Fungicidal activity of human lactoferrin-derived peptides based on the antimicrobial αß region.

Owing to the increasing number of infections in hospitalised patients caused by resistant strains of fungi, there is a need to develop new therapeutic agents for these infections. Naturally occurring antimicrobial peptides may constitute models for developing such agents. A modified peptide sequence (CFQWKRAMRKVR; HLopt2) based on amino acid residues 20-31 of the N-terminal end of human lactoferrin (hLF) as well as a double-sized human lactoferricin-like peptide (amino acid residues 16-40; HLBD1) were investigated for their antifungal activities in vitro and in vivo. By in vitro assay, HLopt2 was fungicidal at concentrations of 12.5-25 µg/mL against Cryptococcus neoformans, Candida albicans, Candida krusei, Candida kefyr and Candida parapsilosis, but not against Candida glabrata. HLopt2 was demonstrated to have ≥ 16-fold greater killing activity than HLBD1. By inducing some helical formation caused by lactam bridges or by extending the assay time (from 2h to 20 h), HLBD1 became almost comparable with HLopt2 in its fungicidal activity. Killing of C. albicans yeast cells by HLopt2 was rapid and was accompanied by cytoplasmic and mitochondrial membrane permeabilisation as well as formation of deep pits on the yeast cell surface. In a murine C. albicans skin infection model, atopic treatment with the peptides resulted in significantly reduced yields of Candida from the infected skin areas. The antifungal activities of HLopt2 in vitro and in vivo suggest possible potential as a therapeutic agent against most Candida spp. and C. neoformans. The greatly improved antifungal effect of the lactam-modified HLBD1 indicates the importance of amphipathic helix formation for lethal activity.

Structure-microbicidal activity relationship of synthetic fragments derived from the antibacterial alpha-helix of human lactoferrin.

There is a need for new microbicidal agents with therapeutic potential due to antibiotic resistance in bacteria and fungi. In this study, the structure-microbicidal activity relationship of amino acid residues 14 to 31 (sequence 14-31) from the N-terminal end, corresponding to the antibacterial alpha-helix of human lactoferrin (LF), was investigated by downsizing, alanine scanning, and substitution of amino acids. Microbicidal analysis (99% killing) was performed by a microplate assay using Escherichia coli, Staphylococcus aureus, and Candida albicans as test organisms. Starting from the N-terminal end, downsizing of peptide sequence 14-31 showed that the peptide sequence 19-31 (KCFQWQRNMRKVR, HL9) was the optimal length for antimicrobial activity. Furthermore, HL9 bound to lipid A/lipopolysaccharide, as shown by neutralizing endotoxic activity in a Limulus assay. Alanine scanning of peptide sequence 20-31 showed that Cys20, Trp23, Arg28, Lys29, or Arg31 was important for expressing full killing activity, particularly against C. albicans. Substituting the neutral hydrophilic amino acids Gln24 and Asn26 for Lys and Ala (HLopt2), respectively, enhanced microbicidal activity significantly against all test organisms compared to the amino acids natural counterpart, also, in comparison with HL9, HLopt2 had more than 10-fold-stronger fungicidal activity. Furthermore, HLopt2 was less affected by metallic salts than HL9. The microbicidal activity of HLopt2 was slightly reduced only at pH 7.0, as tested in the pH range of 4.5 to 7.5. The results showed that the microbicidal activity of synthetic peptide sequences, based on the antimicrobial alpha-helix region of LF, can be significantly enhanced by optimizing the length and substitution of neutral amino acids at specific positions, thus suggesting a sequence lead with therapeutic potential.

Synthetic de novo designed polypeptides for control of nanoparticle assembly and biosensing.

This contribution describes how de novo designed synthetic helix-loop-helix polypeptides are utilized to control the assembly of gold nanoparticles and as scaffolds for biosensing. The synthetic polypeptides are designed to fold into a four-helix bundle upon dimerization. When immobilized on gold nanoparticles, dimerization and folding occur between peptides on neighbouring particles as an effect of particle aggregation and the folded polypeptides are rigid enough to keep the particles separated at a distance corresponding to the size of the four-helix bundle. Moreover, peptide dimerization offers a convenient route to assemble nanoparticles into hybrid multilayers on planar substrates. The drastic change in the resonance conditions of the localized nanoparticle surface plasmon upon particle aggregation is shown to be useful for optical detection of biomolecular interactions.

Alpha-helix-inducing dimerization of synthetic polypeptide scaffolds on gold.

Designed, synthetic polypeptides that assemble into four-helix bundles upon dimerization in solution were studied with respect to folding on planar gold surfaces. A model system with controllable dimerization properties was employed, consisting of negatively and positively charged peptides. Circular dichroism spectroscopy and surface plasmon resonance based measurements showed that at neutral pH, the peptides were able to form heterodimers in solution, but unfavorable electrostatic interactions prevented the formation of homodimers. The dimerization propensity was found to be both pH- and buffer-dependent. A series of infrared absorption-reflection spectroscopy experiments of the polypeptides attached to planar gold surfaces revealed that if the negatively charged peptide was immobilized from a loading solution where it was folded, its structure was retained on the surface provided it had a cysteine residue available for anchoring to gold. If it was immobilized as random coil, it remained unstructured on the surface but was able to fold through heterodimerization if subsequently exposed to a positively charged polypeptide. When the positively charged peptide was immobilized as random coil, heterodimerization could not be induced, probably because of high-affinity interactions between the charged primary amine groups and the gold surface. These observations are intended to pave the way for future engineering of functional surfaces based on polypeptide scaffolds where folding is known to be crucial for function.

Anti-inflammatory activities of human lactoferrin in acute dextran sulphate-induced colitis in mice.

In this study, we investigated the anti-inflammatory effects of orally administered human lactoferrin (hLF) and two peptides, based on the bactericidal region of hLF (HLD1 and HLD2), on the course of experimental colitis. Acute colitis was induced in C57Bl/6 mice by giving 5% dextran sulphate (DX) in the drinking water. The mice were killed after 2 or 7 days of DX exposure. The animals were given hLF or the peptides orally twice a day (2 mg/dose/mouse) during the DX exposure. In the control animals, the hLF or the peptides were replaced by bovine serum albumin or water. The appearance of occult blood in the faeces and macroscopic rectal bleeding were significantly delayed and partly reduced in the hLF-treated animals compared with the control animals. The shortening of the colon, a pathological effect of DX exposure, was significantly less pronounced in the hLF-treated group compared with the control group. Also, the interleukin-1beta (IL-1beta) levels in the blood were significantly diminished in this group after 2 days of DX exposure. A significantly lower crypt score was observed in the distal part of the colon in the hLF-treated group compared with the control group. Also, significantly reduced numbers of CD4 cells, F4/80-positive macrophages and tumour necrosis factor-alpha-producing cells were detected by immunohistochemistry in the distal colon of the hLF-treated animals compared with the control animals after 7 days of DX exposure. A reduction was also observed concerning the IL-10-producing cells in the middle colonic submucosa. The HLD1 and HLD2 treatment, which was carried out for 2 days, only gave results almost identical to those of hLF, concerning clinical parameters after the 2 days of DX exposure. An even stronger effect was observed for HLD2, regarding decreased occult blood in the faeces and colon length. Our results show that perorally given hLF mediates anti-inflammatory effects on the DX-induced acute colitis, and further suggest that the bactericidal region of the hLF molecule may be involved in these activities.

Emerging principles of de novo catalyst design.

Considerable progress has been made in the understanding of how to exploit hydrophobic and charge-charge interactions in forming binding sites for peptides and small molecules in folded polypeptide catalysts. This knowledge has enabled the introduction of feedback and control functions into catalytic cycles and the construction of folded polypeptide catalysts that follow saturation kinetics. Major advances have also been made in the design of metalloproteins and metallopeptides, especially with regards to understanding redox potential control.

Human lactoferrin and peptides derived from a surface-exposed helical region reduce experimental Escherichia coli urinary tract infection in mice.

Lactoferrin (LF) is a multifunctional immunoregulatory protein that has been associated with host defense at mucosal surfaces through its antibacterial properties. The antibacterial and anti-inflammatory properties of LF were further explored with an animal model of experimental urinary tract infection. Bovine LF (bLF), human LF (hLF), and synthetic peptide sequences based on the antibacterial region of hLF (amino acid residues 16 to 40 [HLD1] and 18 to 40 [HLD2]) were given orally to female mice 30 min after the instillation of 10(8) Escherichia coli bacteria into the urinary bladder. The control groups received phosphate-buffered saline or water. C3H/Tif mice were treated with hLF or bLF, and C3H/HeN mice were treated with bLF only. The numbers of bacteria in the kidneys and bladder of C3H/Tif and C3H/HeN mice were significantly reduced 24 h later by the LF treatments compared to the findings for the control group. The hLF-treated group showed the strongest reduction compared with the vehicle-treated-group (P values were 0.009 and 0.0001 for the kidneys and bladder, respectively). The urinary leukocyte response was diminished in the hLF-treated group. The hLF treatment also significantly reduced the urinary interleukin-6 (IL-6) levels at 2 h and the systemic IL-6 levels at 24 h after infection (P values were 0.04 and < 0.002, respectively). In the bLF-treated animals, no such strong anti-inflammatory effects were obtained. In another series of experiments, C3H/Tif mice perorally treated with HLD1 or HLD2 also showed reduced numbers of bacteria in the kidneys compared with the vehicle-treated mice, although the results were significantly different only for HLD2 (P < 0.01). Analysis of urine from hLF-fed C3H/Tif mice showed that hLF was excreted into the urinary tract at 2 h after feeding. Testing of the in vitro bactericidal activity of LF (1 mg/ml) or the peptides (0.1 mg/ml) in mouse urine against the E. coli bacteria revealed moderate killing only by HLD2. In conclusion, these results demonstrate for the first time that oral administration of hLF or peptides thereof is effective in reducing infection and inflammation at a remote site, the urinary tract, possibly through transfer of hLF or its peptides to the site of infection via renal secretion. The antibacterial mechanism is suggested to involve bactericidal capacities of LF, fragments thereof, or its peptides.

Reactive-site design in folded-polypeptide catalysts--the leaving group pKa of reactive esters sets the stage for cooperativity in nucleophilic and general-acid catalysis.

The second-order rate constants for the hydrolysis of nitrophenyl esters catalysed by a number of folded designed polypeptides have been determined, and 1900-fold rate enhancements over those of the 4-methylimidazole-catalysed reactions have been observed. The rate enhancements are much larger than those expected from the pKa depression of the nucleophilic His residues alone. Kinetic solvent isotope effects were observed at pH values lower than the pKa values of the leaving groups and suggests that general-acid catalysis contributes in the pH range where the leaving group is predominantly protonated. In contrast, no isotope effects were observed at pH values above the pKa of the leaving group. A Hammett rho value of 1.4 has been determined for the peptide-catalysed hydrolysis reaction by variation of the substituents of the leaving phenol. The corresponding values for the imidazole-catalysed reaction is 0.8 and for phenol dissociation is 2.2. There is therefore, very approximately, half a negative charge localised on the phenolate oxygen in the transition state in agreement with the conclusion that transition-state hydrogen-bond formation may contribute to the observed catalysis. The elucidation at a molecular level of the principles that control cooperativity in the biocatalysed ester-hydrolysis reaction represents the first step towards a level of understanding of the concept of cooperativity that may eventually allow us to design tailor-made enzymes for chemical reactions not catalysed by nature.

Designed four-helix bundle catalysts--the engineering of reactive sites for hydrolysis and transesterification reactions of p-nitrophenyl esters.

Four-helix bundle proteins have been designed that catalyze the hydrolysis and transesterification reactions of p-nitrophenyl esters by a cooperative nucleophilic and general acid mechanism. The catalysts consist of two 42-residue peptides that fold into helix-loop-helix motifs and dimerise. They have previously been shown to recognize anionic and hydrophobic substrates and to follow saturation kinetics. The catalytic entity is a HisH(+)-His pair in a helical segment spaced i, i+4, which can be supplemented by arginines and lysines in the adjacent helix. The binding residues have now been optimized for the catalysis of mono-p-nitrophenyl fumarate hydrolysis and found to vary with the location of the site. The catalytic efficiency of the HisH(+)-His site in helix II in positions 30 and 34 is enhanced by the introduction of arginine and or lysine residues in positions 11 and 15, but not in 8 and 11 or in 15 and 19. The most efficient catalyst using this site, JNIIR11K15, catalyses the reaction with a second-order rate constant of 0.134 M(-1) s(-1) in aqueous solution at pH 5.1 and 290 K. The second-order rate constant is larger than those of the corresponding sites with 'longer' and 'shorter' binding residues. Similar experiments have shown that the efficiency and selectivity of catalysts based on a HisH(+)-11-His-15 site in helix I are enhanced the most by the introduction of Lys-30 and Arg-34.

Oral cisapride for the control of delayed vomiting following high-dose cisplatin.

Although combination antiemetics prevent vomiting during the initial 24 h after high-dose (> or =100 mg/m2) cisplatin, many patients experience delayed emesis 24-120 h afterwards despite receiving prophylactic dexamethasone and metoclopramide during this time. Cisapride is a prokinetic agent, which stimulates propulsive motility throughout the gastrointestinal tract without causing extrapyramidal effects. In this phase II trial, we tested the ability of cisapride to prevent delayed emesis following cisplatin. Twenty patients receiving initial cisplatin >100 mg/m2 were entered. All patients received intravenous dexamethasone with either metoclopramide or ondansetron to prevent acute emesis 0-24 h after receiving cisplatin. Patients who had experienced two or fewer acute vomiting episodes then received cisapride 20 mg orally four times daily for 4 days (24-120 h after cisplatin). Cisapride prevented delayed emesis in 2 patients (10%) during the entire 4-day period (95% confidence interval, 1-32%). Abdominal cramping and pain occurred in 35%. At the dose and schedule tested, oral cisapride prevented delayed emesis in only 10% of patients receiving cisplatin >100 mg/m2 and caused abdominal cramping in 35%. Since in prior trials among similar patients, placebo prevented delayed emesis in 11%, further study of cisapride and dose escalation for this indication are not recommended.

Functionalization of designed folded polypeptides.

Recent progress in the design of folded polypeptides has led to new catalysts, peptides that bind metal ions, hemes and cofactors, and folded glycopeptides. The development of techniques for postsynthetic and post-translational functionalization promises to further expand the repertoire of accessible motifs. The demonstration of function in complex sites helps to understand protein structure and function and has important implications for the engineering of new proteins with novel properties.

Site-selective control of the reactivity of surface-exposed histidine residues in designed four-helix-bundle catalysts.

BACKGROUND: The structure and function of native proteins often depend on the interplay between ionisable residues with physical properties that have been fine tuned by interactions with neighbouring groups. Here, we systematically vary the environment of histidines in designed helix-loop-helix motifs to modulate histidine pKa values and reactivities. RESULTS: 25 helix-loop-helix motifs were designed in which surface-exposed histidine residues were flanked by neutral, negatively charged and positively charged groups and the histidine's proximity to the hydrophobic core was varied. The 57 histidine pKa values were determined by 1H NMR spectroscopy and found to be in the interval 5.2-7.2 with changes ranging from a decrease of 1.3 pKa units to an increase of 0.7 pKa units compared with the pKa for an unperturbed histidine residue. CONCLUSIONS: A decrease in the pKa of His34 by 1.3 units was accomplished by placing it in close proximity to the hydrophobic core and flanking it by positively charged residues in positions (i, i + 3) and (i, i - 4). Flanking a histidine residue with a lysine or a histidine in positions (i, i + 3), (i, i + 4) or (i, i - 4) resulted in pKa depressions of approximately 0.5 pKa units per residue and additivity was observed. The increase of the histidine pKa by glutamate residues was the most efficient in position (i, i + 3), but less efficient in position (i, i + 4). These principles should be useful in the engineering of novel catalysts.

Assuring the optimal use of serotonin antagonist antiemetics: the process for development and implementation of institutional antiemetic guidelines at Memorial Sloan-Kettering Cancer Center.

PURPOSE: The need to foster the appropriate and cost-effective use of serotonin-antagonist antiemetic drugs spurred the creation of guidelines. The process by which institution-wide guidelines at Sloan-Kettering were developed, implemented, assessed, and modified is described. METHODS: A multidisciplinary group working with disease-specific management teams assigned the emetic potential of chemotherapy programs to one of five categories. Antiemetic regimens, including a specified dose and schedule of a serotonin-antagonist and dexamethasone, were assigned to each emetic category. The information was collated by disease site and chemotherapy program into hospital-wide antiemetic regimen recommendations. Quality assessment was conducted initially and repeated each time the guidelines were modified. RESULTS: Patient surveys demonstrated a high level of satisfaction with emetic control, which was similar to reported results. Data from the latest survey showed zero emetic episodes in 93% and 87% of participants given moderate and highly emetogenic chemotherapy, respectively. Compliance with the guidelines, initially in 73%, has been improved using a standardized chemotherapy order "check box" labeled, "Antiemetics as per Guidelines." Antiemetic drug expenditures decreased from a projected $2.8 million to $1.3 million annually. CONCLUSION: The guidelines became an educational tool that ensured the delivery of optimal antiemetic therapy chosen by professionals with the greatest knowledge of both the particular chemotherapy regimen and cancer site. Implementation of the guidelines resulted in substantial savings while treating more patients. The guidelines were easily modified as new chemotherapeutic agents and antiemetic drugs became available.

The pH-dependent tertiary structure of a designed helix-loop-helix dimer.

BACKGROUND: De novo designed helix-loop-helix motifs can fold into well-defined tertiary structures if residues or groups of residues are incorporated at the helix-helix boundary to form helix-recognition sites that restrict the conformational degrees of freedom of the helical segments. Understanding the relationship between structure and function of conformational constraints therefore forms the basis for the engineering of non-natural proteins. This paper describes the design of an interhelical HisH+-Asp- hydrogen-bonded ion pair and the conformational stability of the folded helix-loop-helix motif. RESULTS: GTD-C, a polypeptide with 43 amino acid residues, has been designed to fold into a hairpin helix-loop-helix motif that can dimerise to form a four-helix bundle. The folded motif is in slow conformational exchange on the NMR timescale and has a well-dispersed 1H NMR spectrum, a narrow temperature interval for thermal denaturation and a near-UV CD spectrum with some fine structure. The conformational stability is pH dependent with an optimum that corresponds to the pH for maximum formation of a hydrogen-bonded ion pair between HisH17+ in helix I and Asp27- in helix II. CONCLUSIONS: The formation of an interhelical salt bridge is strongly suggested by the pH dependence of a number of spectroscopic probes to generate a well-defined tertiary structure in a designed helix-loop-helix motif. The thermodynamic stability of the folded motif is not increased by the formation of the salt bridge, but neighbouring conformations are destabilised. The use of this novel design principle in combination with hydrophobic interactions that provide sufficient binding energy in the folded structure should be of general use in de novo design of native-like proteins.

Structure and dynamics of a designed helix-loop-helix dimer in dilute aqueous trifluoroethanol solution. A strategy for NMR spectroscopic structure determination of molten globules in the rational design of native-like proteins.

BACKGROUND: The overwhelming majority of engineered amino acid sequences designed to fold into well defined tertiary structures show the hallmarks of molten globules. Although imperfectly folded, the structures of these polypeptides are of considerable interest in assessing the predictive power of design strategies and in understanding the structural basis for the formation of proteins with native-like properties. This paper describes a strategy for the structural characterization of molten globules by NMR spectroscopy applied to the study of SA-42, a polypeptide with 42 amino acids that folds into a hairpin helix-loop-helix dimer. RESULTS: The 1H NMR spectrum of SA-42 was assigned in several mixtures of water and trifluoroethanol (TFE) (0-30 vol%) and small amounts of TFE were shown to have a significant effect on the spectrum. The secondary and supersecondary structures of SA-42 were determined. In aqueous solution a helix-loop-helix dimer is formed, but in 30 vol% of TFE the population of hairpin dimers are negligible and SA-42 is monomeric, folding into two non-interacting helical segments. In solutions containing less than 3 vol% of TFE the structure is very similar to that in water and the structural information may be used to develop the motif in aqueous solution. Less well ordered amino acid residue sidechains in the hydrophobic core were identified. Helix distortion in the tetrahelix bundle was found to be small. CONCLUSIONS: Detailed information about molten globule structures in aqueous solution can be obtained from NMR spectroscopy if the spectra are assigned in dilute TFE solution. On the basis of the NMR spectroscopic analysis, the solution structure of SA-42 was found to be close to the designed one. A route for developing native-like properties in SA-42 is suggested based on the identification by NMR spectroscopy of some less well ordered amino acid sidechains in the hydrophobic core and on the observed structural rigidity of the two helices.

Randomized phase II trial comparing two versus three doses of ondansetron when used in combination with dexamethasone in patients receiving cisplatin > or = 100 mg/m2.

Ondansetron controls cisplatin-induced emesis when given in three 0.15 mg/kg doses, and preliminary data suggest that control may be maintained when fewer doses are employed. Prior trials have further shown improved antiemetic effects and fewer adverse effects of cisplatin treatment when neurotransmitter receptor blockers are combined with dexamethasone. This trial was undertaken to determine the effectiveness of the combination of dexamethasone and ondansetron and to see if equivalent results could be obtained with only two doses of ondansetron. There were 44 patients receiving initial cisplatin at a dose > or = 100 mg/m2, each given dexamethasone 20 mg and randomized to receive either two or three 0.15 mg/kg doses of ondansetron. Vomiting prevention was identical (35%) whether two or three doses were given. No new adverse effects were noted and cisplatin-induced diarrhea, usually seen in up to 60% of patients given this dose of cisplatin, was noted in only 5%. Although this trial did not demonstrate enhanced antiemetic effects with the combination, other investigators have done so and all agree that the regimen is safe and reduces adverse effects. Further exploration and use of the combination of ondansetron and dexamethasone, and studies testing fewer doses of ondansetron in this regimen are warranted.

Dose-ranging evaluation of the serotonin antagonist dolasetron mesylate in patients receiving high-dose cisplatin.

PURPOSE: This dose-ranging trial of intravenous dolasetron mesylate (MDL73,147EF) was performed to determine its adverse and antiemetic effects in patients receiving cisplatin at doses > or = 100 mg/m2. PATIENTS AND METHODS: Eighty-nine patients treated with initial cisplatin received a single intravenous dose of dolasetron mesylate administered over 20 minutes beginning 30 minutes before chemotherapy. The following four dose levels were studied: 1.8, 2.4, 3.0, and 5.0 mg/kg. Emesis and adverse effects were measured for 24 hours after cisplatin. RESULTS: All adverse effects were mild and transient including loose stools, headache, serum AST/ALT elevations, and asymptomatic prolongation of ECG intervals. Among the dose levels, no-emesis rates from 24% to 52% were observed, and the percentage of patients having zero, one, or two emetic episodes ranged from 48% to 82%. Complete control of vomiting increased as the dose was escalated to 2.4 mg/kg, but did not improve further with higher doses. CONCLUSION: Dolasetron mesylate can be administered safely at doses up to 5.0 mg/kg, with comparable complete protection rates and increased adverse effects at doses greater than 2.4 mg/kg. Antiemetic activity was seen after cisplatin. Trials comparing single infusions of dolasetron mesylate and ondansetron are under way.

The addition of ondansetron to the combination of metoclopramide, dexamethasone, and lorazepam did not improve vomiting prevention in patients receiving high-dose cisplatin.

BACKGROUND: Serotonin has been shown to be an important mediator of chemotherapy-induced vomiting. Ondansetron is a potent and highly specific antagonist of the 5-HT3 serotonin receptor. The objective of the current trial was to determine if the addition of ondansetron to the combination of metoclopramide, dexamethasone, and lorazepam (MDL) could improve the control of vomiting in patients receiving high-dose cisplatin. The three-drug MDL antiemetic regimen has been shown to prevent vomiting in 67% of patients receiving high-dose cisplatin. METHODS: Thirty-two patients receiving initial cisplatin (greater than or equal to 100 mg/m2) were given intravenous lorazepam, 1.5 mg/m2 (maximum dose, 3 mg), one dose 45 minutes before cisplatin; metoclopramide, 3 mg/kg 40 minutes before and 90 minutes after cisplatin; ondansetron, 0.3 mg/kg 25 minutes before and 3.5 hours after cisplatin; and dexamethasone, 20 mg, one dose 10 minutes before cisplatin. Patients were followed for 24 hours after cisplatin administration. RESULTS: Vomiting was prevented in 67% of patients (95% confidence interval, 47-83%). Adverse effects were mild and transient and included sedation, headache, serum aspartate transaminase, and alanine transaminase elevations, akathisia, and hiccups. CONCLUSIONS: Vomiting was prevented in two thirds of patients treated with MDL plus ondansetron, a result similar to that observed in earlier trials of MDL alone. The lack of improvement in emetic control by the addition of ondansetron suggests that vomiting mediated through 5-HT3 receptors is already effectively blocked. Emesis that occurs despite pretreatment with MDL is likely mediated by other mechanisms.

Enhancing the effectiveness of the specific serotonin antagonists. Combination antiemetic therapy with dexamethasone.

Combinations of drugs have become standard therapy for the prevention of vomiting caused by anticancer drugs like cisplatin. Recently, a new class of antiemetic agents, the potent and specific 5-HT3 receptor antagonists such as ondansetron, granisetron, and tropisetron, have been shown to be more effective and better tolerated than metoclopramide. This report describes the rationale for combination antiemetic therapy, details the testing of metoclopramide-based regimens as a model for combination therapy development, reviews completed trials of ondansetron plus dexamethasone, and offers strategies to further alleviate vomiting during anticancer chemotherapy. The reported trials testing metoclopramide-based combinations were reviewed and that experience was applied to the ongoing studies of ondansetron when used with dexamethasone and other agents. Combinations of metoclopramide, dexamethasone, and lorazepam prevented acute emesis caused by high-dose cisplatin in 63% of patients, lessened side effects, and were convenient enough to administer to outpatients. Completed trials of ondansetron and dexamethasone demonstrated improved vomiting control over ondansetron alone while using less cumbersome schedules. Attempts to improve ondansetron-based antiemetic regimens by developing optimal drug doses and schedules and adding adjuvant and different classes of antiemetic agents are now in clinical testing. Based on previous experience and current results, combinations of a specific serotonin agonist and dexamethasone are the best treatment for prevention of vomiting induced by chemotherapy. Future clinical research should aim to refine antiemetic regimens and improve emetic control through the use of new antiemetic and adjuvant agents.