Sequence-dependent antitumor activity of paclitaxel (taxol) and cisplatin in vivo

The established antitumor efficacy of paclitaxel and cisplatin as single agents and their distinctly different mechanisms of action have prompted laboratory and clinical research into their use in combination. Our in vivo study was performed to investigate the importance of sequence of administration and inter-agent interval. C3Hf/Kam mice bearing OCa-I tumors received paclitaxel and cisplatin. The antitumor efficacy of the combination, measured as re-growth delay and expressed as the enhancement factor (EF), was determined for inter-agent intervals of 1, 9, 24, 48 and 72 hr. Morphometric analysis was used to determine the contribution of induced apoptosis. Our findings showed an additive effect when cisplatin preceded paclitaxel by 1 and 24 hr, producing EF of 1.1 and 1.0, respectively, and a greater than additive effect for 9 and 48 hr, producing EF of 1.3 and 1.8, respectively. This sequence, however, was associated with significant morbidity and mortality. When paclitaxel preceded cisplatin the effect was greater than additive with the EF for 1, 9 and 24 hr, being 1.2, 1.5 and 1.5, respectively, and increasing to a maximum of 1.9 at 48 hr. Thus, for this combination, the therapeutic ratio was improved when paclitaxel preceded cisplatin and was greatest when a 48 hr interval was allowed between drugs. We were unable to attribute the efficacy of the drug combination to increased induction of apoptosis and suggest other possible mechanisms.

Role of reoxygenation in induction of enhancement of tumor radioresponse by paclitaxel

We reported previously (L. Milas et al., Cancer Res., 54: 3506-3510, 1994) that paclitaxel greatly enhances the response of a murine mammary carcinoma to subsequent irradiation and hypothesized that the enhanced radioresponse was mediated by tumor cell reoxygenation caused by treatment with paclitaxel. Because paclitaxel induced massive tumor cell destruction by apoptosis, it was reasoned that as apoptotic cells were removed from the tumor more hypoxic cells would have access to oxygen, be reoxygenated, and, thus, become more sensitive to radiation. The present study tested this hypothesis by assessing the effect of 60 or 40 mg/kg paclitaxel on radioresponse of an 8-mm MCA-4 tumor irradiated under air-breathing or hypoxic conditions 9, 24, 48, or 72 h after paclitaxel administration. If the hypothesis was correct, paclitaxel would enhance tumor radioresponse more under air breathing than under hypoxic conditions, and the enhancement would increase as the time between paclitaxel administration and tumor irradiation increased within a few days after paclitaxel treatment but only when radiation was given under air-breathing conditions. The effect of the treatments was determined by tumor growth delay and the radiation dose required to control 50% of the tumors (TCD50). Paclitaxel greatly enhanced tumor radioresponse under air-breathing (and not hypoxic) conditions, increasing tumor growth delay, and reducing TCD50. These effects increased as the time interval between paclitaxel administration and tumor irradiation increased within the observation period of 72 h after paclitaxel treatment. The enhancement factors for tumor growth delay ranged from 1.19 at 9 h to 1.86 at 48 h and for TCD50, from 1.16 at 9 h to 1.47 at 72 h after paclitaxel. Direct measurements of tumor pO2 showed a median value in untreated tumors of 6.2 mmHg, which increased to 10.5 mmHg at 24 h and to 31.2 mmHg at 48 h after paclitaxel administration. Overall, these results show that paclitaxel is a potent enhancer of tumor radioresponse and that its effect is mediated by reoxygenation of hypoxic tumor cells.

Effect of paclitaxel (taxol) alone and in combination with radiation on the gastrointestinal mucosa

PURPOSE

Paclitaxel is a potentially useful drug for augmenting the cytotoxic action of radiotherapy because it has independent cytotoxic activity against certain cancers and blocks cells in the radiosensitive mitotic phase of the cell cycle. However, all rapidly proliferating tissues, both normal and neoplastic, may be affected by this therapeutic strategy. The aim of this study was to define the in vivo response of rapidly dividing cells of the small bowel mucosa to paclitaxel given alone and in combination with radiation.

METHODS AND MATERIALS

Mice were given single IV doses of 10 or 40 mg/kg paclitaxel or four doses of 10 mg/kg paclitaxel at 6, 12, or 24 h intervals. The kinetics of mitotic arrest and apoptosis in jejunal crypts of mice at 1-24 h after treatment were defined histologically. An in vivo stem cell microcolony assay was used to assess the radiosensitizing potential of paclitaxel when radiation was delivered at the peak of mitosis and at 24 h after drug treatment.

RESULTS

Paclitaxel blocked jejunal crypt cells in mitosis and induced apoptosis in a dose-dependent manner. Fractionating the paclitaxel dose over 1-4 days did not result in any greater accumulation of mitotically blocked cells than did a single dose. Mitosis peaked 2-4 h after paclitaxel and returned to near normal by 24 h. Apoptosis lagged several hours behind mitosis and peaked about 6 h later than mitosis. Despite these kinetic perturbations, there was little or no enhancement of radiation effect when single doses were delivered 2-4 h after paclitaxel administration. The maximum sensitizer enhancement ratio of 1.07 observed after a single paclitaxel dose of 40 mg/kg is consistent with independent crypt cell killing. Conversely, when radiation was given 24 h after paclitaxel, a significant protective effect of the drug (SER 0.89-0.92), most probably due to a regenerative overshoot induced by paclitaxel, was observed.

CONCLUSION

Stem cells of the jejunal mucosa determining radiation response were not radiosensitized by paclitaxel with the drug concentrations and dose delivery schedules used, although additive cytotoxicity was observed with the highest drug dose. A radioprotective effect was observed when radiation was given 24 h after paclitaxel administration.

Kinetics of mitotic arrest and apoptosis in murine mammary and ovarian tumors treated with taxol

The kinetics of taxol-induced mitotic arrest and apoptosis in murine mammary carcinoma MCA-4 and ovarian carcinoma OCA-I tumors were determined to establish a possible causative relationship between mitotic arrest and apoptosis and to see whether these cellular effects of taxol would correlate with the extent of its antitumor efficacy. Mice bearing 8-mm tumors in a hind leg were given taxol i.v. at a dose of 10-80 mg/kg. Both tumors responded to taxol by significant growth delay or transient regression; in general, the response was greater as the dose of taxol was increased. For kinetics studies the mice were treated with 60 mg/kg taxol given once when tumors were 8 mm in size or twice, with the second dose being given 3 days after the first. At various times ranging from 1 to 96 h after treatment with taxol, tumors were histologically analyzed to quantify mitotic and apoptotic activity. After a single dose of taxol, mitotic arrest was visible at 1 h, and the mitotic index increased with time to reach peak values of 36% in MCA-4 tumors and 22% in OCA-I tumors at 9 h. The index then declined to a baseline of 1%-3% at 3 days for MCA-4 tumors and 1 day for OCA-I tumors. Apoptosis followed mitotic arrest, beginning at the time of peak mitotic arrest, increasing to the highest level of about 20% at 18-24 h after treatment and gradually declining to the normal level of 3%-6% after 3-4 days. Nuclear material progressively condensed in mitotically arrested cells, culminating in the frank appearance of multiple apoptotic bodies. The change in cell morphology plus the dynamics of apoptosis development imply that a large percentage of tumor cells arrested in mitosis by taxol die by apoptosis. Kinetic analysis undertaken after the second dose of taxol showed a considerably lower percentage of cells arrested in mitosis as compared with that seen after a single dose, and the induction of apoptosis by the second dose was minimal. However, the antitumor efficacy of the second dose of taxol was similar to or better than that of the first dose, implying that in addition to mitotic arrest and apoptosis, there exist other mechanisms by which taxol exerts its antitumor action.

The identification and partial cloning by PCR of the gene for tyrosinase-related protein-1 in the Mexican axolotl

The tyrosinase gene family is currently composed of three members, tyrosinase and two tyrosinase-related proteins, TRP-1 and TRP-2. These three gene products have all been found to act in the synthesis of melanin pigments with the enzyme tyrosinase catalyzing the initial rate-limiting steps. Thus far these genes have primarily been analyzed in higher vertebrates. We have used degenerate PCR primers to isolate a large fragment of an axolotl tyrosinase-related protein. Sequence analysis of the entire 1,057-bp fragment isolated indicates a high degree of similarity to the mouse TRP-1, the product of the brown locus. Phylogenetic analysis supports the conclusion that the fragment isolated corresponds to the axolotl TRP-1 homolog. This is the first TRP-1 gene to be identified in an amphibian species.

Tumor reoxygenation as a mechanism of taxol-induced enhancement of tumor radioresponse

Paclitaxel is a novel chemotherapeutic agent that arrests cells in the radiosensitive G2 and M phases of the cell cycle and as such may act as a specific cell cycle radiosensitizer. We recently reported that paclitexel induces mitotic arrest in the MCA-4 murine mammary carcinoma and enhances radio-response of this tumor. However, the greatest enhancement was observed not when radiation was given at the time of peak mitotic arrest, which was 9 h after paclitaxel administration, but when it was given 24 h after paclitaxel. This implied the involvement of other mechanisms in radiosensitization; we hypothesized that tumor reoxygenation was a likely mechanism based on the observed massive loss of mitotically arrested cells at 24 h. The present study shows that paclitaxel greatly enhanced MCA-4 tumor radioresponse when radiation was given under air-breathing conditions (DMF = 1.74), but not when it was performed under hypoxic conditions. This observation supports the hypothesis of tumor reoxygenation as a mechanism of enhancement of tumor radioresponse. That reoxygenation occurred in tumors treated with paclitaxel 24 h earlier was confirmed by direct measurements of pO2 values, using the Eppendorf pO2 histograph. Median pO2 values increased from 6.2 mmHg in untreated tumors to 10.0 mmHg in tumors treated with paclitaxel. These observations emphasize the importance of timing of paclitaxel administration in relation to radiation treatment.

Changes in the radiation sensitivity of mouse skin during fractionated and prolonged treatments

Reactions of the skin of the right thigh of mice were used as an experimental model to test possible changes in the radiosensitivity of mouse skin, as represented by changes in the linear-quadratic (LQ) model parameters alpha and beta, as a function of fractionation interval and overall treatment time. In the first series of experiments, variable numbers of 3-Gy fractions with intervals of 6, 24 or 48 h were applied, followed by top-up doses to increase the skin damage to a level that could be scored. The results showed that mouse skin is more sensitive to 3-Gy fractions applied with 48-h intervals than to 3-Gy fractions applied with 6- or 24-h intervals. In the second series of experiments we used single-dose or fractionated test treatments for previously unirradiated mice and mice treated with priming doses of 10, 20 or 30 Gy given 1-18 days before the test treatment. The sensitivity appeared to be higher after intervals of 14-18 days than after 1-10 days after priming treatments of 20 and 30 Gy. The increased sensitivity 18 days after 20 Gy was mainly the result of an increase in the beta component of the LQ model; higher values of alpha were also determined. We conclude that the radiosensitivity of mouse skin is higher during a radiation-induced proliferative response.

Enhancement of tumor radioresponse of a murine mammary carcinoma by paclitaxel

Paclitaxel is a chemotherapeutic agent with potent microtubule stabilizing activity that arrests cells in G2-M. Because G2 and M are the most radiosensitive phases of the cell cycle, paclitaxel has potential as a cell cycle-specific radiosensitizer. In this study, we investigated the ability of paclitaxel to increase tumor radioresponse in vivo using a murine mammary carcinoma and the dependency of this response on accumulation of tumor cells in mitosis. Mice bearing 8-mm tumors were treated with paclitaxel (60 mg/kg i.v.), 9, 15, or 21 Gy of single-dose radiation, or with a regimen of both agents in which radiation was given 1, 9, or 24 h after paclitaxel. The effect of the treatments was determined by tumor growth delay. Microscopically, the percentage of mitotically arrested cells was only 4% 1 h after treatment with paclitaxel, increased to a maximum value of 30% at 9 h, and decreased to 12% 24 h after paclitaxel. Paclitaxel enhanced tumor radioresponse by factors of 1.21 to 2.49. The degree of enhancement increased with increases in both the dose of radiation and the time between paclitaxel administration and radiation delivery. Radiation efficiently destroyed mitotically arrested cells by apoptosis. The greatest enhancement of radiation response was not at the time of the highest mitotic arrest but at 1 day after paclitaxel treatment, showing that paclitaxel potentiates tumor radioresponse by mechanisms in addition to blocking the cell cycle in mitosis, possibly by tumor reoxygenation. Thus, these results show that paclitaxel is a potent in vivo radiopotentiating agent and has the potential to be usefully combined with radiotherapy.

Comparison of continuous and pulsed low dose rate brachytherapy: biological equivalence in vivo

PURPOSE

Recent studies of human cell lines cultured in vitro and mathematical modeling of the response of acute and late responding tissues have predicted conditions for the equivalence in terms of cell killing of continuous and pulsed dose rate brachytherapy. The aim of this study was to test these predictions in vivo using an acutely responding normal tissue.

METHODS AND MATERIALS

The microcolony assay was used to quantify the survival of jejunal stem cells in vivo. Mice were exposed to graded doses of 60Co delivered continuously or as 1- or 10-min pulses given once-per-hour at an average dose rate of 0.7 Gy/hr. In both cases the total dose-per-hour was 0.7 Gy. Overall exposure times ranged between about 30 and 60 h. Mice were sacrificed 3.5 days after exposure, the bowel removed for routine histological preparation, and number of surviving crypts quantified microscopically.

RESULTS

An average dose-per-hour of 0.7 Gy, a pulse width of 10 min, and a pulse frequency of 1 h resulted in biological equivalence of pulsed to continuous treatment. Delivering the pulse in a period of 1 min at a dose rate 10-fold higher resulted in a modest 3-4% shift in the survival curve to lower isoeffective doses. The slopes of the survival curves as described by D(o) values were similar for all treatment regimens tested.

CONCLUSION

This in vivo study validates the prediction of biological equivalence between pulsed and continuous brachytherapy at a clinically relevant average dose rate and may generate further interest in this new treatment modality because of its advantages in radiation protection, dose optimization, and cost relative to standard low dose rate brachytherapy techniques.

Unexpected radiation protection with 13-cis-retinoic acid plus interferon alpha-2a

A recent clinical protocol combining retinoic acid, interferon, and radiotherapy for advanced cervical cancer produced proctitis severe enough to necessitate dose reductions. In an attempt to model this biological response to multimodality therapy, we used a murine model to study the response of the colonic epithelium. Mice were treated with retinoic acid (100 micrograms/day) and interferon (3 x 10(4) units/day) for 5 days before undergoing whole-body irradiation. The functional response of the bowel was assessed by the ability to maintain body weight, and reproductive cell survival was quantified by the colon crypt assay. Both assays indicated a moderate protective effect of treatment with retinoic acid and interferon prior to irradiation. Protection factors in the range of 1.1-1.4 were observed.

Stimulation of hematopoietic cell recovery by tetrachlorodecaoxide in sublethally irradiated mice

This study investigated whether tetrachlorodecaoxide (TCDO), a potent wound-healing agent, promotes recovery of hematopoietic tissue of mice depleted by sublethal X irradiation. Mice were exposed to 3 Gy total-body irradiation and were given 1 ml/kg TCDO intravenously daily from day 1 to 5 or day 4 to 8 after irradiation. The effect was assessed by the change in the total number of nucleated cells in bone marrow and spleen, endogenous spleen colony formation, and 30-day mouse lethality. In the spleen there were profound effects on spleen weight, total organ cellularity, and endogenous colony formation. The TCDO produced radiation dose-modifying factors between 1.4 and 1.5 for endogenous spleen colony formation in mice primed with 3 Gy and reirradiated 4 days after treatment. This stimulated cellular recovery resulted in an increased protection of mice from lethality caused by subsequent total-body irradiation by factors of 1.12-1.18. The results show that TCDO is a potent stimulator of cellular recovery in the spleen of sublethally irradiated mice.

Late effects of radiation on the lumbar spinal cord of guinea pigs: re-treatment tolerance

PURPOSE

Using a guinea pig model of lumbar myelopathy, various factors affecting the tolerance of spinal cord to irradiation were assessed: (a) extent of initial injury (b) time interval between priming and test doses (c) animal age at the time of initial radiation treatment.

METHODS AND MATERIALS

A 3 cm section of lumbar spinal cord of guinea pigs was irradiated with fractionated doses of 4.5 Gy gamma rays given as 9 fractions per week. Guinea pigs were primed with 9 x 4.5 Gy in 7 days which is 60% of the ED50 for a continuous course of treatment. After 28 or 40 weeks, animals were retreated with 6-14 fractions of 4.5 Gy. Animals were observed for 2 years following the priming dose and both the incidence and latency of myelopathy recorded.

RESULTS

Young adult guinea pigs (8 wk old) showed both a decreased radiation tolerance and latency compared to old individuals (40 wk old). At 28 or 40 wk after 9 x 4.5 Gy, only about 8% of the initial injury was remembered in young adult guinea pigs.

CONCLUSION

The amount of residual injury was dependent on the initial damage as a proportion of the tolerance dose. The spinal cord shows a greater capacity for long-term recovery than generally appreciated and re-treatment doses clinically prescribed may be lower than necessary.

Dose-survival curves, alpha/beta ratios, RBE values, and equal effect per fraction for neutron irradiation of jejunal crypt cells

Jejunal crypt cell survival after regimens of one, two, three and five fractions was used to reconstruct composite single-dose survival curves for neutrons of five different energies. There is no obvious shoulder, but there is a gradual divergence from linearity that is most evident at low levels of cell survival (high doses). The effect of dose fractionation is relatively small, especially at the low doses characteristic of each treatment session in neutron radiotherapy. The alpha/beta values for the linear-quadratic survival curves range from 27 to 40 Gy. The curves for neutrons are different from the curves for gamma rays mainly in their alpha coefficients, as predicted by Kellerer and Rossi's theory of dual radiation action, but both alpha and beta values are higher the lower the mean neutron energy, which is not consistent with the theory. The ratio of alpha coefficients reported here for various neutron beams to those for gamma rays reported elsewhere ranges between 3.2 and 4.6. This range of values represents the maximum limits for RBEn/gamma values (at very low doses), and is sometimes referred to as RBEm. These values increase with decreasing neutron energy. The ratios of beta coefficients for neutron and gamma-ray survival curves were lower than the alpha ratios, ranging between 0.9 and 1.9, although not reliably distinguished from 1.0. Each of a series of equal dose fractions given at 3-h intervals produced a constant (logarithmic) decrease in cell survival as evidenced by the consistency of the estimate of cell survival from a certain single dose fraction, regardless of the level of cell survival (number of dose fractions) from which the estimate was made. Even more significant than the overlap of individual data points is the excellent fit of all the data to survival curves reconstructed on the assumption of an equal effect per fraction. An implication of these results is that, with neutrons, too little unrepaired injury persists at 3 h to influence the response to a subsequent exposure measurably.

The number of clonogenic cells in a mouse jejunal crypt

The near linearity of cellular dose-survival curves for neutrons facilities back-extrapolation to their origin at zero dose. This zero dose intercept is the number of clonogenic cells per circumference, from which the average number of clonogenic cells per crypt can be calculated. The average estimate of clonogenic cell number per crypt (k) from back-extrapolation of 11 single dose neutron survival curves to a common intercept was 100. Multifraction experiments provide an even better estimate of k because more complete dose survival curves can be constructed on the assumption of an equal effect per equal dose fraction. The short back-extrapolation of five such curves to a common intercept yields an estimated k value of 123 (108-140, 95% confidence interval) cells per crypt. These k values were higher than those estimated by Hendry's two-dose gamma-ray method.

Alteration in myelin-associated proteins following spinal cord irradiation in guinea pigs

The aim of this study was to investigate the pathological and cellular basis for radiation-induced myelopathy in guinea pigs by monitoring biochemical alterations in levels of myelin basic protein and 2',3'-cyclic nucleotide phosphohydrolase. Guinea pigs were irradiated to the lumbar region with various doses of neutrons or cobalt gamma irradiation. The ED50s for paralysis were 17.2 Gy and 67.5 Gy for neutron and cobalt irradiation, respectively, and was histologically associated with demyelination. In spinal cords taken from animals at the onset of paralysis myelin basic protein levels were decreased in direct relationship to the radiation dose. The lowest doses to cause paralysis led to a 25% decrease in MBP levels. In a separate experiment, alterations in MBP were measured in the spinal cords over the time period leading up to paralysis. Surprisingly, decreases in MBP were found immediately after the end of the 4 week irradiation period. These early changes in MBP were not markedly dose dependent and occurred with nonparalyzing doses. Dose-dependent decreases were found only just before the onset of paralysis. CNPase activity measured in the same specimens showed changes that were essentially similar to those for MBP. In the CSF, MBP levels were essentially constant until onset of paralysis. This study showed that demyelination, as assessed by the levels of the myelin-associated proteins MBP and CNPase, can occur soon after spinal cord irradiation but that profound dose-dependent changes are seen only immediately preceding the onset of paralysis. Although increases in MBP in the CSF were associated with the onset of radiation-induced myelopathy, its assay is unlikely to predict this complication of irradiation.

Repopulation of mouse jejunal crypt cells

The regenerative response to radiation of mouse jejunal crypt cells was investigated using a three fraction experiment. The time between the second and third fraction was varied between 5 and 60 h, and the dose in each of the three fractions was different. The data show that the onset of regeneration is within 14 h of the first dose and possibly earlier. The doubling time of the clonogenic cells during repopulation is estimated to be between 5 and 10 h, with the most likely value approximately 6 to 7 h. The data also show that the time course of repopulation in an acutely responding tissue depended in a complex way on the fractionation scheme. The implications of this for radiotherapy are that simple formulas are unlikely to be accurate predictors of acute effects in altered fractionation schemes. Detailed mathematical modelling of the data is undertaken using a model which consists of a single dose survival curve, a part to incorporate the regenerative response and a part to accommodate the delayed onset of regeneration. The model is shown to give a good, although not perfect, fit to the data. A mathematical derivation is given of the expected number of crypts following the 3 dose radiation schedule. This derivation takes into account the fact that any crypt could be denuded of cells prior to the final dose and hence not repopulate, and thus the formula given is necessarily more complex than previous formulas which were based on simpler models.

Direct analyses of in vivo colony survival after single and fractionated doses of radiation

Several methods are described for analysing the results of in vivo colony assays using the statistical procedure called maximum-likelihood analysis. The methods differ in the way in which they take into account possible sources of variability in the data. The methods described here for analysing microcolony data are direct methods, in that they use the observed colony counts rather than transformed (e.g. Poisson-corrected) data. Each method can be used to estimate the average number of surviving cells per tissue structure (e.g. per jejunal crypt) in a single dose group, together with 95% confidence intervals, or to fit cell-survival models to data from a range of dose groups (e.g. to obtain estimates of D0 or of the linear-quadratic parameters alpha and beta). Experimental microcolony data from murine jejunum, colon, and hair follicles irradiated in anagen (proliferative) or telogen (resting) phase have been analysed. Estimates of D0 have been derived from single-dose data and estimates of alpha, beta, and the initial number of clonogenic cells per structure have been derived from fractionation data. For hair follicles, the half-time of repair of sublethal radiation injury has also been derived from fractionation data.

Alternating zinc-finger motifs in the human male-associated protein ZFY

ZFY, a putative transcription factor encoded by the human Y chromosome, contains a distinctive two-finger repeat: odd-numbered and even-numbered CC/HH metal-binding motifs exhibit systematic alternation in sequence pattern. Such alternation, which is not generally observed in zinc-finger proteins, has also been described in an extensive family of Kruppel-like genes in Xenopus laevis and in the AIDS-associated human DNA-binding protein HIV-EP1. The strict conservation of a two-finger repeat among ZFY-, Kruppel- and HIV-related zinc-finger proteins suggests distinct mechanisms of protein-nucleic acid recognition. To test whether this sequence pattern reflects an underlying alternation in domain structure, we have synthesized and characterized single-finger peptides from the human ZFY gene. Remarkably, systematic differences in metal-dependent folding are observed in the circular dichroism spectra of even- and odd-numbered domains. Our results suggest the existence of distinct CC/HH finger submotifs, which may play different roles in nucleic acid recognition.

Comparison of the gastrointestinal syndrome after total-body or total-abdominal irradiation

In pathogen-free mice, but not standard conventionally housed laboratory rodents, two distinctly different modes of early radiation lethality can be identified by modifying the irradiation technique (total-body versus abdominal irradiation) or by therapeutic intervention such as rescue of total-body-irradiated mice with syngeneic bone marrow or spleen. While damage to the gastrointestinal tract is usually designated as the predominant cause of death occurring within 10 days of radiation exposure, it was demonstrated that damage to the hematopoietic/lymphopoietic system can result in animal lethality over the same period as the gastrointestinal syndrome and that this target cell population is more radiation-sensitive than the gastrointestinal epithelium.

Adhesion formation in experimental chronic radiation enteropathy

We have studied the late changes associated with radiation enteropathy in mice over a period of 224 days following single or split doses of gamma radiation delivered to the total abdomen (TAI). We focused on the importance of adhesion formation as a cause of strictures and gut-associated deaths following TAI. Gut-associated peritoneal adhesions were found in mice 2-7 months after receiving 13.5-17.5 Gy TAI and appeared to constitute the most consistent serious late effect of irradiation. There was a good correlation between adhesion formation and death for both the single and split-doses of radiation. Adhesions primarily involved the large gut, normally near the cecum. They appeared to result from serosal breakdown and were the major cause of partial gut obstruction. Submucosal fibrosis was present but seemed to be a comparatively minor cause of strictures. Local lymphoid hyperreactivity was also seen following TAI and may have contributed to the late sequelae. The complexity of the pathogenesis of chronic radiation enteropathy was indicated by finding three successive waves of non-scheduled deaths following TAI. The first wave (28-70 days) was not related to adhesion formation and may have been due to localized failure of mucosa to regenerate after irradiation with consequent ulceration. The second wave (98-140 days) occurred over the period when adhesion formation and fibrosis were most marked. In the third wave (168-224 days), the additional complication of fluid exudation was seen. Further experimentation is obviously needed to better define the complex pathogenesis of radiation enteropathy with dose and time after radiation but our data strongly support a multifactorial causation with an important role for adhesion formation in the disease complex.

Role of the beta 93-100 determinant loop sequence in receptor binding and biological activity of human luteinizing hormone and chorionic gonadotropin

The intercysteine loop sequence (93-100) in the beta-subunit has been postulated to be important for receptor binding and specificity in the glycoprotein hormones, LH and human CG (hCG). To demonstrate this directly, and to characterize the structural features essential for activity, we prepared a series of synthetic peptides and analogs incorporating this determinant loop region. Peptides were assayed for inhibition of labeled hCG binding to ovarian membrane receptors and stimulation of testosterone production in Leydig cells. Peptides with the native (93-100) sequence from hCG and hLH inhibited hCG binding half maximally at 2.18 and 2.62 x 10(-4) M, respectively, while the sequence from FSH was inactive. Isosteric substitution of Ala for Cys resulted in an inactive peptide, indicating that the (93-100) disulfide bridge is essential for activity. Optimal binding activity requires at least one net positive charge among the side chains, as shown by loss of activity in hybrid analogs with neutral or negative charges conferred by progressive replacement of Arg by Asp at 94 and 95 or by introduction of Asp at 96 and 97. Despite binding to receptors, the native sequence did not promote testosterone production at doses up to 10(-2) M. This contrasts with a second receptor binding sequence, beta (38-57) that activates testosterone production. There are differences between the (93-100) and (38-57) loop sequences in their chemical and physical properties, biological activity and antigenicity. While the cumulative evidence suggests that they associate with counterpart sites in alpha-subunit to form a topographical binding domain in the whole hormone, our results suggest that each sequence may contribute in different ways to activation of postreceptor events.

Dose dependent latency of fatal gastrointestinal and bone marrow syndromes

Two acutely-responding normal tissues, bone marrow and gastrointestinal epithelium, have been shown to exhibit a biphasic dose-latency response to radiation with both a dose-dependent and dose-independent component for expression of radiation injury.

Primary and secondary structural determinants in the receptor binding sequence beta-(38-57) from human luteinizing hormone

The intercysteine "loop" sequence 38-57 in the beta subunit has been shown to be a determinant for expression of biological activity in human lutropin (hLH) and choriogonadotropin (hCG) [Keutmann, H. T., Charlesworth, M. C., Mason, K. A., Ostrea, T., Johnson, L., & Ryan, R. J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 2038]. Together with other sequences, the 38-57 region may contribute to a multicomponent receptor binding domain in hLH/hCG. Because the structural features influencing activity in this important region are not easy to evaluate in the full-length subunit, we have used analogues of hLH beta-(38-57) prepared by solid-phase synthesis. The peptides were tested for inhibition of 125I-labeled hCG binding to rat ovarian membrane receptors. Secondary structure was analyzed by circular dichroism (CD) and by reactivity with antibodies to the native 38-57 peptide. An analogue lacking the 38-57 disulfide linkage retained 20% receptor binding and full immunoreactivity. "Far"-ultraviolet CD profiles were essentially identical with those of the disulfide-intact peptide; a transition from 10% to 30% alpha-helix in 90% trifluoroethanol was characteristic of both. The peptide thus appears not to require the disulfide bridge to retain a looped conformation with amphipathic secondary structure. An essential positive charge at position 43 was shown by complete loss of activity upon substitution of Asp or Ala for the Arg found in all known species of LH. Other analogues showed a requirement for a neutral residue at position 47, also highly conserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Palliative radiotherapy of a mouse mammary carcinoma

A mouse mammary carcinoma was exposed to one of three palliative treatment schemes: rapid, split, and extended. Tumors were treated at either 4 mm diameter or 8 mm diameter to compare the responses of small and large tumors to the three treatment schemes. In addition, acute skin reaction and late skin contracture were assessed. The results were: (1) The rapid treatment resulted in the greatest tumor response for 4 and 8 mm tumors but it also caused the most severe normal tissue reaction. (2) Lengthening the overall treatment time to 5 weeks (extended treatment) resulted in the poorest response for both large and small tumors. (3) The split course technique was almost as effective as the rapid course in treating small tumors, but its effectiveness was reduced if treatment was delayed until the tumor reached 8 mm in diameter. (4) The survival of mice with 4 mm tumors clearly depended upon the type of radiation schedule used, with the rapid treatment being superior. (5) If treatment was delayed until the tumors were large (8 mm diameter), there was no survival advantage between the three treatment schedules. (6) Palliation and survival were better when the tumor was treated when it was small, suggesting that palliation may be better if treatment is given early or electively.

A receptor-binding region in human choriogonadotropin/lutropin beta subunit

Synthetic fragments have not been widely used thus far to evaluate structure-activity relations in the glycoprotein hormones. We prepared a series of peptides representing the intercysteine "loop" sequence (residues 38-57) in human choriogonadotropin (hCG) and lutropin (hLH) beta subunits, anticipating that it might be oriented toward the surface and accessible to receptors. The peptides were characterized chemically and tested for bioactivity by binding to rat ovarian membrane receptor and stimulation of Leydig cell testosterone production. The hCG beta-(38-57) and hLH beta-(38-57) peptides inhibited binding of 125I-labeled hCG half-maximally at 1.51 X 10(-4) and 2.03 X 10(-5) M, respectively, while other peptide hormones and fragments from elsewhere in the beta subunit were inactive. Both peptides stimulated testosterone production, with half-maximal responses at 3.55 X 10(-5) M (hCG) and 2.18 X 10(-5) M (hLH). By radioimmunoassay with an antibody to thyroglobulin-conjugated hCG beta-(38-57) peptide, native hCG and beta subunit were highly reactive, as were the reduced and carboxymethylated subunit and peptide. Helical-wheel projection predicted an amphipathic region in the N-terminal portion of the 38-57 sequence, and circular dichroic measurements showed an increase in ordered structure, especially alpha-helix, when the 38-57 peptides were transferred from an aqueous to a more lipophilic (90% trifluoroethanol) environment. These results indicate that the 38-57 region of beta subunit is exposed on the surface and constitutes a component in the receptor-binding domain for hCG and hLH. A region of amphipathic-helical structure in the 38-57 sequence may promote hormone-receptor interactions in a manner proposed for several other peptide hormones.

Late radiation response of kidney assayed by tubule-cell survival

An assay for the survival of renal tubule cells was developed using mice. It is analogous to other in-situ clonogenic cell survival assays. One kidney was irradiated using a 137Cs irradiator and removed 60-68 weeks later for histological examination. In unirradiated animals there were about 370 tubules in contact with the capsule in a coronal cross section at the middle of the kidney. After irradiation, extensive tubular damage was the dominant lesion. The number of epithelialized tubules in contact with the capsule showed a dose-dependent logarithmic decline. The dose-survival relationship for the clonogenic cells responsible for the regeneration of tubule epithelium was described by a D0 value of 1.5 Gy over the dose range 11-16 Gy. This radiosensitivity resembles that of stem cells in acutely responding tissues. The lack of histological evidence of damage to the arterial vasculature at the time the tubules are initially denuded of epithelium, and the similarity of renal tubule cell radiosensitivity to that of other mammalian cells, support the hypothesis that "late" radiation injury results primarily from depletion of parenchymal cells, not indirectly from injury to blood vessels, as has been the prevailing belief.

Acute effects of a perfluorochemical oxygen carrier on normal tissues of the mouse

A single iv dose of 15 ml/kg fluosol DA (20%), a perfluorochemical oxygen carrier, caused hepatomegaly and splenomegaly which persisted for at least 3 weeks after drug injection. The peak increase in weight was at 3 days in the spleen (1.7x) and at 14 days in the liver (1.5x). Lung and kidney weights were not altered 1-21 days after administration of fluosol DA. The slopes of the single-dose radiation survival curves for intestinal epithelial cells and spermatogenic stem cells in mice breathing air or oxygen were not significantly altered by the administration of fluosol DA 10 min before irradiation, and the doses to achieve an isoeffect were altered by 1.03 or less. When mice were challenged with iv injected FSa tumor cells 24 h after treatment with fluosol DA, no increase in the number of artificial pulmonary metastases was observed.

MR effect on murine spermatogenesis

The cytotoxic effects of magnetic resonance (MR) on spermatogenesis in mice were studied. Mice were exposed to a strong static magnetic field from a 0.3-T MR imaging device. The effect of this treatment on different classes of spermatogenic cells was investigated by counting sperm heads at various times after exposure. Sixty-six hours of continuous exposure did not produce any significant cytotoxicity to these cells. This period of continuous exposure is far longer than any anticipated occupational exposure to humans. Thus, acute and subacute exposure to static magnetic fields associated with diagnostic use of MR imaging devices is unlikely to have any significant adverse effect on spermatogenesis.

A dose-surviving fraction curve for mouse colonic mucosa

A dose-surviving fraction curve representing the response of the mouse colonic mucosa to single doses of 137Cs gamma radiation was obtained from the results of a multifraction in vivo colony assay. Construction of the curve required an estimate of the average number of clonogens initially present per colonic crypt. The estimated clonogen count (88) was determined by a statistical method based on the use of doses per fraction common to different fractionation protocols. Parameters for the LQ and TC models of cell survival were obtained by weighted least-squares fits to the data. A comparison of the survival characteristics of cells from the mouse colonic and jejunal crypts suggested that the epithelium of the colon is less radiosensitive than that of the jejunum.

Effects of hyperthermia and radiation on mouse testis stem cells

The response of mouse testis stem cells to hyperthermia and combined hyperthermia-radiation treatments was assayed by spermatogenic colony regrowth, sperm head counts, testis weight loss, and fertility. With the use of spermatogenic colony assay, thermal enhancement ratios at an isosurvival level of 0.1 were 1.27 at 41 degrees, 1.80 at 42 degrees, and 3.97 at 43 degrees for testes exposed to heat for 30 min prior to irradiation. Sperm head counts were reduced by heat alone from a surviving fraction of 0.58 at 41 degrees to 0.003 at 42.5-43.5 degrees. Curves for sperm head survival measured 56 days after the testes had been heated for 30 min prior to irradiation were biphasic and showed a progressive downward displacement to lower survival with increasing temperature. The 41, 42, and 43 degrees curves were displaced downward by factors of 2, 58, and 175, respectively. The proportion of animals remaining sterile after 30 min of heat (41-43 degrees) and the median sterility period in days increased with increasing temperature. The minimum sperm count necessary to regain fertility was 13% of the normal mouse level.

A simple and inexpensive method for maintaining a defined flora mouse colony

The use of autoclaved cages, feed, bedding, water, and filter caps combined with aseptic techniques of animal husbandry in an existing mouse colony was ineffective in maintaining a defined flora colony. The addition of a laminar air flow bench equipped with a high efficiency particulate air filter provided a sterile environment in which to manipulate mice when the filter caps were removed. The installation of a duct to direct all air entering the room through the bench filter reduced the airborne bacterial counts in the room. This modification combined with the culling or marking of infected cages so that no future breeders would be taken from these cages eliminated a number of bacterial contaminants (Staphylococcus aureus, S epidermidis, and streptococci) from the colony.

RBE of neutrons generated by 50 MeV deuterons on beryllium for control of artificial pulmonary metastases of a mouse fibrosarcoma

Artificial pulmonary metastases of a mouse fibrosarcoma were produced by the intravenous injection of 10(4) cells admixed with 2 X 10(6) plastic microspheres into mice preconditioned with 600 rad whole-body irradiation 24 hours earlier. Four days after injection of tumour cells, mice were irradiated with neutrons generated by 50 MeV deuterons on Be at the Texas A & M Variable Energy Cyclotron or with 137Cs gamma rays. One, three or six fractions of radiation were delivered on a three-hour fractionation schedule. Surviving lung metastases were scored macroscopically 16 days after irradiation. The data indicate that: (1) the RBE (n/gamma) was in the range 1.6-2.6 depending on the size of dose per fraction; (2) the slopes of the gamma-ray curves decreased with increasing fraction number (i.e. decreasing fraction size); (3) the slopes of the neutron curves decreased only slightly with increasing fraction number (and decreasing fraction size); (4) no additional sparing was achieved by further fractionating doses of neutrons of 300 rad or less.

Pitfalls in the use of the lung colony assay to assess T-cell function in irradiated mice

Mice depleted of T lymphocytes by thymectomy, whole-body irradiation and bone-marrow reconstitution showed a marked increase in susceptibility to the development of lung colonies after i.v. injection of cells of an immunogenic fibrosarcoma. However, a similar increase was observed in unthymectomized, irradiated and reconstituted mice that had recovered their T-cell function, as evidenced by rejection of allogeneic skin grafts. In both thymectomized and unthymectomized mice subjected to whole-body irradiation, the lung-colony-forming efficiency was high 1 day after irradiation, declined to a minimum at 7 days, and thereafter increased again, unless the animals were held in a pathogen-free environment. Reconstitution of T-cell-depleted mice with thymocytes and/or a thymic lobe graft tended to increase further, rather than reduce, lung-colony-forming efficiency. Induction of profound lymphopenia, by irradiation of the whole body except the thorax, did not significantly increase lung colony yields. These studies show that the lung colony assay is not a reliable method of assessing T-cell function in irradiated mice.

A role for T lymphocytes in the antitumour action of systemic C. parvum

The frequency of tumours arising from s.c. injection of a syngeneic chemically-induced fibrosarcoma (Fsa) was not influenced by systemic administration of C. parvum (day + 3) except when doses less than the TD50 were injected. Then the number of takes was increased. The tumour normally grows progressively however regression was frequent in intact mice treated with C. parvum. Tumour regression did not occur in T cell-depleted mice treated in the same way. Splenic T cell-enriched populations of cells taken from Fsa-bearing C. parvum-treated mice caused tumour regression when adoptively transferred to Fsa-bearing T cell-depleted mice. Although this assay measures systemic rather than intratumoral T cell activity, it is proposed that C. parvum-induced regression of the fibrosarcoma is to a large extent due to enhanced T cell reactivity.

In vivo transfer of antitumor activity by peritoneal exudate cells from mice treated with C. parvum

We have investigated whether peritoneal exudate cells (PEC) from C. parvum (CP) treated (C3Hf/Bu mice could transfer in vivo the resistance against a syngeneic fibrosarcoma (FSa). Inhibition of tumour development and prolongation of survival of recipients were observed when CP-activated PEC were admixed with FSa cells before their intraperitoneal (ip) or subcutaneous (sc) injections into normal mice. The antitumour activity increased with the increase of the ratio of effector to target cells. Heat killed CP-PEC were unable to transfer the resistance. Also, pretreatment of recipients with 600 rads whole body irradiation (WBI) substantially reduced the efficacy of CP-PEC. Reconstitution of WBI mice with mixed normal spleen and lymph node cells, or spleen cells alone, or bone marrow cells did not restore the antitumor activity of transferred CP-PEC. In fact, reconstituted mice showed a further reduction of transferred antitumor resistance. CP-PEC activity was also inhibited in sc transfer experiments when normal PEC, spleen cells, T-cells or even fetal fibroblasts were admixed with tumor cells and CP-PEC. Possible reasons for the failure of WBI recipients to be fully protected by transferred CP-PEC are discussed.