Five-year outcomes of fractionated stereotactic body radiotherapy for oligometastatic prostate cancer from the TRANSFORM phase II trial.

Metastasis-directed therapy (MDT) for oligometastatic prostate cancer (PCa), including stereotactic body radiotherapy (SBRT), has shown promise but is still considered investigational. This is the 5-year analysis of the TRANSFORM trial, the largest prospective cohort of men with oligometastatic PCa treated with SBRT-based MDT. The primary endpoint was 5-year treatment escalation-free survival (TE-FS), defined as freedom from any new cancer therapy other than further SBRT. In total, 199 men received SBRT; 76.4% were hormone-naïve at baseline. The rate of 5-year TE-FS was 21.7% (95% confidence interval [CI]: 15.7%-28.7%) overall and 25.4% (95% CI: 18.1%-33.9%) in the hormone-naïve subgroup. The subgroups with International Society of Urological Pathology Grade Groups 4-5 disease (hazard ratio [HR] = 1.48, 95% CI: 1.05-2.01, p = .026), a higher baseline prostate-specific antigen (PSA) (HR = 1.06, 95% CI: 1.03-1.09, p < .001) and those who received prior androgen deprivation therapy (ADT) (HR = 2.13, 95% CI: 1.40-3.26, p < .001), were at greater risk of treatment escalation. Outcomes for participants with four or five initial lesions were comparable to those with one to three lesions. At last follow-up, 18.9% (95% CI: 13.2%-25.7%) of participants were free from treatment escalation (median follow-up of 67.9 months) and two participants had an undetectable PSA level. No treatment-related grade three or higher adverse events were reported. The findings of this study demonstrate that SBRT-based MDT is an effective option for delaying systemic treatment escalation in the context of oligometastatic PCa. Future randomised trials comparing SBRT-based MDT to standard-of-care ADT-based approaches are required to evaluate the impact of delaying ADT on survival.

Dose-escalated radiotherapy to 82 Gy for prostate cancer following insertion of a peri-rectal hydrogel spacer: 3-year outcomes from a phase II trial.

BACKGROUND: Dose-escalation to above 80 Gy during external beam radiotherapy for localised prostate cancer leads to improved oncological outcomes but also substantially increased rectal toxicity. The aim of this study was to demonstrate the safety and efficacy of escalating the dose to 82 Gy following insertion of a peri-rectal hydrogel spacer (HS) prior to radiotherapy. METHODS: This was a single arm, open-label, prospective study of men with localised prostate cancer who were prescribed a course of intensity modulated radiotherapy escalated to 82 Gy in 2 Gy fractions following insertion of the SpaceOAR™ HS (Boston Scientific, Marlborough, MA). Patients were prescribed a standard course of 78 Gy in 2 Gy fractions where rectal dose constraints could not be met for the 82 Gy plan. The co-primary endpoints were the rate of grade 3 gastrointestinal (GI) and genitourinary (GU) adverse events (CTCAE, v4), and patient-reported quality of life (QoL) (EORTC QLQ-C30 and PR25 modules), up to 37.5 months post-treatment. RESULTS: Seventy patients received treatment on the study, with 64 (91.4%) receiving an 82 Gy treatment course. The median follow-up time post-treatment was 37.4 months. The rate of radiotherapy-related grade 3 GI and GU adverse events was 0% and 2.9%, respectively. There were 2 (2.9%) grade 3 adverse events related to insertion of the HS. Only small and transient declines in QoL were observed; there was no clinically or statistically significant decline in QoL beyond 13.5 months and up to 37.5 months post-treatment, compared to baseline. No late RTOG-defined grade ≥ 2 GI toxicity was observed, with no GI toxicity observed in any patient at 37.5 months post-treatment. Nine (12.9%) patients met criteria for biochemical failure within the follow-up period. CONCLUSIONS: Dose-escalation to 82 Gy, facilitated by use of a hydrogel spacer, is safe and feasible, with minimal toxicity up to 37.5 months post-treatment when compared to rates of rectal toxicity in previous dose-escalation trials up to 80 Gy. Trials with longer follow-up of oncological and functional outcomes are required to robustly demonstrate a sustained widening of the therapeutic window. Trial registration Australian New Zealand Clinical Trials Registry, ACTRN12621000056897 , 22/01/2021. Retrospectively registered.

Focal low dose-rate brachytherapy for low to intermediate risk prostate cancer: preliminary experience at an Australian institution.

BACKGROUND: Focal treatment for prostate cancer (PCa) is a hybrid approach combining ablative treatment of the involved prostate gland and continued active surveillance (AS) of the unaffected gland. Low dose-rate (LDR) brachytherapy can be used as a lesion-targeted focal therapy, however, further studies are required to support its use. The aim of this study is to evaluate the dosimetry, toxicity and oncological outcomes of men receiving lesion-targeted focal LDR brachytherapy for low to intermediate risk PCa. METHODS: This is a retrospective cohort study of 26 men with unifocal, low to intermediate grade PCa diagnosed on a combination of multiparametric-magnetic resonance imaging (mp-MRI) and targeted plus template transperineal (TP) biopsy, who received focal LDR brachytherapy at a single institution. Brachytherapy involved a single monotherapy implant using iodine-125 seeds to deliver a prescribed dose of 145 Gy to the index lesion. RESULTS: The mean focal planning target volume (F-PTV) as a percentage of the prostate volume was 24.5%. The percentage of the focal gross tumour volume (F-GTV) receiving 100% of the prescription dose was 100% for 12 patients and ≥98% for 18 patients. The median follow-up for toxicity and biochemical control outcomes was 23.1 [interquartile range (IQR) 19.1-31.3] and 24.2 (IQR 17.9-30.0) months, respectively. Grade 2 urinary and erectile toxicities were reported by 29.2% and 45.8% of patients, respectively, with resolution of urinary symptoms to baseline by last follow-up. There were no grade ≥3 urinary or erectile toxicities or grade ≥2 rectal toxicity. All 21 patients who underwent a repeat mp-MRI and TP biopsy at 12-24 months post-treatment were negative for clinically significant disease and 25 (96.2%) patients were free from biochemical failure (FFBF). CONCLUSIONS: Focal LDR brachytherapy is associated with a favourable toxicity profile and a high rate of control of significant PCa at 12-18 months post-treatment. We have commenced the LIBERATE prospective registry in focal LDR brachytherapy based on the highly encouraging outcomes of this initial experience.

Spatially Fractionated X-Ray Microbeams Elicit a More Sustained Immune and Inflammatory Response in the Brainstem than Homogenous Irradiation.

Synchrotron microbeam radiation therapy (MRT) is a preclinical irradiation technique which could be used to treat intracranial malignancies. The goal of this work was to discern differences in gene expression and the predicted regulation of molecular pathways in the brainstem after MRT versus synchrotron broad-beam radiation therapy (SBBR). Healthy C57BL/6 mice received whole-head irradiation with median acute toxic doses of MRT (241 Gy peak dose) or SBBR (13 Gy). Brains were harvested 4 and 48 h postirradiation and RNA was extracted from the brainstem. RNA-sequencing was performed to identify differentially expressed genes (false discovery rate < 0.01) relative to nonirradiated controls and significantly regulated molecular pathways and biological functions were identified (Benjamini-Hochberg corrected P < 0.05). Differentially expressed genes and regulated pathways largely reflected a pro-inflammatory response 4 h after both MRT and SBBR which was sustained at 48 h postirradiation for MRT. Pathways relating to radiation-induced viral mimicry, including HMGB1, NF-κB and interferon signaling cascades, were predicted to be uniquely activated by MRT. Local microglia, as well as circulating leukocytes, including T cells, were predicted to be activated by MRT. Our findings affirm that the transcriptomic signature of MRT is distinct from broad-beam radiotherapy, with a sustained inflammatory and immune response up to 48 h postirradiation.

68Ga-PSMA-PET screening and transponder-guided salvage radiotherapy to the prostate bed alone for biochemical recurrence following prostatectomy: interim outcomes of a phase II trial.

PURPOSE: To evaluate outcomes for men with biochemically recurrent prostate cancer who were selected for transponder-guided salvage radiotherapy (SRT) to the prostate bed alone by 68Ga-labelled prostate-specific membrane antigen positron emission tomography (68Ga-PSMA-PET). METHODS: This is a single-arm, prospective study of men with a prostate-specific antigen (PSA) level rising to 0.1-2.5 ng/mL following radical prostatectomy. Patients were staged with 68Ga-PSMA-PET and those with a negative finding, or a positive finding localised to the prostate bed, continued to SRT only to the prostate bed alone with real-time target-tracking using electromagnetic transponders. The primary endpoint was freedom from biochemical relapse (FFBR, PSA > 0.2 ng/mL from the post-radiotherapy nadir). Secondary endpoints were time to biochemical relapse, toxicity and patient-reported quality of life (QoL). RESULTS: Ninety-two patients (median PSA of 0.18 ng/ml, IQR 0.12-0.36), were screened with 68Ga-PSMA-PET and metastatic disease was found in 20 (21.7%) patients. Sixty-nine of 72 non-metastatic patients elected to proceed with SRT. At the interim (3-year) analysis, 32 (46.4%) patients (95% CI 34.3-58.8%) were FFBR. The median time to biochemical relapse was 16.1 months. The rate of FFBR was 82.4% for ISUP grade-group 2 patients. Rates of grade 2 or higher gastrointestinal and genitourinary toxicity were 0% and 15.2%, respectively. General health and disease-specific QoL remained stable. CONCLUSION: Pre-SRT 68Ga-PSMA-PET scans detect metastatic disease in a proportion of patients at low PSA levels but fail to improve FFBR. Transponder-guided SRT to the prostate bed alone is associated with a favourable toxicity profile and preserved QoL. TRIAL REGISTRATION NUMBER: ACTRN12615001183572, 03/11/2015, retrospectively registered.

The γH2AX DSB marker may not be a suitable biodosimeter to measure the biological MRT valley dose.

PURPOSE: γH2AX biodosimetry has been proposed as an alternative dosimetry method for microbeam radiation therapy (MRT) because conventional dosimeters, such as ionization chambers, lack the spatial resolution required to accurately measure the MRT valley dose. Here we investigated whether γH2AX biodosimetry should be used to measure the biological valley dose of MRT-irradiated mammalian cells. MATERIALS AND METHODS: We irradiated human skin fibroblasts and mouse skin flaps with synchrotron MRT and broad beam (BB) radiation. BB doses of 1-5 Gy were used to generate a calibration curve in order to estimate the biological MRT valley dose using the γH2AX assay. RESULTS: Our key finding was that MRT induced a non-linear dose response compared to BB, where doses 2-3 times greater showed the same level of DNA DSB damage in the valley in cell and tissue studies. This indicates that γH2AX may not be an appropriate biodosimeter to estimate the biological valley doses of MRT-irradiated samples. We also established foci yields of 5.9 ± 0.04 and 27.4 ± 2.5  foci/cell/Gy in mouse skin tissue and human fibroblasts respectively, induced by BB. Using Monte Carlo simulations, a linear dose response was seen in cell and tissue studies and produced predicted peak-to-valley dose ratios (PVDRs) of ∼30 and ∼107 for human fibroblasts and mouse skin tissue respectively. CONCLUSIONS: Our report highlights novel MRT radiobiology, attempts to explain why γH2AX may not be an appropriate biodosimeter and suggests further studies aimed at revealing the biological and cellular communication mechanisms that drive the normal tissue sparing effect, which is characteristic of MRT.

Technical advances in x-ray microbeam radiation therapy.

In the last 25 years microbeam radiation therapy (MRT) has emerged as a promising alternative to conventional radiation therapy at large, third generation synchrotrons. In MRT, a multi-slit collimator modulates a kilovoltage x-ray beam on a micrometer scale, creating peak dose areas with unconventionally high doses of several hundred Grays separated by low dose valley regions, where the dose remains well below the tissue tolerance level. Pre-clinical evidence demonstrates that such beam geometries lead to substantially reduced damage to normal tissue at equal tumour control rates and hence drastically increase the therapeutic window. Although the mechanisms behind MRT are still to be elucidated, previous studies indicate that immune response, tumour microenvironment, and the microvasculature may play a crucial role. Beyond tumour therapy, MRT has also been suggested as a microsurgical tool in neurological disorders and as a primer for drug delivery. The physical properties of MRT demand innovative medical physics and engineering solutions for safe treatment delivery. This article reviews technical developments in MRT and discusses existing solutions for dosimetric validation, reliable treatment planning and safety. Instrumentation at synchrotron facilities, including beam production, collimators and patient positioning systems, is also discussed. Specific solutions reviewed in this article include: dosimetry techniques that can cope with high spatial resolution, low photon energies and extremely high dose rates of up to 15 000 Gy s-1, dose calculation algorithms-apart from pure Monte Carlo Simulations-to overcome the challenge of small voxel sizes and a wide dynamic dose-range, and the use of dose-enhancing nanoparticles to combat the limited penetrability of a kilovoltage energy spectrum. Finally, concepts for alternative compact microbeam sources are presented, such as inverse Compton scattering set-ups and carbon nanotube x-ray tubes, that may facilitate the transfer of MRT into a hospital-based clinical environment. Intensive research in recent years has resulted in practical solutions to most of the technical challenges in MRT. Treatment planning, dosimetry and patient safety systems at synchrotrons have matured to a point that first veterinary and clinical studies in MRT are within reach. Should these studies confirm the promising results of pre-clinical studies, the authors are confident that MRT will become an effective new radiotherapy option for certain patients.

Fractionated stereotactic body radiotherapy for up to five prostate cancer oligometastases: Interim outcomes of a prospective clinical trial.

Stereotactic body radiotherapy (SBRT) can delay escalation to systemic treatment in men with oligometastatic prostate cancer (PCa). However, large, prospective studies are still required to evaluate the efficacy of this approach in different patient groups. This is the interim analysis of a prospective, single institution study of men relapsing with up to five synchronous lesions following definitive local treatment for primary PCa. Our aim was to determine the proportion of patients not requiring treatment escalation following SBRT. In total, 199 patients were enrolled to receive fractionated SBRT (50 Gray in 10 fractions) to each visible lesion. Fourteen patients were castration resistant at enrolment. The proportion of patients not requiring treatment escalation 2 years following SBRT was 51.7% (95% CI: 44.1-59.3%). The median length of treatment escalation-free survival over the entire follow-up period was 27.1 months (95% CI; 21.8-29.4 months). Prior androgen deprivation therapy (ADT) predicted a significantly lower rate of freedom from treatment escalation at 2 years compared to no prior ADT (odds ratio = 0.21, 95% CI: 0.08-0.54, p = 0.001). There was no difference in the efficacy of SBRT when treating 4-5 vs. 1-3 initial lesions. A prostate-specific antigen (PSA) decline was induced in 75% of patients, with PSA readings falling to an undetectable level in six patients. No late grade three toxicities were observed. These interim results suggest that SBRT can be used to treat up to five synchronous PCa oligometastases to delay treatment escalation.

Dose reduction to organs at risk with deep-inspiration breath-hold during right breast radiotherapy: a treatment planning study.

BACKGROUND: The addition of regional nodal radiation (RNI) to whole breast irradiation for high risk breast cancer improves metastases free survival and new data suggests it contributes additional benefit to overall survival. Deep inspiration breath hold (DIBH) has been shown to reduce cardiac and pulmonary dose in the context of left-sided disease treated with or without RNI, yet few studies have investigated its utility for right-breast cancer. This study investigates the potential advantages of DIBH in local and locoregional radiotherapy for right-sided breast cancer. METHODS: Free-breathing (FB) and DIBH computed tomography datasets were obtained from twenty patients who previously underwent radiotherapy for left-sided breast cancer. Ten patients were retrospectively planned for whole right breast only irradiation and ten patients were planned for irradiation to the whole breast plus ipsilateral supra-clavicular (SC) nodes, with and without irradiation of the ipsilateral internal mammary nodes (IMN). Dose-volume metrics for the clinical target volume, lungs, heart, left anterior descending artery, right coronary artery (RCA) and liver were recorded. Differences between FB and DIBH plans were analysed using Wilcoxon signed-rank tests, with P < 0.05 considered statistically significant. RESULTS: DIBH increased the average total lung volume compared to FB in both breast only and breast plus RNI cohorts (P = 0.001). For the breast only group, there was no significant improvement in any ipsilateral lung dose-volume metric between FB and DIBH. However, for the breast plus RNI group, there was an improvement in ipsilateral lung mean dose (18.9 ± 3.2 Gy to 15.9 ± 2.3 Gy, P = 0.002) and V20Gy (45.3 ± 13.3% to 32.9 ± 9.4%, P = 0.002). In addition, DIBH significantly reduced the maximum dose to the RCA for RNI (11.6 ± 7.2 Gy to 5.6 ± 2.9 Gy, P = 0.03). Significant reductions in the liver V20Gy and maximum dose were observed in all cohorts during DIBH compared to FB. CONCLUSIONS: DIBH is a promising approach for right-breast radiotherapy with considerable sparing of normal tissue, particularly when the ipsilateral IMNs are also irradiated.

Identifying optimal clinical scenarios for synchrotron microbeam radiation therapy: A treatment planning study.

PURPOSE: Synchrotron Microbeam Radiation Therapy (MRT) is a pre-clinical modality characterised by spatial dose fractionation on a microscopic scale. Treatment planning studies using clinical datasets have not yet been conducted. Our aim was to investigate MRT dose-distributions in scenarios refractory to conventional treatment and to identify optimal settings for a future Phase I trial. METHODS: MRT plans were generated for seven scenarios where re-irradiation was performed clinically. A hybrid algorithm, combining Monte Carlo and convolution-based methods, was used for dose-calculation. The valley dose to organs at risk had to respect the single fraction tolerance doses achieved in the corresponding re-irradiation plans. The resultant peak dose and the peak-to-valley dose ratio (PVDR) at the tumour target volume were assessed. RESULTS: Peak doses greater than 80 Gy in a single fraction, and PVDRs greater than 10, could be achieved for plans with small (<35 cm3) or shallow volumes, particularly recurrent glioblastoma, head and neck tumours, and select loco-regionally recurrent breast cancer sites. Treatment volume was a more important factor than treatment depth in determining the PVDR. The mean PVDR correlated strongly with the size of the target volume (rs = -0.70, p = 0.01). The PVDRs achieved in these clinical scenarios are considerably lower than those reported in previous pre-clinical studies. CONCLUSION: Our findings suggest that head and neck sites will be optimal scenarios for MRT.

Comparative toxicity of synchrotron and conventional radiation therapy based on total and partial body irradiation in a murine model.

Synchrotron radiation can facilitate novel radiation therapy modalities such as microbeam radiation therapy (MRT) and high dose-rate synchrotron broad-beam radiation therapy (SBBR). Both of these modalities have unique physical properties that could be exploited for an improved therapeutic effect. While pre-clinical studies report promising normal tissue sparing phenomena, systematic toxicity data are still required. Our objective was to characterise the toxicity of SBBR and MRT and to calculate equivalent doses of conventional radiation therapy (CRT). A dose-escalation study was performed on C57BLJ/6 mice using total body and partial body irradiations. Dose-response curves and TD50 values were subsequently calculated using PROBIT analysis. For SBBR at dose-rates of 37 to 41 Gy/s, we found no evidence of a normal tissue sparing effect relative to CRT. Our findings also show that the MRT valley dose, rather than the peak dose, best correlates with CRT doses for acute toxicity. Importantly, longer-term weight tracking of irradiated animals revealed more pronounced growth impairment following MRT compared to both SBBR and CRT. Overall, this study provides the first in vivo dose-equivalence data between MRT, SBBR and CRT and presents systematic toxicity data for a range of organs that can be used as a reference point for future pre-clinical work.

The normal tissue effects of microbeam radiotherapy: What do we know, and what do we need to know to plan a human clinical trial?

Purpose Microbeam Radiotherapy (MRT) is a promising pre-clinical cancer therapy which represents a radical departure from the radiobiological principles of conventional radiotherapy (CRT). In order to translate MRT to human clinical trials, robust normal tissue toxicity data are required. This review summarizes the normal tissue effects reported by pre-clinical MRT animal studies and compares these data to clinical recommendations in CRT. Conclusion Few pre-clinical studies are specifically designed to evaluate the dose-response of normal tissue to MRT. However, it remains clear that a range of normal tissues can tolerate peak MRT doses at least an order of magnitude higher than CRT. Furthermore, the dose deposited in the valley regions, predominantly determined by microbeam spacing, has a greater influence on the normal tissue response to MRT compared to the peak regions. The development of a new normal tissue complication probability model for MRT, in conjunction with a treatment planning system, will be pivotal in the collection of robust normal tissue toxicity data and the translation of MRT to clinical use.

Image guidance protocol for synchrotron microbeam radiation therapy.

The protocol for image-guided microbeam radiotherapy (MRT) developed for the Australian Synchrotron's Imaging and Medical Beamline (IMBL) is described. The protocol has been designed for the small-animal MRT station of IMBL to enable future preclinical trials on rodents. The image guidance procedure allows for low-dose monochromatic imaging at 50 keV and subsequent semi-automated sample alignment in 3D with sub-100 µm accuracy. Following the alignment, a beamline operation mode change is performed and the relevant beamline components are automatically aligned for the treatment (pink) beam to be delivered on the sample. Here, the small-animal MRT station, the parameters and procedures for the image guidance protocol, as well as the experimental imaging results using phantoms are described. Furthermore, the experimental validation of the protocol using 3D PRESAGE(®) dosimeters is reported. It is demonstrated that the sample alignment is maintained after the mode change and the treatment can be delivered within the same spatial accuracy of 100 µm. The results indicate that the proposed approach is viable for preclinical trials of small-animal MRT.

Biological control of vertebrate pests using virally vectored immunocontraception.

Species-specific viruses are being genetically engineered to produce contraceptive biological controls for pest animals such as mice, rabbits and foxes. The virus vaccines are intended to trigger an autoimmune response in the target animals that interferes with their fertility in a process termed virally vectored immunocontraception. Laboratory experiments have shown that high levels of infertility can be induced in mice infected with recombinant murine cytomegalovirus and ectromelia virus expressing reproductive antigens as well as in rabbits using myxoma virus vectors. The strategies used to produce and deliver species-specific immunocontraceptive vaccines to free-living wildlife are presented in this review. Discussion includes coverage of the likely safety of the proposed vaccines as well as the implications of the approach for fertility control in other species.

Species-specificity of a murine immunocontraceptive utilising murine cytomegalovirus as a gene delivery vector.

Cytomegaloviruses are species-specific DNA viruses. Recombinant murine cytomegaloviruse (MCMV) expressing the mouse egg-coat protein zona pellucida 3 (mZP3) has been shown to sterilise female mice by breaking self-tolerance and inducing an immune response against the host ZP3. This virus has the potential to be used for mouse population control, however the effect of this recombinant immunocontraceptive virus in non-host species must be determined. Recombinant MCMV-mZP3, based on both laboratory and wild strains of virus, induced long-lived antibody responses against structural viral proteins and mZP3 when inoculated into laboratory rats, although no viral DNA or replicating virus was identified. The anti-mZP3 antibodies were specific for mouse ZP3, did not cross-react with rat ZP3, and had no effect on the fertility of the rats.

Murine viruses in an island population of introduced house mice and endemic short-tailed mice in Western Australia.

House mice (Mus domesticus) were recently introduced to Thevenard Island, off the northwest coast of Western Australia. This island is also habitat for an endangered native rodent, the short-tailed mouse (Leggadina lakedownensis). Concerns have been raised that house mice may pose a threat to L. lakedownensis both through competition and as a source of infection. To assess the threat to L. lakedownensis posed by viral pathogens from M. domesticus, a serological survey was conducted from 1994 to 1996 of both species for evidence of infection with 14 common murine viruses (mouse hepatitis virus, murine cytomegalovirus, lymphocytic choriomeningitis virus, ectromelia virus, mouse adenovirus strains FL and K87, minute virus of mice, mouse parvovirus, reovirus type 3, Sendai virus, Theiler's mouse encephalomyelitis virus, polyoma virus, pneumonia virus of mice, and encephalomyocarditis virus) and Mycoplasma pulmonis. Despite previous evidence that populations of free-living M. domesticus from various locations on the Australian mainland were infected with up to eight viruses, M. domesticus on Thevenard Island were seropositive only to murine cytomegalovirus (MCMV). Antibodies to MCMV were detected in this species at all times of sampling, although seroprevalence varied. Infectious MCMV could be isolated in culture of salivary gland homogenates from seropositive mice. In contrast, L. lakedownensis on Thevenard Island showed no serological evidence of infection with MCMV, any of the other murine viruses, or M. Pulmonis, and no virus could be isolated in culture from salivary gland homogenates. Although MCMV replicated to high titers in experimentally infected inbred BALB/c laboratory mice as expected, it did not replicate in the target organs of experimentally inoculated L. lakedownensis, indicating that the strict host specificity of MCMV may prevent its infection of L. lakedownensis. These results suggest that native mice on Thevenard Island are not at risk of MCMV infection from introduced house mice, and raise interesting questions about the possible selective survival of MCMV in small isolated populations of M. domesticus.

The effect of enteral carnitine administration in humans.

We previously determined that the L-carnitine uptake by human duodenal tissue occurs by both active (KT 558 mumol/L) and passive mechanisms. The effects of enteral carnitine was studied in humans. A hamburger meal (345 mumol total carnitine) induced peak jejunal fluid free (unesterified) and short-chain acylcarnitine concentrations (SCAC) of 209 and 130 mumol/L, respectively. Plasma carnitine concentrations and the percent renal reabsorption remained unchanged. By contrast, a pharmacologic dose of free carnitine (25,298 mumol) raised peak intraluminal free and SCAC to 20,660 and 4204 mumol/L. Plasma total carnitine concentrations doubled to 93 mumol/L, and the percent renal reabsorption of free and SCAC declined to 76% and 52%, respectively. In triple-lumen perfusions, 200 mumol carnitine/L was absorbed at 484 nmol.min-1.30 cm-1 jejunum, a rate sufficient for prandial but not pharmacologic assimilation. Our findings indicate that absorption of physiologic and pharmacologic amounts of carnitine occurs predominantly by active transport and passive diffusion, respectively.

A study of the molecular pathology of sucrase-isomaltase deficiency. A defect in the intracellular processing of the enzyme.

The intestinal brush-border enzyme sucrase-isomaltase splits sucrose into its component monosaccharides, glucose and fructose. A deficiency of the enzyme leads to sucrose intolerance. We studied the synthesis and intracellular processing of sucrase-isomaltase, using human intestinal explants in organ culture. Pulse-chase experiments with [35S]methionine followed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, and fluorography of labeled sucrase-isomaltase demonstrated that the molecule was initially recognized as a protein with a relative molecular weight (Mr) of 205,000. This was apparently converted to a species of 225,000 Mr within two hours. We studied the glycosylation of the protein using endo-beta-N-acetylglucosaminidase H and peptide-N4-(N-acetyl-beta-glucosaminyl)-asparagine amidase digestion of oligosaccharide side chains of the two forms of sucrase-isomaltase. The results showed that the early-appearing 205-kd (kilodalton) molecule contained high-mannose asparagine-linked oligosaccharides, and that the later-appearing, 225-kd molecule contained highly processed (mature) carbohydrate chains. Studies in a patient with primary sucrase-isomaltase deficiency demonstrated normal translation and high-mannose glycosylation of the precursor but a failure in further processing of the oligosaccharides, with subsequent intracellular degradation of the glycoprotein and undetectable enzymatic activity of intestinal sucrase. Abnormal intracellular processing of the enzyme was the probable mechanism of enzyme deficiency in this patient.