Interactions in recovery and in residual injury from sequential treatments of mouse haemopoietic and stromal marrow cell populations, using X-rays, cyclophosphamide and busulphan

Genomic instability: potential contributions to tumour and normal tissue response, and second tumours, after radiotherapy

PURPOSE

Induced genomic instability generally refers to a type of damage which is transmissible down cell generations, and which results in a persistently enhanced frequency of de novo mutations, chromosomal abnormalities or lethality in a significant fraction of the descendant cell population. The potential contribution of induced genomic instability to tumour and normal tissue response, and second tumours, after radiotherapy, is explored.

RESULTS

The phenomenon of spontaneous genomic instability is well known in some rare genetic diseases (e.g. Gorlin's syndrome), and there is evidence in such cases that it can lead to a greater propensity for carcinogenesis (with shortened latency) which is enhanced after irradiation. It is unclear what role induced genomic instability plays in the response of normal individuals, but persistent chromosomal instability has been detected in vivo in lymphocytes and keratinocytes from irradiated normal individuals. Such induced genomic instability might play some role in tumour response in a subset of tumours with specific defects in damage response genes, but again its contribution to radiocurability in the majority of cancer patients is unclear. In normal tissues, genomic instability induced in wild-type cells leading to delayed cell death might contribute to more severe or prolonged early reactions as a consequence of increased cell loss, a longer time required for recovery, and greater residual injury. In tumours, induced genomic instability reflected in delayed reductions in clonogenic capacity might contribute to the radiosensitivity of primary tumours, and also to a lower incidence, longer latency and slower growth rate of recurrences and metastases.

CONCLUSIONS

The evidence which is reviewed shows that there is little information at present to support these propositions, but what exists is consistent with their expectations. Also, it is not yet clear to what extent mutations associated with genomic instability, particularly gene polymorphisms, or other low penetrant gene mutations, contribute to the recognized spectrum of normal tissue radiosensitivity amongst cancer patients, or in the general population. Tests for such genetic modifications may help in the search for more accurate prognostic markers of response, which hopefully could be used in addition to other strategies to further improve the outcome for cancer patients given radiotherapy.

Alternative testing systems for evaluating noncarcinogenic, hematologic toxicity

Hematopoietic tissues are the targets of numerous xenobiotics. Clinical hematotoxicity is either a decrease or an increase in peripheral blood cell counts in one or more cell lineages--a cytopenia or a cytosis, respectively--that carries a risk of an adverse clinical event. The purpose of in vitro hematotoxicology is the prediction of these adverse hematologic effects from the effects of the toxicants on human hematopoietic targets under controlled experimental conditions in the laboratory. Building on its important foundations in experimental hematology and the wealth of hematotoxicology data found in experimental oncology, this field of alternative toxicology has developed rapidly during the past decade. Although the colony-forming unit-granulocyte/monocyte neutrophil progenitor is most frequently evaluated, other defined progenitors and stem cells as well as cell types found in the marrow stroma can be evaluated in vitro. End points have been proposed for predicting toxicant exposure levels at the maximum tolerated dose and the no observable adverse effect level for the neutrophil lineage, and several clinical prediction models for neutropenia have developed to the point that they are ready for prospective evaluation and validation in both preclinical species and humans. Known predictive end points are the key to successful comparisons across species or across chemical structures when in vitro dose-response curves are nonparallel. Analytical chemistry support is critical for accurate interpretation of in vitro data and for relating the in vitro pharmacodynamics to the in vivo pharmacokinetics. In contrast to acute neutropenia, anemia and acute thrombocytopenia, as well as adverse effects from chronic toxicant exposure, are much more difficult to predict from in vitro data. Pharmacologic principles critical for clinical predictions from in vitro data very likely will apply to toxicities to other proliferative tissues, such as mucositis.

Ultrastructural changes of stromal cells of bone marrow and liver after cyclophosphamide treatment in mice

The direct effect of cyclophosphamide (CY) on bone marrow and liver stromal cells of DBA/2 and C57BL/6 mice after a single intraperitoneal dose of 300 mg/kg, was assessed. Ultrastructural observations were carried out 2,4,6,12,18, and 24 h and 2,3,5,7,10,15,22 and 30 days after CY in femoral bone marrow and liver fixed by immersion or vascular perfusion. A massive depletion of hemopoietic cells was observed in bone marrow as early as 12 h after CY treatment, and normality was recovered only after 10 days. Among stromal cells, sinus endothelial cells, reticular cells, and macrophages were particularly sensitive to CY and showed severe damage as soon as 2 h after treatment. There was also an important dilatation of sinusoids, and the presence of mature red cells in the hemopoietic parenchyma, and macrophages and immature cells in the lumen and in circulating blood demonstrated the loss of integrity of the endothelium. In the liver, injured cells showing vesiculation and disruption of endothelial and Kupffer cells of sinusoids were evident 6 h after CY. The alterations caused by CY were transient. Although recovery of the hemopoietic cells in bone marrow and liver was achieved by day 10, the stromal cells showed damage even 15 days after CY, and a return to normality was only reached on day 30. Thus, the effect of CY on stromal cells, that was longer lasting than the effect on the hemopoietic compartment, demonstrated a higher recovery capacity of hemopoiesis with respect to stromal cells. These results demonstrate that recovery of hemopoiesis occurred even while the severe damage inflicted by CY to the stromal cells remained unrepaired.

Radiation reaction recall following simvastatin therapy: a new observation

A 60-year-old woman was treated postoperatively for carcinoma of the gall bladder with a split course of radiotherapy. The tumour dose (TD) was 61.2 Gy in 34 fractions delivered by an anterior and two lateral wedge fields with 60Co; the Dmax was 70% of TD for the anterior field and 150% of the TD at the thin edge of the wedges. She also underwent 5-FU and leucovorin chemotherapy. No skin reaction was seen during radiotherapy or in 1 year of follow-up. A year after radiotherapy she was treated for hypercholesterolaemia by simvastatin. Within 2-3 days a severe skin and subcutaneous reaction developed in the lateral radiation fields but not in the anterior field. To our knowledge, recall of skin radiation reaction after simvastatin therapy has not been previously reported.