastrin, CGA, and pancreastatin levels. METHODS: Thirty patients who used PPIs for 6 months or more (mean ± SD duration, 3.1 ± 2.5 years) and a separate control group of 30 patients who never used antacid medications were prospectively evaluated with plasma gastrin, CGA, and pancreastatin determinations. RESULTS: Chronic PPI use resulted in significant increases in CGA (15.1 ± 11 vs 131 ± 207 ng/mL; P = 0.005) and significant increases in gastrin (34.8 ± 22.3 vs 167.8 ± 136.2 pg/mL; P = 0.001) compared to controls. In contrast, pancreastatin level in nonusers and chronic PPI users were identical (81.6 ± 36.4 vs 89.4 ± 43.4 pg/mL; P = 0.46). CONCLUSIONS: Pancreastatin levels do not change with chronic PPI use and normal pancreastatin levels may be used to distinguish between drug-induced changes in biomarkers and tumor-related increases in circulating biomarkers.

Do primary neuroendocrine tumors and metastasis have the same characteristics?

BACKGROUND: Only one tumor site is usually biopsied to determine the histologic features of that patient's entire tumor burden. We hypothesized that there are significant histologic and functional differences in primary neuroendocrine tumors (NETS) and their nodal or organ metastases. We also hypothesized that limited tumor sampling could lead to erroneous assumptions about the tumor's histologic characteristics and clinical behavior. MATERIALS AND METHODS: Thirteen patients with metastatic well differentiated midgut NETS underwent simultaneous removal of their primary tumor, nodal metastasis, and organ metastasis. Each tumor site was stained quantitatively for Ki-67, chromogranin A (CGA), synaptophysin, CD31, and Factor VIII. Samples were also evaluated with in vitro tumor angiogenesis and drug chemoresistance assays. RESULTS: Ki-67 staining was nearly identical at all sites tested. Quantitative stains for CGA, synaptophysin, cluster of differentiation 31 (CD31), and Factor VIII varied considerably among the patient's three tissue site samples. Only 6% of the tissue samples tested against a battery of chemotherapeutic agents exhibited susceptibility to a single drug at all three tumor sites. In contrast, several antiangiogenic agents exhibited uniform effectiveness across all three tissue sites in multiple patients. CONCLUSIONS: Sampling only one NET tumor site may lead to erroneous assumptions about the tumor's histologic features and functional behavior. Evaluation of primary tumors and their nodal and organ metastasis may be necessary to optimize clinical decision making.

A study of pipeline drugs in neuroendocrine tumors.

PURPOSE: Inhibition of neovessel development can stabilize tumor growth. A rapid in vitro method that can evaluate the effectiveness of anti-angiogenic drugs would aid in drug development. We tested a series of investigational agents to determine their ability to inhibit angiogenesis in our in vitro human angiogenesis model. METHODS: A total of 74 neuroendocrine tumors were tested with five therapeutic agents for anti-angiogenic activity. Angiogenic responses were assessed visually and the percent of tumor explants that developed an angiogenic response was determined. The extent of neovessel growth was rated using a validated semi-quantitative visual scale. Analysis of variance was used to compare treatment outcome results to control values for these angiogenic parameters. RESULTS: Vatalanib (2 × 10(-5) M) and patupilone (1 × 10(-8) M) were highly effective inhibitors of human tumor angiogenesis (mean overall angiogenic response for drug versus control 1.3 vs. 5.9 and 0.2 vs. 5.2, respectively) and were statistically significant at p <0.0001. Imatinib (2.5 × 10(-6) M) and everolimus (1 × 10(-8) M) were also effective (mean overall angiogenic response for drug versus control 2.2 vs. 5.9 and 4.5 vs. 5.9, respectively), and these were also statistically significant at p <0.0001. Pasireotide (1 × 10(-8) M) had no effect on angiogenesis (mean overall angiogenic response for drug vs. control 5.5 vs. 5.2). CONCLUSIONS: Significant differences in angiogenic response to test drugs were noted in this neuroendocrine patient population. In vitro screening of a large series of fresh human tumors may be a cost-effective way to select drugs for continued clinical development.

Metronomic dosing enhances the anti-angiogenic effect of epothilone B.

BACKGROUND: High doses (10 nM) of epothilone B, a microtubule stabilizer, will inhibit the development of human tumor-derived angiogenesis following short (14 d) drug exposure times. Metronomic dosing regimes use lower drug doses and prolonged drug exposure times in an attempt to decrease toxicity compared with standard dosing schedules. We hypothesized that epothilone B would be an effective anti-angiogenic agent when administered at very low doses over an extended period of time. METHODS: Fragments of four fresh human tumors were cultured in a fibrin-thrombin matrix and maintained in nutrient media plus 20% fetal bovine serum (FBS) for 56 d. Tumor fragments (n=40-60 per group) were exposed to weekly doses of epothilone B at concentrations of 10, 5, 1, 0.5, or 0.1 nM. All of these concentrations are clinically achievable. Tumor angiogenesis was assessed weekly on d 14-56 using a validated visual grading system. This system rates neovessel growth, density, and length on a 0-16 scale [angiogenic index, (AI)]. The average change in AI between d 14 and 56 was calculated for all samples and used to evaluate the metronomic response. RESULTS: Epothilone B produced a dose-dependent anti-angiogenic response in all tumors. Two of the four tumors demonstrated a clear and significant metronomic anti-angiogenic effect over time. CONCLUSIONS: Epothilone B, when dosed by a metronomic schedule may have a significant anti-angiogenic effect on human solid tumors. This study provides evidence for the potential use of epothilone B on a metronomic dosing schedule.

The role of angiogenesis in neuroendocrine tumors.

The first studies to assess in vitro angiogenesis in neuroendocrine tumors used animal-based assays to study the antiangiogenic properties of somatostatin analogs. Current technologies enable investigators to directly appraise the in vitro angiogenic response of an individual's neuroendocrine tumor with and without potential antiangiogenic reagents. This article describes the evolution of methods to assess in vitro angiogenesis in neuroendocrine tumors and describes some of the clinical data.

The effect of AlloDerm on the initiation and growth of human neovessels.

OBJECTIVES/HYPOTHESIS: AlloDerm (LifeCell Corp., Branchburg, NJ) is commonly employed for reconstruction of ablative soft tissue and mucosal defects following surgical resections. Although devoid of growth factors, AlloDerm may serve as an adhesive matrix for binding of growth factors, increasing local angiogenesis, and wound healing. We hypothesized that AlloDerm would enhance angiogenesis and might be altered with autologous blood products to enhance initiation of the angiogenic response. METHODS: We used a human placental vein in a fibrin-thrombin clot-based angiogenesis model. Four groups, human placental vein (HPVM), HPVM with AlloDerm, HPVM with AlloDerm plus platelet-poor plasma, and HPVM with AlloDerm plus platelet-rich plasma were evaluated. Endothelial cell growth was evaluated visually (40x). Hematoxylin and eosin staining and immunofluorescent staining for growth within the AlloDerm matrix were also performed. To assess human umbilical vein endothelial cell (HUVEC) sites of attachment to AlloDerm, we incubated HUVEC cells with AlloDerm for a period of 2 weeks and evaluated attachment with anti-factor VIII immunofluorescence. RESULTS: Angiogenic initiation decreased in the combined placental vein with AlloDerm group (P < .0001 at day 7, 14, 21). Additionally, initiation in the AlloDerm plus platelet-poor plasma group was significantly better than the AlloDerm alone group when placentas 2 and 3 were compared (P < .0001). On hematoxylin and eosin staining and immunofluorescent factor VIII staining, no endothelial growth into the AlloDerm was noted in the samples analyzed. CONCLUSIONS: AlloDerm may be enriched with platelet-poor plasma to stimulate greater initiation and wound healing; however, AlloDerm inhibits angiogenic initiation in this model.

The role of VEGF pathways in human physiologic and pathologic angiogenesis.

BACKGROUND: In preclinical models, VEGF is a potent stimulant of both physiologic and pathologic angiogenesis. Conversely, anti-VEGF regimens have successfully inhibited angiogenesis both in vitro and in vivo. We hypothesized that VEGF would stimulate both physiologic and pathologic angiogenesis in a human-based fibrin-thrombin clot angiogenesis assay. We further speculated that anti-VEGF regimens would inhibit angiogenesis in this assay. METHODS: To test these hypotheses, discs of human placental veins (physiologic model) and fragments of human tumors (pathologic model) were embedded in fibrin-thrombin clots and treated with either VEGF-A165 (VEGF) or anti-VEGF pathway reagents including bevacizumab, IMC-18F1, IMC-1121, and PTK787 (n=30 wells per treatment group, multiple concentrations tested in each specimen). Angiogenic responses were assessed visually using a previously validated grading scheme. The percent of tissue explants that developed angiogenic invasion into the clot (% I) as well as the extent of angiogenic growth (AI) via a semi-quantitative scale were assessed at set intervals. RESULTS: VEGF failed to stimulate angiogenesis in both the physiologic and the pathologic model. While anti-VEGF reagents that targeted only one element of the VEGF pathway failed to consistently inhibit angiogenesis, PTK787, a receptor tyrosine kinase inhibitor that targets multiple VEGF and non-VEGF receptors, profoundly inhibited both physiologic and pathologic angiogenesis. CONCLUSION: These results suggest that VEGF-related pathways may not be solely responsible for stimulating angiogenesis in humans. Targeting the VEGF pathway in combination with elements of other growth factor pathways may provide a more effective means of inhibiting angiogenesis than targeting VEGF alone.

Development of 125I-methylene blue for sentinel lymph node biopsy.

BACKGROUND: Sentinel lymph node biopsy is an established alternative to complete lymph node dissection in some patients. We have developed a novel, radiolabeled methylene blue dye that may be a useful alternative to the traditional two-step procedure involving 99mTc-labeled colloid and unlabeled blue dye. We hypothesize that 125I-labeled methylene blue will be rapidly absorbed into the lymphatics and transported to the drainage basin containing the sentinel nodes. MATERIALS AND METHODS: Rabbits footpads were injected with 1 mCi of 125I-labeled methylene blue admixed with unlabeled dye. A hand-held gamma detection device allowed tracking of radiolabeled dye to nodes in the popliteal and inguinal regions. At pre-established time points animals were sacrificed, and the nodal basin dissected. Nodal radioactivity as well as uptake of blue dye was recorded. RESULTS: The spread of the radiolabeled methylene blue compound from the footpad to the popliteal lymph nodes occurred in 5-10 min. CONCLUSION: The radiolabeled dye rapidly progresses through lymphatics to the draining nodes. Use of radiolabeled methylene blue may be an attractive alternative to current two-step sentinel node techniques, as it may be less painful, and may reduce the cost associated with the time-delay between the injection of the radioactive compound and surgery.

Development of a human cardiac tissue-based angiogenesis model.

BACKGROUND: Previous angiogenesis models use animal tissues such as the chicken chorioallantoic membrane (CAM) or the rabbit cornea. These models may not accurately reflect the mechanisms responsible for human angiogenesis. MATERIALS AND METHODS: We hypothesized that fragments of human myocardial tissue would develop an angiogenic response from the cut edges of vessels contained within the tissue. To test these hypotheses, we obtained human atrial appendage tissue at the time of cardiac bypass. Fragments of atrial tissue were then incorporated into fibrin thrombin clots. Tissue fragments were observed, and the percent of wells that developed neovessel invasion into the clot was calculated (%I). The subsequent growth of cardiac-derived microvessels was rated and scored over time (Angiogenic Index). RESULTS: There were 20 human atrial appendages plated (n = 24 to 60 wells/specimen) and evaluated in this model. Out of the 20, 16 (80%) atrial appendages developed an angiogenic response in the majority (>50%) of wells plated. Neovessel growth was progressive over 14 to 16 days in culture in all specimens tested. The mean angiogenic index of all specimens was 8.59 +/- 0.91. CONCLUSIONS: This human cardiac tissue-based assay might be useful to screen compounds designed for use in human trials or provide highly vascularized cardiac tissue for autotransplantation. Additionally, the assay provides the foundation to study an individual patent's cardiac tissue and its response to angiogenesis stimulators or inhibitors. This may allow the development of patient-specific therapies designed to enhance revascularization or repair of injured cardiac muscle.

In vitro modeling of the clinical interactions between octreotide and 111In-pentetreotide: is there evidence of somatostatin receptor downregulation?

UNLABELLED: Some authors have suggested that chronic octreotide use enhances the efficiency of radiolabeled somatostatin receptor (sst) imaging. Conversely, desensitization of sst on tumor tissue (tachyphylaxis) may occur occasionally in patients on chronic octreotide therapy. Assuming that chronic exposure to octreotide induces tachyphylaxis, we hypothesized that chronic exposure of sst subtype 2 (sst2)-expressing cells to octreotide would downregulate binding of 111In-pentetreotide to sst and that this downregulation would be due to a reduction in the gene copy number for sst2. METHODS: The clinical scenarios of acute (24 h) and chronic (2 wk) octreotide use, followed by either nuclear imaging exposure (8.6 pmol/L) or therapeutic exposure (510 pmol/L) to (111)In-pentetreotide, were modeled in vitro. Receptor binding in IMR-32 human neuroblastoma cells (high sst2 expression) and PANC-1 human pancreatic cancer cells (no detectable sst2 expression) was evaluated. Gene copy numbers for sst subtypes 1-5 in IMR-32 cells were determined by quantitative polymerase chain reaction. RESULTS: Acute or chronic octreotide exposure at low or high doses did not significantly alter sst2 gene copy numbers or binding of either the diagnostic dose or the therapeutic dose of 111In-pentetreotide. CONCLUSION: In vitro exposure of cells to low or high doses of octreotide for 1-14 d does not result in the development of either tachyphylaxis or upregulation of sst as assessed by changes in gene expression or in high-affinity binding.

Black raspberry extract and fractions contain angiogenesis inhibitors.

Targeted therapies, such as agents that inhibit angiogenesis, offer hope as complementary agents in cancer therapy. Angiogenesis-inhibiting agents have the potential for inhibiting tumor growth and limiting the dissemination of metastasis, thus keeping cancers in a static growth state for prolonged periods. Black raspberry (Rubus occidentalis) extract was discovered to be antiangiogenic (0.1% w/v) in a novel human tissue-based in vitro fibrin clot angiogenesis assay. Assay-guided fractionation of a crude black raspberry extract resulted in a highly potent antiangiogenic fraction that accounted for only 1% of the fresh weight of whole black raspberries. At 0.075% (w/v), the active fraction completely inhibited angiogenic initiation and angiogenic vessel growth. Further subfractionation of this active fraction revealed the coexistence of multiple antiangiogenic compounds, one of which has been identified as gallic acid. However, the individual subfractions did not outperform the active whole fraction. These findings suggest that an active black raspberry fraction may be a promising complementary cancer therapy. It is natural and potent enough for manageable dosing regimens. These extracts contain multiple active ingredients that may be additive or synergistic in their antiangiogenic effects. These observations warrant further investigations in animals and human trials.

The effect of drug dose and drug exposure time on the binding, internalization, and cytotoxicity of radiolabeled somatostatin analogs.

BACKGROUND: Creation of protease-resistant somatostatin analogs has allowed development of these peptides as clinically useful drugs. Widespread diagnostic use of radiolabeled somatostatin analogs has enhanced interest in the binding and intracellular distribution of these peptides. The degree of drug internalization and length of drug retention may be critical for drug-induced cytotoxicity. We hypothesized that the ability of a radiolabeled peptide to bind to a cell, be internalized, and induce cytotoxicity is proportional to both the radioligand concentration and the exposure time. MATERIALS AND METHODS: To test this hypothesis, somatostatin receptor-expressing cells (IMR-32) were incubated with (111)In-pentetreotide, a sst 2 preferring somatostatin analogue. Radioligand exposure time and/or concentration were varied. RESULTS: Prolonged exposure to a fixed concentration of radioligand resulted in progressive increases in whole cell binding and internalization over time. Cells exposed to a relatively fixed number of microCi-Hr yielded constant whole cell binding and internalization. Increasing the microCi-Hr resulted in a proportionate increase in binding. Cytotoxicity was also proportional to the dose of radiation regardless of whether the exposure was internalized radiation (microCi-Hr from (111)In-pentetreotide) or from external beam radiation (cGy). CONCLUSION: Both drug exposure time and drug concentration contribute to cell binding and cytotoxicity in this model and their relative contributions are inversely related.

Development of a novel in vitro human tissue-based angiogenesis assay to evaluate the effect of antiangiogenic drugs.

OBJECTIVE: To describe a novel in vitro human tissue-based angiogenic model that can predict an individual tumor's response to antiangiogenic drugs. SUMMARY BACKGROUND DATA: A number of in vitro and in vivo angiogenesis assays exist, but they do not provide potentially useful information for the treatment of an individual patient. Clonogenic assays have been used to evaluate the response of an individual's tumor to antineoplastic agents, but these tumor fragments are cultured in an environment that does not lead to neovessel growth. The authors have previously demonstrated that human vein disks or human tumor xenograft fragments incorporated into a 0.3% fibrin-thrombin clot will develop angiogenic vessel growth from the cut edge of the vessel disk or xenograft fragment. METHODS: Fresh human tumor or normal tissue disks (2 x 1 mm) from fresh surgical specimens were incorporated into fibrin-thrombin clots overlain with nutrient medium containing either 20% fetal bovine serum alone or in combination with Epothilone B, a tubulin inhibitor with antiangiogenic properties. Tissue disks were visually assessed over time to determine the percentage of wells that developed an angiogenic response. Neovessel growth, density, and length were graded at intervals using a semiquantitative visual neovessel growth-rating scheme (angiogenic index, 0-16 scale) devised in the authors' laboratory. RESULTS: Epothilone B treatment at doses of 10-6 mol/L and 10-8 mol/L decreased the number of wells that developed an invasive angiogenic response and limited the development of vessels that invaded the matrix. At these doses, Epothilone B also caused regression of vessels in wells that had been allowed to develop an angiogenic response. Treatment of tumors or normal tissues with Epothilone B at doses less than 10-8 mol/L was ineffective. CONCLUSIONS: Epothilone B may be an effective antiangiogenic agent in a variety of tumor types. The authors speculate that this in vitro model might provide useful information to the clinician on the effect of specific antiangiogenic agents on individual tumors. This may be particularly useful in patients with tumors that, as a group, are unresponsive to treatment with antineoplastic agents.

Effect of human Angiostatin protein on human angiogenesis in vitro.

Angiostatin, a 38-kD fragment of plasminogen, inhibits angiogenesis in both animal tumor models and in vitro endothelial cell models. However, human Angiostatin has not been tested in vitro against an intact human tissue target to determine its ability to inhibit the initiation or subsequent promotion of the human angiogenic response. We hypothesized that high doses of human Angiostatin would inhibit the development of an angiogenic response in an intact human vessel target, and would suppress the subsequent growth of blood vessels following the initiation of an angiogenic response. To test these hypotheses, full-thickness human placental vein disks were cultured for 15 days in an in vitro fibrin-thrombin clot assay. This assay system had been used to evaluate the efficacy of a wide variety of compounds. Vessels were obtained from three placentas. Treatments included a control medium plus fetal bovine serum (FBS), heparin-steroid (300 micro g/ml heparin and 350 micro g/ml hydrocortisone; a treatment known to inhibit angiogenesis) and Angiostatin at doses from 1 x 10(-4) to 1 x 10(-9) M. In the control groups, 81% of vessels initiated an angiogenic response compared to 53% of the vessels treated with heparin-steroid. Angiostatin (10(-4)-10(-9) M) decreased the initiation of an angiogenic response, but this was not statistically significant. Of the disks that initiated an angiogenic response, the mean ( +/- standard error of the mean (SEM)) semi-quantitative visual angiogenic index (AI) of the control vessels was 9 +/- 1.7 on day 15. In comparison, the mean AI of heparin-steroid treated vessels was 3.7 +/- 0.4. Angiostatin at doses of 10(-4)-10(-9) M also failed to inhibit blood vessel growth after initiation of the angiogenic response. Based on these observations, we cannot demonstrate significant activity of human Angiostatin (10(-4)-10(-9) M) against the initiation or promotion of a human angiogenic response in this in vitro model of angiogenesis using an intact human vessel target.

Inhibition of angiogenic initiation and disruption of newly established human vascular networks by juice from Morinda citrifolia (noni).

noni, the juice of the fruit from the Morinda citrifolia plant, has been used for centuries as a medicinal agent. We tested the effects of noni juice in a three-dimensional fibrin clot matrix model using human placental vein and human breast tumor explants as sources for angiogenic vessel development. Noni in concentrations of 5% (vol/vol) or greater was highly effective in inhibiting the initiation of new vessel sprouts from placental vein explants, compared with initiation in control explants in media supplemented with an equivalent amount of saline. These concentrations of noni were also effective in reducing the growth rate and proliferation of newly developing capillary sprouts. When used at a concentration of 10% in growth media, noni was able to induce vessel degeneration and apoptosis in wells with established capillary networks within a few days of its application. We also found that 10% noni juice in media was an effective inhibitor of capillary initiation in explants from human breast tumors. In tumor explants which did show capillary sprouting, the vessels rapidly degenerated (2-3 days) in those exposed to media supplemented with 10% noni.

Effect of human recombinant Endostatin protein on human angiogenesis.

Tumor growth and metastasis are dependent on the development of new blood vessels. Inhibitors of new vessel growth have been widely investigated as anti-tumor agents. Endostatin, a 20 kDa C-terminal fragment of collagen XVIII inhibits endothelial cell proliferation, induces endothelial cell apoptosis, and can both inhibit and reverse tumor growth in mice. However, human recombinant endostatin has had limited testing against human tissue targets. To investigate the effect of human endostatin on a human vessel target over a broad range of concentrations (10(-l2)-10(-4) M), human placental vein disks were grown for a period of 2 weeks in a 0.3% fibrin clot overlayed with growth medium. Disks from five individual placentas were tested. For each placenta utilized, a control (medium and 20% fetal bovine serum [FBS]) group and a group treated with heparin (300 microg/ml) and hydrocortisone 21-phosphate (350 microg/ml) (heparin-steroid) at a dose known to inhibit angiogenesis were included. Endostatin was tested at concentrations of 10(-12)-10(-4) M in medium containing 20% FBS. The rate of initiation and the angiogenic growth index (on a visually graded semi-quantitative scale of 0-16) were determined for all experimental conditions. Endostatin inhibited angiogenesis in our model only in high concentrations. At 10(-5) M, endostatin did not alter the percent of wells that initiated an angiogenic response, but significantly inhibited subsequent vessel growth. At 10(-4) M, endostatin was able to inhibit both initiation and subsequent new vessel growth. Human endostatin can inhibit the initiation of a human angiogenic response and inhibit the subsequent proliferation of human neovessels when used at high doses in a continuous exposure model.