Predicting the maximum-tolerated dose of PNU-159548 (4-demethoxy-3'-deamino-3'-aziridinyl-4'-methylsulphonyl-daunorubicin) in humans using CFU-GM clonogenic assays and prospective validation.

A haematotoxicity model was proposed by Parchment in 1998 to predict the maximum-tolerated dose (MTD) in humans of myelosuppressive antitumour agents by combining data from in vitro clonogenic assays on haematopoietic progenitors and in vivo systemic exposure data in animals. A prospective validation of this model in humans was performed with PNU-159548, a novel agent showing selective dose-limiting myelosuppression in animals. PNU-159548 and its main metabolite, PNU-169884, were tested in vitro on murine, canine and human colony forming units-granulocyte macrophages (CFU-GM) and in vivo on mice and dogs. The IC(90x) ratios (IC(x)=concentration inhibiting x% of colony growth) for CFU-GM and drug plasma protein binding were used to adjust the target plasma concentrations versus time curve (AUC) and predict the human MTD. The predicted MTD was compared with values achieved in phase I studies. Canine CFU-GM were 6-fold more sensitive (P<0.01) and murine CFU-GM 1.7-fold less sensitive (P<0.05) to PNU-159548 treatment than the human progenitors. PNU-169884 behaved similarly to PNU-159548. The predicted MTDs in humans calculated from data in mice and dogs were 15 and 38 mg/m(2), respectively. Overall, 61 patients were treated in two phase I studies, at doses ranging from 1.0 to 16 mg/m(2). Thrombocytopenia was dose-limiting with a MTD of 14 and 16 mg/m(2) in heavily and minimally pretreated/non-pretreated patients, respectively. Adjusting animal MTD data by means of the CFU-GM ratio between species can predict the human MTD with a good quantitative accuracy. Inhibition of common haemopoietic progenitors by PNU-159548 induced neutropenia/thrombocytopenia in animals and thrombocytopenia in patients, probably due to the higher sensitivity to the compound observed in human colony forming units-megakaryocyte (CFU-MK).

Toxicological testing of cytotoxic drugs (review).

Cytotoxic drugs are a unique therapeutic class of fundamental importance in current antineoplastic chemotherapy. These drugs belong to many chemical and chemotherapeutic classes. They are cytotoxic by design and are able to cause serious dose-limiting adverse effects at therapeutic doses. Most antineoplastic dosing strategies focus on minimizing cytotoxicity rather than optimizing efficacy. In turn, cytotoxicity is interconnected with other therapeutic considerations, including cell status (renewing vs. non-renewing cell types), cell membrane transport integrity, intracellular activation status, immune system integrity, cellular repair status, and drug resistance. Regulatory requirements for the development of cytotoxic drugs are not well characterized, and differences exist in regional requirements. A safety assessment package which is utilized and accepted world-wide does not yet exist, despite many efforts of harmonization. In this report, the authors introduce a comprehensive safety assessment package for cytotoxic drugs, based on institutional experience acquired globally with this class of drugs, that fulfills both scientific and world-wide regulatory requirements for this very important therapeutic category.

PNU-159548, a novel cytotoxic antitumor agent with a low cardiotoxic potential.

PURPOSE: PNU-159548 (4-demethoxy-3'-deamino-3'aziridinyl-4'-methylsulphonyl-daunorubicin), a derivative of the anticancer idarubicin, has a broad spectrum of antitumoral activity in vitro and in vivo attributable to its DNA intercalating and alkylating properties. The present study was conducted to determine the cardiotoxic activity of PNU-159548 relative to doxorubicin in a chronic rat model sensitive to anthracycline-induced cardiomyopathy. METHODS: Young adult male rats were allocated to the following treatment groups: group 1, PNU-159548 vehicle control (colloidal dispersion); group 2, doxorubicin control (saline); groups 3, 4, 5, 6, and 7, PNU-159548 at 0.12, 0.25, 0.50, 0.75, and 1.0 mg/kg, respectively; and group 8, 1.0 mg/kg doxorubicin. Treatments were administered intravenously once weekly for 4 weeks (first sacrifice time) or for 7 weeks (rats killed at weeks 8, 12, 22, 27, or 35). Body weights, organ weights, serum chemistry, hematology, serum troponin-T, and cardiac histopathology were followed throughout the study. RESULTS: Doxorubicin caused irreversible cardiomyopathy evident at week 4 in some rats and progressing in severity in all rats by week 8. There were also marked myelotoxicity, increased liver and kidney weights, testicular atrophy, and about 20% mortality by week 27 in doxorubicin-treated rats. The deaths were attributed to cardiomyopathy and/or nephropathy. PNU-159548 caused a dose-dependent myelotoxicity, with the dose of 0.5 mg/kg per week being equimyelotoxic to 1.0 mg/kg per week doxorubicin. PNU-159548 also caused an increase in liver weight that was reversible and a non-reversible testicular atrophy but, unlike doxorubicin, had no effect on kidney weight. At equimyelotoxic doses, the cardiotoxicity caused by PNU-159548, expressed as the mean total score, was less than one-twentieth of that induced by doxorubicin, and much less than that predicted on the basis of its content of idarubicin, which is in turn markedly less cardiotoxic than doxorubicin. CONCLUSIONS: The novel cytotoxic antitumor derivative, PNU-159548, is significantly less cardiotoxic than doxorubicin at equimyelosuppressive doses. The combination of intercalating and alkylating activities within the same molecule without the cardiotoxic side effects of anthracyclines makes PNU-159548 an excellent candidate for clinical development in oncology.

Reproductive toxicity of exemestane, an antitumoral aromatase inactivator, in rats and rabbits.

Exemestane is an orally active, irreversible inactivator of aromatase, structurally related to the natural substrate androstenedione, in clinical use at 25 mg daily for the treatment of advanced breast cancer in postmenopausal women. The reproductive and developmental toxicity of exemestane was assessed in rats and rabbits with oral administration. Pivotal experiments included a fertility study (Segment I), in which female rats received exemestane doses of 4, 20, or 100 mg/kg/day from two weeks premating until GD 20 (cesarean-sectioned dams), or until GD 15 and then from D 1 to D 21 postpartum (dams allowed to deliver), and developmental toxicity studies (Segment II), in which rats and rabbits were treated from GD 6 through GD 17 (rats) or GD 18 (rabbits) at doses of 10, 50, 250, or 810 mg/kg/day and 30, 90, or 270 mg/kg/day, respectively. All rabbits and two-thirds of the rats were cesarean sectioned toward the end of pregnancy to determine litter parameters and examine structural abnormalities in the fetuses; the remaining one-third of the rats was allowed to litter and rear pups to weaning. No pivotal male fertility or peri- and postnatal studies were performed, taking into consideration the therapeutic use. Postnatal effects on the first generation offspring were assessed in both studies in rats, in the portion of dams allowed to deliver. Their F1 offspring were raised to adulthood, when they were evaluated for reproductive performance, and the F1 females were terminated on GD 20. The dosing schedule for the Segment I study in rats, which included a postnatal component, was established to exclude exposure before and during parturition (by withdrawing treatment from GD 16 until the end of parturition). This withdrawal of treatment was put in place because in a preliminary study with treatment including the peripartum period, doses from 5 to 200 mg/kg/day prolonged gestation and interfered with parturition.Overall, studies in rats showed that female fertility was not affected up to 100 mg/kg/day, but doses higher than 4 mg/kg/day, which is approximately the pharmacologically active dose (ED50 = 3.7 mg/kg), prolonged gestation and impaired parturition, leading to maternal deaths in labor and perinatal deaths of offspring. Rats killed on GD 20 showed nondose-related increases in resorptions at doses higher than 10 mg/kg/day, a reduction in fetal body weights at 20 and 100 mg/kg/day (fertility study) and 810 mg/kg/day (developmental toxicity study), and an increase in placental weights at all doses. Female fetuses exposed in utero until GD 20 at 100 mg/kg/day showed an increase in the anogenital distance, very likely related to an increase of the potent androgen DHT as a consequence of aromatase inhibition. Morphologic examinations in fetuses and born pups that were exposed in utero up to the end of the organogenesis period, as well as postnatal investigations on offspring up to adulthood, showed no treatment-related effects. In a developmental toxicity study in rabbits, treatment at 270 mg/kg/day affected maternal food intake and body weight gain, caused abortion or total resorption in about 30% of pregnant females, and reduced body weight and numbers of live fetuses, but did not affect fetal morphology. It was concluded that exemestane did not affect parturition in rats at 4 mg/kg/day or pregnancy in rabbits at 90 mg/kg/day (about 1.5 and 70 times the human dose, respectively, on a mg/m2 basis) and was not teratogenic in rats and rabbits. Exemestane is marketed for use only in postmenopausal women. Its labeling includes a contraindication to use in pregnant or lactating women.

Anthracyclines.

The genotoxicity and carcinogenicity data from in vitro and in vivo studies conducted during preclinical safety assessment of doxorubicin (DOXO), epirubicin (EPI) and idarubicin (IDA), are reviewed. The genotoxicity assays included a) gene mutation in Salmonella typhimurium with 5 tester strains; b) gene mutation in the V79 mammalian (lung) cell line; c) chromosome aberrations in human lymphocytes cultured in vitro; and d) chromosome aberrations in mouse bone marrow cells after intravenous (i.v.) administration in vivo. The long-term toxicity studies in the rat included a) single dose administration (3 mg/kg DOXO, 3.6 EPI and 0.75 IDA) to female rats of two different age groups, i.e. younger (7 weeks old at dosing) and older (13 weeks old), followed by one-year observation; and b) multiple dose administration to male and female rats (7 weeks old at dosing), consisting of i.v. administration of 0.25, 0.5 and 1 mg/kg DOXO or EPI and 0.06, 0.125 and 0.25 mg/kg IDA, once every 3 weeks for 10 cycles, followed by 18 months of observation. The genotoxicity studies revealed activity in gene mutation assays in bacterial and mammalian cells, and in chromosome aberration assays in human lymphocytes in vitro and in mouse bone marrow in vivo. In the two long-term studies in the rat, only mammary tumors were present. This finding was expected and, according to the literature, can be considered as species specific and not directly compound-related. The lack of tumor induction at the usual target organs for DNA reactive compounds, which are almost the same as those considered as target organs in anthracycline-exposed animals, indicates that the type and the extent of DNA damage precludes stimulation for proliferation and induction of neoplasia. Although an epigenetic mechanism can be hypothesized, support for such a mechanism is lacking.

Changes associated with long-term oral administration of the penem antibiotic FCE 22891 to rats and monkeys with particular emphasis on the urinary tract and the urine.

FCE 22891, a synthetic beta-lactam antibiotic of the penem class, was administered by gavage to Sprague-Dawley rats and cynomolgus monkeys for 26 wk (with and without a 6-wk recovery). Rats received the test material at doses of 0, 200, 500, and 1,250 mg/kg/day, and monkeys were given doses of 0, 100, 200, 400, and 600 mg/kg/day. At the end of the 26-wk treatment period, approximately two-thirds of the animals (both species) were sacrificed, and the remaining animals were held without treatment for a further 6 wk. A treatment-related mortality occurred in female monkeys receiving 600 mg/kg. There was a reduction in body weight gain in the high-dose groups of both species. Male rats were more affected than the females and, conversely, female monkeys were affected more than the males. At higher dose levels, both species exhibited an early, but transient, azotemia and oliguria with an increase in specific gravity and reduced pH. In rats, microscopic examination revealed treatment-related renal cortical tubular degenerative and regenerative changes with associated interstitial inflammation and fibrosis and diffuse urothelial hyperplasia in the urinary bladder. In general, female rats were less severely affected, and in both sexes there was a trend to recovery of most of these effects. In monkeys given 600 mg/kg of the test material, renal cortical tubular degeneration was seen only in those females that died in the first 5 wk of dosing. In other animals at this dose level, the renal lesions were determined to be reversible.

Overview of toxicological data on rifabutin.

Rifabutin is a wide spectrum antibiotic particularly active on atypical and rifampicin-resistant mycobacteria. Rifabutin is more potent than rifampicin on Mycobacterium tuberculosis in vitro. Its mode of action is characterized by a high intracellular penetration in treated individuals. Clinical trials have proven the therapeutic value of rifabutin especially in AIDS patients with concomitant MAC. The preclinical safety evaluation of this compound included single and repeated dose toxicity studies of up to one year in rodents and non-rodents, reproduction and carcinogenicity studies and mutagenicity tests. During toxicological studies the most significant finding after repeated administration of rifabutin was the presence of multinucleated hepatocytes (MNH) in rats. This is a species specific finding which did not affect the life span of the hepatocytes. As shown in carcinogenicity studies, there was no tendency to further proliferative changes. Another specific histological feature among the species studied was the presence of a lipofuscin-like brown pigment, which was seen in many organs. This is a common finding with amphipilic compounds, such as rifabutin, which bind lipids and proteins, forming membrane-bound complexes. Even in carcinogenicity studies this change did not constitute a stimulus to cell proliferation and did not cause any secondary changes. In rodents, there was a mild hemolytic anemia at doses higher than 10 mg/kg/day. At doses ranging from 160-200 mg/kg/day rifabutin inhibited the functions of the male gonads in rats. This effect was reflected in a reduction of implantations observed in the fertility studies. Doses of 40 mg/kg/day did not induce any embryotoxic effects or changes in reproductive performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthracyclines - a review of general and special toxicity studies.

Preclinical safety assessment data on doxorubicin (DOXO), epirubicin (EPI), idarubicin (IDA) and methoxymorpholinodoxorubicin (MORPHO), from mouse, rat and dog studies are reviewed. These data are put into perspective allowing for extrapolations across species, doses and dose regimens with recommendations for proper human use. The compounds were administered intravenously or intraperitoneally in studies ranging from single dose to multiple dose studies of different durations. The compounds were given once, daily, weekly or cyclically. In the cyclic administration studies, DOXO, EPI, and IDA were given for 3 consecutive days a week for 6 or 13 weeks; MORPHO was given for 3 consecutive days a week every three weeks for a total of 9 cycles. The duration of the cyclic studies was from 6-26 weeks. Daily dose studies lasted from 4-26 weeks. In the single dose studies the recovery ranged from 4 weeks to one year; in the multiple dose studies from 4 to 8 weeks. A few special studies were also considered. In all studies reviewed, 2 different types of toxicity were observed. These toxicities occur also in man. The first is the acute toxicity, which is the consequence of cytotoxicity and expresses the exaggerated pharmacological activity of the compounds. The target sites in all 3 species and in man include the hemolymphopoietic system (HLPS), the gastrointestinal (GI) tract, skin and testes; all renewing cell types. The second type of toxicity is the chronic progressive toxicity. This toxicity is the expression and result of sustained disruption of cytoplasmic homeostasis and occurs in non-renewing cell types. The target sites include the heart (both animals and man), kidneys (rodents) and peripheral nervous system (PNS) (rodents). From single administration animal data, chronicity, site and magnitude of toxicities can be predicted in man. Despite strong mitogenic stimuli in the rat, there is no evidence that there is a potential for hemolympho- or hepatocarcinogenicity with these compounds.

Urinary bladder hyperplasia in the rat: non-specific pathogenetic considerations using a beta-lactam antibiotic.

Eight of the known chemical substances associated with neoplasia in man are known to target the urinary bladder urothelium. Preneoplastic changes have been identified following exposure to each of these chemicals, and they have also been seen to occur in many species of lab animals. The most important such change is preneoplastic hyperplasia. Adaptive hyperplasia is the first form of hyperplasia to appear. It can be seen both in untreated controls and dosed animals. The distinguishing features are that in treated groups it does not progress with dose or time, and the process is reversible. Reparative hyperplasia involves disruption of homeostasis. Its severity increases with dose and time. It is not seen in controls but it is still reversible during the recovery segment after exposure to a toxic substance. When reparative hyperplasia continues beyond a certain threshold of time and dose, it progresses to preneoplastic hyperplasia, which further progresses with continued stimulation to frank neoplasia. The synthetic beta-lactam penem antibiotic FCE 22891 and its metabolite FCE 22101 caused adaptive urothelial hyperplasia of the urinary bladder only in rats and in no other species. Based on the pharmacokinetic profile of FCE 22891 and FCE 22101, it can be deduced that the morphologic finding of adaptive urothelial hyperplasia is caused by reduction of intravesicular urine pH. This effect has no relevance to therapeutic use in humans. Further, it is important to distinguish adaptive and reparative hyperplasia in preclinical toxicity studies.

Evaluation of 4'-iodo-4'-deoxydoxorubicin-induced cardiotoxicity in two experimental rat models.

In the present study, 1 single-dose and 1 multiple-dose models were applied in studying 4'-iodo-4'-deoxydoxorubicin (I-DX) cardiotoxicity. Anthracycline cardiotoxicity has been reproduced in several animals including mice, rats, hamsters, rabbits, dogs, and monkeys. Of these species the rat can be considered the most suitable species for the study of anthracycline-induced cardiomyopathy. The cardiotoxicity induced by I-DX in male Sprague-Dawley rats was compared to that of doxorubicin (DX), used as standard positive control. Groups of 36-42 rats were observed for up to 35 wk to follow the progression of the lesions. Cardiomyopathy was evaluated through well-established qualitative/quantitative morphological grading. The new DX derivative proved to be clearly less cardiotoxic than DX with both treatment schedules. Although both models can be considered useful for evaluating and comparing the cardiotoxicity of new anthracycline derivatives and mimicking the transvenous endomyocardial biopsies in humans, the chronic test seems to be more suitable for compounds like I-DX, which possess a low cardiotoxic potential and which could go undetected in the single-dose test.

Experience with the preclinical assessment of basic fibroblast growth factor (bFGF).

Repeated intravenous administrations were carried out in cynomolgus monkeys and rats (S.D.) for a maximum of 4 weeks at doses of 1, 10 and 100 micrograms/kg/day in stable formulation. Three main target organs were identified: red blood cells (RBC), kidney glomeruli (KG) and bone at the top dose level. RBC: Normochromic normocytic anaemia started in rats and monkeys during the second week of treatment (decrease in red blood cell production). The kinetics of this anaemia, as well as its recovery, will be discussed. Bone: Dramatic hyperostosis in rats was present by day 10 in long or spongious bone. This became marked on day 29 and regressed after treatment was stopped. KG: In the rat glomerular lesions were present starting from day 16. They consisted of enlargement and vacuolation of podocytes with loss of foot processes and adhesions between glomerular tuft and Bowman's capsule. Proteinuria was a striking feature. In the monkey the lesions were hyperplasia of the parietal epithelium of Bowman's capsule which involved replacement of normally flattened epithelium by cuboidal cells, with some pseudostratification. Proteinuria also occurred in monkeys, accompanied by a lowering of serum protein (albumin). In two animals, death (by day 15) was preceded by high levels of urea and blood creatinine. The above lesions (KG) disappeared almost completely over a recovery period. It is suggested that these phenomena are not the expression of direct toxicity in the form of lethal insults, but rather a manifestation of a change in cell activity.

Toxicological profile of FCE 22101 and its orally available ester FCE 22891.

LD50 values of FCE 22101 iv were 3872 mg/kg and 4392 mg/kg in male and female mice, and 2000 mg/kg and 2201 mg/kg in male and female rats respectively. Oral LD50s of FCE 22891 were 4363 mg/kg in male and 6167 mg/kg in female mice; in the rat this value was over 5000 mg/kg in both males and females. FCE 22101, given iv for two consecutive days was less nephrotoxic in rabbits than cephaloridine and imipenem alone, but more nephrotoxic than imipenem/cilastatin. Dose ranging studies carried out in rats and 13-week studies in rats and monkeys indicated that the kidney was a target organ for both penem compounds. Renal lesions appeared beginning with doses higher than 300 mg/kg/day and were morphologically similar to those induced by cephaloridine and imipenem. Possible targets at high doses were the urinary bladder in rats and the haemopoietic system in monkeys given FCE 22101. The toxicity data available for iv FCE 22101 and oral FCE 22891 in the rat and monkey indicated an adequate tolerance of these compounds, comparable with other beta-lactam antibiotics, including imipenem/cilastatin.