Comparison of the blood-brain barrier and liver penetration of acridine antitumor drugs

Small molecule inhibitors of Ago2 decrease Venezuelan equine encephalitis virus replication

Venezuelan equine encephalitis virus (VEEV) is classified as a Category B Select Agent and potential bioterror weapon for its severe disease course in humans and equines and its potential for aerosol transmission. There are no current FDA licensed vaccines or specific therapies against VEEV, making identification of potential therapeutic targets a priority. With this aim, our research focuses on the interactions of VEEV with host microRNA (miRNA) machinery. miRNAs are small non-coding RNAs that act as master regulators of gene expression by downregulating or degrading messenger RNA, thus suppressing production of the resultant proteins. Recent publications implicate miRNA interactions in the pathogenesis of various viral diseases. To test the importance of miRNA processing for VEEV replication, cells deficient in Ago2, an important component of the RNA-induced silencing complex (RISC), and cells treated with known Ago2 inhibitors, notably acriflavine (ACF), were utilized. Both conditions caused decreased viral replication and capsid expression. ACF treatment promoted increased survival of neuronal cells over a non-treated, infected control and reduced viral titers of fully virulent VEEV as well as Eastern and Western Equine Encephalitis Viruses and West Nile Virus, but not Vesicular Stomatitis Virus. ACF treatment of VEEV TC-83 infected mice resulted in increased in vivo survival, but did not affect survival or viral loads when mice were challenged with fully virulent VEEV TrD. These results suggest that inhibition of Ago2 results in decreased replication of encephalitic alphaviruses in vitro and this pathway may be an avenue to explore for future therapeutic development.

Acridine yellow G blocks glioblastoma growth via dual inhibition of epidermal growth factor receptor and protein kinase C kinases

Amplification of the epidermal growth factor receptor (EGFR), frequently expressed as a constitutively active deletion mutant (EGFRvIII), occurs commonly in glioblastoma multiformes (GBM). However, blockade of EGFR is therapeutically disappointing for gliomas with PTEN deletion. To search for small molecules treating this aggressive cancer, we have established a cell-based screening and successfully identified acridine yellow G that preferentially blocks cell proliferation of the most malignant U87MG/EGFRvIII cells over the less malignant U87MG/PTEN cells. Oral administration of this compound markedly diminishes the brain tumor volumes in both subcutaneous and intracranial models. It directly inhibits EGFR and PKCs with IC(50) values of ~7.5 and 5 μM, respectively. It dually inhibits EGFR and PKCs, resulting in a blockade of mammalian target of rapamycin signaling and cell cycle arrest in the G(1) phase, which leads to activation of apoptosis in the tumors. Hence, combinatorial inhibition of EGFR and PKCs might provide proof of concept in developing therapeutic agents for treating malignant glioma and other human cancers.

Identification of FDA-approved drugs and bioactives that protect hair cells in the zebrafish (Danio rerio) lateral line and mouse (Mus musculus) utricle

The hair cells of the larval zebrafish lateral line provide a useful preparation in which to study hair cell death and to screen for genes and small molecules that modulate hair cell toxicity. We recently reported preliminary results from screening a small-molecule library for compounds that inhibit aminoglycoside-induced hair cell death. To potentially reduce the time required for development of drugs and drug combinations that can be clinically useful, we screened a library of 1,040 FDA-approved drugs and bioactive compounds (NINDS Custom Collection II). Seven compounds that protect against neomycin-induced hair cell death were identified. Four of the seven drugs inhibited aminoglycoside uptake, based on Texas-Red-conjugated gentamicin uptake. The activities of two of the remaining three drugs were evaluated using an in vitro adult mouse utricle preparation. One drug, 9-amino-1,2,3,4-tetrahydroacridine (tacrine) demonstrated conserved protective effects in the mouse utricle. These results demonstrate that the zebrafish lateral line can be used to screen successfully for drugs within a library of FDA-approved drugs and bioactives that inhibit hair cell death in the mammalian inner ear and identify tacrine as a promising protective drug for future studies.

Phase II study of XR 5000 (DACA), an inhibitor of topoisomerase I and II, administered as a 120-h infusion in patients with non-small cell lung cancer

XR5000 is a tricyclic carboxamide-based cytotoxic agent that binds to DNA by intercalation and stimulates DNA cleavage by inhibition of both topoisomerase I and II. The aim of this study was to evaluate the antitumoral activity and safety profile of XR5000 given as second-line chemotherapy in patients with advanced non-small cell lung cancer (NSCLC). Patients received XR5000 at the dose of 3010 mg/m(2) as a 120-h central venous infusion every 3 weeks. The 15 patients (median age 56 years, range 48-71 years) enrolled had an Eastern Cooperative Oncology Group (ECOG) performance status of 0 (3 patients), 1 (11 patients) or 2 (1 patient). A total of 32 cycles of XR5000 (median 2, range 1-6) were given to 14 patients. No objective response (assessed according to World Health Organization (WHO) criteria) was documented in the 12 evaluable patients by an external review panel; in 4 out of the 12 patients disease stabilisation was recorded. The following toxicities graded according to the Common Toxicity Criteria (CTC) version 2.0. were observed: one grade 3 and two grade 4 granulocytopenia, one grade 3 and one grade 4 thrombocytopenia, one grade 3 deep venous thrombosis, one grade 3 fatigue, and grade 3 undocumented epileptic seizures which led to death in 2 patients. With only 4 out of 12 patients reaching stable disease when using this dose and regimen, further evaluation of XR5000 in advanced NSCLC is not justified.

Use of positron emission tomography in pharmacokinetic studies to investigate therapeutic advantage in a phase I study of 120-hour intravenous infusion XR5000

PURPOSE

XR5000 (N-[2-(dimethylamino)ethyl]acridine-4-carboxamide) is a topoisomerase I and II inhibitor. Because the cytotoxicity of XR5000 increases markedly with prolonged exposure, we performed a phase I study of weekly XR5000 by 120-hour continuous infusion over 3 weeks.

PATIENTS AND METHODS

Twenty-four patients with advanced solid cancer were treated at seven dose levels (700 to 4,060 mg/m2/120 hrs) for a total of 67 cycles. Three patients underwent positron emission tomography (PET) studies at the maximum-tolerated dose (MTD) to evaluate normal tissue and tumor carbon-11 radiolabeled XR5000 ([11C]XR5000) pharmacokinetics.

RESULTS

The dose-limiting toxicity was National Cancer Institute Common Toxicity Criteria (version 1) grade 4 chest and abdominal pain affecting the single patient receiving 4,060 mg/m2/120 hours, and the MTD was 3,010 mg/m2/120 hours. Other grade 3-4 toxicities, affecting single patients at the MTD, were myelosuppression (grade 4), raised bilirubin, vomiting, and somnolence (all grade 3). There was one partial response (adenocarcinoma of unknown primary); the remainder had progressive disease. [11C]XR5000 distributed well into the three tumors studied by PET. Tumor uptake (maximum concentration or area under the concentration versus time curve [AUC]) was less than in normal tissue in which the tumors were located. Tumor exposure (AUC; mean +/- SD in m2/mL/sec) increased when [(11)C]XR5000 was administered during an infusion of XR5000 (0.242 +/- 0.4), compared with [11C]XR5000 given alone (0.209 +/- 0.04; P <.05), indicating that tumor drug exposure was not saturated [corrected].

CONCLUSION

The recommended dose for XR5000 in phase II studies is 3,010 mg/m2/120 hours. PET studies with 11C-labeled drug were feasible and demonstrated in vivo distribution into tumors. Saturation of tumor exposure was not reached at the MTD.

Inter-strain variability in aldehyde oxidase activity in the mouse

Aldehyde oxidase (AO) is a cytosolic enzyme expressed predominantly in the liver. AO is involved in the metabolism of many xenobiotics of pharmacological and toxicological importance including antivirals (famciclovir), antimalarials (quinine) and anticancer drugs (5-fluoro-2-pyrimidine and methotrexate). The aim of this study was to characterize AO activity in different strains of mice using two different substrates. AO activity in the cytosolic fraction was characterized using the metabolism of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA), a novel antitumor drug, to form DACA-9(10H)-acridone (quantified by HPLC with fluorescence detection) and benzaldehyde to form benzoic acid (quantified spectrophotometrically). Characterization of mouse AO activity with DACA showed 15-fold variation in K(m), 10-fold variation in apparent V(max) and twofold differences in intrinsic clearance. Nude mice and C129/C57 had the highest intrinsic clearance (0.66 and 0.l53 ml/min per mg protein, respectively). Nude mice cleared DACA faster than nude tumor bearing mice by a factor of 2. Male Swiss CD had higher intrinsic clearance than female Swiss CD (0.36 and 0.28 ml/min per mg protein). A similar pattern of enzyme activity was observed with benzaldehyde; however, the extent of variation was less than that found with DACA. In conclusion, our results show that there are both strain and gender differences in AO activity. These differences are better detected by DACA. Furthermore, these results suggest caution when extrapolating the data obtained from mouse AO studies to humans.

Phase II study of XR5000 (DACA) administered as a 120-h infusion in patients with recurrent glioblastoma multiforme

BACKGROUND

XR5000 is a tricyclic carboxamide that intercalates DNA and inhibits both topoisomerase I and II. The aim of this study was to evaluate the efficacy and tolerability of XR5000 in patients with recurrent glioblastoma multiforme previously untreated with chemotherapy at relapse.

PATIENTS AND METHODS

Patients received XR5000 at a dose of 3010 mg/m2 as a 120-h central venous infusion every 3 weeks. An independent panel assessed response every two cycles using McDonald's criteria (tumour size, steroid intake and neurological status); toxicity was graded according to the National Cancer Institute-Common Toxicity Criteria, version 2.0.

RESULTS

Sixteen patients were enrolled (one ineligible patient was excluded from efficacy evaluation). Performance status was zero (five patients), one (nine patients) or two (one patient). They received 30 cycles of XR5000 (median 2, range 1-5). Haematological toxicity was mild, with only one patient experiencing grade 3 neutropenia. Other related grade 3/4 adverse events included chest pain (one patient), axillary vein thrombosis (one patient) and rigors/fever in the absence of neutropenia (one patient). There were no objective responses, 14 patients progressing on XR5000 and one having stable disease.

CONCLUSIONS

Although XR5000 was generally well tolerated, these results do not support further evaluation in patients with glioblastoma multiforme using this dose and schedule.

Pharmacokinetic evaluation of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in patients by positron emission tomography

PURPOSE

To evaluate tumor, normal tissue, and plasma pharmacokinetics of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA). The study aimed to determine the pharmacokinetics of carbon-11-labeled DACA ([11C]DACA) and evaluate the effect of pharmacologic doses of DACA on radiotracer kinetics.

PATIENTS AND METHODS

[11C]DACA (at 1/1,000 phase I starting dose) was administered to 24 patients with advanced cancer (pre-phase I) or during a phase I trial of DACA in five patients. Positron emission tomography (PET) was performed to assess pharmacokinetics and tumor blood flow. Plasma samples were analyzed for metabolite profile of [11C]DACA.

RESULTS

There was rapid systemic clearance of [11C]DACA over 60 minutes (1.57 and 1.46 L x min(-1) x m(-2) in pre-phase I and phase I studies, respectively) with the production of several radiolabeled plasma metabolites. Tumor, brain, myocardium, vertebra, spleen, liver, lung, and kidneys showed appreciable uptake of 11C radioactivity. The area under the time-versus-radioactivity curves (AUC) showed the highest variability in tumors. Of interest to potential toxicity, maximum radiotracer concentrations (Cmax) in brain and vertebra were low (0.67 and 0.54 m(2) x mL(-1), respectively) compared with other tissues. A moderate but significant correlation was observed for tumor blood flow with AUC (r = 0.76; P =.02) and standardized uptake value (SUV) at 55 minutes (r = 0.79; P =.01). A decrease in myocardial AUC ( P =.03) and splenic and myocardial SUV ( P =.01 and.004, respectively) was seen in phase I studies. Significantly higher AUC, SUV, and Cmax were observed in tumors in phase I studies.

CONCLUSION

The distribution of [11C]DACA and its radiolabeled metabolites was observed in a variety of tumors and normal tissues. In the presence of unlabeled DACA, pharmacokinetics were altered in myocardium, spleen, and tumors. These data have implications for predicting activity and toxicity of DACA and support the use of PET early in drug development.

A two-step reevaluation of high-dose amsacrine for advanced carcinoma of the upper aerodigestive tract: a pilot phase II study

Results of amsacrine studies in different solid tumors with a dose of 85 mg/m2/24 h x 1 quo 3 weeks have been, in general, disappointing. Although only a few patients with head and neck cancer have been included in broad phase II studies, several responses have been reported, but detailed data concerning responders are lacking. In the present study, amsacrine (Amsidil, Godecke-Parke Davis) was administered at an increased dose of 85 mg/m2/24 h x 3 (total dose per cycle 255 mg/m2) quo 3-4 weeks. 25 patients with advanced carcinoma of meso and hypopharynx were included in the first step of this phase II study (11/25 with histological grades I/II and 14/25 with histological grades III/IV; 10/25 pretreated with radical radiotherapy and 15/25 previously untreated), and 5 patients with undifferentiated carcinoma of the nasopharyngeal type (UCNT), all previously treated. 5/30 patients achieved a complete response (CR) and 5/30 a partial response (PR), the overall response rate being 10/30. Regarding the histology grade, only 1/11 patients with grade I/II carcinoma of meso and hypopharynx achieved a PR with no CR, but 5/14 with grade III/IV from the same group achieved a CR. Out of 10 pretreated patients only one achieved any response and none of the 5 patients with UCNT. Thus, in the second step of this study, high dose amsacrine was evaluated in the target group of previously untreated patients with advanced grade III/IV carcinoma of meso and hypopharynx. 20 patients were included in the second step and all were evaluable for activity. A CR was achieved for 6/20 patients and a PR for 7/20 patients (response rate 65%, 95% confidence interval 44%-86%). Hematological toxicity from both steps included grade IV granulocytopenia in 25/50 patients (50%, 95% confidence interval 36%-64%) and grade IV thrombocytopenia in 18/50 patients (36%, 95% confidence interval 23%-49%). High dose amsacrine seems to be a toxic, but very effective drug as first-line treatment for poorly differentiated carcinoma of meso and hypopharynx, and further studies seem warranted.

Carbon-11 labelling of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and determination of plasma metabolites in man

The potential anti-cancer agent N-[2-(dimethylamino)ethyl] acridine-4-carboxamide, DACA has been labelled with carbon-11. N-[2-11C-methyl]DACA was produced in 73% radiochemical yield from [11C]iodomethane in 40 min from EOB. The average radiochemical yield was 3.2 GBq with specific radioactivity of 41.5 GBq mumol-1 at EOS, corresponding to 24 micrograms of stable DACA. The position of labelling was confirmed by co-labelling with [11/13C]iodomethane. PET studies in patients have been performed prior to Phase I trial of DACA and during Phase I trial of DACA. Analysis of serial plasma samples showed that the metabolism of N-[2-11C-methyl]DACA is rapid and extensive in patient plasma.

Experimental solid tumour activity of N-[2-(dimethylamino)ethyl]-acridine-4-carboxamide

N-[2-(Dimethylamino)ethyl]acridine-4-carboxamide (DACA), a DNA intercalator that exerts its antitumour action through the enzyme topoisomerase II, has previously been shown to be curative against the transplantable Lewis lung adenocarcinoma growing as lung tumour nodules in mice. On the basis of this finding as well as its high in vitro activity against multidrug-resistant cell lines, DACA has been chosen for clinical trial under the auspices of the Cancer Research Campaign, United Kingdom. In the present study the activity of DACA was assessed against advanced (5-mm diameter) s.c. colon 38 adenocarcinomas in BDF1 mice using tumour-growth delay as an end point. Its activity was found to be related positively to the total dose given and negatively to the total duration of the dose schedule. Adoption of a split-dose i.p. administration schedule or slow i.v. infusion allowed the administration of large doses without toxicity. The activity of DACA was comparable with that of 5-fluorouracil and superior to that of doxorubicin, cyclophosphamide and the experimental amsacrine analogue CI-921. Mitoxantrone, amsacrine, etoposide, teniposide and daunorubicin showed minimal activity. DACA also demonstrated significant activity against the NZM3 melanoma human cell line growing as a xenograft in athymic mice.

Transcellular permeability of chlorpromazine demonstrating the roles of protein binding and membrane partitioning

Transcellular permeability of the neuroleptic-anesthetic chlorpromazine (CPZ) was examined using a cell type (MDCK) that forms a confluent monolayer of polarized cells resulting in distinct apical (AP) and basolateral (BL) membrane domains separated by tight junctions. Because CPZ is membrane interactive, transmonolayer flux was analyzed as two kinetic events: cell uptake from the AP donor solution and efflux into the BL side receiver. Using the rate of cell uptake in the presence of different concentrations of BSA, an intrinsic cell partition coefficient of 3700 +/- 130 and an operational dissociation binding constant of 0.4 +/- 0.05 mM were calculated. In contrast to uptake, efflux of CPZ from either the AP or the BL side of the cell monolayer was approximately 10(4)-fold slower and was dependent upon the avidity of CPZ for the protein acceptor in the receiver solution. These results emphasized the importance of simultaneously measuring disappearance of a lipophilic molecule from the donor solution and its appearance in the receiver and demonstrated how interactions with proteins on either side of the cellular barrier influence permeability. Appearance kinetics showed that the composition of the receiving environment is critical to model a particular in vivo situation and implied that the intrinsic permeability of membrane-interactive molecules in vitro does not necessarily predict penetration beyond the initial cellular barrier in vivo.

Intraperitoneal administration of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in the mouse: bioavailability, pharmacokinetics and toxicity after a single dose

The pharmacokinetics, tissue distribution and toxicity of the antitumour agent N-[2-(dimethylamino)-ethyl]acridine-4-carboxamide (AC) were studied after i.p. administration of [3H]-AC (410 mumol/kg) to mice. The latter is the optimal single dose for the cure of advanced Lewis lung tumours. AC was rapidly absorbed into the systemic circulation after i.p. administration, with the maximal concentration (Cmax) occurring at the first time point (5 min). There was no reduction in bioavailability as compared with previous i.v. studies, but the shape of the plasma concentration-time profile was considerably different, reflecting a 3-fold lower Cmax value (20.9 +/- 3.6 mumol/l) and a longer t1/2 value (2.7 +/- 0.3 h) as compared with that observed after i.v. administration (1.6 +/- 0.6 h). Model independent pharmacokinetic parameters after i.p. administration were: clearance (C), 17.5 l h-1 kg-1; steady-state volume of distribution (Vss), 14.1 l/kg; and mean residence time (MRT), 1.46 h. High but variable tissue uptake of AC was observed, with tissue/plasma AUC ratios being 5.7 for heart, 8.4 for brain, 18.9 for kidney and 21.0 for liver but with similar elimination t1/2 values ranging from 1.3 to 2.7 h. All radioactivity profiles in plasma and tissues were greater than the respective parent AC profiles and showed prolonged elimination t1/2 values ranging from 21 h in liver to 93 h in brain. However, tissue/plasma radioactivity AUC ratios were near unity, ranging from 0.7 to 1.57, with the exception of the gallbladder (15.6), which contained greater amounts of radioactivity. By 48 h, approximately 70% of the total dose had been eliminated, with the faecal to urinary ratio being approximately 2:1. This i.p. dose was well tolerated by mice, with sedation being the only obvious side effect. No major change was observed in blood biochemistry or haematological parameters. Comparisons of Cmax, tmax and AUC values determined for AC in brain after its i.p. and i.v. administration suggest that the reduction in acute toxicity after i.p. administration is not due to reduced exposure of the brain to AC as measured by AUC but may be associated with the lower Cmax value or the slower rate of entry of AC into the brain after i.p. administration.

Pharmacokinetics and toxicity of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide after i.v. administration in the mouse

The pharmacokinetics, tissue distribution and toxicity of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide(AC) were studied after i.v. administration to mice. Over the dose range of 9-121 mumol/kg (3-40 mg/kg), AC displayed linear kinetics with the following model-independent parameters: clearance (C), 21.0 +/- 1.9 1 h-1 kg-1; steady-state volume of distribution (Vss), 11.8 +/- 1.4 l/kg; and mean residence time (MRT), 0.56 +/- 0.02 h. The plasma concentration-time profiles for AC fitted a two-compartment model with the following parameters: Cc, 19.4 +/- 2.3 1 h-1 kg-1; Vc, 7.08 +/- 1.06 l/kg; t1/2 alpha 13.1 +/- 3.5 min; and t1/2Z, 1.60 +/- 0.65 h. AC displayed moderately high binding in healthy mouse plasma, giving a free fraction of 15.9%-25.3% over the drug concentration range of 1-561 microM. After the i.v. administration of 30 mumol/kg [3H]-AC, high radioactivity concentrations were observed in all tissues (especially the brain and kidney), showing a high t1/2c value (37-59 h). At 2 min (first blood collection), the AC concentration as measured by high-performance liquid chromatography (HPLC) comprised 61% of the plasma radioactivity concentration (expressed as AC equivalents/l). By 48 h, 73% of the dose had been eliminated, with 26% and 47% of the delivered drug being excreted by the urinary and faecal routes, respectively; less than 1% of the total dose was excreted as unchanged AC in the urine. At least five distinct radiochemical peaks were distinguishable by HPLC analysis of plasma extracts, with some similar peaks appearing in urine. The 121-mumol/kg dose was well tolerated by mice, with sedation being the only obvious side effect and no significant alterations in blood biochemistry or haematological parameters being recorded. After receiving a dose of 152 mumol/kg, all mice experienced clonic seizures for 2 min (with one death occurring) followed by a period of sedation that lasted for up to 2 h. No leucopenia occurred, but some mild anaemia was noted. There was no significant change in blood biochemistry. A further 20% increase in the i.v. dose (to 182 mumol/kg) resulted in mortality, with death occurring within 2 min of AC administration.