Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

First Report of Stem Rot of Konjac Caused by Phytophthora nicotianae in China

Konjac (Amorphophallus) is an important economic crop widely used in health products and biomaterials in Asia (2). A serious foliage disease of Konjac was observed in Fuyuan County, Yunnan Province, China, in July 2012. The symptoms began with leaf color changes from light green to yellow, followed by discoloration on the stem base, plant wilting, bulb rotting, and ultimately plant death. Symptomatic tissues were cut into small pieces, surface-sterilized, and cultured on 20% V8 juice agar at 28°C. Five days after incubation, white fluffy colonies with the typical sporangium of Phytophthora sp. were observed from root and stem pieces. Isolates were identified as P. nicotianae based on morphological characteristics and DNA analysis. The growth rate of the colonies was 16 mm/d at 28°C. Sporangia were pyriform, ovoid to spherical, and papillate, and the dimensions of the 80 sporangia measured ranged from 23.7 to 60.4 × 19.4 to 45.7 μm (avg. 42.4 × 31.5 μm) with length-to-breadth ratios of 1.19 to 1.44 (avg. 1.34). The chlamydospores were spherical with a smooth surface, and their dimensions ranged from 20.3 to 47.3 × 18.9 to 45.9 μm (avg. 32.7 × 30.4 μm) (3). DNA was extracted from one colony containing spores and hyphae of the isolated P. nicotianae, and the nuclear ribosomal DNA internal transcribed spacer (ITS) region was amplified with primers ITS6 and ITS4 (4). The obtained 854-bp amplicon was purified and sequenced. NCBI BLAST retrieved a 100% identity with P. nicotianae (GenBank Accession No. KJ506732). A pathogenicity test of the isolated P. nicotianae was conducted in a greenhouse. After 7 days in a humidity-controlled greenhouse, all 10 inoculated plants showed similar symptoms as observed initially in the field, while control plants were symptomless. P. nicotianae was re-isolated from the inoculated stems, thus successfully completing Koch's postulates (1). To our knowledge, this is the first report of P. nicotianae as a pathogen of Konjac in China. References: (1) B. Alvarez-Rodriguez et al. Plant Dis. 97:1257, 2013. (2) H. Ban, et al. Plant Cell Rep. 28:1847, 2009. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. APS Press, St. Paul, MN, 1996. (4) J. M. French et al. Plant Dis. 95:1028, 2011.

A Phase I Trial of Intravenous CG7870, a Replication-Selective, Prostate-Specific Antigen–Targeted Oncolytic Adenovirus, for the Treatment of Hormone-Refractory, Metastatic Prostate Cancer

CG7870 is a replication-selective oncolytic adenovirus genetically engineered to replicate preferentially in prostate tissue. In a previous phase I/II clinical trial of intraprostatic delivery of CG7870 for locally recurrent prostate cancer this virus was well tolerated. In this phase I study CG7870 was administered as a single intravenous infusion in a group-sequential dose escalation design (1 x 10(10) to 6 x 10(12) viral particles (vp)) to 23 patients with hormone-refractory metastatic prostate cancer. Flulike symptoms (fever, fatigue, rigors, nausea, and/or vomiting) were the most common adverse events. Three therapy-related grade 3 adverse events were reported, one of which (fatigue) was serious. At doses greater than 10(12) vp all five patients experienced asymptomatic grade 1 to 2 transaminitis and/or isolated d-dimer elevations starting on day 2 through 8; dose escalation was therefore halted at 6 x 10(12) vp. All tested patients had CG7870 genomes present in the peripheral blood for at least 90 minutes after infusion; patients in the highest dose group had persistence of genomes through 29 days. A "secondary" or "delayed" peak in plasma CG7870 genome copies (defined as a >10-fold increase in CG7870 genomes from nadir concentration) suggestive of active viral replication and shedding into the bloodstream was detected in 16/23 (70%) patients. CG7870 was detected in the saliva of 3 patients, whereas all urine samples tested negative. All patients developed antibodies to CG7870. Dose-related increases in interleukins 6 and 10 (IL-6, IL-10) blood levels were detected. The peak IL-6 concentration after CG7870 treatment was associated with a transient, asymptomatic decrease in blood pressure. No partial or complete prostate-specific antigen (PSA) responses were observed; however, 5 patients had a decrease in serum PSA of 25% to 49% following a single treatment, including 3 of 8 patients at the highest dose levels.

A phase I trial of CV706, a replication-competent, PSA selective oncolytic adenovirus, for the treatment of locally recurrent prostate cancer following radiation therapy

CV706 is a prostate-specific antigen (PSA)-selective, replication-competent adenovirus that has been shown to selectively kill human prostate cancer xenografts in preclinical models. To study the safety and activity of intraprostatic delivery of CV706, a Phase I dose-ranging study for the treatment of patients with locally recurrent prostate cancer after radiation therapy was conducted. Twenty patients in five groups were treated with between 1 x 10(11) and 1 x 10(13) viral particles delivered by a real-time, transrectal ultrasound-guided transperineal technique using a three-dimensional plan. The primary end point was the determination of treatment-related toxicity. Secondary objectives included evaluation of the antitumor activity of CV706 and monitoring for other correlates of antineoplastic action. In this study, CV706 was found to be safe and was not associated with irreversible grade 3 or any grade 4 toxicity. No grade >1 alterations in liver function tests associated with CV706 administration were observed. Posttreatment prostatic biopsies and detection of a delayed "peak" of circulating copies of virus provided evidence of intraprostatic replication of CV706. The study defined the timing of CV706 shedding into blood and urine as well as the appearance of circulating Ad5 neutralizing antibodies. Finally, this study documents the serum PSA response of treated patients and reveals a dose response showing that all five patients who achieved a > or =50% reduction in PSA were treated with the highest two doses of CV706. This study represents the first clinical translation of a prostate-specific, replication-restricted adenovirus for the treatment of prostate cancer. Taken together, this study documents that intraprostatic delivery of CV706 can be safely administered to patients, even at high doses, and the data also suggest that CV706 possesses enough clinical activity, as reflected by changes in serum PSA, to warrant additional clinical and laboratory investigation.

A hepatocellular carcinoma-specific adenovirus variant, CV890, eliminates distant human liver tumors in combination with doxorubicin

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death in the world. Tumor resection remains the only curative treatment but is often not possible because of advanced stage and frequently unsuccessful because of intrahepatic or distant tumor recurrence. alpha-Fetoprotein (AFP), a tumor marker currently used for the diagnosis and management of HCC, is an oncofetal protein expressed in a majority of HCCs but rarely in normal hepatocytes. Because AFP gene expression is tightly regulated at the level of transcription, AFP transcriptional regulatory elements (TRE) are excellent candidates for generating HCC-specific oncolytic adenoviruses. We devised a new strategy for the AFP TRE to control an artificial E1A-IRES-E1B bicistronic cassette in an adenovirus 5 vector (Ad5) and constructed an HCC-specific oncolytic virus, CV890. In vitro, CV890 expression of the E1A and E1B genes, virus replication, and cytopathic effects were examined by Northern blot, Western blot, virus yield assay, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay in AFP-producing cell lines (HepG2, Huh7, Hep3B, PLC/PRF/5, and SNU449), non-AFP-producing cell lines (Sk-Hep-1, Chang liver cell, LNCaP, HBL-100, PA-1, UM-UC-3, SW 780, Colo 201, and U118 MG), and non-AFP-producing human primary cells (lung fibroblast, bladder smooth muscle, and mammary epithelial). CV890 efficiently replicates in and destroys AFP-producing HCC cells as well as wild-type Ad5, but replication is highly attenuated in non-AFP-producing HCC cells or non-HCC cells. CV890 produced 5,000-100,000-fold less virus than wild-type Ad5 in non-AFP-producing cells. CV890 was attenuated 100-fold more than CV732, a virus containing the AFP TRE driving the E1A gene alone, in non-AFP-producing cells. These studies demonstrated that expression of both E1A and E1B genes under the control of a bicistronic AFP-E1A-IRES-E1B cassette yielded improvements in virus specificity equivalent to driving the E1A and E1B genes with two independent TREs yet requires only one TRE thereby conserving genomic space within the virus. Significantly, CV890 produced nearly the same yield of virus in cells that produced AFP over a 75-fold range, from a low of 60 ng AFP/10(6) cells/10 days to as high as 4585 ng AFP/10(6) cells/10 days. In vivo, antitumor efficacy of CV890 was examined in BALB/c-nu/nu mice containing large s.c. HepG2 or Hep3B tumor xenografts. Tumor volume of distant xenografts dropped below baseline 4 weeks after a single i.v. injection. Combination of CV890 with doxorubicin demonstrated synergistic antitumor efficacy, yielding complete elimination of distant Hep3B tumors 4 weeks after a single i.v. administration of both compounds. Our results support the clinical development of CV890 as an antineoplastic agent for the treatment of localized or metastatic HCC.

CV706, a prostate cancer-specific adenovirus variant, in combination with radiotherapy produces synergistic antitumor efficacy without increasing toxicity

Radiation is an effective means of treating localized prostate cancer. However, up to 40% of men with certain risk factors will develop biochemical failure 5 years after radiotherapy. CV706, a prostate cell-specific adenovirus variant, is currently in clinical trials for the treatment of recurrent organ-confined prostate cancer. We demonstrated previously that a single administration of CV706 at 5 x 10(8) particles/mm3 of tumor eliminated established tumors within 6 weeks in nude mouse xenografts (Rodriguez et al., Cancer Res. 57: 2559-2563, 1997). We now demonstrate that CV706-mediated cytotoxicity is synergistic with radiation. In vitro, addition of radiation to CV706 resulted in a synergistic increase of cytotoxicity toward the human prostate cancer cell line LNCaP and a significant increase of virus burst size, with no reduction in specificity of CV706-based cytopathogenicity for prostate cancer cells. In vivo, prostate-specific antigen (+) LNCaP xenografts of human prostate cancer were treated with CV706 (1 x 10(7) particles/mm3 of tumor), 10 Gy of single fraction local tumor radiation, or both. Tumor volumes of the group treated with CV706 or radiation was 97% or 120% of baseline 6 weeks after treatment. However, when the same dose of CV706 was followed 24 h later with the same dose of radiation, the tumor volume dropped to 4% of baseline at this time point and produced antitumor activity that was 6.7-fold greater than a predicted additive effect of CV706 and radiation. Histological analyses of tumors revealed that, compared with CV706 or radiation alone, combination treatment with two agents increased necrosis by 180% and 690%, apoptosis by 330% and 880%, and decreased blood vessel number by 1290% and 600%, respectively. Importantly, no increase in toxicity was observed after combined treatment when compared with CV706 or radiation alone. These data demonstrate that CV706 enhances the in vivo radioresponse of prostate tumors and support the clinical development of CV706 as a neoadjuvant agent with radiation for localized prostate cancer.

Cleaning and shaping the apical third of a root canal system

The apical third of a root canal system is the most difficult section to clean and shape because of its ramifications and tortuosities. This article discusses the clinical anatomy of the root and lists the "10 commandments" of cleaning and shaping to achieve predictably successful endodontics.

Antitumor synergy of CV787, a prostate cancer-specific adenovirus, and paclitaxel and docetaxel

CV787, a PSA+ prostate cell-specific adenovirus variant, is currently in Phase I/II clinical trials for the treatment of prostate cancer. We have previously demonstrated that a single administration of CV787 at 1 x 10(11) particle/animal could eliminate established tumors within 6 weeks in nude mouse xenografts (Yu et al., Cancer Res., 59: 4200-4203, 1999). We now demonstrate that CV787-mediated replication-dependent cytotoxicity is synergistic with the chemotherapeutic agents paclitaxel (Taxol) or docetaxel (Taxotere) both in vitro and in vivo. In vitro, cells were pretreated with CV787 24 h before taxane, pretreated with taxane 24 h before CV787, or treated with both agents simultaneously. Cell viability was determined at various time points by 3-[4,5-dimethylthiazole-2-4]-2,5-diphenyl-2H-tetrazolium bromide assay, and virus yield was examined by plaque assay. Addition of taxane to CV787 resulted in a synergistic increase of cytotoxicity toward the human prostate cancer cell line LNCaP, regardless of the timing of administration. There was no reduction in virus replication or specificity of CV787-based cytopathogenicity for prostate cancer cells (approximately 10,000 to 1) with the taxanes. p53 expression was significantly elevated in the cells treated with CV787 and taxane. In vivo, using the PSA+ LNCaP xenograft model of prostate cancer, a single i.v. dose of 1 x 10(8) particles CV787 and docetaxel in combination eliminates large preexistent distant tumors. Toxicity studies do not show a synergistic increase of toxicity of CV787 and taxane. These experiments demonstrate a synergistic antitumor efficacy for CV787 when combined with taxane and demonstrate an in vivo single-dose curative therapeutic index for CV787 of over 1000:1.

An evaluation of the effectiveness of two canal lubricants in removing smear layer

This study used scanning electron microscopy to compare the effectiveness of two new canal lubricants in conjunction with sodium hypochlorite irrigation in removing smear layer. Both lubricants completely removed the smear layer in the coronal and middle thirds of the root canals, but only partially removed the smear layer in the apical thirds. An explanation of the findings is presented and the clinical significance of smear layer is discussed.

Callosal atrophy correlates with temporal lobe volume and mental status in Alzheimer's disease

BACKGROUND

Recent studies have reported significant atrophy of the corpus callosum (CC) in Alzheimer's Disease (AD). However, it is currently unknown whether CC atrophy is associated with specific cortical volume changes in AD. Moreover, possible atrophy in extra-callosal commissures has not been examined to date. The purpose of the present study was to quantify atrophy in two cerebral commissures [the CC and the anterior commissure (AC)], to correlate this measure with cognitive status, and to relate commissural size to independent measures of temporal lobe volume in AD patients.

METHODS

A sample of AD patients and of age- and education-matched normal control subjects (NCs) underwent MRI and a cognitive test battery including the Dementia Rating Scale and Mini Mental State examination. Mid-sagittal regional areas within CC and AC were measured along with superior, middle and inferior temporal lobes volumes.

RESULTS

Alzheimer's Disease patients had significantly smaller callosa than did NCs. The callosal regions most affected in AD included the midbody, isthmus and genu. The isthmus and midbody areas of the CC were positively correlated with cognitive performance and with superior temporal lobe volume in AD patients. The mid-sagittal area of the AC and the superior temporal volumes did not differ between AD patients and NCs.

CONCLUSIONS

The study demonstrated that the regional morphology of the CC correlates with current cognitive status and temporal lobe atrophy in AD. As well, the lack of difference for the AC suggests that commissural atrophy in AD is regionally specific.

Pre-existent adenovirus antibody inhibits systemic toxicity and antitumor activity of CN706 in the nude mouse LNCaP xenograft model: implications and proposals for human therapy

Pre-existent humoral antibody to adenovirus potentially confounds human clinical trials involving intravascular administration of adenovirus. Using the LNCaP prostate cancer xenograft model in BALB/c nu/nu mice and the prostate-specific attenuated replication-competent adenovirus (ARCATM) CN706, we developed an animal model that systematically controls both the dose of intravascularly administered adenovirus and the titer of the pre-existent anti-Ad5 antibody, and then measures the virus-induced toxicity as well as antitumor activity. We prepared hyperimmune sera to adenovirus in rabbits, passively injected the purified rabbit anti-Ad5 antibody into tumor-bearing mice, and established measurable humoral anti-Ad5 antibody titers. CN706 was intravenously injected into the tail vein of animals 24 hr after passive anti-Ad5 antibody administration. In the absence of pre-existent antibody, the lethal dose (LD100) for BALB/c nu/nu mice was 2.5x10(11) CN706 particles, whereas 1x10(11) CN706 particles was not lethal. However, in the presence of a 1:80 pre-existent titer of Ad5 neutralizing antibody (NAb), intravenous injection of 5x10(11) CN706 particles was no longer lethal. In addition, pre-existent antibody also prevented antitumor activity in a dose-dependent manner: 1x 10(11) CN706 particles prevented LNCaP xenograft tumor progression, but antitumor activity was eliminated by a pre-existent 1:80 NAb titer. These results led us to propose transient removal of pre-existent adenovirus antibody by immunoapheresis. An affinity column of cloned virus capsid proteins was constructed that was able to specifically remove adenovirus antibody from human clinical serum samples. A 5-min disposable immunoassay was also developed to monitor the level of pre-existent antibody in sera before and after immunoapheresis. Clinically, this approach may enable controlled clinical studies of intravenously administered adenovirus in patients with pre-existent anti-adenovirus antibody.

The addition of adenovirus type 5 region E3 enables calydon virus 787 to eliminate distant prostate tumor xenografts

CV787, a novel highly prostate-specific replication-competent adenovirus with improved efficacy, was constructed. CV787 contains the prostate-specific rat probasin promoter, driving the adenovirus type 5 (Ad5) E1A gene, and the human prostate-specific enhancer/promoter, driving the E1B gene. To improve efficacy, we constructed CV787 such that it also contains the entire Ad5 E3 region. CV787 replicates in prostate-specific antigen (PSA)+ cells as well as wild-type adenovirus, but in PSA- cells, CV787 replicates 10(4)-10(5) times less efficiently. CV787 destroys PSA+ prostate cancer cells 10,000 times more efficiently than PSA- cells. Incorporation of the Ad5 E3 region significantly improves the target cell killing ability or efficacy of CV787. In nu/nu mice carrying s.c. LNCaP xenografts, a single i.v. tail vein injection of CV787 eliminates 300-mm3 tumors within 4 weeks. CV787 could be a powerful therapeutic for human metastatic prostate cancer.

[18F]Fluoro-beta-fluoromethylene-m-tyrosine derivatives show stereo, geometrical, and regio specificities as in vivo central dopaminergic probes in monkeys

Stereo (D and L), geometrical (E and Z), and regiospecific (2-, 4-, and 6-[18F]fluoro) analogs of beta-fluoromethylene-m-tyrosine (FMMT) have been investigated in adult vervet monkeys (Cercopithecus aethiops sabaeus, n = 12) in vivo with positron emission tomography (PET). Brain transport through the blood-brain barrier and central aromatic amino acid decarboxylase (AAAD)-mediated decarboxylation rates were established. Results show strict structural dependency of the kinetic behavior of radiofluorinated FMMT analogs, with the E-isomer exhibiting a higher specificity over the (Z) geometrical counterpart for central dopaminergic structures. The 6-[18F]fluoro substituted L-(E)-FMMT was also favored over the 2- and 4-[18F]fluorosubstituted isomers in terms of their ability to localize in the same brain areas. The role of PET in drug development is also exemplified in this work.

Identification of the transcriptional regulatory sequences of human kallikrein 2 and their use in the construction of calydon virus 764, an attenuated replication competent adenovirus for prostate cancer therapy

Human glandular kallikrein (hK2) and prostate-specific antigen (PSA) are related members of the human kallikrein gene family. The genes for hK2 and PSA are expressed predominately in the prostate, are transcriptionally up-regulated by androgens, and share 78% homology. Previously, one functional androgen response element was identified within the proximal promoter (-324 to +33 relative to the cap site) of the hK2 gene. To detect additional upstream regulatory elements, the 12.3 kbp between the PSA gene and 5' to the hK2 gene were amplified by PCR and linked to a promoterless firefly luciferase reporter gene. Transient transfection experiments showed an androgen-dependent enhancer, located between -3.4 and -5.2 kb upstream of the transcription start site of the hK2 gene. This hK2 enhancer increased luciferase expression 100-fold in the presence of the testosterone analogue R1881. The hK2 enhancer contains an androgen response element that lost activity when mutated. The hK2 enhancer/promoter demonstrated activity in PSA(+) LNCaP cells whereas the enhancer/promoter was inactive in PSA(-) 293, A549, HBL100, HUH-7, LoVo, MCF-7, OVCAR-3, and PC-3 cells. Insertion of the hK2 enhancer/promoter into adenovirus to drive the E1A genes of adenovirus type 5 (Ad5) created an attenuated replication competent adenovirus variant Calydon virus (CV) 763, which replicates similarly to wild-type adenovirus in prostate tumor cells but is attenuated in nonprostate tumor cells. In addition, CV764, an adenovirus variant containing the previously cloned prostate-specific enhancer (to drive the Ad5 E1A genes) and the hK2 enhancer/promoter (to drive the Ad5 E1B genes) was constructed. CV764 is significantly attenuated and has a high therapeutic index with a cell specificity of 10,000:1 for PSA(+) LNCaP cells, compared to ovarian cancer OVCAR-3 cells and SK-OV-3 cells and PA-1 cells. CV764 is also highly attenuated in primary human microvascular endothelial cells.

Protein synthesis in Giardia lamblia may involve interaction between a downstream box (DB) in mRNA and an anti-DB in the 16S-like ribosomal RNA

Giardia lamblia, a parasitic protozoan, has been regarded as one of the most conserved eukaryotes evolved from the prokaryotes. One of its unique features appears to be the unusually short 5'-untranslated regions (UTR) (1-6 nucleotides (nts)) and the apparent absence of 5'-cap structures from its mRNAs. Transfection of the Giardia trophozoites with luciferase-encoding chimeric transcripts, flanked by the 5'- and 3'-ends of giardiavirus (GLV) (+)-strand RNA, indicated that the translational efficiency was enhanced by 5000-fold when the 5'-viral sequence extended 264 nts into the capsid coding region and fused with the luciferase open reading frame (ORF). A 13-nt downstream box (DB) was identified within this region which complements a 15-nt sequence between nts # 1382 and 1396 near the 3'-end of the Giardia 16S-like ribosomal RNA (the anti-DB). Deletion or scrambling of this DB in the mRNA leads to a significant loss of the translational efficiency in Giardia. A Shine-Dalgarno (SD)-like element was also identified at 9-14 nts upstream from the initiation codon in the viral (+)-strand RNA, but alteration of its sequence led to no change in translation. Using the sequence complementary to ribosomal anti-DB to probe the Giardia mRNAs available in the databases, each mRNA was found to contain a putative DB with an average length from 8 to 13 nts. It is thus possible that initiation of translation in Giardia may involve a DB in the coding region of mRNA that may bind to a putative anti-DB in the small ribosomal RNA through base pairing. This mechanism of ribosome recruitment, which finds a potential parallel in Escherichia coli, could illustrate a relatively close distance between Giardia and prokaryotes in terms of translation initiation, and may provide a model for studying the evolution of translation machinery.

The significance of locating and filling the canal isthmus in multiple root canal systems. A scanning electron microscopy study of the mesiobuccal root of maxillary first permanent molars

The mesiobuccal (MB) roots of 50 randomly selected maxillary first permanent molars were examined to evaluate the different configurations of canal isthmus and their incidences. Sections of the roots at 3.4, and 5 mm from the apex were prepared, acid etched, washed and dried. The apical side of each section was sputter coated with gold, examined by a Hitachi S-2500 scanning electron microscope and photographed. 36% of the mesiobuccal roots had one canal, whereas 64% had two canals. In the roots with two canals 31.25% contained either a complete isthmus, or accessory canals between the two main canals 31.25% showed partial isthmus formation. The significance of the different configurations is discussed. Our present findings indicate that the mesiobuccal roots of maxillary first permanent molars exhibit complex anatomy. Prudent judgement is essential in the canal isthmus preparation so that operators must provide meticulous skill and care to the patients.

Using fast sequential asymmetric fanbeam transmission CT for attenuation correction of cardiac SPECT imaging

The objective of this study was to determine the feasibility of using a fast (short-duration) transmission computed tomogram (TCT), acquired immediately before or after the emission CT, to correct for photon attenuation in cardiac SPECT.

METHODS

The asymmetric fanbeam geometry with a 99mTc line source was used to acquire TCTs after conventional cardiac emission CT imaging on a triple-head SPECT system. The TCTs were reconstructed to generate patient-specific attenuation maps, which were used with an iterative maximum likelihood algorithm to reconstruct attenuation-corrected cardiac SPECT studies. The results of attenuation correction based on TCTs as short as 1 min were compared with long-duration transmission imaging for a phantom and several human studies.

RESULTS

Attenuation correction based on asymmetric fanbeam TCT significantly improves the uniformity of images of a uniform tracer distribution in a cardiac-thorax phantom configured to simulate a large patient. By using a high-activity line source and a rapid camera rotation, a suitable attenuation map for this phantom can be obtained from a 4-min TCT. A similar result is obtained for patients with thorax widths of <40 cm.

CONCLUSION

A sequential imaging protocol for acquiring a fast TCT can be used for attenuation correction of cardiac SPECT imaging. The sequential TCT can be acquired without significantly extending the duration of the imaging study. This method provides a way to perform attenuation correction on existing triple-head SPECT systems without extensively modifying the system.

Stable coexpression of a drug-resistance gene and a heterologous gene in an ancient parasitic protozoan Giardia lamblia

Manipulation of gene expression in Giardia lamblia, one of the most ancient eukaryotes, may provide insights into the evolutionary transition from prokaryotes to eukaryotes. Two recent successes in transient expression of the firefly luciferase (luc) gene in G. lamblia were mediated by a 5'-untranslated region (UTR) of the Giardia glutamate dehydrogenase (gdh) gene and a giardiavirus (GLV) genomic transcript, respectively. We now report a stable coexpression of luc gene with a neomycin phosphotransferase (neo(r)) gene in G. lamblia. An in vitro transcript of the construct pC670-Neo; containing the neo(r) encoding region flanked with the 5'670 nucleotides (nt) and the 3'2022 nt portion of GLV positive strand RNA, was electroporated into G. lamblia trophozoites that were infected with GLV. G418-resistant Giardia trophozoites were cloned, and the neo(r) mRNA in these clones was found to increase with increasing G418 pressure. This drug resistance remained stable upon continuous in vitro cultivation in the absence of G418 for over 15 days. Another plasmid pNeo/GDH/Luc, was constructed by inserting luc gene downstream from the neo(r) gene and the 193 nt 5' portion of gdh gene in pC670-Neo, and its bicistronic in vitro transcript was introduced into GLV-infected G. lamblia by electroporation. The transfectants demonstrated G418-resistance and persistent luciferase activity at levels parallel to the amount of G418 used for selection, peaking at a level of several thousand-fold above the background. Taken together, these data indicate that the neo(r) gene provides an effective selection marker for transformation of Giardia trophozoites, and the bicistronic RNA transfection vector may open the way for functional analysis of other genes in Giardia.

Amplification, expression, and packaging of a foreign gene by giardiavirus in Giardia lamblia

Giardia lamblia is an intestinal protozoan parasite and one of the earliest eukaryotic divergents. The trophozoite multiplies via asexual binary fission and lacks all natural means of lateral gene transfer. A system is developed here for long-term expression of a foreign gene in this organism by exploiting recombinant virions derived from the giardiavirus (GLV), a double-stranded RNA virus that infects many Giardia isolates. An in vitro transcript of the cloned GLV cDNA, comprising the firefly luciferase-encoding region flanked by 5' and 3' fragments of GLV positive-strand RNA, was electroporated into GLV-infected trophozoites. Luciferase activity in electroporated cells peaked on day 2 at levels 6 orders of magnitude above background. Expression of this foreign gene remained at 80% of its peak level after 30 days in the absence of selective pressure. The chimeric RNA was replicated as double-stranded RNA and packaged into virus-like particles. The recombinant virions were partially purified from the wild-type helper virus by CsCl equilibrium density-gradient centrifugation and used to superinfect Giardia trophozoites. At multiplicities of infection of 100 or higher, these chimeric virions were able to initiate new rounds of expression of luciferase activity in the superinfected cells. Thus, the engineered virion can be successfully used to introduce and efficiently express a heterologous gene in this eukaryotic microorganism.

Automated image registration for FDOPA PET studies

In this study, various image registration methods are investigated for their suitability for registration of L-6-[18F]-fluoro-DOPA (FDOPA) PET images. Five different optimization criteria including sum of absolute difference (SAD), mean square difference (MSD), cross-correlation coefficient (CC), standard deviation of pixel ratio (SDPR), and stochastic sign change (SSC) were implemented and Powell's algorithm was used to optimize the criteria. The optimization criteria were calculated either unidirectionally (i.e. only evaluating the criteria for comparing the resliced image 1 with the original image 2) or bidirectionally (i.e. averaging the criteria for comparing the resliced image 1 with the original image 2 and those for the sliced image 2 with the original image 1). Monkey FDOPA images taken at various known orientations were used to evaluate the accuracy of different methods. A set of human FDOPA dynamic images was used to investigate the ability of the methods for correcting subject movement. It was found that a large improvement in performance resulted when bidirectional rather than unidirectional criteria were used. Overall, the SAD, MSD and SDPR methods were found to be comparable in performance and were suitable for registering FDOPA images. The MSD method gave more adequate results for frame-to-frame image registration for correcting subject movement during a dynamic FDOPA study. The utility of the registration method is further demonstrated by registering FDOPA images in monkeys before and after amphetamine injection to reveal more clearly the changes in spatial distribution of FDOPA due to the drug intervention.

Identification of cis-acting signals in the giardiavirus (GLV) genome required for expression of firefly luciferase in Giardia lamblia

Giardiavirus (GLV) is a 6,277-bp double-stranded RNA virus of Giardia lamblia, one of the earliest eukaryotic divergents from the prokaryotes. Our previous success in GLV-mediated transfection of G. lamblia has provided an effective way of monitoring the mechanisms underlining GLV gene replication and mRNA translation in this organism. Here we have investigated the cis-acting signals in the GLV genome that regulate replication, transcription, and translation of an inserted firefly luciferase gene in GLV-infected G. lamblia. By modifying the two terminal regions of a full-length GLV cDNA clone used to flank a luciferase gene, various in vitro chimeric transcripts were generated and introduced into GLV-infected G. lamblia via electroporation. Expression of luciferase (+) strand and (-) strand RNAs in the transfected cells was monitored and the luciferase activity assayed. The results indicated that the 5'-untranslated region (UTR) of 366 nt and the 3'-terminal 2,022 nt of the viral transcript are both needed for optimal expression of the two RNA strands. Although the entire 5'-UTR is needed for the chimeric mRNA synthesis, both the primary sequence and the secondary structure at the 3' end of GLV transcript are essential for the synthesis of (-) strand RNA. When the 5' end of GLV transcript was extended 265 nt into the capsid protein open reading frame and fused with that of luciferase, there was no change in the level of luciferase chimeric RNA, but a 5,000-fold increase of luciferase activity was observed that may be attributed to an enhanced translational efficiency of the chimeric mRNA in G. lamblia.

Radiofluorinated L-m-tyrosines: new in-vivo probes for central dopamine biochemistry

In this work, we introduce 6-[18F]fluoro-L-m-tyrosine (6-FMT) and compare its in-vivo kinetic and bio-chemical behaviors in monkeys and rodents with those of 4-FMT and 6-[18F]fluoro-L-3, 4-dihydroxyphenylalanine (DOPA) (FDOPA). These radiofluorinated m-tyrosine presynaptic dopaminergic probes, resistant to peripheral 3-O-methylation, offer a nonpharmacological alternative to the use of catechol-O-methyltransferase inhibitors. Like FDOPA, 4-FMT and 6-FMT are analogs that essentially follow the L-DOPA pathway of central metabolism. After i.v. administration in nonhuman primates and rodents, these new radiofluorinated m-tyrosine analogs accumulate selectively in striatal structures and allow for the detection of additional innervation sites (e.g., brain stem) rich in aromatic amino acid decarboxylase. Bio-chemical analyses in rodents and monkeys revealed the specificity of their central and peripheral metabolism. Molecular and enzymatic mechanisms involved in their retention in central brain structures are consistent with involvement of dopaminergic neurons. The high signal-to-noise ratios observed make these radiofluorinated m-tyrosine analogs outstanding candidates for probing the integrity of central dopaminergic mechanisms in humans.

6-[18F]fluoro-L-DOPA-PET studies show partial reversibility of long-term effects of chronic amphetamine in monkeys

The acute and long-term effects of chronic amphetamine administration on the striatal dopamine system in monkeys were assessed with 6-[18F]fluoro-L-DOPA (FDOPA) and positron emission tomography (PET). Vervet monkeys (Cerecopithecus aethiops) were administered amphetamine doses, i.m., that increased from 4 mg/kg/d to 18 mg/kg/d over a 10 day period. Post-amphetamine FDOPA-PET scans at 1-2, 3-4, and 6 week time points in individual subjects showed persistent decrements in dopamine synthesis capacity as reflected by FDOPA influx rate constant (Ki) values being approximately 30% that of pre-drug assessment. In other animals that were administered the same drug regimen, biochemical analysis of striatal regions at 1-2 weeks post-drug indicated that dopamine concentrations were decreased by approximately 95% throughout caudate and putamen regions, while the homovanillic acid/dopamine level ratio was increased 3-10-fold. Post-drug FDOPA-PET Ki values remained consistently low up to 6 weeks; however, at the 5-6 month time point, relative increases in FDOPA-Ki values (approximately 53% of pre-drug values) were observed for all subjects, indicative of partial recovery of striatal dopamine synthesis capacity. These results demonstrate that FDOPA-PET can reveal temporal activity changes within the striatal dopamine system of individual subjects. The apparent, partial reversibility of amphetamine's neurotoxic effects suggests a plasticity of dopaminergic function that may include regeneration of dopaminergic terminals and compensatory increases in residual dopamine synthesis rates. The persistence of the partial decrement in dopamine synthesis capacity, however, may indicate a long term component of amphetamine's toxic effects.

Virus-mediated expression of firefly luciferase in the parasitic protozoan Giardia lamblia

Giardia lamblia, a prevalent human pathogen and one of the lineages that branched earliest from prokaryotes, can be infected with a double-stranded RNA virus, giardiavirus (GLV). The 6,277-bp viral genome has been previously cloned (A.L. Wang, H.-M. Yang, K.A. Shen, and C.C. Wang, Proc. Natl. Acad. Sci. USA 90:8595-8599, 1993; C.-H. Wu, C.C. Wang, H.M. Yang, and A.L. Wang, Gene, in press) and was converted to a transfection vector for G. lamblia in the present study. By flanking the firefly luciferase gene with the 5' and 3' untranslated regions (UTRs) of the GLV genome, transcript of the construct was synthesized in vitro with T7 polymerase and used to transfect G. lamblia WB trophozoites already infected with GLV (WBI). Optimal electroporation conditions used for the transfection were set at 1,000 V/cm and 500 microF, which resulted in expression of significant luciferase activity up to 120 h after electroporation. Furthermore, the mRNA and the antisense RNA of the luciferase gene were both detected by reverse transcription and PCR from 6 to 120 h postelectroporation, whereas no antisense RNA of luciferase was observed in the electroporated virus-free Giardia WB trophozoites. The mRNA of luciferase was detectable in the virus-free trophozoites by reverse transcription and PCR only up to 20 h after the electroporation, indicating that the introduced mRNA was replicated only by the viral RNA-dependent RNA polymerase inside the WBI cells. This expression of luciferase was dependent on the presence of UTRs on both ends of the viral genome transcript, including a putative packaging site that was apparently indispensable for luciferase expression. This is the first time that a viral vector in the form of mRNA URTs has been successfully used in transfecting a protozoan.

Factors to consider for predictable post and core build-ups of endodontically treated teeth. Part II: Clinical application of basic concepts

Post and core build-ups represent an important pre-prosthetic procedure prior to the restoration of an endodontically treated tooth. The dental practitioner is presented with the dilemma of selecting from an ever increasing variety of materials, techniques and designs related to this procedure, many of which are harmful and mired in controversy. Part II of this paper will review some basic theoretical concepts related to post and core build-ups with the objective of applying these concepts to address a number of pertinent clinical questions related to the above selection process. This review should provide the dentist with a reference to produce a more predictable post and core build-up.

Factors to consider for predictable post and core build-ups of endodontically treated teeth. Part I: Basic theoretical concepts

Post and core build-ups represent an important pre-prosthetic procedure prior to the restoration of an endodontically treated tooth. The dental practitioner is presented with the dilemma of selecting from an ever increasing variety of materials, techniques and designs related to this procedure, many of which are harmful and mired in controversy. Part I of this paper reviews some basic theoretical concepts for the dentist to consider when producing a predictable post and core build-up. An understanding of these basic concepts will assist the dentist in gathering data and establishing a risk/benefit equation, and will also provide an additional aid during the decision-making process for the restoration of an endodontically treated tooth.

The assessment of the non-equilibrium effect in the 'Patlak analysis' of Fdopa PET studies

'Patlak analysis' is a common approach used in Fdopa PET studies to calculate the uptake constant (Ki) of the tracer. It is assumed in the Patlak analysis that the reversible compartment of tissue radioactivity used is in effective equilibrium with the tracer in plasma. Therefore, using the data prior to equilibrium is in conflict with the assumption, and its effect on the estimate thus needs to be examined. In this study, we used simulations to investigate the errors due to the violation of the equilibrium assumption. Two factors affecting the estimate of Ki were examined--the eigenvalue of the model response function and the shape of the input function. The Ki estimate obtained from the Patlak analysis was found to be markedly biased because the system is not in equilibrium during the first 2 h post Fdopa injection. The magnitude of the bias was found to be dependent on the time interval used in the analysis (10% difference when comparing results from intervals 30-120 min and 60-120 min) and on the eigenvalue of the response function (10% change in Ki when the eigenvalue was changed by 20% around the nominal value). The estimates are also affected by the intersubject variations in the plasma time-activity curves. Therefore, Patlak analysis users should interpret their results with caution, particularly when examining small intersubject differences and small changes due to physiological or pharmacological interventions.

Methods for improving quantitation of putamen uptake constant of FDOPA in PET studies

To estimate the striatal uptake constant of [18F]-L-6-fluorodopa (FDOPA) in humans, we studied two methods that can account for the image resolution and the background level of FDOPA. These two methods utilize information obtained from multiple ROIs varying in size around the putamen and from profiles crossing the middle of the putamen. The estimation of the uptake constant was based on a model of one-dimensional activity variation. Simulated data were used to evaluate the adequacy of these two methods. Parametric images of FDOPA uptake constants were generated using Patlak analysis for five studies in normals and were then analyzed with the two methods. Results from the simulated data indicated a good agreement between the estimated values and the true simulated values. Results from studies in normals show stable estimates of the FDOPA uptake constant that are not affected by image resolution. The two methods were not sensitive to the misplacement of ROIs and profiles.

Successful treatment of a severe electrical injury involving the stomach

Apparently no report of the survival of a child with severe electrical injuries involving the stomach has been published. We successfully treated a 5-year-old boy with such injuries in August 1991. Our effective treatment included: (1) resection of the necrosis of the stomach immediately after admission; (2) active excision of all surrounding necrotic tissues with conservation of any piece of healthy tissue, including partial degenerative tissues; (3) early coverage of all exposed areas; (4) general comprehensive supportive therapy, and (5) local application of a saline solution containing chloromycetin and lidocaine.

Kinetics and modeling of L-6-[18F]fluoro-dopa in human positron emission tomographic studies

Kinetics of L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) in striatum and cerebellum were measured in 10 normal human subjects with positron emission tomography (PET) from 0 to 120 min after an intravenous bolus injection of the tracer. The time course of the arterial plasma concentrations of the tracer and its metabolites was also assayed biochemically. FDOPA compartmental models that are based on biochemical information were investigated for their consistency with the measured striatal and cerebellar tissue kinetics. A modeling approach was also developed for separating plasma FDOPA and metabolite time-activity curves from the measured total 18F time-activity curve in plasma. Results showed that a model consisting of three separate compartments for tissue FDOPA, tissue 6-[18F]fluorodopamine (FDA) and its metabolites, and tissue L-3,4-dihydroxy-6-[18F]fluoro-3-O-methylphenylalanine (3-OMFD) could describe adequately the striatal kinetics in humans. Based on this model, the FDOPA transport constant across the blood-brain barrier (BBB) (K1), the FDOPA decarboxylation rate constant (k3), and the turn-over rate constant of FDA and its metabolites (k4) could be estimated by model fitting to the tissue kinetics and were found for the normal subjects to be 0.031 +/- 0.006 ml/min/g (mean +/- SD), 0.041 +/- 0.015/min, and 0.004 +/- 0.002/min, respectively. About 50% of the FDOPA that crossed the BBB from plasma to striatum was decarboxylated. The decarboxylation constant with respect to plasma FDOPA (K3) was 0.015 +/- 0.003 ml/min/g. The BBB transport corresponded to a permeability-surface area product of 0.032 ml/min/g for FDOPA. For 3-OMFD, the BBB transport was 1.7 times faster. The effects of tissue heterogeneity on the FDOPA kinetics and on the estimated model parameters were also investigated. The usefulness and implications of these findings for interpretation of PET FDOPA studies are discussed.

The effects of measurement errors in the plasma radioactivity curve on parameter estimation in positron emission tomography

The effects of three error sources in plasma curve measurements on parameter estimation in kinetic analysis of positron emission tomography (PET) fluorodeoxyglucose (FDG) data are investigated by computer simulation. The three error sources are: (1) measurement noise in the radioactivity concentrations of plasma samples; (2) linear interpolation between adjacent plasma sampling points of the plasma time activity curve; and (3) incorrect weights used for the least-squares regression. All three error sources are found to increase the variability of the parameter estimates, with the first one a primary error source in normal PET FDG studies. The performance of five estimation methods which account for the error sources are evaluated. When the noise variances of the plasma and the tissue measurements are not known, an iterative weighting procedure is shown to give accurate and reliable estimates.

Modelling approach for separating blood time-activity curves in positron emission tomographic studies

A modelling approach is developed to generate the full time course of an injected radiotracer and its labelled metabolites in plasma/blood, based on measurements of the total radioactivities in withdrawn plasma/blood samples. A compartmental model is used to describe the conversion of an injected tracer to its metabolites in the body. The model equation is formulated with the total radioactivity concentration curve as the input function. The utility and characteristics of the approach in quantitative positron emission tomographic (PET) studies are shown with two examples. In the first example, using the tracer 6-[18F]fluoro-L-dopa (FDOPA), the approach is shown to derive the full time course of plasma FDOPA and its metabolites. In the second example of dynamic 15O oxygen PET, the approach is used to solve a deconvolution problem to give separated time-activity curves of 15O oxygen and 15O water in blood. The modelling approach improves the separation of blood/plasma time-activity curves and leads to better quantitative interpretation of PET results.

6-[18F]fluoro-L-dopa probes dopamine turnover rates in central dopaminergic structures

6-[18F]Fluoro-L-DOPA (FDOPA) cerebral kinetics and metabolism were correlated in normal primates (Macaca nemestrina) and primates with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced unilateral Parkinsonism. Application of a tracer kinetic model to positron emission tomography (PET) data indicated that the model allows reliable estimation of FDOPA blood brain barrier transport, decarboxylation and release of stored 6-[18F]fluorodopamine (FDA) radioactivity in normal striatum (k4 = 0.005/min, turnover half-time greater than or equal to 2 hr), in agreement with biochemical data. PET scans of MPTP treated monkeys revealed 40-50% reduction in total striatal activity in comparison with pre-MPTP scans. Monkey brain biochemical analysis revealed that the reduction in activity was mainly due to a decrease in FDA and its metabolites, 6[18F]fluorohomovanillic (FHVA) and 6-[18F]fluoro-3, 4-dihydroxyphenylacetic acid (FDOPAC). The remaining activity in tissue was 3-0-methyl-6-[18F]fluoro-L-DOPA (3-OMFD) of peripheral origin. The (FHVA + FDOPAC)/FDA ratio was 1:2 in normal putamen and greater than or equal to 6:1 in the lesioned putamen, indicative of a dramatic increase in turnover of FDA. Both kinetic and biochemical data indicate that FDOPA labels a slow turnover rate pool of dopamine in rat and primate brain. This turnover rate for stored dopamine (DA) is accelerated with dopaminergic cell losses (e.g., MPTP-induced Parkinsonism).