Initial surveillance in men with marker negative clinical stage IIA non-seminomatous germ cell tumours

OBJECTIVES

To assess whether extended surveillance with repeated computed tomography (CT) scans for patients with clinical stage IIA (CS IIA; <2 cm abdominal node involvement) and negative markers (Mk-) non-seminomatous germ cell tumours (NSGCTs) can identify those with true CS I. To assess the rate of benign lymph nodes, teratoma, and viable cancer in retroperitoneal lymph node dissection (RPLND) histopathology for patients with CS IIA Mk- NSGCT.

PATIENTS AND METHODS

Observational prospective population-based study of patients diagnosed 2008-2019 with CS IIA Mk- NSGCT in the Swedish and Norwegian Testicular Cancer Group (SWENOTECA) registry. Patients were managed with surveillance, with CT scans, and tumour markers every sixth week for a maximum of 18 weeks. Patients with radiological regression were treated as CS I, if progression with chemotherapy, and remaining CS IIA Mk- disease with RPLND. The end-point was the number and percentage of patients down-staged to CS I on surveillance and rate of RPLND histopathology presented as benign, teratoma, or viable cancer.

RESULTS

Overall, 126 patients with CS IIA Mk- NSGCT were included but 41 received therapy upfront. After surveillance for a median (range) of 6 (6-18) weeks, 23/85 (27%) patients were in true CS I and four (5%) progressed. Of the remaining 58 patients with lasting CS IIA Mk- NSGCT, 16 received chemotherapy and 42 underwent RPLND. The RPLND histopathology revealed benign lymph nodes in 11 (26%), teratoma in two (6%), and viable cancer in 29 (70%) patients.

CONCLUSIONS

Surveillance with repeated CT scans can identify patients in true CS I, thus avoiding overtreatment. The RPLND histopathology in patients with CS IIA Mk- NSGCT had a high rate of cancer and a low rate of teratoma.

Validation of a prediction model for post-chemotherapy fibrosis in nonseminoma patients

OBJECTIVE

To validate Vergouwe's prediction model using the Swedish and Norwegian Testicular Cancer Group (SWENOTECA) RETROP database and to define its clinical utility.

MATERIALS AND METHODS

Vergouwe's prediction model for benign histopathology in post-chemotherapy retroperitoneal lymph node dissection (PC-RPLND) uses the following variables: presence of teratoma in orchiectomy specimen; pre-chemotherapy level of alpha-fetoprotein; β-Human chorionic gonadotropin and lactate dehydrogenase; and lymph node size pre- and post-chemotherapy. Our validation cohort consisted of patients included in RETROP, a prospective population-based database of patients in Sweden and Norway with metastatic nonseminoma, who underwent PC-RPLND in the period 2007-2014. Discrimination and calibration analyses were used to validate Vergouwe's prediction model results. Calibration plots were created and a Hosmer-Lemeshow test was calculated. Clinical utility, expressed as opt-out net benefit (NBopt-out ), was analysed using decision curve analysis.

RESULTS

Overall, 284 patients were included in the analysis, of whom 130 (46%) had benign histology after PC-RPLND. Discrimination analysis showed good reproducibility, with an area under the receiver-operating characteristic curve (AUC) of 0.82 (95% confidence interval 0.77-0.87) compared to Vergouwe's prediction model (AUC between 0.77 and 0.84). Calibration was acceptable with no recalibration. Using a prediction threshold of 70% for benign histopathology, NBopt-out was 0.098. Using the model and this threshold, 61 patients would have been spared surgery. However, only 51 of 61 were correctly classified as benign.

CONCLUSIONS

The model was externally validated with good reproducibility. In a clinical setting, the model may identify patients with a high chance of benign histopathology, thereby sparing patients of surgery. However, meticulous follow-up is required.

A phase I prospective, non-randomized trial of autologous dendritic cell-based cryoimmunotherapy in patients with metastatic castration-resistant prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) is an immunologically cold disease with dismal outcomes. Cryoablation destroys cancer tissue, releases tumor-associated antigens and creates a pro-inflammatory microenvironment, while dendritic cells (DCs) activate immune responses through processing of antigens. Immunotherapy combinations could enhance the anti-tumor efficacy. This open-label, single-arm, single-center phase I trial determined the safety and tolerability of combining cryoablation and autologous immature DC, without and with checkpoint inhibitors. Immune responses and clinical outcomes were evaluated. Patients with mCRPC, confirmed metastases and intact prostate gland were included. The first participants underwent prostate cryoablation with intratumoral injection of autologous DCs in a 3 + 3 design. In the second part, patients received cryoablation, the highest acceptable DC dose, and checkpoint inhibition with either ipilimumab or pembrolizumab. Sequentially collected information on adverse events, quality of life, blood values and images were analyzed by standard descriptive statistics. Neither dose-limiting toxicities nor adverse events > grade 3 were observed in the 18 participants. Results indicate antitumor activity through altered T cell receptor repertoires, and 33% durable (> 46 weeks) clinical benefit with median 40.7 months overall survival. Post-treatment pain and fatigue were associated with circulating tumor cell (CTC) presence at inclusion, while CTC responses correlated with clinical outcomes. This trial demonstrates that cryoimmunotherapy in mCRPC is safe and well tolerated, also for the highest DC dose (2.0 × 10⁸) combined with checkpoint inhibitors. Further studies focusing on the biologic indications of antitumor activity and immune system activation could be considered through a phase II trial focusing on treatment responses and immunologic biomarkers.

Unilateral or Bilateral Retroperitoneal Lymph Node Dissection in Nonseminoma Patients with Postchemotherapy Residual Tumour? Results from RETROP, a Population-based Mapping Study by the Swedish Norwegian Testicular Cancer Group

BACKGROUND

The distribution of retroperitoneal lymph node metastases for patients with nonseminoma and a residual tumour of 10-49 mm in a population-based setting is unknown. This information is needed to justify selection of patients for a unilateral template resection.

OBJECTIVE

To describe the location of retroperitoneal metastases and recurrences in patients with nonseminoma germ cell tumour (NSGCT) with a residual tumour of 10-49 mm.

DESIGN, SETTING, AND PARTICIPANTS

RETROP is a population-based prospective observational mapping study of 213 patients in Sweden and Norway with a retroperitoneal residual tumour of 10-49 mm who underwent postchemotherapy retroperitoneal lymph node dissection for metastatic NSGCT during 2007-2014 with median follow-up of 100 mo. Patients were classified according to the testis primary tumour and the distribution of unilateral or bilateral lymph node metastases (with reference to the aorta) present on pre- and/or postchemotherapy computed tomography (CT) scans.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The distribution and rate of teratoma or cancer in unilateral or bilateral retroperitoneal fields and the location and rate of retroperitoneal recurrence were measured.

RESULTS AND LIMITATIONS

In total, 65% of the patients had unilateral retroperitoneal lymph node metastases (RLNMs) on CT scans. Patients with unilateral RLNMs had a low risk of contralateral teratoma or cancer (1.6% for right- and 2.6% for left-sided NSGCT) or retroperitoneal recurrence (0% for right- and 4% for left-sided NSGCT). A weakness of the study is that the pathology specimen could not be fully designated to one specific area for some of the patients.

CONCLUSIONS

Men with postchemotherapy residual disease of 10-49 mm and unilateral metastases on pre- and postchemotherapy CT scans have a low risk of contralateral disease and should be considered for a unilateral template resection.

PATIENT SUMMARY

The surgeon can use computed tomography (CT) scans in deciding on the extent of lymph node dissection in patients with testicular cancer.

Preoperative predictors of pathological tumour stage and prognosis may be used when selecting candidates for intensified treatment in upper tract urothelial carcinoma

PURPOSE

Intensified treatment such as extended lymph node dissection (LND) and/or perioperative chemotherapy in addition to radical nephroureterectomy (RNU) has been suggested for high-risk cases of upper tract urothelial carcinoma (UTUC). We aimed to identify preoperative predictors of tumour stage and prognosis in the diagnostic work-up before RNU. Further to evaluate if our findings could be used in selecting patients for intensified treatment.

PATIENTS AND METHODS

A total of 179 patients treated with RNU for UTUC at Haukeland University Hospital (HUS) and Vestfold Hospital Trust (VHT) during 2005-2017 were included in this retrospective study. All relevant preoperative variables regarding the patient, the CT and the ureteroscopy (URS) were registered and analysed regarding their ability to predict non-organ confined disease (NOCD, pT3+ and/or N+) at final pathology after RNU. The prognosis was assessed calculating survival for the cohort and stratified by preoperative variables.

RESULTS

Local invasion and pathological lymph nodes at CT predicted NOCD in uni and multivariate regression analyses (OR 3.36, p=.004 and OR 6.21, p=.03, respectively). Reactive oedema surrounding the tumour (OR 2.55, p=.02), tumour size (4.8 vs. 3.9 cm, p=.006) and high-grade tumour at URS biopsy (OR 3.59, p=.04) predicted NOCD at univariate regression analyses. The 5-year CSS and OS for the entire cohort was 79% and 60%. ECOG, local invasion, pathological lymph nodes and reactive oedema surrounding the tumour at CT predicted CSS.

CONCLUSIONS

Several variables at the CT predicted both stage and survival. Local invasion at CT seems the most promising feature for selecting patients for intensified treatment.

A prospective phase I trial of dendritic cell-based cryoimmunotherapy in metastatic castration-resistant prostate cancer

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Background: Dendritic cell (DC)-based cryoimmunotherapy (CryoIT) was used to treat metastatic castration-resistant prostate cancer in a Phase I clinical trial. Primary objective was safety of treatment. Secondarily, clinical, radiological and immunological treatment responses were investigated. Methods: In 18 patients cryoablation by a freeze-thaw process under general anesthesia was performed, followed by intratumoral autologous immature DC injection. In the last 9 patients checkpoint inhibition of either CTLA-4 or PD-1 was added. Subjects had minimum 46 weeks follow-up. Adverse events (AEs) and blood analyses were registered at all visits. Disease progression was determined by three imaging modalities according to (i)RECISTv1.1 and progression-free survival (PFS) by Kaplan-Meier method. Circulating tumor cells (CTC/7.5 mL, CellSearch) and ultradeep T-cell receptor (TCR) b-chain sequences (TCRSafe) were enumerated. Patients were separated by CTC into none (n=10), 1-4 (n=4) and ≥ 5 (n=4). Health related quality of life (HRQoL) measured by EORTC-QLQ C30 questionnaire were answered at inclusion, and 10, 22 and 46 weeks post CryoIT. Scores were calculated according to the EORTC manual. Results: Subjects progressing within 22 weeks had higher PSA (p=0.03). AE profile of the total cohort (n=18) was comparable with interim reports (n=13); of 20 possible DC-related AEs one was severe (urinary retention) and 19 mild-to-moderate, and spread independent of treatment regime. Maximum tolerated dose of DC was not reached. By 46 weeks, imaging showed 6 patients partial response or stable disease. Median PFS was 150 days in total cohort. Pretreatment CTC counts ≥5 indicated higher progression rates and recurring CTC. Ultradeep TCR-sequencing showed more prevalent and higher expressed (>5-fold) new TCR clonotypes at 2-6 weeks in men without progression. Participants reported high and stable HRQoL scores throughout the study. However, presence of CTC was associated with worse HRQoL scores at week 10 (p=0.031) and 22 (p=0.005). Conclusions: DC treatment seems safe and well tolerated, also combined with checkpoint inhibitors. Effect is indicated in subjects with moderate pre-treatment PSA levels. Immune responses are suggested by higher number of novel TCR clonotypes in men with non-progressive disease. Clinical trial information: NCT02423928 .

Blood steroid levels predict survival in endometrial cancer and reflect tumor estrogen signaling

OBJECTIVE

Blood-based biomarkers are attractive due to ease of sampling and standardized measurement technology, reducing obstacles to clinical implementation. The objective of this study was to evaluate a clinically available method of steroid hormone measurement for its prognostic potential in endometrial cancer.

METHODS

We quantified seven steroid hormones by liquid chromatography-tandem mass spectrometry in 100 endometrial cancer patients from a prospective cohort. Abdominal fat distribution was assessed from abdominal computed tomography (CT) scans. Steroid hormone levels were compared to clinical characteristics, fat distribution and gene expression in primary tumor samples.

RESULTS

Low levels of 17OH-progesterone, 11-deoxycortisol and androstenedione were associated with aggressive tumor characteristics and poor disease specific survival (p = .003, p = .001 and p = .02 respectively). Adjusting for preoperative risk based on histological type and grade, low 17OH-progesterone and 11-deoxycortisol independently predicted poor outcome with hazard ratios of 2.69 (p = .033, 95%CI: 1.09-6.68) and 3.40 (p = .020, 1.21-9.51), respectively. Tumors from patients with low steroid level displayed increased expression of genes related to mitosis and cell cycle progression, whereas high steroid level was associated with upregulated estrogen signaling and genes associated with inflammation. Estrone and estradiol correlated to abdominal fat volume in all compartments (total, visceral, subcutaneous, p < .001 for all), but not to the visceral fat proportion. Patients with higher levels of circulating estrogens had increased expression of estrogen signaling related genes.

CONCLUSION

Low levels of certain endogenous steroids are associated with aggressive tumor traits and poor survival and may provide preoperative information independent of histological biomarkers already in use.

Tumour architecture, grade and location remain predictors of non-organ-confined upper tract urothelial carcinoma at time of radical nephroureterectomy: results from a multicenter Norwegian external validation study

PURPOSE

Selecting patients for intensified treatment for upper tract urothelial carcinoma can be challenging, partly due to the lack of accurate preoperative staging tools. Several preoperative staging models for upper tract urothelial carcinoma have been presented, but none have been externally validated. The aim of the current study was to perform an external validation of the Margulis nomogram for predicting non-organ-confined upper tract urothelial carcinoma at time of nephroureterectomy.

METHODS

209 patients from two high-volume centres in Norway were treated with radical nephroureterectomy during the period 2005-2017. 163 patients with complete data necessary for external validation of the Margulis nomogram were included in the study. All relevant covariates were analysed with uni- and multivariate regression analysis to assess their ability to predict non-organ-confined disease. The Margulis nomogram was applied on the present cohort to calculate predicted risk of non-organ-confined disease. This was compared to the observed risk to assess model calibration. The Margulis nomogram accuracy was measured as the area under the curve in a receiver operator characteristics curve to evaluate model discrimination.

RESULTS

Tumour grade (OR 28.1, p = 0.001) and architecture (OR 4.72, p < 0.001) were independent predictors of non-organ-confined disease. There was a high concordance between predicted and observed risk quantified with a Cronbach alpha of 0.96. The Margulis nomogram had an area under the curve of 0.83 in predicting non-organ-confined disease when applied on the current cohort.

CONCLUSIONS

We consider the Margulis nomogram validated for clinical use.

Abstract CT066: Dendritic cell based cryoimmunotherapy associates with clinical variables and changes in T-cell receptor expression in a prospective phase I trial of metastatic castration resistant prostate cancer

Interim analysis data are presented for 13 patients with metastatic castration resistant prostate cancer treated with dendritic cell based cryoimmunotherapy (CryoIT) and at least three months follow-up (FU). In CryoIT autologous immature dendritic cells (iDCs) mature in cryoablated tumor tissue and engulf tumor associated antigens and thereafter migrate to lymph nodes to instruct systemic immune attacks on heterogenous cancer cells.

Primary endpoint of the trial is to investigate safety of CryoIT while secondary aims include clinical, radiological and immunological responses to treatment.

Adverse events (AEs) and blood analyses were registered at all visits and imaging performed before and three months post-treatment. Norwegian regulatory authorities have approved the study.

CryoIT of the prostate was performed as a freeze-thaw process under anesthesia and autologous iDCs injected after last thawing cycle. Radiologic responses according to RECISTv1.1 could categorize participants into either Group 1; stable disease (n=5) or Group 2; progressive cancer (n=4). Three patients showed mixed response and one had no follow-up imaging. Hematologic and immunologic values were evaluated according to response group.

To identify peripheral blood leukocyte subsets and circulating tumor cells (CTCs), ultradeep T-cell receptor (TCR) β-chain sequences of complementarity-determining region 3, we utilized flow / mass cytometry, Cellsearch System, and TCRSafe Technology, respectively.

At inclusion median age was 69 (62-73) years, BMI 25.9 (25-35), ECOG score 0 (0-1) and median PSA 8 (5-11). Group 2 demonstrated higher PSA (p=0.03), median 3.9 (IQR 2.7-6.8) and 74.6 (IQR 47.4-99.0) for Group 1 and Group 2, respectively.

In total, 13 possible iDC-related AEs were reported by 10 individuals, whereof one severe and 12 mild-to-moderate, with urinary retention in seven subjects. All but one resolved by use of indwelling urinary catheter for median 8 (1-40) days.

Participants with high CTC numbers (&gt;5) before therapy had higher rates of progression, moderate pre-treatment CTC counts (3-5) decreased and no patient acquired CTCs after therapy.

Ultradeep TCR-sequencing showed more prevalent and higher expression (&gt;5-fold) of new TCR clonotypes 2-6 weeks after treatment in Group 1.

The treatment seems safe and well tolerated. Higher PSA indicates more advanced disease at baseline for Group 2. The data indicate immune responses to treatment with higher increases in TCR clonotypes in radiologic stable disease. Clinical trial ID: NCT02423928.

Citation Format: Liv Cecilie V. Thomsen, Alfred Honorè, Bjarte Almås, Lars A. Reisæter, Jannicke Frugård, Einar K. Kristoffersen, Guro Melve, Torjan Haslerud, Jarle Rørvik, Martin Biermann, Svein Inge Helle, Gunnar Kvalheim, Waqas Azeem, Jan Roger Olsen, Ole Johan Halvorsen, Lars Akslen, Duke K. Bahn, Klaus Pantel, Sabine Riethdorf, Haakon Ragde, Bjørn Tore Gjertsen, Anne M. Øyan, Karl-Henning Kalland, Christian Beisland. Dendritic cell based cryoimmunotherapy associates with clinical variables and changes in T-cell receptor expression in a prospective phase I trial of metastatic castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT066.

The effect of high-dose vitamin D on bone mineral density and bone turnover markers in postmenopausal women with low bone mass--a randomized controlled 1-year trial

Vitamin D is widely used in osteoporosis treatment, although the optimal dose is not known. This 1-year clinical study among 297 women aged 50-80 years old showed that a vitamin D(3) dose of 6,500 IU/day was not better than the standard dose of 800 IU/day in improving bone mineral density (BMD) in the hip and spine.

INTRODUCTION

The purpose of this study was to determine whether a high dose of vitamin D(3) was better than the standard dose in improving BMD and reducing bone turnover in postmenopausal women with reduced bone mass.

METHODS

The study was a 1-year randomized double-blind controlled trial comparing high-dose vitamin D(3) with the standard dose. Postmenopausal women (n = 297) with a BMD T-score ≤ -2.0 in either lumbar spine (L2-4) or total hip were included and randomized to 6,500 IU vitamin D(3)/day (20,000 IU twice per week + 800 IU/day) or 800 IU vitamin D(3)/day (placebo twice per week + 800 IU/day). Both groups were given 1,000 mg elemental calcium/day. The primary endpoint was a change in BMD in total hip and lumbar spine (L2-4).

RESULTS

After 1 year, serum 25-hydroxyvitamin D (25(OH)D) increased [mean (SD)] from 71 (23) to 185 (34) nmol/l and from 71 (22) to 89 (17) nmol/l in the high- and standard-dose vitamin D groups, respectively. BMD at all measurement sites was unchanged or slightly improved with no significant differences between the groups. Although bone turnover was reduced in both groups, the more pronounced reduction in serum levels of the bone formation marker P1NP in the standard-dose group may indicate that this treatment was more efficient. Adverse events did not differ between the groups.

CONCLUSIONS

One year treatment with 6,500 IU vitamin D(3)/day was not better than 800 IU/day regarding BMD in vitamin D-replete postmenopausal women with reduced bone mass and was less efficient in reducing bone turnover.

Vitamin K2 supplementation does not influence bone loss in early menopausal women: a randomised double-blind placebo-controlled trial

Vitamin K2 may preserve bone strength and reduce fracture risk. In this randomised double-blind placebo-controlled trial among healthy postmenopausal Norwegian women, 1 year supplementation of vitamin K2 in the form of Natto capsules had no effect on bone loss rates.

INTRODUCTION

Japanese studies indicate that vitamin K2 (menaquinone-7 (MK-7)) intake may preserve bone strength, but this has not been documented in Europeans. The aim of this study was to assess the effect of MK-7 on bone mineral density (BMD) changes in postmenopausal Norwegian women.

METHODS

Three hundred thirty-four healthy women between 50 and 60 years, 1-5 years after menopause, were recruited to a randomised double-blind placebo-controlled trial. The participants were randomly assigned into two groups, one receiving 360 microg MK-7 in the form of Natto capsules and the other the same amount of identical-looking placebo capsules containing olive oil. BMD was measured at total hip, femoral neck, lumbar spine and total body at baseline and 12 months together with serum levels of bone-specific alkaline phosphatase, Crosslaps, total osteocalcin (N-mid OC), carboxylated (cOC) and under-carboxylated osteocalcin (ucOC).

RESULTS

After 12 months, there were no statistical differences in bone loss rates between the groups at the total hip or any other measurement site. Serum levels of cOC increased and ucOC decreased in the treatment versus the placebo group (p < 0.001).

CONCLUSION

MK-7 taken as Natto over 1 year reduced serum levels of ucOC but did not influence bone loss rates in early menopausal women.

Increased lymphatic vascular density is seen before colorectal cancers reach stage II and growth factor FGF-2 is downregulated in tumor tissue compared with normal mucosa

Lymphangiogenesis is an important event in progression of colorectal cancer (CRC), and the estimated lymphatic vascular density (LVD) probably indicates facilitated lymphatic tumor cell invasion and metastasis. However, at what time point during tumor progression this process is triggered, is unclear. The aim of this study was twofold. Firstly, to examine LVD in paired samples of CRC tissue and normal mucosa with specific emphasis on possible difference in LVD between tumors stages II and III, and secondly, the expression of the lymphangiogenic growth factor fibroblast growth factor-2 (FGF-2). Eighteen patients were studied. Immunostaining for podoplanin was performed to highlight lymphatic vessels. FGF-2 mRNA expression was determined by quantitative real-time RT-PCR, whereas protein expression was quantitatively assessed by densitometric analysis of Western blot signal intensity. The immunoblots were further validated by FGF-2 immunostaining of histological sections. LVD was significantly increased in tumor tissue compared with the normal mucosa but no changes in LVD between stages II and III CRC was observed. FGF-2 was found to be downregulated both at the mRNA and protein level in tumor tissues compared with normal mucosa. Lymphangiogenesis was triggered early in tumor development. An increased LVD was established before the tumor reached stage II. FGF-2 was downregulated in tumor tissue. The importance of this finding remains unclear.

A kinetic and conformational study on the interaction of tetrahydropteridines with tyrosine hydroxylase

Tetrahydropterins are obligatory cofactors for tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine biosynthesis. A series of synthetic analogues of 6(R)-L-erythro-5,6,7, 8-tetrahydrobiopterin (BH(4)) with different substituents in positions C2, N3, C4, N5, C6, C7, and N8 on the ring were used as active site probes for recombinant human TH. The enzyme tolerates rather bulky substituents at C6, as seen by the catalytic efficiency (V(max)/K(m)) and the coupling efficiency (mol of L-DOPA produced/mol of tetrahydropterin oxidized) of the cofactors. Substitutions at C2, C4, N5, and N8 abolish the cofactor activity of the pterin analogues. Molecular docking of BH(4) into the crystal structure of the catalytic domain of ligand-free rat TH results in complexes in which the pteridine ring pi-stacks with Phe300 and the N3 and the amino group at C2 hydrogen bonds with Glu332. The pteridine ring also establishes interactions with Leu294 and Gln310. The distance between C4a in the pteridines and the active site iron was 4.2 +/- 0.5 A for the ensemble of docked conformers. Docking of BH(4) analogues into TH also shows that the most bulky substituents at C6 can be well-accommodated within the large hydrophobic pocket surrounded by Ala297, Ser368, Tyr371, and Trp372, without altering the positioning of the ring. The pterin ring of 7-BH(4) shows proper stacking with Phe300, but the distance between the C4a and the active site iron is 0.6 A longer than for bound BH(4), a finding that may be related to the high degree of uncoupling observed for 7-BH(4).

Tyrosine hydroxylase binds tetrahydrobiopterin cofactor with negative cooperativity, as shown by kinetic analyses and surface plasmon resonance detection

Kinetic studies of tetrameric recombinant human tyrosine hydroxylase isoform 1 (hTH1) have revealed properties so far not reported for this enzyme. Firstly, with the natural cofactor (6R)-Lerythro-5,6,7, 8-tetrahydrobiopterin (H4biopterin) a time-dependent change (burst) in enzyme activity was observed, with a half-time of about 20 s for the kinetic transient. Secondly, nonhyperbolic saturation behaviour was found for H4biopterin with a pronounced negative cooperativity (0.39 < h < 0.58; [S]0.5 = 24 +/- 4 microM). On phosphorylation of Ser40 by protein kinase A, the affinity for H4biopterin increased ([S]0.5 = 11 +/- 2 microM) and the negative cooperativity was amplified (h = 0.27 +/- 0.03). The dimeric C-terminal deletion mutant (Delta473-528) of hTH1 also showed negative cooperativity of H4biopterin binding (h = 0.4). Cooperativity was not observed with the cofactor analogues 6-methyl-5,6,7,8-tetrahydropterin (h = 0.9 +/- 0.1; Km = 62.7 +/- 5.7 microM) and 3-methyl-5,6,7, 8-tetrahydropterin (H43-methyl-pterin)(h = 1.0 +/- 0.1; Km = 687 +/- 50 microM). In the presence of 1 mM H43-methyl-pterin, used as a competitive cofactor analogue to BH4, hyperbolic saturation curves were also found for H4biopterin (h = 1.0), thus confirming the genuine nature of the kinetic negative cooperativity. This cooperativity was confirmed by real-time biospecific interaction analysis by surface plasmon resonance detection. The equilibrium binding of H4biopterin to the immobilized iron-free apoenzyme results in a saturable positive resonance unit (DeltaRU) response with negative cooperativity (h = 0.52-0.56). Infrared spectroscopic studies revealed a reduced thermal stability both of the apo-and the holo-hTH1 on binding of H4biopterin and Lerythro-dihydrobiopterin (H2biopterin). Moreover, the ligand-bound forms of the enzyme also showed a decreased resistance to limited tryptic proteolysis. These findings indicate that the binding of H4biopterin at the active site induces a destabilizing conformational change in the enzyme which could be related to the observed negative cooperativity. Thus, our studies provide new insight into the regulation of TH by the concentration of H4biopterin which may have significant implications for the physiological regulation of catecholamine biosynthesis in neuroendocrine cells.

Generation of reactive oxygen species by tyrosine hydroxylase: a possible contribution to the degeneration of dopaminergic neurons?

It has been suggested that idiopathic parkinsonism, characterized by a loss of dopaminergic neurons of the nigrostriatal pathway, is due to the intracellular generation of reactive oxygen species, generated by a nonenzymatic or enzymatic partial reduction of dioxygen. Based on in vitro studies of the iron-containing monooxygenase tyrosine hydroxylase (TH), evidence is presented that this enzyme system may also contribute to such an oxidative stress. Thus, the purified and Fe(2+)-reconstituted recombinant human enzyme shows a time- and temperature-dependent partial uncoupling of the hydroxylation of L-tyrosine with the natural cofactor (6R)-tetrahydrobiopterin, resulting in the formation of H2O2. The degree of uncoupling of the hydroxylation reaction is significantly higher when certain substrate analogues, notably the 7-substituted isomer (7-tetrahydrobiopterin) of the natural cofactor, is used. In the presence of H2O2 and Fe2+, the addition of TH increases the production of the highly reactive.OH radical, probably via a Fenton type of reaction. It is not clear whether this in vitro reaction can mediate cellular injury in vivo. However, it is known that the distribution of TH in the central and peripheral nervous system often corresponds to that of the neuronal degeneration in idiopathic parkinsonism, a finding that is compatible with a pathogenetic effect of TH.

Characterization of a novel pterin intermediate formed in the catalytic cycle of tyrosine hydroxylase

A novel pterin intermediate, in addition to the expected 4a-hydroxytetrahydrobiopterin (4a-OH-BH4) and quinonoid dihydrobiopterin, was generated during catalytic turnover of tyrosine hydroxylase (TH) with tetrahydrobiopterin as the cofactor. Based on chromatographic, spectroscopic and stability properties its structure is proposed to be similar to the product formed by the non-enzymic conversion of synthetic 4a-OH-BH4 [Bailey, Rebrin, Boerth and Ayling (1995) J. Am. Chem. Soc. 117, 10203-10211]. This compound was tentatively described as a 4a-adduct of a side-chain hydroxy group, i.e. the O2', 4a-cyclic-tetrahydrobiopterin (4a-Cyc-BH4). The intermediate generated in the TH reaction has a UV spectrum which is similar to that of 4a-OH-BH4, but elutes with a longer retention time (tR = 1.69 min compared with 1.06 min) on reversed-phase chromatography. Its conversion into quinonoid dihydrobiopterin is catalysed by pterin-4a-carbinolamine dehydratase (EC 4.2.1.96), although 4a-OH-BH4 is the preferred substrate for that enzyme. A precursor-product relationship was demonstrated between 4a-OH-BH4 and the putative 4a-Cyc-BH4 intermediate. The apparent stability of this compound is dependent on pH as well as on the nature of the buffer ions. At pH 8.0 a large amount was generated in Hepes and Tris, but little in phosphate buffer. At pH 7.0 in Hepes (standard assay conditions) and Tris buffer the putative 4a-Cyc-BH4, but no 4a-OH-BH4, was observed. None of the intermediates was observed at pH 6.0. The accumulation of these intermediates in the absence of dehydratase has important implications for the assay of TH and phenylalanine hydroxylase activities, and is also compatible with a possible physiological role of the dehydratase in the synthesis of catecholamines in vivo.

The effects of insulin, cycloheximide and phalloidin on the content of actin and p35 in extracts prepared from the nuclear fraction of Krebs II ascites cells

The nuclear fraction isolated from Krebs II ascites cells following cell disruption by nitrogen cavitation was separated into four fractions by salt/detergent extraction: NP-40 soluble fraction, 130 mM KCl extract, DOC/Triton x 100 soluble fraction and salt/detergent treated nuclei. The protein composition of the individual fractions was studied by SDS-PAGE and the relative amounts of actin and a 35 kDa protein (p35) were measured from gel scans. There was a time-dependent shift of actin from the 130 mM KCl extract to the NP-40 soluble fraction upon storage of the nuclear fraction on ice, indicating a progressive depolymerization of microfilaments. Compared with actin there was a slower release of p35 into the NP-40 soluble fraction. The results suggest that p35 is not integrated in the microfilament network. Phalloidin, which stabilizes the microfilaments, enriched the amount of both proteins in the 130 mM KCl extracts, together with a series of other proteins in the range 50-205 kDa. The presence of phalloidin also resulted in a large increase in the actin content in both the DOC/Triton x 100 extract and the fraction containing salt/detergent treated nuclei. Incubation of cells with insulin and/or cycloheximide enriched the amount of actin in the 130 mM KCl fraction. The results show that short term incubation of cells with phalloidin, insulin or cycloheximide increases the actin content of the nuclear fraction and also affects the presence of several other proteins.

Regulation of recombinant human tyrosine hydroxylase isozymes by catecholamine binding and phosphorylation. Structure/activity studies and mechanistic implications

Three isozymes of human tyrosine hydroxylase (hTH1, hTH2 and hTH4) were expressed in Escherichia coli and purified to homogeneity. Natural catecholamines and related synthetic compounds were found to be potent inhibitors, competitive to the tetrahydrobiopterin cofactor, of all the isozymes. Combining visible spectroscopy and equilibrium-binding studies, it was found that catecholamines bind to hTH1 and hTH2 with a stoichiometry of about 1.0 mol/mol enzyme subunit, interacting with the catalytic iron at the active site. All the isozymes tested were excellent substrates for cAMP-dependent protein kinase (Km = 5 microM, Vmax = 9.5 mumol.min-1.mg kinase-1). The incorporation of about 1.0 mol phosphate/subunit at Ser40 decreased the affinity of dopamine binding by a factor of 10. Conversely, the addition of stoichiometric amounts of Fe(II) and dopamine to the apoenzymes reduced both the affinity and stoichiometry of phosphorylation by cAMP-dependent protein kinase by 2-3-fold. These data provide evidence for a mutual interaction between the presumed regulatory and catalytic domains of hTH, and show that activation of the enzyme by phosphorylation and inactivation by binding of catecholamines are related events, which probably represent important mechanisms for the regulation of the enzyme activity in vivo.