Characteristics and outcomes of critically ill Aboriginal and/or Torres Strait Islander patients in North Queensland.

A retrospective cohort analysis of an admission database for the intensive care unit at The Townsville Hospital was undertaken to describe the characteristics and short-term outcomes of critically ill Aboriginal and Torres Strait Islander patients. The Townsville Hospital is the tertiary referral centre for Northern Queensland and services a region in which Aboriginal and Torres Strait Islander people constitute 9.6% of the population. Aboriginal and Torres Strait Islander patients were significantly younger and had higher rates of invasive mechanical ventilation, emergency admissions and transfers from another hospital. Despite these factors, intensive care mortality did not differ between groups (9.4% versus 7.7%, P=0.1). Higher Acute Physiology and Chronic Health Evaluation III-j scores were noted in the Aboriginal and Torres Strait Islander population requiring emergency admission (65 versus 60, P=0.022) but were lower for elective admission (38 versus 42, P <0.001). Despite higher predicted hospital mortality for Aboriginal and Torres Strait Islander patients requiring emergency admission, no significant difference was observed (20.1% versus 19.1%, P=0.656). In a severity adjusted model, Aboriginal and/or Torres Strait Islander status did not statistically significantly alter the risk of death (odds ratio 0.88, 95% confidence interval 0.65, 1.2, P=0.398). Though Aboriginal and Torres Strait Islander patients requiring intensive care differed in admission characteristics, mortality was comparable to other critically ill patients.

AMD3100, a potent and specific antagonist of the stromal cell-derived factor-1 chemokine receptor CXCR4, inhibits autoimmune joint inflammation in IFN-gamma receptor-deficient mice.

Autoimmune collagen-induced arthritis (CIA) in IFN-gammaR-deficient DBA/1 mice was shown to be reduced in severity by treatment with the bicyclam derivative AMD3100, a specific antagonist of the interaction between the chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4. The beneficial effect of the CXCR4 antagonist was demonstrable when treatment was initiated between the time of immunization and appearance of the first symptoms. Treatment also reduced the delayed-type hypersensitivity response to the autoantigen, collagen type II. These observations are indicative of an action on a late event in the pathogenesis, such as chemokine-mediated attraction of leukocytes toward joint tissues. The notion of SDF-1 involvement was further supported by the observation that exogenous SDF-1 injected in periarthritic tissue elicited an inflammatory response that could be inhibited by AMD3100. The majority of leukocytes harvested from inflamed joints of mice with CIA were found to be Mac-1(+) and CXCR4(+), and AMD3100 was demonstrated to interfere specifically with chemotaxis and Ca(2+) mobilization induced in vitro by SDF-1 on Mac-1(+)/CXCR4(+) splenocytes. We conclude that SDF-1 plays a central role in the pathogenesis of murine CIA, by attracting Mac-1(+)/CXCR4(+) cells to the inflamed joints.

Mutation of Asp(171) and Asp(262) of the chemokine receptor CXCR4 impairs its coreceptor function for human immunodeficiency virus-1 entry and abrogates the antagonistic activity of AMD3100.

The bicyclam AMD3100 is a highly potent and selective CXCR4 antagonist with strong antiviral activity against human immunodeficiency virus (HIV)-1 and HIV-2, which use CXCR4 as coreceptor for host cell entry. Here, we investigated the interaction of AMD3100 with CXCR4 at the molecular level by mutational analysis. We established a set of stably transfected U87.CD4 cell lines expressing different mutant forms of CXCR4 (i.e., CXCR4[WT], CXCR4[D171N], CXCR4[D262N], CXCR4[D171N,D262N], and CXCR4[H281A]), to compare the activity of the compound against mutated versus wild-type CXCR4. We found that the antagonistic action of AMD3100 against CXCR4--as assessed by the inhibitory effects of the compound on stromal cell-derived factor (SDF-1) binding to its receptor and on SDF-1-induced intracellular calcium signaling, and by displacement of the CXCR4-specific antibody, clone 12G5--was greatly reduced by substitution of Asp(171) and/or Asp(262) by neutral asparagine residue(s). Both aspartates, but most particularly Asp(262), also proved essential for the anti-HIV-1 activity of AMD3100 against the viruses NL4.3, IIIB, and HE. In contrast, substitution of His(281) by a neutral alanine potentiated the antagonistic and antiviral effects of the compound in the different assay systems. Importantly, compared with the wild-type receptor, CXCR4[D262N] was much less effective, whereas CXCR4[D171N,D262N] completely failed as a coreceptor for infection by HIV-1 NL4.3. Thus, the negatively charged aspartate residues at positions 171 and 262, located in transmembrane domains 4 and 6 of the 7-transmembrane receptor, respectively, may represent crucial sites for electrostatic interaction of the positive charges of the bicyclams, as well as for the highly basic V3 loop of the gp120 envelope protein of certain HIV-1 strains.

Use of ultrasound to improve the safety of postgraduate training in obstetrics and gynaecology.

Supervised clinical work is perhaps the most valuable component of postgraduate training and has a long-term impact. Senior clinicians not only take the responsibility of teaching and supervising junior doctors but also most of them take the consequences of any clinical failures or mistakes associated with the training. Despite the introduction of simulators and computer-assisted learning, practice on real patients is still required to learn many skills in obstetrics and gynaecology. Training must be safe, because trainees or trainers must not put our patients at risk as part of the process of learning to heal others. Ultrasound can be used to demonstrate and guide several procedures that have been performed 'blindly' in the past. This technology can reduce the risks associated with training and supervision of junior doctors.

Pharmacokinetics and safety of AMD-3100, a novel antagonist of the CXCR-4 chemokine receptor, in human volunteers.

AMD-3100, a bicyclam, is a novel agent that uniquely inhibits the entry of human immunodeficiency virus type 1 (HIV-1) into CD4(+) T cells via selective blockade of the chemokine CXCR-4 receptor. Twelve healthy volunteers were given AMD-3100 as a single 15-min intravenous infusion at 10, 20, 40, or 80 microg/kg. Five subjects also received a single subcutaneous injection of AMD-3100 (40 or 80 microg/kg). Three subjects received two escalating oral doses each (80 and 160 microg/kg). All subjects tolerated their dose(s) well without any grade 2 toxicity or dose adjustment. Six subjects experienced mild, transient symptoms, primarily gastrointestinal in nature and not dose related. All subjects experienced a dose-related elevation of the white blood cell count, from 1.5 to 3.1 times the baseline, which returned to the baseline 24 h after dosing. AMD-3100 demonstrated dose proportionality for the maximum drug concentration in serum (C(max)) and the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) over the entire dose range. At the highest intravenous dose (80 microg/kg), the median C(max) was 515 (range, 470 to 521) ng/ml and the AUC(0-infinity) was 1,044 (range, 980 to 1,403) ng-h/ml. The median systemic absorption after subcutaneous dosing was 87% (range, 67 to 106%). No drug was detectable in the blood following oral dosing. Using a two-compartment model, the median pharmacokinetic parameter estimates (ranges) were as follows: volume of distribution, 0.34 (0. 27 to 0.36) liter/kg; clearance, 1.30 (0.97 to 1.34) liters/h; elimination half-life, 3.6 (3.5 to 4.9) h. After a single, well-tolerated intravenous dose of AMD-3100, concentrations were sustained for 12 h above the in vitro antiretroviral 90% inhibitory concentrations and for 8 h above antiviral concentrations identified in the SCID-hu Thy/Liv mouse model of HIV infection.

The CXCR4 antagonist AMD3100 efficiently inhibits cell-surface-expressed human immunodeficiency virus type 1 envelope-induced apoptosis.

Infection by human immunodeficiency virus type 1 (HIV-1) has been associated with increased cell death by apoptosis in infected and uninfected cells. The envelope glycoprotein complex ([gp120/gp41](n)) of X4 HIV-1 isolates is involved in both infected and uninfected cell death via its interaction with cellular receptors CD4 and CXCR4. We studied the effect of the blockade of CXCR4 receptors by the agonist stromal derived factor (SDF-1alpha) and the antagonist bicyclam AMD3100 on apoptotic cell death of CD4(+) cells in different models of HIV infection. In HIV-infected CEM or SUP-T1 cultures, AMD3100 showed antiapoptotic activity even when added 24 h after infection. In contrast, other antiviral agents, such as zidovudine, failed to block apoptosis under these conditions. The antiapoptotic activity of AMD3100 was also studied in coculture of peripheral blood mononuclear cells or CD4(+) cell lines with chronically infected H9/IIIB cells. AMD3100 was found to inhibit both syncytium formation and apoptosis induction with 50% inhibitory concentrations ranging from 0.009 to 0.24 microg/ml, depending on the cell type. When compared to SDF-1alpha, AMD3100 showed higher inhibitory potency in all cell lines tested. Our data indicate that the bicyclam AMD3100 not only inhibits HIV replication but also efficiently blocks cell-surface-expressed HIV-1 envelope-induced apoptosis in uninfected cells.

Synthesis and structure-activity relationships of phenylenebis(methylene)-linked bis-azamacrocycles that inhibit HIV-1 and HIV-2 replication by antagonism of the chemokine receptor CXCR4.

Bis-tetraazamacrocycles such as the bicyclam AMD3100 are a class of potent and selective anti-HIV-1 and HIV-2 agents that inhibit virus replication by binding to the chemokine receptor CXCR4, the co-receptor for entry of X4 viruses. With the aim of optimizing the anti-HIV-1 and HIV-2 activity of bis-azamacrocycles, a series of analogues were synthesized which contain neutral heteroatom (oxygen, sulfur) or heteroaromatic (of lower pK(a) than a secondary amine) replacements for the amino groups of AMD3100. The introduction of one or more heteroatoms such as oxygen or sulfur into the macrocyclic ring of p-phenylenebis(methylene)-linked dimers (to give N(3)X or N(2)X(2) bis-macrocycles) gave analogues with substantially reduced anti-HIV-1 (III(B)) and anti-HIV-2 (ROD) potency. In addition, the bis-sulfur analogue was also markedly more cytotoxic to MT-4 cells. However, bis-tetraazamacrocycles featuring a single pyridine group incorporated within the macrocyclic framework exhibited anti-HIV-1 and HIV-2 potency comparable to that of their saturated, aliphatic counterparts. The p-phenylenebis(methylene)-linked dimer of the py[14]aneN(4) macrocycle inhibited HIV-1 replication at a 50% effective concentration (EC(50)) of 0.5 microM while remaining nontoxic to MT-4 cells at concentrations approaching 200 microM. A series of analogues containing macrocyclic heteroaromatic groups of varying pK(a) were also synthesized, and their ability to inhibit HIV replication was evaluated. Replacing the pyridine moiety of the py[14]aneN(4) macrocyclic ring with pyrazine or pyridine groups substituted in the 4-position (with electron-withdrawing or -donating groups) either reduced antiviral potency or increased cytotoxicity to MT-4 cells. Finally, we synthesized a series of analogues in which the ring size of the bis-pyridyl macrocycles was varied between 12 and 16 members per ring including the py[iso-14]aneN(4) ring system, an isomer of the py[14]aneN(4) macrocycle. The p-phenylenebis(methylene)-linked dimer of the py[iso-14]aneN(4) (AMD3329) displayed the highest antiviral activity of the bis-azamacrocyclic analogues reported to date, exhibiting EC(50)'s against the cytopathic effects of HIV-1 and HIV-2 replication of 0.8 and 1.6 nM, respectively, that is, about 3-5-fold lower than the EC(50) of AMD3100. AMD3329 also inhibited the binding of a specific CXCR4 mAb and the Ca(2+) flux induced by SDF-1alpha, the natural ligand for CXCR4, more potently than AMD3100. Furthermore, AMD3329 also interfered with virus-induced syncytium formation at an EC(50) of 12 nM.

Evaluation of the potential of ion pair formation to improve the oral absorption of two potent antiviral compounds, AMD3100 and PMPA.

9-(2-phosphonyomethoxypropyl)adenine (PMPA) and AMD3100 are highly potent and selective antiretroviral agents. Since PMPA is negatively charged and AMD3100 positively charged at physiological pH, their transepithelial transport and their potential for oral drug delivery is very low. In this study, ion pair formation was evaluated as a possible strategy to enhance transepithelial transport of PMPA and AMD3100. Positively charged counter ions such as t-hexyl-, t-heptyl-, t-octylammonium bromide and dodecyl-, tetradecyl-, hexadecyltrimethylammonium bromide were used to form ion pairs with PMPA, while sodium taurodeoxycholate (in vitro experiments) and sodium taurocholate (in vivo experiments) were used as counter ions for AMD3100. The effect of counter ions on transepithelial transport of PMPA (1 mM) and AMD3100 (1 mM) was investigated by measuring the flux across Caco-2 monolayers. An enhancement in drug transport could be observed at a concentration of 2 mM of hexadecyltrimethylammonium bromide (counter ion for PMPA) and 10 mM of sodium taurodeoxycholate (counter ion for AMD3100), but at the concentrations used, the absorption enhancing effect could be attributed to a reduction of the integrity of the monolayers. When AMD3100 transport was tested at a concentration of 200 microM, no flux was observed, even in the presence of relatively high concentrations of counter ion (20 times the concentration of AMD3100). Results obtained from partitioning studies of the drugs in the presence or absence of counter ion revealed that competition by other ions was responsible for the absence of an effect: when pure water was used as the aqueous phase, a reduction up to 24.4+/-1.4% and 17.0+/-1.3% of the initial aqueous concentration was observed for PMPA and AMD3100, respectively; however, as soon as other ions were present in the aqueous phase, the effect of the counter ion was diminished (25-50 mOsm) or completely abolished (270-305 mOsm). The absorption enhancing effect of counter ions was also studied in vivo: pharmacokinetic studies in rabbits showed that the oral bioavailability of AMD3100 in the presence of 4 equivalents of taurocholic acid remained very low and was only 3.2-fold better (i.e. 3.6%) in comparison to pure AMD3100. In view of the results obtained in the Caco-2 system, this absorption enhancement can be attributed to an effect on monolayer integrity rather than to the potential to form ion pairs. We can conclude that the formation of ion pairs may not be very efficient as a strategy to enhance transepithelial transport of charged hydrophilic compounds, as competition by other ions may abolish the beneficial effect of counter ions.

Bicyclams, selective antagonists of the human chemokine receptor CXCR4, potently inhibit feline immunodeficiency virus replication.

Bicyclams are low-molecular-weight anti-human immunodeficiency virus (HIV) agents that have been shown to act as potent and selective CXC chemokine receptor 4 (CXCR4) antagonists. Here, we demonstrate that bicyclams are potent inhibitors of feline immunodeficiency virus (FIV) replication when evaluated in Crandell feline kidney (CRFK) cells. With a series of bicyclam derivatives, 50% inhibitory concentrations (IC50s) against FIV were obtained in this cell system that were comparable to those obtained for HIV-1 IIIB replication in the human CD4(+) MT-4 T-cell line. The bicyclams were also able to block FIV replication in feline thymocytes, albeit at higher concentrations than in the CRFK cells. The prototype bicyclam AMD3100, 1-1'-[1,4-phenylene-bis(methylene)]-bis(1,4,8, 11-tetraazacyclotetradecane), was only fourfold less active in feline thymocytes (IC50, 62 ng/ml) than in CRFK cells (IC50, 14 ng/ml). AMD2763, 1,1'-propylene-bis(1,4,8, 11-tetraazacyclotetradecane), which is a less potent CXCR4 antagonist, was virtually inactive against FIV in feline thymocytes (IC50, >66.5 microgram/ml), while it was clearly active in CRFK cells (IC50, 0.9 microgram/ml). The CXC chemokine stromal-cell-derived factor 1alpha had anti-FIV activity in CRFK cells (IC50, 200 ng/ml) but not in feline thymocytes (IC50, >2.5 microgram/ml). When primary FIV isolates were evaluated for their drug susceptibility in feline thymocytes, the bicyclams AMD3100 and its Zn2+ complex, AMD3479, inhibited all six primary isolates at equal potency. The marked susceptibility of FIV to the bicyclams suggests that FIV predominantly uses feline CXCR4 for entering its target cells.

Shift of clinical human immunodeficiency virus type 1 isolates from X4 to R5 and prevention of emergence of the syncytium-inducing phenotype by blockade of CXCR4.

The emergence of X4 human immunodeficiency virus type 1 (HIV-1) strains in HIV-1-infected individuals has been associated with CD4(+) T-cell depletion, HIV-mediated CD8(+) cell apoptosis, and an impaired humoral response. The bicyclam AMD3100, a selective antagonist of CXCR4, selected for the outgrowth of R5 virus after cultivation of mixtures of the laboratory-adapted R5 (BaL) and X4 (NL4-3) HIV strains in the presence of the compound. The addition of AMD3100 to peripheral blood mononuclear cells infected with X4 or R5X4 clinical HIV isolates displaying the syncytium-inducing phenotype resulted in a complete suppression of X4 variants and a concomitant genotypic change in the V2 and V3 loops of the envelope gp120 glycoprotein. The recovered viruses corresponded genotypically and phenotypically to R5 variants in that they could no longer use CXCR4 as coreceptor or induce syncytium formation in MT-2 cells. Furthermore, the phenotype and genotype of a cloned R5 HIV-1 virus converted to those of the R5X4 virus after prolonged culture in lymphoid cells. However, these changes did not occur when the infected cells were cultured in the presence of AMD3100, despite low levels of virus replication. Our findings indicate that selective blockade of the CXCR4 receptor prevents the switch from the less pathogenic R5 HIV to the more pathogenic X4 HIV strains, a process that heralds the onset of AIDS. In this article, we show that it could be possible to redirect the evolution of HIV so as to impede the emergence of X4 strains or to change the phenotype of already-existing X4 isolates to R5.

Activity of different bicyclam derivatives against human immunodeficiency virus depends on their interaction with the CXCR4 chemokine receptor.

Bicyclams represent a novel class of selective anti-HIV inhibitors with potent activity against T-cell tropic strains of HIV. The prototype compound, the bicyclam AMD3100, has an EC50 of 1 to 10 ng/ml against different strains of HIV-1, including clinical isolates. AMD3100 was shown to interact with the CXC-chemokine receptor CXCR4, the main coreceptor used by T-cell tropic strains of HIV. Here we describe the interaction of different bicyclam derivatives with CXCR4. A close correlation (r2 = 0.7) was found between the anti-HIV potency of the bicyclams and their ability to inhibit the binding of an anti-CXCR4 monoclonal antibody or the intracellular Ca++ signal induced by the stromal cell-derived factor-1alpha, the natural ligand of CXCR4. These results indicate that the mechanism of action of bicyclams is primarily mediated by their interaction with CXCR4. The most potent interaction with CXCR4 and thus anti-HIV activity was shown by bicyclam analogs with cyclam rings composed of fourteen members that are linked by an aromatic (phenyl) bridge. Elucidating the structural requirements for receptor interaction and the site(s) of interaction of bicyclams with CXCR4 will aid in the understanding of HIV-cell fusion.

The effect of physiological urine dilution on pregnancy test results in complicated early pregnancies.

This study addresses the likelihood of false negative urine pregnancy test results, due to physiological urine dilution as described in some anecdotal reports. In this prospective study 320 pregnancy tests were performed on urine samples of varying concentrations obtained from 40 women, with suspected complications of early pregnancy, who had presented for ultrasound scans. Four different pregnancy tests were used and serum betahCG levels were measured quantitatively. Despite a mean fivefold increase in urine dilution, the pregnancy tests with low betahCG detection limits maintained maximal sensitivity. The detection of betahCG in dilute urine was adversely affected by using pregnancy tests with higher betahCG detection limits and these tests should be used with caution when assessing gynaecological emergencies.

AMD3100, a small molecule inhibitor of HIV-1 entry via the CXCR4 co-receptor.

The bicyclam AMD3100 (formula weight 830) blocks HIV-1 entry and membrane fusion via the CXCR4 co-receptor, but not via CCR5. AMD3100 prevents monoclonal antibody 12G5 from binding to CXCR4, but has no effect on binding of monoclonal antibody 2D7 to CCR5. It also inhibits binding of the CXC-chemokine, SDF-1alpha, to CXCR4 and subsequent signal transduction, but does not itself cause signaling and has no effect on RANTES signaling via CCR5. Thus, AMD3100 prevents CXCR4 functioning as both a HIV-1 co-receptor and a CXC-chemokine receptor. Development of small molecule inhibitors of HIV-1 entry is feasible.

Inhibition of T-tropic HIV strains by selective antagonization of the chemokine receptor CXCR4.

Bicyclams are a novel class of antiviral compounds that are highly potent and selective inhibitors of the replication of HIV-1 and HIV-2. Surprisingly, however, when the prototype compound AMD3100 was tested against M-tropic virus strains such as BaL, ADA, JR-CSF, and SF-162 in human peripheral blood mononuclear cells, the compound was completely inactive. Because of the specific and potent inhibitory effect of AMD3100 on T-tropic viruses, but not M-tropic viruses, it was verified that AMD3100 interacts with the CXC-chemokine receptor CXCR4, the main coreceptor used by T-tropic viruses. AMD3100 dose dependently inhibited the binding of a specific CXCR4 monoclonal antibody to SUP-T1 cells as measured by flow cytometry. It did not inhibit the binding of the biotinylated CC-chemokine macrophage inflammatory protein (MIP) 1alpha or MIP-1beta, ligands for the chemokine receptor CCR5 (the main coreceptor for M-tropic viruses). In addition, AMD3100 completely blocked (a) the Ca2+ flux at 100 ng/ml in lymphocytic SUP-T1 and monocytic THP-1 cells, and (b) the chemotactic responses of THP-1 cells induced by stromal cell-derived factor 1alpha, the natural ligand for CXCR4. Finally, AMD3100 had no effect on the Ca2+ flux induced by the CC-chemokines MIP-1alpha, regulated on activation normal T cell expressed and secreted (RANTES; also a ligand for CCR5), or monocyte chemoattractant protein 3 (a ligand for CCR1 and CCR2b), nor was it able to induce Ca2+ fluxes by itself. The bicyclams are, to our knowledge, the first low molecular weight anti-HIV agents shown to act as potent and selective CXCR4 antagonists.

Bicyclams, a class of potent anti-HIV agents, are targeted at the HIV coreceptor fusin/CXCR-4.

Bicyclams are a novel class of antiviral compounds which are highly potent and selective inhibitors of the replication of HIV-1 and HIV-2. The prototype compound, AMD3100, has an IC50 of 1-10 ng/ml, which is a least 100,000 fold lower than the cytotoxic concentration. AMD3100 does not inhibit virus binding to the CD4 receptor and based on time-of-addition experiments, has been assumed to interact with the HIV fusion-uncoating process. Resistance of HIV-1 strains to AMD3100 is associated with the accumulation of several mutations in the viral envelope glycoprotein gp120. Here, we demonstrate that AMD3100 interacts with fusin (CXCR-4), the coreceptor used by T-tropic viruses to infect the target cells. The replication of NL4-3 wild type virus and NL4-3 dextran sulfate-resistant virus was inhibited by the CXC-chemokine, stromal cell-derived factor 1 (SDF-1), the natural ligand for CXCR-4. In contrast, the replication of the HIV-1 NL4-3 AMD3100-resistant virus was no longer inhibited by SDF-1. The bicyclams are the first low-molecular-weight anti-HIV agents shown to interact with the coreceptor for T-tropic viruses.

Birthweight for length: ponderal index, body mass index or Benn index?

This study compares how effectively the ponderal index and the body mass index adjust birthweight for length at different gestations, and derives an improved index suitable for all gestations. The study was a cross-sectional survey, in a London teaching hospital, using a total of 999 neonates of 33 weeks gestation or later. Main outcome measures were the ponderal index (birthweight/length3), body mass index (birthweight/length2), and Benn index (birthweight/length(n)), where the length power n varies with gestation and is estimated by log-log regression. Results showed that up to 39 weeks gestation, the ponderal index is uncorrelated with length and so is a good index of birthweight for length. Past 39 weeks gestation, the ponderal index is negatively correlated with length, while the body mass index is uncorrelated, so that the body mass index is better. Neither index is optimal at all gestations. Deriving the Benn index (birthweight/length(n)) for each week of gestation, choosing n to make the index uncorrelated with length, shows that n falls steadily and very significantly (p < 0.0001) with increasing gestation. This in turn means that predicted birthweight for length depends on gestation: for a neonate 48 cm long, predicted birthweight varies from 2485 g at 34 weeks to 3030 g at 43 weeks, a 20% range. However, for a 54 cm long infant, predicted birthweight is the same at all gestations. A Benn index where the value of n changes linearly with gestation is described. We conclude that the ponderal index is not appropriate for measuring intra-uterine malnutrition, as it fails to adjust for length at all gestations. No other index of birthweight/length(n) with constant n is any better, as different gestations require different indices. Birthweight predicted from an infant's length depends on the infant's gestation. If, as Barker proposes, thinness at birth assessed by birthweight for length is used to predict later health status, more account needs to be taken of the complex relationship between birthweight, length and gestation.

Tumor imaging with technetium-99m-labeled hydrazinonicotinamide-Fab' conjugates.

UNLABELLED: This study compares the in vivo properties of direct versus indirect 99mTc-labeling for two Fab' fragments from antibodies that recognize tumor-associated antigens. METHODS: Fab' fragments of two IgG2a monoclonal antibodies were either radiolabeled directly or via the linker bromoacetyl hydrazinonicotinamide hydrobromide (BAHNH) conjugated site specifically at protein thiols. A thiol assay was used to determine the number of thiols in the Fab' and to monitor their consumption during conjugation with BAHNH. Both preparations were labeled to > 95% incorporation of 99mTc, with the isotope tracking the single 50 kD absorbance peak seen on size-exclusion HPLC. The labeled preparations were tested in tumor-bearing and control mice, with dissections at 4 and 24 hr and gamma scintigraphy of the tumor-bearing mice. RESULTS: The major difference between the two labeled preparations for either antibody fragment was the greater accumulation of isotope in the tumor for the indirectly labeled preparations. This increase ranged from 1.5- and 2.7-fold at 4 hr to 2.6- and 3.2-fold at 24 hr for the two antibodies, respectively. Since blood clearance was similar for the two labeling methods, the higher tumor accumulation with the indirectly labeled fragments resulted in higher tumor to blood ratios. Tumors could be imaged with both antibodies with either type of labeling with greater clarity and sensitivity at the 24 hr time point. CONCLUSION: While both labeling methods resulted in tumor detection through imaging, the images obtained with the indirectly labeled antibody fragments were more easily visualized due to the combination of higher radioisotope accumulation in the tumor and similar blood clearances compared to the direct labeled fragment.