A sensitive fluorometric enzyme-linked immunosorbent assay that measures vascular endothelial growth factor165 in human plasma

EORTC Receptor and Biomarker Study Group Report: A Sandwich Enzyme-Linked Immunosorbent Assay for Vascular Endothelial Growth Factor in Blood and Tumor Tissue Extracts

A four-antibody sandwich enzyme-linked immunosorbent assay (ELISA) for vascular endothelial growth factor (VEGF) for application in blood (serum and plasma) and tumor tissue extracts was set up within the framework of the EORTC Receptor and Biomarker Study Group (RBSG). Polyclonal antibodies against VEGF165 were raised in chickens and rabbits, and used in a previously described assay format. The assay was validated and characterized for use in serum, plasma and tumor tissue extracts. The resulting VEGF ELISA was found to be specific for VEGF165 and VEGF121, the main isoforms of VEGF. The assay showed good precision and parallelism in serial dilutions of samples. The assay was not susceptible to interference by heterophilic antibodies because avian antibodies (duck anti-chicken and chicken anti-VEGF) were used in the pre-analyte stage and mammalian antibodies (rabbit anti-VEGF and goat anti-rabbit) in the post-analyte stage. In conclusion, a sensitive, robust and specific VEGF ELISA has been developed. Research into the prognostic value of VEGF employing this assay is currently underway.

Detection and Quantification of VEGF Isoforms by ELISA

Vascular endothelial growth factor (VEGF) is a potent mitogen for endothelial cells and plays an important role in physiological and tumor angiogenesis. The human VEGF gene has eight exons. Different VEGF isoforms are expressed via alternative RNA splicing and VEGF121 and VEGF165 are the major isoforms present in human tissues. The exact roles of these different VEGF isoforms are not totally clear. Assays to detect specific VEGF isoforms in biological samples are needed to understand the biological functions of these different VEGF isoforms and to better assess their potential use as predicative biomarkers for anti-angiogenic therapy. Because monoclonal antibodies specific to different VEGF isoforms are lacking, we used antibodies directed to different epitopes on VEGF165 in a set of three enzyme-linked immunosorbent assays (ELISAs) to assess the amount of VEGF121 and VEGF165 as well as VEGF110, which can be generated by plasmin cleavage in vivo. The first ELISA detects VEGF165. The second ELISA detects both VEGF121 and VEGF165. The third ELISA detects VEGF165, VEGF121, and VEGF110. The concentrations of VEGF121 can be assessed from the difference in VEGF concentrations measured by the second and the first ELISAs; the concentrations of VEGF110 can be assessed from the difference in VEGF concentrations measured by the third and the second ELISAs. The same assay strategy may be used to assess the amount of other VEGF isoforms if antibodies directed against the desired amino acids in those isoforms can be obtained.

A therapeutic anti-VEGF antibody with increased potency independent of pharmacokinetic half-life

Bevacizumab [Avastin; anti-vascular endothelial growth factor (VEGF) antibody] is an antiangiogenic IgG approved for treating patients with certain types of colon, breast, and lung cancer. In these indications, bevacizumab is administered every 2 to 3 weeks, prompting us to study ways to reduce the frequency of administration. Increasing affinity to neonatal Fc receptor (FcRn) may extend the pharmacokinetic half-life of an antibody, but the quantitative effect of FcRn affinity on clearance has not been clearly elucidated. To gain further insight into this relationship, we engineered a series of anti-VEGF antibody variants with minimal amino acid substitutions and showed a range of half-life improvements in primates. These results suggest that, if proven clinically safe and effective, a modified version of bevacizumab could potentially provide clinical benefit to patients on long-term anti-VEGF therapy through less-frequent dosing and improved compliance with drug therapy. Moreover, despite having half-life similar to that of wild-type in mice due to the species-specific FcRn binding effects, the variant T307Q/N434A exhibited superior in vivo potency in slowing the growth of certain human tumor lines in mouse xenograft models. These results further suggest that FcRn variants may achieve increased potency through unidentified mechanisms in addition to increased systemic exposure.

A new ELISA for use in a 3-ELISA system to assess concentrations of VEGF splice variants and VEGF(110) in ovarian cancer tumors

BACKGROUND

Vascular endothelial growth factor (VEGF), which affects tumor angiogenesis, is expressed as different splice variants, including the major isoforms VEGF(165) and VEGF(121), and can be cleaved by plasmin to generate VEGF(110). The amount of VEGF(121) and VEGF(110) in biological samples has not been well studied.

METHODS

We developed an ELISA that detects VEGF(165) and VEGF(121) equally, but does not detect VEGF(110). We used this ELISA together with 2 other ELISAs, one detecting VEGF(165) and the other detecting VEGF(165), VEGF(121), and VEGF(110) equally, to assess the concentrations of VEGF(121) and VEGF(110) in ovarian cancer tumors.

RESULTS

The median concentrations in ovarian cancer tumor lysates were 0.61 (range <0.055-74) fmol/mg protein for VEGF(165), 1.4 (range <0.20-500) fmol/mg protein for VEGF(165) plus VEGF(121), and 2.3 (range <0.079-520) fmol/mg protein for total VEGF including VEGF(110) (n = 248). VEGF concentrations measured by the 3 ELISAs were highly correlated (r = 0.91-0.94). Median estimated VEGF(121) and VEGF(110) concentrations were 0.77 and 0.58 fmol/mg protein, respectively. In lysates with measurable VEGF(165) and total VEGF concentrations, mean VEGF(165) was approximately 31% (SD 23%) of the total VEGF (n = 217). In contrast, VEGF(165) constituted approximately half of the total circulating VEGF.

CONCLUSION

VEGF(165), VEGF(121), and VEGF(110) may be present at significant amounts in ovarian cancer tumors.

Development of time-resolved immunofluorometric assays for vascular endothelial growth factor and application on plasma of patients with gastric tumours

A highly sensitive and accurate time-resolved immunofluorometric assay (TR-IFMA) has been developed, for the first time, to measure plasma vascular endothelial growth factor (VEGF) in patients with gastric tumours. A monoclonal anti-hVEGF antibody and a biotinylated anti-hVEGF antibody were used to develop a non-competitive 'sandwich'-type assay. Fluorescence can be measured by a time-resolved fluorometer after binding of europium (Eu)(3+)-labelled streptavidin to the biotinylated immunoglobulin. Plasma VEGF concentrations were measured by TR-IFMA in 92 healthy controls, in 36 benign stomach disease patients and in 92 gastric cancer patients before surgery. The association between plasma VEGF levels and clinicopathological features was evaluated. A standard curve for VEGF TR-IFMA has been developed with good sensitivity (0.37 pg/ml). Accuracy studies, specificity, parallelism and precision data were determined and all were found to be satisfactory. The validity of the VEGF assay was confirmed by the good correlation between the results obtained by TR-IFMA and commercial enzyme-linked immunosorbent assay (ELISA) (ELISA result = 1.862 + 0.953 (TR-IFMA result), r = 0.944]. The plasma levels of VEGF are higher in gastric cancer patients than in healthy controls. VEGF levels were associated significantly with the presence of distant metastases, as well as invasion depth of the tumour and tumour stage, but not with tumour location, tumour histology, differentiation or the presence of lymph node metastases. At the cut-off of 217.79 pg/ml, the diagnostic sensitivity, specificity and accuracy of the TR-IFMA were 40.2%, 93.7% and 69.9%, respectively. A highly sensitive and reliable TR-IFMA for VEGF has been developed. The determination of plasma VEGF levels may be clinically useful.

Gene expression profiles of bronchoalveolar cells in pulmonary TB

The host response to Mycobacterium tuberculosis includes macrophage activation, inflammation with increased immune effector cells, tissue necrosis, and cavity formation, and fibrosis, distortion, and bronchiectasis. To evaluate the molecular basis of the immune response in the lungs of patients with active pulmonary tuberculosis (TB), we used bronchoalveolar lavage to obtain cells at the site of infection. Affymetrix GeneChip microarrays and cDNA nylon filter microarrays interrogated gene expression in bronchoalveolar lavage (BAL) cells from 11 healthy controls and 17 patients with active pulmonary TB. We found altered gene expression for 69 genes in TB versus normal controls that included cell surface markers, cytokines, chemokines, receptors, transcription factors, and complement components. In addition, TB BAL cell gene expression patterns segregated into 2 groups: one suggestive of a T helper type 1 (Th1) cellular immune response with increased signal transducer and activator of transcription-4 (STAT-4), interferon-gamma (IFN-gamma receptor), and monokine induced by IFN-gamma (MIG) expression with increased IFN-gamma protein levels in BAL fluid; the other group displayed characteristics of Th2 immunity with increased STAT-6, CD81, and IL-10 receptor expression. We were able to demonstrate that a Th2 presentation could change to a Th1 pattern after anti-tuberculous treatment in 1 TB patient studied serially. These gene expression data support the conclusion that pulmonary TB produces a global change in the BAL cell transcriptome with manifestations of either Th1 or Th2 immunity.

pHUSH: a single vector system for conditional gene expression

Background

Conditional expression vectors have become a valuable research tool to avoid artefacts that may result from traditional gene expression studies. However, most systems require multiple plasmids that must be independently engineered into the target system, resulting in experimental delay and an increased potential for selection of a cell subpopulation that differs significantly from the parental line. We have therefore developed pHUSH, an inducible expression system that allows regulated expression of shRNA, miRNA or cDNA cassettes on a single viral vector.

Results

Both Pol II and Pol III promoters have been successfully combined with a second expression cassette containing a codon-optimized tetracycline repressor and selectable marker. We provide examples of how pHUSH has been successfully employed to study the function of target genes in a number of cell types within in vitro and in vivo assays, including conditional gene knockdown in a murine model of brain cancer.

Conclusion

We have successfully developed and employed a single vector system that enables Doxycycline regulated RNAi or transgene expression in a variety of in vitro and in vivo model systems. These studies demonstrate the broad application potential of pHUSH for conditional genetic engineering in mammalian cells.

Species-dependent serum interference in a sandwich ELISA for Apo2L/TRAIL

To support pre-clinical studies of Apo2L/TRAIL in rodents and non-human primates, a sandwich ELISA was developed using two mouse monoclonal anti-Apo2L/TRAIL antibodies. Mouse, rat, cynomolgus monkey, and chimpanzee serum at concentrations of > or =1% were found to interfere with accurate quantitation of Apo2L/TRAIL. Moreover, the characteristics of the serum interference for each species were different. In order to resolve the observed serum effect, studies were performed in which salts, detergents, and blocking proteins were added to the sample diluent, and optimized sample diluents that eliminated serum interference were developed for mouse, cynomolgus monkey, and chimpanzee serum. These buffers consisted of a base assay diluent (PBS/0.5% BSA/0.05% Tween-20/10 ppm ProClin 300) supplemented with: NaCl (mouse serum); NaCl, EDTA, CHAPS, bovine gamma globulin (BGG), and human IgG (cynomolgus monkey serum); and NaCl and EDTA (chimpanzee serum). Full characterization studies were performed for the "buffer" ELISA run in base assay diluent (intended for non-serum samples) as well as the assays optimized for mouse serum and cynomolgus monkey serum. Precision, accuracy, linearity, and specificity were found to be satisfactory. With the availability of a rabbit polyclonal antibody against Apo2L/TRAIL, a new pAb/mAb ELISA was developed. This assay was not only more sensitive by > or =6-fold, but it was also much less subject to serum interference.

Predicting benefit from anti-angiogenic agents in malignancy

A high probability of benefit is desirable to justify the choice of anti-angiogenic therapy from an ever-expanding list of expensive new anticancer agents. However, biomarkers of response to cytotoxic agents are not optimal for predicting benefit from anti-angiogenic drugs. This discussion will focus on both preclinical and clinical research to identify biomarkers for anti-angiogenic therapies that can inform dosing, early clinical benefit, initial drug choice, emerging resistance and second-line treatments.

Maximal COX-2 immunostaining and clinical response to celecoxib and interferon alpha therapy in metastatic renal cell carcinoma

BACKGROUND

Cyclooxygenase-2 (COX-2) plays a major role in the development of cancer through numerous mechanisms. COX-2 is expressed in the majority of renal cell carcinoma (RCC) tumors and correlates with stage, grade, and microvessel density. Based on potential additive or synergistic antitumor effects, interferon-alpha (IFNalpha) and celecoxib, an oral COX-2 inhibitor, were given to metastatic RCC patients in a Phase II trial.

METHODS

Patients with untreated, metastatic RCC received IFNalpha 3 million units (MU) daily and celecoxib 400 mg orally (p.o.) twice daily continuously until disease progression or unacceptable toxicity. Pretreatment, paraffin-embedded RCC tumor samples were immunohistochemically stained for COX-2 expression and plasma basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) levels were assayed to determine predictive or prognostic potential.

RESULTS

There were three partial responses among 25 patients treated (objective response rate, 12%; 95% confidence interval [CI], 3-31%). The observed median time to disease progression (TTP) for the entire cohort was 3.3 months. A significant association between maximal COX-2 staining and clinical response was observed: all patients who experienced an objective response demonstrated 3+ COX-2 tumor immunostaining (trend test: P=0.03). Therapy was well tolerated without cardiac or other notable toxicity.

CONCLUSIONS

The addition of celecoxib to IFNalpha did not increase the objective response rate or TTP of this unselected cohort. Maximal COX-2 tumor immunostaining may identify RCC patents more likely to achieve clinical benefit with COX-2 inhibition in combination with IFNalpha. Further investigation of this combination in 3+ COX-2-overexpressing RCC tumors is warranted.

Vascular endothelial growth factor response to exogenous chorionic gonadotropic hormone in the luteal phase of women with a history of severe ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is a severe complication of ovarian stimulation. No reliable test exists to predict the syndrome. The objective of the present prospective observational study was to examine vascular endothelial growth factor (VEGF) secretion after human chorionic gonadotropin (hCG) administration in the luteal phase of a spontaneous cycle of women with a history of severe OHSS. Five women with a history of severe OHSS were administered 250 mug recombinant hCG intravenously on day 21 of a spontaneous menstrual cycle. Plasma samples were collected at regular intervals from 15 min before hCG to 6 h thereafter and the free VEGF plasma concentrations were determined. Plasma levels of free VEGF remained at the lower detection limit of the assay throughout the observational period. Women with previous severe OHSS do not show a significant short-time response of VEGF secretion upon hCG administration. No evidence was found to support the notion that women inclined to develop a severe form of the syndrome after ovarian stimulation could possibly be identified by the VEGF short-time secretory response to exogenous hCG in the luteal phase of a spontaneous cycle.

Adenoviral vector platform for transduction of constitutive and regulated tricistronic or triple-transcript transgene expression in mammalian cells and microtissues

BACKGROUND

Adenoviral particles can efficiently transduce a broad spectrum of cell types, so they are widely used in basic research and clinical trials.

METHODS

We have developed a novel adenoviral vector platform for delivery of constitutive or streptogramin-inducible expression of up to three therapeutic transgenes into a variety of murine and human cell lines, primary cells and microtissues.

RESULTS

Coordinated expression of three independent transgenes in a compact genetic format was achieved by two different expression configurations: (i) The multicistronic expression format consisting of a single constitutive (simian virus 40 promoter, P(SV40); murine or human cytomegalovirus immediate-early promoter, P(mCMV), P(hCMV)) or regulated (streptogramin-inducible) promoters (P(PIR)ON2) driving the expression of a single multicistronic transcript of which the first cistron is translated in a cap-dependent manner and the two subsequent ones by internal ribosome entry site (IRES)-mediated translation initiation. (ii) The triple-transcript expression configuration, in which a combination of well-established (P(SV40), P(hCMV), P(mCMV)) and novel synthetic constitutive promoters (P(GTX)) control transcription of three expression units. The constitutive multigene expression design enabled coordinated high-level expression of the Bacillus stearothermophilus-derived secreted alpha-amylase (SAMY), the human vascular endothelial growth factor 121 (VEGF(121)) and the human placental secreted alkaline phosphatase (SEAP) in monolayer populations and microtissues of Chinese hamster ovary cells (CHO-K1), human fibrosarcoma cells (HT-1080), primary neonatal rat cardiomyocytes (NRCs) and primary human aortic fibroblasts (HAFs). Streptogramin-inducible tricistronic SAMY-VEGF(121)-SEAP expression provided excellent regulation performance-high-level induction in the presence of the streptogramin antibiotic pristinamycin I (PI), near-undetectable basal expression in the absence of PI, optimal adjustability and perfect reversibility-in all cell types, in particular in NRCs and NRC-derived myocardial microtissues.

CONCLUSIONS

Triple-transcript and tricistronic expression configurations conserve the DNA packaging capacity of the size-constrained viral transduction systems and enable coordinated and regulated expression of up to three therapeutic transgenes for concerted clinical interventions in future gene therapy scenarios.

Cross-species vascular endothelial growth factor (VEGF)-blocking antibodies completely inhibit the growth of human tumor xenografts and measure the contribution of stromal VEGF

To fully assess the role of VEGF-A in tumor angiogenesis, antibodies that can block all sources of vascular endothelial growth factor (VEGF) are desired. Selectively targeting tumor-derived VEGF overlooks the contribution of host stromal VEGF. Other strategies, such as targeting VEGF receptors directly or using receptor decoys, result in inhibiting not only VEGF-A but also VEGF homologues (e.g. placental growth factor, VEGF-B, and VEGF-C), which may play a role in angiogenesis. Here we report the identification of novel anti-VEGF antibodies, B20 and G6, from synthetic antibody phage libraries, which block both human and murine VEGF action in vitro. Their affinity-improved variants completely inhibit three human tumor xenografts in mice of skeletal muscle, colorectal, and pancreatic origins (A673, HM-7, and HPAC). Avastin, which only inhibits the tumor-derived human VEGF, is approximately 90% effective at inhibiting HM-7 and A673 growth but is <50% effective at inhibiting HPAC growth. Indeed, HPAC tumors contain more host stroma invasion and stroma-derived VEGF than other tumors. Thus, the functional contribution of stromal VEGF varies greatly among tumors, and systemic blockade of both tumor and stroma-derived VEGF is sufficient for inhibiting the growth of tumor xenografts.

Association between HER-2/neu and vascular endothelial growth factor expression predicts clinical outcome in primary breast cancer patients

PURPOSE

Activation or overexpression of HER-2/neu is associated with up-regulation of vascular endothelial growth factor (VEGF) in human breast cancer cells in vitro. Preclinical experiments indicate that increased expression of VEGF may in part mediate the biologically aggressive phenotype of HER-2/neu-overexpressing human breast cancer. It was the purpose of this study to: (a). evaluate the association between HER-2/neu and VEGF expression in a large clinical cohort of primary breast cancer patients; (b). compare the prognostic significance of VEGF isoforms; and (c). analyze the combined effects of HER-2/neu and VEGF on clinical outcome.

EXPERIMENTAL DESIGN

HER-2/neu and VEGF were measured by ELISA in primary breast tumor tissue lysates from 611 unselected patients with a median clinical follow-up of 50 months. At least six VEGF isoforms consisting of 121, 145, 165, 183, 189, or 206 amino acids are generated as a result of alternative splicing. The VEGF(121-206) ELISA uses antibodies that bind to VEGF(121) and, therefore, detects all of the VEGF isoforms with 121 and more amino acids. The VEGF(165-206) ELISA uses antibodies that bind to VEGF(165) and, therefore, detects all of the VEGF isoforms with 165 and more amino acids. VEGF(121-206) and VEGF(165-206) were analyzed both as continuous and categorical variables, using detectable expression as a cutoff for positivity. Cell lines with defined HER-2/neu expression levels were used to establish a cutoff point for HER-2/neu overexpression in breast tumor samples.

RESULTS

Our findings indicate a significant positive association between HER-2/neu and VEGF expression. VEGF(121-206) and VEGF(165-206) expression was detectable in 88 (77.2%) and 100 (87.7%), respectively, of the 114 patients with HER-2/neu-overexpressing tumors, in contrast to 271 (54.5%) and 353 (71.0%), respectively, of the 497 patients with nonoverexpressing tumors (chi(2) test: P < 0.001 for both VEGF(121-206) and VEGF(165-206)). VEGF(121-206) and VEGF(165-206) demonstrate a comparable prognostic significance for survival in unselected primary breast cancer patients (univariate analysis: VEGF(121-206), P = 0.0068; VEGF(165-206), P = 0.0046; multivariate analysis: VEGF(121-206), P = 0.1475; VEGF(165-206), P = 0.1483). When the analyses were performed separately for node-negative and node-positive patients, VEGF(121-206) and VEGF(165-206) were of prognostic significance for survival only in node-positive patients (univariate analysis: VEGF(121-206), P = 0.0003; VEGF(165-206), P = 0.0038; multivariate analysis: VEGF(121-206), P = 0.0103; VEGF(165-206), P = 0.0150). A biological concentration-effect relationship between VEGF expression and survival (VEGF(121-206), P = 0.0280; VEGF(165-206,) P = 0.0097) suggests that VEGF levels, as determined by ELISA, could be of importance as a predictive marker for therapeutic strategies that target VEGF. Combining HER-2/neu and VEGF(121-206)/VEGF(165-206) results in additional prognostic information for survival (VEGF(121-206), P = 0.0133; VEGF(165-206), P = 0.0092).

CONCLUSION

The positive association between HER-2/neu and VEGF expression implicates VEGF in the aggressive phenotype exhibited by HER-2/neu overexpression, and supports the use of combination therapies directed against both HER-2/neu and VEGF for treatment of breast cancers that overexpress HER-2/neu.

Biomarkers, validation and pharmacokinetic-pharmacodynamic modelling

Four elements are crucial to successful pharmacokinetic-pharmacodynamic (PK/PD) modelling and simulation for efficient and effective rational drug development: (i) mechanism-based biomarker selection and correlation to clinical endpoints; (ii) quantification of drug and/or metabolites in biological fluids under good laboratory practices (GLP); (iii) GLP-like biomarker method validation and measurements and; (iv) mechanism-based PK/PD modelling and validation. Biomarkers can provide great predictive value in early drug development if they reflect the mechanism of action for the intervention even if they do not become surrogate endpoints. PK/PD modelling and simulation can play a critical role in this process. Data from genomic and proteomics differentiating healthy versus disease states lead to biomarker discovery and identification. Multiple genes control complex diseases via hosts of gene products in biometabolic pathways and cell/organ signal transduction. Pilot exploratory studies should be conducted to identify pivotal biomarkers to be used for predictive clinical assessment of disease progression and the effect of drug intervention. Most biomarkers are endogenous macromolecules, which could be measured in biological fluids. Many exist in heterogeneous forms with varying activity and immunoreactivity, posting challenges for bioanalysis. Reliable and selective assays could be validated under a GLP-like environment for quantitative methods. While the need for consistent reference standards and quality control monitoring during sample analysis for biomarker assays are similar to that of drug molecules, many biomarkers have special requirements for sample collection that demand a well coordinated team management. Bioanalytical methods should be validated to meet study objectives at various drug development stages, and possess adequate performance to quantify biochemical responses specific to the target disease progression and drug intervention. Protocol design to produce sufficient data for PK/PD modelling would be more complex than that of PK. Knowledge of mechanism from discovery and preclinical studies are helpful for planning clinical study designs in cascade, sequential, crossover or replicate mode. The appropriate combination of biomarker identification and selection, bioanalytical methods development and validation for drugs and biomarkers, and mechanism-based PK/PD models for fitting data and predicting future clinical endpoints/outcomes provide powerful insights and guidance for effective and efficient rational drug development, toward safe and efficacious medicine for individual patients.

Biomarkers in drug discovery and development: from target identification through drug marketing

Biomarkers of disease play an important role in medicine and have begun to assume a greater role in drug discovery and development. The challenge for biomarkers is to allow earlier, more robust drug safety and efficacy measurements. Their role in drug development will continue to grow for the foreseeable future. For biomarkers to assume their rightful role, greater understanding of the mechanism of disease progression and therapeutic intervention is needed. In addition, greater understanding of the requirements for biomarker selection and validation, biomarker assay method validation and application, and clinical endpoint validation and application is needed. Biomarkers need to be taken into account while the therapeutic target is still being identified and the concept is being formulated. Biomarkers need to be incorporated into a continuous cycle that takes what is learned from the discovery and development of one series of biomarkers and translates it into the next series of biomarkers. Optimum biomarker development and application will require a team approach because of the multifaceted nature of biomarker selection, validation, and application, using such techniques as pharmacoepidemiology, pharmacogenetics, pharmacogenomics, and functional proteomics; bioanalytical method development and validation; disease process and therapeutic intervention assessments; and pharmacokinetic/pharmacodynamic modeling and simulation to improve and refine drug development. The potential for biomarkers in medicine and drug development will be limited by the least effective component of the processes. The team approach will minimize the potential for the least effective component to be fatal to the rest of the process. As scientific/regulatory foundations for biomarkers in medicine and drug development begin to be established, successes and applications will need to be effectively communicated with all of the stakeholders, including not only internal and external drug developers and regulators but also the medical community, to ensure that biomarkers are totally integrated into drug discovery and development as well as the practice of medicine.

Bloodborne biomolecular markers in prostate cancer development and progression

Prostate cancer is notoriously difficult to treat, which makes its early detection a priority. Biomarkers have been used to diagnose and monitor prostate cancer for more than 50 years, and the discovery of the serum marker prostate-specific antigen (PSA) significantly altered the detection and management of prostate cancer. But imperfect correlation with cancer hinders the usefulness of PSA. The elucidation and validation of new biological markers of prostate cancer should aid detection, and improve the application of the available therapeutics.

Characterization of the vascular endothelial growth factor-receptor interaction and determination of the recombinant protein by an optical receptor sensor

Vascular endothelial growth factor (VEGF) is one of the most important factors controlling angiogenesis. It is a homodimeric glycoprotein belonging to the family of cysteine-knot proteins. The biological activity is transduced via membrane-spanning receptors of the tyrosine kinase receptor family. Each biologically active VEGF has two receptor binding sites leading to receptor dimerization as first step following ligand binding. The ligand-binding site of the receptor is localized on extracellular Ig-like domains. The extracellular part of the receptor Flt-1 (VEGFR-1) was expressed as soluble protein and was used as receptor in an optical affinity sensor system (BIAcore). Suitable conditions allowed the determination of the association and dissociation rate constants as k(a)=4+/-1.2 x 10(6) M(-1) s(-1) and k(d)=3+/-0.8 x 10(-5) s(-1), respectively, leading to an affinity constant of K(D)=7.5+/-3 pM, which is within the range published already from other investigations and methods. Increasing receptor loadings of the sensor surface decreased the binding efficiency, as the ratio of bound VEGF-molecules to theoretically available binding sites increased from 1:1.5 to 1:2.6. Increasing the surface loading further, allowed the establishment of a quantitative assay with the analytical performance being influenced by the receptor loading and the contact time between sample and immobilized receptor, i.e. sample volume. This assay was used for VEGF determination during the cultivation of a recombinant Pichia pastoris strain.

A phase II study of thalidomide in advanced metastatic renal cell carcinoma

OBJECTIVES

To evaluate the toxicity and activity of thalidomide in patients with advanced metastatic renal cell cancer and to measure changes of one angiogenic factor, vascular endothelial growth factor (VEGF)165, with therapy.

PATIENTS AND METHODS

29 patients were enrolled on a study of thalidomide using an intra-patient dose escalation schedule. Patients began thalidomide at 400 mg/d and escalated as tolerated to 1200 mg/d by day 54. Fifty-nine per cent of patients had had previous therapy with IL-2 and 52% were performance status 2 or 3. Systemic plasma VEGF165 levels were measured by dual monoclonal ELISA in 8 patients.

RESULTS

24 patients were evaluable for response with one partial response of 11 months duration of a patient with hepatic and pulmonary metastases (4%), one minor response, and 2 patients stable for over 6 months. Somnolence and constipation were prominent toxicities and most patients could not tolerate the 1200 mg/day dose level. Systemic plasma VEGF165 levels did not change with therapy.

CONCLUSION

These results are consistent with a low level of activity of thalidomide in renal cell carcinoma. Administration of doses over 800 mg/day was difficult to achieve in this patient population, however lower doses were practical. The dose-response relationship, if any, of thalidomide for renal cell carcinoma is unclear.

Pitfalls in the Measurement of Circulating Vascular Endothelial Growth Factor

Background: Vascular endothelial growth factor (VEGF) is a protein with antiapoptotic, mitogenic, and permeability-increasing activities specific for vascular endothelium. VEGF mRNA, which has five isoforms, is produced by nonmalignant cells in response to hypoxia and inflammation and by tumor cells in constitutively high concentrations. Because VEGF plays a crucial role in physiological and pathophysiological angiogenesis, measurements of circulating VEGF are of diagnostic and prognostic value, e.g., in cardiovascular failures, inflammatory diseases, and malignancies. However, there are major quantitative differences in the published results. This review attempts to identify reasons for these disparities.

Approach: The literature was reviewed through a Medline search covering 1995 to 2000. A selection of exemplary references had to be made for this perspective overview.

Content: Data are included from studies on healthy humans, gynecological patients, and persons suffering from inflammatory or malignant diseases. The results indicate that competitive immunoassays detect the total amount of circulating VEGF, which enables observations regarding the increase in VEGF in pregnancy and preeclampsia to be made. In these cases, capture immunoassays utilizing neutralizing antibodies are insufficient because of an accompanying increase in VEGF-binding soluble receptors (sFlt-1). Measurements of circulating free VEGF are useful for study of malignant diseases, which are associated with both genetically and hypoxia-induced overproduction of VEGF. The VEGF isoform specificity of the antibodies is also critical because both VEGF121 and VEGF165 are secreted. It is important to consider that platelets and leukocytes release VEGF during blood clotting.

Conclusions: Future efforts should concentrate on the balance between free VEGF, total VEGF, and sFlt-1. Plasma, rather than serum, should be used for analysis.

Detection and plasma pharmacokinetics of an anti-vascular endothelial growth factor oligonucleotide-aptamer (NX1838) in rhesus monkeys

Aptamers are oligonucleotide ligands selected, in vitro, to bind a specified target protein. The first aptamer to reach human clinical testing is NX1838, a polyethylene glycol conjugated aptamer that inhibits vascular endothelial growth factor. This paper describes the validation of a high-performance liquid chromatographic anion-exchange method for the determination of NX1838 in plasma. Measurements of intact NX1838 had a coefficient of variation of less than 8% and an accuracy between 107% and 115%. The assay was utilized to determine NX1838 plasma pharmacokinetics in rhesus monkeys following a single 1 mg/kg intravenous or subcutaneous dose. Following intravenous administration, the maximum achieved plasma concentration was 25.5 microg/ml with a terminal half-life of 9.3 h and clearance rate of 6.2 ml/h. After subcutaneous administration, the fraction of the dose absorbed into the plasma compartment was 0.78 with a time to peak concentration (4.9 microg/ml) of 8 to 12 h.