A review of new agents evaluated against pediatric acute lymphoblastic leukemia by the Pediatric Preclinical Testing Program

Acute lymphoblastic leukemia (ALL) in children exemplifies how multi-agent chemotherapy has improved the outcome for patients. Refinements in treatment protocols and improvements in supportive care for this most common pediatric malignancy have led to a cure rate that now approaches 90%. However, certain pediatric ALL subgroups remain relatively intractable to treatment and many patients who relapse face a similarly dismal outcome. Moreover, survivors of pediatric ALL suffer the long-term sequelae of their intensive treatment throughout their lives. Therefore, the development of drugs to treat relapsed/refractory pediatric ALL, as well as those that more specifically target leukemia cells, remains a high priority. As pediatric malignancies represent a minority of the overall cancer burden, it is not surprising that they are generally underrepresented in drug development efforts. The identification of novel therapies relies largely on the reappropriation of drugs developed for adult malignancies. However, despite the large number of experimental agents available, clinical evaluation of novel drugs for pediatric ALL is hindered by limited patient numbers and the availability of effective established drugs. The Pediatric Preclinical Testing Program (PPTP) was established in 2005 to provide a mechanism by which novel therapeutics could be evaluated against xenograft and cell line models of the most common childhood malignancies, including ALL, to prioritize those with the greatest activity for clinical evaluation. In this article, we review the results of >50 novel agents and combinations tested against the PPTP ALL xenografts, highlighting comparisons between PPTP results and clinical data where possible.

Dissolution and absorption of caffeine from guarana

The rate of release of caffeine from capsules of guarana was compared with that from capsules containing an equivalent amount of caffeine using the British Pharmacopoeia dissolution test apparatus. Determinations were carried out in media of pH 2 and 6·8 and caffeine concentrations in the dissolution fluid were determined by HPLC. No significant differences in release rates were found between the two preparations at either pH. The rate of absorption of caffeine across rat intestine using the everted gut was also compared for a guarana suspension and a solution containing an equivalent amount of caffeine. Experiments were carried out using fluids of pH 4·0 and 7·4. No significant differences in absorption between the two preparations were observed. These results show that the release and uptake of caffeine from guarana is the same as for preparations containing free caffeine.

Ethnobotanical survey and cytotoxicity testing of plants of South-western Nigeria used to treat cancer, with isolation of cytotoxic constituents from Cajanus cajan Millsp. leaves

ETHNOPHARMACOLOGICAL RELEVANCE

There is only scant literature on the anticancer components of medicinal plants from Nigeria, yet traditional healers in the area under study claim to have been managing the disease in their patients with some success using the species studied.

AIM OF STUDY

To document plants commonly used to treat cancer in South-western Nigeria and to test the scientific basis of the claims using in vitro cytotoxicity tests.

METHODS

Structured questionnaires were used to explore the ethnobotanical practices amongst the traditional healers. Methanol extracts of the most common species cited were screened for cytotoxicity using the sulforhodamine B (SRB) assay in both exposure and recovery experiments. Three cancer cell lines (human breast adenocarcinoma cell line MCF-7, human large cell lung carcinoma cell line COR-L23 and human amelanotic melanoma C32) and one normal cell line (normal human keratinocytes SVK-14) were used for the screening of the extracts and the fractions obtained. The extract of Cajanus cajan showed considerable activity and was further partitioned and the dichloromethane fraction was subjected to preparative chomatography to yield six compounds: hexadecanoic acid methyl ester, alpha-amyrin, beta-sitosterol, pinostrobin, longistylin A and longistylin C. Pinostrobin and longistylins A and C were tested for cytotoxicity on the cancer cell lines. In addition, an adriamycin-sensitive acute T-lymphoblastic leukaemia cell line (CCRF-CEM) and its multidrug-resistant sub-line (CEM/ADR5000) were used in an XTT assay to evaluate the activity of the pure compounds obtained.

RESULTS

A total of 30 healers from S W Nigeria were involved in the study. 45 species were recorded with their local names with parts used in the traditional therapeutic preparations. Cytotoxicity (IC(50) values less than 50 microg/mL) was observed in 5 species (Acanthospermum hispidum, Cajanus cajan, Morinda lucida, Nymphaea lotus and Pycnanthus angolensis). Acanthospermum hispidum and Cajanus cajan were the most active. The dichloromethane fraction of Cajanus cajan had IC(50) value 5-10 microg/mL, with the two constituent stilbenes, longistylins A and C, being primarily responsible, with IC(50) values of 0.7-14.7 microM against the range of cancer cell lines.

CONCLUSIONS

Most of the species tested had some cytotoxic effect on the cancer cell lines, which to some extent supports their traditional inclusion in herbal preparations for treatment of cancer. However, little selectivity for cancer cells was observed, which raises concerns over their safety and efficacy in traditional treatment. The longistylins A and C appear to be responsible for much of the activity of Cajanus cajan extract.

Pediatric Preclinical Testing Program (PPTP) testing of the CENP-E inhibitor GSK923295A

10015

Background: GSK923295A is a small molecule inhibitor of centromere-associated protein E (CENP-E), a mitotic kinesin that is required for metaphase chromosome alignment and integration of mitotic spindle mechanics with mitotic checkpoint signaling. An initial phase I clinical trial in adults is ongoing. Methods: The PPTP includes a molecularly characterized in vitro panel of cell lines (n = 27) and in vivo panel of xenografts (n = 60) representing most of the common types of childhood solid tumors and childhood acute lymphoblastic leukemia (ALL). GSK923295A was tested in vitro at concentrations from 1.0 nM to 10.0 μM (96 hour exposure) and was tested in vivo using a daily × 3 for 2 weeks schedule, repeated at day 21. GSK923295A was administered IP at a dose of 125 mg/kg. Three measures of antitumor activity were used: 1) an objective response measure modeled after the clinical setting; 2) a time to event measure based on the median event-free survival (EFS); and 3) a treated to control (T/C) tumor volume measure. Results: GSK923295A demonstrated potent in vitro activity against the PPTP cell line panel with a median IC50 of 27 nM (range 12 nM to > 10 μM). 35 of 37 solid tumor xenograft models were evaluable. GSK923295A induced significant differences in EFS distribution compared to controls in 32 of 35 evaluable models. Objective responses were noted in 13 of 35 xenografts, including 9 with maintained complete responses (MCR), 3 with complete response (CR), and 1 with partial response (PR). Three of 5 Ewing sarcoma xenografts achieved MCR or CR, as did 2 of 3 rhabdoid tumor, and 2 of 5 rhabdomyosarcoma models. For the neuroblastoma panel, the best response was progressive disease (PD) with growth delay compared to controls (PD2 response), which was observed in 5 of 6 xenografts. GSK923295A showed activity against the ALL panel, but unexplained toxicity (generally on or after day 21) precluded formal analysis. Conclusions: GSK923295A has substantial in vitro and in vivo activity against the PPTP's preclinical models. The observed high level of preclinical activity for GSK923295A will need to be evaluated in the context of systemic exposures achieved in the xenograft models and those achievable in humans at tolerable doses. (Supported by NCI NO1CM42216)

[Table: see text]

Toxicity studies of Tithonia diversifolia A. Gray (Asteraceae) in rats

OBJECTIVE

To investigate the toxicity of an ethanolic extract of the aerial parts of Tithonia diversifolia, used in Nigeria to treat malaria, in rats.

MATERIALS AND METHODS

A 70% ethanol extract was administered orally to adult Wistar rats at various dosages (400-1600 mg/kg) and the animals sacrificed and various organs examined at a range of times from 30 min up to 24 h after administration.

RESULTS

The studies showed a dose- and time-dependent toxic effect, which was reversible on the kidney and liver while there was no noticeable adverse effect on the morphology of the heart, spleen and brain.

CONCLUSION

A 70% ethanol extract of the aerial parts of Tithonia diversifolia, which had previously been shown to reduce parasitemia in mice infected with Plasmodium, displayed kidney and liver toxicity at the lowest dose tested. The use of this plant extract against malaria therefore raises concerns over its safety.

Tyrosinase inhibition by extracts and constituents of Sideroxylon inerme L. stem bark, used in South Africa for skin lightening

OBJECTIVE

To investigate the stem bark of Sideroxylon inerme L. and its compounds for tyrosinase-inhibition activity and to evaluate the mechanism involved of the most potent compounds in tyrosinase inhibition.

MATERIALS AND METHODS

Three different extracts (acetone, methanol and dichloromethane) of Sideroxylon inerme L. were evaluated for their inhibitory effect in vitro on the monophenolase and diphenolase activated forms of tyrosinase, using a colorimetric procedure. This test was used for bioactivity-guided isolation of two active compounds using column chromatography and TLC. Active extracts were also investigated for their inhibitory effect on melanogenesis in cultured B16 melanoma cells. Antioxidant activities of the methanolic extract of Sideroxylon inerme and purified compounds were investigated using the 1,2-diphenyl-2-picrylhydrazyl (DPPH) antioxidant assay. The inhibition of tyrosinase activity relative to the inhibition of its activity at the transcriptional level was also studied by determination of the degree of expression of mRNAs for this gene by using extract of Sideroxylon inerme-treated cells (B16F10) and semi-quantitative RT-PCR.

RESULTS

Methanolic and acetonic extracts of the stem bark of Sideroxylon inerme showed significant inhibition of monophenolase activity (IC50 values of 63 microg/ml and 82 microg/ml, respectively). The methanolic extract also exhibited 37% reduction of melanin content at 6.2 microg/ml in melanocytes without being significantly toxic to the cells. Examination for inhibition of monophenoloxidase in situ on TLC, followed by column chromatographic purification of the stem bark extract of Sideroxylon inerme, resulted in the isolation of two active compounds, epigallocatechin gallate and procyanidin B1, with IC50 values against monophenolase of 30 microg/ml and > 200 microg/ml, respectively. Epigallocatechin gallate exhibited a greater anti-tyrosinase activity than arbutin. Sideroxylon inerme bark extracts, epigallocatechin gallate and procyanidin B1 exhibited antioxidant DPPH radical scavenging activities with EC50 values of 1.54 microg/ml, 1.33 microg/ml and 1.68 microg/ml, respectively and were not particularly cytotoxic. During mechanism studies it was evident that at the transcription level, Sideroxylon inerme (25 microg/ml) was acting as a potent tyrosinase inhibitor compared to controls (untreated cells and kojic acid).

CONCLUSION

The bark extract of Sideroxylon inerme and the two isolated compounds warrant further investigation in clinical studies to be considered as skin-depigmenting agents.

Antiplasmodial compounds from Cassia siamea stem bark extract

Cassia siamea L. (Fabaceae) was identified from the southwest Nigerian ethnobotany as a remedy for febrile illness. This led to the bioassay-guided fractionation of stem bark of the plant extract, using the parasite lactate dehydrogenase assay and multi-resistant strain of Plasmodium falciparum (K1) for assessing the in vitro antimalarial activity. Emodin and lupeol were isolated from the ethyl acetate fraction by a combination of chromatographic techniques. The structures of the compounds were determined by spectroscopy, co-spotting with authentic samples and comparison with literature data. Both compounds were found to be the active principles responsible for the antiplasmodial property with IC(50) values of 5 microg/mL, respectively.

An improved human carboxylesterase for enzyme/prodrug therapy with CPT-11

CPT-11 is a potent antitumor agent that is activated by carboxylesterases (CE) and intracellular expression of CEs that can activate the drug results in increased cytotoxicity to the drug. As activation of CPT-11 (irinotecan-7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin) by human CEs is relatively inefficient, we have developed enzyme/prodrug therapy approaches based on the CE/CPT-11 combination using a rabbit liver CE (rCE). However, the in vivo application of this technology may be hampered by the development of an immune response to rCE. Therefore, we have developed a mutant human CE (hCE1m6), based on the human liver CE hCE1, that can activate CPT-11 approximately 70-fold more efficiently than the wild-type protein and can be expressed at high levels in mammalian cells. Indeed, adenoviral-mediated delivery of hCE1m6 with human tumor cells resulted in up to a 670-fold reduction in the IC(50) value for CPT-11, as compared to cells transduced with vector control virus. Furthermore, xenograft studies with human tumors expressing hCE1m6 confirm the ability of this enzyme to activate CPT-11 in vivo and induce antitumor activity. We propose that this enzyme should likely be less immunogenic than rCE and would be suitable for the in vivo application of CE/CPT-11 enzyme/prodrug therapy.

Proapoptotic compound ARC targets Akt and N-myc in neuroblastoma cells

We have previously described the identification of a nucleoside analog transcriptional inhibitor ARC (4-amino-6-hydrazino-7-beta-D-ribofuranosyl-7H-pyrrolo[2,3-d]-pyrimidine-5-carboxamide) that was able to induce apoptosis in cancer cell lines of different origin. Here, we report the characterization of ARC on a panel of neuroblastoma cell lines. We found that these cell lines were more than 10-fold sensitive to ARC than to the well-known nucleoside analog DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole), and that ARC-induced apoptosis proceeds through mitochondrial injury. Also, we observed that ARC-mediated cell death was accompanied by caspase-3 cleavage and repression of antiapoptotic proteins such as Mcl-1 and survivin. Conversely, we found that overexpression of Mcl-1-protected neuroblastoma cell line NB-1691 from ARC-induced apoptosis. Furthermore, we found that while ARC inhibited the phosphorylation of Akt Ser-473 in multiple cancer cell lines, forced expression of myristoylated Akt promoted resistance to ARC-induced apoptosis in neuroblastoma cells. In addition, we observed that ARC was able to downregulate the protein levels of N-myc, a commonly amplified oncogene in neuroblastomas, and Akt protected N-myc from ARC-induced downregulation. These data suggest that ARC may antagonize different antiapoptotic pathways and induce apoptosis in neuroblastoma cells via multiple mechanisms. Overall, ARC could represent an attractive candidate for anticancer drug development against neuroblastomas.

A phase I study of oxaliplatin (OXA) and irinotecan (IRN) in pediatric patients with refractory solid tumors: A Children's Oncology Group study

9546

Background: Platinum analogues in combination with topoisomerase 1 inhibitors have been shown in in vitro studies to have synergistic anti-tumor activity. This study estimated the maximum tolerated dose (MTD) of OXA in combination with a protracted schedule of IRN in children with refractory solid tumors. Methods: OXA was administered over 2 hrs on days 1 and 8 in combination with IRN iv over 1 hr on days 1–5 and 8–12 of a 21-day cycle. An oral cephalosporin was administered daily to ameliorate IRN-associated diarrhea. Pharmacokinetic studies of OXA and UGT1A1 genotyping were performed during course 1 in consenting patients. Results: 13 patients (median age 16 yrs, 4 M) were enrolled. Dose-limiting diarrhea (n=3), serum lipase elevation (n=3), serum amylase elevation (n=2), colitis (n=1), abdominal pain (n=1) and headache (n=1) occurred at the 1st dose level (60 mg/m2/dose OXA; 20 mg/m2/dose of IRN) in the first 3 patients. Only 1/7 patients treated with reduced doses of both agents (40 mg/m2/dose OXA; 15 mg/m2/dose IRN) experienced DLT, diarrhea. When the OXA dose (60 mg/m2) was increased with the reduced IRN dose (15 mg/m2) 2/3 patients had DLT (1 diarrhea, 1 hypokalemia). Myelosuppression was minimal at all dose levels. One patient with alveolar rhabdomyosarcoma previously treated with irinotecan (dose level 2: 40 mg/m2/dose OXA; 15 mg/m2/dose IRN) had an unconfirmed complete response of her breast metastases and one patient with refractory neuroblastoma had disease stabilization through 6 courses of therapy. The frequency of 6/6, 6/7, and 7/7 UGT1A1 promoter genotypes were 5/10, 4/10, and 1/10, respectively. Conclusions: The MTD using this schedule with oral cephalosporin support was oxaliplatin 40 mg/m2/dose with irinotecan 15 mg/m2/dose. There was some evidence of benefit but significant toxicity, both expected (diarrhea) and unexpected (elevation in pancreatic enzymes), was also observed.

[Table: see text]

Pediatric preclinical testing program (PPTP) efficacy and pharmacodynamic evaluation of the Hsp90 inhibitor 17-DMAG

3575

Background: 17-DMAG is a small-molecule inhibitor of the protein chaperone HSP90 that is being developed as an anticancer agent because of the multiple HSP90 client proteins involved in cancer cell growth and survival. Methods: The PPTP includes an in vitro panel (n=27) as well as panels of xenografts (n=61) representing most of the common types of childhood solid tumors and childhood ALL. 17-DMAG was tested against the in vitro panel at concentrations from 1 nM to 10 microM and was tested against the in vivo tumor panels by IP administration using a 50 mg/kg BID twice weekly x 6 weeks dose and schedule. The PPTP’s 3 measures of antitumor activity were used (Houghton et al. Ped Blood Cancer 2006): 1) an objective response measure; 2) treated to control (T/C) tumor volume at day 21; and 3) a time to event (EFS T/C) measure. HSP70 induction was was used as a pharmacodynamic measure of HSP90 inhibition and was determined in tumor and liver tissue at 8 and 24 hours following the second of two doses of 17-DMAG (50 mg/kg IP) administered at 12 hour intervals. Results: 17-DMAG had an EC50 of 62 nM against the PPTP’s in vitro panel, with a trend for lower EC50 values for the rhabdomyosarcoma panel (median EC50 31 nM) compared to the remaining PPTP in vitro cell lines (p=0.06) and for higher EC50 values for the neuroblastoma lines (median EC50 396 nM, p=0.01). 17-DMAG induced significant differences in EFS distribution in 15 of 30 of the solid tumor xenografts, and in 4 of 6 of the evaluable ALL xenografts. Using the time to event activity measure, 17-DMAG had intermediate or high activity against 4 of 28 evaluable solid tumor xenografts (1 of 2 rhabdoid tumor and 3 of 4 alveolar rhabdomyosarcoma). The only objective response (a PR) observed was for an alveolar rhabdomyosarcoma xenograft. HSP70 induction was observed in both liver and tumor tissue, with robust induction (up to 450% increase versus control) occurring in both responding and non-responding tumors. Conclusions: 17-DMAG produced its greatest antitumor activity against alveolar rhabdomyosarcoma xenografts. Robust HSP70 induction was observed in both responding and non-responding xenografts, suggesting that tumor-specific downstream effects of HSP90 inhibition are primary determinants of response. (Supported by NCI NO1CM42216)

No significant financial relationships to disclose.

In vitrohypoglycemic and antimicrobial activities ofSenecio leucanthemifoliusPoiret

This study reports on the alpha-amylase inhibitory and antimicrobial activities of Senecio leucanthemifolius Poiret. Extracts of S. leucanthemifolius were tested for their antimicrobial and antifungal activities against seven different pathogenic microorganisms using the microdilution technique. The ethyl acetate extract exhibited a strong antibiotic activity against Staphylococcus aureus with a MIC value of 31.25 microg mL(-1), while the n-hexane extract showed a significant activity against dermatophytic fungi. S. leucanthemifolius extracts were tested also for their potential hypoglycemic activity through the in vitro inhibition of alpha-amylase. The dichloromethane extract inhibited alpha-amylase with a value of 56.6% at 0.05 mg mL(-1) and the n-butanol extract showed a value of 89.2% at 1 mg mL(-1).

Uses and abuses of in vitro tests in ethnopharmacology: visualizing an elephant

Although in vivo models give a more accurate reflection of the activity of substances used in traditional medicine, their use in many countries is severely restricted due to economic and ethical concerns, and this has resulted in the widespread use of in vitro tests in ethnopharmacological studies. Such tests are very useful where the identity of compounds responsible for the biological activity of an extract is being investigated and where limited supplies of material are available, but it is important to consider a variety of factors before making over-predictive claims of that activity in one particular system explains the traditional use. The use of only one bioassay gives a very incomplete picture of the effect of the extract on the whole system involved. A symptom may be due to a number of disease states and, consequently, a variety of mechanisms may serve as targets for bioassays. In a similar way, it is very unusual for there to be only one target for a particular disease so a variety of test systems must be employed. Examples are given of batteries of test systems used to test plants and other materials with a reputation of being useful in wound-healing, diabetes, cancer and to treat cognitive decline associated with old age. In addition, consideration must be given to factors such as absorption into the body and metabolism of any substances present, either to decrease or increase the effect of the 'actives'.

Bioactive extracts fromSenecio samnitumHuet

The antimicrobial and cytotoxic activities of extracts from Senecio samnitum Huet are reported. Extracts from S. samnitum were able to inhibit the in vitro proliferation of four human tumor cell lines. The dichloromethane extract demonstrated effective cytotoxic activity with IC50 of 22.89 microg mL(-1) on the Caco-2 cell line and the EtOAc extract had IC50 value of 11.91 microg mL(-1) against the COR-L23 cell line. The n-hexane extract displayed the best antibacterial activity against Gram positive bacteria, particularly Staphylococcus aureus. The antifungal activity of all extracts was also seen, particularly against the dermatophytes Trichophyton tonsurans and Microsporum gypseum for the methanol and n-hexane extracts.

In vitrocytotoxicity activity on several cancer cell lines of acridone alkaloids andN-phenylethyl-benzamide derivatives fromSwinglea glutinosa(Bl.) Merr

The methanol extract from the stems and fruits of Swinglea glutinosa (Rutaceae) afforded 11 known acridone alkaloids and three N-phenylethyl-benzamide derivatives, glycocitrine-IV, 1,3,5-trihydroxy-4-methoxy-10-methyl-2,8-bis(3-methylbut-2-enyl)acridin-9(10H)-one, 1,3,5- trihydroxy-2,8-bis(3-methylbut-2-enyl)-10-methyl-9-acridone, citbrasine, citrusinine-II, citrusinine-I, 5-dihydroxyacronycine, pyranofoline, 3,4-dihydro-3,5,8-trihydroxy-6-methoxy-2,2,7-trimethyl-2H-pyrano[2,3-a]acridin-12(7H)-one, 2,3-dihydro-4,9-dihydroxy-2-(2-hydroxy-propan-2-yl)-11-methoxy-10-methylfuro[3,2-b]acridin-5(10H)-one, bis-5-hydroxyacronycine, N-(2-{4-[(3,7-dimethylocta-2,6-dien-1-yl)oxy]phenyl}ethyl)benzamide, N-(2-{4-[(3,7-dimethyl-4-acethyl-octa-2,6-dien-1-yl)oxy]phenyl}ethyl)benzamide, and severine acetate. All compounds isolated were examined for their activity against three cancer cell lines: human lung carcinoma (COR-L23), human breast adenocarcinoma (MCF7), human melanoma (C32), and normal human fetal lung cell line, MRC-5. The acridones tested exhibited weak cytotoxicity but the amides showed moderate nonselective cytotoxic activity.

mTOR and cancer therapy

Proteins regulating the mammalian target of rapamycin (mTOR), as well as some of the targets of the mTOR kinase, are overexpressed or mutated in cancer. Rapamycin, the naturally occurring inhibitor of mTOR, along with a number of recently developed rapamycin analogs (rapalogs) consisting of synthetically derived compounds containing minor chemical modifications to the parent structure, inhibit the growth of cell lines derived from multiple tumor types in vitro, and tumor models in vivo. Results from clinical trials indicate that the rapalogs may be useful for the treatment of subsets of certain types of cancer. The sporadic responses from the initial clinical trials, based on the hypothesis of general translation inhibition of cancer cells are now beginning to be understood owing to a more complete understanding of the dynamics of mTOR regulation and the function of mTOR in the tumor microenvironment. This review will summarize the preclinical and clinical data and recent discoveries of the function of mTOR in cancer and growth regulation.

alpha-Amylase inhibitory activity of some Malaysian plants used to treat diabetes; with particular reference to Phyllanthus amarus

Extracts of six selected Malaysian plants with a reputation of usefulness in treating diabetes were examined for alpha-amylase inhibition using an in vitro model. Inhibitory activity studied by two different protocols (with and without pre-incubation) showed that Phyllanthus amarus hexane extract had alpha-amylase inhibitory properties. Hexane and dichloromethane extracts of Anacardium occidentale, Lagerstroemia speciosa, Averrhoa bilimbiPithecellobium jiringa and Parkia speciosa were not active when tested without pre-incubation. Extraction and fractionation of Phyllanthus amarus hexane extract led to the isolation of dotriacontanyl docosanoate, triacontanol and a mixture of oleanolic acid and ursolic acid. Dotriacontanyl docosanoate and the mixture of oleanolic acid and ursolic acid are reported from this plant species for the first time. All compounds were tested in the alpha-amylase inhibition assay and the results revealed that the oleanolic acid and ursolic acid (2:1) mixture was a potent alpha-amylase inhibitor with IC(50)=2.01 microg/ml (4.41 microM) and that it contributes significantly to the alpha-amylase inhibition activity of the extract. Three pure pentacyclic triterpenoids, oleanolic acid, ursolic acid and lupeol were shown to inhibit alpha-amylase.

Predicted mechanisms of resistance to mTOR inhibitors

The serine/threonine kinase, mTOR (mammalian Target of Rapamycin) has become a focus for cancer drug development. Rapamycins are highly specific inhibitors of mTOR and potently suppress tumour cell growth by retarding cells in G1 phase or potentially inducing apoptosis. Currently, both rapamycin and several analogues are being evaluated as anticancer agents in clinical trials. Results indicate that many human cancers have intrinsic resistance and tumours initially sensitive to rapamycins become refractory, demonstrating acquired resistance. Here, we consider mechanisms of resistance to inhibitors of mTOR.

Hydroperoxysterols from the Brazilian Brown Seaweeds Dictyopteris justii and Spatoglossum schroederi (Dictyotales): A Defensive Strategy against Herbivory

Extracts of the Brazilian brown seaweeds Dictyopteris justii and Spatoglossum schroederi showed the presence of a cytotoxic mixture of 24R- and 24S-epimers of 24-hydroperoxy-24-vinylcholesterol (1). The derivation of 1 from fucosterol is proposed. Laboratory experiments assessed the anti-herbivory properties against the crab, Pachygrapsus transversus, of the crude extract and the epimers of 1 found in D. justii. The crude extract did not inhibit feeding, but the mixture of 1 epimers had a significant inhibitory effect. We propose that these unusual sterol compounds cannot be easily converted to assimilable compounds by this crustacean, thus acting as a defensive strategy for the seaweed against herbivory.

Fibroblast growth stimulation by extracts and compounds of Onosma argentatum roots

The roots of Onosma argentatum are used traditionally in Turkey for wound healing and burns. The n-hexane-dichloromethane extract of the roots, and four shikonin derivatives (deoxyshikonin, acetyl shikonin, 3-hydroxy-isovaleryl shikonin and 5,8-O-dimethyl acetyl shikonin) isolated from the n-hexane-dichloromethane extract were investigated for their ability to stimulate the growth of human amnion fibroblasts. A range of concentrations was studied and the extract found to stimulate the growth of human amnion fibroblasts in vitro at 0.1 microg/mL whilst 5,8-O-dimethyl acetyl shikonin had the same effect at 0.05-5 microg/mL, although cytotoxicity was observed at 50 microg/mL for all samples. The extract and all the other isolated compounds showed cytotoxicity at 10 microg/mL with the extract and 3-hydroxy-isovaleryl shikonin showing cytotoxicity at 5 microg/mL. It is suggested that any wound healing effect of the roots of Onosma argentatum might be partly due to an additive effect of the shikonin derivatives present.

Anti-inflammatory activities of the methanol extracts and an isolated furanoditerpene constituent of Sphenocentrum jollyanum Pierre (Menispermaceae)

Sphenocentrum jollyanum crude extracts and an isolated constituent were evaluated for anti-inflammatory activity using the carrageenan-induced hind paw oedema of healthy adult albino rats and utilizing the oral route of administration. The fruit methanol extract (79.58% inhibition at 200 mg kg(-1)) gave a higher anti-inflammatory activity than the root extract (53.75% inhibition at 200 mg ml(-1)). Further purification of the most active fruit methanol extract (MFE) led to the isolation of three furanoditerpenes identified as columbin, isocolumbin, fibleucin (uv, ir, nmr and ms) as well as a flavonoid-rich fraction (FDE). Both columbin (67.08% inhibition at 20 mg kg(-1), p<0.05) and FDE (76.25% inhibition at 200 mg kg(-1); p<0.05) gave significant anti-inflammatory activities in comparable range with reference acetylsalicylic acid (72.5% inhibition at 100 mg kg(-1)). The results provide some justification for the folkloric uses of Sphenocentrum jollyanum in the treatment of inflammatory-based diseases across the West African sub-region.

Antimicrobial, resistance-modifying effects, antioxidant and free radical scavenging activities ofMezoneuron benthamianum Baill.,Securinega virosa Roxb. &Wlld. andMicroglossa pyrifolia Lam

Mezoneuron benthamianum, Securinega virosa and Microglossa pyrifolia are used in folk medicine in Ghana for the treatment of dermal infections and wounds. Petroleum spirit, chloroform and ethanol extracts of the plants were tested for antimicrobial activity against a battery of organisms using the agar well diffusion technique and a serial dilution microassay. The resistance modifying activities of these extracts on standard antibiotics against Staphylococcus aureus possessing efflux mechanisms of resistance have also been assessed. A 4-fold potentiation of the activity of norfloxacin was observed for ethanol and chloroform extracts of M. benthamianum and S. virosa, respectively, whilst the petroleum spirit extract resulted in a 2-fold potentiation with minimum inhibitory concentration (MIC) values in the range 8-16 microg/mL. Ethanol extracts of all three species, the petroleum spirit extract of M. benthamianum and the chloroform extracts of M. benthamianum and S. virosa, showed interesting antimicrobial activities. Antioxidant and free radical scavenging activities using DPPH spectrophotometric and TBA lipid peroxidation assays were also conducted. Of the five extracts that showed antioxidant activities, the petroleum spirit and chloroform extracts of M. benthamianum rated most highly by displaying strong free radical scavenging activity with IC50 values of 15.33 and 19.72 microg/mL, respectively. Lipid peroxidation inhibition provided by the same two extracts also produced the lowest IC50 values for all the extracts tested, of 23.15 and 30.36 microg/mL. These findings therefore give some support to the ethnopharmacological use of the plants in the treatment of various skin diseases and wounds, as well as demonstrating the potential of some of the plants as sources of compounds possessing the ability to modulate bacterial multidrug resistance.

In-vitro antiproliferative effects on human tumour cell lines of extracts and jacaranone from Senecio leucanthemifolius Poiret

We have studied the cytotoxic activity of extracts and jacaranone from Senecio leucanthemifolius Poiret. Extracts from S. leucanthemifolius were able to inhibit the in-vitro proliferation of a series of human tumour cell lines. The dichloromethane extract demonstrated effective cytotoxic activity with an IC50 of 20.1 microg mL(-1) on the large cell carcinoma cell line COR-L23. The ethyl acetate extract showed an IC50 value of 5.0 microg mL(-1) and the butanol extract an IC50 value of 6.4 microg mL(-1) on the same cell line. A major active constituent of the dichloromethane extract was shown to be jacaranone, which was demonstrated to have a very strong activity against all of the tumour cell lines with IC50 values between 2.86 and 3.85 microg mL(-1), although it did not account for all the activity observed. Constituents of S. leucanthemifolius extracts were identified by GC/MS analysis and NMR.

In vitro tests and ethnopharmacological investigations: wound healing as an example

In vitro tests are now widely employed in ethnopharmacological research because of ethical reasons and their usefulness in bioactive-guided fractionation and determination of active compounds. For many disease conditions, a variety of in vitro tests can now be employed as the biochemical mechanisms underlying disease and healing processes are understood. Approaches to the in vitro investigations of wound healing processes are exemplified by studies on extracts of Buddleja species and three Ghanaian species Spathodea campanulata, Commelina diffusa and Secamone afzelii. Most studies have been carried out on Buddleja officinalis or Buddleja globosa. The extracts have been shown to have anti-inflammatory and antioxidant properties due to flavonoids, triterpenoids, diterpenoids and caffeic acid derivatives. There appears to a slight effect on proliferation of fibroblasts at lower concentrations, but this was not significant, and higher concentrations appeared to be cytotoxic. Novel findings are the ability of Buddleja globosa leaf extracts to induce differentiation in keratinocytes and to alter the profile of proteins produced by cultured fibroblasts. Extracts also had some effect on lattice contraction. The three Ghanaian species examined show a mixture of antimicrobial and antioxidant activities. The evolution over recent years of tests for wound healing, from in vivo tests to cell-based systems and chemical reactions and on to investigations into effects on secondary messengers and protein expression, is described.

Evaluation of the antioxidant and free radical scavenging properties ofSecamone afzelii Rhoem

The antioxidant activity of a methanol extract of Secamone afzelii stems was tested using the DPPH assay and the active compound was identified as alpha-tocopherol. HPLC determination showed that 0.12% w/w alpha-tocopherol was present in the plant. The total extract also showed effective free radical scavenging activity in the assay for non-enzymatic lipid peroxidation in liposomes with an IC50 value of 90 microg/mL, with alpha-tocopherol isolated from the plant having an IC50 of 15 microg/mL in the same system, thus demonstrating the presence of other antioxidants.

Structure-activity relationship for antiinflammatory effect of luteolin and its derived glycosides

Luteolin and its derived glycosides such as a cynaroside, cesioside, isoorientin and stereolensin have been isolated and identified from different kinds of plant species. A (13)C NMR spectroscopic analysis of stereolensin has been done for the first time. These structurally related flavonoids were examined in vitro for their abilities to inhibit enzymes for the synthesis of thromboxane B(2) and leukotriene B(4) as well as hydrogen peroxide scavenging activity. Luteolin exhibited a high inhibitory activity against both thromboxane and leukotriene synthesis. In particular, a remarkable inhibitory effect was observed against leukotriene enzyme activity. The glycosides, cynaroside and cesioside, possessed a moderate inhibition activity against both enzyme synthesis pathways, while isoorientin and stereolensin exhibited selectively good activity against thromboxane synthesis. All the flavonoids showed excellent scavenging activity for the hydrogen peroxide at all the concentrations tested. The results demonstrated that the reactivities of luteolin and its related glycosides against arachidonic acid synthesis and hydrogen peroxide scavenging are dependent on their molecular structures. The presence of ortho-dihydroxy groups at the B ring and OH substitution pattern at C-5 position of the A ring could significantly contribute to the antiinflammatory and antioxidant activities of flavonoids.

Screening of Korean herbal medicines used to improve cognitive function for anti-cholinesterase activity

Methanolic extracts of seven herbs (Acorus calamus, Acorus gramineus, Bupleurm facaltum, Dioscorea batatas, Epimedium koreanum, Poria cocos and Zizyphi jujuba) used in traditional Korean medicine for improvement of memory and cognition in old age were tested for cholinesterase inhibitory properties using the Ellman colorimetric method. Significant inhibition of the enzyme at 200 microg/ml was observed for extracts from A. calamus and E. koreanum. The possible bases for the reputation of these and the other herbs tested are discussed in the light of previous investigations into their chemistry and biological activity.

Antioxidant and cytotoxic activities ofRetama raetam subsp.Gussonei

The aim of this study was to evaluate the in vitro antioxidant and cytotoxic activities of the methanol extracts of Retama raetam subsp. gussonei leaves and seeds. The antioxidant activity of the extracts was assessed by means of two different tests: (1) bleaching of the stable 2,2-diphenyl-1-picrylhydrazil (DPPH) radical; and (2) lipid peroxidation of liposomes which were prepared from bovine brain extract. In both tests used leaves extract showed a significant antioxidant effect. The extract of leaves also demonstrated a good cytotoxic activity against COR-L23 (large cell carcinoma) cell line.

Integrating pharmacology and in vivo cancer models in preclinical and clinical drug development

Historically, cancer drug development has been a roller coaster. Numerous agents have shown exciting activity in preclinical models and yet have had minimal activity clinically. These disappointments have led to reasonable scepticism about the true value of both syngeneic and xenograft rodent tumour models in accurately identifying agents that will have important clinical utility. Whereas the development of newer techniques, including transgenic mouse models of cancer, offers the potential to develop more predictive models, the role of such mice in cancer drug development is not yet validated. To advance in our understanding of predictive model systems it may be wise to analyse both the successes and the failures of conventional models in order to understand some of their limitations and perhaps to avoid making the same mistakes in the future. Here we review the value and limitations of xenograft models, and the role of integrating preclinical pharmacology in developing new treatments for solid tumours of childhood.

Antioxidant and antimicrobial activities of Onosma argentatum and Rubia peregrina

The n-hexane-dichloromethane (1:1) extract of the roots of Onosma argentatum and the methanol extract (partitioned between water and chloroform, ethyl acetate and n-butanol, respectively), of the underground parts (roots and rhizomes) of Rubia peregrina were tested in vitro for their antioxidant and antimicrobial activities. The highest antioxidant activity (98%) was observed at 0.1% concentration for the roots of O. argentatum. It was 96% at 0.25% concentration on the ethyl acetate fraction of R. peregrina. O. argentatum extract was effective on Staphylococcus aureus, Bacillus subtilis and Escherichia coli. The ethyl acetate and chloroform fractions of R. peregrina were effective on S. aureus and E. coli, respectively. These two species did not have any antifungal activity.

mTOR as a Target for Cancer Therapy

The target of rapamycin, mTOR, acts as a sensor for mitogenic stimuli, such as insulin-like growth factors and cellular nutritional status, regulating cellular growth and division. As many tumors are driven by autocrine or paracrine growth through the type-I insulin-like growth factor receptor, mTOR is potentially an attractive target for molecular-targeted treatment. Further, a rationale for anticipating tumor-selective activity based on transforming events frequently identified in malignant disease is becoming established.

Activities of extract and constituents of Banisteriopsis caapi relevant to parkinsonism

Dopamine deficiency is characteristic of Parkinson's disease (PD) and treatments aim at elevating levels by administration of its precursor L-dihydroxyphenylalanine (L-DOPA), or inhibiting monoamine oxidases (MAOs), thus preventing its breakdown. Reports of improvements in PD patients treated with Banisteriopsis caapi extracts stimulated investigation of B. caapi stem extract and its two ingredients, harmine and harmaline for these activities. Tests for MAO inhibition using liver homogenate showed that extract and harmaline showed a concentration-dependent inhibition of MAO A (IC(50) 1.24 microg/ml and IC(50) 4.54 nM, respectively) but had little effect on MAO B activity. The extract at 2.5 mg/ml caused a highly significant increase in release of [3H]dopamine from rat striatal slices, as did 200 microM harmine and 6 microM harmaline. In both these experiments, the amount of harmine present could not account for the total activity of the extract. The ability of harmine and harmaline to stimulate dopamine release is a novel finding. These results give some basis to the reputed usefulness of B. caapi stem extract in the treatment of PD.

An evaluation of the activity related to inflammation of four plants used in Thailand to treat arthritis

The leaves of Acanthus ebracteatus, stembark of Oroxylum indicum and the stems of Cryptolepis buchanani and Derris scandens are used as traditional remedies in Thailand for arthritis. Aqueous and alcoholic extracts were tested using three different in vitro systems for effects relevant to anti-inflammatory activity. The aqueous extracts of O. indicum and D. scandens significantly reduced myeloperoxide release. Eicosanoid production was reduced only by the aqueous extracts of A. ebracteatus and D. scandens. D. scandens extract showed potent inhibitory activity against generation of leukotriene B(4) and also displayed antioxidant activity. In the rat hind paw edema test, D. scandens extract showed significant activity when given intraperitoneally but did not produce a significant reduction when given orally. The results therefore supported to some extent the traditional use of D. scandens for arthritic conditions and provided slight indication of activity which could explain the use of O. indicum and A. ebracteatus. No relevant activity was demonstrated in any of the tests for C. buchanani extracts.

The activity against leukocyte eicosanoid generation of essential oil and polar fractions of Adesmia boronioides Hook.f

The polar fractions (methanol and aqueous extract) and essential oil of Adesmia boronioides aerial parts were tested in vitro at concentrations of 15 and 50 microg/mL, for their effects on the COX and 5-LOX pathways of eicosanoid generation (TXB2, PGE2 and LTB4) in stimulated rat peritoneal leukocytes. Potent inhibition of LTB4 generation was displayed by the methanol extract and the essential oil, whereas the aqueous extract was essentially inactive. The methanol extract also caused potent inhibition of TXB2 generation but the essential oil and the aqueous extract were much less active. The effects on PGE2 production were much less striking, implying that the main effect is on thromboxane synthetase rather than on COX. Although the essential oil caused LDH release in leukocytes treated concurrently with ionophore, suggesting substantial toxicity to the cells, this extract did not affect cell viability according to the MTT test when incubated with the cells in the absence of ionophore. The two other extracts did not affect cell viability at the concentrations tested. It is concluded that Adesmia boronioides contains substance(s) that preferentially inhibit the 5-lipoxygenase activity of arachidonic acid metabolism and suggest that this may contribute to the antiinflammatory actions of extracts of this plant.