Pharmacokinetic Problems Research Articles

EB1627: a soluble prodrug of the potent anticancer cyanoguanidine CHS828

To overcome pharmacokinetic and solubility problems observed in early clinical trials with the potent anticancer compound CHS828, we synthesised a series of prodrugs with improved properties. The best compound obtained was EB1627, with a tetraethyleneglycol moiety attached to the parent drug via a carbonate linkage. This compound was found soluble enough to be given i.v. and the drug was rapidly released in vivo exerting a very potent inhibitory activity alone and in combination with known cytostatics (etoposide) in animal models in vivo.

Aromatase Inhibitors: A New Paradigm in Breast Cancer Treatment

Microsomal cytochrome P450 (CYP 450) enzyme aromatase belongs to CYP 19 super family. It is involved in the conversion of androgens to estrogens. In postmenopausal women the main sites of aromatisation are skin, adipose tissue and breast. Aromatase localized in breast tumor produces sufficient estrogen for its proliferation. Hence it is an important target for the treatment of hormone dependent breast cancer in postmenopausal women. There are mainly two types of aromatase inhibitors, one is steroidal another is nonsteroidal type. The first and second generation aromatase inhibitors encounter the undesirable drug- drug interactions besides being not very specific and plagued with pharmacokinetic problems. Third generation aromatase inhibitors developed recently are more potent and specific with a greater capacity to annihilate circulating estrogen levels. These agents have satisfactory pharmacokinetic profiles and are devoid of major drug-drug interactions. Third generation aromatase inhibitors became drugs of choice for both first and second line treatment of advanced breast cancer. Aromatase inhibitors can also be used for neoadjuvant therapy of breast cancer in which they have achieved better therapeutic efficacy than tamoxifen. Early results of ATAC (Armidex Tamoxifen Alone or Combination) trial suggest that anastrozole is superior to tamoxifen in adjuvant setting for disease free survival, particularly in receptor positive patients, and in reducing the incidence of contralateral breast cancer. Therapeutic potential of aromatase inhibitors stretches beyond the postmenopausal breast cancer treatment as they also play a role in the treatment of estrogen dependent benign and malignant conditions such as gynaecomastia, prostate cancer, fibroadenomata and the induction of ovulation. By virtue of their ability to reduce estrogen levels they pose problems like demineralization of bone, hot flushes and anti-implantation effects.

Mechanisms and Issues Relating to the Use of D1-like Dopamine Receptor Agonists for Age-related Illnesses: Parkinson?s Disease and Memory and Cognition

Parkinson's disease is the second most common age related neurodegenerative disorder that, along with age-related declines in memory and cognition, represents an area of medicine in which there have not been major advances in decades. This paper will focus on the great potential that D 1 -like dopamine agonists may have in these arenas. Although levodopa has been the most effective treatment for Parkinson's disease (PD), pharmacokinetic and bioconversion problems have led to efforts to develop direct acting dopamine agonists for PD. Although the large majority of research and development has been focused on D 2 -like direct agonists, this talk will show data illustrating why D 1 agonists should be a high priority pharmacotherapeutic target for treatment of PD. This presentation will review the neurobiological and molecular pharmacological evidence that supports this hypothesis, some of the scientific hurdles, and the current state of the medicinal chemistry of D 1 agonist development. The concluding portion of the talk will review the experimental evidence suggesting that D 1 -like agonists can lead to improvements in memory and cognitive function, and review the current status of drug discovery and development for these uses.

Selective COX-2 Inhibitors and Dual Acting Anti-inflammatory Drugs: Critical Remarks

Non steroidal anti-inflammatory drugs (NSAIDs) are still the most commonly used remedies for rheumatic diseases. But NSAIDs produce serious adverse effects, the most important being gastric injury up to gastric ulceration and renal damage. Several strategies have been adopted in order to avoid these shortcomings, especially gastrointestinal toxicity. So, non steroidal anti-inflammatory drugs have been associated with gastroprotective agents that counteract the damaging effects of prostaglandin synthesis suppression: however, a combination therapy introduces problems of pharmacokinetics, toxicity, and patient s compliance. Also incorporation of a nitric oxide (NO)-generating moiety into the molecule of several NSAIDs was shown to greatly attenuate their ulcerogenic activity: however, several findings suggest a possible involvement of NO in the pathogenesis of arthritis and subsequent tissue destruction. A most promising approach seemed to be the preparation of novel NSAIDs, specific for the inducible isoform of cyclooxygenase (COX-2): they appear to be devoid of gastrointestinal toxicity, in that they spare mucosal prostaglandin synthesis. However, a number of recent studies raised serious questions about the two central tenets that support this approach, namely that the prostaglandins that mediate inflammation and pain are produced solely via COX-2 and that the prostaglandins that are important in gastrointestinal and renal function are produced solely via COX-1. So, increasing evidence shows that COX-2 (not only COX-1) also plays a physiological role in several body functions and that, conversely, COX-1 (not only COX-2) may also be induced at sites of inflammation. Moreover, COX-2 selective NSAIDs have lost the cardiovascular protective effects of non-selective NSAIDs, effects which are mediated through COX-1 inhibition (in addition, COX-2 has a role in sustaining vascular prostacyclin production). The products generated by the 5-lipoxygenase pathway (leukotrienes) are particularly important in inflammation: indeed, leukotrienes increase microvascular permeability and are potent chemotactic agents; moreover, inhibition of 5-lipoxygenase indirectly reduces the expression of TNF-alpha (a cytokine that plays a key role in inflammation). This explains the efforts to obtain drugs able to inhibit both 5-lipoxygenase and cyclooxygenases: the so-called dual acting anti-inflammatory drugs. Such compounds retain the activity of classical NSAIDs, while avoiding their main drawbacks, in that curtailed production of gastroprotective prostaglandins is associated with a concurrent curtailed production of the gastro-damaging and bronchoconstrictive leukotrienes. Moreover, thanks to their mechanism of action, dual acting anti-inflammatory drugs could not merely alleviate symptoms of rheumatic diseases, but might also satisfy, at least in part, the criteria of curative drugs. Indeed, leukotrienes are pro-inflammatory, increase microvascular permeability, are potent chemotactic agents and attract eosinophils, neutrophils and monocytes into the synovium. Finally, recent data strongly suggest that dual inhibitors may have specific protective activity also in neurodegeneration.

Modeling HIV dynamics and antiviral response with consideration of time-varying drug exposures, adherence and phenotypic sensitivity

Highly active antiretroviral therapies consisting of reverse transcriptase inhibitor drugs and protease inhibitor drugs, which can rapidly suppress HIV below the limit of detection, are currently the most effective treatment for HIV infected patients. In spite of this, many patients fail to achieve viral suppression, probably due to existing or developing drug resistance, poor adherence, pharmacokinetic problems and other clinical factors. In this paper, we develop a viral dynamic model to evaluate how time-varying drug exposure and drug susceptibility affect antiviral response. Plasma concentrations, in turn, are modeled using a standard pharmacokinetic (PK) one-compartment open model with first order absorption and elimination as a function of fixed individual PK parameters and dose times. Imperfect adherence is considered as missed doses in PK models. We discuss the analytic properties of the viral dynamic model and study how time-varying treatment efficacies affect antiviral responses, specifically viral load and T cell counts. The relationship between actual failure time (the time at which the viral growth rate changes from negative to positive) and detectable failure time (the time at which viral load rebounds to above the limit of detection) is investigated. We find that an approximately linear relationship can be used to estimate the actual rebound failure time from the detectable rebound failure time. In addition, the effect of adherence on antiviral response is studied. In particular, we examine how different patterns of adherence affect antiviral response. Results suggest that longer sequences of missed doses increase the chance of treatment failure and accelerate the failure. Simulation experiments are presented to illustrate the relationship between antiviral response and pharmacokinetics, time-varying adherence and drug resistance. The proposed models and methods may be useful in AIDS clinical trial simulations.

Efficacy of mycophenolate sodium as monotherapy and in combination with FTY720 in a DA-to-Lewis-rat heart-transplantation model.

Mycophenolate sodium (MPS), which is in clinical development as an enteric-coated tablet (Myfortic), has not yet been characterized as a combination partner of FTY720. We therefore report here the effects of MPS and FTY720 mono and combination therapy in a rat heart allograft model. Heterotopic heart allotransplantation was performed in the DA-to-Lewis-strain combinations. Groups of six rats were treated with placebo, MPS monotherapy, FTY720 monotherapy, and their combination. To circumvent pharmacokinetic problems, MPS was administered by Alza minipumps, while FTY720 was administered by gavage, both for 4 weeks. Graft survival was monitored daily, followed up by histology. Body weight and hematological parameters were determined at 1 and 4 weeks. The median survival time (MST) was 6 days for placebo, 6, 14.5, and more than 56 days for doses 3, 10, and 30 mg/kg per day MPS, with severe side effects (diarrhea, weight loss, lymphopenia) at the highest dose, and 7 and 8 days for the 0.03 and 0.1 mg/kg per day FTY720. The combination of 3 mg/kg per day MPS with these two FTY720 doses still resulted in rejection under treatment. However, 10 mg/kg per day MPS in combination with 0.03 or 0.1 mg/kg per day FTY720 yielded MSTs of 41 and 43.5 days, respectively, well beyond the 4-week treatment period. Both combination regimens were well tolerated. Both FTY720 doses combined with the highest MPS dose again caused severe side effects. MPS in monotherapy and combined with FTY720 resulted in steep dose-response curves. However, well tolerated combination regimens could be defined that prevented rejection.

Fuzzy system modeling in pharmacology: an improved algorithm

In this paper, we propose an improved fuzzy system modeling algorithm to address some of the limitations of the existing approaches identified during our modeling with pharmacological data. This algorithm differs from the existing ones in its approach to the cluster validity problem (i.e., number of clusters), the projection schema (i.e., input membership assignment and rule determination), and significant input determination. The new algorithm is compared with the Bazoon–Turksen model, which is based on the well-known Sugeno–Yasukawa approach. The comparison was made in terms of predictive performance using two different data sets. The first comparison was with a two variable nonlinear function prediction problem and the second comparison was with a clinical pharmacokinetic modeling problem. It is shown that the proposed algorithm provides more precise predictions. Determining the degree of significance for each input variable, allows the user to distinguish their relative importance.

Selective COX-2 inhibitors and dual acting anti-inflammatory drugs: critical remarks.

Non steroidal anti-inflammatory drugs (NSAIDs) are still the most commonly used remedies for rheumatic diseases. But NSAIDs produce serious adverse effects, the most important being gastric injury up to gastric ulceration and renal damage. Several strategies have been adopted in order to avoid these shortcomings, especially gastrointestinal toxicity. So, non steroidal anti-inflammatory drugs have been associated with gastroprotective agents that counteract the damaging effects of prostaglandin synthesis suppression: however, a combination therapy introduces problems of pharmacokinetics, toxicity, and patient s compliance. Also incorporation of a nitric oxide (NO)-generating moiety into the molecule of several NSAIDs was shown to greatly attenuate their ulcerogenic activity: however, several findings suggest a possible involvement of NO in the pathogenesis of arthritis and subsequent tissue destruction. A most promising approach seemed to be the preparation of novel NSAIDs, specific for the inducible isoform of cyclooxygenase (COX-2): they appear to be devoid of gastrointestinal toxicity, in that they spare mucosal prostaglandin synthesis. However, a number of recent studies raised serious questions about the two central tenets that support this approach, namely that the prostaglandins that mediate inflammation and pain are produced solely via COX-2 and that the prostaglandins that are important in gastrointestinal and renal function are produced solely via COX-1. So, increasing evidence shows that COX-2 (not only COX-1) also plays a physiological role in several body functions and that, conversely, COX-1 (not only COX-2) may also be induced at sites of inflammation. Moreover, COX-2 selective NSAIDs have lost the cardiovascular protective effects of non-selective NSAIDs, effects which are mediated through COX-1 inhibition (in addition, COX-2 has a role in sustaining vascular prostacyclin production). The products generated by the 5-lipoxygenase pathway (leukotrienes) are particularly important in inflammation: indeed, leukotrienes increase microvascular permeability and are potent chemotactic agents; moreover, inhibition of 5-lipoxygenase indirectly reduces the expression of TNF-alpha (a cytokine that plays a key role in inflammation). This explains the efforts to obtain drugs able to inhibit both 5-lipoxygenase and cyclooxygenases: the so-called dual acting anti-inflammatory drugs. Such compounds retain the activity of classical NSAIDs, while avoiding their main drawbacks, in that curtailed production of gastroprotective prostaglandins is associated with a concurrent curtailed production of the gastro-damaging and bronchoconstrictive leukotrienes. Moreover, thanks to their mechanism of action, dual acting anti-inflammatory drugs could not merely alleviate symptoms of rheumatic diseases, but might also satisfy, at least in part, the criteria of curative drugs. Indeed, leukotrienes are pro-inflammatory, increase microvascular permeability, are potent chemotactic agents and attract eosinophils, neutrophils and monocytes into the synovium. Finally, recent data strongly suggest that dual inhibitors may have specific protective activity also in neurodegeneration.

Invasive Aspergillosis: Focus on New Approaches and New Therapeutic Agents

Infections caused by Aspergillus species are an emerging cause of morbidity and mortality in a variety of immunocompromised patients, despite profound environmental protection and the widespread prophylactic use of agents with anti-Aspergillus activity. At the present time, no firm conclusions can be drawn on the use of chemoprophyla xis, mainly due to the lack of reliable, randomized trials. Therefore, universal prophylaxis should be discouraged and prevention should be targeted towards well-defined high-risk patients, although only as part of a properly designed clinical trial. The crude mortality rate of invasive aspergillosis remains unacceptably high and results at least partly from difficulties in obtaining a reliable diagnosis at an early stage of the disease. The concept of empirical antifungal therapy has been introduced in an effort to overcome these diagnostic obstacles, especially since the early implementation of antifungal therapy appears to be the crucial prerequisite to improve the detrimental outcome of established disease. However, the concept has not been sufficiently validated and is not devoid of significant risks and disadvantages. The implementation of sensitive and predictive new diagnostic tools, such as galactomannan detection, high-resolution pulmonary CT-scanning and detection of aspergillar DNA, may allow a more targeted pre-emptive approach, directed towards the high-risk patients and based upon a battery of clinical, radiological and microbiological clues, though without histopathological proof. The high mortality rate results also from shortcomings of the currently available therapeutic arsenal. Amphotericin B, flucytosine and itraconazole are associated with low success rates and are hampered by serious infusion- or drug-related toxicity, by hazardous drug-drug interactions, by pharmacokinet ic problems and by the development of resistance. In recent years, several companies have launched new compounds into preclinical and clinical trials. Some of these agents target the fungal cell wall in stead of the cell membrane. They exert their action through inhibition of the synthesis of critical compounds of that fungal cell wall, not present in mammalian cells (e.g. inhibitors of β-(1,3)-D-glucan synthesis). This article will focus on new therapeutic approaches (risk-adapted or targeted strategy) and upcoming antifungal agents with anti-Aspergillus activity, in particular voriconazole and caspofungin acetate.

Dual acting anti-inflammatory drugs: a reappraisal

Rheumatic diseases are the most prevalent causes of disability in western countries, and non-steroidal anti-inflammatory drugs (NSAIDs) are still the most commonly used remedies. However, NSAIDs cause several serious adverse effects, the most important being from gastric injury to gastric ulceration and renal damage. Attempts to develop non-steroidal anti-inflammatory remedies devoid of these shortcomings—especially gastrointestinal toxicity—have followed several strategies. Non-steroidal anti-inflammatory drugs have, therefore, been associated with gastroprotective agents that counteract the damaging effects of prostaglandin synthesis suppression; however, a combination therapy introduces other problems of pharmacokinetics, toxicity, and patient’s compliance. More recently, incorporation of a nitric oxide (NO)-generating moiety into the molecule of several NSAIDs was shown to greatly attenuate their ulcerogenic activity; however, several findings suggest a possible involvement of NO in the pathogenesis of arthritis and subsequent tissue destruction. A most promising approach seemed to be the preparation of novel NSAIDs, targeted at the inducible isoform of prostaglandin synthase (COX-2); they appear to be devoid of gastrointestinal toxicity, in that they spare mucosal prostaglandin synthesis. However, a number of recent studies have raised serious questions about the two central tenets that support this approach, namely that the prostaglandins that mediate inflammation and pain are produced solely via COX-2 and that the prostaglandins that are important in gastrointestinal and renal function are produced solely via COX-1. So, a growing body of evidence shows that COX-2 (not only COX-1) also plays a physiological role in several body functions and that, conversely, COX-1 (not only COX-2) may also be induced at sites of inflammation. More recent and puzzling data shows that COX-2 is induced during the resolution of an inflammatory response, and at this point it produces anti-inflammatory (PGD 2and PGF 2α), but not proinflammatory (PGE 2) prostaglandins; inhibition of COX-2 at this point thus results in persistence of the inflammation. Moreover, COX-2 selective NSAIDs have lost the cardiovascular protective effects of non-selective NSAIDs, effects which are mediated through COX-1 inhibition (in addition, COX-2 has a role in sustaining vascular prostacyclin production). The generation of other very important products of the arachidonic acid cascade (besides cyclooxygenase-produced metabolites) is inhibited neither by non-selective nor by COX-2 selective NSAIDs. The products generated by the 5-lipoxygenase pathway (leukotrienes) are particularly important in inflammation; indeed, leukotrienes increase microvascular permeability and are potent chemotactic agents. Moreover, inhibition of 5-lipoxygenase indirectly reduces the expression of TNF- α(a cytokine that plays a key role in inflammation). These data and considerations explain the efforts to obtain drugs able to inhibit both 5-lipoxygenase and cyclooxygenases, the so-called dual acting anti-inflammatory drugs. Such compounds retain the activity of classical NSAIDs, while avoiding their main drawbacks, in that curtailed production of gastroprotective prostaglandins is associated with a concurrent curtailed production of the gastro-damaging and bronchoconstrictive leukotrienes. Moreover, thanks to their mechanism of action, dual acting anti-inflammatory drugs could not merely alleviate symptoms of rheumatic diseases, but might also satisfy, at least in part, the criteria of a more definitive treatment. Indeed, leukotrienes are pro-inflammatory, increase microvascular permeability, are potent chemotactic agents and attract eosinophils, neutrophils and monocytes into the synovium.

The therapeutic monitoring of antimicrobial agents

To review the basis and optimal use of therapeutic drug monitoring of antimicrobial agents. Antimicrobial agents for which a reasonable case exists for therapeutic drug monitoring are reviewed under the following headings: pharmacokinetics, why monitor, therapeutic range, individualization of therapy, sampling times, methods of analysis, interpretative problems and cost-effectiveness of monitoring. There is a strong historical case for monitoring aminoglycosides. The recent move to once-daily dosing means that criteria for therapeutic drug monitoring need to be redefined. Vancomycin has been monitored routinely but many questions remain about the most appropriate approach to this. A case can be made for monitoring teicoplanin, flucytosine and itraconazole in certain circumstances. The approach to monitoring aminoglycosides is being redefined in the light of once daily dosing. It may be that less stringent monitoring is required in some circumstances but toxicity, especially ototoxicity, remains a problem with these drugs. Monitoring to avoid high AUCs (areas under the concentration-time curve) is recommended. The ideal method for monitoring vancomycin remains to be defined although a reasonable case exists for measuring trough concentrations, mainly to ensure efficacy. Teicoplanin is sometimes monitored to ensure efficacy while flucytosine may be monitored to avoid high concentrations associated with toxicity. Itraconazole has various pharmacokinetic problems and monitoring has been suggested to ensure that adequate concentrations are achieved.

DEVELOPMENTO F DRUG METABOLISMS TUDY IN DRUG DISCOVERY

It is important to predict and evaluate drug metabolism in drug discovery, because there are many pharmacokinetic problems arising from drug metabolism. Particularly, construction of the rapid and reliable prediction. evaluation methods is important in this study. The drug metabolism items that should be investigated are raised as follows: (1) hepatic clearance, (2) metabolite profile, (3) CYP identification, (4) CYP inhibition, (5) enzyme induction. In this presentation, I will discuss the construction and application of the prediction evaluation methods for hepatic clearance, metabolic profile and CYP inhibition in drug discovery.

Controversies in blood-level monitoring: reexamining its role in the treatment of epilepsy.

This article reexamines the role of blood-level monitoring (therapeutic drug monitoring, TDM) of antiepileptic drugs (AEDs) in the current treatment of epilepsy and identifies situations in which TDM can be useful. Basic pharmacokinetic and pharmacodynamic principles are reviewed, with specific emphasis on kinetics of absorption/distribution/metabolism, elimination half-life, time to steady state, and plasma drug concentrations. The relationship between AED intensity of effect (pharmacodynamics) and plasma concentration (pharmacokinetics) is expressed mathematically, examined in the context of the major old and new AEDs, and integrated with a historical look at the role of TDM. Situations in which TDM can be useful in the modern treatment of epilepsy are presented and discussed. For both older and newer AEDs, TDM is useful in six clinical situations: establishing "baseline" effective concentrations, evaluating potential causes for lack of efficacy, evaluating potential causes for toxicity, evaluating potential causes for loss of efficacy, judging "room to move" or when to change AEDs, and minimizing predictable problems. TDM remains a valuable tool in the modern treatment of epilepsy. It can be selectively and appropriately utilized to help maximize seizure control and minimize side effects if levels are obtained in response to a patient-specific pharmacokinetic or pharmacodynamic issue or problem.

Fungal cell wall inhibitors: emphasis on clinical aspects.

Invasive fungal infections, mainly caused by Candida and Aspergillus species, are an emerging cause of morbidity and mortality among all categories of immunocompromised patients. Currently available antifungal agents, both polyenes, flucytosine and (tri)azoles are hampered by serious infusion- or drug-related toxicity, by hazardous drug-drug interactions, or by pharmacokinetic problems and by the development of resistance, in vitro as well as in vivo. In recent years, several companies have become interested in antifungal drug development and have launched new compounds into preclinical and clinical trials. Some of these agents target the fungal cell wall in stead of the cell membrane. They exert their fungicidal action through inhibition of the synthesis of critical compounds of that fungal cell wall, not present in mammalian cells. Exciting and promising agents include inhibitors of beta-(1,3)-D-glucan synthase and inhibitors of chitin synthase. These drugs appear well tolerated in Phase I-II studies and will soon enter Phase III studies. This review wants to provide the clinical framework for assessing the utility of these agents compared to existing antifungals, thereby focusing on invasive fungal disease and emphasising the changing fungal epidemiology and susceptibility in immunocompromised hosts.

Pharmacokinetic curve fitting using numerical inverse Laplace transformation

The combination of the nonlinear regression program ADAPT II with Talbot's method of numerical Laplace transformation, that allows parameter estimation when the model function is given only in the Laplace domain, is described and successfully applied to pharmacokinetic problems. The accuracy and precision of the method has been found satisfactory; its performance is comparable to that achieved in parameter estimation based on functions defined in the time domain.

The therapeutic monitoring of antimicrobial agents.

To review the basis and optimal use of therapeutic drug monitoring of antimicrobial agents. Antimicrobial agents for which a reasonable case exists for therapeutic drug monitoring were reviewed under the following headings: pharmacokinetics, why monitor, therapeutic range, individualisation of therapy, sampling times, methods of analysis, interpretative problems and cost-effectiveness of monitoring. There is a strong historical case for monitoring aminoglycosides. The recent move to once-daily dosing means that criteria for therapeutic drug monitoring need to be redefined. Vancomycin has been monitored routinely but many questions remain about the most appropriate approach to this. A case can be made for monitoring teicoplanin, flucytosine and itraconazole in certain circumstances. The approach to monitoring aminoglycosides needs to be redefined in the light of once-daily dosing. It is premature to suggest that less stringent monitoring is necessary as toxicity remains a problem with these drugs. The ideal method of monitoring vancomycin remains to be defined although a reasonable case exists for measuring trough concentrations, mainly to ensure efficacy. Teicoplanin is monitored occasionally to ensure efficacy while flucytosine is monitored occasionally to avoid high concentrations associated with toxicity. Itraconazole has various pharmacokinetic problems and monitoring has been suggested to ensure that adequate concentrations are achieved.

Extended quasi-likelihood is useful for analyzing intra-individual variability in pharmacokinetic regression models.

The method of maximum extended quasi-likelihood (MEQL) can be viewed as an estimation method in the framework of generalized linear models. The method was applied to a pharmacokinetic problem in which the pharmacokinetic model was a nonlinear function of its parameters. The behavior of the method toward the estimation of a variance function was numerically compared with those of the generalized least squares (GLS) and extended least squares methods. In general, the MEQL and GLS methods were equally better. However, the MEQL estimator often showed smaller mean squared errors for the scaling parameter than the other two estimators. Such a generally comparable but partially distinct property of the MEQL method, as compared with the GLS method, is useful to pharmacokinetic analysis.

Enzymes hydrolyzing organophosphates as potential catalytic scavengers against organophosphate poisoning

Enzymes hydrolyzing organophosphates could be used as catalytic scavengers for treatment of organophosphate poisoning and for decontamination. Two organophosphorus hydrolases (OPH) were selected: the Flavobacterium sp./ Pseudomonas diminuta phosphotriesterase (PTE) and human paraoxonase (HuPON). Genes encoding these enzymes were cloned and functional recombinant enzymes expressed. PTE was expressed in E. coli. Natural HuPON was purified from human plasma; recombinant HuPON was expressed in human embryonic kidney 293 T cells. Although HuPON displays interesting catalytic properties, a site-directed mutagenesis program was undertaken to improve its catalytic efficiency. PTE has high efficiency in hydrolysis of organophosphates, including nerve agents. PTE injected in rat has a half-life of 100 min. However, to overcome pharmacokinetic problems of injected OPH and/or immunological incompatibility, the model enzyme (recombinant PTE) was immobilized onto a hollow-fiber reactor. This reactor designed for extracorporeal blood circulation is under experimentation for post-exposure detoxification.

Codominant interference, antieffectors, and multitarget drugs

The insufficient selectivity of drugs is a bane of present-day therapies. This problem is significant for antibacterial drugs, difficult for antivirals, and utterly unsolved for anticancer drugs, which remain ineffective against major cancers, and in addition cause severe side effects. The problem may be solved if a therapeutic agent could have a multitarget, combinatorial selectivity, killing, or otherwise modifying, a cell if and only if it contains a predetermined set of molecular targets and lacks another predetermined set of targets. An earlier design of multitarget drugs [Varshavsky, A. (1995) Proc. Natl. Acad. Sci. USA 92, 3663-3667] was confined to macromolecular reagents such as proteins, with the attendant difficulties of intracellular delivery and immunogenicity. I now propose a solution to the problem of drug selectivity that is applicable to small (</=1 kDa) drugs. Two ideas, codominant interference and antieffectors, should allow a therapeutic regimen to possess combinatorial selectivity, in which the number of positively and negatively sensed macromolecular targets can be two, three, or more. The nature of the effector and interference moieties in a multitarget drug determines its use: selective killing of cancer cells or, for example, the inhibition of a neurotransmitter-inactivating enzyme in a specific subset of the enzyme-containing cells. The in vivo effects of such drugs would be analogous to the outcomes of the Boolean operations "and," "or," and combinations thereof. I discuss the logic and applications of the antieffector and interference/codominance concepts, and the attendant problem of pharmacokinetics.

Putting the taxanes to work: unanswered questions.

The promising activity of taxanes in advanced breast cancer patients has prompted the investigators to explore their role in the adjuvant setting. Methodological issues, still unsolved pharmacokinetic and pharmacodynamic problems, and potential severe toxicities could jeopardize these attractive regimens and should be taken into account in the design and interpretation of adjuvant trials. In order to minimize the methodological drawbacks, the potential role of taxanes in the adjuvant setting should be assessed in clinical trials powered to detect an absolute survival increase of near 7% at 10 years. The use of paclitaxel in combination with anthracyclines is complicated by pharmacokinetic interactions which may be responsible for unexpected side effects and/or subadditive cytotoxicity. Moreover, possible interactions between taxanes and tamoxifen are still unclear, and therefore more data are necessary before recommending the combined use of the two drugs in the adjuvant setting. Nowadays, the majority of breast cancer patients receive conservative surgery followed by radiotherapy; when adjuvant taxanes are used, radiotherapy should be delayed because of their radiosensitization effect, with potential detrimental effects. Finally, the majority of side effects of taxane-containing regimens are short-lasting and reversible, but other potential toxicities, such as the cardiotoxicity and long-term possible sequelae of the use of high-dose steroids, need long-term evaluation.