Dose-response effects of radiation on the permeability of endothelial cells in culture

Increased permeability is an early and universal response of the vasculature to radiation injury, yet the biological basis of this reaction is poorly understood. The present study determined the time course and the dose-response relationship of radiation-induced hyperpermeability in cultured bovine pulmonary artery endothelial (BPAE) cells. BPAE cells were grown to a confluent monolayer on microcarrier beads, and column chromatography methods were used to evaluate permeability to two low molecular weight compounds: sodium fluorescein (NaFlsc, mol. wt. = 342) and cyanocobalamin (B12, mol. wt. = 1355). This is a novel in vitro model to study mechanisms and modifiers of radiation-induced permeability of endothelial cells under flow conditions using nonradioactive tracers. Cell-covered beads were exposed to a single dose of 10 Gy Of 137Cs gamma rays and placed in the column, and permeability was measured every 30 min for 3 h. There was a time-dependent increase in permeability to both tracers, reaching significance by 2 h. Increased permeability was accompanied by perturbations in F-actin distribution in the BPAE cells as determined by rhodamine-phalloidin fluorescence microscopy. Neither catalase nor captopril ameliorated this hyperpermeability, but dibutyryl cAMP partially prevented it. At 3 h after 0, 1, 2, 5 and 10 Gy irradiation, permeability values of 11.8 +/- 2.1, 13.9 +/- 2.2, 20.9 +/- 3.6, 24.8 +/- 2.8 and 27.2 +/- 3.3 (10(-5) cm/s, +/- SEM), respectively, were observed using NaFlsc. The increase was significant (P < 0.05) at 2 Gy or higher. Permeability to B12 was significantly elevated after 5 or 10 Gy. These results suggest that permeability of endothelial cells to low molecular weight solutes increases within 3 h after therapeutic doses of radiation, and that cAMP ameliorates this response.

Evidence that two latency-associated transcripts of herpes simplex virus type 1 are nonlinear

The latency-associated transcripts (LATs) of herpes simplex virus type 1 (HSV-1) are the only viral gene products that accumulate to abundant levels in latently infected cells. Others have reported species of 2.0, 1.50, and 1.45 kb; only the 2.0-kb species is seen in productively infected cells, and there is evidence that it behaves as an intron. We examined the LATs both in trigeminal ganglia of latently infected mice and in productively infected cultures of monkey CV-1 cells. After glyoxalation, RNA was subjected to high-resolution agarose gel electrophoresis and Northern (RNA) analysis, a procedure capable of resolving linear and nonlinear RNA species. Under these conditions, we resolved the 2.0-kb LAT into two species; the slower species was much more abundant and had a mobility significantly slower than expected for a linear RNA. To test the hypothesis that this RNA was in fact nonlinear, we used partial hydrolysis by sodium carbonate and oligonucleotide-directed RNase H digestion. These procedures changed the mobility of the slower species into that of the faster species. Similarly, the mobility of the 1.50-kb LAT, which was much more abundant than the 1.45-kb LAT, was changed by these procedures to that of the 1.45-kb LAT. Our data show that the two major LAT species are nonlinear, and they support an interpretation of stable lariat structures.

Structural requirements for G(o) activation by receptor-derived peptides: activation and modulation domains of the alpha 2-adrenergic receptor i3c region

Synthetic peptides are important tools for understanding the sites and mechanisms of receptor/G protein interactions. We examined the structural determinants of receptor-fragment peptides for G protein binding and activation. A dimer of peptides from the carboxyl-terminal (i3c) and amino-terminal (i3n) regions of the alpha 2A-adrenergic receptor is most potent in stimulating guanine-nucleotide exchange of any peptides studied. Stimulation of GTPase by i3n is partially blocked by pertussis toxin treatment, whereas stimulation by i3c is not, which is consistent with action of i3c at the amino terminus of Gi. Both peptides inhibit adenylyl cyclase in Chinese hamster ovary cell membranes, but only the i3c effect is consistent with a pure Gi stimulation. We also examined the mechanism and defined a minimal structural subset of i3c required for G protein activation. Residues 361-365 from the receptor were essential for GTPase stimulation, whereas determinants in the region 368-373 modulated that activity. A specific role for arginines is defined beyond just their positive charge. Complex effects of modifications of Thr373 suggest a regulatory or conformational role of that residue in the previously defined constitutive activation of the alpha 2-adrenergic receptor [J. Biol. Chem. 268:16483-16487 (1993)]. Thus, our data plus recent mutagenesis results support a role for hydrophobicity in the i3n region and a positively charged/arginine-rich region approximately 15-20 residues from the sixth transmembrane span in G protein activation. In contrast, the immediate perimembrane region of i3c seems to have largely conformational effects in producing constitutive activation of the receptors.

Randomized clinical trial on accelerated 7 days per week fractionation in radiotherapy for head and neck cancer. Preliminary report on acute toxicity

PURPOSE

Toxicity of an accelerated 7 days per week fractionation schedule (arm A) was evaluated and compared with a conventional 5 days per week treatment (arm B) in a randomized trial.

MATERIALS AND METHODS

Forty-four patients with squamous cell carcinoma of the head and neck in stage T2-4Nzero-1Mzero were included in the study. Total dose and dose per fraction of 2.0 Gy given once-a-day at 24 h intervals were the same in both arms of the trial. The only difference was the overall treatment time being 5 weeks in arm A and 7 weeks in arm B.

RESULTS

Analysis of severe mucosal reactions shows significant difference between arm A and B, with regard to both maximum score and duration of severe mucositis. Confluent mucositis (score > 15 according to the Dische system) lasting longer than 3 weeks developed in 48% of patients in arm A and only in 5% in arm B. In group A seven (30%) late effects (osteo- and soft tissue necrosis) occurred during 7-12 month follow-up with two reactions (10%) in group B being suspected as late effects. There was significant association between acute reactions and late effects in arm A, suggesting that the late effects are consequential.

CONCLUSION

The high incidence of severe acute reactions and consequential late effects suggests that the accelerated treatment in arm A (using daily fractions of 2.0 Gy, 7 days per week) gives unacceptable toxicity.

Replacing time since human immunodeficiency virus infection by marker values in predicting residual time to acquired immunodeficiency syndrome diagnosis. Multicenter AIDS Cohort Study

It is widely assumed that the time since human immunodeficiency virus (HIV) infection is an important indicator of HIV disease stage, yet for most infected individuals the date of infection is unknown. We consider whether marker values, such as CD4 lymphocyte number or percent and levels of serum beta2 microglobulin or serum neopterin, render time since infection unimportant for predicting the residual time to acquired immunodeficiency syndrome (AIDS) diagnosis. The Multicenter AIDS Cohort Study (MACS) contains a subsample of homosexual men whose date of HIV seroconversion is known within +/-6 months and who provide data for this analysis. From this subsample, we extract two overlapping data subsets. The first subset consists of 370 persons whose 3,723 study visits include complete data on the cellular markers CD4 lymphocyte number and percent for a period of 9 years. The second consists of 272 persons whose 1,593 visits include complete information on cellular markers and on the serological markers beta2-microglobulin and neopterin for a period of 5 1/2 years. We model the residual time to AIDS diagnosis with a regression model, in which cellular and serologic markers are the explanatory covariates (independent variables) and the residual time to AIDS is the responses variable (dependent variable). A robust estimate of the variance-covariance matrix corrects for the dependence of repeated measurements in the same individual. In the case of CD4 number and percent, the results indicate that time since infection is of none or at most little importance if the marker value is known, suggesting that time since infection can be adequately replaced by the combination of marker values. However, the serological markers alone do not eliminate the importance of the time since infection.

Evidence for two patterns of inheritance of sensitivity to induction of lung fibrosis in mice by radiation, one of which involves two genes

We showed previously that autosomal recessive determinants control the development of pulmonary fibrosis in mice during the early and late phases after irradiation. The extent of fibrosis was inversely correlated with the intrinsic lung activity of both plasminogen activator (PLA) and angiotensin-converting enzyme (ACE). To test these observations further, two groups of mice were given a dose of 15 Gy to the thorax: offspring of a backcross between C57L/J ("fibrosing mice") and the F1 of CBA/J ("non-fibrosing in the early phase") x C57L/J, and additional F1 individuals of CBA/J x C57L/J. Mice were euthanized upon developing a substantial respiratory deficiency (50% reduction in carbon monoxide uptake) during the early phase (14-25 weeks postirradiation). Seventeen mice from the backcross were heavily fibrosed, 38 were classed as intermediate, and 15 contained no fibrosis. No evidence of sex linkage was seen. These data strongly support our earlier conclusions and suggest that two autosomal genes which function additively determine the extent of the principal type of fibrosis in these strains. As no indication of a bimodal distribution of lung PLA or ACE activity was obtained, it is unlikely that one of the genes controls the level of either enzyme. The F1 mice unexpectedly showed small amounts of an unusual type of fibrosis which was not associated with hyaline material or fibrin deposits, in contrast to all previous reports of fibrosis during the early phase in mice. Similar, fibrin-free fibrosis was found during the early phase in mast cell-deficient WBB6F1/J mice (and their normal siblings). In the F1 mice this unusual fibrosis appears to be regulated independently by two additional genes, one of which is sex-linked.

Expression of a novel human apolipoprotein (apoC-IV) causes hypertriglyceridemia in transgenic mice

The human apolipoprotein (apo) C-IV gene has been recently identified: it is closely linked to the promoter region of the apoC-II gene (Allan, C.M., D. Walker, J. Segrest, and J. M. Taylor. 1995. Genomics. 28: 291-300). To determine the effect of apoC-IV gene expression on lipoprotein metabolism, transgenic mice were generated using a human apoC-IV cDNA construct. Human apoC-IV was found associated with plasma lipoproteins (d < 1.21 g/ml), mainly in very low density lipoproteins (VLDL), and higher molecular mass isoforms were present, due to N-linked glycosylation and variable sialylation of apoC-IV. Human apoC-IV transgenic mice were hypertriglyceridemic compared to nontransgenic controls; the accumulated plasma triglycerides were present mainly in VLDL. There was little change in plasma cholesterol levels, although apoC-IV expression redistributed cholesterol to VLDL and larger particles in low density lipoprotein/large high density lipoprotein fractions. By immunoblot analysis, apoC-IV was not detected in normal adult human plasma or isolated plasma lipoproteins, a finding consistent with our previous observation of very low levels of human apoC-IV mRNA in human liver. However, our analysis of transgenic mice provides unequivocal evidence that human apoC-IV is a lipid-binding protein belonging to the apolipoprotein family and that it has the potential to alter lipoprotein metabolism.

An SH3 domain-containing GTPase-activating protein for Rho and Cdc42 associates with focal adhesion kinase

The integrin family of cell surface receptors mediates cell adhesion to components of the extracellular matrix (ECM). Integrin engagement with the ECM initiates signaling cascades that regulate the organization of the actin-cytoskeleton and changes in gene expression. The Rho subfamily of Ras-related low-molecular-weight GTP-binding proteins and several protein tyrosine kinases have been implicated in mediating various aspects of integrin-dependent alterations in cell homeostasis. Focal adhesion kinase (FAK or pp125FAK) is one of the tyrosine kinases predicted to be a critical component of integrin signaling. To elucidate the mechanisms by which FAK participates in integrin-mediated signaling, we have used expression cloning to identify cDNAs that encode potential FAK-binding proteins. We report here the identification of a cDNA that encodes a new member of the GTPase-activating protein (GAP) family of GTPase regulators. This GAP, termed Graf (for GTPase regulator associated with FAK), binds to the C-terminal domain of FAK in an SH3 domain-dependent manner and preferentially stimulates the GTPase activity of the GTP-binding proteins RhoA and Cdc42. Subcellular localization studies using Graf-transfected chicken embryo cells indicates that Graf colocalizes with actin stress fibers, cortical actin structures, and focal adhesions. Graf mRNA is expressed in a variety of avian tissues and is particularly abundant in embryonic brain and liver. Graf represents the first example of a regulator of the Rho family of small GTP-binding proteins that exhibits binding to a protein tyrosine kinase. We suggest that Graf may function to mediate cross talk between the tyrosine kinases such as FAK and the Rho family GTPase that control steps in integrin-initiated signaling events.

A novel form of hepatitis delta antigen

Hepatitis delta virus (HDV) is known to express a protein termed the small delta antigen, a structural protein which is also essential for genome replication. During replication, posttranscriptional RNA editing specifically modifies some of the HDV RNA, leading to the production of an elongated form of the delta antigen, the large form, which is essential for virus assembly. The present study showed that yet another form of HDV protein is expressed during genome replication. This novel form is not produced in all infected cells, but it arises during replication in transfected cells and in infected woodchucks, and as was previously reported, patients infected with HDV do make antibodies directed against it. These findings are an indicator of the complexity of gene expression during HDV infection and replication.

Normal range estimation for repeated immunologic measures

A method for estimating a normal range from a set of immunologic measurements on control subjects when there may be more than one observation per subject is described. The method is nonparametric, makes efficient use of all observations, and is very simple to apply. It is illustrated on a set of 152 CD38 measurements from 58 healthy men.

Receptor and membrane interaction sites on Gbeta. A receptor-derived peptide binds to the carboxyl terminus

The functional organization of Gbetagamma is poorly understood. Regions of bovine brain Gbetagamma that interact with a photoaffinity derivative of an alpha2-adrenergic receptor-derived peptide from the third intracellular loop (diazopyruvoyl-modified peptide Q (DAP-Q)) and a hydrophobic membrane probe (3-trifluoromethyl-3-(m-iodophenyl)diazirine (TID)) were examined. We previously showed that DAP-Q cross-links to specific, competable sites on both the alpha and beta subunits of Go/Gi but not on the gamma subunit and that betagamma subunit was required for stimulation of Go/Gi GTPase activity (Taylor, J. M., Jacob Mosier, G. G., Lawton, R. G., Remmers, A. E., and Neubig, R. R. (1994) J. Biol. Chem. 269, 27618-27624). Similarly, we show here that the membrane-associated photoprobe [125I]TID labels alpha and beta but not gamma. We have now mapped the sites of incorporation of DAP-Q and TID into the beta subunit. TID labels both the 14-kDa amino-terminal and the 23-kDa carboxyl-terminal fragments from a partial tryptic digest of beta while DAP-Q labels only the carboxyl-terminal fragment. Further mapping with endopeptidase Lys C reveals substantial labeling of multiple fragments by TID while DAP-Q labels predominantly a approximately 6-kDa fragment within the carboxyl-terminal 60 amino acids of beta1. Thus, regions within the 7th (or possibly 6th) WD-40 repeat of the beta subunit of G protein interact with the receptor-derived peptide while membrane interaction involves multiple sites throughout the beta subunit.

Models for residual time to AIDS

The distributions of the time from Human Immunodeficiency Virus (HIV) infection to the onset of Acquired Immune Deficiency Syndrome (AIDS) and of the residual time to AIDS diagnosis are important for modeling the growth of the AIDS epidemic and for predicting onset of the disease in an individual. Markers such as CD4 counts carry valuable information about disease progression and therefore about the two survival distributions. Building on the framework set out by Jewell and Kalbfleisch (1992), we study these two survival distributions based on stochastic models for the marker process (X(t)) and a marker-dependent hazard (h(.)). We examine various plausible CD4 marker processes and marker-dependent hazard functions for AIDS proposed in recent literature. For a random effects plus Brownian motion marker process X(t) = (a + bt + BM(t))4, where a has a normal distribution, b < 0 is an unknown parameter and BM(t) is Brownian motion, and marker-dependent hazard h(X(t)), we prove that, given CD4 cell count X(t), the residual time to AIDS distribution does not depend on the time since infection t. Using simulation and numerical integration, we find the marginal incubation period distribution, the marginal hazard and the residual time distribution for several combinations of marker processes and marker-dependent hazards. An example using data from the Multicenter AIDS Cohort Study is given. A simple regression model relating the cube root of residual time to AIDS to CD4 count is suggested.

Injury-specific cytotoxic response of tumor cells and endothelial cells

Cytotoxicity indicated by increased release of prelabeled 51chromium (51Cr) and lactate dehydrogenase (LDH) was studied in human prostate cancer and melanoma cells in cell culture following irradiation or exposure to several injurious substances. These changes were compared to those observed in bovine aortic endothelial cells (BAEC) subjected to identical treatments. Further, the effect of irradiation on plasminogen activator (PA) secretion from prostate cancer cells, and the effect of glycine on radiation-induced cytotoxicity in BAEC were also investigated. Radiation, lipopolysaccharide and xanthine/xanthine oxidase stimulated no release of 51Cr or LDH from tumor cells, while these treatments induced a dose- and time-related loss of those cytotoxic indicators from BAEC. Protease, elastase and Triton X-100 incited loss of 51Cr and LDH from all three cell types. Radiation, lipopolysaccharide and xanthine/xanthine oxidase have been shown to cause cell injury via a common pathogenic pathway of oxidant generation. Tumor cells appear quite resistant to oxidant stress. Cell damage precipitated by protease, elastase and Triton probably involves hydrolysis of proteins and phospholipids in the cell membrane, leading to an increased leakage of intracellular proteins such as LDH and those bound with 51Cr. Radiation caused a dose- and time-related reduction in the secretion of PA from prostate cancer cells. PA is alleged to play a role in tumor metastasis; the reduced secretion could be another beneficial effect of radiation, in addition to interruption of cell proliferation, in the impediment of tumor growth and spread. Glycine diminished cytotoxic injury of BAEC inflicted by radiation. This amino acid may prove useful in offering a degree of protection of normal tissue against radiation associated side-effects.

The effect of interleukin-1 beta or transforming growth factor-beta on radiation-impaired murine skin wound healing

The ability of exogenous interleukin-1 beta (IL-1 beta) or transforming growth factor-beta (TGF-beta) to reverse radiation-induced defective wound healing was investigated. Mice were irradiated with 8.5 or 11 Gy to total body (TB), 12 or 16 Gy to hemibody (HB), or 20 or 26 Gy to skin alone immediately prior to surgical wounding in order to determine the effect of hematopoietic system depletion on cytokine action. A single dose of IL-1 beta or TGF-beta or vehicle control was applied to each wound. All radiation doses and types resulted in a deficit in wound healing when measured on Days 11 and 14. IL-1 beta enhanced wound tensile strength (WTS) in TB-irradiated mice, while TGF-beta enhanced WTS in HB-irradiated mice. Neither cytokine was effective at enhancing WTS in unirradiated or skin-only irradiated animals. In addition IL-1 beta and TGF-beta showed distinct differences in their effects on the kinetics of healing with time after wounding. The effects of TGF-beta appeared to be transient with compromise of the gain in WTS. The differences in the effects of these two cytokines in affecting wound healing reflect their involvement in different cellular events in the wound healing process.

Evolutionary duplication of a hepatic control region in the human apolipoprotein E gene locus. Identification of a second region that confers high level and liver-specific expression of the human apolipoprotein E gene in transgenic mice

We have identified a second hepatic control region (HCR-2) in the human apolipoprotein (apo) E gene locus that confers liver expression of the human apoE gene in transgenic mice. This HCR-2 sequence is located 27 kilobases downstream of the apoE gene and 10 kilobases downstream of the previously described liver-specific enhancer (HCR-1). Nucleotide sequence analysis of the HCR-2 region revealed a sequence that shares 85% identity to the functional 319-base pair domain of HCR-1. To test its activity, transgenic mice were prepared with a fusion construct containing a human apoE gene fragment, which is not normally expressed in the liver, ligated to a 632-base pair region containing the HCR-2 sequence. This construct resulted in high levels of liver-specific apoE transgene expression, indicating that HCR-2 can function as a hepatic enhancer and has an activity similar to that of HCR-1. Hence, these findings suggest that there are at least two hepatic control regions, HCR-1 and HCR-2, capable of controlling the liver expression of this human apolipoprotein gene locus.

Hepatitis delta virus mutant: effect on RNA editing

During the replication cycle of hepatitis delta virus (HDV), RNA editing occurs at position 1012 on the 1679-nucleotide RNA genome. This changes an A to G in the amber termination codon, UAG, of the small form of the delta antigen (delta Ag). The resultant UGG codon, tryptophan, allows the translation of a larger form of the delta Ag with a 19-amino-acid C-terminal extension. Using HDV cDNA-transfected cells, we examined the editing potential of HDV RNA mutated from G to A at 1011 on the antigenome, adjacent to normal editing site at 1012. Four procedures were used to study not only the editing of the A at 1012, but also that of the new A at 1011: (i) nucleotide sequencing, (ii) a PCR-based RNA-editing assay, (iii) immunoblot assays, and (iv) immunofluorescence. Five findings are reported. (i) Even after the mutation at 1011, editing still occurred at 1012. (ii) Site 1011 itself now acted as a novel RNA-editing site. (iii) Sites 1011 and 1012 were edited independently. (iv) At later times, both sites became edited, thereby allowing the synthesis of the large form of the delta Ag (delta Ag-L). (v) Via immunofluorescence, such double editing became apparent as a stochastic event, in that groups of cells arose in which the changes had taken place. Evaluation of these findings and of those from previous studies of the stability of the HDV genomic sequence (H.J. Netter et al., J. Virol. 69:1687-1692, 1995) supports both the recent reevaluation of HDV RNA editing as occurring on antigenomic RNA (Casey and Gerin, personal communication) and the interpretation that editing occurs via the RNA-modifying enzyme known as DRADA.

Macrophage-specific expression of human apolipoprotein E reduces atherosclerosis in hypercholesterolemic apolipoprotein E-null mice

apoE deficiency causes hyperlipidemia and premature atherosclerosis. To determine if macrophage-specific expression of apoE would decrease the extent of atherosclerosis, we expressed human apoE in macrophages of apoE-null mice (apoE-/-) and assessed the effect on lipid accumulation in cells of the arterial wall. Macrophage-specific expression of human apoE in normal mice was obtained by use of the visna virus LTR. These animals were bred with apoE-/- mice to produce animals hemizygous for expression of human apoE in macrophages in the absence of murine apoE (apoE-/-,hTgE+/0). Low levels of human apoE mRNA were present in liver and spleen and high levels in lung and peritoneal macrophages. Human apoE was secreted by peritoneal macrophages and was detected in Kupffer cells of the liver. Human apoE in the plasma of apoE-/-,hTgE+/0 mice (n = 30) was inversely correlated (P < 0.005) with the plasma cholesterol concentration. After 15 wk on a normal chow diet, atherosclerosis was assessed in apoE-/-,hTgE+/0 animals and in apoE-/-,hTgE0/0 littermates matched for plasma cholesterol level (approximately 450 mg/dl) and lipoprotein profile. There was significantly less atherosclerosis in both the aortic sinus and in the proximal aorta (P < 0.0001) in the animals expressing the human apoE transgene. In apo-E-/-,hTgE+/0 animals, which had detectable atherosclerotic lesions, human apoE was detected in the secretory apparatus of macrophage-derived foam cells in the arterial wall. The data demonstrate that expression of apoE by macrophages is antiatherogenic even in the presence of high levels of atherogenic lipoproteins. The data suggest that apoE prevents atherosclerosis by promoting cholesterol efflux from cells of the arterial wall.

Overexpression of human apolipoprotein B-100 in transgenic rabbits results in increased levels of LDL and decreased levels of HDL

In this study, and 80-kb human genomic DNA fragment spanning the human apoB gene was used to generate transgenic New Zealand White rabbits that expressed human apoB-100. The concentration of human apoB in the plasma of the transgenic rabbits ranged between 5 and 100 mg/dL. The transgenic rabbits had nearly threefold elevations in the plasma levels of triglycerides and cholesterol compared with nontransgenic controls. Nearly all the cholesterol and human apoB in the plasma was in the LDL fraction. Pronounced triglyceride enrichment of the LDL fraction was a striking feature of human apoB overexpression in the transgenic rabbits, in which the LDL fraction contained more than 75% of the plasma triglycerides. The triglyceride-enriched LDL particles were smaller and more dense than the native rabbit LDL and contained markedly increased amounts of apoE and apoC-III. In the nontransgenic control animals most of the triglycerides were in the VLDL, and most of the apoE and apoC-III were in the VLDL and HDL fractions. In addition to increased LDL levels, overexpression of human apoB in rabbits resulted in lower plasma levels of HDL cholesterol and apoA-I. In our prior studies on transgenic mice expressing human apoB, we documented triglyceride-rich LDL and reduced levels of HDL cholesterol. These prior findings in mice, together with the present findings in transgenic rabbits, suggest that triglyceride-rich LDL and lowered levels of HDL cholesterol may be hallmark features of apoB overexpression.

Local control of carcinoma of the tonsil by radiation therapy: an analysis of patterns of fractionation in nine institutions

PURPOSE

To investigate the importance to outcome of treatment for squamous cell carcinomas of the tonsillar fossa, of dose per fraction, overall treatment duration, and total dose.

METHODS AND MATERIALS

A collaborative retrospective study was undertaken in nine centers that used widely different dose-fractionation patterns for external beam radiation therapy.

RESULTS

There were 676 eligible cases treated only with photon beams during the years 1976-1985. The probability of local control (of the tonsillar fossa primary) was influenced by both T-stage and N-stage. Significant treatment parameters were total dose and overall treatment duration, but not dose per fraction. Over the range of about 40 to 90% and for a constant overall treatment duration, local tumor control probability increased by nearly 2% for each 1 Gy increase in total dose. For a constant total dose there was a decrease in the probability of local control associated with prolongation of overall treatment duration, presumed to result from accelerated regrowth of surviving tumor clonogens during the course of treatment. If it is assumed that accelerated regrowth occurred at a constant rate and began within 9 days of the start of treatment, an average of 0.53 Gy extra dose per day's extension of treatment would be required to maintain a constant probability of local control. Correspondingly, the probability of local control from a constant dose would be lowered by an average of at least 1% for each day's extension of treatment duration. However, the data are slightly more consistent with an average delay of as long as 30 days before onset of accelerated repopulation, with a consequent increase to an average of 0.73 Gy per day for the value of the compensatory dose. The alpha/beta ratio for this tumor is high enough that the effect of fraction size on the probability of local control can be ignored; a precise estimate is not possible because the best value for beta was close to zero. After accounting for the significant variables studied (treatment time, T-stage, N-stage), the dose-response curves for tumor control were still shallow, suggesting that there are additional causes for heterogeneity of responses among these tumors.

CONCLUSIONS

Total dose is important to treatment outcome: After accounting for other treatment variables, there is about a 2% per Gy increase in probability of tumor control over the ranges of control commonly achieved. Overall treatment duration is important. There is at least a 1% per day decrease in tumor control probability if delivery of a constant total dose is prolonged, requiring a compensatory increase in dose by 0.5-0.7 Gy per day to achieve a constant rate of tumor control. Fraction size is not, of itself, an important factor in the response of primary carcinoma of the tonsil. If a tumor has demonstrated a capacity for metastatic spread to lymph nodes, a higher total dose should be considered to achieve control rates at the primary site equivalent to those in node negative patients. Even after accounting for variables such as tumor stage, total dose, and overall treatment duration, there is sufficient heterogeneity in other undocumented determinants of tumor control to cause the tumor control probability curve to be a shallow function of dose.

Late normal tissue sequelae from radiation therapy for carcinoma of the tonsil: patterns of fractionation study of radiobiology

PURPOSE

To evaluate the influence of dose fractionation and other factors on the development of late complications in mandibular bone, muscle, and mucosa of the oral cavity after external beam radiation therapy for carcinoma of the tonsil.

METHODS AND MATERIALS

A retrospective analysis was made of the results in 676 patients treated with a spectrum of fractionation regimens in nine centers during the years 1976-1985. Only severe (Grades 3-4) late complications were analyzed.

RESULTS

With more than 5 years follow-up, it was found that total dose was a factor for all three types of complications, but that in other respects, the radiobiology of late-(> 3 months) developing mucosal ulcerations was different from that for mandibular necrosis and muscle injury. Dose per fraction was a significant factor for bone and muscle (estimated alpha/beta values of 0.85 Gy and 3.1 Gy, respectively). By contrast, mucosa showed no influence on response from change in fraction size over the range of approximately 1.0-3.5 Gy. Complications in bone and muscle were not related to overall treatment duration, whereas there was a significant inverse relationship for mucosa breakdown. The rate of development of complications was fastest in mucosa and slowest in bone. The appearance of complications by 4 years after treatment was about 80% of those developing by 8 years in the mucosa, 66% in muscle, and about 50% in bone. The high alpha/beta ratio, inverse relationship with overall treatment duration, and faster development of mucosal complications suggests that they may develop as a consequence of earlier mucosal injury. As anticipated, adequate retrospective analysis of acute complications could not be made even when objective criteria such as weight loss, unplanned delays in completing treatment, or hospitalization during treatment were the measures. Field size was a significant factor for mandible complications, but not for muscle or mucosa.

CONCLUSION

The radiobiological characteristics of bone and muscle were those characteristic of other late-responding tissues, whereas late sequelae in mucosa had radiobiological parameters similar to those for acute responses. Field size was a significant factor for bone complications but not for others.

Semi-parametric estimation in failure time mixture models

A mixture model is an attractive approach for analyzing failure time data in which there are thought to be two groups of subjects, those who could eventually develop the endpoint and those who could not develop the endpoint. The proposed model is a semi-parametric generalization of the mixture model of Farewell (1982). A logistic regression model is proposed for the incidence part of the model, and a Kaplan-Meier type approach is used to estimate the latency part of the model. The estimator arises naturally out of the EM algorithm approach for fitting failure time mixture models as described by Larson and Dinse (1985). The procedure is applied to some experimental data from radiation biology and is evaluated in a Monte Carlo simulation study. The simulation study suggests the semi-parametric procedure is almost as efficient as the correct fully parametric procedure for estimating the regression coefficient in the incidence, but less efficient for estimating the latency distribution.

Apolipoprotein B mRNA-editing protein induces hepatocellular carcinoma and dysplasia in transgenic animals

Apolipoprotein (apo-) B mRNA editing is the deamination of cytidine that creates a new termination codon and produces a truncated version of apo-B (apo-B48). The cytidine deaminase catalytic subunit [apo-B mRNA-editing enzyme catalytic polypeptide 1 (APOBEC-1)] of the multiprotein editing complex has been identified. We generated transgenic rabbits and mice expressing rabbit APOBEC-1 in their livers to determine whether hepatic expression would lower low density lipoprotein cholesterol concentrations. The apo-B mRNA from the livers of the transgenic mice and rabbit was extensively edited, and the transgenic animals had reduced concentrations of apo-B100 and low density lipoproteins compared with control animals. Unexpectedly, all of the transgenic mice and a transgenic rabbit had liver dysplasia, and many transgenic mice developed hepatocellular carcinomas. Many of the mouse livers were hyperplastic and filled with lipid. Other hepatic mRNAs with sequence motifs similar to apo-B mRNA were examined for this type of editing (i.e., cytidine deamination). One of these, tyrosine kinase, was edited in livers of transgenic mice but not of controls. This result demonstrates that other mRNAs can be edited by the overexpressed editing enzyme and suggests that aberrant editing of hepatic mRNAs involved in cell growth and regulation is the cause of the tumorigenesis. Finally, these findings compromise the potential use of APOBEC-1 for gene therapy to lower plasma levels of low density lipoproteins.

Identification and characterization of a new human gene (APOC4) in the apolipoprotein E, C-I, and C-II gene locus

We have identified and characterized a previously unreported human gene that is found within the apolipoprotein (apo) E/C-I/C-II gene locus. On the basis of its location and its properties, this new gene has been designated APOC4. Nucleotide sequence analysis of genomic DNA and liver cDNA clones revealed a 3.3-kb gene consisting of three exons and two introns. Its 3' terminus lies 555 bp upstream of APOC2, giving both genes the same transcriptional orientation. The promoter of the APOC4 gene lacks a typical TATA box, consistent with an apparent heterogeneity in transcription start sites. RNase protection analysis indicated relatively low apoC-IV mRNA levels in human liver, compared to apoC-II mRNA levels. The predicted apoC-IV protein sequence, comprising 127 amino acid residues, contains a putative 25-residue signal peptide and two potential amphipathic alpha-helical domains. Amino acid sequence comparisons indicate a limited homology between apoC-IV and either apoC-I or apoC-II. Since its hepatic expression and predicted protein structure are characteristic of the other genes in this cluster, we propose that the APOC4 gene is a member of the apolipoprotein gene family.