Bleomycin-induced pulmonary toxicity in chemotherapy for testicular cancer

Bleomycin is an antibiotic agent with antitumour activity, discovered in 1966 by Umezawa et al. Today, bleomycin is commonly used in chemotherapy for various tumour types. In testicular cancer especially, bleomycin is one of the key drugs in induction chemotherapy. It has the advantage of less myelotoxicity; however, its severe and potentially fatal pulmonary toxicity has limited its dose intensity. Several clinical trials have focused on eliminating bleomycin from the regimen or reducing the bleomycin dose for testicular cancer patients with good prognosis. However, the results indicate that bleomycin is still an essential component of induction chemotherapy when only three courses are administered. This review will focus on bleomycin-induced pulmonary toxicity in chemotherapy for testicular cancer, followed by a brief review of recent basic understanding of the pathogenesis of lung fibrosis.     

Intoxication pulmonaire fatale à la bléomycine

Bleomycin is an antibiotic agent with antitumour activity, discovered in 1966 by Umezawa et al. Today, bleomycin is commonly used in chemotherapy for various tumour types. In several cancer especially, bleomycin is one of the key drugs in induction chemotherapy. It has the advantage of less myelotoxicity; however, its severe and potentially fatal pulmonary toxicity has limited its use and dose intensity.Postulated risk factors include cumulative bleomycin dose, reduced glomerular filtration rate (GFR), raised creatinine, older age and supplemental oxygen exposure.We report a case of undifferenciated naso-tracheal carcinoma diagnosed in a 15 year old boy who was treated by bleomycin. Subsequently his pulmonary function deteriorated acutely and, after intermittent stabilization, irreversibly.This review will focus on bleomycin-induced pulmonary toxicity in chemotherapy, followed by a brief review of recent basic understanding of the pathogenesis of lung fibrosis.     

Clinical pharmacology of bleomycin and cisplatin

Bleomycin (Blenoxane) and cisplatin (Platinol) are two anticancer drugs, with activity for head and neck tumors, that were introduced into clinical use in the past ten years. Bleomycin is used primarily in the chemotherapy of squamous cell carcinomas, lymphomas, and testicular carcinoma, while cisplatin possesses significant activity against testicular and ovarian carcinoma, head and neck cancer, bladder cancer, and neuroblastoma. Bleomycin is rapidly excreted renally (terminal phase half-life = 2-4 h), although enzymatic inactivation also occurs in many tissues. Cisplatin is nonenzymatically converted to highly protein bound metabolites, which then undergo renal elimination, but total body clearance occurs much more slowly than with bleomycin (terminal phase half-life = 40-50 h). Both agents have acute and chronic toxicities; the acute toxicities are generally reversible but cause a great deal of patient discomfort, while the chronic toxicities are often irreversible and dose-limiting. For bleomycin, the acute toxicities are mucocutaneous are pyretic; severe nausea and vomiting represents the major acute toxicity of cisplatin therapy. Cumulative dose-related pulmonary toxicity is the most serious chronic toxicity of bleomycin. The clinical, radiographic, and pathologic presentations are nonspecific, although identification of high risk patients may be possible with serial pulmonary function tests. Cumulative nephrotoxicity occurs with cisplatin use, and its incidence and severity can be reduced by maintaining adequate hydration and diuresis during and following administration of the drug.     

The value of ifosfamide in the polychemotherapy of metastasized testicular cancer pretreated with chemotherapy

Ifosfamide (Holoxan) has an effect as a single drug on testicular carcinoma and shows synergism with cisplatinum in mice. In combination chemotherapy of testicular cancer ifosfamide has great value as an alternative to bleomycin when the total bleomycin dose has reached a toxic level. The VIP regimen is effective on lung nodules (a marked regression can be seen) and tumor markers (the levels fall). In combination with surgery 8 of 14 patients (= 60%) with disseminated disease (Stage IIIa and IIIb) can reach NED status even after having extended tumor manifestations (bulky disease) after more than 4 cycles of previous combination chemotherapy.     

博来霉素A_6对小鼠肺毒性的电子显微镜观察

用电子显微镜观察比较博来霉素A_6和目前临床使用的博来霉素(复合物)对小鼠的肺毒性。博来霉素A_6和博来霉素分别以相当于1/40、1/20和1/10 LD_(50)剂量给小鼠ip 7d或10 d。病变表现为肺毛细血管的损伤,内皮细胞胞浆空泡、皂泡样变、网状化、伪足样突起、血小板粘着和微血栓形成等最为常见。博来霉素A_6引起的肺病变明显地较博来霉素为轻,提示博来霉素A_6有可能成为肺毒性较低的博来霉素类抗癌药物。     

Role of melatonin in mitigating chemotherapy-induced testicular dysfunction in Wistar rats

Testicular cancer is the most common cancer affecting men of reproductive age, and its incidence is increasing steadily. A regimen of cisplatin (P), vinblastin (V) and bleomycin (B) (PVB) is the standard chemotherapy for testicular cancer. Though PVB-based chemotherapy has been widely used against germ cell tumors, it is associated with induction of oxidative toxicity and a transient or permanent loss of fertility. However, the mechanism of action of PVB on the testis is not thoroughly elucidated. Using a rat model, we investigated the persistence of the effects of PVB on steroidogenesis, spermatogenesis and testicular oxidative status and architecture. Further, we have also studied whether administration of melatonin has any protective effect on testicular physiology in the PVB-treated rats, since melatonin exerts influence on the antioxidant defense system. The body weight of the PVB-treated rats did not show significant change as compared with the control group. Significant decrease in the weight of the testis was observed with a reduction in volume in the PVB-treated rats. Administration of PVB caused a reduction in the testicular steroidogenesis and spermatogenesis. The circulatory levels of testosterone were also significantly reduced with an elevation of FSH and LH in the PVB-treated rats. Testicular architecture was severely affected with a reduction in seminiferous tubule diameter and epithelial height. The activities of superoxide dismutase and catalase were decreased while the levels of lipid peroxidation increased significantly in the testis of the PVB-treated rats indicating depletion of antioxidant defence system and elevation of oxidative stress. Co-administration of melatonin mitigated these changes in the PVB-treated rats.     

Long-term complications of chemotherapy for germ cell tumours

Testicular cancer is the most common solid tumour among young males aged 15-35 years. Cisplatin-based combination chemotherapy has changed the outlook of this disease. Disseminated testicular cancer, once uniformly fatal, now has a cure rate of more than 80% with combination chemotherapy. Systematic randomised trials have shown that cisplatin, etoposide and bleomycin (PEB) combination chemotherapy remains the mainstay of treatment. While there is a high cure rate with chemotherapy in patients with this disease, some long-term complications from chemotherapy have now been recognised, including secondary leukaemia, therapy-related solid tumours, nephrotoxicity, neurotoxicity, pulmonary toxicity, vascular toxicity and infertility. Etoposide, a DNA topoisomerase II inhibitor, is a significant risk factor for developing leukaemia; the risk appears to be correlated with the total dose given. Patients receiving cisplatin-based combination chemotherapy for testicular cancer also appear to have a higher relative risk for developing second non-germ cell malignancies; the greatest risks for therapy-related solid tumours were seen with a combination of radiation therapy plus chemotherapy. Long-term vascular toxicities associated with chemotherapy include Raynaud's phenomenon, acute myocardial infarction and cerebrovascular events. Bleomycin is thought to be the most important drug in the pathogenesis of Raynaud's phenomenon, while cisplatin is the most likely agent involved in myocardial infarction. Peripheral neuropathy is the most common form of neurotoxicity observed with cisplatin-based chemotherapy. Risk factors for the development of neural damage include a high cumulative dose of cisplatin, the use of vinblastine and the concomitant development of Raynaud's phenomenon. Cisplatin is also well known to cause significant nephrotoxicity. Approximately 25% of patients present with azoospermia after undergoing combination chemotherapy with a follow up of 2-5 years. Physician awareness of complications associated with chemotherapy is vital to maximise efficacy, minimise toxicity, and preserve quality of life after treatment. Sperm cryopreservation should be considered for patients who desire children. Close monitoring during therapy allows for the early diagnosis of complications, and close follow up of patients after the completion of therapy is necessary to monitor for relapse and development of long-term complications such as myelodysplastic syndrome and leukaemia. Despite these complications, given the potential for cure rates in this young group of patients, the benefits far outweigh the risks.     

Assessment of pulmonary and hematologic toxicities of liblomycin,a novel bleomycin analog

Summary The antitumor efficacy as well as hematologic and pulmonary toxicity of Liblomycin, a new lipophilic analog of bleomycin, was evaluated in BDF1 mice. In comparison to bleomycin which was without any antitumor efficacy against P388 leukemia, a dose of 10 mg/kg Liblomycin administered on a daily schedule for 10 consecutive days resulted in a significant increase in animal survival (% T/C of 190). This therapeutic dose and schedule of drug administration did not produce any evidence of pulmonary histopathologic injury; at a similar dose and schedule bleomycin resulted in greater than 40% consolidation of alveolar lung space. Mouse lung collagen synthesis measured as rate of [³H]hydroxyproline formation was increased almost 4-fold by bleomycin 7 days following a single maximally tolerated i.v. injection (133 mg/kg); in contrast, Liblomycin (60 mg/kg) did not significantly alter the rate of lung collagen synthesis compared to saline injected control animals. Lung function was assessed by whole body plethysmography. Bleomycin produced an increase in breathing rates above control values by day 15 following administration of drug at 10 mg/kg (d1–10). Mice treated with Liblomycin did not exhibit an increased rate of breathing. Liblomycin, in contrast to bleomycin, produced mild and transient leukopenia and thrombocytopenia suggesting that this toxicity will be a limiting one in future clinical trials. The only other toxicity noted in this study was the appearance after repeated intraperitoneal administration of Liblomycin of a hepatic collagenous fibrous capsule. The capsule formation resulted in an abnormal and grossly lobulated liver which was believed to have affected animal survival. Intravenous administration of Liblomycin, however, was not associated with any detectable hepatic injury.     

Late pulmonary complications of treating Hodgkin lymphoma: bleomycin-induced toxicity

Introduction: Survival of Hodgkin lymphoma (HL) patients has significantly improved in recent decades. The current first-line therapy is doxorubicin, bleomycin, vinblastine, dacarbazine (ABVD) ± irradiation and may cause pulmonary toxicity. Strategies to reduce late toxicity as well as increase survival rate are of interest.

Patients and methods: Pulmonary function of previously treated HL patients was collected over a 12-month period using St. George Respiratory Questionnaire (SGRQ), chest X-ray, dynamic inhalation lung scintigraphy and spirometry.

Results: A total of 137 patients’ data were reviewed. Median time elapsed since diagnosis was 11 years (range was 2 – 30 years). Chest irradiation did not significantly worsen pulmonary function. Number of ABVD cycles with consequential bleomycin dose showed significant correlation with SGRQ total score in patients receiving ABVD plus chest irradiation (p = 0.01). Scintigraphy results correlated with bleomycin dose in patients receiving ABVD without chest irradiation (right side: p = 0.099, left side: p = 0.051).

Discussion: An additive negative effect of chest irradiation was not confirmed as reflected in the literature; however, increasing cumulative bleomycin dose worsened pulmonary function.     

Section Review Oncologic,Endocrine & Metabolic: Bleomycin antibiotics and their role in cancer chemotherapy

The bleomycins are a group of glycopeptide anticancer cytotoxic agents which have been used in the clinical treatment of several human malignancies as single or combination chemotherapy for over two decades. However, the risk of dose-dependent pulmonary toxicity, which ultimately results in pulmonary fibrosis, limits the scale of application. Meanwhile, the unique mechanism of the antitumour effects of bleomycins has also attracted considerable interest from biologists. Extensive studies at the molecular level have provided a guide to attempts to obviate the pulmonary toxicity. Recent progress made in the areas of drug delivery, electropermeabilisation and conjugate synthesis has provided valuable additional information to improve bleomycin chemotherapy. The patents and publications discussed in this review are selected from those covering the period from 1992 to date based on a Chemical Abstracts search.     

Elevation of the Erythrocyte Sedimentation Rate Precedes Exacerbation of Bleomycin-Induced Pulmonary Toxicity: Report of Two Cases and Review of Literature

Bleomycin is included in a number of potentially curative chemotherapy regimens. It is associated with distinct forms of pulmonary toxicity, with interstitial pneumonitis the most common. Early detection of pulmonary toxicity is not always predictable by monitoring serial chest radiographs and pulmonary function tests. Even newer serum markers are not useful indicators of bleomycin-induced pulmonary damage. Two patients developed bleomycin pulmonary toxicity, in both of whom increases in erythrocyte sedimentation rate (ESR) preceded clinical deterioration and radiographic changes. The ESR may have potential significance as a monitoring test in patients receiving bleomycin.     

Interstitial lung disease in lung cancer: separating disease progression from treatment effects.

Lung cancer often develops in individuals with pre-existing pulmonary and cardiac pathology. Many of these individuals with pre-existing pathology are also at risk of occupational lung disease. New and worsening symptoms can be secondary to pre-existing pathology, progressive cancer or treatment. Pulmonary toxicity, including interstitial lung disease, following radiotherapy and conventional cytotoxic chemotherapy (e.g. cyclophosphamide, bleomycin), has been recognised for many years. Pulmonary toxicity also occurs with the newer classes of cytotoxic agents, including the deoxycytidine analogue gemcitabine. A small percentage (0.88%) of patients treated with the epidermal growth factor receptor tyrosine kinase inhibitor gefitinib have developed interstitial lung disease. This complication has been reported at a higher frequency in Japanese patients than in US patients (1.9% vs 0.34%, respectively) and in those with pre-existing pulmonary fibrosis. This review discusses the difficulties in both recognition and treatment of gefitinib-associated interstitial lung disease. Symptoms are vague, such as dyspnoea, cough and fever and can be difficult to differentiate from progressive disease, co-existing morbidity and new pulmonary pathology. Diagnosis is, therefore, by rigorous investigation to exclude all other differential diagnoses. Treatment, at present, is supportive and includes discontinuation of gefitinib, oxygen supplementation, high-dose corticosteroids and antibacterials.     

The toxicological evaluation of tallysomycin s10b--biosynthetic tallysomycin derivative

Tallysomycin S10b, a biosynthetic derivative of tallysomycin B, was subjected to intravenous toxicologic studies in mice and dogs. LD50 and LD10 values from lethality studies in mice were utilized to establish dose levels for single and five daily dose toxicity studies in mice and dogs. Nephrotoxicity was the most consistent and prominent drug-related alteration in single and multiple dose studies in both species and was considered the dose limiting toxicity. Other toxicities included pulmonary toxicity, lymphopenia and necrosis of extremities in mice and dogs and testicular degeneration and focal vacuolation of adrenal cortical cells in the dog. Bleomycin was administered to dogs as a reference control agent at a single dose of 270 mg/m2 which was approximately equivalent to the highest tallysomycin S10b dose of 240 mg/m2. Tallysomycin S10b showed a greater nephrotoxic potential than bleomycin at earlier time periods. However, at termination there was no meaningful difference in the degree of chronic nephrotoxicity. The pulmonary toxicity of both drugs was comparable.     

Epigenetic alterations in sperm DNA associated with testicular cancer treatment

DNA methylation, a key component of the epigenome involved in regulating gene expression, is initially acquired in the germ line at millions of sites across the genome. Altered sperm methylation patterns are associated with infertility and transgenerational effects in humans and rodents. Testicular cancer is the most common form of cancer among men of reproductive age and has a high cure rate associated with chemotherapy treatment with bleomycin, etoposide, and cis-platinum (BEP). Although these drugs result in improved survival, they also affect the number and quality of germ cells. Our goal was to assess germ cell methylation patterns in a rodent model emulating the BEP treatment regimens used in human testicular cancer treatment. Animals were treated with control, or 0.3× (low) or 0.6× (high) dose of BEP, where a 1× dose is equivalent to human treatment regimens. Both dose-dependent and germ cell-dependent DNA methylation alterations were found at numerous loci throughout the genome. Of about 3000 loci tested, 42 loci were affected by BEP at the round spermatid stage of germ cell development, whereas 101 loci were affected in spermatozoa; 15 loci were consistently altered in spermatozoa of all high dose-treated rats. Both hyper- and hypomethylation were detected, suggesting either an interference with normal methylation patterning or abnormal repair of damaged patterns during spermatogenesis. The results indicate that a combination chemotherapy regimen used for testicular cancer treatment can result in altered DNA methylation patterns in spermatozoa and that some loci are more susceptible to damage than others.     

Silymarin alleviates bleomycin-induced pulmonary toxicity and lipid peroxidation in mice

Context: The application of bleomycin is limited due to its side effects including lung toxicity. Silymarin is a flavonoid complex isolated from milk thistle [Silybum marianum L. (Asteraceae)] which has been identified as an antioxidant and anti-inflammatory compound.

Objective: This study evaluates the effect of silymarin on oxidative and inflammatory parameters in the lungs of mice exposed to bleomycin.

Materials and methods: BALB/c mice were divided into four groups of control, bleomycin (1.5?U/kg), bleomycin plus silymarin (50 and 100?mg/kg). After bleomycin administration, mice received 10?d intraperitoneal silymarin treatment. On 10th day, blood and lung samples were collected for measurement of oxidative and inflammatory factors.

Results: Silymarin led to a decrease in lung lipid peroxidation (0.19 and 0.17?nmol/mg protein) in bleomycin-injected animals. Glutathione-S-transferase (GST) which was inhibited by bleomycin (32.4?nmol/min/mg protein) induced by higher dose of silymarin (41?nmol/min/mg protein). Silymarin caused an elevation in glutathione (GSH): 2.6 and 3.1?µmol/g lung compare with bleomycin-injected animals 1.8?µmol/g lung. Catalase (CAT) was increased due to high dose of silymarin (65.7?µmol/min/ml protein) compare with bleomycin treated-mice. Myeloperoxidase (MPO) which was induced due to bleomycin (p?p?Conclusions: Silymarin attenuated bleomycin induced-pulmonary toxicity. This protective effect may be due to the ability of silymarin in keeping oxidant–antioxidant balance and regulating of inflammatory mediator release.     

Phase I trial of tallysomycin S10b,a bleomycin analogue

Summary Bleomycin is an agent with significant antitumor efficacy whose major dose limiting toxicity is pulmonary fibrosis. Attempts have thus been made to identify congeners with reduced toxicity and with comparable or greater antitumor activity. Tallysomycin S_10b is a bleomycin analogue possessing significantly greater potency, equal or reduced lung toxicity, and slightly greater antineoplastic activity when compared to the parent compound in preclinical studies. This report describes our experience with tallysomycin S_10b in 30 patients with a variety of non-hematologic neoplasms. Pulmonary toxicity, occurring in 4 patients, was the major toxicity. The recommended cumulative dose of tallysomycin S_10b was difficult to establish from the results of this study, as pulmonary toxicity appeared to be more idiosyncratic than dose-or schedule-dependent. The employment of more sensitive methods for detecting pulmonary toxicity in this study suggest that tallysomycin S_10b may have reduced pulmonary toxicity compared to the parent compound.Both bleomycin and tallysomycin S_10b have similar t_1/2 half-lives of 2–4 h. Six patients had prolonged terminal elimination half-lives of tallysomycin S_10b, but no clear relationship between this phenomenon and efficacy or toxicity was evident.No complete or partial responses occurred. Disease stabilization occurred in 4 of 15 patients with diagnoses of renal cell carcinoma [2], rectal cancer [1] and lung cancer [1]. Five of eight patients with non-measurable disease had stable disease, including one with mesothelioma, one with carcinoma of the head and neck, two with renal cell cancer and one with colon carcinoma.     

肺纤维化大鼠肺组织钙含量及钙调素活性的研究

目的 :探讨Ca2 + 及钙调素 (Calmodulin ,CaM )在肺纤维化形成中的作用。方法 :将32只SD大鼠随机分为2组 :(1)正常组 (8只 ) :不接受任何处理。 (2)模型组 (24只 ) :1次性气管内注入博莱霉素A5(BLMA5)制备肺纤维化模型。在实验的第7、14、28d分批处死后作病理切片进行病理学检查 ;应用电子计算机图像分析仪进行肺泡炎和肺间质纤维化定量分析 ;采用火焰原子吸收分光光度法及磷酸二酯酶 (PDE)法分析测定肺组织Ca2 + 含量及CaM活性 ,同时与正常组比较。结果 :模型组肺组织Ca2 +含量及CaM活性较正常组明显增高 (P<0 001) ,组织病理学显示典型的肺间质纤维化病理改变。结论 :BLMA5 诱导的肺纤维化存在着Ca2 + 及CaM平衡紊乱 ,提示Ca2 + -CaM系统在BLMA5 诱导的肺纤维化形成过程中起一定作用     

Mechanisms of bleomycin-induced lung damage

Bleomycins are a family of compounds produced byStreptomyces verticillis. They have potent tumour killing properties which have given them an important place in cancer chemotherapy. They cause little marrow suppression, but pulmonary toxicity is a major adverse effect. The mechanisms of cell toxicity are well described based on in vitro experiments on DNA. The bleomycin molecule has two main structural components; a bithiazole component which partially intercalates into the DNA helix, parting the strands, as well as pyrimidine and imidazole structures, which bind iron and oxygen forming an activated complex capable of releasing damaging oxidants in close proximity to the polynucleotide chains of DNA. This may lead to chain scission or structural modifications leading to release of free bases or their propenal derivatives. The mechanisms are well described based on in vitro experiments on DNA, but how they relate to intact cells in whole animals is more tenuous. Bleomycin is able to cause cell damage independent from its effect on DNA by inducing lipid peroxidation. This may be particularly important in the lung and in part account for its ability to cause alveolar cell damage and subsequent pulmonary inflammation. The lung injury seen following bleomycin comprises an interstitial oedema with an influx of inflammatory and immune cells. This may lead to the development of pulmonary fibrosis, characterized by enhanced production and deposition of collagen and other matrix components. Several polypeptide mediators capable of stimulating fibroblasts replication or excessive collagen deposition have been implicated in this, but the precise role of these in bleomycin-induced fibrosis is yet to be demonstrated. Current therapy for bleomycin-induced lung damage is inadequate, with corticosteroids most often used. Given the mechanism of action described above, antioxidants and iron chelators might be beneficial. Although, studies to date are equivocal and there is insufficient evidence to promote their use clinically. Novel drugs are currently being developed and it is hoped these may be more useful.     

Therapeutic drug monitoring in oncology. Problems and potential in antineoplastic therapy

Therapeutic drug monitoring is now widely used in many areas of medicine. With its proliferation has come an understanding of the clinical situations in which it is likely to be of value. Factors that can limit the usefulness of therapeutic drug monitoring and situations where it is less likely to be of benefit have also been identified. At present, the routine use of therapeutic drug monitoring in antineoplastic therapy is limited to measurement of plasma methotrexate concentrations after high-dose methotrexate therapy. The lack of a more widespread application of therapeutic drug monitoring in oncology has been due to deficiencies in knowledge about the clinical pharmacology of antineoplastic agents and to factors specific to the chemotherapy of neoplasms. These factors include the broad heterogeneity of malignant neoplasms, the complexities of the drug-tumour interaction, difficulties in assessment of this interaction and the use of combinations of antineoplastic agents with cumulative efficacies and toxicities. Despite these problems, there are many areas in antineoplastic therapy where the use of therapeutic drug monitoring could prove of benefit. The prevention of the chronic pulmonary toxicity of bleomycin, the assessment of the bioavailability of oral chemotherapy, and monitoring drug disposition in the presence of hepatic or renal dysfunction are just some of the potential applications. If recent emphasis on dose as a critical factor in the success of cancer chemotherapy is substantiated, then the need to apply therapeutic drug monitoring within oncology will become more pressing.     

Fibrogenic structure-activity study of the bleomycin molecule

In the present study the fibrogenic potential of intact bleomycins as well as their acetyldipeptide and terminal polyamine constituents have been assessed. Administration of Blenoxane, bleomycin A2, or bleomycin B2 to rats produced histopathologic evidence of pulmonary fibrosis when tissues were examined 28 days following a single intratracheal dose. These compounds also produced a readily detectable increase in pulmonary collagen synthesis as evidenced by an approximate twofold increase over control values in the formation of [3H]hydroxyproline in an in vitro lung mince system. Lung collagen synthetic activity remained significantly elevated over control values for up to 2 weeks. However, neither the acetyldipeptides nor the polyamine constituents of bleomycin A2 and B2 produced detectable increases in lung collagen synthesis or in histopathologic evidence of pulmonary injury. Spermine and spermidine, the terminal amine components associated with bleomycin-A6 and with tallysomycin A, tallysomycin B, and bleomycin-A5, respectively, did produce significant pulmonary fibrotic injury in rats following intratracheal administration. Out of an extensive series of polyamines, bleomycin acetyldipeptides and intact bleomycin and tallysomycin analogs, only spermine and spermidine were found to produce hydrogen peroxide and acrolein upon incubation in vitro with amine oxidase, a common pulmonary enzyme. Conclusions regarding the relative toxicity of different bleomycin analogs based solely on the toxicity produced by administration of their terminal amine constituent must therefore be made with caution.