Enhancement of radiation-induced regrowth delay by gemcitabine in a human tumor xenograft model.

Gemcitabine, a cytidine nucleoside analogue, has schedule-dependent antitumor activity in vitro and in vivo. Gemcitabine also has dose- and time-dependent radiosensitization properties in vitro. Thus it may have therapeutic application in combination with radiation. The aims of this study were to investigate whether gemcitabine could enhance radiation-induced tumor regrowth delay in a human squamous carcinoma (FaDu) xenograft in nude mice and to examine the effect of gemcitabine on radiation-induced apoptosis in in vivo tumors. Radiation was given locally to the tumors twice daily in 2 Gy fractions over 2 weeks for 5 days/week. Significant regrowth delay enhancement was observed which was dependent on gemcitabine schedule. Effective schedules using maximum tolerated gemcitabine doses were twice weekly and once weekly, but not daily. Significant toxicity occurred with radiation plus twice weekly gemcitabine, but enhancement was seen using gemcitabine doses well below the maximum tolerated dose. Both gemcitabine and radiation led to apoptotic cell death, but this was not increased when both treatments were combined. These results indicate that gemcitabine may be of therapeutic value as a radiation enhancer in the treatment of human cancers. Preliminary studies suggest that increased apoptotic cell death is not a mechanism leading to this enhancement.

Radioenhancement by cisplatin with accelerated fractionated radiotherapy in a human tumour xenograft.

The aim of the present study was to investigate whether cisplatin would enhance the radioresponse of a human tumour xenograft when given in different schedules combined with accelerated fractionated radiation therapy. A human squamous carcinoma of the hypopharynx, FaDu, was grown in the thigh of athymic nude mice. Tumours were exposed to twice-daily 2-Gy fractions, applied 6 h apart over 2 weeks, 5 days a week, alone or combined with cisplatin given at maximally tolerated doses in three different schedules: (1) i.p. as a single bolus (SB) or (2) i.p. as a daily bolus at 30 min before the first daily radiation fraction or (3) s.c. as a continuous infusion through a mini-osmotic pump over 13 days, commencing 24 h prior to the first daily radiation fraction. The end point for the study was tumour growth delay (TGD), calculated as the difference between the delay in regrowth to 200% of the initial tumour size in treated versus control mice. SB cisplatin plus radiation showed only an additive effect on TGD, whereas daily-bolus and continuous-infusion cisplatin demonstrated a greater than additive effect when combined with accelerated fractionated radiation in this human tumour model. Cisplatin appears to be especially beneficial as a radiation enhancer when given throughout the course of radiation.

The teratogenic effects of salicylic acid on the developing nervous system in rats in vitro.

Aspirin ingestion in humans and animals has been reported to lead to a range of undesirable outcomes, including fetal death, growth retardation, and congenital abnormalities. Rat embryos were cultured for 48 h in 100-300 micrograms/ml of salicylic acid, a metabolite of aspirin, days 9.5-11.5 of gestation. When compared to growth in control embryos, a significant dose-dependent decrease in crown-rump lengths, somite numbers, and yolk sac diameters was observed. There was also a significant increase in overall dysmorphology, including eye, brachial arch, and heart anomalies, and an absence of forelimb buds. The neural tube was especially vulnerable and had frequently failed to close. Cellular and ultrastructural examination revealed extensive cell death in the neuroepithelium, with a lesser effect on the mesenchymal cells. Large condensed blebs projected into the ventricular lumen, and cell membranes as well as the basal lamina were severely disrupted, with all cytoplasmic organelles affected in dying cells. It is likely that the extensive cell necrosis and blebbing in the developing neuroepithelium at the site of neural tube fusion may be involved in failed neurulation, while necrosis at other sites in the cranial neuroepithelium may be linked with previously reported intellectual and behavioural abnormalities.

A quantitative and morphological study of ectodermal microvilli in ten areas in the control and experimental prenatal rat.

This study provides a baseline of mainly quantitative morphologic information in relation to the ectodermal microvilli in ten areas in the control and experimental prenatal rat with special reference to the period of neural tube closure. Embryos from six litters were used and ten areas were examined mainly with the scanning electron microscope. Statistical analysis showed no significant difference between litters nor between the ten areas examined. In the 376 hr (day 15.6) fetus only the ectodermal cells of the nostril region demonstrated a rich population of microvilli, a fact possibly associated with late maturation of that region. Some evidence is provided to show that there is an increase in the population of microvilli in the 276 hr (day 11.5) embryo following experimentally induced zinc deficiency and introduction of nicotine in the culture medium. The possible mechanisms underlying the increase in ectodermal microvilli are i) an attempt by ectodermal cells to absorb nutrients, ii) a reflection of cells under stress, iii) failure of early embryonic ectodermal cells to shed microvilli normally associated with developmental changes, and iv) a generalized developmental delay rather than some cellular response to a trace element nutritional deficiency and a teratogen.

The teratogenic effects of nicotine in vitro in rats: a light and electron microscope study.

Cigarette smoking in pregnant women has been shown to lead to intrauterine growth retardation and fetal death, and possibly also to neural dysmorphology and long-term learning deficits in the offspring. Because the teratogenic agent in cigarette smoke remains controversial, the present study on rat embryos in culture examined specifically whether nicotine can cause neural dysmorphology and, hence, act as a nervous system teratogen. This in vitro study confirmed previous reports in utero that nicotine leads to growth retardation, and, in addition, demonstrated that development of the nervous system, particularly the forebrain, as well as the branchial arches was impaired, possibly leading to microcephaly and cleft palate respectively in term fetuses. Cellular disruption and necrosis occurred in the neuroepithelium and underlying mesenchyme, with the effect being dose dependent. Ultrastructurally, there was severe disruption of cell and organelle membranes, with many healthy cells containing engulfed, whole condensed or remnants of dead cells. This study demonstrates that nicotine acts as a nervous system teratogen leading to gross and cellular dysmorphology. Suggested mechanisms for nicotine action include the possibility that the highly lipid soluble teratogen may exert its effects directly on the membranes or indirectly through oxidative membrane damage.

Cortico-cortical connections of the motor cortex in the brushtailed possum (Trichosurus vulpecula).

Cortico-cortical connections of motor cortex in the marsupial brushtailed possum were traced by making injections of horseradish peroxidase (HRP) into two parts of motor cortex: the rostral agranular part which does not overlap somatosensory cortex, and the caudal part which does. Following injections in motor cortex, labelled neurons were observed on the same side of the brain within somatosensory areas 1 and 2 and in parietal cortex just caudal to S1, with most neurons in cortical Layers 2-4. Commissural connections were found in half of the experiments, with many labelled neurons in cortical Layer 5. We have compared the pattern of cortico-cortical connections in the possum with those seen in some other mammals, which appear generally similar.