Diagnosis of periprosthetic loosening of total hip and knee arthroplasty using 68Gallium-Zoledronate PET/CT.

PURPOSE: Periprosthetic loosening is a major complication after total hip and knee arthroplasty. Early and accurate diagnosis is essential to choose the right therapeutic path and to avoid further complications. The aim of the study was to evaluate the diagnostic performance of 68Gallium-Zoledronate ([68Ga]Ga-DOTAZol) PET/CT in detecting periprosthetic loosening in total hip (THA) and total knee arthroplasty (TKA). METHODS: This retrospective study included 26 patients with painful prosthesis (THA n = 17; TKA n = 16) and clinical suspicion of periprosthetic loosening, but without a confirmed diagnosis. Patients underwent [68Ga]Ga-DOTAZol PET/CT at least one year post-implantation. Diagnosis was confirmed through revision surgery or long-term clinical follow-up, with an observation period of at least 6 months. The analysis included both an assessment of the prosthesis as a unit and a separate evaluation of the individual components. Statistical analysis involved calculating sensitivity, specificity and accuracy using SPSS. RESULTS: Overall, a sensitivity of 77.8%, a specificity of 95.8% and an accuracy of 90.9% were found for detecting periprosthetic loosening, when considering the prosthesis as a unit. Individual component analyses showed a sensitivity of 71.4% and specificity of 96.2%. CONCLUSION: The use of [68Ga]Ga-DOTAZol PET/CT in periprosthetic loosening is a remarkable diagnostic tool and a promising approach. In comparison to established radionuclide tracers, 68Gallium-Zoledronate offers notable advantages due to its availability via 68Ge/68Ga-generators, improving its potential for clinical application.

DEPROMP Trial: the additive value of PSMA-PET/CT-guided biopsy for prostate cancer management in biopsy naïve men-study protocol for a randomized trial.

BACKGROUND: The primary objective is to determine the proportion of men with suspected prostate cancer (PCA) in whom the management plans are changed by additive gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA-PET/CT) guided prostate biopsy (PET-TB) in combination with standard of care (SOC) using systematic (SB) and multiparametric magnetic resonance imaging-guided biopsy (MR-TB) compared with SOC alone. The major secondary objectives are to determine the additive value of the combined approach of SB + MR-TB + PET-TB (PET/MR-TB) for detecting clinically significant PCA (csPCA) compared to SOC; to determine sensitivity, specificity, positive and negative predictive value and diagnostic accuracy of imaging techniques, respective imaging classification systems, and each biopsy method; and to compare preoperatively defined tumor burden and biomarker expression and pathological tumor extent in prostate specimens. METHODS: The DEPROMP study is a prospective, open-label, interventional investigator-initiated trial. Risk stratification and management plans after PET/MR-TB are conducted randomized and blinded by different evaluation teams of experienced urologists based on histopathological analysis and imaging information: one including all results of the PET/MR-TB and one excluding the additional information gained by PSMA-PET/CT guided biopsy. The power calculation was centered on pilot data, and we will recruit up to 230 biopsy-naïve men who will undergo PET/MR-TB for suspected PCA. Conduct and reporting of MRI and PSMA-PET/CT will be performed in a blinded fashion. DISCUSSION: The DEPROMP Trial will be the first to evaluate the clinically relevant effects of the use of PSMA-PET/CT in patients with suspected PCA compared to current SOC. The study will provide prospective data to determine the diagnostic yields of additional PET-TB in men with suspected PCA and the impact on treatment plans in terms of intra- and intermodal changes. The results will allow a comparative analysis of risk stratification by each biopsy method, including a performance analysis of the corresponding rating systems. This will reveal potential intermethod and pre- and postoperative discordances of tumor stage and grading, providing the opportunity to critically assess the need for multiple biopsies. TRIAL REGISTRATION: German Clinical Study Register DRKS 00024134. Registered on 26 January 2021.

Antihormone treatment differentially regulates PSA secretion, PSMA expression and 68Ga-PSMA uptake in LNCaP cells.

BACKGROUND: In recent years, a variety of innovative therapeutics for castration-resistant prostate cancer have been developed, including novel anti-androgenic drugs, such as abiraterone or VPC-13566. Therapeutic monitoring of these pharmaceuticals is performed either by measuring PSA levels in serum or by imaging. PET using PSMA ligands labeled with Fluor-18 or Gallium-68 is the most sensitive and specific imaging modality for detection of metastases in advanced prostate cancer. To date, it remains unclear how PSMA expression is modulated by anti-hormonal treatment and how it correlates with PSA secretion. METHODS: We analyzed modulation of PSMA-mRNA and protein expression, 68Ga-PSMA uptake and regulation of PSA secretion by abiraterone or VPC-13566 in LNCaP cells in vitro. RESULTS: We found that abiraterone and VPC-13566 upregulate PSMA protein and mRNA expression but block PSA secretion in LNCaP cells. Both anti-androgens also enhanced 68Ga-PSMA uptake normalized by the number of cells, whereas abiraterone and VPC-13566 reduced 68Ga-PSMA uptake in total LNCaP monolayers treated due to cell death. CONCLUSION: Our data indicate that PSA secretion and PSMA expression are differentially regulated upon anti-androgen treatment. This finding might be important for the interpretation of 68Ga-PSMA PET images in monitoring therapies with abiraterone and VPC-13566 in prostate cancer patients, but needs to be validated in vivo.

Clinical evaluation of [68Ga]Ga-DATA-TOC in comparison to [68Ga]Ga-DOTA-TOC in patients with neuroendocrine tumours.

INTRODUCTION: [68Ga]Ga-DATA-TOC is a new radiolabelled somatostatin-analogue for positron emission tomography (PET) imaging of neuroendocrine tumours. Its advantage over DOTA-conjugated compounds is the possibility for high-efficiency labelling with gallium-68 quickly at room temperature with high reliability and without the need for product purification, which enables the development of an instant kit-type labelling method. We evaluated its imaging characteristics in patients with neuroendocrine tumours in comparison to [68Ga]Ga-DOTA-TOC. METHODS: 19 patients imaged with [68Ga]Ga-DATA-TOC were retrospectively analysed and uptake in normal tissues was compared with a group of 19 patients imaged with [68Ga]Ga-DOTA-TOC. 10 patients imaged with [68Ga]Ga-DATA-TOC had a history of [68Ga]Ga-DOTA-TOC imaging before and were additionally analysed to obtain biodistribution data of both tracers in the same patients. In 5 patients showing stable disease between both examinations, tumour uptake, lesion detectability and lesion conspicuity of both tracers were evaluated. RESULTS: Uptake of [68Ga]Ga-DATA-TOC in normal organs with expression of the somatostatin receptor was 25-47% lower compared to [68Ga]Ga-DOTA-TOC. Background of [68Ga]Ga-DATA-TOC was 40-41% lower in the liver. A higher retention of [68Ga]Ga-DATA-TOC was observed in the blood (up to 67%) and in the lungs (up to 44%). Tumour uptake (SUV) was 22-31% lower for [68Ga]Ga-DATA-TOC. However, no significant differences were observed for tumour-to-background ratios and lesion detectability. Regarding liver metastases, [68Ga]Ga-DATA-TOC uptake (SUV) reached 69-73% of [68Ga]Ga-DOTA-TOC uptake, but tumour-to-background ratios of [68Ga]Ga-DATA-TOC were 105-110% of [68Ga]Ga-DOTA-TOC ratios. CONCLUSIONS, ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: We demonstrated the feasibility of the new PET tracer [68Ga]Ga-DATA-TOC for imaging of patients with neuroendocrine tumours, showing a comparable performance to [68Ga]Ga-DOTA-TOC. [68Ga]Ga-DATA-TOC has the potential for development of an instant kit-type labelling method at room temperature similar to 99mTc-labelled radiopharmaceuticals, which might help to increase the availability of 68Ga-labelled somatostatin analogues for clinical routine use.

[Lutetium-177-PSMA radioligand therapy : Consensus within the framework of GKV-funded care between the university hospitals in Aachen, Bonn, Düsseldorf, Essen, and Cologne and the MDK Nordrhein]. / Lutetium-177-PSMA-Radioligandentherapie : Konsensus im Rahmen der GKV-finanzierten Versorgung zwischen den Hochschulkliniken in Aachen, Bonn, Düsseldorf, Essen und Köln und dem MDK Nordrhein.

In the last 3 years, Lutetium-177 prostate-specific membrane antigen radioligand therapy (Lu-177-PSMA-RLT) has received increasing attention in nuclear medicine as a new form of treatment for castration-resistant metastatic prostate cancer. This therapy combines the radionuclide Lutetium-177, which has been therapeutically used in nuclear medicine for many years, with a molecular target of the transmembrane prostate-specific membrane antigen expressed by prostate cancer cells. Since there are no prospective randomized studies on Lu-177-PSMA-RLT and the question of reimbursement has repeatedly been the subject of review by the MDK Nordrhein (Medischenische Dienst der Krankenversicherung), there was a desire because of the increasing number of patients being treated to clarify under which circumstances Lu-177-PSMA-RLT can be reimbursed by German statutory health insurance. The goals of this article are to help treating physicians understand how this new therapy option works, to integrate it in the overall therapy concept for castration-resistant metastatic prostate cancer, and, above all, to use Lu-177-PSMA-RLT-based on the current data-at the right place in the therapy sequence of castration-resistant metastatic prostate cancer.

PSMA targeted radioligandtherapy in metastatic castration resistant prostate cancer after chemotherapy, abiraterone and/or enzalutamide. A retrospective analysis of overall survival.

AIM: Our aim was to evaluate overall survival and parameters prognosticating longer survival in a large and homogeneous group of patients treated with 177Lu-PSMA-617 radioligand therapy with heavily pretreated advanced metastatic castration resistant prostate cancer. METHODS: A total of 104 patients were treated with 351 cycles of 177Lu-PSMA-617. Prostate specific antigen (PSA) changes after the first cycle of therapy were documented prior to a second cycle. Patients were followed-up for overall survival (OS). Any PSA decline, PSA decline ≥50%, initial PSA, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), visceral metastases and cumulative injected activity were analyzed and evaluated according to OS. Multivariable analysis with parameters with a p-value ≤0.05 in univariate analysis was performed, additionally adjusting for age and presence of visceral metastases. RESULTS: A total of 51 patients (49%) died during the observation period. The majority of patients (97%) presented with bone metastases, 77% with lymph node metastases and 32% with visceral metastases. All patients were treated with at least one line of chemotherapy. Either abiraterone or enzalutamide had been given in 100% of the patients. Any PSA decline occurred in 70 (67%) and a PSA decline ≥50% in 34 (33%) of patients after the first cycle. The median OS was 56.0 weeks (95%CI: 50.5-61.5). Initial PSA decline ≥50%, initial LDH, visceral metastases, second line chemotherapy or prior radium-223 did not have an effect on survival, whereas any initial PSA decline, initial ALP <220 U/L and cumulative injected activity ≥18.8 GBq were associated with a longer survival. A step-by-step analysis revealed a PSA decline ≥20.87% as the most noticeable cut-off prognosticating longer survival, which remained an independent prognosticator of improved OS in the multivariate analysis. CONCLUSION: 177Lu-PSMA-617 RLT is a new effective therapeutic and seems to prolong survival in patients with advanced mCRPC pretreated with chemotherapy, abiraterone and/or enzalutamide.

[PET-CT in head and neck cancer]. / PET-CT bei Karzinomen im Kopf­Hals­Bereich.

The importance of 18F-fluorodesoxyglucose positron-emission tomography (FDG-PET) for the diagnosis of malignant disease is increasing. On one hand, this is due to the high sensitivity of this method, on the other, because the entire body can be examined. FDG-PET can be particularly advantageous for the diagnosis of head and neck tumors, where tumor staging is an important prognostic parameter and essentially determines the therapeutic regimen. This article presents the different possibilities for combined evaluation with PET and computed tomography (CT) for the diagnosis of patients with head and neck cancer. Special focus is placed on primary staging and tumor follow-up, as well as on the role of PET-CT in the diagnosis of patients with cancer of unknown primary origin (CUP). The use of PET-CT for radiotherapy planning and new aspects of PET technology are also discussed.

A Step-by-Step Clinical Approach for the Management of Neuroendocrine Tumours.

Neuroendocrine tumours (NET) are rare neoplasms, but the incidence is permanently increasing. Most of the NETs are slow proliferating and clinically silent, and for that reason, they are often diagnosed at a stage with advanced disease. The complexity and diversity of the NET-biology require the treatment of patients in specialised centres to guarantee a qualified, multidisciplinary treatment planning. At our institution, we developed an interdisciplinary model for the assessment and treatment of NET. The aim was to adapt the guidelines to the clinical practice, exchange of current knowledge, and a tailored approach to the individual patient. In our team are included medical professionals from pathology, radiology, oncology, gastroenterology, oncological surgery, and nuclear medicine. In this paper, we describe step-by-step a procedural algorithm for the management of patients with neuroendocrine tumours, focusing on midgut-NETs in terms of therapy.

Positron-emission tomography CT to identify local recurrence in stage I lung cancer patients 1 year after stereotactic body radiation therapy.

PURPOSE: To evaluate the diagnostic value of positron-emission tomography/computed tomography (PET/CT) in stage I lung cancer patients treated with stereotactic body radiation therapy (SBRT), who have suspicious or unclear local recurrence findings in CT 1 year after treatment. PATIENTS AND METHODS: A group of 29 patients with unclear or suspicious CT findings 1 year after SBRT were examined with PET/CT. The ability of standard uptake values (SUVmax, SUVmean and posttherapeutic reduction in SUV) to detect local failure and identify patients at a high risk of disease-specific death was evaluated using logrank statistics. Histology and clinical follow-up were the gold standards for local recurrence. RESULTS: SUVmean greater than 3.44 (p = 0.001); SUVmax greater than 5.48 (p = 0.009) or a relative reduction in SUVmean or SUVmax of less than 43 (p = 0.030) or 52 % (p = 0.025), respectively, was indicative of local recurrence. These parameters also correlated with an increased risk of disease-specific death: SUVmean greater than 2.81 (p = 0.023); SUVmax greater than 3.45 (p = 0.007) or a relative reduction in SUVmean or SUVmax of less than 32 (p = 0.015) or 52 % (p = 0.013), respectively, was indicative of an increased risk of disease-specific death. CONCLUSION: PET/CT performed 1 year after SBRT can reliably identify local recurrence and therefore help to clarify unclear CT findings. As posttherapeutic glucose metabolism also correlates with disease-specific survival, PET/CT may help to stratify lung cancer patients for additional treatment 1 year after SBRT.

Measuring and modeling patient-specific distributions of material properties in abdominal aortic aneurysm wall.

Both the clinically established diameter criterion and novel approaches of computational finite element (FE) analyses for rupture risk stratification of abdominal aortic aneurysms (AAA) are based on assumptions of population-averaged, uniform material properties for the AAA wall. The presence of inter-patient and intra-patient variations in material properties is known, but has so far not been addressed sufficiently. In order to enable the preoperative estimation of patient-specific AAA wall properties in the future, we investigated the relationship between non-invasively assessable clinical parameters and experimentally measured AAA wall properties. We harvested n = 163 AAA wall specimens (n = 50 patients) during open surgery and recorded the exact excision sites. Specimens were tested for their thickness, elastic properties, and failure loads using uniaxial tensile tests. In addition, 43 non-invasively assessable patient-specific or specimen-specific parameters were obtained from recordings made during surgery and patient charts. Experimental results were correlated with the non-invasively assessable parameters and simple regression models were created to mathematically describe the relationships. Wall thickness was most significantly correlated with the metabolic activity at the excision site assessed by PET/CT (ρ = 0.499, P = 4 × 10(-7)) and to thrombocyte counts from laboratory blood analyses (ρ = 0.445, P = 3 × 10(-9)). Wall thickness was increased in patients suffering from diabetes mellitus, while it was significantly thinner in patients suffering from chronic kidney disease (CKD). Elastic AAA wall properties had significant correlations with the metabolic activity at the excision site (PET/CT), with existent calcifications, and with the diameter of the non-dilated aorta proximal to the AAA. Failure properties (wall strength and failure tension) had correlations with the patient's medical history and with results from laboratory blood analyses. Interestingly, AAA wall failure tension was significantly reduced for patients with CKD and elevated blood levels of potassium and urea, respectively, both of which are associated with kidney disease. This study is a first step to a future preoperative estimation of AAA wall properties. Results can be conveyed to both the diameter criterion and FE analyses to refine rupture risk prediction. The fact that AAA wall from patients suffering from CKD featured reduced failure tension implies an increased AAA rupture risk for this patient group at comparably smaller AAA diameters.

Respiratory gated [18F]FDG PET/CT for target volume delineation in stereotactic radiation treatment of liver metastases.

PURPOSE: The use of 4D-[(18)F]fluorodeoxyglucose (FDG) PET/CT in combination with respiratory gated magnet resonance imaging (MRI) in target volume definition for stereotactic radiation of liver metastases was investigated. METHODS AND MATERIALS: A total of 18 patients received respiration gated FDG-PET/CT and MRI. Data were fused using a rigid co-registration algorithm. The quality of the co-registration was rated on a scale from 1 (excellent) to 5 (poor) for co-registration of MRI with gated PET and ungated PET. Gross tumor volume (GTV) was delineated in CT (GTV (CT)), MRI (GTV(MRI)), and PET (GTV(PET)). MRI- and PET-based GTVs were defined by three observers each. Interobserver variability was calculated for all patients as well as for subgroups with and without previous treatment of liver metastases. All GTVs were compared for all patients and separately for patients with previous local therapy. In addition, a semiautomatic segmentation algorithm was applied on the PET images. RESULTS: Co-registration between MR and PET images was rated with 3.3 in average when non-gated PET was used and improved significantly (p < 0.01) to 2.1 using gated PET. The average GTV(CT) was 51.5 ml, GTV(MRI) 51.8 ml, and the average GTV(PET) 48.1 ml. Volumes delineated in MRI were 9.9% larger compared to those delineated in CT. Volumes delineated in PET were 13.8% larger than in MRI. The differences between the GTVs were more pronounced in patients with previous treatment. The GTVs defined in MRI showed an interobserver variability of 47.9% (84.1% with previous treatment and 26.2% without previous treatment). The PET-defined GTVs showed an interobserver variability of 21% regardless of previous treatment. Semiautomatic segmentation did not provide satisfying results. CONCLUSION: FDG-PET can distinguish vital tumor tissue and scar tissue, and therefore alters the GTV especially in patients with previous local treatment. In addition, it reduces the interobserver variability significantly compared to MRI. However, respiratory gated PET is necessary for good co-registration of PET and MRI.

Renal accumulation of [111In]DOTATOC in rats: influence of inhibitors of the organic ion transport and diuretics.

AIM: Radiation exposure to the kidney limits therapy with radiometal labelled DOTATOC. This study evaluates the organic anion and cation transport (inhibitors: probenecid and cimetidine/dexamethasone) as well as diuresis (furosemide and mannitol) regarding renal uptake of [(111)In]DOTATOC. METHODS: One hundred eight male Fisher rats were injected with [(111)In]DOTATOC via the tail vein. Prior to activity injection a total of 84 rats underwent injection with probenecid vs. sodium chloride 0.9% (48 rats), cimetidine vs. dexamethasone vs. sodium chloride 0.9% (18 rats), and furosemide vs. mannitol vs. sodium chloride 0.9% (18 rats). Rats were sacrificed at predetermined time points up to 48 h after activity injection. Kidneys, adrenal glands, pancreas, spleen, blood, liver, and muscle were harvested and injected activity per gram tissue was determined. Autoradiographic images of the kidneys were acquired in a total of 24 rats. RESULTS: Probenecid led to a reduction in renal uptake by up to 30% while not significantly changing the activity accumulation in the other organs investigated. This reduction was attributable to the renal cortex (ratio cortex/medulla 1.72 vs. 1.99; p = 0.006). Cimetidine and dexamethasone had no effect in any of the organs. Furosemide led to a 44% increase in renal activity accumulation attributable to enhanced renal medullary uptake (ratio cortex/medulla 1.44 versus 1.69; p = 0.006). Mannitol had no effect on renal activity uptake. CONCLUSION: Inhibition of the organic anion transport by probenecid may help reduce renal uptake regarding therapy with radiometal labelled DOTATOC. The enhancing effect of furosemide may be unfavourable for therapy. The results must be confirmed by human studies.

Cyclic AMP blocks bacterial lipopolysaccharide-induced myosin light chain phosphorylation in endothelial cells through inhibition of Rho/Rho kinase signaling.

During Gram-negative sepsis bacterial LPS induces endothelial cell contraction, actin reorganization, and loss of endothelial integrity by an unknown signal mechanism. In this study, we provide evidence that LPS-stimulation of endothelial cells (HUVEC) decreases myosin light chain (MLC) phosphatase, resulting in an increase in MLC phosphorylation followed by cell contraction. All of these LPS effects could be blocked by the Rho-GTPase inhibitor C3 transferase from Clostridium botulinum or the Rho kinase inhibitor Y-27632. These data suggest that LPS induces MLC phosphorylation via Rho/Rho kinase-mediated inhibition of MLC phosphatase in HUVEC. Furthermore, we observed that cAMP-elevating drugs, known to exert a vasoprotective function, mimicked the effects of C3 transferase and Y-27632, i.e., inhibited LPS-induced MLC phosphatase inactivation and MLC phosphorylation. cAMP elevation did not inhibit myosin phosphorylation induced by constitutively active V14Rho or the MLC phosphatase inhibitor calyculin and did not induce phosphorylation of RhoA in HUVEC, indicating inhibition of an upstream regulator of Rho/Rho kinase. Taken together, Rho/Rho kinase appears to be a central target for inflammatory mediators causing endothelial cell contraction such as bacterial toxins, but also for vasoprotective molecules elevating intracellular cAMP.

Dichotomous regulation of myosin phosphorylation and shape change by Rho-kinase and calcium in intact human platelets.

Both Rho-kinase and the Ca(2+)/calmodulin-dependent myosin light chain (MLC) kinase increase the phosphorylation of MLC. We show that upon thrombin receptor stimulation by low-dose thrombin or the peptide ligand YFLLRNP, or upon thromboxane receptor activation by U46619, shape change and MLC phosphorylation in human platelets proceed through a pathway that does not involve an increase in cytosolic Ca(2+). Under these conditions, Y-27632, a specific Rho-kinase inhibitor, prevented shape change and reduced the stimulation of MLC-phosphorylation. In contrast, Y-27632 barely affected shape change and MLC-phosphorylation by adenosine diphosphate (ADP), collagen-related peptide, and ionomycin that were associated with an increase in cytosolic Ca(2+) and inhibited by BAPTA-AM/EGTA treatment. Furthermore, C3 exoenzyme, which inactivates Rho, inhibited preferentially the shape change induced by YFLLRNP compared with ADP and ionomycin. The results indicate that the Rho/Rho-kinase pathway is pivotal in mediating the MLC phosphorylation and platelet shape change by low concentrations of certain G protein-coupled platelet receptors, independent of an increase in cytosolic Ca(2+). Our study defines 2 alternate pathways, Rho/Rho-kinase and Ca(2+)/calmodulin-regulated MLC-kinase, that lead independently of each other through stimulation of MLC-phosphorylation to the same physiological response in human platelets (ie, shape change).

Bacterial toxins block endothelial wound repair. Evidence that Rho GTPases control cytoskeletal rearrangements in migrating endothelial cells.

We investigated the effect of bacterial toxins that modify and inactivate Rho GTP-binding proteins on the migratory response of endothelial cells to wounding. C3-transferase from Clostridium botulinum, EDIN from Staphylococcus aureus, and toxin A from Clostridium difficile blocked migration of human umbilical vein endothelial cells (HUVECs) in an in vitro wound repair assay. Migrating HUVECs expressed actin microspikes (maximum at 10 minutes after wounding), ruffles (maximum at 12 hours), and fibers (maximum at 24 hours), and within these actin structures, vinculin-containing focal complexes/adhesions were formed. C3-Transferase ADP ribosylated RhoA, RhoB, and RhoC in HUVECs and abolished the formation of actin stress fibers/focal adhesions but had no effect on expression of microspikes, ruffles, or the associated vinculin-containing focal complexes. Similar results were obtained with EDIN and toxin A. These results indicate that endothelial cells migrating into a wounded area express distinct combinations of actin/vinculin structures in a spatially and temporally coordinated manner. The GTPase Rho selectively controls the formation of actin fibers/focal adhesions that occurs 2 to 24 hours after wounding. A mechanism is proposed by which Rho-specific bacterial toxins could influence vascular repair, angiogenesis, or atherosclerosis.

ADP-ribosylation of the GTP-binding protein RhoA blocks cytoplasmic division in human myelomonocytic cells.

To test the role of Rho GTP-binding proteins in growth regulation of human myelomonocytic tumour cells we used recombinant C3 exoenzyme of Clostridium botulinum to specifically ADP-ribosylate and inactivate Rho proteins in situ. In homogenates of HL60 cells, the C3 exoenzyme [32P]ADP-ribosylated one protein that was identified as RhoA by immunoblot and two-dimensional gel electrophoresis. [32P]ADP ribosylation of RhoA in HL60 homogenates in vitro was reduced to 10-20% when cells in culture were pretreated with C3 exoenzyme (10 micrograms, 24 h), indicating that 80-90% of RhoA could be ADP-ribosylated in situ. The C3 exoenzyme inhibited HL60 cell proliferation by up to 80% and the degree of growth inhibition correlated with the amount of in situ ADP-ribosylated RhoA in a time- and dose-dependent manner. Cell cycle analysis demonstrated that the C3 exoenzyme-treated HL60 cells accumulated in mitosis, and nuclear staining revealed binucleated cells. These findings suggest that RhoA has a key role in human myelomonocytic tumour cell growth by regulating cytoplasmic division.