Distribution of hexadecylphosphocholine and octadecyl-methyl-glycero-3-phosphocholine in rat tissues during steady-state treatment

Approaches for Targeting Naegleria fowleri Using Nanoparticles and Artificial Peptides

Naegleria fowleri is a free-living amoeba which causes primary amoebic meningoencephalitis (PAM). Although PAM is rare, the fatality rate is staggering at over 97%. So, the importance of finding an effective treatment and cure for PAM caused by N. fowleri is a crucial area of research. Existing research on developing novel therapeutic strategies to counter N. fowleri infection is limited. Since the blood-brain barrier (BBB) presents an obstacle to delivering drugs to the site of infection, it is important to employ strategies that can effectively direct the therapeutics to the brain. In this regard, our review focuses on understanding the physiology and mechanisms by which molecules pass through the BBB, the current treatment options available for PAM, and the recent research conducted in the decade of 2012 to 2022 on the use of nanomaterials to enhance drug delivery. In addition, we compile research findings from other central nervous system (CNS) diseases that use shuttle peptides which allow for transport of molecules through the BBB. The approach of utilizing BBB shuttles to administer drugs through the BBB may open up new areas of drug discovery research in the field of N. fowleri infection.

Determining tissue distribution of the oral antileishmanial agent miltefosine: a physiologically-based pharmacokinetic modeling approach

Miltefosine (MTS) is the only approved oral drug for treating leishmaniasis caused by intracellular Leishmania parasites that localize in macrophages of the liver, spleen, skin, bone marrow, and lymph nodes. MTS is extensively distributed in tissues and has prolonged elimination half-lives due to its high plasma protein binding, slow metabolic clearance, and minimal urinary excretion. Thus, understanding and predicting the tissue distribution of MTS help assess therapeutic and toxicologic outcomes of MTS, especially in special populations, e.g., pediatrics. In this study, a whole-body physiologically-based pharmacokinetic (PBPK) model of MTS was built on mice and extrapolated to rats and humans. MTS plasma and tissue concentration data obtained by intravenous and oral administration to mice were fitted simultaneously to estimate model parameters. The resulting high tissue-to-plasma partition coefficient values corroborate extensive distribution in all major organs except the bone marrow. Sensitivity analysis suggests that plasma exposure is most susceptible to changes in fraction unbound in plasma. The murine oral-PBPK model was further validated by assessing overlay of simulations with plasma and tissue profiles obtained from an independent study. Subsequently, the murine PBPK model was extrapolated to rats and humans based on species-specific physiological and drug-related parameters, as well as allometrically scaled parameters. Fold errors for pharmacokinetic parameters were within acceptable range in both extrapolated models, except for a slight underprediction in the human plasma exposure. These animal and human PBPK models are expected to provide reliable estimates of MTS tissue distribution and assist dose regimen optimization in special populations.

Efficacy of oleylphosphocholine in experimental cutaneous leishmaniasis

OBJECTIVES

Cutaneous leishmaniasis (CL) is a neglected tropical disease causing a range of skin lesions for which safe and efficacious drugs are lacking. Oleylphosphocholine (OLPC) is structurally similar to miltefosine and has previously demonstrated potent activity against visceral leishmaniasis. We here present the in vitro and in vivo efficacy of OLPC against CL-causing Leishmania species.

METHODS

The antileishmanial activities of OLPC were evaluated and compared with miltefosine in vitro against intracellular amastigotes of seven CL-causing species. Following the confirmation of significant in vitro activity, the performance of the maximum tolerated dose of OLPC was evaluated in an experimental murine model of CL followed by a dose-response titration and the efficacy evaluation of four OLPC formulations (two with a fast-release and two with a slow-release profile) using bioluminescent Leishmania major parasites.

RESULTS

OLPC demonstrated potent in vitro activity of the same order as miltefosine in the intracellular macrophage model against a range of CL-causing species. A dose of 35 mg of OLPC/kg/day administered orally for 10 days was well-tolerated and able to reduce the parasite load in the skin of L. major-infected mice to a similar extent as the positive control paromomycin (50 mg/kg/day, intraperitoneally) in both in vivo studies. Reducing the dose of OLPC resulted in inactivity and modifying the release profile using mesoporous silica nanoparticles led to a decrease in activity when solvent-based loading was used in contrast to extrusion-based loading, which had no impact on its antileishmanial efficacy.

CONCLUSIONS

Together, these data suggest that OLPC could be a promising alternative to miltefosine treatment for CL. Further investigations exploring experimental models with additional Leishmania species and skin pharmacokinetic and dynamic analyses are required.

Miltefosine and Benznidazole Combination Improve Anti-Trypanosoma cruzi In Vitro and In Vivo Efficacy

Drug repurposing and combination therapy have been proposed as cost-effective strategies to improve Chagas disease treatment. Miltefosine (MLT), a synthetic alkylphospholipid initially developed for breast cancer and repositioned for leishmaniasis, is a promising candidate against Trypanosoma cruzi infection. This study evaluates the efficacy of MLT as a monodrug and combined with benznidazole (BZ) in both in vitro and in vivo models of infection with T. cruzi (VD strain, DTU TcVI). MLT exhibited in vitro activity on amastigotes and trypomastigotes with values of IC_{50 =} 0.51 µM (0.48 µM; 0,55 µM) and LC_{50 =} 31.17 µM (29.56 µM; 32.87 µM), respectively. Drug interaction was studied with the fixed-ration method. The sum of the fractional inhibitory concentrations (ΣFICs) resulted in ∑FIC= 0.45 for trypomastigotes and ∑FIC= 0.71 for amastigotes, suggesting in vitro synergistic and additive effects, respectively. No cytotoxic effects on host cells were observed. MLT efficacy was also evaluated in a murine model of acute infection alone or combined with BZ. Treatment was well tolerated with few adverse effects, and all treated animals displayed significantly lower mean peak parasitemia and mortality than infected non-treated controls (p<0.05). The in vivo studies showed that MLT led to a dose-dependent parasitostatic effect as monotherapy which could be improved by combining with BZ, preventing parasitemia rebound after a stringent immunosuppression protocol. These results support MLT activity in clinically relevant stages from T. cruzi, and it is the first report of positive interaction with BZ, providing further support for evaluating combined schemes using MLT and exploring synthetic alkylphospholipids as drug candidates.

Antileishmanial Drugs Modulate IL-12 Expression and Inflammasome Activation in Primary Human Cells

Leishmaniases are neglected tropical diseases. The treatment of leishmaniasis relies exclusively on chemotherapy including amphotericin B (AmB), miltefosine (hexadecylphosphocholine), and pentamidine. Besides the fact that these molecules are harmful for patients, little is known about the impact of such antileishmanial drugs on primary human cells in relation to immune function. The present study demonstrates that all antileishmanial drugs inhibit CD4 and CD8 T cell proliferation at the doses that are not related to increased cell death. Our results highlight that antileishmanial drugs have an impact on monocytes by altering the expression of IL-12 induced by LPS, whereas only AmB induced IL-10 secretion; both cytokines are essential in regulating Th1 cell-mediated immunity. Interestingly, IL-12 and anti-IL-10 Abs improved T cell proliferation inhibited by AmB. Furthermore, our results show that in contrast to hexadecylphosphocholine and pentamidine, AmB induced gene expression of the inflammasome pathway. Thus, AmB induced IL-1β and IL-18 secretions, which are reduced by specific inhibitors of caspase activation (Q-VD) and NLRP3 activation (MCC950). Our results reveal previously underestimated effects of antileishmanial drugs on primary human cells.

Minimal Cerebrospinal Fluid Concentration of Miltefosine despite Therapeutic Plasma Levels during the Treatment of Amebic Encephalitis

Miltefosine is an alkylphosphocholine compound that is used primarily for treatment of leishmaniasis and demonstrates in vitro and in vivo antiamebic activity against Acanthamoeba species. Recommendations for treatment of amebic encephalitis generally include miltefosine therapy. Data indicate that treatment with an amebicidal concentration of at least 16 μg/ml of miltefosine is required for most Acanthamoeba species. Although there is a high level of mortality associated with amebic encephalitis, a paucity of data regarding miltefosine levels in plasma and cerebrospinal fluid in vivo exists in the literature. We found that despite aggressive dosing (oral miltefosine 50 mg every 6 h) and therapeutic plasma levels, the miltefosine concentration in cerebrospinal fluid was negligible in a patient with AIDS and Acanthamoeba encephalitis.

Alkylphospholipids are Signal Transduction Modulators with Potential for Anticancer Therapy

BACKGROUND

Alkylphospholipids (APLs) are synthetically derived from cell membrane components, which they target and thus modify cellular signalling and cause diverse effects. This study reviews the mechanism of action of anticancer, antiprotozoal, antibacterial and antiviral activities of ALPs, as well as their clinical use.

METHODS

A literature search was used as the basis of this review.

RESULTS

ALPs target lipid rafts and alter phospholipase D and C signalling cascades, which in turn will modulate the PI3K/Akt/mTOR and RAS/RAF/MEK/ERK pathways. By feedback coupling, the SAPK/JNK signalling chain is also affected. These changes lead to a G2/M phase cell cycle arrest and subsequently induce programmed cell death. The available knowledge on inhibition of AKT phosphorylation, mTOR phosphorylation and Raf down-regulation renders ALPs as attractive candidates for modern medical treatment, which is based on individualized diagnosis and therapy. Corresponding to their unusual profile of activities, their side effects result from cholinomimetic activity mainly and focus on the gastrointestinal tract. These aspects together with their bone marrow sparing features render APCs well suited for modern combination therapy. Although the clinical success has been limited in cancer diseases so far, the use of miltefosine against leishmaniosis is leading the way to better understanding their optimized use.

CONCLUSION

Recent synthetic programs generate congeners with the increased therapeutic ratio, liposomal formulations, as well as diapeutic (or theranostic) derivatives with optimized properties. It is anticipated that these innovative modifications will pave the way for the further successful development of ALPs.

Clinical Pharmacokinetics of Systemically Administered Antileishmanial Drugs

This review describes the pharmacokinetic properties of the systemically administered antileishmanial drugs pentavalent antimony, paromomycin, pentamidine, miltefosine and amphotericin B (AMB), including their absorption, distribution, metabolism and excretion and potential drug–drug interactions. This overview provides an understanding of their clinical pharmacokinetics, which could assist in rationalising and optimising treatment regimens, especially in combining multiple antileishmanial drugs in an attempt to increase efficacy and shorten treatment duration. Pentavalent antimony pharmacokinetics are characterised by rapid renal excretion of unchanged drug and a long terminal half-life, potentially due to intracellular conversion to trivalent antimony. Pentamidine is the only antileishmanial drug metabolised by cytochrome P450 enzymes. Paromomycin is excreted by the kidneys unchanged and is eliminated fastest of all antileishmanial drugs. Miltefosine pharmacokinetics are characterized by a long terminal half-life and extensive accumulation during treatment. AMB pharmacokinetics differ per drug formulation, with a fast renal and faecal excretion of AMB deoxylate but a much slower clearance of liposomal AMB resulting in an approximately ten-fold higher exposure. AMB and pentamidine pharmacokinetics have never been evaluated in leishmaniasis patients. Studies linking exposure to effect would be required to define target exposure levels in dose optimisation but have only been performed for miltefosine. Limited research has been conducted on exposure at the drug’s site of action, such as skin exposure in cutaneous leishmaniasis patients after systemic administration. Pharmacokinetic data on special patient populations such as HIV co-infected patients are mostly lacking. More research in these areas will help improve clinical outcomes by informed dosing and combination of drugs.

Target identification and intervention strategies against amebiasis

Entamoeba histolytica is the etiological agent of amebiasis, which is an endemic parasitic disease in developing countries and is the cause of approximately 70,000 deaths annually. E. histolytica trophozoites usually reside in the colon as a non-pathogenic commensal in most infected individuals (90% of infected individuals are asymptomatic). For unknown reasons, these trophozoites can become virulent and invasive, cause amebic dysentery, and migrate to the liver where they cause hepatocellular damage. Amebiasis is usually treated either by amebicides which are classified as (a) luminal and are active against the luminal forms of the parasite, (b) tissue and are effective against those parasites that have invaded tissues, and (c) mixed and are effective against the luminal forms of the parasite and those forms which invaded the host's tissues. Of the amebicides, the luminal amebicide, metronidazole (MTZ), is the most widely used drug to treat amebiasis. Although well tolerated, concerns about its adverse effects and the possible emergence of MTZ-resistant strains of E. histolytica have led to the development of new therapeutic strategies against amebiasis. These strategies include improving the potency of existing amebicides, discovering new uses for approved drugs (repurposing of existing drugs), drug rediscovery, vaccination, drug targeting of essential E. histolytica components, and the use of probiotics and bioactive natural products. This review examines each of these strategies in the light of the current knowledge on the gut microbiota of patients with amebiasis.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Molecular detection of infection homogeneity and impact of miltefosine treatment in a Syrian golden hamster model of Leishmania donovani and L. infantum visceral leishmaniasis

Control of visceral leishmaniasis caused by Leishmania infantum and Leishmania donovani primarily relies on chemotherapy using an increasingly compromised repertoire of antileishmanial compounds. For evaluation of novel drugs, the Syrian golden hamster is considered as a clinically relevant laboratory model. In this study, two molecular parasite detection assays were developed targeting cathepsin-like cysteine protease B (CPB) DNA and 18S rRNA to achieve absolute amastigote quantification in the major target organs liver and spleen. Both quantitative PCR (qPCR) techniques showed excellent agreement with a strong correlation with the conventional microscopic reading of Giemsa-stained tissue smears. Using multiple single tissue pieces and all three detection methods, we confirmed homogeneity of infection in liver and spleen and the robustness of extrapolating whole organ burdens from a small single tissue piece. Comparison of pre- and post-treatment burdens in infected hamsters using the three detection methods consistently revealed a stronger parasite reduction in the spleen compared to the liver, indicating an organ-dependent clearance efficacy for miltefosine. In conclusion, this study in the hamster demonstrated high homogeneity of infection in liver and spleen and advocates the use of molecular detection methods for assessment of low (post-treatment) tissue burdens.

Assessment of blood-brain barrier penetration of miltefosine used to treat a fatal case of granulomatous amebic encephalitis possibly caused by an unusual Balamuthia mandrillaris strain

Balamuthia mandrillaris, a free-living ameba, causes rare but frequently fatal granulomatous amebic encephalitis (GAE). Few patients have survived after receiving experimental drug combinations, with or without brain lesion excisions. Some GAE survivors have been treated with a multi-drug regimen including miltefosine, an investigational anti-leishmanial agent with in vitro amebacidal activity. Miltefosine dosing for GAE has been based on leishmaniasis dosing because no data exist in humans concerning its pharmacologic distribution in the central nervous system. We describe results of limited cerebrospinal fluid (CSF) and serum drug level testing performed during clinical management of a child with fatal GAE who was treated with a multiple drug regimen including miltefosine. Brain biopsy specimens, CSF, and sera were tested for B. mandrillaris using multiple techniques, including culture, real-time polymerase chain reaction, immunohistochemical techniques, and serology. CSF and serum miltefosine levels were determined using a liquid chromatography method coupled to tandem mass spectrometry. The CSF miltefosine concentration on hospital admission day 12 was 0.4 μg/mL. The serum miltefosine concentration on day 37, about 80 h post-miltefosine treatment, was 15.3 μg/mL. These are the first results confirming some blood-brain barrier penetration by miltefosine in a human, although with low-level CSF accumulation. Further evaluation of brain parenchyma penetration is required to determine optimal miltefosine dosing for Balamuthia GAE, balanced with the drug's toxicity profile. Additionally, the Balamuthia isolate was evaluated by real-time polymerase chain reaction (PCR), demonstrating genetic variability in 18S ribosomal RNA (18S rRNA) sequences and possibly signaling the first identification of multiple Balamuthia strains with varying pathogenicities.

Could miltefosine be used as a therapy for toxoplasmosis?

Toxoplasmosis is a zoonotic protozoal disease affecting more than a billion people worldwide. The shortfalls of the current treatment options necessitate the development of non-toxic and well-tolerated, efficient alternatives especially against the cyst form. The current study was undertaken to investigate, for the first time, the potential potency of miltefosine against Toxoplasma gondii infection in acute and chronic experimental toxoplasmosis. Results showed that there is no evidence of anti-parasitic activity of miltefosine against T. gondii tachyzoites in acute experimental toxoplasmosis. However, anti-parasitic activity of miltefosine against T. gondii cyst stage in chronic experimental toxoplasmosis could not be excluded as demonstrated by significant reduction in brain cyst burden. Moreover, considerable morphological changes in the cysts were revealed by light and electron microscopy study and also by amelioration of pathological changes in the brain. Future studies should focus on enhancement of anti-toxoplasma activity of miltefosine against chronic toxoplasmosis using formulation based nanotechnology. To the best of our knowledge, this is the first study highlighting efficacy of miltefosine against chronic toxoplasmosis, thus, increasing the list of diseases that can be targeted by this drug.

Miltefosine: a review of its pharmacology and therapeutic efficacy in the treatment of leishmaniasis

Miltefosine is an alkylphosphocholine drug with demonstrated activity against various parasite species and cancer cells as well as some pathogenic bacteria and fungi. For 10 years it has been licensed in India for the treatment of visceral leishmaniasis (VL), a fatal neglected parasitic disease. It is the first and still the only oral drug that can be used to treat VL and cutaneous leishmaniasis (CL). The standard 28 day miltefosine monotherapy regimen is well tolerated, except for mild gastrointestinal side effects, although its teratogenic potential severely hampers its general use in the clinic and roll-out in national elimination programmes. The pharmacokinetics of miltefosine are mainly characterized by its long residence time in the body, resulting in extensive drug accumulation during treatment and long elimination half-lives. At the moment, different combination therapy strategies encompassing miltefosine are being tested in multiple controlled clinical trials in various geographical areas of endemicity, both in South Asia and East Africa. We here review the most salient pre-clinical and clinical pharmacological aspects of miltefosine, its mechanism of action against Leishmania parasites and other pathogens, and provide a systematic overview of the efficacy and safety data from all clinical trials of miltefosine, either alone or in combination, in the treatment of VL and CL.

Optimal dosing of miltefosine in children and adults with visceral leishmaniasis

Only anecdotal data are available on the pharmacokinetics (PK) of miltefosine in children suffering from visceral leishmaniasis (VL). While failure rates were higher in children with VL, steady-state concentrations appeared lower than those seen with adults. We hypothesized that the current linear dosage (in milligrams per kilogram of body weight) is too low for children and that a new dosing algorithm based on an appropriate body size model would result in an optimal exposure. A population PK analysis was performed on three historic pooled data sets, including Indian children, Indian adults, and European adults. Linear and allometric scaling of PK parameters by either body weight or fat-free mass (FFM) was evaluated for body size models. Based on the developed PK model, a dosing algorithm for miltefosine in children and adults was proposed and evaluated in silico. The population PK model employing allometric scaling fitted best to the pooled miltefosine data. Allometric scaling by FFM reduced between-subject variability, e.g., for drug clearance, from 49.6% to 32.1%. A new allometric miltefosine dosing algorithm was proposed. Exposure to miltefosine was lower in children than adults receiving 2.5 mg/kg/day: a C(max) of 18.8 μg/ml was reached by 90% of adults and 66.7% of children. The allometric daily dose resulted in similar levels of exposure to miltefosine for adults and children. The use of a new allometric dosing algorithm for miltefosine in VL patients results in optimal exposure to miltefosine in both adults and children and might improve clinical outcome in children.

Akt inhibitors as an HIV-1 infected macrophage-specific anti-viral therapy

BACKGROUND

Unlike CD4+ T cells, HIV-1 infected macrophages exhibit extended life span even upon stress, consistent with their in vivo role as long-lived HIV-1 reservoirs.

RESULTS

Here, we demonstrate that PI3K/Akt inhibitors, including clinically available Miltefosine, dramatically reduced HIV-1 production from long-living virus-infected macrophages. These PI3K/Akt inhibitors hyper-sensitize infected macrophages to extracellular stresses that they are normally exposed to, and eventually lead to cell death of infected macrophages without harming uninfected cells. Based on the data from these Akt inhibitors, we were able to further investigate how HIV-1 infection utilizes the PI3K/Akt pathway to establish the cytoprotective effect of HIV-1 infection, which extends the lifespan of infected macrophages, a key viral reservoir. First, we found that HIV-1 infection activates the well characterized pro-survival PI3K/Akt pathway in primary human macrophages, as reflected by decreased PTEN protein expression and increased Akt kinase activity. Interestingly, the expression of HIV-1 or SIV Tat is sufficient to mediate this cytoprotective effect, which is dependent on the basic domain of Tat - a region that has previously been shown to bind p53. Next, we observed that this interaction appears to contribute to the downregulation of PTEN expression, since HIV-1 Tat was found to compete with PTEN for p53 binding; this is known to result in p53 destabilization, with a consequent reduction in PTEN protein production.

CONCLUSION

Since HIV-1 infected macrophages display highly elevated Akt activity, our results collectively show that PI3K/Akt inhibitors may be a novel therapy for interfering with the establishment of long-living HIV-1 infected reservoirs.

In vitro activities of miltefosine and two novel antifungal biscationic salts against a panel of 77 dermatophytes

The susceptibilities of 77 dermatophytes to miltefosine (MI), 1,12-bis(4-pentylpyridinium)dodecane (PYR), 1,12-bis(tributylammonium)dodecane (AM), itraconazole (ITC), terbinafine (TRB), and butenafine (BTF) were compared. Geometric mean MICs of TRB, BTF, ITC, MI, PYR, and AM were 0.039, 0.059, 1.718, 0.671, 6.006, and 4.771 microg/ml, respectively. MI was more active than ITC (P < 0.001).

Intestinal Absorption of Miltefosine: Contribution of Passive Paracellular Transport

PURPOSE

This study aimed to characterize the transepithelial transport of miltefosine (HePC), the first orally effective drug against visceral leishmaniasis, across the intestinal barrier to further understand its oral absorption mechanism.

MATERIALS AND METHODS

Caco-2 cell monolayers were used as an in vitro model of the human intestinal barrier. The roles of active and passive mechanisms in HePC intestinal transport were investigated and the relative contributions of the transcellular and paracellular routes were estimated.

RESULTS

HePC transport was observed to be pH-independent, partially temperature-dependent, linear as a function of time and non-saturable as a function of concentration. The magnitude of HePC transport was quite similar to that of the paracellular marker mannitol, and EDTA treatment led to an increase in HePC transport. Furthermore, HePC transport was found to be similar in the apical-to-basolateral and basolateral-to-apical directions, strongly suggesting that HePC exhibits non-polarized transport and that no MDR-mediated efflux was involved.

CONCLUSIONS

These results demonstrate that HePC crosses the intestinal epithelium by a non-specific passive pathway and provide evidence supporting a concentration-dependent paracellular transport mechanism, although some transcellular diffusion cannot be ruled out. Considering that HePC opens epithelial tight junctions, this study shows that HePC may promote its own permeation across the intestinal barrier.

In-vitro activity of miltefosine and voriconazole on clinical isolates of free-living amebas: Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri

The anticancer agent miltefosine and the antifungal drug voriconazole were tested in vitro against Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri. All three amebas are etiologic agents of chronic (Balamuthia, Acanthamoeba) or fulminant (Naegleria) encephalitides in humans and animals and, in the case of Acanthamoeba, amebic keratitis. Balamuthia exposed to <40 microm concentrations of miltefosine survived, while concentrations of >or=40 microM were generally amebacidal, with variation in sensitivity between strains. At amebastatic drug concentrations, recovery from drug effects could take as long as 2 weeks. Acanthamoeba spp. recovered from exposure to 40 microM, but not 80 microM miltefosin. Attempts to define more narrowly the minimal inhibitory (MIC) and minimal amebacidal concentrations (MAC) for Balamuthia and Acanthamoeba were difficult due to persistence of non-proliferating trophic amebas in the medium. For N. fowleri, 40 and 55 microM were the MIC and MAC, respectively, with no trophic amebas seen at the MAC. Voriconazole had little or no inhibitory effect on Balamuthia at concentrations up to 40 microg/ml, but had a strong inhibitory effect upon Acanthamoeba spp. and N. fowleri at all drug concentrations through 40 microg/ml. Following transfer to drug-free medium, Acanthamoeba polyphaga recovered within a period of 2 weeks; N. fowleri amebas recovered from exposure to 1 microg/ml, but not from higher concentrations. All testing was done on trophic amebas; drug sensitivities of cysts were not examined. Miltefosine and voriconazole are potentially useful drugs for treatment of free-living amebic infections, though sensitivities differ between genera, species, and strains.

In vitro and in vivo interactions between miltefosine and other antileishmanial drugs

The interaction of miltefosine with amphotericin B, sodium stibogluconate, paromomycin, and sitamaquine was assessed in vitro and additionally for the first three combinations in vivo. In vitro interactions were indifferent for miltefosine combined with amphotericin B (mean sums of fractional inhibitory concentrations [mean summation operatorFICs] ranging from 1.22 to 1.51 at the 50% effective concentration [EC50] level and 1.08 to 1.38 at the EC90 level), sitamaquine (mean summation operatorFICs from 1.33 to 1.38 and 1.0 to 1.02, respectively), and paromomycin (mean summation operatorFICs from 0.79 to 0.93 at the EC50 and 0.77 to 1.35 at the EC90 level). Some synergy was observed for miltefosine combined with sodium stibogluconate (mean summation operatorFICs from 0.61 to 0.75 at EC50 and 0.49 to 0.97 at EC90). Different interactions were found in vivo, where the highest potentiation of miltefosine activity was achieved with amphotericin B (activity enhancement index [AEI] of up to 11.3). No significant interaction was observed when miltefosine was combined with sodium stibogluconate (AEI of up to 2.38). The potentiation of miltefosine in vivo was also achieved with the combination of miltefosine and paromomycin (AEI of up to 7.22).

Hexadecylphosphocholine (miltefosine) has broad-spectrum fungicidal activity and is efficacious in a mouse model of cryptococcosis

The alkyl phosphocholine drug miltefosine is structurally similar to natural substrates of the fungal virulence determinant phospholipase B1 (PLB1), which is a potential drug target. We determined the MICs of miltefosine against key fungal pathogens, correlated antifungal activity with inhibition of the PLB1 activities (PLB, lysophospholipase [LPL], and lysophospholipase-transacylase [LPTA]), and investigated its efficacy in a mouse model of disseminated cryptococcosis. Miltefosine inhibited secreted cryptococcal LPTA activity by 35% at the subhemolytic concentration of 25 microM (10.2 microg/ml) and was inactive against mammalian pancreatic phospholipase A2 (PLA2). At 250 microM, cytosolic PLB, LPL, and LPTA activities were inhibited by 25%, 51%, and 77%, respectively. The MICs at which 90% of isolates were inhibited (MIC90s) against Candida albicans, Candida glabrata, Candida krusei, Cryptococcus neoformans, Cryptococcus gattii, Aspergillus fumigatus, Fusarium solani, Scedosporium prolificans, and Scedosporium apiospermum were 2 to 4 microg/ml. The MICs of miltefosine against Candida tropicalis (n = 8) were 2 to 4 microg/ml, those against Aspergillus terreus and Candida parapsilosis were 8 microg/ml (MIC90), and those against Aspergillus flavus (n = 8) were 2 to 16 microg/ml. Miltefosine was fungicidal for C. neoformans, with rates of killing of 2 log units within 4 h at 7.0 microM (2.8 microg/ml). Miltefosine given orally to mice on days 1 to 5 after intravenous infection with C. neoformans delayed the development of illness and mortality and significantly reduced the brain cryptococcal burden. We conclude that miltefosine has broad-spectrum antifungal activity and is active in vivo in a mouse model of disseminated cryptococcosis. The relatively small inhibitory effect on PLB1 enzyme activities at concentrations exceeding the MIC by 2 to 20 times suggests that PLB1 inhibition is not the only mechanism of the antifungal effect.

In vitro activity of hexadecylphosphocholine (miltefosine) against metronidazole-resistant and -susceptible strains of Trichomonas vaginalis

OBJECTIVES

Trichomonas vaginalis is the causative agent of trichomoniasis, a sexually transmitted disease with worldwide significance. Trichomoniasis can be treated with metronidazole; however, resistant strains of T. vaginalis have been isolated and there is a lack of useful alternative drugs. The aim of the present study was to examine the activity of hexadecylphosphocholine (HePC; miltefosine), a membrane-active alkylphospholipid, that is licensed as an antileishmanial agent against T. vaginalis.

METHODS

The efficacy of HePC after 30 min, 1 h, 16 h and 24 h against four different T. vaginalis strains (with varying resistance to metronidazole) was evaluated.

RESULTS

It was shown that all isolates, including the metronidazole-resistant strains, were susceptible to HePC, with EC50s of between 8 and 40 microM and EC90s of between 8 and 80 microM depending on time and on the medium used for the experiments. Treatment of trichomonads with HePC resulted in rounding up and, at concentrations of >or=40 microM, in subsequent total lysis of the organisms.

CONCLUSIONS

HePC may be a promising new candidate for the treatment of trichomoniasis.

Tumor and normal tissue pharmacokinetics of perifosine, an oral anti-cancer alkylphospholipid

Clinical use of anti-cancer alkylphospholipids is limited by gastrointestinal toxicity. However, new interest has emerged since it was shown that these drugs enhance the cytotoxic effect of conventional chemotherapy and radiotherapy in preclinical models. The aim of this study was to characterize the pharmacokinetic profile of perifosine, an oral analog of alkylphosphocholine (APC), and to compare in vitro drug uptake with in vivo drug accumulation in three human-derived squamous cell carcinomas (A431, HNXOE and KB). In vitro, KB cells showed a remarkably high uptake and sensitivity for perifosine compared with A431 and HNXOE cells. In vivo, perifosine reached a clinically relevant plasma concentration in mice after a single oral dose of 40 mg/kg. Perifosine was not metabolized and displayed slow elimination, with a terminal half-life of 137 (+/- 20) hours and an apparent volume of distribution of 11.3 l/kg. Comparable tumor accumulation was observed for A431 and HNXOE tumors, whereas perifosine uptake by KB xenografts was substantially higher. Tissue distribution occurred throughout the whole body reaching high perifosine levels in the gastro-intestinal tract, while heart and brain tissue contained relatively low levels. Based on its stability and relatively high tumor uptake in vivo, perifosine is an attractive candidate for further evaluation, e.g. as radiosensitizer.

Antiprotozoal activities of phospholipid analogues

The antiprotozoal activity of phospholipid analogues, originally developed as anti-cancer drugs, has been determined in the past decade. The most susceptible parasites are Leishmania spp. and Trypanosoma cruzi with activity also shown against Trypanosoma brucei spp., Entamoeba histolytica and Acanthamoeba spp. Miltefosine, an alkylphosphocholine, was registered for the oral treatment of visceral leishmaniasis (VL) in India in March 2002. This review will focus on the biological activities of phospholipid analogues. Biochemical and molecular targets and mechanism(s) of action have been studied extensively in tumor cells but have not been determined in protozoa.

Quantitative determination of perifosine, a novel alkylphosphocholine anticancer agent, in human plasma by reversed-phase liquid chromatography-electrospray mass spectrometry

A sensitive and selective reversed-phase LC-ESI-MS method to quantitate perifosine in human plasma was developed and validated. Sample preparation utilized simple acetonitrile precipitation without an evaporation step. With a Develosil UG-30 column (10 x 4 mm I.D.), perifosine and the internal standard hexadecylphosphocholine were baseline separated at retention times of 2.2 and 1.1 min, respectively. The mobile phase consisted of eluent A, 95% 9 mM ammonium formate (pH 8) in acetonitrile-eluent B, 95% acetonitrile in 9 mM ammonium formate (pH 8) (A-B, 40:60, v/v), and the flow-rate was 0.5 ml/min. The detection utilized selected ion monitoring in the positive-mode at m/z 462.4 and 408.4 for the protonated molecular ions of perifosine and the internal standard, respectively. The lower limit of quantitation of perifosine was 4 ng/ml in human plasma, and good linearity was observed in the 4-2,000 ng/ml range fitted by linear regression with 1/x weight. The total LC-MS run time was 5 min. The validated LC-MS assay was applied to measure perifosine plasma concentrations from patients enrolled on a phase I clinical trial for pharmacokinetic/pharmacodynamic analyses.

Effects of miltefosine and other alkylphosphocholines on human intestinal parasite Entamoeba histolytica

The protozoan parasite Entamoeba histolytica is the cause of amoebic dysentery and liver abscess. It is therefore responsible for significant morbidity and mortality in a number of countries. Infections with E. histolytica are treated with nitroimidazoles, primarily with metronidazole. At this time, there is a lack of useful alternative classes of substances for the treatment of invasive amoebiasis. Alkylphosphocholines (alkyl-PCs) such as hexadecyl-PC (miltefosine) were originally developed as antitumor agents, but recently they have been successfully used for the treatment of visceral leishmaniasis in humans. We examined hexadecyl-PC and several other alkyl-PCs with longer alkyl chains, with and without double bond(s), for their activity against two strains of E. histolytica. The compounds with the highest activity were oleyl-PC, octadecyl-PC, and nonadecenyl-PC, with 50% effective concentrations for 48 h of treatment between 15 and 21 microM for strain SFL-3 and between 73 and 98 microM for strain HM-1:IMSS. We also tested liposomal formulations of these alkyl-PCs and miltefosine. The alkyl-PC liposomes showed slightly lower activity, but are expected to be well tolerated. Liposomal formulations of oleyl-PC or closely related alkyl-PCs could be promising candidates for testing as broad-spectrum antiprotozoal and antitumor agents in humans.

Short- and long-term efficacy of hexadecylphosphocholine against established Leishmania infantum infection in BALB/c mice

In the immunocompetent host, visceral leishmaniasis (VL) is a fatal disease if untreated. In immunosuppressed patients, VL is an opportunistic infection for which there is no effective treatment for relapses. Here we report on the long-term activity of orally administered hexadecylphosphocholine (HDPC) against established Leishmania infantum infection in BALB/c mice. HDPC is a synthetic phospholipid with antiproliferative properties that has been extensively studied for its cancerostatic activity. Its short-term leishmanicidal effects in mice recently infected with viscerotropic Leishmania species have been previously reported. First, we show that 5 days of oral therapy with HDPC (20 mg/kg of body weight/day) led to amastigote suppression in the liver and the spleen of 94 and 78%, respectively (versus 85 and 55% suppression by meglumine antimonate in the liver and spleen, respectively), in mice infected 6 weeks before treatment and examined 3 days after the end of treatment. These results demonstrate the short-term efficacy of HDPC against an established Leishmania infection. Next, the long-term efficacy of HDPC was examined. In HDPC-treated mice both the hepatic and splenic amastigote loads were significantly reduced (at least 89%) 10, 31, and 52 days after the end of the treatment. In the treated mice, the increase of the splenic load was significantly slower than that in the untreated mice, demonstrating that the HDPC-exerted inhibition of Leishmania growth persisted for at least 7 to 8 weeks. Orally administered HDPC--the safe doses and side effects of which are at least partially known--appears to be a promising candidate for the treatment of VL.