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)

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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.

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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'.