Abstract
The purpose of this study was to evaluate the prevalence of serum alanine transaminase (ALT) increases in cats treated with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU, lomustine). The medical records of 95 cats treated with CCNU were reviewed, 29 of which met study criteria (at least one treatment with CCNU as a single agent, and at least one pretreatment and one post-treatment complete biochemical profile). Cats that received concurrent prednisone or dexamethasone were included, but those that received concurrent hepatoprotective or hepatotoxic medications were excluded. Cats included in the study were diagnosed with hepatic carcinoma, mammary carcinoma, lymphoma, mast cell tumor, plasma cell tumor and gastrointestinal leiomyoma. CCNU was given as a single agent at 31–60 mg/m2, once every 4–8 weeks. Serum alanine transaminase (ALT) activity was measured after at least one dose of CCNU. Four cats (13.7%) had increased ALT activity above the reference interval before starting treatment. Two additional cats (6.8%) developed increased ALT activity above the reference interval 1 month after treatment with CCNU. One cat developed clinical signs potentially associated with hepatotoxicity, without a concurrent increase in ALT, 3 weeks following the final dose of CCNU. No association between dosing frequency, cumulative dose, initial starting dose or concurrent medications, and increases in ALT were found. Clinically significant hepatic injury is seemingly uncommon in cats treated with CCNU.
Introduction
An alkylating agent in the nitrosourea subclass, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU, lomustine), is rapidly and completely absorbed after oral administration. 1 It is highly lipid soluble and readily crosses the blood-brain barrier. 2 Metabolic transformation within the liver is responsible for its degradation in most species.1,3 Following biotransformation, CCNU metabolites are excreted by the kidneys, with minimal biliary excretion and gastrointestinal reabsorption. 1 However, specific metabolism studies in cats, to our knowledge, have not been completed.
In dogs and cats, CCNU has been shown to be an effective treatment for round cell tumors, including mast cell tumors, lymphoma, histiocytic sarcomas and, in some cases, primary brain tumors.4–6 Toxicities in dogs include severe hepatotoxicity, 1 , myelotoxicity, delayed thrombocytopenia and, rarely, renal toxicity, pulmonary fibrosis and pyrexia.5,7–9
Canine clinical hepatopathy is characterized by clinical signs of liver damage, including anorexia, vomiting and icterus. CCNU-induced liver injury or hepatotoxicity in dogs is suspected upon finding increases in alanine transaminase (ALT) and alkaline phosphatase (ALP) activities, mild hypoalbuminemia and hyperbilirubinemia days-to-weeks after drug administration. 5 Merely finding the increased enzyme activity cannot definitively confirm drug-related liver injury, especially as the pattern of enzyme activity is inconsistent. In some dogs, the hallmark of CCNU hepatotoxicity is a progressive rise in ALT activity, whereas in others, a dual increase in ALT and ALP activity is observed.5,10 Toxicity in dogs is apparently cumulative, dose-related, irreversible and fatal. 5 An inverse relationship between CCNU dose and the development of marked increase in ALT activity has been shown. Dogs receiving higher dosages (near 200 mg/m2/day based on a 10 kg dog) are more likely to experience a sudden increase in ALT activity. Lower CCNU dose exposure (10–40 mg/m2/day based on a 10 kg dog) may lead to a delayed onset of liver injury for up to 1 month after treatment.11–13 Scrutiny of many dogs treated with CCNU illustrates that absence of ALT activity after initial drug exposure does not guarantee there will be no late onset liver injury.5,11
In dogs, concurrent CCNU and corticosteroid administration heightens the risk for moderate increases in ALT activity, and, seemingly, younger dogs have a greater risk for severely increased ALT activity. 11 While the magnitude of ALT activity reflects the severity and mass of liver injury, sequential, persistent increases in ALT activity indicates a high likelihood of continuing membrane damage. However, release of ALT can reflect either reversible membrane expansion or leakage associated with lethal loss of membrane integrity. As no liver enzyme can predict hepatic functional reserve, liver function tests are useful in definitively recognizing important liver injury. 14
There is limited information available regarding the potential toxicity of CCNU in feline cancer patients. An initial study in a small number of cats (n = 13) revealed no evidence of gastrointestinal, renal or hepatic toxicity based on monitoring, physical examination and biochemical assessments. 15 The most common drug-induced toxicity was hematologic, associated with neutropenia and thrombocytopenia. 16 Rarely, pulmonary fibrosis has been encountered, but only after high cumulative CCNU dosages (552 mg/m2 over 12 months). 17 The purpose of this retrospective study was to more broadly investigate feline patients treated with CCNU for evidence of hepatocellular or other associated toxicities.
Materials and methods
The medical records of 95 cats treated with CCNU at VCA West Los Angeles Animal Hospital between 2001 and 2010 were reviewed. Potential cats were found through review of pharmacy and invoice logs, identifying those that were dispensed CCNU. Inclusion criteria were: at least one treatment with CCNU as a single agent; one pretreatment complete biochemical profile within 6 months of the first CCNU dose; and at least one complete biochemical profile after treatment with CCNU. The dose given and treatment interval were varied owing to differences in primary disease, response to treatment and treatment protocol. Cats with increased liver enzymes prior to treatment were included in the study, as long as diagnostic testing (ultrasound and fine needle aspirate, when indicated) determined that any primary liver disease was most likely attributable to neoplasia. One cat with increased liver enzymes did not have an abdominal ultrasound on presentation. The ALT and aspartate aminotransferase (AST) increases [Veterinary Cooperative Oncology Group Common Terminology Criteria for Adverse Events (VCOG-CTCAE) grade 3] were attributed to previously diagnosed hyperthyroidism and the cat was admitted to the study. Cats receiving concurrent prednisone or dexamethasone were allowed entry. No cats were concurrently receiving known hepatotoxic or hepatoprotective medications, such as non-steroidals or silymarin, respectively. One cat did receive diazepam for travel beginning half-way through the CCNU protocol. No increases in ALT, ALP, gamma-glutamyl transpeptidase (GGT), bilirubin or hypoalbuminemia were observed.
Data recorded from each case included: signalment; primary neoplastic disease and stage; concurrent diseases and medications; number of CCNU doses; cumulative CCNU dose (mg/m2 body surface area); and use of compounded drug. Chemistry values, which were taken at varied intervals throughout the course of each patient’s treatment, were recorded for each visit and recheck. Changes in ALT, ALP, AST, GGT, bilirubin and albumin concentrations were noted, and severity of the change quantified. The standard VCOG-CTCAE scheme was used.
Results
Twenty-nine of 95 records met the study criteria and were available for review, along with all diagnostic images (16 had no initial blood work; 44 had no blood work post-CCNU; six had incomplete medial records; none were excluded owing to concurrent hepatotoxic or heptoprotective medications). There were 15 castrated males, one intact male and 13 spayed females. Breeds included 20 domestic shorthairs, four domestic mediumhairs, two domestic longhairs and one Siamese, one Ocicat and one Abyssinian. Median weight was 3.7 kg (range 2.4–5.8 kg) with a median age of 13 years (range 1–17 years). Twenty-two cats had lymphoma and three cats had mast cell tumors. Tumors diagnosed in the remaining four cats were plasma cell tumor, hepatic carcinoma, mammary carcinoma and leiomyoma.
The initial median dose of CCNU was 44 mg/m2 (range 31–60 mg/m2). The mean total number of treatments was 5.7 (median 4; range 1–20), depending on response to treatment and owner compliance. The median cumulative dose was 204.7 mg/m2 (range 37–656 mg/m2). Four cats (11.7%) received compounded drug. Twenty-eight cats (96%) received concurrent corticosteroids (5–10 mg/cat/day); one (3.4%) did not. Sixteen cats (55.1%) received prednisone before treatment with CCNU. Six cats (20.6%) received at least a partial combination therapy with prednisone, l-asparaginase, cyclophosphamide, vincristine, and doxorubicin (CHOP protocol) prior to treatment with CCNU. Two cats (6.8%) received other chemotherapy protocols prior to treatment with CCNU (oral chlorambucil or injectable vinblastine). No cats received concurrent chemotherapy. Discontinuation of CCNU occurred because of progressive disease/failure of treatment or loss to follow-up.
Full chemistry panels were completed at diagnosis in 10 cats, within 1 month in nine cats, within 2 months in five cats, within 3 months in one cat and within 6 months in four cats. Pretreatment ALT activity was within the reference range (10–100 IU/l) in 25 cats (86%) and was above the upper reference limit (URL) in four cats (13.7%) (Table 1). Of those four cats, two had confirmed neoplastic liver involvement; one had a suspect biliary cyst adenoma, but grossly normal liver; and one did not have an ultrasound on presentation. Pretreatment ALT elevation according to the VCOG-CTCAE scheme was grade 1 [1/4 (25%)], grade 2 (0/4), grade 3 [3/4 (75%)], and grade 4 (0/4) (Table 2). After treatment with CCNU, the initial ALT increases in those four cats were stable or decreased at subsequent biochemical measurements.
Cats that experienced ALT elevation before or after administration of CCNU
DSH = domestic shorthair; DLH = domestic longhair; GI = gastrointestinal; LSA = lymphoma
Note: These two cats experienced ALT increases after treatment with CCNU
Prevalence and definition of serum ALT activity elevation in cats receiving CCNU
URL = upper reference limit
Note: Two of these cats experienced ALT increases after treatment with CCNU
Two additional cats that did not have an increased ALT prior to treatment with CCNU developed increases in ALT following the course of treatment (Table 1). In both cases, it was detected when a chemistry panel was completed 1 month after the final CCNU dose; no ultrasound was completed to determine presence of structural liver damage. One cat had cutaneous lymphoma and received two doses of CCNU with a total cumulative dose of 90 mg/m2. The second cat had mammary carcinoma and received one dose of CCNU at 55 mg/m2. The evaluation of ALT increase according to the VCOG-CTCAE scheme was grade 1 [2/2 (100%)] (Table 2). Neither cat was symptomatic for hepatotoxicity; both cats were euthanased within a month of developing ALT increases (one for progression of initial clinical signs). No ALT increases higher than 1.5 URL were observed.
Four cats (13.7%) had increases in ALP [VCOG-CTCAE grade 3 (1/4) and grade 4 (3/4); two prior to treatment, two following treatment], two (6.8%) had increases in AST [VCOG-CTCAE grade 2 (2/2); one prior to treatment, one following treatment] and three (10.3%) had increases in bilirubin [VCOG-CTCAE grade 2 (2/3) and grade 4 (1/3); two prior to treatment, one following treatment]. Three cats (10.3%) developed hypoalbuminemia [VCOG-CTCAE grade 1 (2/3) and grade 2 (1/3); two prior to treatment, one following treatment]. The one cat, described above, that developed post-therapy changes in both bilirubin and albumin was diagnosed with small cell gastrointestinal lymphoma and had received a total of 13 dosages of CCNU (cumulative dose of 360 mg/m2). These biochemical changes were noted 3 weeks following discontinuation. It was hospitalized on supportive care and euthanased 2 days later owing to lack of improvement to treatment. Unfortunately, no necropsy to determine extent of disease or potential etiology was completed. No cats experienced increases in GGT.
Clinical toxicities observed during the course of treatment included decreased appetite or mild anorexia, and occasional vomiting and diarrhea. No cats had concurrent hematologic toxicity and no VCOG-CTCAE grade 3 gastrointestinal toxicity occurred. All toxicities resolved with conservative management. One cat required delay of chemotherapy and one cat discontinued therapy. At time of writing, 19 cats had died or been euthanased, six cats were lost to follow-up and four cats were alive. No necropsies were completed to histologically evaluate the liver for neoplasia or hepatotoxicity. Median duration of continued monitoring following last treatment with CCNU was 1 month (range: 0–8 months; cats with 0 months of follow-up were either euthanased at the last visit, lost to follow-up following the last visit, or the last visit coincided with completion of the study and the cat was still alive).
Discussion
Increases in ALT were observed in six cats (20.6%) included in this study. Four of those had ALT increases prior to treatment with CCNU. Therefore, those increases cannot be attributed to CCNU toxicity. ALT levels in those four cats decreased, though did not normalize, with continued administration of CCNU. Of the two cats with increases of ALT after treatment, it is unclear if the increase was caused by progression of primary disease, development of concurrent, unrelated liver disease or drug toxicity (CCNU), as no further diagnostics were completed at development of increased ALT. Both of those cats were euthanased shortly after the final biochemical profiles were taken. One had progression of initial clinical signs (lethargy, anorexia and diarrhea). It was not noted if the other cat had progressive disease or worsening of clinical signs.
Increases in canine ALT activity have been reported at dosages of 40 mg/m2. 5 A phase I study completed in cats has shown a dosage of 50–60 mg/m2 administered every 6 weeks to be appropriate for tumor-bearing cats. 16 In that study, liver enzyme increases were not reported to have occurred. 16 In a subsequent study in cats, a dosage of 32–59 mg/m2 every 3 weeks was utilized. Again, no biochemical or clinical hepatopathy was noted. 4 In the present study, initial treatment was begun at a median of 43 mg/m2, given every 4–8 weeks. No treatment-related changes in ALT occurred, even in those that received high cumulative dosages of up to 656 mg/m2.
The two cats in the current study that developed increases in ALT following treatment with CCNU did not have ultrasound examinations completed. Ultrasonography is useful for detecting focal liver disease and space-occupying lesions. However, it is limited in the detection of diffuse liver disease and hepatocellular damage. 18
One cat did have signs attributable to liver disease (anorexia, vomiting and icterus) 3 weeks after the final dose of CCNU. This cat also had hypoalbuminemia and increases in bilirubin and ALP, but no corresponding elevation in ALT. This cat received 13 treatments of CCNU — well above the mean number of 5.5 treatments, but not at the upper end of the range, which was 20 treatments. Unfortunately, no further diagnostics were completed to determine the cause and extent of liver disease. An ALT elevation may not have been detected at the time of hospitalization or euthanasia owing to the assumed short half-life of ALT and the timing of the blood work. Therefore, it is possible that this cat experienced liver damage as a result of the use of CCNU.
In animals, the exact mechanism by which hepatotoxicity occurs is not known and it is uncertain why dogs experience extreme liver damage, while cats do not seem to be as severely affected.19–21
Ninety-six percent of the cats within the study received concurrent prednisone or dexamethasone. However, ALT elevation and the associated hepatotoxicity are not associated with prednisone or dexamethasone use in the cat. 22 Other concurrent medications in this population of cats were neither hepatoprotective or hepatotoxic. Although CCNU-induced liver enzyme elevation in two cats during CCNU therapy may have occurred, progression of disease or undiagnosed concurrent disease cannot be excluded.
There are many limitations to the current study owing to its retrospective nature. The number of cats that ultimately fit the study criteria was low. Hepatotoxicity cannot be defined by ALT elevation alone, but should rather be evaluated in conjunction with other biochemical values and clinical signs. Full biochemical assessment of liver enzymes and function was not consistently completed in all cases; therefore, correlation of levels with specific dose intervals or cumulative doses was not possible. Similarly, dosage and dosing interval were not standardized. In addition, although recommended, not all cats were fully staged at presentation, nor was new blood work collected on all cats at the start of treatment. As long as there were no significant health changes before starting treatment, blood work within 6 months was considered to be acceptable as these cats were suffering from chronic disease. The effect of compounded drug was not examined.
Because the only two cats in the present study with possible CCNU hepatotoxicity did not have definitive assessment for liver injury, we cannot completely dismiss this concern in feline patients. Considering data present herein, a total of 42 cats with CCNU exposure have been described in the veterinary literature (the 29 cats described here and the 13 described by Rassnick et al 15 ) with only rare potential for hepatotoxicity and certainly nothing akin to the canine hepatotoxicity syndrome. Although there are limitations, the current data suggest that cats may not be susceptible to, or rarely develop, CCNU-induced, clinically-significant hepatopathy — even after high cumulative doses.
Footnotes
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors do not have any potential conflicts of interest to declare.