Rivaroxaban for thromboprophylaxis among patients recently hospitalized for acute infectious diseases: a subgroup analysis of the MAGELLAN study.

Essentials Net benefit of venous thromboprophylaxis (VTE) in patients hospitalized for infections is unknown. MAGELLAN trial subgroup analysis was performed for patients hospitalized for acute infectious diseases. At day 35, prolonged rivaroxaban prophylaxis reduced VTE compared to enoxaparin (4.2% vs. 6.6%). Rivaroxaban prophylaxis reduced VTE in patients hospitalized for active lung infections. SUMMARY: Background Despite the well-established association between infection and venous thromboembolism (VTE), there are few data specifically assessing the efficacy and safety of the VTE prophylaxis strategies for patients hospitalized for acute infectious diseases. Objectives To estimate the incidence of VTE and bleeding outcomes, comparing prolonged prophylaxis with rivaroxaban 10 mg daily for 35 days with enoxaparin 40 mg daily for 10 days. Patients/Methods A subgroup analysis of patients hospitalized for acute infectious diseases in the MAGELLAN trial was performed. The primary efficacy outcome was the composite of asymptomatic proximal or symptomatic VTE at days 10 and 35. The principal safety outcome was the composite of major or clinically relevant non-major bleeding. Results Three thousand one hundred and seventy-three patients with acute infectious diseases leading to hospitalization were randomized to either rivaroxaban (n = 1585) or enoxaparin/placebo (n = 1588), and received at least one dose of study medication. At day 10, primary composite efficacy outcomes did not differ between prophylaxis strategies (rivaroxaban, 2.7%; and enoxaparin, 3.7%). At day 35, there were fewer VTE events with rivaroxaban (4.2%) than with enoxaparin (6.6%) (relative risk [RR] 0.64; 95% confidence interval [CI] 0.45-0.92). Patients with pulmonary infections randomized to rivaroxaban had a lower incidence of VTE both at 10 days (RR 0.50, 95% CI 0.28-0.90) and at 35 days (RR 0.54, 95% CI 0.33-0.87). Primary safety outcome events were increased with rivaroxaban (RR 2.42, 95% CI 1.60-3.66). Conclusions Prolonged rivaroxaban prophylaxis reduced the incidence of VTE in patients hospitalized for acute infectious diseases, particularly those involving the lungs. Efficacy benefits were, in part, offset by bleeding outcomes. ClinicalTrials.gov Number: NCT 00571649.

D-dimer as a predictor of venous thromboembolism in acutely ill, hospitalized patients: a subanalysis of the randomized controlled MAGELLAN trial.

BACKGROUND: D-dimer concentrations have not been evaluated extensively as a predictor of increased venous thromboembolism (VTE) risk in acutely ill, hospitalized medical patients. OBJECTIVES: To analyze the relationships between D-dimer concentration, VTE and bleeding in the MAGELLAN trial (NCT00571649). PATIENTS/METHODS: This was a multicenter, randomized, controlled trial. Patients aged ≥ 40 years, hospitalized for acute medical illnesses with risk factors for VTE received subcutaneous enoxaparin 40 mg once daily for 10 ± 4 days then placebo up to day 35, or oral rivaroxaban 10 mg once daily for 35 ± 4 days. Patients (n = 7581) were grouped by baseline D-dimer ≤ 2 × or > 2 × the upper limit of normal. VTE and major plus non-major clinically relevant bleeding were recorded at day 10, day 35, and between days 11 and 35. RESULTS: The frequency of VTE was 3.5-fold greater in patients with high D-dimer concentrations. Multivariate analysis showed that D-dimer was an independent predictor of the risk of VTE (odds ratio 2.29 [95% confidence interval 1.75-2.98]), and had a similar association to established risk factors for VTE, for example cancer and advanced age. In the high D-dimer group, rivaroxaban was non-inferior to enoxaparin at day 10 and, unlike the low D-dimer group, superior to placebo at day 35 (P < 0.001) and days 11-35 (P < 0.001). In both groups, bleeding outcomes favored enoxaparin/placebo. CONCLUSIONS: Elevated baseline D-dimer concentrations may identify acutely ill, hospitalized medical patients at high risk of VTE for whom extended anticoagulant prophylaxis may provide greater benefit than for those with low D-dimer concentrations.

The association of metabolic syndrome with triple-negative breast cancer.

Metabolic syndrome, a conglomerate of obesity, insulin resistance, dyslipidemia, and hypertension has been linked with an increased risk of breast cancer. We investigated the possible association of highly aggressive triple-negative breast cancer and the metabolic syndrome. Information on metabolic syndrome components and tumor characteristics were reviewed in a cohort of 176 patients (including 86 triple-negatives). Retrospective comparison was performed using Pearson Chi-square test or Student's t test for data analysis. A statistically significant association of triple-negative breast cancer with the metabolic syndrome was observed. In accordance with the NCEP (National Cholesterol Education Program) definition, 58.1% of triple-negative patients had metabolic syndrome compared to only 36.7% of non-triple-negative patients (P = 0.004). Consistently, by the AACE (American Association of Clinical Endocrinologists) criteria, 52.3% of triple-negative patients had metabolic syndrome as compared to 34.4% of non-triple-negative patients (P = 0.017). Blood glucose, triglyceride, and HDL levels but not hypertension or BMI (body mass index) showed significant independent association with triple-negative breast cancer. Additionally, triple-negative tumors displayed a significantly higher histological grade and relative paucity of ductal carcinoma in situ (DCIS) when compared to the non-triple-negative tumors (P < 0.001). Our study suggests that metabolic syndrome is significantly more prevalent in triple-negative breast cancer patients as opposed to non-triple-negative patients. Furthermore, triple-negative breast cancer showed a significantly higher histological grade and a relative absence of DCIS. Whether the presence of metabolic syndrome preferentially increases the risk of developing triple-negative-breast cancer remains to be elucidated with future prospective studies.

A quantum-chemical picture of hemoglobin affinity.

Understanding the molecular mechanism of hemoglobin cooperativity remains an enduring challenge. Protein forces that control ligand affinity are not directly accessible by experiment. We demonstrate that computational quantum mechanics/molecular mechanics methods can provide reasonable values of ligand binding energies in Hb, and of their dependence on allostery. About 40% of the binding energy differences between the relaxed state and tense state quaternary structures result from strain induced in the heme and its ligands, especially in one of the pyrrole rings. The proximal histidine also contributes significantly, in particular, in the alpha-chains. The remaining energy difference resides in protein contacts, involving residues responsible for locking the quaternary changes. In the alpha-chains, the most important contacts involve the FG corner, at the "hinge" region of the alpha(1)beta(2) quaternary interface. The energy differences are spread more evenly among the beta-chain residues, suggesting greater flexibility for the beta- than for the alpha-chains along the quaternary transition. Despite this chain differentiation, the chains contribute equally to the relaxed substitute state energy difference. Thus, nature has evolved a symmetric response to the quaternary structure change, which is a requirement for maximum cooperativity, via different mechanisms for the two kinds of chains.

Heme-based sensors: theoretical modeling of heme-ligand-protein interactions.

Heme proteins are uniquely adapted to bind the important diatomic molecules O(2), NO and CO. An increasing number of heme proteins are being discovered that sense these molecules and thereby regulate a variety of biochemical responses. The interactions of diatomic molecules with heme, and with the surrounding protein, are therefore of great interest. Recent theoretical modeling, using density functional theory, captures many features of these interactions, as exemplified by the well-characterized heme protein myoglobin. Important details, however, especially the mutual influence of the bound diatomic molecule and the proximal ligand, remain to be clarified.

Sequential tumor biopsies in early phase clinical trials of anticancer agents for pharmacodynamic evaluation.

PURPOSE: In the setting of target-based anticancer drug development, it is critical to establish that the observed preclinical activity can be attributed to modulation of the intended target in early phase trials in human subjects. This paradigm of target modulation allows us to determine a Phase II or III dose (optimal biochemical/biological modulatory dose) that may not necessarily be the maximum tolerated dose. A major obstacle to target-based (often cytostatic) drug development has been obtaining relevant tumor tissue during clinical trials of these novel agents for laboratory analysis of the putative marker of drug effect. EXPERIMENTAL DESIGN: From 1989 to present, we have completed seven clinical trials in which the end point was a biochemical or biological modulatory dose in human tumor tissues (not surrogate tissue). Eligibility enrollment required that patients have a biopsiable lesion either with computerized tomography (CT) guidance or direct visualization and consent to sequential (pre and posttreatment) biopsies. RESULTS: A total of 192 biopsies were performed in 107 patients. All but 8 patients had sequential pre and posttreatment biopsies. Seventy-eight (73%) of the 107 patients had liver lesion biopsies. In eight patients, either one or both biopsies contained insufficient viable tumor tissue or no tumor tissue at all for analysis. Of a total of 99 patients in whom we attempted to obtain paired biopsies, a total of 87 (88%) were successful. Reasons for failure included patient refusal for a second biopsy (n = 2), vasovagal reaction with first biopsy precluding a second biopsy (n = 1), subcapsular hepatic bleeding (n = 1), and most commonly obtaining necrotic tumor, fibrous, or normal tissue in one of the two sequential biopsies (n = 8). CONCLUSIONS: This is the first and largest reported series demonstrating that with adequate precautions and experience, sequential tumor biopsies are feasible and safe during early phase clinical trials.

Differential degradation rates of inactivated alkyltransferase in blood mononuclear cells and tumors of patients after treatment with O(6)-benzylguanine.

O(6)-Alkylguanine-DNA alkyltransferase (AGT) repairs O(6)-alkylating DNA adducts generated by alkylating therapeutic agents. Therefore, AGT activity may be an important marker of tumor and normal tissue sensitivity to chemotherapeutic agents and a predictor for the success of chemotherapeutic regimens. It is rapidly inactivated by O(6)-benzylguanine (BG) that mimics its substrates, O(6)-methylguanine and O(6)-chloroethylguanine DNA adducts. In a Phase I clinical trial, BG was given in increasing doses (from 10 to 120 mg/m(2)) by 1-h infusion. We previously reported depletion of AGT activity, and in this report, we demonstrate the relationship between degradation of BG-inactivated AGT protein and the depletion of AGT activity in peripheral blood mononuclear cells (PBMCs) and tumor samples obtained by computed tomography-guided cutting needle biopsy from patients prior to BG and either 2 or 18 h after BG. In PBMCs, BG inactivated AGT activity by over 95-100% at the end of a 1-h infusion, and depletion was maintained for 18 h. In contrast, AGT protein remained almost unchanged for up to 18 h after BG, suggesting that inactivated AGT proteins remain immunoreactive and are not rapidly degraded in PBMCs. In patient tumor biopsies, AGT activity was depleted approximately 90% 2 h after BG. Tumor AGT protein levels were reduced to approximately 40% of pretreatment values when detected by either Western blot or immunohistochemistry staining. In tumor samples obtained 18 h after BG, >95% inactivation of tumor AGT activity was observed at BG doses of 36-80 mg/m(2), and complete depletion of tumor AGT activity occurred at 120 mg/m(2) BG. However, residual AGT protein (5-10% of baseline) was detectable in all tumor samples. Therefore, the degradation of BG-inactivated AGT protein appeared to be much more rapid in tumors than that in PBMCs, which may impact on AGT regeneration rates as well. Because degradation of BG-inactivated AGT takes place slowly, antibody-based measurements of AGT protein correlate poorly with depletion of AGT activity immediately after BG. Thus, biochemical activity measurements remain the appropriate monitor of AGT during therapeutic modulation. These data provide the first and conclusive evidence of differential degradation rates of inactivated AGT in PBMCs and tumors of patients after treatment with BG and suggest that immunoreactive AGT measurements in PBMCs are a poor surrogate for AGT activity in tumor tissue.

Temozolomide: the effect of once- and twice-a-day dosing on tumor tissue levels of the DNA repair protein O(6)-alkylguanine-DNA-alkyltransferase.

Temozolomide (TMZ) is a methylating agent of the imidotetrazine class, whose cytotoxic product is O(6)-methylguanine DNA adducts, which initiate a futile recycling of the mismatch repair pathway causing DNA strand breaks and apoptotic cell death in mismatch repair proficient cells. The DNA repair protein O(6)-alkylguanine DNA alkyltransferase (AGT) repairs these adducts in a suicide manner and reduces the cytotoxic action of TMZ. An antitumor threshold is reached when sufficient adducts are formed by TMZ to inactivate AGT. In this study, we evaluated the relation between TMZ dosing and AGT depletion in patients with deep visceral tumors and in peripheral blood mononuclear cells (PBMCs) to determine whether the dose of TMZ was sufficient to inactivate AGT and lead to therapeutic efficacy. To do so, we compared single dose therapy with a novel twice daily regimen in a laboratory correlate-driven Phase I dose escalation study. p.o. bolus dose TMZ 200 mg/m(2) daily times five was compared with the same bolus on day 1 followed by nine doses at 12-h intervals of 50, 75, 90, or 100 mg/m(2). Dose-limiting toxicity in the bid regimen (grade IV thrombocytopenia and neutropenia) was seen at 100 mg/m(2), cumulative dose 1100 mg/m(2), and the maximum tolerated dose was 1010 mg/m(2). The degree of tumor tissue AGT activity depletion measured in biopsies before and on day 5 of therapy varied widely, between 0 (in 3 patients) and 99% (in 1), with the majority of patients (10 of 15) having 52-84% tumor AGT depletion. In contrast, AGT activity in PBMCs fell rapidly during TMZ administration to undetectable levels in all dosage groups on day 5 but did not correlate with tumor AGT depletion. TMZ pharmacokinetics were dose proportional; no accumulation occurred >5-day period in the bid regimen. Two partial responses were seen, lasting 3 and 4 months. Five additional patients achieved prolonged stabilization of disease for 4-6 monthly cycles. This is the first study to document that at maximum tolerated doses, TMZ depletes PBMC AGT but only partially and variably depletes visceral tumor AGT in most patients, even during twice daily dosing. Drug combinations or schedules designed to maximally deplete tumor AGT might improve TMZ efficacy.

Carbon monoxide binding by de novo heme proteins derived from designed combinatorial libraries.

Carbon monoxide binding was studied in a collection of de novo heme proteins derived from combinatorial libraries of sequences designed to fold into 4-helix bundles. The design of the de novo sequences was based on the previously reported "binary code" strategy, in which the patterning of polar and nonpolar amino acids is specified explicitly, but the exact identities of the side chains are varied extensively.(1) The combinatorial mixture of amino acids included histidine and methionine, which ligate heme iron in natural proteins. However, no attempt was made to explicitly design a heme binding site. Nonetheless, as reported previously, approximately half of the binary code proteins bind heme.(2) This collection of novel heme proteins provides a unique opportunity for an unbiased assessment of the functional potentialities of heme proteins that have not been prejudiced either by explicit design or by evolutionary selection. To assess the capabilities of the de novo heme proteins to bind diatomic ligands, we measured the affinity for CO, the kinetics of CO binding and release, and the resonance Raman spectra of the CO complexes for eight de novo heme proteins from two combinatorial libraries. The CO binding affinities for all eight proteins were similar to that of myoglobin, with dissociation constants (K(d)) in the low nanomolar range. The CO association kinetics (k(on)) revealed that the heme environment in all eight of the de novo proteins is partially buried, and the resonance Raman studies indicated that the local environment around the bound CO is devoid of hydrogen-bonding groups. Overall, the CO binding properties of the de novo heme proteins span a narrow range of values near the center of the range observed for diverse families of natural heme proteins. The measured properties of the de novo heme proteins can be considered as a "default" range for CO binding in alpha-helical proteins that have neither been designed to bind heme or CO, nor subjected to genetic selections for heme or CO binding.

Accidents and injuries among U.S. Navy crewmembers during extended submarine patrols, 1997 to 1999.

Accidents and injuries, the most common cause of morbidity in military populations, result in a significant number of work days lost each year and account for 75% of all active duty deaths. Rates of accidents and injuries during U.S. Navy submarine deployments have not been evaluated previously. A database designed to monitor the health of submarine crew-members was used to examine the rates and causes of accidents among deployed crewmembers aboard 196 submarine patrols between 1997 and mid 1999. The most common category of injuries was open wounds, followed by sprains and strains, contusions, superficial injuries, burns, and others. Rates of accidents and injuries decreased with increasing age and duration of military service. Among submariners working in supply departments, the rates were more than two times those of crewmembers working in other departments. Based on these data, among a submarine crew of 100 men at sea for 100 days, approximately four to five accidents or injuries might be expected and would result in an average of about 2 days of light or no duty per injury. Rates of accidents and injuries were very low; however, focused safety training could reduce rates among younger and less experienced crewmembers as well as among those working in particular areas of the submarine.

Prevention of venous thromboembolic disease following primary total knee arthroplasty. A randomized, multicenter, open-label, parallel-group comparison of enoxaparin and warfarin.

BACKGROUND: Patients treated with total knee arthroplasty are at high risk for the development of venous thromboembolism postoperatively. This study compared the efficacy and safety of two common thromboprophylactic agents, enoxaparin (a low-molecular-weight heparin) and warfarin. METHODS: Three hundred and forty-nine patients were included in a prospective, randomized, multicenter, open-label, parallel-group clinical trial. Treatment with enoxaparin (30 mg, administered subcutaneously twice daily) or warfarin (adjusted to an international normalized ratio of 2 to 3) was initiated during the immediate postoperative period, within eight hours after the surgery, and was continued for four to fourteen days. Venous thromboembolism was defined as deep-vein thrombosis documented by contrast venography, symptomatic deep-vein thrombosis documented by lower-extremity ultrasonography, or symptomatic pulmonary embolism confirmed by a positive lung scan or pulmonary angiography. RESULTS: In the all-treated-patients group, eighty (45%) of the 176 warfarin-treated patients had venous thromboembolism: fifty-nine (34%) had distal deep-vein thrombosis; twenty (11%), proximal deep-vein thrombosis; and one (0.6%), pulmonary embolism. Venous thromboembolism developed in significantly fewer (p = 0.0001) enoxaparin-treated patients (forty-four of 173; 25%): forty-one (24%) had distal deep-vein thrombosis, three (2%) had proximal deep-vein thrombosis, and none had pulmonary embolism. The enoxaparin-treated patients also had a significantly lower prevalence of proximal deep-vein thrombosis (p = 0.002). The estimated odds for the development of venous thromboembolism were 2.52 times greater (95% confidence interval, 2.00 to 3.19) with warfarin than they were with enoxaparin. Major hemorrhage occurred in four warfarin-treated patients and nine enoxaparin-treated patients; with the numbers available, this difference was not significant (p = 0.17). Clinically important operative-site hemorrhage occurred in six (3%) of the warfarin-treated patients and twelve (7%) of the enoxaparin-treated patients (p = 0.15). CONCLUSIONS: A fixed 30-mg subcutaneous dose of enoxaparin, administered twice daily, with the first dose administered within eight hours after the completion of surgery, was significantly more effective than adjusted-dose warfarin in reducing the occurrence of asymptomatic venous thromboembolism, including proximal deep-vein thrombosis, in patients undergoing total knee arthroplasty. With the numbers available, there was no significant difference between groups with regard to the occurrence of major hemorrhagic complications; however, the rate of overall hemorrhagic complications was higher in the enoxaparin group.

Assignment of the 1511 cm(-1) UV resonance Raman marker band of hemoglobin to tryptophan.

New UV resonance Raman (UVRR) data provide convincing evidence that a characteristic 1511 cm(-1) band in the T - R difference spectra of hemoglobin is due to the overtone of the Trp W18 fundamental at 756 cm(-1). Measured isotope shifts for 2-H and 15-N substitution at the indole NH group are twice as large for the 1511 cm(-1) band as for W18, and the 1511 cm(-1) intensity scales with that of W18 in the difference spectrum. Moreover, the UVRR excitation profile of the 1511 cm(-1) band tracks that of another tryptophan band, W16. Both are redshifted in hemoglobin, relative to aqueous tryptophan, reflecting H bonding within a hydrophobic environment in the protein. The 2xW18 assignment had been thrown into question by the observation of remnant 1511 cm(-1) intensity in the T - R spectra of hemoglobin labeled with tryptophan-d(5), a substitution that shifts W18 over 50 cm(-1). However, reexamination of the data suggests that this remnant intensity may result from a subtraction artifact arising from the downshift of another difference band, W3, from 1549 cm(-1) in unlabeled protein to 1522 cm(-1) in labeled protein. Restoration of the 2xW18 assignment establishes that the 1511 cm(-1) difference band, which is a useful indicator of the extent of T-state formation in hemoglobin, arises from the same residue, Trpbeta37, that gives rise to essentially all of the T - R signal from tryptophan.

Phase I clinical and pharmacokinetic study of rebeccamycin analog NSC 655649 given daily for five consecutive days.

PURPOSE: Rebeccamycin analog (NSC 655649) is active against a variety of both solid and nonsolid tumor cell lines. We performed a phase I trial to determine the maximum-tolerated dose (MTD) of rebeccamycin analog when given on a daily x 5 schedule repeated every 3 weeks, characterize the toxicity profile using this schedule, observe patients for antitumor response, and determine the pharmacokinetics of the agent and pharmacodynamic interactions. PATIENTS AND METHODS: Thirty assessable patients received a total of 153 cycles according to the following dose escalation schema: 60, 80, 106, 141, and 188 mg/m(2)/d x 5 days. RESULTS: Grade 2 phlebitis occurred in all patients before the use of central venous access, placed at dose level 4 and higher. Dose-limiting toxicity (DLT), grade 4 neutropenia, occurred at 188 mg/m(2)/d x 5 days in both previously treated and chemotherapy-naive patients. Pharmacokinetic analysis revealed a three-compartmental model of drug elimination and a long terminal half-life (154 +/- 55 hours). The percentage drop in absolute neutrophil count correlates with the area under the curve infinity. The presence of a second peak during the elimination phase as well as a high concentration of NSC 655649 in biliary fluid compared with the corresponding plasma measurement (one patient) is suggestive of enterohepatic circulation. Two partial responses, two minor responses, and six prolonged (> 6 months) cases of stable disease were observed. Of these, three patients with gallbladder cancer and one patient with cholangiocarcinoma experienced either a minor response or a significant period of freedom from progression. CONCLUSION: The recommended phase II dose for NSC 665649 on a daily x 5 every 3 weeks schedule is 141 and 165 mg/m(2)/d for patients with prior and no prior therapy, respectively, with DLT being neutropenia. During this phase I trial, encouraging antitumor activity was been observed.

Prolonged enoxaparin therapy to prevent venous thromboembolism after primary hip or knee replacement. Enoxaparin Clinical Trial Group.

BACKGROUND: Patients undergoing hip or knee joint replacement are at risk for venous thromboembolic complications for up to twelve weeks postoperatively. We evaluated the efficacy and safety of a prolonged post-hospital regimen of enoxaparin, a low-molecular-weight heparin, in this patient population. METHODS: Following elective total hip or knee replacement, 968 patients received subcutaneous enoxaparin (30 mg twice daily) for seven to ten days, and 873 were then randomized to receive three weeks of double-blind outpatient treatment with either enoxaparin (40 mg once daily) or a placebo. The primary efficacy end point was the prevalence of objectively confirmed venous thromboembolism or symptomatic pulmonary embolism during the double-blind phase of treatment. RESULTS: Of the 873 randomized patients, 435 underwent elective total hip replacement and 438 underwent elective total knee replacement. Enoxaparin was superior to the placebo in reducing the prevalence of venous thromboembolism in patients treated with hip replacement: 8.0% (eighteen) of the 224 patients treated with enoxaparin had venous thromboembolism compared with 23.2% (forty-nine) of the 211 patients treated with the placebo (p < 0.001; odds ratio, 3.62; 95% confidence interval, 2.00 to 6.55; relative risk reduction, 65.5%). Enoxaparin had no significant benefit in the patients treated with knee replacement: thirty-eight (17.5%) of the 217 patients treated with enoxaparin had venous thromboembolism compared with forty-six (20.8%) of the 221 patients treated with the placebo (p = 0.380; odds ratio, 1.24; 95% confidence interval, 0.76 to 2.02; relative risk reduction, 15.9%). Symptomatic pulmonary embolism developed in three patients, one with a hip replacement and two with a knee replacement; all had received the placebo. There was no significant difference in the prevalence of hemorrhagic episodes or other types of toxicity between the enoxaparin and placebo-treated groups. CONCLUSIONS: Prolonging enoxaparin thromboprophylaxis following hip replacement for a total of four weeks provided therapeutic benefit, by reducing the prevalence of venous thromboembolism, without compromising safety. A similar benefit was not observed in patients treated with knee replacement.

Is the CO adduct of myoglobin bent, and does it matter?

Early reports of a severely bent CO adduct in myoglobin inspired the idea that heme proteins discriminate against CO, relative to O(2), via steric hindrance imposed by a distal histidine residue. Recent results showing that the bound CO is only slightly distorted do not by themselves overthrow the steric hypothesis, because the steric energy could be stored in displacements of the protein. However, experimental data on site-directed mutants show that the main determinant of ligand affinity changes is the polarity of the binding pocket and that H-bonding by the distal histidine accounts for about 85% of the O(2)/CO discrimination while steric hindrance accounts for the remaining 15%.

Subcutaneous enoxaparin once or twice daily compared with intravenous unfractionated heparin for treatment of venous thromboembolic disease.

BACKGROUND: Low-molecular-weight heparins administered subcutaneously once or twice daily have been reported to be as safe and efficacious as intravenous unfractionated heparin in the treatment of acute venous thromboembolic disease. OBJECTIVE: To determine whether subcutaneous enoxaparin administered once or twice daily is as effective as continuously infused unfractionated heparin in acute symptomatic venous thromboembolic disease. DESIGN: Randomized, controlled, partially blinded equivalence trial. SETTING: 74 hospitals in 16 countries. PATIENTS: 900 patients with symptomatic lower-extremity deep venous thrombosis, including 287 (32%) with confirmed pulmonary embolism. INTERVENTIONS: Initial therapy with dose-adjusted intravenous unfractionated heparin compared with subcutaneous enoxaparin at fixed dosages of 1.0 mg/kg of body weight twice daily or 1.5 mg/kg once daily. Long-term oral anticoagulation was started in all patients within 72 hours of randomization. MEASUREMENTS: Clinical end points assessed during a 3-month follow-up period. RESULTS: Equivalent efficacy was seen in the heparin group and both enoxaparin groups. Symptomatic venous thromboembolism recurred in 12 of 290 patients receiving unfractionated heparin (4.1%), 13 of 298 patients receiving once-daily enoxaparin (4.4%), and 9 of 312 patients receiving twice-daily enoxaparin (2.9%). Compared with unfractionated heparin, the treatment difference was 0.2% (95% CI, -3.04% to 3.49%) for once-daily enoxaparin and -1.2% (CI, -4.2% to 1.7%) for twice-daily enoxaparin. Incidence of major hemorrhage did not differ among the three treatment groups. Major hemorrhage occurred in 6 of 290 patients (2.1%) in the unfractionated heparin group, 5 of 298 patients (1.7%) in the once-daily enoxaparin group, and 4 of 312 patients (1.3%) in the twice-daily enoxaparin group. CONCLUSIONS: Subcutaneous enoxaparin once or twice daily is as effective and safe as dose-adjusted, continuously infused unfractionated heparin in the prevention of recurrent symptomatic venous thromboembolic disease.

Cost for inpatient care of venous thrombosis: a trial of enoxaparin vs standard heparin.

BACKGROUND: Enoxaparin, a low-molecular-weight heparin administered to hospitalized patients once or twice daily, has shown efficacy and safety equivalent to unfractionated heparin in the treatment of acute venous thromboembolic disease. Although the cost of either enoxaparin regimen is greater than that of unfractionated heparin, the overall cost of care for each of these 3 treatment strategies is unknown. METHODS: A cost minimization analysis of a 3-month, partially blinded, randomized, controlled efficacy and safety trial of anticoagulant therapy for deep vein thrombosis. Three hundred thirty-nine hospitalized patients with symptomatic lower extremity deep vein thrombosis were randomly assigned to initial therapy with subcutaneous enoxaparin either once (n = 112) or twice (n = 123) daily, or with dose-adjusted intravenous unfractionated heparin (n = 104), followed by long-term oral anticoagulant therapy. Estimated 1997 total cost from a third-party payer perspective for the 3-month episode of care was calculated by assigning standard unit costs to counts of medical resources used by each patient in the clinical trial. RESULTS: Average total cost for the 3-month episode of care was similar across all 3 treatment regimens: once-daily dose of enoxaparin, $12,166 (95% confidence interval [CI], $10,744-$13,588); twice-daily dose of enoxaparin, $11,558 (95% CI, $10,201-$12,915); and unfractionated heparin, $12,146 (95% CI, $10,670-$12,622). Bootstrapped estimates and sensitivity analyses did not significantly change findings. CONCLUSIONS: There was no significant difference in the overall cost for the 3-month episode of care for patients treated with either enoxaparin or unfractionated heparin. Additional acquisition costs for anticoagulant medication among patients treated with enoxaparin were offset by savings associated with lower incidence of hospital readmission and shorter duration of venous thromboembolism-related readmissions.

New cytotoxic agents for the treatment of metastatic malignant melanoma: temozolomide and related alkylating agents in combination with guanine analogues to abrogate drug resistance.

The chloroethylating nitrosoureas (lomustine, fotemustine, cystemustine (BCNU) and methylating agents temozolomide (TMZ), dacarbazine (DTIC), procarbazine) have documented activity in metastatic malignant melanoma with single agent response rates of 15-25%. Chloroethylating agents form chloroethyl adducts at the O6 position of guanine, resulting in N1-guanine, N3-cytosine interstrand crosslinks which are cytotoxic. Methylating agents attack DNA at multiple sites, although most of their cytotoxic activity is due to the formation of methyl adducts at the O6 position of guanine. The presence of these adducts results in a futile recycling of the mismatch repair pathway resulting in DNA strand breaks and apoptotic cell death. An intact mismatch repair system is required to achieve their cytotoxic effect. Repair of adducts by the DNA repair protein O6-alkylguanine DNA alkyltransferase (AGT) impairs the cytotoxic action of both methylating and chloroethylating agents, and mediates a major resistance pathway to these drugs. During DNA repair, irreversible inactivation of AGT occurs. To regenerate AGT activity, synthesis of new molecules is required. Increased but variable AGT activity is found in malignant melanoma, is higher in metastatic lesions than in primary tumours, and is higher in tumours than normal skin. Expression of AGT activity, is higher in melanoma metastases after DTIC chemotherapy compared to expression prior to therapy. TMZ alone depletes human AGT in tumour tissue and peripheral blood progenitor cells. As the t1/2 of TMZ via the oral route is short (approximately 1.8 hours), and the anti-tumour activity of the drug is known to be schedule-dependent, twice daily or prolonged administration schedules of TMZ prevent regeneration of AGT, and render tumour cells more sensitive to the drug. O6-benzylguanine (BG) is a potent AGT inactivating agent. BG and its analogues reduce AGT activity, and increase the in vitro and in vivo efficacy of both methylating and chloroethylating agents. In clinical trials, non-toxic doses of BG deplete AGT to undetectable levels. AGT depleting agents in combination with methylating and chloroethylating agents are now in clinical testing, and may result in greater clinical efficacy in metastatic malignant melanoma.

Selective enhancement of resonance Raman spectra of separate bacteriopheophytins in Rb. sphaeroides reaction centers.

Tunable dye laser excitation of carefully prepared samples of Rb. sphaeroides reaction centers provides richly detailed resonance Raman (RR) spectra of the bacteriopheophytins, H, and the accessory bacteriochlorophylls, B. These spectra demonstrate selective enhancement of the separate bacteriopheophytins on the active (H(L)) and inactive (H(M)) sides of the reaction centers. The spectra are assigned with the aid of normal coordinate analyses using force fields previously developed for porphyrins and reduced porphyrins. Comparison of the H(L) and H(M) vibrational mode frequencies reveals evidence for greater polarization of the acetyl substituent in H(L) than H(M). This polarization is expected to make H(L) easier to reduce, thereby contributing to the directionality of electron transfer from the special pair, P. In addition, the acetyl polarization of H(L) is increased at low temperature (100 K), helping to account for the increase in electron transfer rate. The polarizing field is suggested to arise from the Mg(2+) of the neighboring accessory bacteriochlorophyll, which is 4.9 A from the acetyl O atom. The 100 K spectra show sharpening and intensification of a number of RR bands, suggesting a narrowing of the conformational distribution of chromophores, which is consistent with the reported narrowing of the distribution in electron transfer rates. Excitation at 800 nm produces high-quality RR spectra of the accessory bacteriochlorophylls, and the spectral pattern is unaltered on tuning the excitation to 810 nm in resonance with the upper exciton transition of P. Either the resonance enhancement of P is weak, or the bacteriochlorophyll RR spectra are indistinguishable for P and B.