Xanthine scaffold: scope and potential in drug development

Medicinal plants have been the basis for discovery of various important marketed drugs. Xanthine is one such lead molecule. Xanthines in various forms (caffeine, theophylline, theobromine, etc) are abode in tea, coffee, cocoa, chocolate etc. giving them popular recognition. These compounds are best known for their diverse pharmaceutical applications as cyclic nucleotide phosphodiesterase inhibition, antagonization of adenosine receptor, anti-inflammatory, anti-microbial, anti-oxidant and anti-tumor activities. These properties incentivize to use xanthine as scaffold to develop new derivatives. Chemical synthesis contributes greater diversity in xanthine based derivatisation. With highlighting the existing challenges in chemical synthesis, the present review focuses the probable solution to fill existing lacuna. The review summarizes the available knowledge of xanthine based drugs development along with exploring new xanthine led chemical synthesis path for bringing diversification in xanthine based research. The main objective of this review is to explore the immense potential of xanthine as scaffold in drug development.

Pentoxifylline, propentofylline and pentifylline for acute ischaemic stroke

BACKGROUND

Methylxanthine derivatives are vasodilators. They also inhibit platelet aggregation and thromboxane A2 synthesis, decrease the release of free radicals and may be neuroprotective. NOTE: This review covers an area where no active research is taking place. It will be updated if relevant information becomes available, e.g. on completion of an appropriate study.

OBJECTIVES

To assess the effect of intravenous or oral methylxanthines (pentoxifylline, propentofylline, or pentifylline) in patients with acute ischaemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group trials register (last searched November 2003). For the first version, we also searched EMBASE (1980 to 1999), MEDLINE (1966 to 1999), Science Citation Index (1981 to 1999) and the Ottawa Stroke Trials Registry. We also contacted the manufacturers of methylxanthines and the principal investigators of the identified trials.

SELECTION CRITERIA

Randomised trials comparing pentoxifylline, propentofylline or pentifylline with placebo or control in patients with definite or presumed acute ischaemic stroke. Trials were included if treatment was started within one week of stroke onset.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied the inclusion criteria. Trial quality was assessed.

MAIN RESULTS

Five trials were included. Four trials tested pentoxifylline in 763 people, and one tested propentofylline in 30 people. No trials of pentifylline were found. The odds of early death (within four weeks) was non-significantly reduced in patients given a methylxanthine drug as compared with those given placebo (odds ratio (OR) 0.64, 95% confidence interval (CI) 0.41 to 1.02). This non-significant trend to less deaths was due mainly to one pentoxifylline trial that found a highly significant reduction in early deaths. Two trials reported early death or disability and found a non-significant reduction (OR 0.49, 95% CI 0.20 to 1.20). There was no significant difference in late death (beyond four weeks), as reported in the propentofylline trial involving 30 patients, although the confidence interval was wide (OR 0.70, 95% CI 0.13 to 3.68). Data for neurological impairment and disability were not in a form suitable for analysis. Data on quality of life, stroke recurrence, thromboembolism and bleeding were not reported.

REVIEWERS' CONCLUSIONS

There is not enough evidence to assess adequately the effectiveness and safety of methylxanthines after acute ischaemic stroke.

Pentoxifylline, propentofylline and pentifylline for acute ischaemic stroke

BACKGROUND

Methylxanthine derivatives are vasodilators. They also inhibit platelet aggregation and thromboxane A2 synthesis, decrease the release of free radicals and may be neuroprotective.

OBJECTIVES

The objective of this review was to assess the effect of intravenous or oral methylxanthines (pentoxifylline, propentofylline, or pentifylline) in patients with acute ischaemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group trials register, Medline (from 1965), Embase (from 1981), ISI (from 1981) and the Ottawa stroke trials registry. We contacted drug companies.

SELECTION CRITERIA

Randomised trials comparing pentoxifylline, propentofylline or pentifylline with placebo or control in patients with definite or presumed acute ischaemic stroke. Trials were included if treatment was started within one week of stroke onset.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied the inclusion criteria. Trial quality was assessed.

MAIN RESULTS

Five trials were included. Four trials tested pentoxifylline in 763 people, and one tested propentofylline in 30 people. No trials of pentifylline were found. Early death (within four weeks) occurred in 34 of 408 patients given a methylxanthine drug compared with 49 of 385 given placebo (odds ratio 0.64, 95% confidence interval 0.41 to 1.02). This non-significant trend to less deaths was due mainly to one pentoxifylline trial that found a highly significant reduction in early deaths. Two trials reported early death or disability and found a non-significant reduction (odds ratio 0.49, 95% confidence interval 0.20 to 1.20). Late death (beyond four weeks) was reported in the propentofylline trial involving 30 patients, with no difference between treatment and placebo (odds ratio 0.70, 95% confidence interval 0.13 to 3.68). Data for neurological impairment and disability were not in a form suitable for analysis. Data on quality of life, stroke recurrence, thromboembolism and bleeding were not reported.

REVIEWER'S CONCLUSIONS

There is not enough evidence to assess the effectiveness and safety of methylxanthines after acute ischaemic stroke.

Prostacyclin and analogues for acute ischaemic stroke

BACKGROUND

Prostacyclin is an agent with a number of effects on platelets, blood vessels and nerve cells which might improve outcome after acute ischaemic stroke.

OBJECTIVES

The objective of this review was to assess the effect of prostacyclin or analogues on survival in people with acute ischaemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group trials register (last searched: March 1999), Medline (from 1965), Embase (from 1980) and ISI (from 1981). We contacted drug companies.

SELECTION CRITERIA

Randomised trials comparing prostacyclin or analogues with placebo or control. Trials where people were entered within one week of stroke onset were included.

DATA COLLECTION AND ANALYSIS

Trial quality was assessed.

MAIN RESULTS

Five trials involving 191 people were included. Six early deaths (within four weeks) occurred with prostacyclin and nine with placebo (odds ratio of 0.63, 95% confidence interval 0.22 to 1.85). One trial of 32 patients reported late deaths (by 10 to 18 months) in 50% of patients in each group.

REVIEWER'S CONCLUSIONS

Too few patients have been studied in randomised trials to allow conclusions to be drawn about the effect of prostacyclin treatment on survival of people with acute stroke.

Increased ATP production during long-term brain ischemia in rats in the presence of propentofylline

Forty adult rats were subjected to stepwise two- and four-brain vessel occlusion and propentofylline 25 mg/day per kilogram body weight was intraperitoneally administered for 1 week or 3 weeks. Adenosine 5'-triphosphate, creatine phosphate, adenosine 5'-diphosphate and adenosine were determined in rat parietotemporal cortex by high-pressure liquid chromatography; lactate and pyruvate were measured spectrophotometrically. Stepwise and permanent long-term brain vessel occlusion gradually reduced the concentration of energy-rich phosphates and induced a marked increase in the concentration of adenosine, a parameter of ischemia. Three weeks of propentofylline treatment resulted in a significant increase in cerebral adenosine 5'-triphosphate concentration from 2.16 +/- 0.15 [(-)-propentofylline] to 2.70 +/- 0.24 nmol/mg wet weight during four-vessel occlusion (+25%). This was associated with an enhancement of the adenosine 5'-triphosphate/adenosine 5'-diphosphate ratio (+33%), mainly because of the significant reduction in adenosine 5'-diphosphate concentration. Propentofylline did not prevent the increase in lactate concentration during permanent brain vessel occlusion, but significantly reduced the tissue concentration of adenosine. In summary, the results demonstrate that continuous propentofylline administration over 3 weeks induced a striking increase in rat cortical adenosine 5'-triphosphate concentration during long-term brain vessel occlusion. Thus, propentofylline may have possible neuroprotective effects and could be used in the treatment of patients with chronic cerebrovascular disorders.

Effect of propentofylline on regional cerebral glucose metabolism in acute ischemic stroke

In a randomized double-blind placebo-controlled study in 30 patients with acute ischemic stroke, the effect of the adenosine uptake blocker propentofylline on regional brain glucose metabolism (rCMRglu) was investigated using repeated positron emission tomography (PET) with 2-[18F]fluoro-2-deoxy-D-glucose (FDG). Treatment was initiated within 48 h after onset of symptoms. The clinical course was followed for 3 months. In the propentofylline group, after 14 days rCMRglu was increased in the infarct by 37.3% and was practically unchanged in other brain regions, whereas in the control group glucose metabolism had decreased in all regions (1.4-13.4%). These differences were significant between the two groups [Analysis of variance (ANOVA) p = 0.005]. Although there was a trend toward greater clinical improvement in the propentofylline-treated patients, this did not reach statistical significance. The results correspond to experimental data showing that propentofylline improves energy metabolism in cerebral ischemia. A clinical trial is needed to determine whether this new therapeutic principle can be successfully used in acute human stroke.

Effect of propentofylline on the biochemical lesion of the rat brain in aluminium-induced neurotoxicity

Acute and chronic administration of Al-gluconate (12.7% Al) at the concentration of 1 mg/kg produces edema in the rat brain, as reflected by the increase in water and Na+ content. The permeability for Evans blue is also increased, which indicates the opening of the blood-brain barrier. Higher concentrations of the Al-gluconate (10 mg/kg) change, in acute experiments, the pattern of energy metabolites in the rat brain toward a profile observed in a deep hypoxia. Chronic administration of a low concentration of Al-gluconate (1 mg/kg) increases the local utilization of glucose in 20 of 39 rat brain structures examined. This increase was particularly evident in the structures of the limbic system. Xanthine derivative propentofylline reverses the edema formation in acute and chronic experiments. Hypoxia-like changes in energy metabolism are also reversed by propentofylline. In preliminary experiments propentofylline also suppressed the increased utilization of glucose observed after administration of Al-gluconate. These results suggest that (i) the Al-gluconate model in rats can be used to study Al-neurotoxicity at a very low level of Al, and (ii) the xanthine derivative propentofylline can eventually be used to abolish the Al-neurotoxicity.