Quality-adjusted time without symptoms or toxicity analysis of pazopanib versus sunitinib in patients with renal cell carcinoma

BACKGROUND

In a phase 3, randomized, open-label trial (Pazopanib versus Sunitinib in the Treatment of Locally Advanced and/or Metastatic Renal Cell Carcinoma, COMPARZ; NCT00720941), pazopanib was found to be noninferior to sunitinib in terms of progression-free survival in patients with metastatic renal cell carcinoma with no prior therapy. Overall treatment differences were evaluated in a post hoc analysis with a quality-adjusted time without symptoms or toxicity (Q-TWiST) methodology.

METHODS

Each patient's overall survival was partitioned into 3 mutually exclusive health states: time with grade 3 or 4 toxicity (TOX), time without symptoms of disease or grade 3/4 toxicity of treatment, and time after tumor progression or relapse (REL). The time spent in each state was weighted by a health-state utility associated with that state and summed to calculate the Q-TWiST. A threshold utility analysis was used, and utilities were applied across the range of 0 (similar to death) to 1 (perfect health).

RESULTS

A total of 1110 patients were enrolled (557 on pazopanib and 553 on sunitinib). The mean TOX was 31 days (95% confidence interval, 13-48 days) longer for sunitinib versus pazopanib. In the threshold utility analysis, the difference in the Q-TWiST ranged from -11 days (utility for TOX, 1; utility for REL, 0) to 43 days (utility for TOX, 0; utility for REL, 1) in favor of pazopanib across most utility combinations. Differences were significant in less than half of the utility combinations examined, and this typically occurred when the utility for TOX was lower than the utility for REL.

CONCLUSIONS

Patients randomized to pazopanib had a slightly longer Q-TWiST in comparison with sunitinib patients, and this was primarily due to the reduced length of TOX.

IL8 polymorphisms and overall survival in pazopanib- or sunitinib-treated patients with renal cell carcinoma

BACKGROUND

We evaluated germline single nucleotide polymorphisms (SNPs) for association with overall survival (OS) in pazopanib- or sunitinib-treated patients with advanced renal cell carcinoma (aRCC).

METHODS

The discovery analysis tested 27 SNPs within 13 genes from a phase III pazopanib trial (N=241, study 1). Suggestive associations were then pursued in two independent datasets: a phase III trial (COMPARZ) comparing pazopanib vs sunitinib (N=729, study 2) and an observational study of sunitinib-treated patients (N=89, study 3).

RESULTS

In study 1, four SNPs showed nominally significant association (P≤0.05) with OS; two of these SNPs (rs1126647, rs4073) in IL8 were associated (P≤0.05) with OS in study 2. Because rs1126647 and rs4073 were highly correlated, only rs1126647 was evaluated in study 3, which also showed association (P≤0.05). In the combined data, rs1126647 was associated with OS after conservative multiple-test adjustment (P=8.8 × 10(-5); variant vs reference allele hazard ratio 1.32, 95% confidence interval: 1.15-1.52), without evidence for heterogeneity of effects between studies or between pazopanib- and sunitinib-treated patients.

CONCLUSIONS

Variant alleles of IL8 polymorphisms are associated with poorer survival outcomes in pazopanib- or sunitinib-treated patients with aRCC. These findings provide insight in aRCC prognosis and may advance our thinking in development of new therapies.

Health care costs among renal cancer patients using pazopanib and sunitinib

BACKGROUND

Pazopanib was noninferior to sunitinib in progression-free survival in a phase III, open-label, randomized clinical trial comparing the efficacy and safety of the 2 drugs for treatment of patients with advanced renal cell carcinoma (RCC). A secondary analysis of this trial conducted on patient-reported health care resource utilization (HCRU) endpoints revealed significantly fewer monthly telephone consultations and emergency department visits among patients treated with pazopanib over the first 6 months of treatment.

OBJECTIVES

To (a) compare total costs of HCRU and adverse events (AEs) in patients with advanced RCC receiving first-line pazopanib or sunitinib from the phase III clinical trial and (b) perform a post hoc economic analysis that applied direct medical care and pharmacy unit costs, obtained from the Truven Health MarketScan Databases, to HCRU and AE rates.

METHODS

Total HCRU costs included components for provider contacts, diagnostics, hospitalizations, procedures, and study/nonstudy drugs. Patients were stratified by the presence or absence of an AE in order to estimate costs attributable to AEs. Costs were adjusted to 2013 U.S. dollars. The highest 1% of cost outliers were equally excluded from each group. Univariate (t-test and Kaplan-Meier sample average [KMSA]) and multivariate (using treatment group and region as covariates) analyses were performed.

RESULTS

A total of 906 patients (pazopanib, n = 454; sunitinib, n = 452) reported HCRU; higher rates were observed for sunitinib. In unadjusted cost analyses, the mean total costs for pazopanib-treated patients were 8.0% lower than those treated with sunitinib ($80,464 vs. $86,886; P = 0.20). The difference in KMSA-estimated costs was significantly higher for sunitinib versus pazopanib ($156,128 vs. $143,585; P = 0.003). Adjusted cost differences between arms consistently suggested higher costs for sunitinib. Among patients who experienced greater than or equal to 1 AE, costs were $8,118 higher for pazopanib-treated patients and $14,343 for sunitinib-treated patients.

CONCLUSIONS

The findings suggest that health care costs were lower among patients with advanced RCC treated first-line with pazopanib versus sunitinib.

An open-label extension study to evaluate safety and efficacy of pazopanib in patients with advanced renal cell carcinoma

OBJECTIVES

Evaluation of the safety and efficacy of pazopanib, a multikinase angiogenesis inhibitor, in a single-arm, open-label, extension study (VEG107769/NCT00387764) for placebo-treated patients with advanced renal cell carcinoma (RCC) from a randomized, double-blind, placebo-controlled phase III study (VEG105192/NCT00334282).

METHODS

Patients received pazopanib 800 mg/day. The primary endpoint was the safety and tolerability of pazopanib treatment. Secondary endpoints included response rate per Response Evaluation Criteria in Solid Tumors, progression-free survival (PFS), and overall survival (OS).

RESULTS

Seventy-nine placebo-treated patients from VEG105192/NCT00334282 who experienced disease progression and one pazopanib-treated patient (an exemption) were enrolled. Forty-one patients (51%) were treatment-naive; 39 (49%) were cytokine-pretreated. Median exposure to pazopanib was 9.7 months. All patients had discontinued pazopanib at the time of analysis. The most common reason for discontinuation was disease progression (61%). The most common adverse events were hypertension (45%), diarrhea (45%), hair color changes (44%), anorexia (30%), and nausea (25%). The response rate was 37.5% [95% confidence interval (CI): 26.9-48.1]; median PFS was 9.2 months (95% CI: 7.3-12.0); median OS was 23.5 months (95% CI: 16.3-28.0).

CONCLUSIONS

Efficacy and safety profiles for pazopanib in this extension study of patients with RCC previously treated with placebo were very similar to those observed for pazopanib-treated patients in the pivotal phase III study.

Correlation of PDL1 tumor expression and treatment outcomes in patients with renal cell carcinoma (RCC) receiving tyrosine kinase inhibitors: COMPARZ study analysis

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Background: The interaction of PDL1 (B7H1) with its receptor PD-1 on activated T cells contributes to suppression of antitumor immune responses. Tumor PDL1 expression has been associated with poor outcomes in RCC but has not been investigated as a biomarker of response in RCC patients receiving standard vascular endothelial growth factor (VEGF)-targeted therapy. Methods: Formalin-fixed paraffin-embedded tumor samples were collected at baseline from consenting patients enrolled in COMPARZ—a phase lll clinical trial comparing pazopanib and sunitinib as first-line interventions for metastatic RCC (Motzer et al, NEJM 2013). PDL1 expression was evaluated using the anti-PDL1 mouseIgG1 (clone 5H1; Thompson) on the Leica automated immunohistochemistry platform. Additional dual PDL1/CD68 staining was performed on tumor associated macrophages (TAMs). Tumor PDL1 expression was quantified by an H-score (HS). PDL1+ TAMs were assessed semiquantitatively. In addition, intra-tumor CD8+ T cells were quantified morphometrically. The association between PDL1 HS, CD8+T cell counts, and survival was investigated using Kaplan-Meier analysis. Results: HS data were available from 453 of 1110 patients. 64% of patients had negative (HS = 0) PDL1 expression (HS range 0-290), but PDL1 expression was associated with tumours containing higher numbers of infiltrating macrophages. Peripheral CD8+ T cells in the invasive margin surrounding the tumor were also observed. Patients with HS >50 (n = 61, 13%) had significantly shorter overall survival (OS) in both pazopanib (19.7 vs 31.6 mo) and sunitinib (15.3 vs 27.7 mo) arms. In both arms, patients with HS >50 with intratumoral CD8+T cell counts >300 had the shortest OS. Results were similar for progression-free survival and persisted on multivariate analysis. Conclusions: This is the largest report to show that tumors’PDL1 expression and CD8+ T cell counts are associated with treatment outcome in metastatic RCC patients. Increased PDL1, or increased PDL1 plus tumor CD8+ T cell counts, were associated with shorter OS. These findings may have major implications for future trial designs that involve PD-1 inhibitors.

Association of IL8 polymorphisms with overall survival in patients with renal cell carcinoma in COMPARZ (pazopanib versus sunitinib phase III study)

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Background: Pazopanib and sunitinib are angiogenesis inhibitors approved for treatment of advanced renal cell carcinoma (RCC). COMPARZ, a phase III randomized clinical trial comparing pazopanib vs sunitinib for RCC, demonstrated similar efficacies for the two therapies but safety profiles differed. Our genetic analyses of previous pazopanib clinical trials found that IL8 polymorphisms may be associated with progression-free survival (PFS) and overall survival (OS). We attempted to validate these associations in the COMPARZ study. Methods: Of the 1110 participants in COMPARZ, 724 (65%) provided consent and DNA for pharmacogenetic analyses (pazopanib, N = 371; sunitinib, N = 353).Associations of IL8 polymorphisms (rs1126647 and rs4073) with PFS and OS were tested using the Cox proportional hazards model with baseline factors as covariates in a combined analysis of all patients and also separately in pazopanib-treated and sunitinib-treated patients. One-tailed P values were calculated for effects in the same direction as previously observed. Results: For PFS there was no significant association in the combined analysis or in pazopanib-treated patients, but there was a significant association in sunitinib-treated patients (P = 0.017). For OS there were significant associations in the combined analysis (P = 0.010) and in sunitinib-treated patients (P = 0.0043) but not in pazopanib-treated patients (P = 0.30). Hazard ratios (HRs) for genetic effects were not significantly different between sunitinib- and pazopanib-treated patients (two-tailed P = 0.23 for genotype-by-treatment interaction). Kaplan-Meier plots suggested a recessive genetic model in the combined data set, with median OS (95% CI) 23.7 months (15.4–29.1) for rs1126647 TT genotype compared to 35.5 months (30.8–∞) for AA or AT genotypes (HR = 1.66, P = 0.0007). Similar associations were seen for rs4073. Conclusions: Germline variants in IL8 are associated with survival outcome in patients with RCC who have received angiogenesis inhibitors. These findings may provide additional scientific insights in making treatment decisions and developing alternative therapies.

Association of hyperbilirubinemia in pazopanib- or sunitinib-treated patients in COMPARZ with UGT1A1 polymorphisms

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Background: A phase III randomized clinical trial (COMPARZ) comparing pazopanib vs sunitinib for treatment of advanced renal cell carcinoma demonstrated similar efficacies but different safety profiles for the two therapies. Elevations in serum total bilirubin have been observed in patients receiving either therapy. UGT1A1 polymorphisms are associated with elevated bilirubin in the general population (Gilbert’s syndrome). This study investigated the association between functional UGT1A1 polymorphisms and on-therapy serum total bilirubin in the COMPARZ study. Methods: Patients homozygous or compound heterozygous for UGT1A1 *28, *37, and *6 alleles were predicted to have reduced UGT1A1 function. Logistic regression adjusted for ancestry principal components was used to compare patients with on-therapy hyperbilirubinemia (≥1.5 × upper limit of normal [ULN]; pazopanib, N = 62; sunitinib, N = 34) against patients exposed to treatment and with maximum on-therapy bilirubin ≤1 × ULN (pazopanib, N = 213; sunitinib, N = 215), excluding patients with maximum on-therapy bilirubin between 1 and 1.5 × ULN (pazopanib, N = 96; sunitinib, N = 104). Results: Patients with predicted reduced UGT1A1 function had higher baseline bilirubin and also were more likely to experience hyperbilirubinemia when receiving either pazopanib (P = 6.9×10–8) or sunitinib (P = 1.8×10–3). After adjusting for baseline bilirubin, patients with predicted reduced UGT1A1 function remained more likely to experience hyperbilirubinemia when receiving pazopanib (P = 0.015) or sunitinib (P = 0.026), with odds ratio (95% CI) 3.53 (1.28–9.76) and 4.41 (1.23–15.75), respectively. Conclusions: The data suggest that some instances of hyperbilirubinemia in patients treated with pazopanib or sunitinib may be benign manifestations of Gilbert’s syndrome. Bilirubin fractionation or, if not available, UGT1A1 genotyping, would enable further characterization of liver safety risk and help in making treatment decisions.

Quality of life (QoL) among patients with renal cell carcinoma (RCC) treated with pazopanib versus sunitinib in the COMPARZ study

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Background: Pazopanib and sunitinib are targeted therapies associated with particular treatment-related side effects that may affect patients’ QoL. COMPARZ was a randomized, open-label, parallel group, phase III study of pazopanib vs. sunitinib in 1,110 subjects with advanced RCC who had not received prior systemic therapy. The study demonstrated pazopanib is non-inferior to sunitinib with respect to progression-free survival. The study also confirmed the differentiated safety profiles of the two drugs. Methods: QoL endpoints were assessed using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F), the Functional Assessment of Cancer Therapy-Kidney Symptom Index-19 (FKSI-19), the Cancer Therapy Satisfaction Questionnaire (CTSQ), and a Supplementary Quality of Life Questionnaire (SQLQ). Research to validate the SQLQ is currently ongoing. Each instrument was administered at baseline (except CTSQ) and then day 28 of every cycle. Changes in mean scores over time were analyzed and compared using a repeated measures analysis of covariance. Comparisons were pre-specified at the first 6 months of treatment as this time was expected to be a key interval during which tolerability issues may have occurred. Results: During the first 6 months, treatment differences in change from baseline for 11 of the 14 QoL domains studied were statistically significant (p < 0.05), all of which favored pazopanib. Further analysis up to 12 months of treatment, showed the treatment differences observed for fatigue scores increased over time with pazopanib improving and sunitinib remaining relatively flat. The difference in limitations due to foot soreness between the two treatments also progressively increased with time over 12 months favoring pazopanib. Conclusions: In this study, better patient-reported QoL scores for pazopanib indicate subjects experienced less worsening of fatigue, as well as mouth/throat, hands, and feet soreness, and fewer limitations due to soreness, while on pazopanib compared with sunitinib. The differences observed are likely to be clinically meaningful. The FACIT-F and SQLQ results are also highly consistent with the previously-reported PISCES study.

Comparison of PFS and safety for Asian compared to North American and European populations in the phase III trial of pazopanib versus sunitinib in patients with treatment-naive RCC (COMPARZ)

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Background: Pazopanib (P) and sunitinib (S) are multi-kinase angiogenesis inhibitors that positively impact progression-free survival (PFS) in patients (pts) with metastatic renal cell carcinoma (mRCC) (NEJM 2007 356:115; JCO 2009 29:475). The safety profile of multi-kinase angiogenesis inhibitors has been shown to vary depending upon ethnic background (Oncology 2011 80:395). Methods: Treatment naïve pts with clear cell mRCC and measurable disease were randomized 1:1 to P, 800mg QD continuous dosing or S, 50 mg QD for 4 weeks followed by 2 weeks off treatment. Primary endpoint was PFS. A subgroup analysis compared PFS (Cox analysis with treatment as only covariate) and AEs between the Asian, North American (NA), and European (EU) populations. Of the 1,110 pts 367 were from Asia (188 P, 179 S). Results: PFS in the Asian subgroup was consistent with NA and EU. HR (95% CI): Asia 1.07 (0.81, 1.42); NA 1.18 (0.90, 1.53); EU 1.03 (0.79, 1.36). Median PFS mos (95% CI) P: Asia 8.4 (8.3,11.1); EU 8.5 (8.0, 11.0); NA 8.3 (6.6, 11.0); S: Asia 11.1 (8.2, 14.3); EU 9.0 (8.1, 12.9); NA 10.5 (8.2, 13.4). AEs in >25% of pts in any arm in any region and a difference of 15% between any region within an arm are shown. Conclusions: In both arms, PFS in the Asian population was similar to NA and EU. In the Asian population increased incidences of hematotoxicity, hypertension, HFS, LFT increase, proteinuria, and decreased incidences of GI symptoms, headache were observed in both arms. Consistent with NA and EU, more frequent AEs in the Asian population (>10% difference between arms): ALT increase (P); HFS, thrombocytopenia, neutropenia (S). [Table: see text]

Molecular function of the CD4 D1 domain in coreceptor-mediated entry by HIV type 1

The surface molecule CD4 plays a key role in initiating cellular entry by the human immunodeficiency virus type 1 (HIV-1), and it is now recognized as acting synergistically with select chemokine receptors (coreceptors) in the infection process. The present study was undertaken to determine whether the extracellular region of CD4 is sufficient to induce fusion of HIV-1 virions with target cells in the absence of its anchoring function. Using pseudotype reporter viruses to quantitate infection, soluble CD4 (sCD4) was tested for its ability to induce fusion by viruses utilizing CCR5 as their coreceptor. We found that sCD4 was competent to replace membrane-bound CD4 to trigger infection mediated by several HIV-1 envelopes. Furthermore, in a comparison of the envelopes of HIV-1 NL4-3 and a chimera containing the gp120 V3 loop of Ba-L, the V3 region was found to be one factor affecting susceptibility to induction by sCD4. In addition, using truncated and mutant derivatives of sCD4, the amino-terminal D1 domain of CD4 was found to be necessary and sufficient for induction of fusion and to require an intact gp120-binding site for this activity. These results delineate determinants on CD4 and gp120 required for fusion induction in collaboration with a coreceptor, and suggest a mechanism whereby CD4 may contribute to viral infection in trans.

Reciprocal expression of the TNF family receptor herpes virus entry mediator and its ligand LIGHT on activated T cells: LIGHT down-regulates its own receptor

The TNF receptor (TNFR) family plays a central role in the development of the immune response. Here we describe the reciprocal regulation of the recently identified TNFR superfamily member herpes virus entry mediator (HVEM) (TR2) and its ligand LIGHT (TL4) on T cells following activation and the mechanism of this process. T cell activation resulted in down-regulation of HVEM and up-regulation of LIGHT, which were both more pronounced in CD8(+) than CD4(+) T lymphocytes. The analysis of HVEM and LIGHT mRNA showed an increase in the steady state level of both mRNAs following stimulation. LIGHT, which was present in cytoplasm of resting T cells, was induced both in cytoplasm and at the cell surface. For HVEM, activation resulted in cellular redistribution, with its disappearance from cell surface. HVEM down-regulation did not rely on de novo protein synthesis, in contrast to the partial dependence of LIGHT induction. Matrix metalloproteinase inhibitors did not modify HVEM expression, but did enhance LIGHT accumulation at the cell surface. However, HVEM down-regulation was partially blocked by a neutralizing mAb to LIGHT or an HVEM-Fc fusion protein during activation. As a model, we propose that following stimulation, membrane or secreted LIGHT binds to HVEM and induces receptor down-regulation. Degradation or release of LIGHT by matrix metalloproteinases then contributes to the return to baseline levels for both LIGHT and HVEM. These results reveal a self-regulating ligand/receptor system that contributes to T cell activation through the interaction of T cells with each other and probably with other cells of the immune system.

Temperature-sensitive differential affinity of TRAIL for its receptors. DR5 is the highest affinity receptor

TRAIL is a member of the tumor necrosis factor (TNF) family of cytokines which induces apoptotic cell death in a variety of tumor cell lines. It mediates its apoptotic effects through one of two receptors, DR4 and DR5, which are members of of the TNF receptor family, and whose cytoplasmic regions contain death domains. In addition, TRAIL also binds to 3 "decoy" receptors, DcR2, a receptor with a truncated death domain, DcR1, a glycosylphosphatidylinositol-anchored receptor, and OPG a secreted protein which is also known to bind to another member of the TNF family, RANKL. However, although apoptosis depends on the expression of one or both of the death domain containing receptors DR4 and/or DR5, resistance to TRAIL-induced apoptosis does not correlate with the expression of the "decoy" receptors. Previously, TRAIL has been described to bind to all its receptors with equivalent high affinities. In the present work, we show, by isothermal titration calorimetry and competitive enzyme-linked immunosorbent assay, that the rank order of affinities of TRAIL for the recombinant soluble forms of its receptors is strongly temperature dependent. Although DR4, DR5, DcR1, and OPG show similar affinities for TRAIL at 4 degrees C, their rank-ordered affinities are substantially different at 37 degrees C, with DR5 having the highest affinity (K(D) </= 2 nm) and OPG having the weakest (K(D) = 400 nm). Preferentially enhanced binding of TRAIL to DR5 was also observed at the cell surface. These results reveal that the rank ordering of affinities for protein-protein interactions in general can be a strong function of temperature, and indicate that sizeable, but hitherto unobserved, TRAIL affinity differences exist at physiological temperature, and should be taken into account in order to understand the complex physiological and/or pathological roles of TRAIL.

Osteoprotegerin is a receptor for the cytotoxic ligand TRAIL

TRAIL is a tumor necrosis factor-related ligand that induces apoptosis upon binding to its death domain-containing receptors, DR4 and DR5. Two additional TRAIL receptors, TRID/DcR1 and DcR2, lack functional death domains and function as decoy receptors for TRAIL. We have identified a fifth TRAIL receptor, namely osteoprotegerin (OPG), a secreted tumor necrosis factor receptor homologue that inhibits osteoclastogenesis and increases bone density in vivo. OPG-Fc binds TRAIL with an affinity of 3.0 nM, which is slightly weaker than the interaction of TRID-Fc or DR5-Fc with TRAIL. OPG inhibits TRAIL-induced apoptosis of Jurkat cells. Conversely, TRAIL blocks the anti-osteoclastogenic activity of OPG. These data suggest potential cross-regulatory mechanisms by OPG and TRAIL.

The genetic analysis of the HIV envelope binding domain on CD4

Through mutagenesis, we identified a single high-affinity binding site for gp120 on the human CD4 protein. This site is localized in the V1 domain within residues 41 to 55. The collection of mutants was also used to define the epitopes for 55 anti-CD4 monoclonal antibodies. The locations of these epitopes are consistent with a V kappa-like structure for the V1 domain. In the context of this structure, the gp120 binding site encompasses the small CDR2 loop. Through deletion mutagenesis at the termini of the V1 domain, we further defined the minimal region required to retain high-affinity binding to gp120. Short deletions at both termini disrupt binding to gp120 and recognition by conformation-sensitive anti-CD4 monoclonal antibodies. We conclude that amino acids at both the amino and carboxy termini are critical to the conformation of the V1 domain and, in particular, to the integrity of the gp120 binding site.

Identification of the residues in human CD4 critical for the binding of HIV

The CD4 molecule is a T cell surface glycoprotein that interacts with high affinity with the envelope glycoprotein of the human immunodeficiency virus, HIV, thus serving as a cellular receptor for this virus. To define the sites on CD4 essential for binding to gp120, we produced several truncated, soluble derivatives of CD4 and a series of 26 substitution mutants. Quantitative binding analyses with the truncated proteins demonstrate that the determinants for high affinity binding lie solely with the first 106 amino acids of CD4 (the V1 domain), a region having significant sequence homology to immunoglobulin variable regions. Analysis of the substitution mutants further defines a discrete binding site within this domain that overlaps a region structurally homologous to the second complementarity-determining region of antibody variable domains. Finally, we demonstrate that the inhibition of virus infection and virus-mediated cell fusion by soluble CD4 proteins depends on their association with gp120 at this binding site.

Structural features of CD4 required for binding to HIV

A soluble form of the human CD4 glycoprotein (sCD4), the cellular receptor for human HIV, was treated with various physical, chemical, and enzymic regimens and tested over a range of concentrations for its capacity to inhibit the binding of HIV to CD4+ T cells. Reduction of disulfide bonds and alkylation in denaturing buffer (8 M urea) destroyed the inhibitory activity of sCD4, whereas reduction and alkylation in PBS had no effect. Derivatization or digestion of carbohydrate groups by periodate oxidation or by glycolytic enzyme digestion did not affect sCD4 inhibitory capacity. Digestion with trypsin or endoproteinase Glu-C destroyed activity. A limited digestion of sCD4 with endoproteinase Glu-C resulted in a mixture of fragments, however, and the mixture had inhibitory activity equivalent to that of intact sCD4. Within this mixture, a fragment of 23 kDa was identified that binds to HIV. Although sCD4 can be digested to yield fully active fragments, the requirement for intrachain disulfide bonding indicates that the minimum sized portion of CD4 that will retain full affinity for HIV will have to be formulated with a proper tertiary structure.

Structural features of CD4 required for binding to HIV

A soluble form of the human CD4 glycoprotein (sCD4), the cellular receptor for human HIV, was treated with various physical, chemical, and enzymic regimens and tested over a range of concentrations for its capacity to inhibit the binding of HIV to CD4+ T cells. Reduction of disulfide bonds and alkylation in denaturing buffer (8 M urea) destroyed the inhibitory activity of sCD4, whereas reduction and alkylation in PBS had no effect. Derivatization or digestion of carbohydrate groups by periodate oxidation or by glycolytic enzyme digestion did not affect sCD4 inhibitory capacity. Digestion with trypsin or endoproteinase Glu-C destroyed activity. A limited digestion of sCD4 with endoproteinase Glu-C resulted in a mixture of fragments, however, and the mixture had inhibitory activity equivalent to that of intact sCD4. Within this mixture, a fragment of 23 kDa was identified that binds to HIV. Although sCD4 can be digested to yield fully active fragments, the requirement for intrachain disulfide bonding indicates that the minimum sized portion of CD4 that will retain full affinity for HIV will have to be formulated with a proper tertiary structure.

Soluble CD4 blocks the infectivity of diverse strains of HIV and SIV for T cells and monocytes but not for brain and muscle cells

The CD4 antigen has been subverted as a receptor by the human and simian immunodeficiency viruses (HIV-1, HIV-2 and SIV). Several groups have reported that recombinant, soluble forms of the CD4 molecule (sCD4) block the infection of T lymphocytes by HIV-1, as CD4 binds the HIV envelope glycoprotein, gp120, with high affinity. We now report that sCD4 blocks diverse strains of HIV-1, HIV-2 and SIV, but is less effective for HIV-2. The blocking effect is apparent even after adsorption of virions to CD4 cells. Soluble CD4 prevents HIV infection of T-lymphocytic and myelomonocytic cell lines, but neither sCD4 nor anti-CD4 antibodies inhibit infection of glioma and rhabdomyosarcoma cell lines.

Gene transactivation mediated by the TAT gene of human immunodeficiency virus in transgenic mice

Transgenic mice were generated carrying either the long terminal repeat of Human Immunodeficiency Virus fused to the bacterial chloramphenicol acetyl transferase reporter gene or a control element of the murine alpha A crystallin gene fused to the tat gene of human immunodeficiency virus. By crossing these two strains, progeny were obtained which carried both transgenes. The bacterial reporter gene was specifically transactivated in the eyes of these animals.

A soluble form of CD4 (T4) protein inhibits AIDS virus infection

CD4 (T4) is a glycoprotein of relative molecular mass 55,000 (Mr 55K) on the surface of T lymphocytes which is thought to interact with class II MHC (major histocompatibility complex) molecules, mediating efficient association of helper T cells with antigen-bearing targets. The CD4 protein is also the receptor for HIV, a T-lymphotropic RNA virus responsible for the human acquired immune deficiency syndrome (AIDS) (refs 4-7). To define the mechanisms of interaction of CD4 with the surface of antigen-presenting cells and with HIV, we have isolated the CD4 gene and expressed this gene in several different cellular environments. Here we describe an efficient expression system in which a recombinant, soluble form of CD4 (sCD4) is secreted into tissue culture supernatants. This sCD4 retains the structural and biological properties of CD4 on the cell surface, binds to the envelope glycoprotein (gp110) of HIV and inhibits the binding of virus to CD4+ lymphocytes, resulting in a striking inhibition of virus infectivity.

Use of T4 DNA polymerase replacement synthesis for specific labeling of plasmid-cloned inserts

A strategy employing T4 DNA polymerase replacement synthesis is described whereby only the insert portion of recombinant plasmids are radioisotopically labeled. Prior purification of the inserted DNA is not required. The recombinant plasmid is first digested with one or more restriction endonucleases selected to cleave the vector segment into fragments at least 30% shorter than the insert DNA segment. This mixture of fragments is then digested by the T4 DNA polymerase-associated 3' exonuclease in the absence of deoxynucleoside triphosphates (dNTPs) for a length of time which allows complete degradation of all fragments shorter than the insert. The remaining insert DNA, which is now partially single-stranded, is then resynthesized by addition of dNTPs, one or more of which is labeled. The resulting DNA is full length, double-stranded, and unnicked. The strategy is widely applicable, and reliably and reproducibly yields DNA of high specific activity. We have used this method to label more than 15 cloned inserts ranging in size from 3.2 to 25 kilobases.

Urethane anesthesia in rats. Altered ability to regulate hydration

Anesthesia in rats produced by urethane administered intraperitoneally caused (1) peritoneal fluid accumulation; (2) inability to undergo a renal response to NaCl or water loading, and (3) pronounced hyperosmolality of body fluids without affecting plasma [Na+]. The impairment of the renal function appears not to be due to anesthesia per se, angiotensin, aldosterone, vasopressin or renal nerves. It probably is attributable to osmotoxicity of the mesenteric vasculature. By contrast, urethane administered intravenously evokes a brisk osmotic diuresis without fluid leakage into the peritoneum. Plasma osmolality is still increased. The osmotic toxicity to the mesenteric vasculature, poor renal function and altered composition of body fluids that occur after intraperitoneal urethane may complicate the interpretation of data obtained in rats anesthetized in this manner.