Enhancement of tumor radioresponse by docetaxel: Involvement of immune system

Docetaxel, a potent chemotherapeutic drug and a strong enhancer of tumor radioresponse, possesses immunomodulating properties. We previously reported that 40% of murine tumors responding to docetaxel by growth delay showed heavy infiltration with macrophages or lymphocytes. The present study explored the effect of whole body irradiation on antitumor action of docetaxel alone or docetaxel plus tumor irradiation. Mice bearing 8-mm MCa-K mammary carcinoma in the leg received 33 mg/kg docetaxel i.v., 5 to 65 Gy tumor irradiation, or both (radiation given 24 h after docetaxel). Docetaxel delayed tumor growth and enhanced the efficacy of radiation: it dramatically reduced TCD50 (radiation dose yielding 50% tumor cure) from the control value of 38.6 Gy to 11.8 Gy, for an enhancement factor of 3.27. In addition to enhancing tumor radioresponse, docetaxel decreased the lung metastatic rate in mice with local tumor control from 26% in mice receiving radiation alone to 11% in mice receiving docetaxel plus radiation. Docetaxel induced heavy infiltration of tumors with lymphocytes, determined 2-4 days after treatment: the percentage of lymphocytes increased from the control value of <2% to 27% in mice that received docetaxel 3 days earlier. This increase was due to the influx of helper/inducer T-lymphocytes and natural killer cells. Immunosuppression of tumor-bearing mice with 6 Gy whole-body irradiation prior to tumor isotransplantation reduced docetaxel-induced lymphocyte infiltration of tumors, antitumor and anti-metastatic action of docetaxel, and docetaxel-induced enhancement of tumor radioresponse. Thus, our results showed that docetaxel stimulates tumor infiltration with immune cells, which then participate in antitumor action of docetaxel alone or when combined with radiotherapy.

Reactive pocket epithelium in untreated chronic periodontal disease: possible derivation from developmental remnants of the enamel organ and root sheath

The pathological lining epithelium of destructive periodontitis was studied by analysis of the expression of intermediate filament proteins in biopsies of untreated advanced periodontitis. The cytokeratin (CK) pair 8/18 characteristic of simple epithelia was expressed consistently in a distribution pattern confined to the reactive pocket epithelium. The pattern of CK8/18 expression was complex with two broad presentations evident. In two-thirds of the advanced disease biopsies, the entire pathological lining epithelium was strongly reactive for both CK8 and CK18. In the remainder, the more superficial lining epithelium was mixed with foci of reactive and unreactive cells, with the deeper epithelium uniformly reactive. Only occasional highly localised reactivity for the simple keratins (CK8/18) was found in the lining epithelia of biopsies from minimally inflamed periodontal tissues. The pathological lining epithelium of advanced periodontitis was further characterised by the co-expression in basal layers of CK14, and of CK13 but not CK4, which are characteristic of suprabasal layers of stratified squamous epithelia. Cytokeratin 17, a marker of high turnover and migrating epithelial cells was extremely variable with no clear association between expression pattern and location of the epithelium ordisease status. There was no reactivity for CK10/11 typical of cornifying cells nor of vimentin, the characteristic intermediate filament of mesenchymal cells. The intermediate filament protein profile of the reactive lining epithelium was indistinguishable from the reactive epithelium present in three of five biopsies of periapical granulomas containing hyperplastic epithelium from activation of the developmental remnants of Hertwig's sheath, known as the cell rests of Malassez. The data reported are compatible with a contribution by remnants of developmental epithelium, including the reduced enamel epithelium and the cell rests of Malassez, to the reactive lining epithelium of the subgingival pocket in the pathogenesis of chronic periodontitis.

Clinical signs, histopathology and genetics of experimental transmission of BSE and natural scrapie to sheep and goats

This paper compares the dinical signs, histopathology, detection of PrPSc protein and PrP genetics of the transmission of BSE to sheep and goats, with the effects of the transmission of natural scrapie from a brain homogenate from a single sheep. After intracerebral and oral inoculations there were similarities in the clinical signs due to the two sources of infection, but there were differences in pathology at the end stage of disease and in the genotypes of the sheep which succumbed to the challenges. The incubation period of BSE was associated with the sheep PrP codon 171 genotype, but the natural scrapie source, despite inducing disease only in known susceptible genotypes, showed no clear association with PrP genotype.

The effects of low level laser irradiation on osteoblastic cells

Low level laser therapy has been used in treating many conditions with reports of multiple clinical effects including promotion of healing of both hard and soft tissue lesions. Low level laser therapy as a treatment modality remains controversial, however. The effects of wavelength, beam type, energy output, energy level, energy intensity, and exposure regime of low level laser therapy remain unexplained. Moreover, no specific therapeutic window for dosimetry and mechanism of action has been determined at the level of individual cell types. The aim of this study was to investigate the effects of low level laser irradiation on the human osteosarcoma cell line, SAOS-2. The cells were irradiated as a single or daily dose for up to 10 days with a GaAlAs continuous wave diode laser (830 nm, net output of 90 mW, energy levels of 0.3, 0.5, 1, 2, and 4 Joules). Cell viability was not affected by laser irradiation, with the viability being greater than 90% for all experimental groups. Cellular proliferation or activation was not found to be significantly affected by any of the energy levels and varying exposure regimes investigated. Low level laser irradiation did result in a heat shock response at an energy level of 2 J. No significant early or late effects of laser irradiation on protein expression and alkaline phosphatase activity were found. Investigation of intracellular calcium concentration revealed a tendency of a transient positive change after irradiation. Low level laser irradiation was unable to stimulate the osteosarcoma cells utilised for this research at a gross cell population level. The heat shock response and increased intracellular calcium indicate that the cells do respond to low level laser irradiation. Further research is required, utilising different cell and animal models, to more specifically determine the effects of low level laser irradiation at a cellular level. These effects should be more thoroughly investigated before low level laser therapy can be considered as a potential accelerator stimulus for orthodontic tooth movement.

A centuries-long epidemic of scrapie in British sheep?

The apparent persistence of scrapie in British sheep for more than 250 years is difficult to explain. Susceptibility to scrapie is associated with particular alleles at a single locus, the PrP gene. As the only known effect of these alleles is to confer susceptibility to a fatal disease, natural selection is expected to reduce their frequency, as has been observed in practice during scrapie outbreaks in single sheep flocks. Susceptibility alleles, and hence scrapie itself, are therefore expected to become rare, yet the disease remains widespread. We suggest that the paradox of scrapie's persistence can be explained by the exceptionally long time-scales inherent in the epidemiology of the disease. It is proposed that scrapie should be regarded as epidemic in British sheep but, unlike more familiar epidemics, which have time-scales of months or years, the scrapie epidemic has a time-scale of centuries. This interpretation implies that scrapie should eventually disappear from the sheep population.

Potentiation of ovarian OCa-1 tumor radioresponse by poly (L-glutamic acid)-paclitaxel conjugate

PURPOSE

It has been shown that paclitaxel (TXL) can strongly enhance tumor cells' sensitivity to radiation. We examined whether the radiosensitizing effect of paclitaxel can be further enhanced when it is delivered systemically as a polymer-drug conjugate that provides enhanced tumor uptake and prolonged release of TXL in the tumor.

METHODS AND MATERIALS

C3Hf/Kam mice bearing 8-mm murine ovarian OCa-1 tumors were treated with i.v.-injected Poly(L-glutamic acid)-paclitaxel (PG-TXL) at an equivalent TXL dose of 80 mg/kg, followed 24 h later by single doses of local radiation ranging from 5 to 15 Gy. To determine how long the radiopotentiation persisted at extended times after PG-TXL administration, mice with OCa-1 tumors were given i.v. PG-TXL and 4, 24, 48, 72, 120, or 168 h later their tumors were irradiated at a dose of 10 Gy. Antitumor activity was determined by delay in tumor growth. Cell cycle distribution was assayed using flow cytometry. Tumor vascular volume was estimated using Tc-99 m-labeled red blood cells.

RESULTS

PG-TXL strongly potentiated the radioresponse of the OCa-1 tumor. The enhancement factors ranged from 2.79 to 4.28, depending on radiation dose, when PG-TXL preceded radiation by 24 h. The enhancement factor derived from radiation dose-response curves was as high as 5.13. The radiosensitizing effect of PG-TXL was also dependent on the interval between PG-TXL administration and radiation delivery, with greater enhancement been observed when the interval was decreased. The percentage of G2/M cells was significantly increased to 21.4% 48 h after PG-TXL but declined to a preinjection level of 14.8% 72 h after PG-TXL. PG-TXL only moderately increased the tumor vascular volume by 37% 24 h after PG-TXL administration.

CONCLUSION

PG-TXL markedly potentiated response of OCa-1 tumor to radiation. When compared to literature data obtained from the same tumor model used here, PG-TXL exhibited stronger radiosensitization effect than TXL. Although its action is possibly mediated by arrest of cells in G2/M phases of cell cycle and by increased tumor blood supply, PG-TXL may exert its radiopotentiation activity through increased tumor uptake of PG-TXL and sustained release of TXL in the tumor. Our results show that conjugation of TXL to a polymer has the potential to further enhance its radiosensitizing activity and that clinical trials of PG-TXL in combination with radiation is warranted.

Vascular remodelling in chronic inflammatory periodontal disease

Periodontitis is a chronic inflammatory disease of the highly vascularised supporting tissues of the teeth. Little is known about the vascular changes in untreated advanced periodontitis. Using confocal immunofluorescence microscopy and morphometry, we defined and quantified vascular remodelling in this lesion. In the connective tissue subjacent to the altered epithelium lining of the periodontal pocket, there was a significant increase in the numerical density of vascular profiles, primarily accounted for by vessels > or = 25 microm in diameter. In addition, vascular basement membranes were thickened and there was accumulation of non-vascular basement membrane remnants. We investigated the distribution of major angiogenic growth factors in periodontitis using immunohistochemistry. Basic fibroblast growth factor, although consistently associated with blood vessels, showed no regional variation in its distribution. In contrast, there was a marked regional variation in the intensity of immunostaining for vascular endothelial growth factor, with significantly reduced staining of the pocket epithelium. The changes in the vascularity of the periodontal connective tissues in untreated advanced periodontitis may be, in part, a consequence of altered expression of angiogenic activity by the epithelium. In turn, this may reflect the epithelial response to microbial flora in the microenvironment of the periodontal pocket.

The signature of scrapie: differences in the PrP genotype profile of scrapie-affected and scrapie-free UK sheep flocks

The amino-acid sequence of the PrP protein plays an important role in determining whether sheep are susceptible to scrapie. Although the genetics of scrapie susceptibility are now well understood, there have been few studies of the PrP gene at the population level, especially in commercially farmed sheep. Here we describe the PrP genetic profiles of the breeding stock of four UK sheep flocks, comprising nearly 650 animals in total. Two flocks had been scrapie affected for about eight years and two were scrapie free. Scrapie-resistant PrP genotypes predominated in all flocks but highly susceptible genotypes were present in each case. The distribution of PrP genotypes was similar in the scrapie-affected and scrapie-free flocks. The former, however, showed a slight but significant skew towards more susceptible genotypes despite their previous losses of susceptible sheep. Surprisingly, this skew was apparent in younger, but not older, sheep. We suggest that these patterns may occur if sheep flocks destined to become scrapie affected are predisposed by a genetic profile skewed towards susceptibility. The age structure of the scrapie-affected flocks suggests that the number of losses attributable directly or indirectly to scrapie considerably exceeds that recognized by the farmers, and also that significant losses may occur even in sheep of a moderately susceptible genotype. Similar patterns were not detected in the scrapie-free flocks, indicating that these losses are associated with scrapie infection as well as genotype.

Airway inflammation in a murine model of chronic asthma: evidence for a local humoral immune response

BACKGROUND

Asthma is an acute-on-chronic inflammatory disease of the airways characterized by recruitment of eosinophils into the epithelial layer, chronic inflammation in the lamina propria, as well as variable accumulation of mast cells in the airway wall. The role of local production of allergen-specific immunoglobulins in triggering mast cell-mediated asthmatic inflammation is unknown.

METHODS

We used a chronic inhalational exposure model of asthma in ovalbumin-sensitized BALB/c mice to examine the phenotype of immunoglobulin-secreting cells and mast cells in the airway wall. In parallel, we assayed ovalbumin-specific IgG and total IgE in the plasma of these animals.

RESULTS

In sensitized mice exposed to aerosolized ovalbumin for 6 weeks, aggregates of chronic inflammatory cells consisted of a majority of plasmacytoid cells, including numerous IgG-synthesizing cells, which were significantly increased in sensitized animals compared to controls. IgA-synthesizing cells were also present, but were not increased in the sensitized exposed mice. Immunoglobulins in the cytoplasm of the plasma cells were demonstrated to be antigen-specific. No IgM-or IgE-synthesizing cells were observed, although levels of total IgE in the plasma were significantly increased. There was no recruitment of mast cells of either the mucosal or the connective tissue phenotype into the lamina propria or the epithelium.

CONCLUSION

In this experimental model of chronic asthma, the pattern of inflammation in the airway wall is consistent with development of a local IgG-mediated humoral immune response. However, there is no evidence of local production of IgE or recruitment of mast cells.

Transmission of BSE by blood transfusion in sheep

We have shown that it is possible to transmit bovine spongiform encephalopathy (BSE) to a sheep by transfusion with whole blood taken from another sheep during the symptom-free phase of an experimental BSE infection. BSE and variant Creutzfeldt-Jakob disease (vCJD) In human beings are caused by the same infectious agent, and the sheep-BSE experimental model has a similar pathogenesis to that of human vCJD. Although UK blood transfusions are leucodepleted--a possible protective measure against any risk from blood transmission--this report suggests that blood donated by symptom-free vCJD-infected human beings may represent a risk of spread of vCJD infection among the human population of the UK.

Expression patterns of E-cadherin, involucrin, and connexin gap junction proteins in the lining epithelia of inflamed gingiva

The structural integrity and functional differentiation of the lining epithelium were studied in relation to inflammatory changes associated with destructive periodontitis. In the different regions of lining epithelia from clinically healthy gingiva and periodontitis, comparisons were made of the expression patterns of E-cadherin, which is critical in intercellular adhesion; of proteins associated with gap junction communication channels; and of involucrin, which is a key marker of differentiation in stratified epithelia. Filamentous actin (F-actin), which is important in cell structural integrity, attachment, and migration, was also examined. Semiquantitative immunohistochemical analysis revealed that in both clinically healthy gingiva and lesions of advanced periodontitis, expression patterns of E-cadherin, involucrin, and connexins 26 and 43 were similar, with a statistically significant reduction in staining intensity from the external oral epithelium, through the gingival sulcus, to the junctional epithelium or pocket epithelium, respectively. Furthermore, there was a striking reduction in staining for E-cadherin, involucrin, and both connexins in the pathological lining epithelium of the periodontal pocket. These changes were associated with marked alterations of filamentous actin expression, collectively indicating profound perturbation of the epithelial structure. The data reported support the concept that the ability of the pathological lining epithelium to function as an effective barrier against the ingress of microbial products into the tissues is severely compromised.

Methodologic concerns regarding estimates of physical violence in sexual coercion: overstatement or understatement?

Self-report measures of sexual violence that ask women whether they have experienced threats of physical violence have attracted criticism in recent years; detractors claim that these measures lead researchers to overestimate the prevalence of sexual violence. Our study explored this issue by collecting data on the prevalence of threats versus force in the context of sexual aggression. Female undergraduates at two universities (n1 = 69; n2 = 111) were asked about their experiences with sexual coercion using a revised version of the Sexual Experiences Scale (Koss and Gidycz, 1985). Four of the original items were modified to distinguish between sexual contact that occurred as a result of a perpetrator using physical force and sexual contact that occurred because a perpetrator threatened physical violence. Analyses of the revised items revealed that the use of physical force was at least as likely as threats and that for some types of sexual acts, physical force was actually more likely than verbal threats. Furthermore, prevalence figures for three of the four types of sexual acts considered were not significantly altered by collapsing threat of force with use of force. Implications for future research on women's experiences of sexual coercion are discussed.

[Recent studies on anti-angiogenesis in cancer therapy]

Angiogenesis is known to be a critical process for the tumor growth and metastasis. There are many indigenous role-players in tumor angiogenesis and anti-angiogenesis, where tumor-host interaction may work. A lot of agents with anti-angiogenic activity have been developed for anti-cancer treatment. Several agents including Marimastat, Primostat, Neovastat, Bay-12-9566m, Interferon-alpha, SU101, retinoids, and IM862, are/were under phase-three study. There are still many future-promising results of basic or clinical studies on inhibitors of MMPs, and inhibitors of VEGF/R, Endostatin, somatostatin analogues, COX-2 inhibitors, and others. Most of the combination treatments of antiangiogenetic agent and conventional anticancer agents therapy, or radiation therapy as we reported, showed relatively small or minute increase in toxicity of these cytotoxic treatments.

Tumor irradiation enhances the tumor-specific distribution of poly(L-glutamic acid)-conjugated paclitaxel and its antitumor efficacy

The poly(L-glutamic acid)-paclitaxel (PG-TXL) conjugate has been shown to exhibit significantly greater antitumor activity than conventionally formulated paclitaxel (TXL) against solid tumors (Li et al., Cancer Res., 58: 2404-2409, 1998). Here we report that local tumor irradiation enhanced the distribution of PG-TXL given 24 h later to ovarian OCa-1 carcinoma implanted i.m. in C3Hf/Kam mice. Radiation significantly increased tumor uptake of PG-TXL and tumor vascular permeability, caused elevation of the serum concentration of vascular endothelial growth factor, and arrested OCa-1 cells in the G1 phase of cell cycle. The enhancement factors, as measured by incremental tumor growth delay compared with PG-TXL alone, ranged from 1.36-4.44. Complete tumor regression was also observed at a higher radiation dose (>10 Gy) and a higher PG-TXL dose (>80 mg equivalentTXL/kg). Furthermore, combined radiation and PG-TXL produced a significantly greater tumor growth delay than treatment with radiation and TXL when both drugs were given at the same equivalent TXL dose of 60 mg/kg 24 h after tumor irradiation (enhancement factors, 4.44 versus 1.50). These data suggest that conjugation of TXL to poly(L-glutamic acid) is necessary for improved response and that the supra-additive effect of combined radiation and PG-TXL therapy is due in part to modulation of the enhanced permeability and retention effect of macromolecules by radiation. We propose a treatment strategy combining radiation and macromolecular chemotherapy that may have important clinical implications in terms of scheduling and optimization of the therapeutic ratio.

Detection of polymorphisms in the prion protein gene in a population of Irish Suffolk sheep

Natural scrapie is associated with polymorphisms in the prion protein (PrP) gene. In Suffolks, codon 171 is the codon at which most variation is found; RR171 is thought to be associated with resistance to developing the clinical signs of the disease and QQ171 is associated with susceptibility to the disease. The objectives of this study were first to determine the PrP genotypes of Suffolk stock rams in Ireland, and secondly to compare the genotype profiles of ram lambs from flocks where a breeding programme based on the genotype AA136RR154RR171 had been initiated and from flocks where there was no breeding programme based on PrP genotype. Approximately 13 per cent of the stock rams genotyped in the Irish population were genetically susceptible to showing the clinical signs of the disease. However, lambs from farms that had initiated a selective breeding strategy for RR171 over the past year had a larger proportion of RR171 and a smaller proportion of QQ171 than the stock rams or ram lambs from farms not applying a breeding strategy.

Knowledge of display rules in prelingually deaf and hearing children

Deaf children of elementary and secondary school age participated in a study designed to examine their understanding of display rules, the principles governing the expression and concealment of emotion in social situations. The results showed that deaf children's knowledge of display rules, as measured by their reported concealment of emotion, was comparable to that of hearing children of the same age. However, deaf children were less likely to report that they would conceal happiness and anger. They were also less likely to produce reasons for concealing emotion and a smaller proportion of their reasons were prosocial, that is, relating to the feelings of others. The results suggest that the understanding of display rules (which function to protect the feelings of other people) may develop more gradually in deaf children raised in a spoken language environment than it does in hearing children.

Preferential enhancement of tumor radioresponse by a cyclooxygenase-2 inhibitor

Cyclooxygenase-2 (COX-2), an inducible isoform of cyclooxygenase, is overexpressed in many types of malignant tumors, where it mediates production of prostaglandins (PGs), which in turn may stimulate tumor growth and protect against damage by cytotoxic agents. This study investigated whether SC-'236, a selective inhibitor of COX-2, potentiates antitumor efficacy of radiation without increasing radiation injury to normal tissue. Mice bearing the sarcoma FSA in the hind legs were treated daily for 10 days with SC-'236 (6 mg/kg given in the drinking water) when tumors were 6 mm in diameter. When tumors reached 8 mm in diameter, the mice were given 11- to 50-Gy single-dose local tumor irradiation with or without SC-'236. SC-'236 inhibited tumor growth on its own, and it greatly enhanced the effect of tumor irradiation. The growth delay was increased from 14.8 days after 25-Gy single dose to 28.4 days after the combined treatment (P = 0.01). SC-'236 reduced TCD50 (radiation dose yielding 50% tumor cure) from 39.2 Gy to 20.9 Gy (enhancement factor = 1.87). SC-'236 did not appreciably alter radiation damage to jejunal crypt cells and tissue involved in the development of radiation-induced leg contractures. The SC-'236-induced enhancement of tumor radioresponse was associated with a decrease in PGE2 levels in FSA tumors. The drug had no effect on radiation-induced apoptosis. Neoangiogenesis was inhibited by SC-'236, which could account for some of the increase in tumor radioresponse. Overall, our findings demonstrated that treatment with a selective inhibitor of COX-2 greatly enhanced tumor radioresponse without markedly affecting normal tissue radioresponse. Thus, COX-2 inhibitors have a high potential for increasing the therapeutic ratio of radiotherapy.

In vivo enhancement of tumor radioresponse by C225 antiepidermal growth factor receptor antibody

Overexpression of epidermal growth factor receptor (EGFR) has been correlated with tumor resistance to cytotoxic agents, including radiation (T. Akimoto et al., Clin. Cancer Res., 5: 2884-2890, 1999), and thus is a candidate target for anticancer treatment. This study investigated whether treatment with C225 anti-EGFR antibody would improve tumor response to radiotherapy. Nude mice bearing 8-mm-diameter A431 tumor xenografts in the hind leg were treated with C225 antibody, 18 Gy of single-dose local tumor irradiation, or both. C225 was given i.p. at a dose of 1 mg/mouse 6 h before irradiation or 6 h before and 3 and 6 days after irradiation. Delay in tumor growth was the treatment end point. C225 dramatically improved the efficacy of local tumor irradiation, particularly when multiple injections of C225 were administered. Tumor radioresponse was enhanced by a factor of 1.59 by a single dose and by a factor of 3.62 by a doses of C225. Histological analyses of tumors revealed that C225 caused a striking increase in central tumor necrosis associated with hemorrhage and vascular thrombosis when combined with radiotherapy. In addition, C225 induced heavy tumor infiltration with granulocytes, increased tumor cell terminal differentiation, and inhibited tumor angiogenesis. We conclude that C225 anti-EGFR antibody enhances tumor radioresponse by multiple mechanisms that may involve direct and indirect actions on tumor cell survival.

Rapid disappearance of the medial epithelial seam during palatal fusion occurs by multifocal breakdown that is preceded by expression of alpha smooth muscle actin in the epithelium

Breakdown of the medial epithelial seam (MES) is essential to allow bridging of the mesenchyme during palatal fusion. Evidence exists for three mechanisms for this breakdown that are incompatible at the level of individual cells in the seam. To determine if breakdown of the seam was regionally restricted, 3-dimensional reconstructions were generated using volume rendering software from 1 micron serial sections in the sagittal plane of rat palates fixed during the process of fusion. The earliest break detected in electron micrographs was cell separation and in reconstructions was a discrete defect, with a rounded outline, nearer to the nasal than to the oral margin of the seam. Further breakdown produced a pattern of rounded defects along the nasal margin of the seam resulting in interconnected columns of cells preferentially attached to the oral epithelium. Computer generated slicing of reconstructed seams showed that groups of cells evident in cross-sections as islands at this stage of breakdown of the MES could be artifacts. Unequivocal islands of epithelial cells formed later in fusion had a rounded outline, an incomplete basal lamina and a halo of cells containing phagocytosed apoptotic debris. The pattern of breakdown indicated that the MES breaks down under tension. Laser confocal microscopy of sections and whole-mounts of palates demonstrated alpha-smooth muscle actin preferentially localized in the epithelial cells of the palatal shelves immediately before and during formation of the seam. Expression in epithelial cells of the isoform of actin normally restricted to smooth muscle cells engaged in tonic contraction supported an interpretation that the epithelial cells of the seam may be capable of generating tension during the palatal fusion event.

Effect of docetaxel on the therapeutic ratio of fractionated radiotherapy in vivo

The aim of this investigation was to determine whether docetaxel increases the therapeutic ratio of fractionated radiotherapy in vivo. Two tumor types were chosen based on their sensitivity to docetaxel as a single agent: (a) docetaxel-sensitive MCa-4 mammary adenocarcinoma, which responds to docetaxel by G2-M-phase cell cycle arrest, apoptosis, and subsequent reoxygenation of surviving tumor cells; and (b) docetaxel-resistant SCC-VII squamous cell carcinoma, which responds to docetaxel treatment only by G2-M-phase arrest. Response of the normal jejunal mucosa in mice was compared to the response of both tumor types to confirm therapeutic gain. We conducted micromorphometric analysis of tumor cell mitosis, assayed apoptosis by its histological appearance in tissue sections, and determined tumor response by tumor growth delay. Normal tissue response of the jejunum was assayed by micromorphometric analysis of mitotic and apoptotic indices, and clonal crypt stem cell survival was measured using the microcolony assay. Two clinically relevant treatment schedules were tested for both antitumor efficacy and normal tissue toxicity: (a) a single bolus of docetaxel (33 mg/kg i.v.) 24 h before five daily fractions of radiation; and (b) daily administration of docetaxel (8 mg/kg i.v.) with radiation delivered at the peak of mitotic arrest (9 h for MCa-4 and 6 h for SCC-VII tumors). The best therapeutic gain for docetaxel-sensitive MCa-4 was achieved with a single bolus of drug 24 h before the start of fractionated radiotherapy (therapeutic gain = 2.04). This schedule takes advantage of reoxygenation of hypoxic tumor cells during the interval between drug treatment and radiation delivery. The best therapeutic gain for docetaxel-resistant SCC-VII was achieved with intermittent multiple doses of docetaxel given during the course of fractionated radiotherapy. This schedule maximized the exposure of cells to radiation while they were arrested by docetaxel in the radiosensitive G2-M phases of the cell cycle (enhancement factor = 2.0). Final therapeutic gain was reduced to 1.59 because of increased normal tissue toxicity in mice treated with multiple intermittent doses of docetaxel in combination with fractionated radiotherapy. Thus, docetaxel greatly enhanced tumor response to fractionated radiotherapy, but the magnitude of therapeutic efficacy depended on drug-radiation scheduling. The greatest therapeutic gain in the treatment of docetaxel-sensitive tumors was achieved by a single large dose of docetaxel administered 1 day before the initiation of fractionated radiotherapy and in the treatment of docetaxel-resistant tumors by daily concomitant docetaxel-radiation treatments.

Functional specificity of MutL homologs in yeast: evidence for three Mlh1-based heterocomplexes with distinct roles during meiosis in recombination and mismatch correction

The yeast genome encodes four proteins (Pms1 and Mlh1-3) homologous to the bacterial mismatch repair component, MutL. Using two hybrid-interaction and coimmunoprecipitation studies, we show that these proteins can form only three types of complexes in vivo. Mlh1 is the common component of all three complexes, interacting with Pms1, Mlh2, and Mlh3, presumptively as heterodimers. The phenotypes of single deletion mutants reveal distinct functions for the three heterodimers during meiosis: in a pms1 mutant, frequent postmeiotic segregation indicates a defect in the correction of heteroduplex DNA, whereas the frequency of crossing-over is normal. Conversely, crossing-over in the mlh3 mutant is reduced to approximately 70% of wild-type levels but correction of heteroduplex is normal. In a mlh2 mutant, crossing-over is normal and postmeiotic segregation is not observed but non-Mendelian segregation is elevated and altered with respect to parity. Finally, to a first approximation, the mlh1 mutant represents the combined single mutant phenotypes. Taken together, these data imply modulation of a basic Mlh1 function via combination with the three other MutL homologs and suggest specifically that Mlh1 combines with Mlh3 to promote meiotic crossing-over.

Bcl-2 expression correlates with apoptosis induction but not tumor growth delay in transplantable murine lymphomas treated with different chemotherapy drugs

PURPOSE

Previously, we have reported that the bcl-2-expressing murine lymphoma cell line LY-ar is resistant to chemotherapy-induced apoptosis when compared to the non-bcl-2-expressing LY-as cell line. The intent of the present study was to determine whether this relationship extends to lymphomas produced from these cell lines in syngeneic mice, after treatment with the same chemotherapy agents.

METHODS

LY-ar and LY-as tumors were grown in the hind legs of syngeneic mice. They were subsequently exposed to graded doses of cisplatin (CP), etoposide (VP-16), Adriamycin (ADR), cytarabine (ara-C), cyclophosphamide (CY), or camptothecin (CAM). Apoptotic bodies were scored in histological sections of tumors that had been stained with hematoxylin and eosin. Tumor growth delay was determined on tumors that were treated when they were 8 mm in diameter. Thereafter, tumor diameter was measured daily with a vernier caliper until they had grown to a maximum of 16 mm in diameter.

RESULTS

When transplanted into host animals, tumors derived from these two cell lines and treated in vivo with CP, VP-16, ADR, ara-C, CY, and CAM displayed apoptotic propensities similar to those seen in the same cell lines when treated in vitro. Generally, for all the drugs tested, apoptotic indices in LY-as tumors were significantly higher than in LY-ar tumors. However, tumor growth delay measurements could not be predicted with any accuracy from the apoptotic indices. For some drugs LY-ar tumors were more sensitive than LY-as tumors (CP, Vp-16, ADR, ara-C), yet LY-ar tumors were more resistant to CY.

CONCLUSIONS

Despite considerable interest in using apoptotic indices as predictors of treatment outcome, the data presented here suggest that these relationships are very complex. This may be especially true for chemotherapy agents for which effects in vivo are complicated by pharmacokinetics, host effects, and tumor cell heterogeneity.