Soft tissue tumors in the rat. Pathogenesis and histopathology

Regulatory Forum Opinion Piece: Review-Toxicological Pathology Profile and Regulatory Expectations for Nonclinical Development of Insulins and Insulin Analogues

The toxicological profile of insulins is exclusively due to exaggerated pharmacology resulting in hypoglycemic findings. Insulin analogues displaying modifications and aimed at improving pharmacokinetics do not induce different toxicity. The main target is the brain displaying neuronal necrosis. Wallerian degeneration of nerves occurs rarely after severe hypoglycemia. These findings are of potential human relevance; nevertheless, these changes are induced in normoglycemic animals whereas diabetic patients suffer from hyperglycemia. Therefore, it is usually not difficult to achieve a therapeutic window for subsequent use in patients. Based upon this and in the absence of classical toxicity, there has been no scientific need for diabetic animal models. A greater challenge is the mitogenicity already inherent with regular insulin. Thus, the focus for preclinical safety evaluation of analogues is to demonstrate that modifications in regular insulin do not result in enhanced mitogenicity. The approaches used to assess the mitogenic potential of insulin analogues have changed over time driven by scientific progression and changes within the regulatory environment. Therefore, in vitro and in vivo evaluation of cell proliferation has become common practice, and to date there has been no evidence that the mitogenic potential of insulin analogues may be increased compared to regular insulin.

Induction of sarcomas by a single subcutaneous injection of 7,12-dimethylbenz[a]anthracene into neonatal male Sprague-Dawley rats: histopathological and immunohistochemical analyses

Animal experiments have shown that carcinogenicity of chemicals is higher in fetal or neonatal periods than adult. We investigated sensitivities to a carcinogen in peri-neonatal rats with a model of sarcomas-induction by a subcutaneous injection of chemo-carcinogen that has rarely done in neonatal rats. Neonatal male SD rats were injected with 7,12-DMBA 10, 100, and 500 microg, which resulted in sarcomas-induction in 0, 62, and 94% of rats. Male SD rats were injected with DMBA 500 microg at 0, 3, 7, 14, and 21 days, which resulted in sarcomas-induction in 94, 70, 64, 50, and 44% of rats. Although the induced sarcomas were occasionally in mixed morphological feature as previous reports for sarcomas of rat, each was immunohistochemically in almost monotonous pattern, and classification was feasible. The incidence of rhabdomyosarcomas was higher in rats neonatally injected with a higher dose of DMBA than a lower dose, and in rats injected at peri-neonatal periods than later periods. In histological observations for the site of injection before overt sarcomas develop, clusters of atypical mesenchymal cells emerged as previous studies, but also those were immunohistochemically differentiated into rhabdomyocytes and other mesenchymal cells. We consider these findings may contribute a little to elucidation of process of sarcomas-induction in rats.

Feedback in cancer

The theory presented regards cancer as a systemic disease initiated by carcinogens, and neoplasia as the organism's main defence against it. Carcinogens are assumed to destroy a vital substance "A" which is replenished by a second, "B", produced by neoplastic stem cells. Cancer progression is manifested by a gradual deterioration of the "A" producing machinery accompanied by a compensatory proliferation of neoplastic "B" producing stem cells whose size is therefore closely regulated so as to meet the organism's demands. Any stem cell pool reduction leading to a loss of "A" or "B" is followed by a proliferation of the remaining stem cells to replenish the loss. Such may be observed in chronic lymphoblastic leukemia maintaining a nearly constant elevated peripheral lymphoblast count. Following selective lymphoblast destruction the count is rapidly replenished to its pretreatment level. The same mechanism is assumed to explain the detrimental effect of some surgical interventions on cancer patients. Neoplastic progression is postulated to a obey a "stem cell conservation" principle which when violated is followed either by a stem cell replenishment or aggrevates the patient's conditions. This conservation law introduces a new definition of carcinogenesis: Any process reducing the "A" or "B" producing machinery is regarded as a carcinogen. A definition embracing, surgical extirpation of normal or neoplastic stem cells or cell destruction by irradiation, chemotherapy or chemical carcinogens.

The influence of embryonal bursectomy on benzpyrene-induced sarcoma of the chicken

160 chickens hormonally bursectomized before hatching, and 160 controls were twice given a dose of 10 mg 3,4-benzo(a)pyrene 2 weeks and 6 weeks after hatching. After 24 weeks the controls had developed muscle sarcomas at a significantly higher rate than the bursectomized animals (49.6--32.1%). The tumors were identified as malignant polymorphocellular rhabdomyosarcomas in light and electron microscopy. When the experiment was stopped after 27 weeks, the controls showed more tumors than the bursectomized chickens (65.1% versus 58.9%). The effect of bursectomy lies in a prolongation fo tumor latency. The frequency of metastases is equally decreased to a significant degree (41.7% versus 21.7%). These results are interpreted as an illustration of the disturbed equilibrium between the T and B cell responses.