Site-directed cation ordering in chabazite-type AlxGa1-xPO4-34 frameworks revealed by NMR crystallography.

We report the first synthesis of the mixed-metal chabazite-type AlxGa1-xPO4-34(mim) solid solution, containing 1-methylimidazolium, mim, as structure directing agent (SDA), from the parent mixed-metal oxide solid solution, γ-(AlxGa1-x)2O3. This hitherto unreported family of materials exhibits complex disorder, arising from the possible distributions of cations over available sites, the orientation of the SDA and the presence of variable amounts of water, which provides a prototype for understanding structural subtleties in nanoporous materials. In the as-made forms of the phosphate frameworks, there are three crystallographically distinct metal sites: two tetrahedral MO4 and one octahedral MO4F2 (M = Al, Ga). A combination of solid-state NMR spectroscopy and periodic DFT calculations reveals that the octahedral site is preferentially occupied by Al and the tetrahedral sites by Ga, leading to a non-random distribution of cations within the framework. Upon calcination to the AlxGa1-xPO4-34 framework, all metal sites are tetrahedral and crystallographically equivalent in the average R3̄ symmetry. The cation distribution was explored by 31P solid-state NMR spectroscopy, and it is shown that the non-random distribution demonstrated to exist in the as-made materials would be expected to give remarkably similar patterns of peak intensities to a random distribution owing to the change in average symmetry in the calcined materials.

Expectations and experiences of practising veterinarians throughout an 8-week mindfulness-based stress reduction programme.

AIMS: To explore practising veterinarians' expectations of an 8-week mindfulness training programme, their perceived barriers to participating in the programme, their experiences of the programme and the extent to which they continued to engage in mindfulness practices following training. METHODS: Participants were 10 companion animal veterinarians practising in Auckland, New Zealand. All took part in an 8-week mindfulness-based training programme. A longitudinal qualitative design was used: data were collected by structured interviews prior to the programme, upon completion of the programme and 3 months after completion. Data were analysed using thematic analysis to identify recurring themes, or patterns, within the data. RESULTS: Before commencing the programme, participants generally thought mindfulness training would provide some benefits for wellbeing but were otherwise not clear on what to expect. The main concerns about taking part were time constraints and apprehensions about potentially having to share personal information, and consequently how they might be perceived by other participants. On completion of the training programme, the opportunity to share experiences within the group with the support of a trained facilitator was reported as the most valuable aspect of the programme, rather than the mindfulness practices themselves. At the 3-month follow-up, participants reported they had learnt some useful techniques for managing stressful thoughts and situations, but despite the perceived benefits, few were still practicing mindfulness techniques. CONCLUSIONS AND CLINICAL RELEVANCE: Training in mindfulness practices may have some value for helping practicing veterinarians manage their wellbeing, but it is not a complete solution in itself. Participants reported that the greatest benefits came from facilitated peer support.

Membranous nephropathy associated with viral infection.

BACKGROUND: Membranous nephropathy (MN) can be associated with hepatitis infection and less commonly with human immunodeficiency virus (HIV) infection. The significance of anti-phospholipase A2 receptor (PLA2R) and anti-thrombospondin type 1 domain-containing 7A (THSD7A) antibodies in this setting is unclear. METHODS: We describe the clinical, histopathological and outcome data of 19 patients with MN and hepatitis B virus (HBV), hepatitis C virus (HCV) or HIV infection identified through our renal biopsy database and the association with anti-PLA2R antibodies and anti-THSD7A antibodies. RESULTS: The cohort consisted of 19 patients, 8 male and 11 female, with a median age of 42 years (range 23-74). HBV infection was found in six cases, HCV in four and HIV in nine (two HIV patients had HBV co-infection and one HCV co-infection). PLA2R staining on biopsy was positive in 10/19 patients: 4 with HBV-MN, 3 with HCV-MN and 3 with HIV-MN and circulating anti-PLA2R antibodies were detected in 7/10 cases. THSD7A staining on biopsy was positive in three PLA2R-negative cases, one with HBV-MN and two with HIV-MN. Mean proteinuria was higher in the PLA2R-positive group and the median urinary protein:creatinine ratio (uPCR) was 963 mg/mmol (range 22-2406) compared with the PLA2R-negative group [median uPCR 548 mg/mmol (range 65-1898); P = 0.18 Mann-Whitney]. Spontaneous remission occurred in 6/19 patients and after-treatment remission occurred in 7/11 patients. Renal function was preserved in all but two patients who required haemodialysis 2 and 11 years from diagnosis. CONCLUSIONS: We describe a cohort of patients with MN associated with viral infection, including rare cases of HIV-MN with PLA2R and THSD7A positivity. The mechanism of coincidental or viral-related MN needs to be investigated further.

The NF-κB subunit c-Rel regulates Bach2 tumour suppressor expression in B-cell lymphoma.

The REL gene, encoding the NF-κB subunit c-Rel, is frequently amplified in B-cell lymphoma and functions as a tumour-promoting transcription factor. Here we report the surprising result that c-rel-/- mice display significantly earlier lymphomagenesis in the c-Myc driven, Eµ-Myc model of B-cell lymphoma. c-Rel loss also led to earlier onset of disease in a separate TCL1-Tg-driven lymphoma model. Tumour reimplantation experiments indicated that this is an effect intrinsic to the Eµ-Myc lymphoma cells but, counterintuitively, c-rel-/- Eµ-Myc lymphoma cells were more sensitive to apoptotic stimuli. To learn more about why loss of c-Rel led to earlier onset of disease, microarray gene expression analysis was performed on B cells from 4-week-old, wild-type and c-rel-/- Eµ-Myc mice. Extensive changes in gene expression were not seen at this age, but among those transcripts significantly downregulated by the loss of c-Rel was the B-cell tumour suppressor BTB and CNC homology 2 (Bach2). Quantitative PCR and western blot analysis confirmed loss of Bach2 in c-Rel mutant Eµ-Myc tumours at both 4 weeks and the terminal stages of disease. Moreover, Bach2 expression was also downregulated in c-rel-/- TCL1-Tg mice and RelA Thr505Ala mutant Eµ-Myc mice. Analysis of wild-type Eµ-Myc mice demonstrated that the population expressing low levels of Bach2 exhibited the earlier onset of lymphoma seen in c-rel-/- mice. Confirming the relevance of these findings to human disease, analysis of chromatin immunoprecipitation sequencing data revealed that Bach2 is a c-Rel and NF-κB target gene in transformed human B cells, whereas treatment of Burkitt's lymphoma cells with inhibitors of the NF-κB/IκB kinase pathway or deletion of c-Rel or RelA resulted in loss of Bach2 expression. These data reveal a surprising tumour suppressor role for c-Rel in lymphoma development explained by regulation of Bach2 expression, underlining the context-dependent complexity of NF-κB signalling in cancer.

Central nervous system penetration and enhancement of temozolomide activity in childhood medulloblastoma models by poly(ADP-ribose) polymerase inhibitor AG-014699.

BACKGROUND: Temozolomide shows activity against medulloblastoma, the most common malignant paediatric brain tumour. Poly(ADP-ribose) polymerase (PARP) inhibitors enhance temozolomide activity in extracranial adult and paediatric human malignancies. METHODS: We assessed the effect of AG-014699, a clinically active PARP inhibitor, on temozolomide-induced growth inhibition in human medulloblastoma models. Pharmacokinetic, pharmacodynamic and toxicity assays were performed in tumour-bearing mice. RESULTS: Sensitivity to temozolomide in vitro was consistent with methylguanine methyltransferase (MGMT) and DNA mismatch repair (MMR) status; MGMT(+) MMR(+) D384Med cells (temozolomide GI(50)=220 µM), representative of most primary medulloblastomas, were sensitised fourfold by AG-014699; MGMT⁻ MMR(+) D425Med cells were hypersensitive (GI(50)=9 µM) and not sensitised by AG-014699, whereas MGMT(+) MMR⁻ temozolomide-resistant D283Med cells (GI50=807 µM) were sensitised 20-fold. In xenograft models, co-administration of AG-014699 produced an increase in temozolomide-induced tumour growth delay in D384Med xenografts. Consistent with the in vitro data, temozolomide caused complete tumour regressions of D425Med xenografts, whereas D283Med xenografts were relatively resistant. AG-014699 was not toxic, accumulated and reduced PARP activity ≥75% in xenograft and brain tissues. CONCLUSION: We show for the first time central nervous system penetration and inhibition of brain PARP activity by AG-014699. Taken together with our in vitro chemosensitisation and toxicity data, these findings support further evaluation of the clinical potential of AG-014699-temozolomide combinations in intra-cranial malignancies.

Effects of streamlining cervical cancer screening the Dutch way: consequences of changes in the Dutch KOPAC-based follow-up protocol and consensus-based limitation of equivocal cytology.

OBJECTIVE: To analyze the impact of the 1995 revision of the Dutch cervical screening program guidelines (e.g., the introduction of more stringent criteria for cytologic diagnosis of atypical squamous cells of undetermined significance [ASCUS]) on the negative side effects of screening in Region West. STUDY DESIGN: The data for this study were retrieved as two complementary datasets, both of which contained data on the invited screenees, including their cytology and histology follow-up. One dataset additionally included data on other smears. For invited screenees, we analyzed changes in cytoscores and histoscores between 1994, the last year before new screening guidelines were implemented, and 2003, the latest year for which follow-up to screening abnormalities was available in the retrieved data. Additionally, we analyzed changes in the total number of primary and repeat smears made. RESULTS: Between 1994 and 2003, the cytoscore for ASCUS decreased from 19.4% to 1.3% of screenee smears. The total number of smears taken decreased by 30%. The cervical intraepithelial neoplasia 3+ histoscore remained the same (OR = 0.97, p = 0.91). CONCLUSION: The reduction of equivocal ASCUS diagnoses resulted in a decrease of costly repeat smears, without measurably decreasing the effectiveness of the screening program.

Exploiting the Achilles heel of cancer: the therapeutic potential of poly(ADP-ribose) polymerase inhibitors in BRCA2-defective cancer.

Poly(ADP-ribose) polymerase-1 (PARP-1) facilitates DNA single-strand break-base excision repair to maintain genomic stability. Inhibition or loss of PARP activity leads to a recombinogenic phenotype characterized by increased sister chromatid exchange. Deficiency in homologous recombination (HR) owing to loss of BRCA1 or BRCA2 is associated with hereditary cancers of the breast, ovary, pancreas and prostate. We investigated the therapeutic potential of PARP inhibitors in HR and BRCA2-defective cells. We exposed cells defective in the HR component XRCC3 (irs1SF) and BRCA2 (V-C8) and their parental (AA8, V79) or deficiency corrected (CXR3, V-C8+B2) cells to the PARP inhibitors NU1025 and AG14361. Mice bearing BRCA2-deficient and BRCA2-proficient tumours were treated with AG14361. All HR-defective cells were hypersensitive to normally non-cytotoxic concentrations of PARP inhibitors. Cells lacking BRCA2 were 20 times more sensitive to PARP inhibitor-induced cytotoxicity. Three out of five BRCA2-defective xenografts responded to the potent PARP inhibitor, AG14361, and one tumour regressed completely, compared with non-responses in the BRCA2-proficient tumours treated with AG14361 or any mice treated with vehicle control. Untreated PARP-1(-/-) mouse embryo fibroblasts (MEFs) accumulated more DNA double-strand breaks than did PARP-1(+/+) MEFs. We believe the underlying cytotoxic mechanism is due to PARP inhibitor-mediated suppression of repair of DNA single-strand breaks, which are converted to DNA double-strand breaks at replication. These replication-associated double-strand breaks, which are normally repaired by HR, become cytotoxic in cells defective in HR. Using a DNA repair inhibitor alone to selectively kill a tumour represents an exciting new concept in cancer therapy.

Molecular targeting of retinoic acid metabolism in neuroblastoma: the role of the CYP26 inhibitor R116010 in vitro and in vivo.

Isomerisation to all-trans-retinoic acid (ATRA) is widely accepted as the key mechanism underlying the favourable clinical properties of 13-cis-retinoic acid (13cisRA). As intracellular metabolism of ATRA by CYP26 may result in clinical resistance to 13cisRA, an increase in efficacy may be achieved through modulation of this metabolic pathway. We have evaluated the effect of the CYP26 inhibitor R116010 on retinoid metabolism in neuroblastoma cell lines and a xenograft model. In neuroblastoma cells, which showed a high level of CYP26 induction in response to ATRA, R116010 selectively inhibited ATRA metabolism. In addition, siRNA-mediated knockdown of CYP26 selectively increased ATRA levels and the expression of retinoid-responsive marker genes was potentiated by R116010. Treatment of mice bearing SH-SY5Y xenografts with 13cisRA (100 mg kg(-1)) revealed substantial levels (16%) of intratumoral ATRA after 6 h, despite plasma ATRA levels representing only 1% total retinoids under these conditions. Co-administration of R116010 with 13cisRA in this mouse model resulted in significant increases in plasma ATRA and 13cisRA concentrations. Furthermore, R116010 induced significant decreases in levels of 4-oxo metabolites in hepatic tissue after co-administration with either ATRA or 13cisRA. These data suggest considerable potential for CYP26 inhibitors in the future treatment of neuroblastoma with 13cisRA.

Optimized quality of histologic images allows the use of neural network scanning in diagnosis of fungal infection of abnormal nails.

OBJECTIVE: The neural network scanning (NNS) system, formerly known as Papnet, is capable of selecting fungi in cervical smears. The objective of this study was to investigate whether the optimized quality of histologic images created using a combination of coagulant fixation and microwave histoprocessing allows the application of this computer-assisted microscopy in the diagnostic process. STUDY DESIGN: In a prospective study, 117 abnormal nails clinically suspect for fungal disease werefixed in a coagulant fixative, BoonFix, processed in a microwave histoprocessor to obtain optimal paraffin sections and stained with the periodic acid-Schiff (PAS) method. The stained paraffin sections were randomly numbered and screened by two independent pathologists for diagnosis of fungal hyphae and spores. The same sections were subsequently scanned by a neural network, and a maximum of 128 digital images produced by the system were screened and diagnosed by pathologists. Using light microscopy as the gold standard for diagnosis of fungi, the usefulness of NNS was then assessed. RESULTS: The fungi and spores were clearly demonstrated in the paraffin sections, and the NNS system detected and recorded them efficiently. The hyphae and spores could be identified in these pixilated images with relative ease. Of the 117 examined cases, 50 were positive and 47 negative by both methods. In the 20 remaining cases, NNS did not present images of fungi that were present in the histologic sections. In practice, this implies that only 67 out of 117 cases (57%) must be screened by light microscopy. NNS recorded not only fungi and spores in the 128 digital images but also artifacts, such as round, deeply PAS-positive granules of talcum powder, which by light microscopy might be mistaken for fungal spores. CONCLUSION: NNS proves applicable for the selection of spores and fungi if the histologic sections are of sufficiently high quality. As a result, the number of slides to be screened by light microscopy can be reduced substantially. In a throughput diagnostic laboratory handling a large number of such cases this technology can be highly valuable.

Pharmacological study of paclitaxel duration of infusion combined with GFR-based carboplatin in the treatment of ovarian cancer.

PURPOSE: To determine the effect on systemic pharmacology and clinical toxicity of dose and mode of administration of paclitaxel combined with carboplatin in the treatment of ovarian cancer. PATIENTS AND METHODS: A total of 18 patients were treated with a dose of carboplatin determined by GFR, to attain a target AUC of 6 or 7 mg/ml x min. The paclitaxel dose was 175 or 200 mg/m2 administered over approximately 1 or 3 h. The duration of infusion was randomized, crossing over to the alternative treatment for the second course. Blood samples were analysed for carboplatin, paclitaxel and for the excipients of the paclitaxel formulation, ethanol and Cremophor. RESULTS: Overall the three-weekly schedule of administration of the combination of carboplatin and paclitaxel was well tolerated. There were no clinical differences in the toxicities observed between courses where a 1-h infusion was used compared with those with a 3-h infusion. The target AUC of carboplatin was achieved (mean +/- SD 114 +/- 20% of target). Analysis of paclitaxel pharmacokinetics did not show a difference in the AUC or time above a pharmacological threshold for the two infusion durations. The peak concentration of paclitaxel obtained at the end of the infusion (9.1 vs 4.5 microg/ml), and the plasma ethanol concentration (40.0 vs 20.5 mg/dl) were higher following the shorter duration infusion. Peak concentrations of Cremophor were not different. CONCLUSION: The combination of paclitaxel at a dose of 175 mg/m2 and carboplatin at a target AUC of 6-7 mg/ml min can safely be administered every 3 weeks. Also, a 1-h infusion of paclitaxel has no acute clinical disadvantage over a 3-h infusion and these durations of administration are pharmacologically equivalent.

In vitro and in vivo properties of novel nucleoside transport inhibitors with improved pharmacological properties that potentiate antifolate activity.

The activity of antimetabolite inhibitors of de novo deoxyribonucleotide biosynthesis can be compromised by the salvage of extracellular preformed nucleosides and nucleobases. Dipyridamole (DP) is a nucleoside transport inhibitor that has been used clinically in an attempt to increase antimetabolite activity; however, DP binds tightly to the serum protein alpha1-acid glycoprotein (AGP) thereby rendering this therapeutic strategy largely ineffective. Four novel DP analogues (NU3076, NU3084, NU3108, and NU3121) have been developed with substitutions at the 2,6- and 4,8-positions of the pyrimidopyrimidine ring. The novel DP analogues inhibit thymidine (dThd) uptake into L1210 cells in vitro (NU3076 IC(50), 0.25 microM; NU3084 IC(50), 0.27 microM; NU3108 IC(50), 0.31 microM; NU3121 IC(50), 0.26 microM; and DP IC(50), 0.37 microM), but, unlike DP, their activity remains largely unaffected in the presence of 5 mg/ml AGP. The four DP analogues inhibit dThd and hypoxanthine rescue from Alimta (multitargeted antifolate)-induced growth inhibition in A549 and COR L23 human lung carcinoma cell lines in the presence of 2.5 mg/ml AGP, whereas the activity of DP is completely abolished. i.p. administration of 10 mg/kg NU3108, NU3121, and DP produced peak plasma concentrations of 4.4, 2.1, and 6.7 microM, respectively, and levels were sustained above 1 microM for approximately 45 min (DP) and 120 min (NU3108 and NU3121). [3H]thymidine incorporation into COR L23 xenografts grown in CD1 nude mice was reduced by 64% (NU3108), 44% (NU3121), and 65% (DP) 2 h after administration of the nucleoside transport inhibitors. In conclusion, two novel DP analogues (NU3108 and NU3121) have been identified that do not bind to AGP and that display superior pharmacokinetic profiles in comparison to DP and inhibit [3H]thymidine incorporation into human tumor xenografts in vivo.

Hypoxanthine transport in human tumour cell lines: relationship to the inhibition of hypoxanthine rescue by dipyridamole.

Hypoxanthine (HPX) uptake was investigated in four human tumour cell lines previously characterised as being sensitive (ds: A549 and MCF7) or insensitive (di: COR-L23 and T-47D) to dipyridamole (DP)-induced inhibition of HPX rescue from antipurine antifolate-induced growth inhibition. The aim of the study was to determine the mechanism underlying the differential sensitivity of HPX rescue to DP. The time-course of HPX uptake in the two ds cell lines was different in comparison to the two di cell lines. The initial rate of HPX uptake in the di cell lines was more rapid than in the ds cell lines such that at 60 sec the amount of HPX taken up by the former was 2-6 times higher than that taken up by the later. The K(t) and T(max) for HPX transport in di COR-L23 cells were 870 microM and 4.75 microM/10(6) cells/min and 1390 microM and 1.78 microM/10(6) cells/min in ds A549 cells. HPX transport was not sodium-dependent in these cells. Equilibrative nucleoside transporter 2 (ENT2)-mediated thymidine transport was also higher in di cells. DP inhibited HPX uptake into ds cell lines by > or =48% and by < or =20% in the di cell lines. Competition studies with HPX and thymidine transport via ENT2 indicated an overlap between nucleoside and nucleobase transport transporters in the breast cancer cell lines (MCF7 and T-47D). These studies showed that more rapid and extensive HPX uptake, as well as reduced sensitivity to DP inhibition, is associated with the inability of DP to prevent HPX rescue from antipurine antifolate-induced growth inhibition in certain human tumour cell lines.

Pharmacokinetics of carboplatin administered in combination with the bradykinin agonist Cereport (RMP-7) for the treatment of brain tumours.

INTRODUCTION: Cereport (RMP-7) is a novel bradykinin agonist which is being developed as a modulator of the blood-brain barrier (BBB). In order to investigate the pharmacokinetics of carboplatin in combination with Cereport, we performed pharmacological studies in conjunction with early clinical trials. METHODS: Pharmacokinetic samples were collected from eight patients in a phase I study (Cereport 100-300 ng/ kg) and ten patients in a phase II study (Cereport 300 ng/kg). Pharmacokinetic parameters for carboplatin were compared with respect to the dose of Cereport and with historical controls. RESULTS: Cereport combined with carboplatin was well-tolerated, with mild haematological toxicities consistent with the target area under the concentration time curve (AUC) of 7 mg/ml x min. Although the clearance of carboplatin was within the range reported for this drug alone, the addition of Cereport resulted in a higher than expected carboplatin AUC. This effect was related to the dose of Cereport in the phase I study (AUC values 104-133% of target, Spearman rank correlation coefficient = 0.71, P < 0.001). The higher than expected AUC value was confirmed in the phase II study (AUC values 106-189% of target). CONCLUSIONS: Co-administration of Cereport with carboplatin may result in a greater than predicted AUC. The mechanism of this possible interaction remains to be determined, although this did not result in any increased toxicity. Thus, the clinical potential of this combination in the treatment of brain tumours warrants further investigation.

High-dose cyclosporin with etoposide--toxicity and pharmacokinetic interaction in children with solid tumours.

The tolerability, anti-tumour activity and pharmacokinetic interaction of high-dose intravenous cyclosporin combined with intravenous etoposide was evaluated in children. Eighteen patients with recurrent or refractory tumours, all of whom had previously received etoposide, were treated with a combination of high-dose cyclosporin and etoposide. In 13, cyclosporin was given as a continuous infusion (15 mg kg(-1) per 24 h for 60 h) and in five a short 3-hour infusion of 30 mg kg(-1) day(-1) on three consecutive days. Pharmacokinetic profiles of etoposide were determined with and without cyclosporin. Cyclosporin levels ranged from 1359 to 4835 ng ml(-1) and cyclosporin increased the median area under the concentration time for etoposide curve from 7.2 to 12.5 mg ml(-1) min. The major toxicity was acute with varying forms of hypersensitivity reactions. In four cases this was severe. Hyperbilirubinaemia was present in 25 of 32 courses but was of short duration. In 14 courses, creatinine and/or urea was elevated, but was also transient. Significant hypertension was seen in six courses. Four of 17 patients evaluable for response obtained a partial response and one showed stable disease. It is concluded that in children given the combination of high-dose cyclosporin and etoposide, the etoposide dose should be halved in order to achieve an area under the drug concentration-time curve similar to that with etoposide alone. A continuous infusion schedule of cyclosporin is better tolerated during the period of administration but is associated with similar hepatic and renal dysfunction to a short schedule. The 24% response rate in children who had previously received etoposide suggests that this may be an effective method of enhancing drug sensitivity and further phase II evaluation is justified.

A clinical and pharmacokinetic study of the combination of carboplatin and paclitaxel for epithelial ovarian cancer.

The aim of this phase I study was to determine the maximum tolerated dose of a 3-h infusion of paclitaxel, combined with carboplatin at a fixed AUC of 7 mg ml-1 min every 4 weeks for up to six cycles and to evaluate any possible pharmacokinetic interaction. Twelve chemonaive patients with ovarian cancer were treated with paclitaxel followed by a 30-min infusion of carboplatin. Paclitaxel dose was escalated from 150 mg m-2 to 225 mg m-2 in cohorts of three patients. Carboplatin dose was based on renal function. Pharmacokinetic studies were performed in nine patients (at least two at each dose level). A total of 66 courses were evaluable for assessment. Grade 3 or 4 neutropenia was seen in 70% of the courses, however hospitalization was not required. Grade 3 or 4 thrombocytopenia occurred in 24% of the courses. Alopecia, myalgia and peripheral neuropathy were common but rarely severe. The pharmacokinetics of paclitaxel was non-linear and did not appear to be influenced by co-administration of carboplatin. The AUC of carboplatin was 7.0 +/- 1.4 mg ml-1 min, indicating that there was no pharmacokinetic interaction. The combination of carboplatin and paclitaxel may be administered as first-line treatment for advanced ovarian cancer. Although myelosuppression is the dose-limiting toxicity of the component drugs, the severity of thrombocytopenia was less than anticipated. The results of this study, with only a small number of patients, need to be confirmed in future investigations.

RMP-7 : Potential as an Adjuvant to the Drug Treatment of Brain Tumours.

The chemotherapy of tumours located in the brain is far from satisfactory, with very poor response rates even with tumour types known to be sensitive when they occur extracranially. The brain is protected by the blood-brain barrier, which consists of tight capillary endothelial cell junctions. As a result, many drugs cannot penetrate into the tumour to achieve cytotoxic concentrations. Although the vasculature of some tumours may allow greater uptake of drugs than into normal brain tissue, the poor uptake of drugs into CNS tumours is still seen as a barrier to effective chemotherapy.The permeability of the blood-brain barrier may be affected by osmotic agents or mediators of inflammation. Notable among the latter is bradykinin, which induces a transient, specific increase in permeability that is more pronounced in tumour than in normal brain.The nonapeptide RMP-7 [H-Arg-Pro-Hyp-Gly-Thi-Ser-Pro-Tyr(Me)-ψ(CH2NH)-Arg-OH] was developed as a bradykinin analogue. This peptide displays greater stability in plasma than the parent compound. Preclinical investigations in animal tumour models showed that RMP-7 increased the uptake of a number of markers in RG2 gliomas implanted into rat brain. More importantly, RMP-7 also increased carboplatin uptake in the tumour and brain surrounding the tumour, without affecting uptake into normal brain. Animals treated with RMP-7 and carboplatin showed significantly prolonged survival compared with controls. The doses used in these animal studies were quite high, administered via the intracarotid artery.In studies in humans, lower doses of RMP-7 were used and the drug was usually administered intravenously. Adverse effects were mild and transient, mostly related to vasodilation. Phase I and II studies in patients with brain tumours confirmed the increased uptake of radiochemical markers into tumours that had been seen in animal models. Recently published data suggest that the combination of carboplatin with RMP-7 has activity in malignant brain tumours, both in terms of neurological improvement and overall survival, and was well tolerated. In particular, the neurotoxicity reported with other methods of increasing blood-brain barrier permeability has not been reported. Using a reliable method of individualised carboplatin administration, based on renal function, any effect of RMP-7 on the elimination of carboplatin may be determined.Overall, the use of RMP-7 as an adjunct to the treatment of tumours within the CNS may potentially be effective in terms of increasing tumour drug concentrations.

A phase I clinical study of the antipurine antifolate lometrexol (DDATHF) given with oral folic acid.

Lometrexol is an antifolate which inhibits glycinamide ribonucleotide formyltransferase (GARFT), an enzyme essential for de novo purine synthesis. Extensive experimental and limited clinical data have shown that lometrexol has activity against tumours which are refractory to other drugs, notably methotrexate. However, the initial clinical development of lometrexol was curtailed because of severe and cumulative antiproliferative toxicities. Preclinical murine studies demonstrated that the toxicity of lometrexol can be prevented by low dose folic acid administration, i.e. for 7 days prior to and 7 days following a single bolus dose. This observation prompted a Phase I clinical study of lometrexol given with folic acid supplementation which has confirmed that the toxicity of lometrexol can be markedly reduced by folic acid supplementation. Thrombocytopenia and mucositis were the major toxicities. There was no clear relationship between clinical toxicity and the extent of plasma folate elevation. Associated studies demonstrated that lometrexol plasma pharmacokinetics were not altered by folic acid administration indicating that supplementation is unlikely to reduce toxicity by enhancing lometrexol plasma clearance. The work described in this report has identified for the first time a clinically acceptable schedule for the administration of a GARFT inhibitor. This information will facilitate the future evaluation of this class of compounds in cancer therapy.

Polymorphism of a CAG trinucleotide repeat within Sry correlates with B6.YDom sex reversal.

Breeding the Y chromosome from certain Mus musculus domesticus strains onto the inbred laboratory mouse strain, C57BL/6J (B6), results in hermaphroditic progeny. This strain-dependent sex reversal suggests that there may be significant allelic variation in the murine sex determining gene, Sry. We have analysed the Sry genes from several domesticus-type Y chromosomes and show that they encode smaller proteins than the molossinus-type alleles SryB6 and Sry129. We have also identified a polymorphic stretch of trinucleotide repeats that is unique to strains causing sex reversal and show that specific changes in the predicted polyglutamine amino acid sequence at this site are associated with different degrees of sex reversal.

Control of protein synthesis by amino acid supply. The effect of asparagine deprivation on the translation of messenger RNA in reticulocyte lysates.

The enzyme asparaginase, which hydrolyses asparagine to aspartic acid, inhibited cell-free protein synthesis by reticulocyte lysates. The inhibition was rapid and complete when sufficient enzyme was added but could be prevented or reversed by the addition of asparagine. The initial effect of asparaginase appears to be a block in polypeptide chain elongation due to asparagine deprivation, but there are some indications that prolonged incubation under these conditions may give rise to a secondary decrease in initiation of protein synthesis.