Deadly diving? Physiological and behavioural management of decompression stress in diving mammals

Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N(2)) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N(2) tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N(2) loading to management of the N(2) load. This suggests several avenues for further study, ranging from the effects of gas bubbles at molecular, cellular and organ function levels, to comparative studies relating the presence/absence of gas bubbles to diving behaviour. Technological advances in imaging and remote instrumentation are likely to advance this field in coming years.

Implications for psychedelic-assisted psychotherapy: functional magnetic resonance imaging study with psilocybin

BACKGROUND

Psilocybin is a classic psychedelic drug that has a history of use in psychotherapy. One of the rationales for its use was that it aids emotional insight by lowering psychological defences.

AIMS

To test the hypothesis that psilocybin facilitates access to personal memories and emotions by comparing subjective and neural responses to positive autobiographical memories under psilocybin and placebo.

METHOD

Ten healthy participants received two functional magnetic resonance imaging scans (2 mg intravenous psilocybin v. intravenous saline), separated by approximately 7 days, during which they viewed two different sets of 15 positive autobiographical memory cues. Participants viewed each cue for 6 s and then closed their eyes for 16 s and imagined re-experiencing the event. Activations during this recollection period were compared with an equivalent period of eyes-closed rest. We split the recollection period into an early phase (first 8 s) and a late phase (last 8 s) for analysis.

RESULTS

Robust activations to the memories were seen in limbic and striatal regions in the early phase and the medial prefrontal cortex in the late phase in both conditions (P<0.001, whole brain cluster correction), but there were additional visual and other sensory cortical activations in the late phase under psilocybin that were absent under placebo. Ratings of memory vividness and visual imagery were significantly higher after psilocybin (P<0.05) and there was a significant positive correlation between vividness and subjective well-being at follow-up (P<0.01).

CONCLUSIONS

Evidence that psilocybin enhances autobiographical recollection implies that it may be useful in psychotherapy either as a tool to facilitate the recall of salient memories or to reverse negative cognitive biases.

Ultrastructure of Thiothrix spp. and "Type 021N" Bacteria

The ultrastructural features of two groups of filamentous sulfur bacteria, Thiothrix spp. and an unnamed organism designated "type 021N," were examined by transmission electron microscopy. Negative staining of whole cells and filaments with uranyl acetate revealed the presence of tufts of fimbriae located at the ends of individual gonidia of Thiothrix sp. strain A1 and "type 021N" strain N7. Holdfast material present at the center of mature rosettes was observed in thin sections stained with ruthenium red. A clearly defined sheath enveloped the trichomes of two of three Thiothrix strains but was absent from "type 021N" filaments. The outer cell wall appeared more complex in "type 021N" strains than in Thiothrix isolates. Bulbs or clusters of irregularly shaped cells, often present in filaments of "type 021N" bacteria, appeared to result from crosswalls which formed at angles oblique to the filament axis. The multicellular nature of these sulfur bacteria was apparent in that only the cytoplasmic membrane and peptidoglycan layer of the cell wall were involved in the septation process. Sulfur inclusions which developed in the presence of sodium thiosulfate were enclosed by a single-layered envelope and located within invaginations of the cytoplasmic membrane.

The effects of water temperature on the energetic costs of juvenile and adult California sea lions (Zalophus californianus): the importance of skeletal muscle thermogenesis for thermal balance

As highly mobile marine predators, many pinniped species routinely encounter a wide range of water temperatures during foraging and in association with seasonal, geographical and climatic changes. To determine how such variation in environmental temperature may impact energetic costs in otariids, we determined the thermal neutral zone of adult and juvenile California sea lions (Zalophus californianus) by measuring resting metabolic rate using open-flow respirometry. Five adult female (body mass range =82.2-107.2 kg) and four juvenile (body mass=26.2-36.5 kg) sea lions were examined over experimental water temperatures ranging from 0 to 20 degrees C (adults) or 5 to 20 degrees C (juveniles). The metabolic rate of adult sea lions averaged 6.4+/-0.64 ml O(2) kg(-1) min(-1) when resting within the thermal neutral zone. The lower critical temperature of adults was 6.4+/-2.2 degrees C, approximately 4 degrees C lower than sea surface temperatures routinely encountered off coastal California. In comparison, juvenile sea lions did not demonstrate thermal neutrality within the range of water temperatures examined. Resting metabolic rate of the younger animals, 6.3+/-0.53 ml O(2) kg(-1) min(-1), increased as water temperature approached 12 degrees C, and suggested a potential thermal limitation in the wild. To determine whether muscle thermogenesis during activity could mitigate this limitation, we measured the active metabolic rate of juveniles swimming at water temperature (T(water))=5, 12 and 20 degrees C. No significant difference (F=0.377, P=0.583) in swimming metabolic rate was found among water temperatures, suggesting that thermal disadvantages due to small body size in juvenile sea lions may be circumvented by recycling endogenous heat during locomotor activity.

Causes and consequences of marine mammal population declines in southwest Alaska: a food-web perspective

Populations of sea otters, seals and sea lions have collapsed across much of southwest Alaska over the past several decades. The sea otter decline set off a trophic cascade in which the coastal marine ecosystem underwent a phase shift from kelp forests to deforested sea urchin barrens. This interaction in turn affected the distribution, abundance and productivity of numerous other species. Ecological consequences of the pinniped declines are largely unknown. Increased predation by transient (marine mammal-eating) killer whales probably caused the sea otter declines and may have caused the pinniped declines as well. Springer et al. proposed that killer whales, which purportedly fed extensively on great whales, expanded their diets to include a higher percentage of sea otters and pinnipeds following a sharp reduction in great whale numbers from post World War II industrial whaling. Critics of this hypothesis claim that great whales are not now and probably never were an important nutritional resource for killer whales. We used demographic/energetic analyses to evaluate whether or not a predator-prey system involving killer whales and the smaller marine mammals would be sustainable without some nutritional contribution from the great whales. Our results indicate that while such a system is possible, it could only exist under a narrow range of extreme conditions and is therefore highly unlikely.

The ontogeny of aerobic and diving capacity in the skeletal muscles of Weddell seals

Our objective was to determine the ontogenetic changes in the skeletal muscles of Weddell seals that transform a non-diving pup into an elite diving adult. Muscle biopsies were collected from pups, juveniles and adults and analyzed for changes in fiber type, mitochondrial density, myoglobin concentrations and aerobic, lipolytic and anaerobic enzyme activities. The fiber type results demonstrated a decrease in slow-twitch oxidative (Type I) fibers and a significant increase in fast-twitch oxidative (Type IIA) fibers as the animals mature. In addition, the volume density of mitochondria and the activity of lipolytic enzymes significantly decreased as the seals matured. To our knowledge, this is the first quantitative account describing a decrease in aerobic fibers shifting towards an increase in fast-twitch oxidative fibers with a significant decrease in mitochondrial density as animals mature. These differences in the muscle physiology of Weddell seals are potentially due to their three very distinct stages of life history: non-diving pup, novice diving juvenile, and elite deep diving adult. During the first few weeks of life, pups are a non-diving terrestrial mammal that must rely on lanugo (natal fur) for thermoregulation in the harsh conditions of Antarctica. The increased aerobic capacity of pups, associated with increased mitochondrial volumes, acts to provide additional thermogenesis. As these future elite divers mature, their skeletal muscles transform to a more sedentary state in order to maintain the low levels of aerobic metabolism associated with long-duration diving.

Allelic diversity within the high frequency Mamu-A2*05/Mane-A2*05 (Mane-A*06)/Mafa-A2*05 family of macaque MHC-A loci

Macaque species serve as important animal models of human infection and immunity. To more fully scrutinize their potential in both the analysis of disease pathogenesis and vaccine development, it is necessary to characterize the major histocompatibility complex (MHC) class I loci of Macaca mulatta (Mamu), Macaca nemestrina (Mane), and Macaca fascicularis (Mafa) at the genomic level. The oligomorphic Mamu-A2*05/Mane-A2*05 (previously known as Mane-A*06) family of macaque MHC-A alleles has recently been shown to be present at high frequency in both Indian rhesus and pig-tailed macaque populations. Using a locus-specific amplification and direct DNA typing methodology, we have additionally found that the locus encoding this family is very prevalent (75%) among a sampling of 182 Chinese rhesus macaques and has a high prevalence (80%) within a larger, independent cohort of 309 pig-tailed macaques. Interestingly, among the Chinese rhesus macaques, only six alleles previously identified in Indian-origin animals were observed, while three recently identified in Chinese-origin animals and 25 new alleles were characterized. Among the pig-tailed macaques, we observed 1 previously known (Mane-A*06) and 19 new alleles. Examination of the orthologous locus in a preliminary sampling of 30 cynomolgus macaques showed an even higher presence (87%) of Mafa-A2*05 family alleles, with 5 previously identified and 15 new alleles characterized. The continued discovery of novel alleles and thus further diversity within the Mamu-A2*05/Mane-A2*05/Mafa-A2*05 family indicates that this MHC-A locus, although highly conserved across the three species of macaques, has remained a dynamic entity during evolution.

Validation of genomic markers that predict distant recurrence risk via FISH assays in women with early stage breast carcinoma

10506

Background: Biomarkers offer the potential to better predict recurrence risk in early stage invasive breast cancer, especially if adaptable to common assays such as fluorescent in situ hybridization (FISH). We studied the ability of tumor copy numbers (CN) of 3 genes, BIRC5, CYP24, and PDCD6IP, to predict distant recurrence in women with breast cancer. Methods: We conducted a blinded, multi-site study of 350 women with lymph node negative, estrogen/progesterone receptor positive (ER/PR+), invasive ductal carcinomas with archived paraffin-embedded biopsy specimens available. Eligible women received local surgical and radiation treatment only (93) (LTO) or local treatment and tamoxifen therapy only (257), and had distant metastases or no evidence of distant recurrence with at least 5 years follow-up (FU). Tumors were subjected to FISH with DNA probes for the 3 genes to assess CN. A prognostic index (PI) was calculated for each patient based on the 3 genes’ CN. A predetermined threshold (3.0) was used to categorize PI's as low or high. Data were assessed by Fisher's exact analysis and by categorical and continuous Cox modeling. Results: The study included 350 women with Stage I (288) and II (62) disease. FU averaged 7.3 years. Distant recurrence occurred in 32 women (9.1%) overall and in 5.2% of women with Stage I disease. In a multivariate Cox analysis including continuous PI, age, tamoxifen treatment, grade, and tumor size, PI remained a significant predictor of recurrence for Stage I patients: OR=1.56, p=0.019, and Stage I/LTO patients: OR=6.02, p=0.00007. Using the PI as a categorical classifier, the high/low recurrence rates were significantly different: OR=2.24, p= 0.045. Similar results were seen in Stage I patients: OR=3.53, p=0.021 with recurrence rates of 3.5% and 11.5% in the low and high risk groups, respectively, and for the Stage I/LTO patients: OR=5.33, p=0.041. Conclusions: FISH analysis of 3 genes allows metastasis risk prediction in women with early stage ER/PR+ cancers. This may be particularly useful for Stage I cancers traditionally considered low risk. The markers are prognostic in that they predict metastasis in patients receiving only local therapy.

No significant financial relationships to disclose.

Susceptibility of Escherichia coli to L-selenaproline and other L-proline analogues in laboratory culture media and normal human urine

AIMS

The aims of this study were to identify analogues of L-proline which inhibit the growth of Escherichia coli in both laboratory culture media and normal human urine and to study their mechanisms of uptake.

METHODS AND RESULTS

The susceptibility of E. coli to L-proline analogues was studied by radial streak assays on agar plates and by minimal inhibitory concentration determinations in liquid media. Only L-selenaproline (SCA) inhibited growth in Mueller-Hinton medium and human urine as well as in glucose minimal medium. L-Proline did not prevent the inhibition of growth by SCA and strains defective in L-proline transport were as susceptible to SCA as wild-type strains. However, E. coli was resistant to SCA in the presence of L-cysteine and L-cystine. Spontaneous mutants selected for resistance to SCA or L-selenocystine were resistant to the other compound and had reduced growth in minimal medium containing L-cysteine or L-cystine as the sole sulfur source.

CONCLUSIONS

L-selenaproline inhibited the growth of E. coli under conditions that may occur in the urinary tract and appeared to be taken up by the L-cystine transport system.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although urinary tract infections caused by E. coli can be treated with sulfamethoxazole/trimethoprim and quinolones, resistance to these antibiotics has been increasing. These results suggest that L-selenaproline may represent a new class of compounds that could be used to treat these infections.

Growth of aligned ZnO nanorods

Growth of high-density and aligned ZnO nanorods on ZnO film substrate has been demonstrated using vapor-transport of thermally evaporated Zn metal powders followed by condensation. Morphological studies show that the nanorods grow preferentially from a hexagonal ZnO base with a uniform hexagonal structure following three-dimensional island-like growth mechanism. Structural and spectroscopic properties clearly indicate that the nanorods are relatively good and defect-free in quality. These nanorods have potential for technological implications.

The development of diving bradycardia in bottlenose dolphins (Tursiops truncatus)

Bradycardia is an important component of the dive response, yet little is known about this response in immature marine mammals. To determine if diving bradycardia improves with age, cardiac patterns from trained immature and mature bottlenose dolphins ( Tursiops truncatus) were recorded during three conditions (stationary respiration, voluntary breath-hold, and shallow diving). Maximum (mean: 117+/-1 beats.min(-1)) and resting (mean: 101+/-5 beats.min(-1)) heart rate (HR) at the water surface were similar regardless of age. All dolphins lowered HR in response to apnea; mean steady state breath-hold HR was not correlated with age. However, the ability to reduce HR while diving improved with age. Minimum and mean steady state HR during diving were highest for calves. For example, 1.5-3.5-year-old calves had significantly higher mean steady state diving HR (51+/-1 beats.min(-1)) than 3.5-5.5-year-old juveniles (44+/-1 beats.min(-1)). As a result, older dolphins demonstrated greater overall reductions in HR during diving. Longitudinal studies concur; the ability to reduce HR improved as individual calves matured. Thus, although newly weaned calves as young as 1.7 years exhibit elements of cardiac control, the capacity to reduce HR while diving improves with maturation up to 3.5 years postpartum. Limited ability for bradycardia may partially explain the short dive durations observed for immature marine mammals.

Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling?

Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up nutritional limitation mechanism induced by physical oceanographic change or competition with fisheries was long thought to be largely responsible for these declines. The current weight of evidence is more consistent with top-down forcing. Increased predation by killer whales probably drove the sea otter collapse and may have been responsible for the earlier pinniped declines as well. We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales' foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus "fishing-down" this element of the marine food web. The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis.

New HLA haplotype frequency reference standards: high-resolution and large sample typing of HLA DR-DQ haplotypes in a sample of European Americans

A collaborative study involving a large sample of European Americans was typed for the histocompatibility loci of the HLA DR-DQ region and subjected to intensive typing validation measures in order to accurately determine haplotype composition and frequency. The resulting tables have immediate application to HLA typing and allogeneic transplantation. The loci within the DR-DQ region are especially valuable for such an undertaking because of their tight linkage and high linkage disequilibrium. The 3798 haplotypes, derived from 1899 unrelated individuals, had a total of 75 distinct DRB1-DQA1-DQB1 haplotypes. The frequency distribution of the haplotypes was right skewed with haplotypes occurring at a frequency of less than 1% numbering 59 and yet constituting less than 12% of the total sample. Given DRB1 typing, it was possible to infer the exact DQA1 and DQB1 composition of a haplotype with high confidence (>90% likelihood) in 21 of the 35 high-resolution DRB1 alleles present in the sample. Of the DRB1 alleles without high reliability for DQ haplotype inference, only *0401, *0701 and *1302 were common, the remaining 11 DRB1 alleles constituting less than 5% of the total sample. This approach failed for the 13 serologically equivalent DR alleles in which only 33% of DQ haplotypes could be reliably inferred. The 36 DQA1-DQB1 haplotypes present in the total sample conformed to the known pattern of permissible heterodimers. Four DQA1-DQB1 haplotypes, all rare, are reported here for the first time. The haplotype frequency tables are suitable as a reference standard for HLA typing of the DR and DQ loci in European Americans.

Energy reserve utilization in northern elephant seal (Mirounga angustirostris) pups during the postweaning fast: size does matter

During fasting most mammals preferentially utilize lipid reserves for energy while sparing protein reserves. This presents a potential problem for marine mammals that also depend on lipids as a major component of blubber, the primary thermoregulatory structure. Because of this dual function for lipid, rates of lipid and protein utilization should be closely regulated during the postweaning fast in northern elephant seals (Mirounga angustirostris). To quantify energy expenditure during the fast, we measured body mass and composition of 60 pups at 2.3+/-0.2 days and 55.9+/-0.3 days postweaning in 1999 and in 2000. Body condition differed significantly between years. At weaning, body mass (125.9+/-3.8 kg) and percentage lipid content (39.3+/-0.6% of body mass) in 2000 were significantly greater than body mass (115.2+/-3.1 kg) and percentage lipid content (35.8+/-0.6%) in 1999. In general, percentage lipid content increased with body mass, and fatter pups utilized lipid at relatively higher rates during the fast. Lipid fueled 85-95% and 88-98% of energy expended by pups in 1999 and 2000, respectively. Postweaning fast duration (32-78 days) was positively correlated with body mass and hence lipid content at weaning. This suggests that body composition at weaning influences lipid utilization patterns and ultimately the duration of the postweaning fast in northern elephant seal pups.

Addiction

Alcohol and psycho-active substance misuse has far-reaching social, psychological and physical consequences. Advances in neuroimaging technology have allowed neurobiological theories of addiction to become better characterized. We describe the neurobiology of dependence, withdrawal, abstinence and craving states in alcohol, stimulant and opiate misuse. Structural neuroimaging techniques such as CT and MRI with new analytical approaches such as voxel-based morphometry have shown wide-spread changes in stimulant and opiate abuse and atrophy, particularly in the frontal lobes, in alcoholism. Functional neuroimaging techniques such as PET, SPECT and fMRI reveal altered regional cerebral activity by all drugs of abuse. The neurochemistry of addiction, particularly involving dopamine, serotonin, opiate and GABA, has been studied with PET and SPECT and similarities between all drugs of abuse have been found such as reduced dopaminergic markers. The evidence derived from these advances in neuroimaging is likely to herald the emergence of new biological treatments in this important field.

Aerobic capacities in the skeletal muscles of Weddell seals: key to longer dive durations?

In contrast to terrestrial animals that function under hypoxic conditions but display the typical exercise response of increasing ventilation and cardiac output, marine mammals exercise under a different form of hypoxic stress. They function for the duration of a dive under progressive asphyxia,which is the combination of increasing hypoxia, hypercapnia and acidosis. Our previous studies on short-duration, shallow divers found marked adaptations in their skeletal muscles, which culminated in enhanced aerobic capacities that are similar to those of atheltic terrestrial mammals. The purpose of the present study was to assess the aerobic capacity of skeletal muscles from long-duration divers. Swimming and non-swimming muscles were collected from adult Weddell seals, Leptonychotes weddelli, and processed for morphometric analysis, enzymology, myoglobin concentrations and fiber-type distribution. The results showed that the skeletal muscles of Weddell seals do not have enhanced aerobic capacities compared with those of terrestrial mammals but are adapted to maintain low levels of an aerobic lipid-based metabolism, especially under the hypoxic conditions associated with diving. The lower aerobic capacity of Weddell seal muscle as compared with that of shorter-duration divers appears to reflect their energy-conserving modes of locomotion, which enable longer and deeper dives.

A nonsense mutation in exon 3 results in the HLA-B null allele B*5127N

A new HLA-B null allele has been identified within the B*51 group by combined serological and molecular typing of an Italian Caucasoid family. Serological data indicated that the proband typed homozygous for A2 and B60. Confirmatory typing using sequence specific oligonucleotide hybridization (SSPOH) detected a second B allele within the B*51 group. Allele specific typing (SSP) for B*51 subtypes, including the known B*5111N allele, was performed, and typing results were consistent with B*5101, suggesting the presence of a new null variant. Cloning and sequencing of this allele identified a B*5101 variant with a nonsense mutation in exon 3. This new null allele has been designated B*5127N. The combined use of serologic and DNA-based typing methods facilitates the identification of null and low-expression alleles. An overview of null alleles of class I HLA is presented.

New HLA-B alleles identified and sequences extended in potential bone marrow donors: B*5804, B*4418, B*1558, and B*4805

Nucleic acid-based methods for allele identification have revealed more than 470 polymorphic variants at the HLA-B locus. Screening of potential bone marrow donors with sequence specific primer polymerase chain reactions and sequence specific oligonucleotide probe hybridization assays revealed apparent variants within the B*58, *44, *15, and *48 allele groups. DNA sequencing of cloned DNA identified the new alleles B*5804, B*4418, and B*1558 within these groups and observed new sequence information for the previously reported allele B*4805. These findings further extend our knowledge of the substantial genetic variation present at the HLA-B locus within human populations.

Identification and sequencing of HLA-B*0714 and B*2718 alleles and novel exon 1 sequences of B*0709 and B*2714 alleles in potential bone marrow donors

Sequence specific oligonucleotide probe hybridization and sequence specific primer PCR typing of volunteer bone marrow donors suggested the presence of variants of known HLA-B alleles in two individuals. PCR products encompassing HLA-B locus exons 1, 2, and 3 were prepared, subcloned and sequenced. A Hispanic individual had a novel B*07 allele (B*0714) and a Chinese individual had a novel B*27 allele (B*2718). In two other individuals, a previously unknown sequence of exon 1 was determined for HLA-B*0709 (African American) and B*2714 (Native American). These findings further illustrate the substantial genetic variation present at the HLA-B locus within human populations. We discuss the structural variation in the protein sequence for these HLA-B alleles and its potential functional effects.

Evaluation of farnesyl:protein transferase and geranylgeranyl:protein transferase inhibitor combinations in preclinical models

Farnesyl:protein transferase (FPTase) inhibitors (FTIs) were originally developed as potential anticancer agents targeting the ras oncogene and are currently in clinical trials. Whereas FTIs inhibit the farnesylation of Ha-Ras, they do not completely inhibit the prenylation of Ki-Ras, the allele most frequently mutated in human cancers. Whereas farnesylation of Ki-Ras is blocked by FTIs, Ki-Ras remains prenylated in FTI-treated cells because of its modification by the related prenyltransferase, geranylgeranyl:protein transferase type I (GGPTase-I). Hence, cells transformed with Ki-ras tend to be more resistant to FTIs than Ha-ras-transformed cells. To determine whether Ki-ras-transformed cells can be targeted by combining an FTI with a GGPTase-I inhibitor (GGTI), we evaluated potent, selective FTIs, GGTIs, and dual prenylation inhibitors (DPIs) that have both FTI and GGTI activity. We find that in human PSN-1 pancreatic tumor cells, which harbor oncogenic Ki-ras, and in other tumor lines having either wild-type or oncogenic Ki-ras, treatment with an FTI/GGTI combination or with a DPI blocks Ki-Ras prenylation and induces markedly higher levels of apoptosis relative to FTI or GGTI alone. We demonstrate that these compounds can inhibit their enzyme targets in mice by monitoring pancreatic and tumor tissues from treated animals for inhibition of prenylation of Ki-Ras, HDJ2, a substrate specific for FPTase, and Rap1A, a substrate specific for GGPTase-I. Continuous infusion (72 h) of varying doses of GGTI in conjunction with a high, fixed dose of FTI causes a dose-dependent inhibition of Ki-Ras prenylation. However, a 72-h infusion of a GGTI, at a dose sufficient to inhibit Ki-Ras prenylation in the presence of an FTI, causes death within 2 weeks of the infusion when administered either as monotherapy or in combination with an FTI. DPIs are also lethal after a 72-h infusion at doses that inhibit Ki-Ras prenylation. Because 24 h infusion of a high dose of DPI is tolerated and inhibits Ki-Ras prenylation, we compared the antitumor efficacy from a 24-h FTI infusion to that of a DPI in a nude mouse/PSN-1 tumor cell xenograft model and in Ki-ras transgenic mice with mammary tumors. The FTI and DPI were dosed at a level that provided comparable inhibition of FPTase. The FTI and the DPI displayed comparable efficacy, causing a decrease in growth rate of the PSN-1 xenograft tumors and tumor regression in the transgenic model, but neither treatment regimen induced a statistically significant increase in tumor cell apoptosis. Although FTI/GGTI combinations elicit a greater apoptotic response than either agent alone in vitro, the toxicity associated with GGTI treatment in vivo limits the duration of treatment and, thus, may limit the therapeutic benefit that might be gained by inhibiting oncogenic Ki-Ras through dual prenyltransferase inhibitor therapy.

Three new DP alleles identified in a study of 800 unrelated bone marrow donor-recipient pairs

HLA-DP genotyping of 800 unrelated donor-recipient pairs in phase 5 of a retrospective analysis of unrelated bone marrow transplantation, sponsored by the National Marrow Donor Program (NMDP), has identified two new DPB1 alleles (DPB1*8701 and DBP1*8801) and one new DPA1 (DPA1*0108) allele. Sequencing confirmed that all three of these new alleles represent novel combinations of previously described sequence motifs, reinforcing the notion that "gene conversion-like" events play an important role in generating HLA allelic diversity. The identification of these new alleles brings the total number of DPA1 alleles to 20 and the total number of DPB1 alleles to 94.