Metabolic fate of 1-hexylcarbamoyl-5-fluorouracil in rats

Versatile use of Carmofur: A comprehensive review of its chemistry and pharmacology

Carmofur, 1-hexylcarbamoyl-5-fluorouracil (HCFU) is an antineoplastic drug, which has been in clinics in Japan since 1981 for the treatment of colorectal cancer. Subsequently, it was also introduced in China, Korea, and Finland. Besides colorectal cancer, it has also shown antitumor activity in other cancers such as breast, head and neck, pancreatic, gastrointestinal, and solid brain tumors. A prodrug of 5-fluorouracil (5-FU), carmofur has shown better gastrointestinal stability and superior antiproliferative activity compared to its active counterpart 5-FU. Recently, carmofur has gained attention as an acid ceramidase inhibitor and as a potential lead compound against several noncancerous diseases such as coronavirus disease 2019, Krabbe disease, acute lung injury, Parkinson's disease, dementia, childhood ependymoma etc. Carmofur has also been reported to have antifungal, and antimicrobial properties. Nevertheless, no comprehensive review is available on this drug. Herein, we summarized the chemistry, pharmacokinetics, and pharmacology of carmofur based on the literature published between January 1976 and March 2022 as identified from PubMed and Google Scholar search engines.

A New Use for an Old Drug: Carmofur Attenuates Lipopolysaccharide (LPS)-Induced Acute Lung Injury via Inhibition of FAAH and NAAA Activities

Acute lung injury (ALI), characterized by a severe inflammatory process, is a complex syndrome that can lead to multisystem organ failure. Fatty acid amide hydrolase (FAAH) and N-acylethanolamine acid amidase (NAAA) are two potential therapeutic targets for inflammation-related diseases. Herein, we identified carmofur, a 5-fluorouracil-releasing drug and clinically used as a chemotherapeutic agent, as a dual FAAH and NAAA inhibitor. In Raw264.7 macrophages, carmofur effectively reduced the mRNA expression of pro-inflammatory factors, including IL-1β, IL-6, iNOS, and TNF-α, and down-regulated signaling proteins of the nuclear transcription factor κB (NF-κB) pathway. Furthermore, carmofur significantly ameliorated the inflammatory responses and promoted resolution of pulmonary injury in lipopolysaccharide (LPS)-induced ALI mice. The pharmacological effects of carmofur were partially blocked by peroxisome proliferator-activated receptor-α (PPARα) antagonist MK886 and cannabinoid receptor 2 (CB2) antagonist SR144528, indicating that carmofur attenuated LPS-induced ALI in a PPARα- and CB2-dependent mechanism. Our study suggested that carmofur might be a novel therapeutic agent for ALI, and drug repurposing may provide us effective therapeutic strategies for ALI.

Discovery of highly potent acid ceramidase inhibitors with in vitro tumor chemosensitizing activity

The expression of acid ceramidase (AC) - a cysteine amidase that hydrolyses the proapoptotic lipid ceramide - is abnormally high in several human tumors, which is suggestive of a role in chemoresistance. Available AC inhibitors lack, however, the potency and drug-likeness necessary to test this idea. Here we show that the antineoplastic drug carmofur, which is used in the clinic to treat colorectal cancers, is a potent AC inhibitor and that this property is essential to its anti-proliferative effects. Modifications in the chemical scaffold of carmofur yield new AC inhibitors that act synergistically with standard antitumoral drugs to prevent cancer cell proliferation. These findings identify AC as an unexpected target for carmofur, and suggest that this molecule can be used as starting point for the design of novel chemosensitizing agents.

A preliminary study for clinical pharmacokinetics of oral fluorine anticancer medicines using the commercial MRI system 19F-MRS

These preliminary studies of dynamic natural abundance 19F-magnetic resonance spectroscopy (19F-MRS) on 5-FU based medicines were performed in the human liver using commercial 1.5 T MRI equipment. A single tuned, custom-made circular shape surface coil with a diameter of 15 cm operating at 60 MHz was used for the 19F-MRS study. Localized proton shimming with a whole body coil was performed with adequate volume to include the observing area of the surface coil, and the line width of the water signal was less than 40 Hz. Very different spectroscopic appearance patterns of 5-FU were observed. We examined whether the pharmacokinetics in the liver of orally administered 1-hexylcarbamoyl-5-fluorouracil (HCFU) differ from those of orally administered 5'-deoxy-5-fluorouridine (5'-DFUR). This preliminary study suggested the 19F-MRS technique could be a useful method of evaluating in vivo the metabolism of 5-FU based medicines.

Postoperative chemotherapy for colorectal cancer by combining 5-fluorouracil infusion and 1-hexylcarbamoyl-5-fluorouracil administration after curative resection

BACKGROUND

Colorectal cancer is one of the major malignant diseases and, recently, its incidence appears to be increasing. Surgical resectability is an important prognostic determinant; however, recurrent tumors are commonly noted, even after apparently curative surgery. Because such metastatic disease cannot be cured, better adjuvant therapies are urgently called for.

METHODS

We studied the effect of postoperative chemotherapy using 5-fluorouracil (5-FU) infusions and 1-hexylcarbamoyl-5-fluorouracil (HCFU) oral administration for curatively resected Stage II to IV colorectal cancer. This study was prospectively randomized and controlled and 251 (93.3%) of 269 patients were determined to be candidates for statistical assessment. The inductive regimen for Group A included a total of 6 5-FU intravenous injections, 10 mg/kg, on postoperative days 0, 1, 2, 7, 8, and 9. For maintenance therapy, Group A also received oral HCFU, 300 mg daily for 52 weeks beginning 2 weeks after surgery. The regimen for Group B included only 5-FU injections of Group A.

RESULTS

There were no differences in the prognostic factors or doses of 5-FU between Groups A and B. In addition, no difference was observed in the toxicity rate between the two groups. Group A, with 5-FU infusions plus oral HCFU administration, produced a reduction in the recurrence rate and a prolongation of the survival time for patients with rectal cancer. In a retrospective analysis, this protocol was also effective for patients with Stage III to IV, wall invasion-positive, and lymph node metastasis-positive colorectal cancers.

CONCLUSIONS

This study suggests that the combination of 5-FU infusions and the continuous oral administration of HCFU is a reasonable therapeutic approach for patients with surgically resected colorectal cancer and a high risk of recurrence.

Low dose 1-hexylcarbamoyl-5-fluorouracil (HCFU) recommended for cirrhotic patients with hepatocellular carcinoma

The metabolism of 1-hexylcarbamoyl-5-fluorouracil (HCFU), a drug prescribed for treating patients with hepatocellular carcinoma (HCC), was studied in relation to liver function, with the objective of clarifying the occurrence of any adverse side-effects on the central nervous system. Twenty-five HCC patients were administered 3.4 mg/kg HCFU once orally, after which the blood levels of HCFU and its derivatives (5-FU, CPEFU, CPRFU, HHCFU, OHCFU and F-beta-alanine) were serially measured using high performance liquid chromatography. The area under the concentration curve (AUC) of HCFU in the group of ICG R15 greater than or equal to 30% (group 2) was 5.35 +/- 1.73 h.micrograms/ml, a value which was significantly higher than the 2.60 +/- 1.19 h.micrograms/ml recorded for the group of ICG R15 less than 30% (group 1) (P less than 0.001). The AUC of HCFU had a significant positive correlation with the value of ICG R15 (P = 0.002) or the serum total bilirubin (P = 0.0005). The AUC of 5-FU showed no difference between the two groups. The AUC of CPRFU in group 2 was 0.16 +/- 0.25 h.micrograms/ml, a value significantly lower than the 0.48 +/- 0.39 h.micrograms/ml in group 1 (P = 0.023). There was no correlation between the AUC of other derivatives and the markers of liver function. These data suggest that, in patients with advanced cirrhosis, the accumulation of HCFU is related to the occurrence of side-effects from the administered drug, ingested over a long-term period. Therefore, when HCFU is given to cirrhotic patients with both HCC and 30% or more ICG R15, a careful monitoring for side-effects is required.

Subacute neurotoxicity of 5-fluorouracil and its derivative, carmofur, in cats

The subacute neurotoxicity of 5-fluorouracil (FU) and its derivative, carmofur (HCFU), in cats was morphologically examined; both these drugs were orally administered once daily for a maximum of three months. The dosis of FU and HCFU was 2 mg/kg/day and 10 mg/kg/day, respectively. Both FU and HCFU induced two sorts of changes in the brain, i.e., vacuolation and softening-like change. The former was distributed in the white matter of the cerebrum and cerebellum and in areas of the gray matter such as the tectum and tegmentum of the brain stem, while the latter was distributed exclusively in the gray matter of the tectum and tegmentum of the brain stem. The tectum, especially the inferior colliculus, was most frequently affected by both types of change. Ultrastructurally, vacuolation was found to be due to lamellar splitting or separation between the axon and innermost myelin layer. These findings were compared with those in dogs and as the etiopathogenesis vacuolation due to direct toxic effect of FU or its metabolites to myelin and softening-like change due to local circulatory disturbance caused by vacuolation were proposed.

1-Hexylcarbamoyl-5-fluorouracil is more cytostatic than 5-fluorouracil against human tumors in vitro

The sensitivity of HeLa cells and 15 human tumors, including eight gastric cancers, five colorectal cancers and two lung cancers to 1-hexylcarbamoyl-5-fluorouracil (HCFU) was compared with that to 5-fluorouracil (5-FU) in vitro. HeLa cells were doubly sensitive to HCFU, as compared to 5-FU. After the HeLa cells had been treated with 5-FU or HCFU at 77 microM for 1-5 h, the intracellular levels of 5-FU and HCFU were determined, using gas chromatographic-mass spectrometric methods. The level of HCFU plus 5-FU in the HCFU-treated cells was twice as high as the level of 5-FU in the 5-FU-treated cells. The sensitivity to HCFU in 15 tumor tissues varied with the tissue; however, all tissues tested were more sensitive to HCFU than to 5-FU, assessed using the succinate dehydrogenase inhibition test. These results suggest that the hexylcarbamoyl structure facilitates the rapid uptake of HCFU through the cell membrane. HCFU may prove to be more effective for treating each individual patient with a malignant lesion.

Subacute leucoencephalopathy induced by carmofur, a 5-fluorouracil derivative

Three cases of leucoencephalopathy induced by carmofur (1-hexylcarbamoyl-5-fluorouracil), an antineoplastic derivative of 5-fluorouracil are reported and the literature is reviewed. Initial symptoms were unsteady gait and dementia developing several weeks or months after carmofur had been started. Symptoms increased gradually even after stopping the drug. Severe encephalopathy with confusion, delirium or coma appeared frequently. Symptoms were usually reversible but death occasionally occurred. The EEG showed marked slowing. Computed tomography of the brains of severely intoxicated patients showed marked hypodensity of the entire cerebral white matter. Carmofur must be discontinued immediately if any psychomotor symptoms develop.

Intestinal absorption of 5-fluorouracil and its alkylcarbamoyl derivatives in the rat small intestine

The intestinal absorption of 5-fluorouracil (1) and its alkylcarbamoyl derivatives possessing various lipophilic pro-moieties including the butylcarbamoyl, hexylcarbamoyl, octylcarbamoyl, and nonylcarbamoyl groups, was investigated in the rat using both in situ and in vitro techniques. All compounds showed greater apparent partition coefficients and lipophilic indices (k') (by HPLC) and lower solubilities in water than 1. Although enhancement of uptake by the everted intestine in vitro was observed when the alkylcarbamoyl chain length was increased, the appearance of the prodrugs in the mesenteric vein in the in situ intestinal loop (complete venous collection) was decreased and sustained. The conversion of alkylcarbamoyl derivatives to 1 was noted in the absorption process.

Neuropathologic study on chronic neurotoxicity of 5-fluorouracil and its masked compounds in dogs

5-Fluorouracil (FU) and its masked compounds tegafur (FT) and carmofur (HCFU) were administered orally to Beagle dogs daily for 6 months, and their chronic neurotoxic effects were examined morphologically. In ten dogs that survived the 6-month treatment large vacuoles produced by splitting of the intraperiod line of myelin were observed in the fornix in the wall of the third ventricle. In severely affected dogs large vacuoles developed in the medial preoptic area, medial portion of the internal capsule, the area around the subthalamic nucleus and the mammillo-thalamic tract. Axons of myelinated fibers affected by vacuolation were generally well maintained, and destruction of myelin was not detected. Though proliferation of glia cells or abnormality of oligodendroglia was not detected, a lipid deposit covered by a single layer membrane was observed in the cell bodies and processes of astrocytes. No abnormality was detected by electron microscopy in the cerebrum, inferior colliculus, cerebellum, or pons. Of eight dogs that died during the treatment period, large vacuoles were observed in the fornix in the wall of the third ventricle of four dogs treated for more than 1 month, and large vacuoles were present in the inferior colliculus in two dogs of the FT group in the above four dogs. In the HCFU group, the interruption of treatment for 6 months resulted in alleviation or disappearance of the vacuolar lesions. The above findings suggest that the neurotoxicity of FU and its masked compounds FT and HCFU in long-term treatment produces changes morphologically identical with one another in respect to the site of their manifestation and nature of lesion, that their common degraded product alpha-fluoro-beta-alanine (FBAL) plays a crucial role in their neurotoxic actions, and that vacuolar lesions, to which myelin was more vulnerable than neurons, can develop where the toxic substance readily deposits and accumulates.

Quantitative determination of 1-hexylcarbamoyl-5-fluorouracil and its metabolites in man

A high-performance liquid chromatographic (HPLC) method for the quantitative determination of 1-hexylcarbamoyl-5-fluorouracil (HCFU) and its metabolites using mu Bondapak C18 and mu Porasil has been developed. Two mobile phases containing PIC-B7 (consisting of acetic acid and 1-heptanesulphonic acid) were used for the separation, and good separations were obtained. With methanol-water (56:44) as the mobile phase, the separation of HCFU and its three metabolites was achieved within 4 min. With methanol-water (32:68) a new metabolite, 1-omega-carboxymethylcarbamoyl-5-fluorouracil, was revealed in human plasma. The recovery of each substance was 80% or greater and the sensitivity was at the nanograms per millilitre level. The coefficient of variation was less than 3.6% for each component.

Metabolism of 1-hexylcarbamoyl-5-fluorouracil (HCFU), a new antitumour agent, in rats, rabbits and dogs

1. 1-Hexylcarbamoyl-5-fluoro[6-14C]uracil (14C-HCFU) administered orally to rats, rabbits and dogs at a dose of 20 mg/kg was well absorbed and rapidly excreted via the kidney. 2. HCFU was extensively biotransformed, and its six metabolites including two new metabolites were detected in plasma and urine of all three species. Two new metabolites were identified by spectral analysis as 1-(5-hydroxyhexylcarbamoyl)5-fluorouracil and 1-(5-oxohexylcarbamoyl)-5-fluorouracil. 3. The metabolic pathways of HCFU in the three species involved oxidations and scission of the side-chain with successive degradation of the fluorouracil (FU) released. 4. The two main routes of oxidations of the side chain were omega-oxidation and omega-1-oxidation. Rats metabolized HCFU preferentially by the former reaction, while in rabbits and dogs the latter reaction predominated.

Metabolic fate of 1-hexylcarbamoyl-5-fluorouracil after oral administration in mice

1. The metabolic fate of a new antitumour agent, 1-hexylcarbamoyl-5-fluoro[6-14C]uracil (14C-HCFU) was compared with that of 5-fluoro[6-14C]uracil (14C-FU) after oral administration to mice. 2. 1-(5-Hydroxyhexylcarbamoyl)-5-fluorouracil (5-hydroxy-HCFU) and 1-(5-oxohexylcarbamoyl)-5-fluorouracil (5-keto-HCFU) were found as major intermediate metabolites of 14C-HCFU and were produced by omega-1 oxidation. 3. FU was detected in plasma 180 min after oral administration of 14C-HCFU, whereas unchanged FU disappeared within 60 min after 14C-FU. 4. 14C-HCFU and resulting FU were retained in tissues for a long period after oral administration, while administered 14C-FU was rapidly degraded.