Increased Drug Uptake Research Articles

Electrochemotherapy with Intravenous Bleomycin in the Local Treatment of Skin Melanoma Metastases

Electrochemotherapy (ECT) combines chemotherapy and electroporation to increase drug uptake. Its role in cutaneous melanoma metastasis treatment is not well defined; indeed, few studies have been reported, without complete follow-up data. To prospectively evaluate clinical activity and tolerability of ECT with i.v. bleomycin, and to analyze the response increase associated to repeated sessions, in the largest series of cutaneous melanoma metastases reported to date (n = 233). 14 stage III relapsed/refractory patients were enrolled according to European Standard Operating Procedures of Electrochemotherapy (ESOPE) guidelines and treated under general sedation using the Cliniporator(TM) pulse generator. A response was obtained in 13/14 patients (93%) after the first ECT, with a complete regression (CR) in 7 (50%). Seven patients underwent a second and three a third ECT on newly appearing and residual lesions, all achieving a response. Overall, a response was obtained in 93% metastases, with lower response rates in >1 cm(2) lesions. The CR rate was 58%; none of the CR nodules relapsed. The repeated ECT sessions gave rise to a new response in 21/29 (72%) re-treated lesions. The local tumor control rate was 74.5% at 2 years. ECT is a safe procedure, easily performed in terms of toxicities and cost-effectiveness ratios, and constitutes a therapeutic tool for relapsed/refractory cutaneous melanoma patients. The repeated ECT sessions are associated with a response increase in re-treated lesions which could allow to overcome the reduced activity in >1 cm(2) sized metastases.

Improving chemotherapeutic drug penetration in melanoma by imatinib mesylate

Imatinib mesylate has specific activity in inhibiting select tyrosine kinase receptors, including platelet-derived growth factor receptors (PDGFRs) and c-kit. In general, melanomas widely express PDGFR and c-kit, and their in vivo resistance to chemotherapy is attributable to high tumor interstitial fluid pressure (IFP). Recent studies have suggested that PDGFR-beta inhibition reduces tumor IFP, and thus increases the uptake of concomitantly administered drugs. The present study was designed to investigate the potential of imatinib mesylate as a therapy for melanoma or as an adjuvant to chemotherapeutics. Using in vivo mouse models, the effect of imatinib mesylate on the growth of melanoma with or without dacarbazine was studied. Imatinib mesylate enhanced the antitumor effect of dacarbazine on in vivo growth and lung metastases of melanoma cells, although treatment with only imatinib mesylate had no effect. We could detect perivascular expression of PDGF beta-receptor in melanoma tumors. Interestingly, dacarbazine uptake in melanoma was more than three-times increased by treatment with imatinib mesylate, while its uptake in serum or bone marrow was not affected by imatinib mesylate. These data suggest interference with PDGF receptors, or their ligands, as a novel strategy to increase drug uptake and therapeutic effectiveness of chemotherapy for melanoma.

Peptide-Induced Inflammatory Increase in Vascular Permeability Improves Photosensitizer Delivery and Intersubject Photodynamic Treatment Efficacy

Photodynamic therapy (PDT) treatment can exhibit high intersubject variability due to the inherent differences in drug delivery within the tissue to be treated. In this study, the increased perfusion of the lipid-associated photosensitizer verteporfin was studied using substance P, a peptide known to increase vascular permeability. The transvascular permeability coefficient was quantified before and after administration of substance P, and the mean value increased from 0.026 to 0.043 microm/s with the induced inflammation. Correspondingly, there was a 40-50% increase in uptake of verteporfin in the tumor parenchyma in tumors injected with substance P compared to those without. This increased drug uptake resulted in a modest increase in tumor doubling time from 4 days with regular PDT to 6.2 days with substance P and PDT. There was also a significant reduction in the interindividual variability in with substance P plus PDT from 64% to 13%. The resulting treatment was therefore more effective and there was less variability in dose between subjects.

Use of an Artificial Lymphatic System During Carboplatin Infusion to Improve Canine Osteosarcoma Blood Flow and Clinical Response

The artificial lymphatic system (ALS), a mechanical system designed to reduce increased interstitial fluid pressure in solid tumors and enhance the delivery of chemotherapy, was evaluated within a randomized clinical trial treating spontaneously occurring canine appendicular osteosarcoma (OS), a tumor similar to its human OS counterpart. An ALS was investigated for its ability to increase OS blood flow and increase uptake of intravenously administered carboplatin. Blood flow increased by 314% in tumors with active ALS drains versus 126% in control tumors (P < .03). Tumor carboplatin uptake increased by 51% after drain activation (P = .07). Microvascular density (MVD) was measured in tumors after surgical amputation and in corresponding bone regions in a cohort of normal dogs. The OS tumors had equivalent MVD as normal bone, and MVD was higher in the humerus than the femur (P < .03) in both tumor and normal bone. Median survival between the ALS-treated and control cohorts was not different despite increased drug uptake or ALS manipulation. Compared with historic controls, ALS drain insertion into tumors to reduce interstitial fluid pressure did not worsen the prognosis. The findings in canine spontaneously occurring OS indicate that an ALS may be of value as a chemotherapy adjunct for enhancing the delivery of chemotherapy to tumor interstitium.

Addition of low-dose tumor necrosis factor-?? to systemic treatment with STEALTH liposomal doxorubicin (Doxil) improved anti-tumor activity in osteosarcoma-bearing rats

Improved efficacy of Doxil (STEALTH liposomal doxorubicin) compared to free doxorubicin has been demonstrated in the treatment of several tumor types. We have shown that addition of low-dose tumor necrosis factor (TNF) to systemic Doxil administration dramatically improved tumor response in the highly vascularized rat soft tissue sarcoma BN175. Whether a similar enhanced efficacy can be achieved in less vascularized tumors is uncertain. We therefore examined the effect of systemic administration of Doxil in combination with low-dose TNF in intermediate vascularized osteosarcoma-bearing rats (ROS-1). Small fragments of the osteosarcoma were implanted s.c. in the lower limb. Treatment was started when the tumors reached an average diameter of 1 cm. Rats were treated with five i.v. injections at 4-day intervals with Doxil or doxorubicin and TNF. Systemic treatment with Doxil resulted in a better tumor growth delay than free doxorubicin, but with progressive diseases in all animals. The 3.5-fold augmented accumulation of Doxil compared to free doxorubicin presumably explains the enhanced tumor regression. Addition of low-dose TNF augmented the anti-tumor activity of Doxil, although no increased drug uptake was found compared to Doxil alone. In vitro studies showed that ROS-1 is sensitive to TNF, but systemic treatment with TNF alone did not result in a tumor growth delay. Furthermore, we demonstrated that treatment with Doxil alone or with TNF resulted in massive coagulative necrosis of tumor tissue. In conclusion, combination therapy of Doxil and low-dose TNF seems attractive for the treatment of highly vascularized tumors, but also of intermediate vascularized tumors like the osteosarcoma.

Vitamin-mediated targeting as a potential mechanism to increase drug uptake by tumours

Targeted chemotherapy for cancer treatment offers a great potential advantage in tumour treatment due to greater specificity of delivery which leads to increased dose of the cytotoxin delivered to the tumour relative to the rest of the body. In order to achieve such selective targeted delivery one needs to identify generic markers that are over-expressed on the surface of tumour cells but are not over-expressed on normal tissue. Work of several authors has shown that some cells, such as those of rapidly dividing, aggressive tumours, over-express surface receptors involved in the uptake of vitamin B 12 [B. Rachmilewitz, M. Rachmilewitz, B. Moshkowitz, J. Gross, J. Lab. Clin. Med. 78 (1971) 275–279; B. Rachmilewitz, A. Sulkes, M. Rachmilewitz, A. Fuks, Israel J. Med. Sci. 17 (1981) 874–879] or folate [P. Garin-Chesa, I. Campbell, P.E. Saigo, J.L. Lewis Jr., L.J. Old, W.J. Rettig, Am. J. Pathol. 142 (1993) 557–567; O.C. Boerman, C.C. van Niekerk, K. Makkink, T.G.J.M. Hanselaar, P. Kenemans, L.G. Poels, Int. J. Gynecol. Pathol. 10 (1991) 15–25; G. Toffoli, C. Cernigoi, A. Russo, A. Gallo, M. Bagnoli, M. Boiocchi, Int. J. Cancer 74 (1997) 193–194; J.A. Reddy, D. Dean, M.D. Kennedy, P.S. Low, J. Pharm. Sci. 88 (1999) 1112–1118; J.A. Reddy, P.S. Low, Crit. Rev. Ther. Drug Carrier Syst. 15 (1998) 587–627; G.J. Russell-Jones, K. McTavish, J.F. McEwan, in: Proceedings of the 2nd International Symposium on Tumor Targeted Delivery Systems, 2002]. Furthermore the degree of over-expression has been found to correlate with the stage of tumour growth, with the highest levels found on stage IV carcinomas. Using fluorescently-labelled polymers to which are linked the targeting agents, vitamin B 12, folate or biotin, the relative uptake of these polymers into various types of tumour cell lines grown both in vitro and in vivo has been examined. These studies have shown that while some tumour types do NOT over-express receptors involved in vitamin uptake, most tumour types over-express receptors for folate, or vitamin B 12. In either case there is also a greatly increased expression of a yet to be identified biotin receptor. In cases of receptor over-expression, binding of the targeted fluorochrome leads to rapid internalization of these molecules within the cells to levels that are two to thirty times higher than with non-targeted polymers. Using a number of cancer models, these studies were extended further and it was found that the increased expression of receptors also leads to increased levels of killing with targeted cytotoxins. Thus the preliminary data described suggests that the use of vitamins as targeting agents has enormous potential for use in cancer diagnosis and chemotherapy.

Increasing tumor uptake of anticancer drugs with imatinib

Solid malignancies often exhibit high interstitial fluid pressure (IFP), which causes poor uptake of anticancer drugs. While there are several mechanisms that regulate IFP in tumors, activation of platelet-derived growth factor receptor, which is expressed in various cell types within the tumor microenvironment, has been observed to play an important role in elevating IFP. In preclinical studies, treatment with imatinib, which inhibits both α- and β–platelet-derived growth factor receptors, as well as KIT, ABL, ARG, and BCR-ABL tyrosine kinases, has been shown to decrease tumor IFP and concomitantly augment uptake of chemotherapeutic drugs, thereby enhancing the efficacy of chemotherapy. This review discusses preclinical studies showing the ability of imatinib to lower IFP and increase drug uptake within solid tumors, as well as the scientific rationale for clinical use of imatinib as combination therapy for chemotherapy.

In vitro pharmacokinetic study of the novel anticancer agent E7070: red blood cell and plasma protein binding in human blood.

E7070 is a novel sulfonamide anticancer agent that arrests the G(1)/S phase of the cell cycle. Preclinical and phase I studies have demonstrated non-linear pharmacokinetics (PK) of the drug. A population PK analysis revealed that the human plasma concentration-time data were best described by a three-compartment model with non-linear distribution. We have studied the in vitro interaction of 14C-radiolabeled E7070 with red blood cells (RBC) and its binding to plasma proteins in the concentration range where non-linearity in disposition was observed in humans to get more insight into the behavior of the drug. After the addition of E7070 to whole blood at 37 degrees C, the drug is taken up or binds to RBC in a concentration-dependent manner. The addition of sodium azide, however, did not result in a decrease of drug uptake by RBC, indicating passive diffusion processes. A non-linear increase in drug uptake was observed at incubation concentrations above 4 microg/ml E7070 in whole blood. This non-linearity was confirmed by lower partition coefficients between RBC and plasma at higher incubation concentrations (from 2.37 at 4 microg/ml to 0.31 at 200 microg/ml). The plasma protein binding of E7070 was high (98-99%) and linear in the concentration range studied (20-200 microg/ml). In conclusion, E7070 in whole blood is preferentially bound to RBC and exhibits high plasma protein binding. The non-linear distribution of E7070 in humans can be caused, in part at least, by saturable binding of E7070 to RBC.

Epirubicin and meglumine gamma-linolenic acid: a logical choice of combination therapy for patients with superficial bladder carcinoma.

Anthracyclines have been established as first-line drugs for intravesical use in the treatment of patients with superficial bladder carcinoma, although they result only in a modest reduction in tumor recurrence rates. The essential fatty acid gamma-linolenic acid (GLA) also is an effective cytotoxic agent against superficial bladder carcinoma when it is applied topically. The objective of this study was to assess the efficacy of combined epirubicin and GLA with the purpose of developing a suitable model for modification of existing intravesical regimens. The human urothelial carcinoma cell lines MGH-U1 and RT112 were used in standard cytotoxicity assays and were exposed to meglumine GLA (MeGLA) and epirubicin in two-dimensional concentration matrices. A thiozolyl blue (methyl-thiazoldiphenyl tetrazolium) assay was used to determine residual cell biomass. Drug interaction was quantified by median-effect analysis software (CalcuSyn), and the evaluation of drug uptake utilized fluorescence confocal microscopy (FCM) and flow cytometry. MeGLA caused a significant enhancement of anthracycline uptake, viewed by FCM, from 92 fluorescence units to 222 fluorescence units (P < 0.001). Flow cytometry confirmed the increased drug uptake and showed that the mean epirubicin content per cell increased from 23 to 57 units and from 8 to 24 units for MGH-U1 and RT112 cells, respectively (99% confidence interval < 0.3). This resulted in improved cytotoxicity, and it was shown that the drugs acted synergistically with all but the highest MeGLA concentrations. The efficacy of epirubicin was enhanced significantly when it was used in combination with most concentrations of MeGLA (< 300 microg/mL), and the two agents acted synergistically. There was a corresponding increase in epirubicin uptake by cells under these conditions. At high MeGLA concentrations, however, anthracycline solubility was compromised, and drug synergy was lost.

Carriers involved in targeting the cytostatic bile acid-cisplatin derivatives cis-diammine-chloro-cholylglycinate-platinum(II) and cis-diammine-bisursodeoxycholate-platinum(II) toward liver cells.

Molecular bases for targeting bile acid-cisplatin derivatives Bamet-R2 [cis-diammine-chloro-cholylglycinate-platinum(II)] and Bamet-UD2 [cis-diammine-bisursodeoxycholate-platinum(II)] toward liver cells were investigated. Carriers for bile acids [human Na(+)-taurocholate cotransporting polypeptide (NTCP)], organic anions [organic anion transporting polypeptide (OATP)], and organic cations [organic cation transporter (OCT)] were expressed in Xenopus laevis oocytes (XO) and Chinese hamster ovary (CHO) cells. Drug uptake was measured by flameless atomic absorption of platinum. Rat Oatp1- or rat Ntcp-transfected CHO cells were able to take up Bamets, but not cisplatin, severalfold more efficiently than wild-type cells. This uptake was enhanced by butyrate-induced expression of both carriers. Uptake of both Bamets by Ntcp-transfected CHO cells was stimulated by extracellular sodium. The amount of Bamets, but not cisplatin, taken up by XO was enhanced when expressing OATP-A, OATP-C, NTCP, OCT1, or OCT2, a nonhepatic OCT isoform used for comparative purposes. Bamet uptake by XO was inhibited by known substrates of these carriers (glycocholate for NTCP and OATP-C, ouabain for OATP-A, and quinine for OCT1 and OCT2). Drug uptake versus substrate concentration revealed saturation kinetics (K(m) was in the 8-58 microM range), with the following order of efficiency of transport (V(max)/K(m)) for Bamet-R2: OATP-C > OCT2 > OATP-A > NTCP > OCT1; and the following order of efficiency of transport for Bamet-UD2: OATP-C > OCT2 > OATP-A > OCT1 > NTCP. Increasing the generation of cationic forms of Bamets by incubation in the absence of chloride increased drug uptake by OATP-A, OCT1, and OCT2 but reduced that achieved by NTCP and OATP-C. These results suggest a role for carriers of organic anions and cations in Bamet-R2 and Bamet-UD2 uptake, which may determine their ability to accumulate in liver tumor cells and/or be taken up and efficiently excreted by hepatocytes.

Biological basis for chemo-radiotherapy interactions

For over 10 years, chemo-radiotherapeutic combinations have been used to treat locally advanced epithelial tumours. The rationale for these combinations relies on spatial cooperation or interaction between modalities. Interactions may take place (i) at the molecular level, with altered DNA repair or modification of the lesions induced by drugs or radiation, (ii) at the cellular level, notably through cytokinetic cooperation arising from differential sensitivity of the various compartments of the cell cycle to the drug or radiation, and (iii) at the tissue level, including reoxygenation, increased drug uptake or inhibition of repopulation or angiogenesis. Some mechanisms underlying interaction of radiation with cis-diammino-platinum (II) ( cis-Pt), 5-fluoro-2′-deoxyuridine (5-FU), taxanes and gemcitabine are described. It is shown how various mechanisms including cell synchronisation and reoxygenation concur to paclitaxel-induced radiosensitisation. In the future, specific targeting of tumours, for example, with the epidermal growth factor receptor (EGFR) or angiogenesis inhibitors, should be achieved in order to increase the therapeutic index.

Ultrasound-induced mild hyperthermia as a novel approach to increase drug uptake in brain microvessel endothelial cells.

Drug delivery to the central nervous system (CNS) is limited by the blood-brain barrier (BBB). Thus, a noninvasive and reversible method to enhance BBB permeation of drugs is highly desirable. In the present work, we studied if ultrasound-induced mild hyperthermia (USHT, 0.4 watts (W)/cm2 at 41 degrees C) can enhance drug absorption in BBB endothelial cells, and we elucidated the mechanism of USHT on cellular accumulation. To accomplish these aims, we studied the effects of hyperthermia (41 degrees C), USHT, P-glycoprotein (P-gp) modulator (PSC 833), and combination of USHT and PSC 833 on accumulation of P-gp substrate (R123) and non-P-gp substrates (sucrose, 2-deoxyglucose, and antipyrine) in monolayers of primary bovine brain microvessel endothelial cells (BBMEC). USHT, through its thermal effect, produces a significant (relative to controls; no USHT) and comparable increase in R123 accumulation with PSC 833. We also demonstrate that USHT increases permeability of hydrophobic (R123 and [14C]-antipyrine) and not hydrophilic molecules ([14C]-sucrose and 2-[3H]-deoxy-D-glucose). The enhanced permeability is reversible and size dependent, as USHT produces a much larger effect on cellular accumulation of [14C]-antitpyrine (molecular weight of 188 D) than that of R123 (molecular weight of 380.8 D). Although USHT increases membrane permeability, it did not affect P-gp activity or the activity of glucose transporters. Our results point to the potential use of USHT as a reversible and noninvasive approach to increase BBB permeation of hydrophobic drugs, including P-gp-recognized substrates.

P-glycoprotein in Acute Myeloid Leukaemia: Therapeutic Implications of its Association With Both a Multidrug-resistant and an Apoptosis-resistant Phenotype

P-glycoprotein (Pgp) expression is an independent prognostic factor for response to remission-induction chemotherapy in acute myeloblastic leukaemia, particularly in the elderly. There are several potential agents for modulating Pgp-mediated multi-drug resistance, such as cyclosporin A and PSC833, which are currently being evaluated in clinical trials. An alternative therapeutic strategy is to increase the use of drugs which are unaffected by Pgp. However, in this review, we explain why this may be more difficult than it appears. Evidence from in vitro studies of primary AML blasts supports the commonly held supposition that chemoresistance may be linked to apoptosis-resistance. We have found that Pgp has a drug-independent role in the inhibition of in vitro apoptosis in AML blasts. Modulation of cytokine efflux, signalling lipids and intracellular pH has all been suggested as ways by which Pgp may affect cellular resistance to apoptosis include modulation of cytokine efflux, signalling lipids and intracellular pH; these are discussed in this review. For a chemosensitising agent to be successful, it may be more important for it to enhance apoptosis than to increase drug uptake.

Mechanism of the ultrasonic activation of micellar drug delivery

The mechanism of the ultrasonic enhancement of the uptake of cytotoxic drugs, doxorubicin (DOX) and ruboxyl (Rb) by HL-60 cells from Pluronic micelles was studied. DOX and Rb sorption from either PBS or micellar Pluronic solutions is described by Langmuir-type isotherms characteristic of substrates with limited number of sorption centers. The sorption limits for Rb from PBS and Pluronic were considerably higher than those for DOX, presumably due to much higher Rb partitioning into cell membranes. The overall number of drug sorption centers for both drugs decreased in the presence of Pluronic implying the effect of Pluronic on the DNA conformation, which was confirmed by the electron paramagnetic resonance (EPR) experiments using Rb as a spin probe. Ultrasound increased drug uptake by the cells from PBS and Pluronic solutions. The fluorescence microscopy and flow cytometry experiments using fluorescently-labeled Pluronic showed that ultrasound enhanced both the intracellular uptake of Pluronic micelles and Pluronic trafficking into cell nuclei. A scheme is suggested that describes various equilibria controlling drug/cell interactions and effect of ultrasound on these equilibria. Under the action of ultrasound, the equilibrium between the micellar-encapsulated and free drug is shifted in the direction of free drug due to micelle perturbation; the equilibrium between extracellular and internalized drug is shifted to the intracellular drug due to the ultrasound-induced cellular changes that enhance the accessibility of various cellular structures to drug. An important advantage offered by ultrasound is that the same degree of the intracellular drug uptake may be achieved at a substantially lower drug concentration in the incubation medium.

PII: S0003-4975(00)01169-3

PII: S0003-4975(00)01169-3

Effect of γ-linolenic acid on cellular uptake of structurally related anthracyclines in human drug sensitive and multidrug resistant bladder and breast cancer cell lines

This study investigated the effect on drug uptake in multidrug resistant cells by the incorporation of the essential fatty acid γ-linolenic acid (GLA). The cell lines used were the MCF-7/R resistant human breast cancer and MGH-U1/R bladder cancer. Uptake of drug (doxorubicin, epirubicin, mitoxantrone and idarubicin) after the incorporation of GLA was investigated quantitatively by flow cytometry and qualitatively by confocal microscopy. There was no observable overall increase in drug uptake due to GLA incorporation into the cells as shown by flow cytometry. However, an increase in uptake of the chemotherapeutic agent idarubicin was observed in GLA-treated resistant cells compared with untreated cells using the confocal microscope. This overall increase in cellular drug uptake was not accompanied by a change in cellular drug distribution. Only one drug, mitoxantrone, displayed a change in intracellular drug distribution due to GLA incorporation into MCF-7/R cells. This suggests that essential fatty acid incorporation into the cellular membranes of some resistant cells may cause a shift in the intracellular distribution of certain chemotherapeutic drugs.

Skin Delivery of Oestradiol from Deformable and Traditiona Liposomes: Mechanistic Studies

Deformable vesicles and traditional liposomes were compared as delivery systems for oestradiol to elucidate possible mechanisms of drug delivery through human skin. Accordingly, epidermal permeation of oestradiol from optimized deformable vesicles and traditional liposome formulations was studied under low dose non-occluded conditions. Five mechanisms were investigated. A free drug mechanism compared low-dose permeation through skin with drug release determined after separation of the free drug. Penetration enhancement was researched by studying skin pretreatment with empty vesicles. Improved drug uptake by skin was monitored by dipping stratum corneum into different formulations for 10 min and determining drug uptake. The possibility that intact vesicles permeate through the epidermis was tested by comparing permeation from 136-nm vesicles with that from >500-nm vesicles, assuming that penetration depends on vesicle size. The possibility that different entrapment efficiencies in alternative formulations could be responsible for the difference in delivery was also evaluated. Lipid vesicles improved the skin delivery of oestradiol compared with delivery from an aqueous control. Maximum flux (Jmax) was increased 14- to 17-fold by use of deformable vesicles and 8.2- to 9.8-fold by use of traditional liposomes. Deformable vesicles were thus superior to traditional liposomes. Drug release was negligible over the period during which skin flux was maximum. Pretreatment with empty vesicles resulted in an enhancement ratio of 4.3 for pure phosphatidylcholine (PC) vesicles but the enhancement ratio ranged from only 0.8 to 2.4 for other formulations. Vesicles increased drug uptake into the stratum corneum 23- to 29-fold. Relative flux values obtained from small and large vesicles were similar. No correlation was found between entrapment efficiency and skin delivery. The results showed no evidence of a free drug mechanism, but revealed a possible penetration-enhancing effect for pure PC vesicles, although this was not the only mechanism operating. The positive uptake suggested that lipid vesicles increased drug partitioning into the skin. The data provided no evidence for in-vitro liposome penetration through skin as distinct from vesicle penetration into the stratum corneum.

Pentamidine-loaded poly(D,L-lactide) nanoparticles: Adsorption and drug release

This work describes the loading capacity of poly(D,L-lactide) nanoparticles, the factors influencing pentamidine release, and the cytotoxicity of nanoparticles. The nanoprecipitation method was used to prepare pentamidine-loaded poly(D,L-lactide) nanoparticles. Various concentrations of pentamidine base and polymer were tested. The influence of the dilution, temperature, and ionic strength was evaluated. The cytotoxicity on J 774 cells of unloaded nanoparticles, pentamidine-loaded nanoparticles, and pentamidine isethionate were tested. The percentage of binding decreased significantly with drug load. A nonlinear increase in drug uptake per unit mass of polymer with the equilibrium pentamidine concentration was found. A Langmuir-type sorption was suggested (r = 0.998). 390 μg/ml was found to be the highest level of drug incorporation. The increase of polymer concentration did not improve the pentamidine fixation yield. The increase in temperature or buffer molarity induced a significant release of pentamidine. The increase in dilution also induced an increase in release of pentamidine. The cytotoxicity of pentamidine-loaded nanoparticles and unloaded nanoparticles was superimposable. After 24 h of incubation, pentamidine-loaded nanoparticles presented an IC50 value significantly lower than that of free drug (0.39 vs. 6.5 g/ml). Drug Dev. Res. 43:98–104, 1998. © 1998 Wiley-Liss, Inc.

Quinoline resistance mechanisms in Plasmodium falciparum: the debate goes on

Despite considerable therapeutic success with the antimalarial 4-aminoquinolines such as chloroquine, there is serious doubt about the future of this drug class due mainly to the development and spread of parasite resistance throughout endemic areas. In this article we review the possible biochemical and molecular basis of resistance. Based on our current understanding we have considered the possibility of developing strategies which may allow the aminoquinolines to once again be used effectively against P. falciparum. Our conclusions are that drug resistance is the result of a reduced rate of drug uptake which in turn reduces the amount of drug available to bind the target. The basis for this reduced accumulation could be an altered pH gradient making the food vacuole more alkaline or the parasite cytosol more acidic, an efflux pump removing drug directly from the membrane or any other process which will reduce the rate of drug uptake. Central to the effectiveness of this resistance mechanism is the transient availability of a high affinity, low capacity drug binding site (possibly haem) within the parasite. Resistance reversers such as verapamil influence the apparent Ka for this drug binding phenomenon via an increased drug uptake rate. We demonstrate that by chemical modification of the aminoquinolines, producing predictable alterations in their physicochemical properties, that it is possible to minimise the verapamil sensitive component of resistance and reduce significantly cross-resistance patterns without loss in absolute activity. Based on these views we suggest that the aminoquinoline antimalarials still have a role to play in the cheap, safe and effective chemotherapy of falciparum malaria.

Linking AZT to ceramide increases drug uptake, retention and antiviral action while decreasing bone marrow toxicity: M.B. Yatvin 1, W. Li 1, M.H.B. Stowell 2, V.S. Gallicchio 3, W.A. Shaw 4 & S.W. Burgess 4; OHSU, Portland, OR 1, Calif Inst. Tech., Pasadena, CA 2, Univ. Kentucky, Lexington, KY 3, Avanti Polar Lipids, Inc., Alabaster, AL 4, U.S.A.

Linking AZT to ceramide increases drug uptake, retention and antiviral action while decreasing bone marrow toxicity: M.B. Yatvin 1, W. Li 1, M.H.B. Stowell 2, V.S. Gallicchio 3, W.A. Shaw 4 & S.W. Burgess 4; OHSU, Portland, OR 1, Calif Inst. Tech., Pasadena, CA 2, Univ. Kentucky, Lexington, KY 3, Avanti Polar Lipids, Inc., Alabaster, AL 4, U.S.A.