Biological activity of EDQM CRS for Interferon alfa-2a and Interferon alfa-2b - assessment in two in vitro bioassays.

The European Directorate for the Quality of Medicines (EDQM) supplies Chemical Reference Substances (CRS) for Interferon (IFN) alfa-2a (CRS I0320300) and for IFN alfa-2b (CRS I0320301) for specified physicochemical tests. However, no information is provided as to their biological activity. In contrast, the World Health Organization (WHO) provides the 2nd International Standards (IS) for IFN alfa-2a (code 95/650) and for IFN alfa-2b (code 95/566), with activity defined in International Units (IU) for calibration of biological activity of preparations of IFN. We have compared the EDQM CRSs with the WHO ISs in two bioassay systems, one measuring the anti-proliferative activity in the Daudi cell line and the other measuring a reporter gene activation in an A549 cell line. In each of these assay systems, the CRSs gave dose - response relations, which were similar to those for the WHO ISs. Estimates of relative activity for each CRS, in terms of the respective IS, showed specific biological activity for the CRSs of the same order as the nominal specific activity for the ISs. However, the estimates of relative activity were not consistent between the two assays systems, emphasizing the need for calibration within each system, if the CRS were to be used as a working standard for bioassays. For structure-activity studies, both physicochemical and biological activity characterisation are required for the same biopharmaceutical preparation. CRS I0320300 and CRS I0320301 may prove useful as working standards for some bioassay systems.

Statistical considerations in the design and analysis of parallel line assays.

Underlying the design of any assay and further, interpretation of the results, are multitudes of assumptions and implications, ranging from 'biological' assumptions about the nature of the assay system and its response to the materials assayed to 'statistical' assumptions about the form of the dose-response relationship and the distribution of the response data. As far as possible, assays should be designed and analysis carried out to assess these assumptions. Implications for the individual assay are discussed, since this is where all studies of assays necessarily begin. Consideration is then extended to implications for the combination of data and results of several assays.

An ECVAM pre-validation study of physicochemical methods for predicting the biological potency of recombinant follicle stimulating hormone.

A pre-validation study was carried out, by six laboratories from six countries, of two physicochemical methods for predicting the in vivo biological potency of recombinant follicle stimulating hormone (follitropin beta), based on quantitative measures of isoform distribution by isoelectric focusing (IEF) and by capillary zone electrophoresis. Each of these methods was used to estimate the predicted bioactivities of four preparations of follitropin beta differing widely in their isoform compositions and specific bioactivities. The results of this study indicate that these methods, and particularly IEF, are transferable between laboratories, and produce results which are sufficiently accurate, precise, and reproducible, for them to be used for predicting the bioactivity of follitropin beta, especially if used with a standard preparation. The performance of these two methods for predicting the bioactivity of other types of follicle stimulating hormone, such as follitropin alfa, would need to be assessed separately, and might involve quantitatively different relationships between the responses measured in the physicochemical method and the bioactivities of preparations estimated by bioassay.

International Standards for hepatocyte growth factor/scatter factor: initial assessment of candidate materials and their evaluation by multicentre collaborative study.

Hepatocyte growth factor/scatter factor (HGF/SF) is a potent paracrine growth factor with motogenic, mitogenic and morphogenic activities, and a potential therapeutic role in hepatic and renal disease, as well as diagnostic and prognostic applications. It is synthesised as an inactive, single-chain precursor that is cleaved by serine proteases to give a biologically active, heterodimeric form. To develop World Health Organization (WHO) International Standards (IS) for HGF/SF, candidate preparations of the two forms were assessed in a multicentre study in which they were compared with local standards by bioassay and immunoassay. Among laboratories, there was a wide variation in the estimates of potencies of the candidate standards in terms of in-house reference preparations, but between-assay and within-assay variabilities were low within laboratories. In some assay systems, the precursor and heterodimer showed different responses. Since both molecular forms are widely used in current assay systems, this suggested that a reference preparation was required for each form of the HGF/SF molecule. Accordingly, the Expert Committee on Biological Standardization of WHO established the heterodimeric material (96/564) as the first IS for HGF/SF, human, recombinant, with an assigned unitage of 4000 IU/ampoule and, for the purpose of immunoassay calibration, a nominal HGF/SF content of 4 microg/ampoule. The precursor preparation (96/556) was established as the first IS for HGF/SF (precursor) with an assigned unitage of 2000 IU/ampoule and, for the purpose of immunoassay calibration, a nominal HGF/SF (precursor) content of 4 microg/ampoule. The preparations can be obtained upon written request to the National Institute for Biological Standards and Control (NIBSC, PO Box 1193), by e-mail (standards@nibsc.ac.uk) or ordered at http://www.nibsc.ac.uk.

The fourth International Standard for Human Urinary FSH and LH: specificities of LH seminal vesicle weight gain assays in the collaborative study differ between laboratories.

The fourth International Standard for Human Urinary FSH and LH (IS; in ampoules coded 98/704) was compared with the third International Standard for Urinary FSH and LH (IS 71/264) by 10 laboratories in nine countries, using FSH and LH in vivo bioassays. Estimates of the FSH content of the IS by augmented ovarian weight gain assays were homogeneous within each laboratory and over all laboratories. The combined weighted geometric mean estimate of FSH content of the IS (with 95% fiducial limits) in terms of IS 71/264 was 71.9 (69.0-74.9) IU/ampoule. Although estimates by seminal vesicle weight gain (SVW) assays of the relative LH activities of the IS and IS 71/264 were homogeneous within laboratories, estimates were heterogeneous between laboratories. This indicated differences between the spectrum of LH isoforms in the IS and IS 71/264, which were obtained from different manufacturers, and differences between the specificities of SVW assays performed in different laboratories. The differences between the specificities of SVW assays appeared to be related to interactions among mean laboratory seminal vesicle weights, age and genetic strain of rat. The finding of inter-laboratory differences in the specificities of SVW assays is of some significance, as this assay method has been generally adopted by Pharmacopoeias for the control of the LH content of therapeutic products. The combined unweighted geometric mean estimate of LH content of the IS (with 95% fiducial limits) in terms of IS 71/264 by SVW and ovarian ascorbate depletion assays was 70.2 (61.7-80.0) IU/ampoule. Estimates of the FSH and LH content of ampoules of the IS kept at increased temperatures suggested that the IS would be adequately stable under normal storage conditions. On the basis of these results, the World Health Organization Expert Committee on Biological Standardization established the preparation in ampoules coded 98/704 as the fourth International Standard for Human Urinary FSH and LH, and assigned to the contents of each ampoule an activity of 72 International Units of urinary FSH and an activity of 70 International Units of urinary LH.

Multicentre collaborative study to calibrate IGF-II by bioassay and immunoassay: establishment of the First WHO Reference Reagent.

A preparation of recombinant insulin-like growth factor-II (IGF-II) (NIBSC code 96/538) was compared with local standards in bioassays and immunoassays by eight laboratories in four countries to assess its suitability for use as a World Health Organisation (WHO) reference reagent. Estimates of relative potencies for the bioassays gave a geometric mean of 1.04 (0.94--1.16) microg of local standard per microg of 96/538. Estimates of relative immunological activities by immunoassay gave a geometric mean of 1.15 (0.94--1.38) microg of local standard per microg of 96/538. The study provided evidence that a common standard for rhIGF-II would be helpful and that 96/538 was sufficiently stable to serve as a reference reagent. Accordingly 96/538 was established as the First WHO Reference Reagent for IGF-II, human, recombinant, and assigned a unitage of 5000 units per ampoule and on the basis of the immunoassay results a nominal mass content of 5 microg per ampoule.

Definition and measurement of follicle stimulating hormone.

FSH has a key role in the development and function of the reproductive system and is widely used both diagnostically and therapeutically in developmental and reproductive medicine. The accurate measurement of FSH levels, in patients for diagnosis and monitoring and in therapeutic preparations for clinical use, is essential for safe and successful treatment. Historically, FSH was defined on the basis of classical in vivo endocrine activity, and early therapeutic preparations were calibrated using in vivo bioassays. There was early recognition that reference preparations were required for calibration if the results from different laboratories were to be comparable. In response to the perceived need, the World Health Organization established the first standard for such preparations in 1959. Subsequent developments in biotechnology have led to recognition that there is no single molecule that can be uniquely defined as FSH, and that FSH can induce a range of biological activities. Several highly purified standards for FSH are now available, but discontinuity and heterogeneity of estimates of FSH activity in terms of these standards made using in vitro assays and binding assays have been noted. It is thus essential that any measurement of FSH include specification both of the standard with which the measured FSH is compared and the assay method used for that comparison.

Assessment of assay precision: a case study of an ELISA for anti-pertussis antibody.

Assay evaluation and validation is essential to ensure that assays are sufficiently specific and provide estimates with sufficient precision for the required purposes. This must be an on-going process, and assays should therefore be designed to permit some degree of both direct and indirect measurement of intra- and inter-assay variation. Quality control procedures may contribute relevant information, but may not be sufficient. Results obtained by two laboratories using as nearly as possible identical reagents and samples in an ELISA for anti-pertussis antibodies are described. These results illustrate aspects of assay performance which may be overlooked once a formal "validation exercise" has been carried out and assays are in routine use. This study also illustrates the information, in addition to that available from in-house studies, which may be provided by appropriately designed inter-laboratory studies, such as the collaborative studies carried out for characterization and calibration of reference materials and standards.

Validation of in vitro assays for botulinum toxin: a case study.

Ensuring the reliability and precision of assay results requires careful attention to assay design. In this case study we describe validation studies of an in vitro assay for botulinum neurotoxin type A based on its endopeptidase activity towards immobilised synthetic substrate. This assay, in common with many in vitro assays, is sensitive to changes in reagents and assay conditions and is time dependent. In addition, the toxin is not stable in solution. Differences in estimates of potency, resulting from positional factors, which are not significant in individual assays, are shown to be consistent and statistically significant over a longer series of assays. This study emphasizes that assay validation should not be viewed as a single step in assay development but must be considered as a continuing process if assay results are to be reliable and reproducible.

The first international standard for serum amyloid A protein (SAA). Evaluation in an international collaborative study.

An ampouled preparation of acute phase serum rich in serum amyloid A protein (SAA) was evaluated in seven laboratories in six countries for its suitability to serve as the international standard for immunoassay of SAA. A variety of different immunoassays were used. On the basis of the results reported here and with the authorization of the Expert Committee on Biological Standardization of the World Health Organization (WHO) this preparation (coded 92/680) was established as the first international standard of SAA.

Characterisation, calibration and comparison by international collaborative study of international standards for the calibration of therapeutic preparations of FSH.

Therapeutic preparations of FSH, used primarily for treatment of infertility, are calibrated by in vivo bioassay against international standards (IS) derived from different sources deemed appropriate to their use according to pharmacopoeial monographs. Menotrophins, which have been used for several decades to treat infertility, have been calibrated against the IS for urinary FSH and LH (ISU) but are now being replaced by highly purified urinary FSH or rDNA-derived FSH (rFSH). The aim of this study was to evaluate two preparations of human rFSH and one preparation of highly purified urinary FSH as candidate WHO IS for bioassay in an international collaborative study by 27 laboratories in 12 countries, and to characterise them in a range of in vitro bioassays and immunoassays. The biological activity of the three candidate standards was confirmed by all laboratories using all assays contributed to the study. Dose-response relationships by in vivo bioassay for any of the candidate standards did not differ significantly from that for the ISU. Dose-response relationships obtained in in vitro bioassays and immunoassays were also broadly similar among these preparations although dose-response lines for some preparations appeared to be non-parallel in some immunoassays. For each of the three candidate IS, estimates of the relative potency in terms of ISU by in vivo bioassay did not differ significantly between laboratories. In contrast estimates by immunoassays and in vitro bioassays showed significant differences between laboratories. Estimates of relative potency of the highly purified candidate IS materials in terms of one another exhibited less inter-laboratory variability than estimates in term of ISU. Each of the candidate standards showed adequate stability to serve as an IS. On the basis of the results of this study rFSH (code 92/642) was established as the first IS for FSH, human, recombinant for bioassay with an assigned unitage of 138 IU per ampoule and urinary FSH (code 92/512) was established as the first IS for FSH, human, urinary (urofollitropin) for bioassay with an assigned unitage of 121 IU per ampoule, based on their respective calibration by in vivo bioassay in terms of ISU. These assignments of unitage maintain continuity of unitage for preparations in therapeutic use and also appear to be consistent with one another.

Epoetin alfa and beta differ in their erythropoietin isoform compositions and biological properties.

Epoetin alfa and beta are the two forms of recombinant DNA-derived erythropoietin (rEPO), both synthesized in Chinese hamster ovary cells, which are used for the treatment of erythropoietin (EPO)-responsive anaemias. Several batches of each of these rEPOs were compared for differences in their EPO isoform compositions by isoelectric focusing (IEF) and in a range of lectin-binding assays, and for differences in their EPO activities by in-vivo and in-vitro mouse bioassays and by immunoassay. Epoetin beta was found to differ from epoetin alfa in containing: (a) a greater proportion of more basic isoforms, (b) a greater proportion of EPO binding to Erythrina cristagalli agglutinin (which binds N-glycans with nonsialylated outer Gal beta1-4GlcNAc moieties), and (c) isoforms with higher in-vivo:in-vitro bioactivity ratios. Epoetin beta also contained slightly more than epoetin alfa of EPO binding to Lycopersicon esculentum agglutinin (which binds N-glycans containing repeating Gal beta1-4GlcNAc sequences), to the leucoagglutinin of Phaseolus vulgaris (which binds tetraantennary and 2,6-branched triantennary N-glycans) and to Agaricus bisporus agglutinin (which binds Gal beta1-3GalNAc containing O-glycans). No differences were found between the two rEPOs in their binding to a further five lectins. The differences between the isoform composition of epoetin alfa and beta, and the smaller inter-batch differences appear to be due to differences in glycosylation. The higher murine in-vivo:in-vitro bioactivity ratio of epoetin beta compared to epoetin alfa could not be explained in terms of differences in their degrees of sialylation, but was consistent with differences in their pharmacokinetics and pharmacodynamics observed in human subjects. There have been no reports that epoetin alfa differs from epoetin beta in its clinical efficacy, but the differences between epoetin alfa and beta in some analytical systems suggest that there might be a need for separate international standards for these two types of rEPO.

Lectin-binding assays for the isoforms of human erythropoietin: comparison of urinary and four recombinant erythropoietins.

Assays have been developed for the isoforms of erythropoietin (EPO) based on their binding to eight different lectins. These assays were used to compare the isoform compositions of two preparations of human urinary EPO (uEPO) and four preparations of recombinant DNA-derived human EPO (rEPO), which had been shown to differ in their biological and immunological properties and in their isoform composition as judged by isoelectric focusing and electrophoresis. Agarose-bound Ricinus communis agglutinin I (RCA), Erythrina cristagalli agglutinin (ECA), Maackia amurensis leukoagglutinin (MAL), Sambucus nigra agglutinin (SNA), Lycopersicon esculentum agglutinin (LEA), concanavalin A (Con A), Phaseolus vulgaris agglutinin-L4 (L-PHA) and Agaricus bisporus agglutinin (ABA) were used to bind EPO isoforms possessing: N-glycans containing non-sialylated outer Gal beta 1-4GlcNAc (RCA and ECA), NeuAc alpha 2-3Gal beta 1-4GlcNAc (MAL), NeuAc alpha 2-6Gal (SNA), or repeating Gal beta 1-4GlcNAc sequences (LEA); biantennary N-glycans (Con A); tetraantennary and 2,6-branched triantennary N-glycans (L-PHA); and O-glycans containing NeuAc alpha 2-6GalNAc (SNA) and Gal beta 1-3GalNAc (ABA). Free EPO was measured by mouse spleen cell bioassay or immunoassay. Estimates from most lectin-binding assays were reproducible between assays and batches of lectin-agarose, although batches of MAL- and ABA-agarose, and to a lesser extent LEA-agarose, differed in their EPO-binding. Lectin-binding assays showed differences between the isoform compositions of all EPOs, including the two Chinese hamster ovary cell-derived rEPOs, with RCA- and ECA-binding assays being the most discriminating. Lectin-binding estimates provided evidence that uEPO differs from these rEPOs in its lower content of isoforms with biantennary N-glycans and higher content of those with multiantennary N-glycans, and in its lower content of isoforms with N-glycans possessing repeating Gal beta 1-4GlcNAc sequences and of those with O-glycans containing Gal beta 1-3GalNAc. Lectin-binding estimates also indicated that, contrary to some reports, uEPO possesses Gal beta 1-3GalNAc-containing O-glycans but not NeuAc alpha 2-6GalNAc-containing O-glycans or NeuAc alpha 2-6Gal-containing N-glycans. Most groups of lectin-bound EPO isoforms did not differ in their relative bioactivities and immunoreactivities. However, estimates for ABA-bound EPO isoforms suggested that O-glycans might influence the bioactivity of EPO differently to its immunoreactivity. Furthermore, the bioactivities of some ECA-bound EPO isoforms were higher, and those of some of the MAL-bound EPO isoforms lower, than their immunoreactivities, consistent with the reported enhancement of EPO in vitro bioactivity by desialylation.

Therapeutic botulinum type A toxin: factors affecting potency.

The type A neurotoxin produced by Clostridium botulinum is a potent neuromuscular blocking agent which causes paralysis by preventing the release of neurotransmitter from motor neurons. This property has resulted in the use of the toxin in the treatment of a number of neuromuscular diseases involving muscle spasms. At present, the only recognised assay to estimate accurately the potency of botulinum toxin in clinical preparations is bioassay, in which lethality is used as the endpoint. Such bioassay is inherently variable and large interlaboratory variability has been reported, highlighting problems for standardisation of activity in the absence of any commonly used reference preparation. In the present study, we have confirmed that many different assay conditions can affect potency estimates of clinical formulations of type A botulinum toxin. Further, our studies indicate that different preparations, because of their unique formulation and stability, are differentially affected by some of these assay conditions and that these differences might well contribute to the differences observed in their clinical use.

International collaborative study by in vitro bioassays and immunoassays of the First International Standard for Inhibin, Human Recombinant.

The First International Standard for Inhibin, Human Recombinant, (ISI), a lyophilized preparation of rDNA-derived human 32 kDa Inhibin A in ampoules coded 91/624, was evaluated by international collaborative study for its suitability to serve as an International Standard. This study, which involved 15 laboratories in nine countries, included a variety of in vitro bioassays and immunoassays. The ISI was compared with two other lyophilized preparations of human recombinant inhibin, the International Standard for Porcine inhibin (ISP) and preparations of human follicular fluid inhibin. Predicted loss of activity based on estimates of potency of contents of ampoules which had been stored under conditions of accelerated thermal degradation indicated that the ISI has satisfactory stability. On the basis of the results of this study, the ISI was deemed suitable to serve as a standard for in vitro bioassays and immunoassays and was established by the Expert Committee on Biological Standardization of the World Health Organization as the First International Standard for inhibin, recombinant human, with an assigned unitage of 150,000 International Units per ampoule. This unitage maintains an approximate continuity of units with the ISP.

Evaluation of assay designs for assays using microtitre plates: results of a study of in vitro bioassays and immunoassays for tumour necrosis factor (TNF).

Biological assays for tumour necrosis factor (TNF) are primarily based on its cytotoxic effect in tumour cell lines, and many of these bioassays are carried out using microtitre plates. Many immunoassays for TNF also routinely use microtitre plates. Data from an international collaborative study, carried out by twenty participants in nine countries, each of whom evaluated seven different ampouled preparations of human tumour necrosis factor alpha (hTNF-alpha), one ampouled preparation of human tumour necrosis beta (hTNF-beta) and one ampouled preparation of mouse tumour necrosis factor alpha (mTNF-alpha) provided a unique opportunity for a broadly based evaluation and comparison of assay designs and results. The results of this evaluation can be applied to a wide range of in vitro assays based on cell cytotoxicity or proliferation. The results of this evaluation indicated that although it is difficult to achieve control of all factors which contribute to the variability of assay responses, assays may be designed to provide measures of the variation due to some factors and to improve reliability of estimates of relative potency.

Enhanced potency of human calcitonin when fibrillation is avoided.

The peptide hormone calcitonin (CT) is a potent drug for the therapy of different bone diseases. Salmon CT (sCT) is reported to be more active than human CT (hCT). Human CT, but not sCT, has a strong tendency to aggregate and fibrillate in aqueous solutions. Recent investigations of the fibrillation mechanisms contributed to the development of hCT solutions in which fibrillation is inhibited. Taking into consideration these new findings, we tested the relative activities of hCT handled so as to avoid aggregation/fibrillation, sCT handled in exactly the same way, and hCT handled carefully but without regard to possible fibrillation (denoted R-hCT). The effect of the CTs on bone resorption by isolated osteoclasts was measured. This assay measures the activity of interest (bone resorption) by the cell (the osteoclast) at which therapy is directed. The concentration that inhibits 50% of resorption (EC50) for hCT is 10(-5)-10(-4) pg/mL, compared with 10(-2)-1 pg/mL for R-hCT and 10(-3)-10(-1) pg/mL for sCT. The results show that when aggregation and fibrillation are avoided, hCT at the EC50 is 2-4 orders of magnitude more active than R-hCT. Thus, earlier reports of lower potency of hCT compared with sCT may have been based on inadvertent use of partially aggregated/fibrillated samples of hCT. This finding may have implications for the dose and dosage forms advised for human therapy.

Dimensional analysis of osteoclastic bone resorption and the measurement of biologically active calcitonin.

Calcitonin inhibits bone resorption through a direct action on the osteoclast. We report a quantitative analysis of bone resorption by disaggregated rat osteoclasts. We then used our findings to develop a formal bioassay for calcitonin. Osteoclasts were mechanically disaggregated from neonatal rat long bones and dispersed at low densities on slices of devitalized bovine cortical bone. The resulting areas of bone excavation were quantified to micrometric precision by scanning electron microscopy together with computer-assisted image analysis. These findings were correlated with the volumes of bone resorption in the same slices measured by confocal scanning microscopy for the first time. The total planar areas of bone resorption per slice correlated linearly (r = 0.78) with the confocal microscopic measurements of total volume resorbed, provided that volume was expressed to its two-thirds power. The latter transformation resulted in representations of the determined areas ([length]2) and volumes ([length]3) which were dimensionally consistent. These findings thus demonstrate that osteoclastic bone excavations show a consistent relationship between area and volume and that assessments of the area of excavations accordingly provide an empirical representation of the volume of bone resorbed. Furthermore, in view of the skewed nature of the distributions of area measurements, we assessed the effect of transforming the response variable to derive a metameter, (planar area of resorption)1/2. Such transformed data points, which expressed the data in the dimensions of [length], were more normally distributed than the raw data points and had more stable variances over a wider concentration range. We accordingly determined relative potencies using parallel line analyses on the transformed data. The latter offered a consistent correlation to the volume measurements when these were also converted to dimensions of [length] (r = 0.805). It was confirmed that the inhibition of bone resorption by calcitonins from various species, namely, pig, salmon and eel, was quantitatively dependent upon concentration of the respective peptides. The resulting assay was also found to be sufficiently sensitive to measure picomolar peptide concentrations with a precision, lambda (standard deviation/slope), ranging between 0.3 and 0.8. Finally, we identified factors affecting assay precision and sensitivity.