Structure-based secondary structure-independent approach to design protein ligands: Application to the design of Kv1.2 potassium channel blockers

We have developed a structure-based approach to the design of protein ligands. This approach is based on the transfer of a functional binding motif of amino acids, often referred as to the "hot spot", on a host protein able to reproduce the functional topology of these residues. The scaffolds were identified by a systematic in silico search in the Protein Data Bank for proteins possessing a group of residues in a topology similar to that adopted by the functional motif in a reference ligand of known 3D structure. In contrast to previously reported studies, this search is independent of the particular secondary structure supporting the functional motif. To take into account the global properties of the host protein, two additional criteria were taken into account in the selection process: (1) Only those scaffolds sterically compatible with the positioning of the functional motif as observed in a reference complex model were retained. (2) Host proteins displaying electrostatic potentials, in the region of the transferred functional motif, similar to that of the reference ligand were selected. This approach was applied to the development of protein ligands of the Kv1.2 channel using BgK, a small protein isolated from the sea anemone Bunodosoma granulifera, as the reference ligand. Four proteins obtained by this approach were produced for experimental evaluation. The X-ray structure of one of these proteins was determined to check for similarity of the transferred functional motif with the structure it adopts in the reference ligand. Three of these protein ligands bind the Kv1.2 channel with inhibition constants of 0.5, 1.5, and 1.6 microM. Several mutants of these designed protein ligands gave binding results consistent with the presumed binding mode. These results show that protein ligands can be designed by transferring a binding motif on a protein host selected to reproduce the functional topology of this motif, irrespective to the secondary structure supporting the functional motif, if the host protein possesses steric and electrostatic properties compatible with the binding to the target. This result opens the way to the design of protein ligands by taking advantage of the considerable structural repertoire of the Protein Data Bank.

Isolation of a tarantula toxin specific for a class of proton-gated Na+ channels

Acid sensing is associated with nociception, taste transduction, and perception of extracellular pH fluctuations in the brain. Acid sensing is carried out by the simplest class of ligand-gated channels, the family of H(+)-gated Na(+) channels. These channels have recently been cloned and belong to the acid-sensitive ion channel (ASIC) family. Toxins from animal venoms have been essential for studies of voltage-sensitive and ligand-gated ion channels. This paper describes a novel 40-amino acid toxin from tarantula venom, which potently blocks (IC(50) = 0.9 nm) a particular subclass of ASIC channels that are highly expressed in both central nervous system neurons and sensory neurons from dorsal root ganglia. This channel type has properties identical to those described for the homomultimeric assembly of ASIC1a. Homomultimeric assemblies of other members of the ASIC family and heteromultimeric assemblies of ASIC1a with other ASIC subunits are insensitive to the toxin. The new toxin is the first high affinity and highly selective pharmacological agent for this novel class of ionic channels. It will be important for future studies of their physiological and physio-pathological roles.

Mapping the functional anatomy of BgK on Kv1.1, Kv1.2, and Kv1.3. Clues to design analogs with enhanced selectivity

BgK is a peptide from the sea anemone Bunodosoma granulifera, which blocks Kv1.1, Kv1.2, and Kv1.3 potassium channels. Using 25 analogs substituted at a single position by an alanine residue, we performed the complete mapping of the BgK binding sites for the three Kv1 channels. These binding sites included three common residues (Ser-23, Lys-25, and Tyr-26) and a variable set of additional residues depending on the particular channel. Shortening the side chain of Lys-25 by taking out the four methylene groups dramatically decreased the BgK affinity to all Kv1 channels tested. However, the analog K25Orn displayed increased potency on Kv1.2, which makes this peptide a selective blocker for Kv1.2 (K(D) 50- and 300-fold lower than for Kv1.1 and Kv1.3, respectively). BgK analogs with enhanced selectivity could also be made by substituting residues that are differentially involved in the binding to some of the three Kv1 channels. For example, the analog F6A was found to be >500-fold more potent for Kv1.1 than for Kv1.2 and Kv1.3. These results provide new information about the mechanisms by which a channel blocker distinguishes individual channels among closely related isoforms and give clues for designing analogs with enhanced selectivity.

Conformational and functional variability supported by the BPTI fold: solution structure of the Ca2+ channel blocker calcicludine

Calcicludine, a 60-amino acid protein isolated from the green mamba venom, has been recently identified as blocking a large set (i.e., L-, N- and P-type) of Ca2+ channels. The three-dimensional structure of calcicludine has been determined by NMR and molecular modeling using a data set of 723 unambiguous and 265 ambiguous distance restraints, as 33 phi and 13 chi1 dihedral angle restraints. Analysis of the 15 final structures (backbone root-mean-square deviation = 0.6 A) shows that calcicludine adopts the Kunitz-type protease inhibitor fold. Its three-dimensional structure is similar to that of snake K+ channel blockers dendrotoxins. Conformational differences with protease inhibitors and dendrotoxins are localized in the 3(10) helix and loop 1 (segments 1-7 and 10-19), the extremity of the beta-hairpin (segment 27-30), and loop 2 (segment 39-44). These regions correspond to the functional sites of bovine pancreatic trypsin inhibitor (BPTI) and dendrotoxins. The positioning of the N-terminal segment 1-7 relative to the rest of the protein is characteristic of calcicludine. The involvement of this segment and the positively charged K31 at the tip of the beta-hairpin in the biological activity of calcicludine is discussed.

Delineation of the functional site of alpha-dendrotoxin. The functional topographies of dendrotoxins are different but share a conserved core with those of other Kv1 potassium channel-blocking toxins

We identified the residues that are important for the binding of alpha-dendrotoxin (alphaDTX) to Kv1 potassium channels on rat brain synaptosomal membranes, using a mutational approach based on site-directed mutagenesis and chemical synthesis. Twenty-six of its 59 residues were individually substituted by alanine. Substitutions of Lys5 and Leu9 decreased affinity more than 1000-fold, and substitutions of Arg3, Arg4, Leu6, and Ile8 by 5-30-fold. Substitution of Lys5 by norleucine or ornithine also greatly altered the binding properties of alphaDTX. All of these analogs displayed similar circular dichroism spectra as compared with the wild-type alphaDTX, indicating that none of these substitutions affect the overall conformation of the toxin. Substitutions of Ser38 and Arg46 also reduced the affinity of the toxin but, in addition, modified its dichroic properties, suggesting that these two residues play a structural role. The other residues were excluded from the recognition site because their substitutions caused no significant affinity change. Thus, the functional site of alphaDTX includes six major binding residues, all located in its N-terminal region, with Lys5 and Leu9 being the most important. Comparison of the functional site of alphaDTX with that of DTX-K, another dendrotoxin (Smith, L. A., Reid, P. F., Wang, F. C., Parcej, D. N., Schmidt, J. J., Olson, M. A., and Dolly, J. O. (1997) Biochemistry 36, 7690-7696), reveals that they only share the predominant lysine and probably a leucine residue; the additional functional residues differ from one toxin to the other. Comparison of the functional site of alphaDTX with those of structurally unrelated potassium channel-blocking toxins from venomous invertebrates revealed the common presence of a protruding key lysine with a close important hydrophobic residue (Leu, Tyr, or Phe) and few additional residues. Therefore, irrespective of their phylogenetic origin, all of these toxins may have undergone a functional convergence. The functional site of alphaDTX is topographically unrelated to the "antiprotease site" of the structurally analogous bovine pancreatic trypsin inhibitor.

On the convergent evolution of animal toxins. Conservation of a diad of functional residues in potassium channel-blocking toxins with unrelated structures

BgK is a K+ channel-blocking toxin from the sea anemone Bunodosoma granulifera. It is a 37-residue protein that adopts a novel fold, as determined by NMR and modeling. An alanine-scanning-based analysis revealed the functional importance of five residues, which include a critical lysine and an aromatic residue separated by 6.6 +/- 1.0 A. The same diad is found in the three known homologous toxins from sea anemones. More strikingly, a similar functional diad is present in all K+ channel-blocking toxins from scorpions, although these toxins adopt a distinct scaffold. Moreover, the functional diads of potassium channel-blocking toxins from sea anemone and scorpions superimpose in the three-dimensional structures. Therefore, toxins that have unrelated structures but similar functions possess conserved key functional residues, organized in an identical topology, suggesting a convergent functional evolution for these small proteins.

Development of highly potent and selective phosphinic peptide inhibitors of zinc endopeptidase 24-15 using combinatorial chemistry

Several hundred phosphinic peptides having the general formula Z-(L,D)Phe psi (PO2CH2)(L,D)Xaa'-Yaa'-Zaa', where Xaa' = Gly or Ala and Yaa' and Zaa' represent 20 different amino acids, have been synthesized by the combinatorial chemistry approach. Peptide mixtures or individual peptides were evaluated for their ability to inhibit the rat brain zinc endopeptidases 24-15 and 24-16. Numerous phosphinic peptides of this series act as potent (Ki in the nanomolar range) mixed inhibitors of these two peptidases. However, our systematic and comparative strategy led us to delineate the residues located in P2' and P3' positions of the inhibitors that are preferred by these two peptidases. Thus, endopeptidase 24-15 exhibits a marked preference for inhibitors containing a basic residue (Arg or Lys) in the P2' position, while 24-16 prefers a proline in this position. The P3' position has less influence on the inhibitory potency and selectivity, both peptidases preferring a hydrophobic residue at this position. On the basis of these observations, we have prepared highly potent and selective inhibitors of endopeptidase 24-15. The Z-(L,D)Phe psi-(PO2CH2)(L,D)Ala-Arg-Met compound (mixture of the four diastereoisomers) displays a Ki value of 70 pM for endopeptidase 24-15. The most selective inhibitor of endopeptidase 24-15 in this series, Z-(L,D)Phe psi (PO2-CH2)(L,D)Ala-Arg-Phe, exhibits a Ki value of 0.160 nM and is more than 3 orders of magnitude less potent toward endopeptidase 24-16 (Ki = 530 nM). Furthermore, at 1 microM this selective inhibitor is unable to affect the activity of several other zinc peptidases, namely endopeptidase 24-11, angiotensin-converting enzyme, aminopeptidase M, leucine aminopeptidase, and carboxypeptidases A and B. Therefore, Z-(L,D)Phe psi (PO2CH2)(L,D)Ala-Arg-Phe can be considered as the most potent and specific inhibitor of endopeptidase 24-15 developed to date. This new inhibitor should be useful in assessing the contribution of this proteolytic activity in the physiological inactivation of neuropeptides known to be hydrolyzed, at least in vitro, by endopeptidase 24-15. Our study also demonstrates that the combinatorial chemistry approach leading to the development of phosphinic peptide libraries is a powerful strategy for discovering highly potent and selective inhibitors of zinc metalloproteases and should find a broader application in studies of this important class of enzymes.

Three-dimensional structure of cyclohexapeptides containing a phosphinic bond in aqueous solution: a template for zinc metalloprotease inhibitors. A NMR and restrained molecular dynamics study

The 3D structures of two phosphinic cyclic hexapeptide inhibitors of bacterial collagenase, cyclo-(Gly1-Pro2-Phe3 psi[PO2-CH2]Gly4-Pro5-Nle6) (compound I) and cyclo(Gly1-Pro2-D-Phe3 psi[PO2-CH2]-Gly4-Pro5-Nle6) (compound II), in aqueous solution, as derived from NMR spectroscopy and molecular dynamics simulations, are described. The general structures of these cyclic hexapeptides closely resemble the "canonic" two-reverse-turn structure, with the proline occupying the (i + 1) position of the turns and the glycine the connecting positions. The phosphinic bond is located between the (i + 2) and (i + 3) positions of one of these turns. However, a striking feature of the backbone structure of these peptides is the presence of double type VIII-turns in compound I, and in compound II of type VIII- and tentatively named type IX-turns. The comparison of the 3D structures of these two cyclic hexapeptides shows that the stereochemistry of the phenylalanylphosphinyl residue influences not only the local conformation but also the global topology of the peptide macrocycle. The differences in the 3D structure of these compounds are discussed in relation to their inhibitory potencies and with the view of using these constrained cyclic peptides as a scaffold for the development of rigid metalloproteases inhibitors.

Phosphinic peptide analogues as potent inhibitors of Corynebacterium rathayii bacterial collagenase

Pseudo-substrate analogues of collagenase from Corynebacterium rathayii, in which the scissile peptide bond is replaced by a phosphinic moiety, were synthesized and evaluated as inhibitors of this enzyme. The phosphinic tetrapeptide, Z-Phe-psi(PO2CH2)-Gly-Pro-Nle (1), was found to be a potent inhibitor of collagenase with a Ki value of 8 nM. Increasing the length of the phosphinic-containing inhibitors from tetra- to hepta-peptide size further improves the potency of these compounds. The heptapeptide analogue, Z-Phe-Gly-Pro-Phe-psi(PO2CH2)-Gly-Pro-Nle-OMe, with a Ki value of 0.6 nM, is the most potent inhibitor reported to date for bacterial collagenases. A comparison between the phosphinic analogue Z-Phe-psi(PO2CH2)-Gly-Pro-Nle (1) and the phosphonamide peptide Z-Phe-psi(PO2NH)-Gly-Pro-Nle (2) shows that for bacterial collagenase the replacement of a CH2 by an NH group results only in a modest increase in affinity from Ki = 8 nM for compound 1 to Ki = 6 nM for compound 2. Most of the phosphorus-containing inhibitors of this series are slow- or slow-tight-binding inhibitors with second-order rate constants for association and dissociation varying respectively for the kon values from 1 x 10(3) to 26 x 10(3) M-1.s-1 and for the koff values from 3 x 10(-4) to 2 x 10(-5) s-1. Interestingly, the lower affinity of the molecule containing a D residue in the P1 position of the inhibitor, compared with the molecule with an L residue in this position, is mainly the consequence of a lower rate constant for association of these D stereoisomers with the enzyme. This study demonstrates that phosphinic peptide analogues are potent inhibitors of a bacterial collagenase. The development of new phosphinic peptides should lead to the discovery of potent inhibitors of other zinc metalloproteases. Details of how the analogues were synthesized are given in Supplementary Publication SUP 50176 (14 pages), which has been deposited with the British Library Document Supply Centre, Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, from whom copies can be obtained on the terms indicated in Biochem. J. (1994) 297, 9.

Cyclic peptides with a phosphinic bond as potent inhibitors of a zinc bacterial collagenase

A series of cyclic peptides containing a phosphinic bond were synthesized and evaluated as inhibitors of a zinc bacterial collagenase from Corynebacterium rathaii. Among this series of pseudopeptides of different sizes of cycles, only two molecules Ia (cyclo[Gly-Pro-Phe psi(PO2CH2)-Gly-Pro-Ahx]) and Va (cyclo[beta Ala-Pro-Phe psi (PO2CH2)Gly-Pro-Ahx]) were found to be rather potent inhibitors of this protease, with Ki values of 120 and 90 nM, respectively. Besides the influence of the peptide ring size, this study suggests that both the stereochemical and the conformational properties of the pseudophenylalanine residue in these cyclic peptides may determine their potency. Interestingly, the kinetic analysis for the binding of the cyclic peptide inhibitors Ia and Va to the collagenase, as compared to a linear parent compound, reveals that the lower potency of the cyclic peptides is mostly the consequence of a lower rate constant for association to the enzyme. To our knowledge, this is the first report on cyclic phosphinic peptides and on their activities as inhibitors of a zinc protease.

Controlled comparison of nefazodone and amitriptyline in major depressive inpatients

Nefazodone, a phenylpiperazine antidepressant, exhibits novel dual activity on serotonin (5-HT) neurons; it binds to 5-HT2 receptors and inhibits 5-HT reuptake. Flexible doses of nefazodone (100-400 mg/day) and amitriptyline (50-200 mg/day) were compared in 106 major depressive inpatients in a 6-week double-blind study. Results showed significant superiority of amitriptyline over nefazodone on all rating instruments: Montgomery and Asberg depression rating scale (P < 0.0001), Hamilton depression scale (P < 0.0006), Clinical Global Impressions (P < 0.0001) and Patient Global Assessment (P < 0.01). A total of 65% of patients under amitriptyline and 56% of patients under nefazodone reported adverse events during the study, with significantly more dry mouth in the amitriptyline group (39% versus 11%, P = 0.001). Modal daily doses within the last treatment week reached 242 mg with nefazodone and 124 mg with amitriptyline. The lower efficacy of nefazodone, which contradicts comparative trials with imipramine in US patients, is discussed with regard to the dose of nefazodone, probably below the optimal therapeutic range for melancholic patients, and to the clinical differences between the patient samples.

X-ray conformational study of hydrazino peptide analogues

We have solved the crystal structures of nine pseudo-peptide analogues deriving from the hydrazino analogue of glycine or valine (N beta H2-N alpha H-C alpha HR-CO2H, R = H or iPr) or proline (N beta H2-N alpha-C alpha H-CO2H) and containing the hydrazide (CO-N beta H-N alpha less than) or N beta-Z-aminoamide [formula; see text] [CO-N alpha(N beta HZ)] peptidomimetic link. This study gives access to the average geometry of these two links, to their inter- and intramolecular interaction modes, and to their influence on the conformational properties of the molecules.

Effects of human chorionic gonadotropin, androgens, adrenocorticotropin hormone, dexamethasone and hyperprolactinemia on plasma sex steroid-binding protein

This presentation reports the effects of androgens, glucocorticoids and some pituitary hormones on plasma sex steroid-binding protein (SBP). The latter was measured by a solid phase method after desteroidation of the plasma. An hCG test (1500 I.U. every other day X 7) was given to 60 boys. In the children with a normal testosterone (T) rise, plasma SBP decreased (% of basal values) either significantly (38.3 +/- 9.3%, group A; n = 29), or moderately (13.4 +/- 4.4%, group B; n = 9) or did not change (-1.6 +/- 6.4%, group C; n = 10). In the 3 infants tested at an age when SBP normally rise sharply, hCG partially prevented this rise. The administration of either fluoxymesterone (10 mg/m2 for 10 days) or depot-T (4 I.M. injections of 100 mg/m2 every 2 weeks) induced a significant drop (about 2-fold) in plasma SBP in a control group of infants or children, but did not change SBP in 3 infants with the androgen insensitivity syndrome. A single injection of 0.25 mg of ACTH did not significantly alter SBP levels. In contrast, at the end of a 3-day ACTH test (0.5 mg/m2 12 hourly X 6) SBP levels had significantly decreased (mean 35% fall) with no age or sex differences, and with no correlation with the cortisol levels reached. However, the lowering effect of ACTH on SBP levels is likely mediated by glucocorticoids, since its effect was reproduced by high doses (8 mg/day for 3 days) of dexamethasone given at once or after 3 days of treatment at lower dose (20 micrograms/kg BW). It would appear that the depressive effect of ACTH and/or dexamethasone is observed for a threshold dose of glucocorticoids (greater than 5-fold physiological levels) and a certain time (greater than or equal to 3 days) of exposure. The mechanism by which androgens and glucocorticoids lower SBP levels in vivo is not yet understood. From recent experiments, showing that both stimulate the secretion of SBP in hepatoma cells in vitro, it would appear that both hormones may alter SBP metabolism. In a selected population of hyperprolactinemic women, with normal weight and no hirsutism, plasma SBP levels were found in the normal female range. The discrepancy with previous studies in the literature may be explained by differences in the degree of hyperprolactinemia and/or associated hyperandrogenim. This study further documents the multifactorial and intricated hormonal influences involved in the regulation of plasma SBP in vivo.

[Videotape recording of the French-language AMDP system]

To improve the objectivity and the quantification of psychopathology necessitates the rating and analysis of audiovisual recordings. After a brief survey of applications of video in psychiatry, the author describes the original methodology elaborated by the French-speaking section of the AMDP under the direction of the Liège team: semi-structured interview, combination of a "clinical" analysis of the reasons for a poor interrater-reliability (through one or several "observers" of the discussions which follow a projection) and of a multivariate statistical analysis adapted to single cases (through a modification of the obverse factor analysis or Q-technique), "consensus" item scores and final "reference" rating of a patient. Finally, the author briefly discusses the technical and ethical problems linked to the circulation of videotapes.

[Critical flicker fusion frequency in psychopathology and psychopharmacology. Review of the literature]

As far back as the second century, Ptolemy reported the apparent immobility of wheel radius at a certain speed. The psychophysical laws of this flicker fusion phenomenon related to the frequency of the light stimulus were established in 1834-1835 by the Englishman Talbot and by the Belgian Plateau, whose thesis in Liège is described as a landmark in the field. CFF is more a measurement of cortical arousal than of visual functions. In psychophysiology, CFF underwent periods of success and oblivion, at the mercy of researcher's enthusiasm or disappointment. At the turn of this century, Pierre Janet measured CFF in the laboratory of physiology of the Salpêtrière Hospital and demonstrated its decrease 'in hysteria, in states of depression, of lowered tension'. All reviewers of CFF literature have overlooked these observations, reported by Henri Piéron in the 'Melanges dedicated to Monsieur Pierre Janet'. When CFF falls into disgrace, it is because of the variability of its results, due to differences in apparatus and designs of the trials as well as the great number and the intrication of the variables which modify CFF thresholds, among them the nonsensory variables. When CFF is reappraised, as it has been the case in psychopharmacology in recent years, the reason is that it represents a brief, easy and economical measure of vigilance which, under certain conditions, seems to be also reliable, valid and sensitive. In the present monograph, the first in French on CFF, the authors try to analyze the most important contributions of the literature from the standpoint of the most relevant variables: characteristics of the stimulus (light intensity, wave form, wavelength, light-dark-ratio, diameter of the flickering point), test procedure (light vs. dark adaptation, visual angle, continuous vs. discontinuous presentation, monocular vs. binocular vision), influence of various physiological or psychological conditions (pupillary diameter, age, training, IQ; anxiety, depression, motivation etc.). The authors summarize the prerequisite for CFF to measure vigilance or aging in psychopharmacological research. The present Monograph is dedicated to the authors' 'Maîtres', who recently became Emeritus Professors, namely the ophthalmologist Roger Weekers, the pioneer of the clinical application of CFF in Belgium, and the psychiatrist Jean Bobon, who pioneered clinical psychopharmacology in Belgium.

Concentration of 14 steroid hormones in human amniotic fluid of midpregnancy

Amniotic fluid (AF) levels of all steroids leading from pregnenolone (delta 5Preg) to androgens and estrogens of both the delta 5 and the delta 4 pathways and those of cortisol and cortisone have been determined in 63 normal pregnancies (12-19 weeks gestation). The 12 unconjugated steroids [delta 5Preg, 17 alpha-hydroxypregnenolone, progesterone, 17 alpha-hydroxyprogesterone, dehydroepiandrosterone (DHA), delta 4-androstenedione, delta 5-androstene-3 beta,17 beta-diol (delta 5Adiol), testosterone (T), estrone, 17 beta-estradiol (E2), cortisol, and cortisone] were measured by specific RIAs after appropriate purification by Celite or LH-20 column chromatography, while the sulfates of DHA and delta 5Preg were assayed directly on diluted samples. There were distinct sex differences; T and delta 4-androstenedione levels were higher (P < 0.001) in males than in females, while AF levels of delta 5Preg, 17 alpha-hydroxypregnenolone, 17-hydroxyprogesterone, DHA, and delta 5Adiol were higher (P < 0.05) in females than in males. AF levels of E2 were significantly higher in females only between 15 and 19 weeks gestation. There was no difference between sexes in AF levels of progesterone, estrone, cortisone, and cortisol. AF levels of T, delta 4-androstenedione, and E2 decreased with age in males, and AF levels of DHA increased in females during the period examined. These observed sex differences suggest that T and delta 4-androstenedione may reflect fetal testicular activity, while E2 and 17-hydroxyprogesterone might reflect fetal ovarian activity. Determination of AF levels of T would appear to be a valuable screening test for antenatal diagnosis of sex (predictive error, less than or equal to 15%), but not in the presence of steroidogenic enzyme defects. Elevated levels of 17-hydroxyprogesterone were found in the AF of two fetuses with either a 17-20 desmolase defect or 21-hydroxylase deficiency; AF levels of androgens were low in the former and high in the latter.

Kinetics of the HCG-induced steroidogenic response of the human testis. III. Studies in children of the plasma levels of testosterone and HCG: rationale for testicular stimulation test

Little information is available regarding the time, rhythm, number, and appropriate dosage of human chorionic gonadotropin (HCG) for adequate testing of testicular function in human. The time course of the effect of two, three, or seven HCG injections at intervals of one, five, and two days, respectively, on the plasma levels of testosterone was studied in 11 boys. The first injection induced a progressive and modest rise of T. The second given one day later had little additive effect, maximal values being seen 72 to 120 hr later. In the prepubertal boys to whom several HCG injections were given, testosterone levels reached comparable levels after four injections every five days or seven injections every other day. Although the number of subjects studied was relatively small, these results give some rational basis for the following HCG test: two or four injections at four-day intervals.