The Stapled AKAP Disruptor Peptide STAD-2 Displays Antimalarial Activity through a PKA-Independent Mechanism

Drug resistance poses a significant threat to ongoing malaria control efforts. Coupled with lack of a malaria vaccine, there is an urgent need for the development of new antimalarials with novel mechanisms of action and low susceptibility to parasite drug resistance. Protein Kinase A (PKA) has been implicated as a critical regulator of pathogenesis in malaria. Therefore, we sought to investigate the effects of disrupted PKA signaling as a possible strategy for inhibition of parasite replication. Host PKA activity is partly regulated by a class of proteins called A Kinase Anchoring Proteins (AKAPs), and interaction between HsPKA and AKAP can be inhibited by the stapled peptide Stapled AKAP Disruptor 2 (STAD-2). STAD-2 was tested for permeability to and activity against Plasmodium falciparum blood stage parasites in vitro. The compound was selectively permeable only to infected red blood cells (iRBC) and demonstrated rapid antiplasmodial activity, possibly via iRBC lysis (IC₅₀ ≈ 1 μM). STAD-2 localized within the parasite almost immediately post-treatment but showed no evidence of direct association with PKA, indicating that STAD-2 acts via a PKA-independent mechanism. Furosemide-insensitive parasite permeability pathways in the iRBC were largely responsible for uptake of STAD-2. Further, peptide import was highly specific to STAD-2 as evidenced by low permeability of control stapled peptides. Selective uptake and antiplasmodial activity of STAD-2 provides important groundwork for the development of stapled peptides as potential antimalarials. Such peptides may also offer an alternative strategy for studying protein-protein interactions critical to parasite development and pathogenesis.

Abstract 3707: Captopril inhibits colorectal cancer liver metastases following 70% partial hepatectomy in a mouse model

Background: Blockade of the renin-angiotensin system (RAS) with the angiotensin-converting enzyme inhibitor, Captopril, has been shown to inhibit CRCLM. Partial hepatectomy (PH) for colorectal cancer liver metastases (CRCLM) can stimulate tumour recurrence. Aim: This study investigated the effects of Captopril on liver regeneration (LR), as well as on CRCLM in the regenerating liver. Methods: Male CBA mice were used for 70% PH as well as 70% PH following CRCLM induction. Mice were randomly assigned to control or Captopril-treated groups. Liver and tumour samples were collected on days 1, 2, 4, 6 and 8, 16 and 21 post-surgery. The rate of LR was measured by liver-to-body weight (LBW) ratio. The percentage of liver metastases was quantified using quantitative stereology and immunohistochemistry was performed to quantify hepatocyte and tumour cell proliferation (anti-Ki67) and apoptosis (anti-caspase-3). Results: Captopril increased LBW (0.57 ± 0.02 Captopril, 0.49 ± 0.02 control, p = 0.027) compared to controls on day 2 following 70% PH. At day 6, Captopril had decreased LBW (0.5 ± 0.03, 0.73 ± 0.06, p = 0.006). However, by day 8, LBW was not different between the control and Captopril groups. At day 21, Captopril decreased the percentage of liver metastases compared to controls (24.4 ± 6.2%; 48.7 ± 4.7%, p = 0.008) in the regenerating liver. Tumour volume (388.3 ± 150.4; 1046.2 ± 200.2mm3, p = 0.02) and tumour nodule count per image field (68 ± 17.6; 181.1 ± 28.5, p = 0.005) were also decreased by Captopril. In contrary, Captopril did not significantly alter liver volume compared to controls (886.1 ± 65.2; 1044.1 ± 115.8, p = 0.254). Furthermore, LBW during LR in the presence of CRCLM at day 2 (0.53 ± 0.01; 0.51 ± 0.02, p = 0.449) and day 6 (0.71 ± 0.01; 0.73 ± 0.03, p = 0.51) were not different between Captopril and control groups. Conclusion: Captopril enhanced the early stage of LR following 70% PH. Captopril inhibits CRCLM in the regenerating liver without inhibiting LR. Understanding the mechanisms of actions of Captopril is required to improve CRCLM patient outcomes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3707. doi:1538-7445.AM2012-3707

Hydrogen transfer between methanogens and fermentative heterotrophs in hyperthermophilic cocultures

Interactions involving hydrogen transfer were studied in a coculture of two hyperthermophilic microorganisms: Thermotoga maritima, an anaerobic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic methanogen. Cell densities of T. maritima increased 10-fold when cocultured with M. jannaschii at 85 degrees C, and the methanogen was able to grow in the absence of externally supplied H(2) and CO(2). The coculture could not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximity. The significance of spatial proximity was also supported by cell cytometry, where the methanogen was only found in cell sorts at or above 4.5 microm in samples of the coculture in exponential phase. An unstructured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophilic cocultures. Calculations suggest the increases in methanogenesis rates with temperature result from greater interactions between the methanogenic and fermentative organisms, as evidenced by the sharp decline in H(2) concentration in the proximity of a hyperthermophilic methanogen. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations at elevated temperatures.

Solution structure and folding characteristics of the C-terminal SH3 domain of c-Crk-II

Crk-II is a signaling adaptor protein that is involved in many cellular processes including apoptosis, proliferation, and differentiation. It has a modular domain architecture consisting of an Src homology 2 domain (SH2) followed by two Src homology 3 (SH3) domains. The structures and ligand-binding properties of the SH2 and the middle SH3 domains are well-characterized. Several studies suggest that the C-terminal SH3 domain plays an important regulatory role in the protein; however, no structural information is available on this domain, and relatively little is known about its binding partners. In the current work, we have solved the solution NMR structure of the C-terminal SH3 domain. The domain adopts the standard SH3 fold comprising a five-stranded beta barrel. In agreement with alignment and modeling studies, the structure indicates that the canonical-binding surface of the SH3 domain is unusually polar and suggests that this domain may not bind typical PXXP ligands or that it may bind them with reduced affinity. Thermodynamic and kinetic studies show that the domain folds in a reversible two-state manner and that the stability of the fold is similar to that observed for other SH3 domains. These studies offer some insight into the likely structural and thermodynamic consequences of point mutations in the cSH3 domain that are known to deregulate Crk-II function. Our results set the stage for a better understanding the role of the cSH3 domain in the context of the full-length protein.

Protein ligation: an enabling technology for the biophysical analysis of proteins

Biophysical techniques such as fluorescence spectroscopy and nuclear magnetic resonance (NMR) spectroscopy provide a window into the inner workings of proteins. These approaches make use of probes that can either be naturally present within the protein or introduced through a labeling procedure. In general, the more control one has over the type, location and number of probes in a protein, then the more information one can extract from a given biophysical analysis. Recently, two related approaches have emerged that allow proteins to be labeled with a broad range of physical probes. Expressed protein ligation (EPL) and protein trans-splicing (PTS) are both intein-based approaches that permit the assembly of a protein from smaller synthetic and/or recombinant pieces. Here we provide some guidelines for the use of EPL and PTS, and highlight how the dovetailing of these new protein chemistry methods with standard biophysical techniques has improved our ability to interrogate protein function, structure and folding.

Patterns of heat shock protein (HSP70) expression and Kupffer cell activity following thermal ablation of liver and colorectal liver metastases

The time course and extent of thermal ablative injury differs in liver compared to tumour tissue. This may be influenced by differences in the expression of heat shock proteins (HSP) and the response of Kupffer cells to thermal injury. This study determines the expression and response of HSP70 and Kupffer cells to thermal ablative injury in a Murine model of colorectal liver metastases. Thermal ablation by laser (Nd-YAG wavelength 1064 nm) was induced in liver and colorectal cancer liver metastases in CBA strain mice. Laser energy was applied at 2 W for 50 s and produced incomplete tumour ablation. Established tissue injury was assessed in separate groups of animals at time points ranging from 12 h to 21 days following therapy. HSP70 and Kupffer cell expression at the margins of coagulated tissue was determined by immunohistochemical staining for HSP70 and F4/80 antigens, respectively. HSP70 was faintly expressed in the cytoplasm of all tumour cells, with distinct clusters exhibiting intense cytoplasmic and nuclear HSP70 staining (130+/-19 cells mm-2). Comparatively, HSP70 expression was uncommon in untreated control liver specimens (2+/-2 cells mm-2, p<0.001). Thermal ablation increased expression of HSP70 at coagulated tissue margins. The peak response in tumours occurred at 2 days post-ablation and was significantly greater than the peak response in liver, occurring at 12 h (809+/-80 cells mm-2 vs. 454+/-52 cells mm-2, p<0.001). HSP70 expression remained significantly elevated for 7 days following therapy in tumour tissue, compared to 3 days in liver. Kupffer cell numbers in untreated control tumours were significantly lower than in untreated control livers (285+/-23 cells mm-2 vs. 451+/-30 cells mm-2, p<0.001). Following thermal ablation, there was an initial decrease in Kupffer cell numbers at the margin of coagulation with subsequent persistent increases thereafter. In liver tissue, the peak Kupffer cell response occurred at 5 days post-therapy and was significantly greater than the peak response in tumour tissue 3 days post-thermal ablation (1074+/-34 cells mm-2 vs. 860+/-53 cells mm-2, p=0.007). Thermal ablation produces a greater and more prolonged HSP70 response in colorectal liver metastases than in liver tissue. It also induces persistent increases in Kupffer cell activity in liver and tumour tissue.

Domain-specific incorporation of noninvasive optical probes into recombinant proteins

An integrated approach is described that allows the domain-specific incorporation of optical probes into large recombinant proteins. The strategy is the combination of two existing techniques, expressed protein ligation (EPL) and in vivo amino acid replacement of tryptophans with tryptophan (Trp) analogues. The Src homology 3 (SH3) domain from the c-Crk-I adaptor protein has been labeled with a Trp analogue, 7-azatryptophan (7AW), using Escherichia coli Trp auxotrophs. Structural, biochemical, and thermodynamic studies show that incorporation of 7AW does not significantly perturb the structure or function of the isolated domain. Ligation of the 7AW-labeled SH3 domain to the c-Crk-I Src homology 2 (SH2) domain, via EPL, generated the multidomain protein, c-Crk-I, with a domain-specific label. Studies of this labeled protein show that the biochemical and thermodynamic properties of the SH3 domain do not change within the context of a larger multidomain protein. The technology described here is likely to be a useful tool in enhancing our understanding of the behavior of modular domains in their natural context, within multidomain proteins.

Scanning electron microscopy study of the blood supply of human colorectal liver metastases

AIMS

The failure of hepatic artery directed treatment of colorectal liver metastases may reflect a major portal venous contribution to tumour blood supply. This study provides ultrastructural details of the blood supply of colorectal liver metastases and their association with the portal vein and hepatic artery.

METHODS

Resected liver specimens from six patients with colorectal liver metastases were examined by histology and scanning electron microscopy (SEM), following vascular resin casting.

RESULTS

Nine metastatic colorectal adenocarcinomas were identified. The main feature of all tumours on SEM was direct communication between hepatic sinusoids and tumour vessels. A direct portal venous connection with tumour vessels was observed in a single specimen, whilst a direct arteriole connection was not identified.

CONCLUSIONS

It appears that both the hepatic artery and portal vein contribute to the blood supply of colorectal liver metastases through sinusoidal connections with tumour specific blood vessels. SEM provides useful additional information on the morphological features of tumour vasculature.

Primary hepatic carcinoid tumours

BACKGROUND

Carcinoid tumours of the liver are predominantly metastases from the gastrointestinal tract. Primary hepatic carcinoids are extremely rare.

DISCUSSION

In contrast to metastases, primary hepatic carcinoids are usually solitary and resectable. It is important that these tumours are differentiated from metastases. Complete surgical resection should be contemplated and is generally curative.

Interstitial laser hyperthermia and the biological characteristics of tumor: study in a murine model of colorectal liver metastases

BACKGROUND DATA

Percutaneously applied interstitial laser hyperthermia (ILH) is a minimally invasive therapy that is currently used in the treatment of liver metastases. Despite its documented efficacy, theoretical considerations and evidence based on animal studies suggest the potential for stimulating tumor growth, especially following surgery. This study investigates the influence of ILH on tumor behaviour in an animal model of colorectal liver metastases.

MATERIALS AND METHODS

A model of colorectal cancer liver metastases in male inbred CBA mice was used. Laser hyperthermia was applied to tumor tissue using a bare optical quartz from a Medilas fibertom 4100 Nd:YAG surgical laser generator. Liver injury by ILH was initially produced in three experimental groups of animals at different time points in the development of metastases. ILH was applied (i) to normal liver 10 days prior to tumor induction, (ii) immediately prior to tumor induction, and (iii) 15 days after tumor induction to achieve approximately 8% liver destruction. Animals were killed 21 days after tumor induction, and the effects of ILH on overall tumor development were compared with controls using stereological assessment of tumor volume and by histology. In a separate experimental group, the effects of ILH on fully established tumors were examined. Suitable tumors were selected 21 days after induction and partially destroyed by ILH at a standard energy setting. Animals were then killed 15 days later, and the growth rate of the residual viable tumors was compared to control tumors having undergone sham procedures.

RESULTS

No significant stimulation of tumor growth was evident in any of the experimental groups following ILH, irrespective of the time of application. Incomplete tumor destruction also had no influence on subsequent tumor growth.

CONCLUSION

ILH does not influence the biological characteristics of tumors during any stage of the metastatic process.

Interstitial laser hyperthermia for colorectal liver metastases: the effect of thermal sensitization and the use of a cylindrical diffuser tip on tumor necrosis

OBJECTIVE

Our aim in this study was to investigate the characteristics of a diffuser-tipped optical fiber in producing tumor necrosis, compared to a standard bare-tipped fiber. The potential synergistic effect between thermal sensitization by metronidazole and interstitial laser hyperthermia (ILH)-induced tumor necrosis is also evaluated.

BACKGROUND DATA

ILH is a minimally invasive technique for the treatment of colorectal liver metastases. One of the major limitations is the size of tissue necrosis achieved by a single optical fiber. Use of cylindrical diffuser-tipped fibers and thermal sensitization of tumor cells by metronidazole may increase the size of tumor necrosis achieved by a single optical fiber.

MATERIALS AND METHODS

A model of colorectal cancer liver metastases in male inbred CBA mice was used. Laser hyperthermia was applied to tumor tissue using either a bare optical quartz fiber or a cylindrical diffuser-tipped fiber from a Medilas fibertom 4100 Nd:YAG surgical laser generator. Six hundred joules of energy was applied at two power settings, 5 and 10 watts, using bare- and diffuser-tipped fibers, respectively. The extent of necrosis was assessed by histological techniques. A similar study with three experimental groups was treated with 300 J of applied energy. Extent of immediate tumor necrosis was compared to that seen 24 h after ILH treatment. The third group, which had been treated with intraperitoneal metronidazole prior to ILH, was also assessed for tumor necrosis after 24 h and results compared with both the previous groups.

RESULTS

ILH delivered using a cylindrical diffuser-tipped fiber resulted in a significantly larger diameter of tumor necrosis when compared to a bare-tipped fiber, for a given amount of applied energy. The differences were more significant at higher power settings. Six hundred joules of energy applied by ILH using a bare-tipped fiber at 5 and 10 watts produced 6.7 +/- 1.1 mm and 5.9 +/- 0.6 mm diameter of tumor necrosis, respectively. At equivalent settings, the diffuser-tipped fiber produced 7.7 +/- 1.0 mm and 8.1 +/- 0.6 mm diameter of tumor necrosis (p = 0.02 and p < 0.001). Using a diffuser-tipped fiber and an applied energy of 300 J delivered at 5 watts power, mean diameter of tumor necrosis immediately after treatment was 6.7 +/- 1.1 mm and after 24 h 7.9 +/- 1.3 mm (p = 0.006). Mean diameter of tumor necrosis 24 h after ILH in animals treated with metronidazole was 8.3 +/- 1.9 mm (p = 0.11).

CONCLUSION

Diffuser-tipped optical fiber appears to significantly increase the diameter of ILH-induced tumor necrosis compared to the bare fiber. In contrast to the bare fiber, it enables the application of laser energy using higher power settings without compromising the diameter of tumor necrosis achieved. In animals treated with metronidazole, a trend towards increased tumor destruction at the tumor-host interface was seen on histolopathology. In addition, a trend towards increased diameter of tumor necrosis was also seen; however, statistical significance was not achieved.

Effect of blood flow occlusion on laser hyperthermia for liver metastases

BACKGROUND

Interstitial laser hyperthermia (ILH) is an in situ ablative technique for the treatment of colorectal liver metastases. A significant factor limiting tumor destruction is hepatic blood flow. Modulation of hepatic blood flow may increase the size of tumor necrosis achieved. Our aim was to investigate the effect of blood flow occlusion on ILH-induced necrosis in both tumor and normal liver tissue.

MATERIALS AND METHODS

A model of colorectal liver metastases in male inbred CBA mice was used. ILH was applied to normal liver and tumor tissue using a bare optical quartz fiber from an SYL500 Nd:YAG surgical laser generator, with and without hepatic blood flow occlusion, and the extent of necrosis was studied. Tumor blood flow was assessed by laser Doppler flowmetry and scanning electron microscopy.

RESULTS

Hepatic blood flow occlusion resulted in a significant reduction in blood flow in normal liver tissue (37.9% +/- 5.8, P < 0.001) and in the periphery of the tumor (17.5% +/- 7.8, P < 0.001). It did not affect the blood flow in the center of the tumor (13.4% +/- 4.3, P = 0.07). ILH of normal liver tissue, at low power (2 W), with hepatic blood flow occlusion, resulted in a significant increase in the diameter of necrosis. This effect was not seen when higher power (5 W) was used in normal liver. No significant effect was noted within tumor tissue at either power setting.

CONCLUSION

The overall effect of hepatic blood flow occlusion in ILH-induced tissue necrosis appears to be negligible in tumor tissue. Its main applicability appears to be at the tumor-host interface, where a decrease in blood flow may lead to higher temperatures and therefore to a greater degree of tumor cell destruction.

Effect of interstitial laser hyperthermia in a murine model of colorectal liver metastases

Interstitial laser hyperthermia (ILH) is an in situ ablative technique used for the treatment of colorectal liver metastases. At present, few data exist concerning the optimum power settings required to maximize tissue necrosis. The aim of this study was to establish the dose-response relationship between the laser power setting and the extent of tissue necrosis produced in liver and tumor tissue, as well as the pattern of necrosis in a murine model of liver metastases. An intrasplenic induction model of liver metastases in 4- to 6-week-old male inbred CBA mice was used. Laser hyperthermia was applied to liver and tumor tissue using a bare optical quartz fiber from a Laserex SLY500 Nd:YAG surgical laser generator. Two-watt and 5-watt power settings were used at specific time intervals. The livers were then excised, fixed in formalin, and the extent and degree of necrosis were measured. Results were expressed as mean +/- standard deviation and were normally distributed. Analysis of variance was performed, and the least significant difference was used for post hoc tests. A P value of less than 0.05 was considered significant. Interstitial laser hyperthermia at 5 watts of power produced larger diameters of necrosis than did 2 watts for specific exposure times in normal liver tissue. However, when the total energy applied was compared, there was no significant difference in the diameters of tissue necrosis produced by the two power settings. The diameter of tissue necrosis in the normal liver increased from 2 mm at 10 joules to 8 mm at 600 joules of energy. Within tumor tissue, ILH at 2 and 5 watts produced similar diameters of necrosis for specific exposure times. When amounts of total energy applied were compared, ILH at the lower power setting (2 watts) produced a significantly larger diameter of necrosis than the higher power setting (5 watts). The diameter of necrosis achieved in tumor tissue was significantly larger than that in normal liver tissue at both power settings, for an equivalent amount of applied energy. The difference was more pronounced when ILH was performed at the lower power setting. The maximum diameter of necrosis achieved was 6.8 +/- 0.7 mm in normal liver tissue and 7.7 +/- 0.8 mm in tumor tissue. Charring of the fiber tip was delayed when the lower power setting was used, occurring after 20 seconds of exposure, compared to 5 seconds at the higher power setting. Similarly, cavitation occurred initially at 50 seconds at 5 watts of power and was delayed until 90 seconds of exposure at 2 watts of power. Histopathologic findings revealed an elliptical area of homogeneous necrosis, with a central acellular coagulum surrounded by intact but non-viable tissue. ILH is capable of producing highly reproducible, uniform, and complete tissue necrosis. The diameter of necrosis is related to the total energy applied. At low-power settings at any given amount of applied energy, a significantly larger diameter of tissue necrosis was achieved in tumor tissue compared to normal liver tissue.

Local resection of ampullary adenocarcinomas of the duodenum

BACKGROUND

Pancreaticoduodenectomy (PD) is considered to be the optimal treatment for ampullary adenocarcinomas. Local resection (LR) is a less invasive and potentially equally effective alternative for cancers with favourable prognostic features. Identification of these prognostic parameters may allow selection of patients suitable for LR.

METHODS

Twenty-five patients were treated for a primary Vater's ampulla adenocarcinoma at the Alfred Hospital, Melbourne, Australia, between January 1989 and January 2000. Risk factors for cancer recurrence were evaluated and the specific role of LR was defined.

RESULTS

Fourteen patients had PD, five had LR and six had bypass procedures (five biliary stents; one operative bypass). Presenting symptoms included jaundice (64%), abdominal pain (54%) and weight loss (32%). Adenocarcinomas that were resected had a median diameter of 2.5 cm, and were limited to the ampulla in 26% (T1), invaded the duodenal wall in 42% (T2) and infiltrated 2 cm or less into the pancreas in 32% (T1) of cases. Locally resected cancers were confined to the ampulla or invaded the duodenum and recurred in one patient following excision. Six recurrences occurred in total, influenced significantly by T staging (P = 0.009). Patient age, preoperative symptoms, laboratory tests, tumour size, differentiation, ulceration, lymphovascular spread and perineural invasion had no effect on recurrence. Patients undergoing LR had lower morbidity and mortality, reduced blood transfusion requirements and shorter hospital stay than those treated by PD.

CONCLUSIONS

T staging predicts the risk of tumour recurrence and can be determined using endoscopic ultrasound. Local resection is a suitable alternative to pancreaticoduodenal resection in patients with T1 and T2 adenocarcinomas with a maximum diameter of 3 cm or less.

Treatment of hepatocellular carcinoma by percutaneous laser hyperthermia

BACKGROUND AND AIM

The majority of patients with hepatocellular carcinoma (HCC) are unsuitable for partial liver resection or transplantation because of unfavorable tumor characteristics or underlying severe liver disease. Techniques of in situ tumor ablation may be an alternative to resection and have the advantage of reduced morbidity and mortality. Percutaneous laser-induced hyperthermia produces predictable areas of tumor necrosis with minimal complications. This study assesses the effectiveness of percutaneous interstitial laser hyperthermia in eight patients with hepatocellular carcinoma occurring on a background of chronic liver disease.

METHODS

Patients with confirmed HCC with less than five tumor nodules of less than 7 cm maximum diameter were selected for treatment. Tumor response was monitored by dynamic CT, alpha-fetoprotein levels and liver function tests. Patients were discharged within 24 h.

RESULTS

There were six males and two females, with liver disease of Child-Pugh grade C in five, and grade B in the others. Two patients had tumor recurrence following previous segmental resection. Four had solitary lesions, and individual lesion size ranged between 3 and 7 cm. Avascularity and significant necrosis of the tumor was achieved on all lesions less than 4 cm, but was unsuccessful in tumors greater than 5 cm despite repeated treatments. Survival of patients ranged from 3 to 18 months.

CONCLUSIONS

Percutaneous laser hyperthermia produces significant tumor necrosis and has the advantage of low morbidity, and cost effectiveness. Further refinement is needed to achieve elimination of viable tumor cells at the tumor host interface by further knowledge of appropriate dosimetry levels, manipulation of blood flow and synergistic effects with other therapeutic modalities.

Combretastatin A4 prodrug study of effect on the growth and the microvasculature of colorectal liver metastases in a murine model

Combretastatin A4P (CA4P) is a prodrug that, in active form, binds to tubulin microtubules of capillary endothelial cells. Studies to date indicate it has significant activity as a specific tumor vascular targeting agent. The goals were to assess the effects of CA4P on tumor growth and microvasculature of colorectal liver metastases in the mouse model, using stereological and histological methods to measure tumor growth, and vascular corrosion casting and laser doppler flowmetry to assess effect on the microvasculature. Continuous s.c. infusion of CA4P produced a major reduction in tumor growth. The percentage of the liver occupied by metastases decreased from 20.55 +/- 13.3% in controls to 7.46 +/- 5.99% in treated animals (P = 0.03). Ultrastructural study of tumor microvasculature after a single dose of CA4P revealed marked effects 1 h after treatment. There was loss of patent microvessels at the normal liver-tumor interface. Central microvascular density was reduced, with constriction and tapering of vessels. CA4P appeared to cause no damage to normal liver tissue or vasculature. Tumor blood flow decreased from 37.6 +/- 13.9% in controls to 24.4 +/- 6.1% in tumors >5 mm in diameter, 1 h after treatment with CA4P (P < 0.03). Quantitative histology of tissue at 6 and 24 h after CA4P treatment showed a significant increase in tumor necrosis (48.7 +/- 21% and 55.5 +/- 19% compared with controls, 20.6 +/- 8%; P = 0.01). Continuous infusion with CA4P causes marked reduction in tumor volume. A single dose of CA4P causes major changes of the tumor microvasculature, reduction of tumor blood flow, and increase in tumor necrosis. CA4P has a potential role in the management of patients with liver metastases.

Regulation of Puralpha gene transcription: evidence for autoregulation of Puralpha promoter

The single-stranded DNA and RNA binding protein, Puralpha, has recently received special attention as this protein, by associating with the specific nucleotide sequence (GGN repeats) and/or several important cellular and viral proteins regulates crucial biological events such as transcription, replication, and cell proliferation. In this study, we focused on the promoter activity of the Puralpha upstream DNA sequence and demonstrated that the sequence spanning 6,000 nucleotides upstream of the Puralpha transcription start site has promoter activity in various cell types. Results from promoter deletion studies revealed that this region encompasses various regulatory motifs which differentially participate in the promoter activity of Puralpha in various cells. The transcription start site of Puralpha is surrounded by the GA/GC-rich sequence which exhibits the ability to interact with Puralpha, suggesting a role for autoregulation of Puralpha transcription. Results from co-transfection studies revealed that ectopic expression of Puralpha reduced transcriptional activity of the Puralpha promoter and the region located between amino acid residues, 1-85 of Puralpha is important for the observed autoregulatory event. The regulatory protein of the human neurotropic virus, JCV, T-antigen, which interacts with Puralpha, decreased transcriptional activity of the Puralpha promoter. Co-expression of JCV T-antigen and Puralpha had no significant effect on the suppression of Puralpha gene transcription by either protein. The importance of this finding in light of earlier results showing down regulation of Puralpha during JCV infection of glial cells is discussed.

Interstitial laser thermotherapy in the treatment of colorectal liver metastases

Metastatic liver disease is the commonest cause of death in patients with colorectal cancer. A small proportion of these patients (10%) may be treated by surgical resection with five year survival approaching 35-40%. Alternative treatment modalities for localised hepatic disease include in situ ablative techniques that have the advantages of percutaneous application and minimal morbidity. These include Interstitial Laser Thermotherapy (ILT), Radio Frequency Ablation, Percutaneous Microwave therapy, and Focussed Ultrasound Therapy. This article focuses specifically on the development and utilisation of ILT in the treatment of colorectal liver metastases. It provides a review of the pathophysiological factors involved, present status of clinical studies, and future directions. ILT is a safe technique for the treatment of colorectal liver metastases. It may be delivered by minimally invasive techniques to lesions considered unresectable by present criteria. Limitations include the extent and completeness of tumour necrosis achieved as well as imaging techniques. Clinical problems include a lack of controlled studies. Assessment of long-term survival in prospective randomised trials is needed to assess the efficacy of this procedure.

Molecular characterization and chromosomal localization of mouse Puralpha gene

Puralpha is a 39-kDa sequence-specific single-stranded DNA/RNA binding protein with the ability to modulate transcription of several genes containing the Pur element in their promoter region. Human and mouse Puralpha exhibit an extraordinary degree of conservation with only two changes at amino acid residues 49 and 306. A 15-kb genomic clone encompassing the mouse Puralpha gene was isolated by screening the mouse genomic library, using a PCR-amplified fragment from human Puralpha cDNA. Results from sequencing analysis confirmed the isolated genomic clone to be Puralpha and not the other members of the Pur family, including Purbeta. Characterization of the mouse Puralpha gene by restriction analysis/Southern blotting and sequencing revealed that the Puralpha gene contains only one intron within the 5' UTR and the open reading frame was intact. Using chromosomal markers, the Puralpha gene was mapped to chromosome 18 in mouse and rat.

Evidence for inhibition of MyEF-2 binding to MBP promoter by MEF-1/Pur alpha

Myelin basic protein (MBP) is a major component of the myelin sheath whose production is developmentally controlled during myelinogenesis. Earlier studies have indicated that programmed expression of the MBP gene is regulated at the level of transcription. Evidently, the MB1 regulatory motif located between nucleotides -14 to -50 plays an important role in transcription of the MBP promoter in both in vivo systems. The MB1 element contains binding sites for the activator protein MEF-1/Pur alpha and the repressor protein MyEF-2. In this study we use bandshift assays with purified MEF-1/Pur alpha and MyEF-2 and demonstrate that binding of MyEF-2 to its target sequence is inhibited by MEF-1/Pur alpha. Under similar conditions, MyEF-2 enhances the association of MEF-1/Pur alpha with MB1 DNA. MEF-1/Pur alpha binds to MB1 in mono- and dimeric forms. Inclusion of MyEF-2 in the binding reaction increases the dimeric association of MEF-1/Pur alpha with the MB1 sequence. The use of MEF-1/Pur alpha variants in the bandshift assay suggests that two distinct regions of this protein may be involved in its binding to the MB1 sequences, and its ability to block MyEF-2 interaction with the MB1 sequence. Based on previous studies on the programmed expression of MEF-1/Pur alpha and MyEF-2 during myelination and the current findings on their interplay for binding to the MB1 motif, a model is proposed for their involvement in transcriptional regulation of the MBP gene during the course of brain development.