Lyndon Sheppard

1,2-Dimethyl-3-hydroxypyrid-4-one, an orally active chelator for treatment of iron overload.

Subcutaneous desferrioxamine, though effective in preventing or reducing iron overload in transfusion-dependent refractory anaemia, is expensive and inconvenient. One potentially cheaper and orally active alternative is 1,2-dimethyl-3-hydroxypyrid-4-one (L1). This drug has been tested in three multiply transfused patients with myelodysplasia. Gelatin capsules were taken at doses ranging from 0.5 g to 3.0 g. Urinary iron excretion increased substantially in all three patients and in the one tested was equal to that achieved with comparable doses of subcutaneous desferrioxamine. The amounts of iron excreted were related to the dose of L1 administered and the iron load of the patients. The urinary excretion of zinc, magnesium, and calcium did not increase, and the drug was well tolerated.

Effective chelation of iron in beta thalassaemia with the oral chelator 1,2-dimethyl-3-hydroxypyrid-4-one.

The main iron chelator used for transfusional iron overload is desferrioxamine, which is expensive, has toxic side effects, and has to be given subcutaneously. An orally active iron chelator is therefore required. The effects of oral 1,2-dimethyl-3-hydroxypyrid-4-one on urinary iron excretion were studied in eight patients who had received multiple transfusions: four had myelodysplasia and four beta thalassaemia major. Different daily doses of the drug up to 100 mg/kg/day, alone or in combination with ascorbic acid, were used. In three patients with thalassaemia the effect of the drug was compared with that of subcutaneous desferrioxamine at the same daily dose. In all eight patients a single dose of oral 1,2-dimethyl-3-hydroxypyrid-4-one resulted in substantial urinary iron excretion, mainly in the first 12 hours. Urinary iron excretion increased with the dose and with the degree of iron loading of the patient. Giving two or three divided doses over 24 hours resulted in higher urinary iron excretion than a single dose of the same amount over the same time. In most patients coadministration of oral ascorbic acid further increased urinary iron excretion. 1,2-Dimethyl-3-hydroxypyrid-4-one caused similar iron excretion to that achieved with subcutaneous desferrioxamine at a comparable dose. In some cases the iron excretion was sufficiently high (maximum 99 mg/day) to suggest that a negative iron balance could be easily achieved with these protocols in patients receiving regular transfusions. No evidence of toxicity was observed on thorough clinical examination or haematological and biochemical testing in any of the patients. None of the patients had any symptoms that could be ascribed to the drug. These results suggest that the oral chelator 1,2-dimethyl-3-hydroxypyrid-4-one is as effective as subcutaneous desferrioxamine in increasing urinary iron excretion in patients loaded with iron. Its cheap synthesis, oral activity, and lack of obvious toxicity at effective doses suggest that it should be developed quickly and thoroughly tested for the management of transfusional iron overload.

Pharmacokinetic studies in humans with the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one.

Pharmacokinetic studies have been carried out with the oral iron chelator 1,2‐dimethyl‐3‐hydroxypyrid‐4‐one (L1). HPLC analysis of serum of a normal volunteer and seven transfusional iron loaded patients who ingested a 3 gm dose of L1 revealed that L1 was most probably absorbed from the stomach and was transferred to the blood with a half‐life of 0.7 to 32 minutes. L1 reached maximum concentration in the serum 12 to 120 minutes after administration with 85% to 90% elimination within the first 5 to 6 hours, with a half‐life of 47 to 134 minutes. L1 and its glucuronide metabolite were identified in serum and urine but not in feces. In most cases hydrolysis of 24‐hour urine samples with use of β‐glucuronidase resulted in almost complete recovery of the administered dose. Urinary iron excretion was proportional to the iron load but not to the serum or urine concentration of L1. The therapeutic efficiency of L1 can therefore be improved by repeated administration of 2 to 3 gm doses at least every 6 hours.

Long-term trial with the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) I. IRON CHELATION AND METABOLIC STUDIES

Summary A long‐term clinical trial of 1‐15 months has been carried out with the oral iron chelator 1.2‐dimethyl‐3‐hydroxypyrid‐4‐one (L1) in 13 transfusion‐dependent ironloaded patients. Urinary iron excretion was greatest in patients with thalassaemia major and was related to the number of previous transfusions but not to the serum ferritin level. Substantial increases of urinary iron were observed in all the patients when the frequency of the daily dose was doubled and in response to 2 ± 3 g L1 daily 11 of 12 patients tested excreted > 2 5 mg iron daily, the mean daily intake of iron from transfusion. Serum ferritin levels have fluctuated but overall have remained unchanged. Pharmacological studies in five patients have indicated rapid absorption probably from the stomach and variable plasma half life of 77 ± 35 min (SD). Glucuronation was identified as a major route of L1 metabolism. Short‐term intensive chelation studies using repeated administration of L1 resulted in further increases of urinary iron excretion by comparison to a single dose. In one case 325 mg of iron were excreted in the urine following the administration of 16g (5 ± 2g + 2 ± 3g) within 24 h. Iron excretion studies were carried out in six transfusional iron‐loaded patients who were maintained on a low iron diet before and during chelation. No significant increases of faecal iron excretion were observed with L1 using daily doses of up to 3.3 g and 4 ± 2 g. The high level of compliance during treatment with L1 and the levels of urine iron excretion that can be achieved increase the prospects for oral chelation in transfusional iron‐loaded patients.

Simple synthesis of the potent iron chelators 1-alkyl-3-hydroxy-2-methylpyrid-4-ones

The current treatment of transfusional iron overload using desferrioxamine is limited to a small number of patients worlwide because this chelator is highly expensive and thus unobtainable by most countries that need it and also orally inactive [ 1,2]. One of the most promising experimental groups of chelators which could replace desferrioxamine are the 1alkyl-3-hydroxy-2-methylpyrid4one derivatives which are orally and parenterally effective in the removal of iron in vivo from rabbits [3] and mice [4] and also from transferrin [5] and ferritin [7] in vitro. Although several methods for the preparation of these chelators have already been reported [7-91 including one shown in Scheme 1 [9], the need for an inexpensive synthesis and the knowledge that these hydroxypyridones and malt01 are generally highly

Synthetic methods and in vitro iron binding studies of the novel 1-alkyl-2-ethyl-3-hydroxypyrid-4-one iron chelators

Abstract Three novel iron chelators namely the 1-methyl-, 1-ethyl- and 1-propyl-2-ethyl-3-hydroxypyrid-4-ones were prepared in high yields from ethyl maltol and the related alkylamine in a one step reaction. These chelators formed 3 chelator:1 iron stable, coloured, neutral complexes at physiological pH and mobilise iron from transferrin, ferritin and haemosiderin. The rate of iron mobilisation from these proteins was of the order transferrin > haemosiderin > ferritin. The cheap synthesis and strong iron binding properties of the 1-alkyl-2-ethyl-3-hydroxypyrid-4-ones at physiological pH requires the need for further investigation and development of these compounds and their homologues, for the treatment of iron overload and other diseases of iron imbalance and toxicity.

Differential toxicity of α-keto hydroxypyridine iron chelators and desferrioxamine to human haemopoietic precursors in vitro

Abstract:  Compliance with iron chelation therapy improves life expectancy in transfusion‐dependent haematological disorders. However, failure of compliance with parenteral desferrioxamine (DF) therapy and the expense incurred makes this drug unavailable for most patients in the developing world. We have been evaluating the orally active iron chelator 1,2‐dimethyl‐3‐hydroxypyrid‐4‐one (L1) in both preclinical and clinical trials. Five patients have developed reversible agranulocytosis during treatment with this agent. We have now studied the effects of L1, other α‐ketohydroxypyridines and DF on bone marrow myeloid progenitors using the CFU‐GM system. The results show that L1 is less toxic than DF to normal bone marrow myeloid progenitors (ID50:130 μmol/l versus 7.9 μmol/l). The L1 ID50 is within the previously reported range of peak plasma values (80–450 μmol/l). When saturating concentrations of iron were added to the cultures, the mean toxicity of all the chelators was significantly decreased over the range of doses tested, e.g. L1 ID50, 567 μmol/l; DF ID50, > 1000 μmol/l. The toxicity of L1 in vitro was similar for marrows from 3 normal donors and for the recovery marrow from a patient with thalassaemia major who had experienced agranulocytosis. Further studies are required to elucidate the mechanisms of L1 ‐induced agranulocytosis.