Regulation of apoptosis by C. elegans CED-9 in the absence of the C-terminal transmembrane domain.

Bcl-2 proteins regulate apoptosis in organisms as diverse as mammals and nematodes. These proteins are often localized at mitochondria by a C-terminal transmembrane domain. Although the transmembrane domain and mitochondrial localization are centrally involved in specific cases of vertebrate Bcl-2 activity, the significance of this localization is not clear for all species. Studying the Caenorhabditis elegans Bcl-2 homolog CED-9, we found that the transmembrane domain was both necessary and sufficient for localization at mitochondrial outer membranes. Furthermore, we found that in our assays, ced-9 transgenes lacking the transmembrane domain, although somewhat less active than equivalent transgenes derived from wild-type ced-9, rescued embryonic lethality of ced-9(lf) animals and responded properly to upstream signals in controlling the fate of Pn.aap neurons. Both of these apoptotic activities were retained in a construct where CED-9 lacking the transmembrane domain was targeted to the cytosolic surface of the endoplasmic reticulum and derived organelles, suggesting that in wild-type animals, accumulation at mitochondria is not essential for CED-9 to either inhibit or promote apoptosis in C. elegans. Taken together, these data are consistent with a multimodal character of CED-9 action, with an ability to regulate apoptosis through interactions in the cytosol coexisting with additional evolutionarily conserved role(s) at the membrane.

Suppression of spontaneous and hydrogen peroxide-induced mutagenesis by the antioxidant ascorbate in mismatch repair-deficient human colon cancer cells.

Genomic instability associated with deficiencies in mismatch repair (MMR) plays a critical role in tumorigenesis. Here we have investigated the contribution of oxidative damage to this instability in MMR-defective cells. Treatment with H(2)O(2) produced less cytotoxicity in MMR-deficient cells than in those proficient in MMR, supporting a role for MMR in the recognition and/or processing of oxidative damage. Additionally, growth of MMR-defective cells in the presence of the antioxidant ascorbate (500 microM) reduced the spontaneous mutation rate at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus by up to 50% and reduced microsatellite instability by 30%. Induction of HPRT mutants by exogenously added H(2)O(2) was also significantly suppressed by ascorbate. Collectively, these results suggest that (i) oxidative damage contributes significantly to the spontaneous mutator phenotype in MMR-defective cells, (ii) this damage may select for MMR-deficient cells due to their increased resistance to cell killing and (iii) dietary antioxidants may help to suppress the mutator phenotype and resulting carcinogenesis in individuals with compromised MMR.

Bcl-xL promotes the open configuration of the voltage-dependent anion channel and metabolite passage through the outer mitochondrial membrane.

The diffusion of metabolites across the outer mitochondrial membrane is essential for coupled cellular respiration. The outer membrane of mitochondria isolated from growth factor-deprived cells is impaired in its ability to exchange metabolic anions. When added to mitochondria, recombinant Bcl-x(L) restores metabolite exchange across the outer membrane without inducing the loss of cytochrome c from the intermembrane space. Restoration of outer membrane permeability to anionic metabolites does not occur directly through Bcl-x(L) ion channels. Instead, recombinant Bcl-x(L) maintains the outer mitochondrial membrane channel, VDAC, in an open configuration. Consistent with these findings, when ADP-induced oxidative phosphorylation is limited by exogenous beta-NADH, recombinant Bcl-x(L) can sustain outer mitochondrial membrane permeability to ADP. beta-NADH limits respiration by promoting the closed configuration of VDAC. Together these results demonstrate that following an apoptotic signal, Bcl-x(L) can maintain metabolite exchange across the outer mitochondrial membrane by inhibiting VDAC closure.

A polar, solvent-exposed residue can be essential for native protein structure.

BACKGROUND: A large energy gap between the native state and the non-native folded states is required for folding into a unique three-dimensional structure. The features that define this energy gap are not well understood, but can be addressed using de novo protein design. Previously, alpha(2)D, a dimeric four-helix bundle, was designed and shown to adopt a native-like conformation. The high-resolution solution structure revealed that this protein adopted a bisecting U motif. Glu7, a solvent-exposed residue that adopts many conformations in solution, might be involved in defining the unique three-dimensional structure of alpha(2)D. RESULTS: A variety of hydrophobic and polar residues were substituted for Glu7 and the dynamic and thermodynamic properties of the resulting proteins were characterized by analytical ultracentrifugation, circular dichroism spectroscopy, and nuclear magnetic resonance spectroscopy. The majority of substitutions at this solvent-exposed position had little affect on the ability to fold into a dimeric four-helix bundle. The ability to adopt a unique conformation, however, was profoundly modulated by the residue at this position despite the similar free energies of folding of each variant. CONCLUSIONS: Although Glu7 is not involved directly in stabilizing the native state of alpha(2)D, it is involved indirectly in specifying the observed fold by modulating the energy gap between the native state and the non-native folded states. These results provide experimental support for hypothetical models arising from lattice simulations of protein folding, and underscore the importance of polar interfacial residues in defining the native conformations of proteins.

Pubertal African-American girls expend less energy at rest and during physical activity than Caucasian girls.

Between 1963 and 1991, the most dramatic increases in the prevalence of overweight in the United States have been reported in African-American girls. Lower basal energy expenditure and lack of physical activity are believed to be risk factors for excessive weight gain. We hypothesized that energy expenditure at rest and during physical activity are lower in pubertal African-American girls than in Caucasian girls. Basal metabolic rate and sleeping energy expenditure of 40 Caucasian and 41 African-American pubertal girls (matched for age, physical characteristics, body fat, and energy intake) were measured by whole-room calorimetry, energy expended for physical activity by the doubly labeled water method, sexual maturity by physical examination, body composition by dual-energy x-ray absorptiometry, physical fitness by treadmill testing, and energy intake by 3-day food record. After adjusting for soft lean tissue mass, the basal energy expenditure (1333 +/- 132 vs. 1412 +/- 132 kcal/day, P = 0.01) and energy expended for physical activity (809 +/- 637 vs. 1271 +/- 162 kcal/day, P < 0.01) were significantly lower in the African-American girls than in the Caucasian girls. The differences remained the same after controlling for differences in sexual maturity and/or physical fitness. The lower energy expenditure of the pubertal African-American girls suggests that they are at a higher risk of becoming overweight than their Caucasian counterparts.

Chromosome aberrations in vitro related to cytotoxicity of nonmutagenic chemicals and metabolic poisons.

Chromosome aberrations can occur by secondary mechanism(s) associated with cytotoxicity, induced by chemicals that do not attack DNA. Aberrations are formed from DNA double-strand breaks, and DSBs are known to be induced by nonmutagenic (Ames test negative) noncarcinogens at toxic levels [Storer et al. (1996): Mutat Res 368:59-101]. Here, 8 of 12 of these chemicals caused aberrations in CHO cells at cytotoxic doses, and often only when cell counts (survival) at 20 hr approached < or =50% of controls. Five of eight noncarcinogens (2,4,-dichlorophenol, dithiocarb, menthol, phthalic anhydride, and ethionamide) and one of two equivocal carcinogens (bisphenol A) caused aberrations, usually over a narrow dose range with steeply increasing cytotoxicity. Phthalic anhydride and ethionamide were positive only at doses with precipitate. Phenformin was negative even at toxic doses and ephedrine and phenylephrine were negative and gave little toxicity. Aberrations were also induced by metabolic poisons, 2,4-dinitrophenol, (uncouples oxidative phosphorylation), and sodium iodoacetate, (Nal; blocks ATP production). Five of the chemicals that induced aberrations in CHO cells were tested in human TK6 cells and four were positive, the fifth being equivocal. Stable aberrations (translocations) were induced in human cells by Nal. Clearly, chemicals can give "false-positive" results in the chromosome aberration assay at cytotoxic levels, though cytotoxicity does not always produce aberrations, so that further information (e.g., DNA reactivity) is needed to determine whether a result is a "false-positive." Primary DNA-damaging chemicals such as alkylators are also cytotoxic, but give strong increases in aberrations without marked initial toxicity by the measures used here, although the aberrations they induce do reduce long-term survival in colony-forming assays.

Fewer chromosome aberrations and earlier apoptosis induced by DNA synthesis inhibitors, a topoisomerase II inhibitor or alkylating agents in human cells with normal compared with mutant p53.

The human lymphoblastoid cell lines TK6 (normal p53) and WI-L2-NS or WTK1 (mutant p53) differ in sensitivity to killing and induction of gene mutations and chromosome aberrations by ionizing radiation. This may be related to decreased apoptosis in the cells with mutated p53, such that more damaged cells survive. We compared the response of the two cell types to various chemicals. First, to ensure that the thymidine kinase deficiency does not increase the sensitivity of TK6 tk+/- cells to mutagens, we demonstrated that they were not hypersensitive to aberration induction by altered DNA precursor pools or DNA synthesis inhibition, by aphidicolin (APC), methotrexate, hydroxyurea (HU), cytosine arabinoside and thymidine. TK6 cells were then compared with WI-L2-NS or WTK1 cells. With APC, HU, methyl methanesulfonate (MMS), ethyl nitrosourea (ENU) and etoposide (etop), TK6 cells had more apoptosis in the first two days after treatment. Fewer aberrations were seen in normal p53 TK6 cells than the mutant p53 WI-L2-NS cells, ranging from very little difference between the two cell types with MMS to very large differences with ENU and etop. For MMS and ENU we followed cultures for several days, and found that WI-L2-NS cells underwent delayed apoptosis 3 to 5 days after treatment, in parallel with published observations with ionizing radiation. WI-L2-NS cells also had a delayed increase in aberrations (up to 5 days post-treatment) when no aberrations remained in TK6 cells. Colony forming efficiency was measured for APC, MMS and ENU, and was greater in the p53 mutant cells. Our results show that normal p53 function is required for rapid and efficient apoptosis in these lymphoblastoid cells with DNA synthesis inhibitors, alkylating agents and a topoisomerase II inhibitor, and support the hypothesis that induced levels of aberrations are higher in p53 mutant cells because of a failure to remove damaged cells by apoptosis.

Alpha-1 acid glycoprotein is an immunosuppressive factor found in ascites from ovaria carcinoma.

BACKGROUND: Although the ascites of patients with ovarian carcinoma has been reported to contain immunosuppressive factors, the identity and source of this activity has not been fully elucidated. The objective of this study was to describe the purification of a single immunosuppressive protein, alpha-1 acid glycoprotein, from ovarian carcinoma ascites, identify its site of production, and describe a possible mechanism by which it inhibits lymphocytes. METHODS: Ascites from proteins from five patients with epithelial ovarian carcinoma first were differentially precipitated by size with different concentrations of polyethylene glycol and then separated on the basis of isoelectric focusing. The protein factions then were placed in a lymphocyte proliferation assay to determine immunosuppressive activity. Western blot analysis was used to identify alpha-1 acid glycoprotein as an immunosuppressive protein in ascites. Total RNA was extracted from ovarian and hepatic cell lines as well as primary and recurrent ovarian tumor samples. Reverse-transcriptase polymerase chain reaction then was utilized to identify the site of production of this protein. Purified alpha-1 acid glycoprotein was placed in lymphocyte culture and its effects on lymphocyte interleukin-2 (IL-2) production were measured by enzyme-linked immunoadsorbent assay. RESULTS: Addition of purified alpha-1 acid glycoprotein to the lymphocyte assay resulted in a 60% decrease in lymphocyte proliferation (P < 0.05). Alpha-1 acid glycoprotein transcript was not identified in ovarian tumor cells. The addition of purified alpha-1 acid glycoprotein to the lymphocyte culture resulted in a 65% decrease in IL-2 secretion into the media (P < 0.05). CONCLUSIONS: Alpha-1 acid glycoprotein is an immunosuppressive protein purified from ovarian carcinoma ascites. It is not expressed primarily by ovarian carcinoma cells. It appears to inhibit IL-2 secretion by lymphocytes.

The in vitro effect on T cell function of soluble IL-2Ralpha from advanced ovarian cancer ascites.

Activated T cells not only secrete interleukin-2 (IL-2) and express cell surface interleukin 2 receptor alpha (IL-2R alpha), but also shed IL-2R alpha. This soluble receptor is a truncated form of the membrane-bound p55 receptor with a similar binding affinity. It has been proposed that soluble IL-2R alpha (sIL-2R alpha) could negatively modulate local immune response. High levels of sIL-2R alpha have been found in the serum and ascites of ovarian cancer patients. The purpose of this investigation is to determine the amount of in vitro T cell inhibition seen in ovarian cancer ascites that is attributable to high levels of sIL-2R alpha. Purified sIL-2R alpha at levels up to 100,000 pg/ml was placed in lymphocyte proliferation assays. Soluble IL-2R alpha was removed from the ascites of three patients with advanced ovarian cancer. Lymphocyte proliferation assays utilizing phytohemaglutin (PHA) stimulation were carried out with this ascites. Untreated ascites from each patient served as control. Addition of purified sIL-2R alpha to lymphocyte proliferation assays failed to demonstrate significant lymphocyte suppression. Addition of ascites to the lymphocyte assays resulted in up to an 80% decrease in lymphocyte proliferation. Neutralization of ascites sIL-2R alpha as well as removal of sIL-2R alpha via a protein G column failed to reverse any of the observed lymphocyte suppression. We conclude that although sIL2R alpha is elevated in ascites of patients with ovarian cancer, it does not account for the profound ascites-induced T cell suppression observed in vitro.

Thalidomide: lack of mutagenic activity across phyla and genetic endpoints.

The human and rabbit teratogen thalidomide has been tested for mutagenicity in a wide range of assays, ranging from bacterial gene mutation assays conducted in vitro to in vivo cytogenetic assays conducted using rabbits, and including a variety of human-derived tissues. Thalidomide was not mutagenic to 6 strains of Salmonella when tested both in the presence and absence of Aroclor-induced rat liver S9 mix. This inactivity was confirmed in strains TA98 and TA100 using a 1-h pre-incubation assay protocol with the same S9 mix (10% S9), and additionally, in strain TA98 using 3 concentrations of S9 (4%, 10% and 30% S9 in S9 mix). Thalidomide was not clastogenic either to cultured human lymphocytes (whole blood cultures, minus S9 mix) or to Chinese hamster ovary (CHO) cells treated in vitro. Further, no cytotoxicity was observed in purified human lymphocytes when exposed to thalidomide up to the limit of its solubility in the medium in the presence and absence of liver S9 from Aroclor-induced pregnant rabbit. The CHO assays were conducted without metabolic activation and in the presence of a variety of sources of auxiliary metabolic activation (PB/beta NP-induced rat liver S9 mix, pooled male and female human liver S9 mix, uninduced and Aroclor-induced pregnant rabbit liver S9 mix and foetal rabbit S9 mix). Thalidomide did not induce micronuclei in isolated human lymphocytes (minus S9 mix) and it was non-mutagenic to mouse lymphoma L5178Y TK+/- cells when tested to the limits of its solubility in the culture medium (+/- S9 mix). No indication of recombinogenic or clastogenic activity was observed for thalidomide when tested in Drosophila. In addition, it failed to induce chromosome aberrations in grasshopper neuroblasts when tested in the presence and absence of Aroclor-induced rat liver S9 mix. Some unusual chromosome morphologies were observed in the grasshopper cytogenetic preparations indicating a potential of thalidomide to interact with chromosomal proteins. However, this potential was not evident in the human lymphocyte micronucleus assay, and thalidomide was apparently not reactive to the proteins of the mouse skin, as it gave negative results in a mouse local lymph node assay for skin sensitizing agents. Thalidomide was inactive in bone marrow micronucleus assays conducted using males and females from two strains of mice, and female New Zealand white rabbits. It is concluded that thalidomide is neither a mutagen nor an aneugen. This conclusion is discussed within the context of the results of earlier mutagenicity studies, the recent claim that thalidomide may be a heritable germ cell mutagen to humans, and the current interest in thalidomide for the treatment of immune system-related diseases.

Electrical and mechanical characteristics of the atrium of the whelk Busycon canaliculatum.

1. The mean resting potential of 22 atrial preparations of Busycon heart was 42.5 mV, examined by the sucrose gap technique. Spontaneous action potentials of 8-18 mV amplitude occurred in repeated cycles of burst activity, generating burst patterned phasic contractile activity. 2. Isolated ventricles showed slow (1-3 beats min-1) constant myogenic contractile activity, suggesting that the primary driving pacemaker may reside in the atrium. 3. The atrial electrocardiogram commenced with a small prepotential leading to a plateau-like phase and terminated with a sharp spike potential. 4. Acetylcholine (ACh) at high concentrations depolarised the atrium by 5-8 mV and induced strong tonic contractures while suppressing spontaneous action potentials, suggesting an overall inhibitory role in downregulating cardiac intrinsic myogenic rhythms. 5. Serotonin (5-hydroxytryptamine, 5HT) was consistently excitatory, enhancing both action potential amplitude and rhythmic contractions by up to 50% at concentrations of 5 x 10(-7) to 10(-5)M. Neither methysergide nor metoclopramide affected atrial responses to 5HT and the 5HT1 antagonist metitipine simply increased action potential discharge in the rhythmic cycle. The vertebrate 5HT1-3 receptor classification is inappropriate to this molluscan preparation. 6. The atrium was very sensitive to the tetrapeptides FMRF- and FLRFamide, but the enhanced phasic contractions were not accompanied by alteration of resting potential or action potential amplitude, suggestive of neuromodulatory upregulation involving a secondary messenger. The related peptide SCP-B was without effect on the preparation, but GAPFLRFamide was excitatory, although much less so than FMRF- and FLRFamide. 7. Neither adenosine and ATP nor guanosine and GTP affected intrinsic atrial electrical or mechanical activity, suggesting that there was no noncholinergic, nonaminergic element to cardiac neuromodulation in this species. Only ACh, 5HT and FMRF/FLRFamide could be assigned clear roles in this respect.

Modulatory mechanisms in the isolated internally perfused ventricle of the whelk Busycon canaliculatum.

1. Isolated cannulated ventricles commenced spontaneous beating on application of perfusion pressure of 10 cm water. Complete hearts showed a fast patterned cyclical rhythm, whereas ventricles devoid of atrial material showed a continuous slow rhythm. 2. Perfused ventricles were inhibited by ACh with a threshold at 10(-8) mol l-1 and arrested at 10(-7) mol l-1, and ventricles under stimulation by 5HT could be arrested by ACh at this concentration. 3. Perfused ventricles were stimulated by 5HT, with threshold at 10(-9) mol l-1 and maximum at 10(-5) mol l-1. Metoclopramide was without affect on 5HT responses, but metitipine and methysergide did inhibit such responses suggesting that the 5HT receptor present possessed mixed properties of the vertebrate 5-HT1 and 5-HT2 receptor subtypes. 4. Ventricles were very sensitive to the excitatory actions of FMRFamide in the 10(-9) to 10(-5) mol l-1 range. Preparations were insensitive to GAPFLRFamide, but SCP-B was modestly excitatory (threshold 10(-7) mol l-1). 5. Preparations were not significantly affected by adenosine, ATP, and guanosine, but GTP was strongly excitatory at 10(-7) mol l-1. 6. 5HT and FMRFamide responses were additive. Preparations responded strongly to the adenylate cyclase activator forskolin and dibutyryl cAMP enhanced spontaneous contractions and 5HT responses, suggesting that the 5HT receptor may operate via a cAMP secondary mechanism. 7. The IP3 inhibitor lithium (10 mmol l-1), caused slight inhibition of FMRFamide responses, suggesting that the receptor to this peptide may operate via IP3 as a second messenger. 8. Neuromodulation in this preparation would appear to involve ACh as inhibitor, 5HT and FMRFamide as upregulators, with no clear roles for FMRFamide-related peptides and GTP.

Effect of the antiglucocorticoid RU486 on adrenal steroidogenic enzyme activity and steroidogenesis.

RU486, a synthetic steroid receptor antagonist, has strong antiprogesterone and antiglucocorticoid properties. Chronic RU486 administration in two patients with ectopic secretion of adrenocorticotropin (ACTH) has been associated with decreasing plasma cortisol concentrations. One explanation of this finding is that RU486 may directly inhibit adrenal steroidogenesis. To test this hypothesis, we measured the effect of RU486 on specific steroidogenic enzymatic steps using an in vivo rat and an in vitro monkey model. Hypophysectomized-castrated-ACTH-replaced Sprague-Dawley rats were given RU486 i.p. at daily doses of 0, 0.0005, 0.005, 0.05, 0.5 and 5 mg/kg body weight per day for 7 days. The animals were sacrificed, and blood and adrenal glands collected. Adrenal cortical mitochondria and microsomes were purified from the rats and from two untreated Cynomolgus macaque monkeys. Specific steroidogenic enzyme activities were measured in the rat by the incorporation of 14C-labeled steroid substrates into products. A similar protocol was used to assay the steroidogenesis in the monkey adrenal fractions in the presence and absence of added RU486. Although rat adrenal weights decreased significantly at the highest RU486 dose, plasma levels of corticosterone were similar in control and treated rats. Rat adrenal 3 beta-hydroxysteroid dehydrogenase/isomerase (3-HSD), 21-hydroxylase (21-OH) and 11-hydroxylase (11-OH) activities decreased with increasing RU486 doses, with 21-OH and 11-OH being most severely affected. Monkey adrenal 3-HSD, 21-OH, 11-OH, 17-hydroxylase and 17,20-desmolase similarly decreased in the presence of increasing in vitro concentrations of RU486.(ABSTRACT TRUNCATED AT 250 WORDS)

Selection of low frequency tumor cells from cell culture by growth in nude mice.

Tissue cultures of tumor cells are frequently utilized to characterize chromosomal changes when direct cytogenetic preparations on tumors fail. The present study demonstrates that chromosomal markers found in direct tumor preparations can become undetectable in cell culture at variable rates presumably because of overgrowth of normal cell components in the culture. Injection of cultured tumor cells into nude mice followed by direct chromosomal preparations on the resulting nude mouse tumors can be used to select cells with the original tumor karyotype. This is true even when the tumor cell frequency in the culture is so low that they are not found in routine chromosomal preparations of the cultured cells. This technique can thus complement tissue culture findings and provide additional useful information about the original karyotype in cases where direct chromosomal preparations from tumors have failed.

Medical uncertainty and the autopsy: occult benefits for students.

The autopsy has been of great importance in educating students regarding medical uncertainty. The marked decline in the use of the autopsy in medical education and continuing education has contributed significantly to the current discomfort among physicians regarding medical uncertainty and medical errors, which, in turn, has furthered the decline of the autopsy. Inordinate guilt, denial, and other defensive behaviors that many physicians marshall in response to uncertainty and error prevent these individuals from learning from their mistakes. The autopsy experience during medical school, properly utilized, helps students to confront fallibility and sets the stage for later successful management of uncertainty and error.

The current status of the autopsy in academic medical centers in the United States.

As viewed by pathology chairmen, the primary reasons for the decline in interest in the autopsy are: (1) a feeling among physicians that everything is known about the case; (2) poor education of medical students and clinical house staff concerning the importance of the autopsy, which carries over to the practitioner; and (3) lack of interest on the part of pathologists. Negative attitudes on the part of clinicians were seen as the primary factor that serves to inhibit enthusiasm for the autopsy on the part of pathology house staff. Lack of prompt and appropriate communication with the attending physician and uneven quality of prosectors are seen as major inhibitors to successful autopsy services. Chairmen of departments of pathology support an approximate doubling of the autopsy rate in their institutions (from 30% to 64%), although 42.5% of chairmen had not discussed their wishes concerning autopsy with the next of kin and only 42% regularly attend gross conference. These perceptions are remarkably similar to those provided by chairmen of departments of medicine and surgery as a part of a previous survey. On the basis of these inputs, several recommendations designed to improve the local emphasis on the autopsy service are provided.

The sensitivity and specificity of clinical diagnostics during five decades. Toward an understanding of necessary fallibility.

Published studies encompassing more than 50,000 autopsies were assessed to determine the sensitivity and specificity of clinical diagnostics (the diagnostic process) in persons dying of 1 of 11 specific diseases during the period 1930 through 1977. The accuracy of clinical diagnostics, as reflected in these two determinations, appeared to improve over this period with respect to some of the diseases studied (rheumatic heart disease and leukemia), while for others it worsened (pulmonary tuberculosis, peritonitis, carcinoma of the lung, gastric carcinoma, and carcinoma of the liver and extrahepatic biliary tract) and for a significant number diagnostic accuracy seemed refractory to sustained change (pulmonary embolism, primary cirrhosis of the liver, gastric/peptic ulcer, and acute coronary thrombosis/myocardial infarction). The findings suggest a new way in which the autopsy can be used to monitor clinical diagnostics to identify possible sources of systematic weaknesses and provide data that can be used to approach the difficult subject of necessary fallibility.

Acute and long-term cytogenetic effects of treatment in childhood cancer: sister-chromatid exchanges and chromosome aberrations.

The incidence of chromosomal aberrations in banded karyotypes and of sister-chromatid exchanges (SCEs) was determined in the lymphocytes of survivors of childhood cancer as 2 parameters which are pertinent in assessing the genetic damage induced by chemotherapy. The proportion of cells with chromosome breakage or structural rearrangement-type aberration was 1 cell in 67 in a control group of 8 untreated cancer patients and 2 parents of cancer patients, 1 cell in 8 in 12 patients currently on therapy, and 1 cell in 50 in 17 patients sampled 6 months to 35 years post-treatment. The range of mean SCE levels per cell was 4.5-6.5 in the untreated cancer patients, 4.0-9.6 in non-cancer controls, 3.3-33.7 in patients on therapy, and 4.6-9.7 in post-therapy survivors. Considerably variability was observed between individuals with both SCE and breakage assays but therapy-induced increases in SCEs were not necessarily correlated with increased levels of aberrations arising from chromosomal breakage.