Long-term survival and biomarker correlates of tasquinimod efficacy in a multicenter randomized study of men with minimally symptomatic metastatic castration-resistant prostate cancer

PURPOSE

Tasquinimod (Active Biotech) is an oral immunomodulatory, anti-angiogenic, and anti-metastatic agent that delayed metastatic disease progression in a randomized placebo-controlled phase II trial in men with metastatic castration-resistant prostate cancer (mCRPC). Here, we report long-term survival with biomarker correlates from this trial.

EXPERIMENTAL DESIGN

Two hundred and one (134 tasquinimod and 67 placebo) men with mCRPC were evaluated. Forty-one men randomized to placebo crossed over to tasquinimod. Survival data were collected with a median follow-up time of 37 months. Exploratory biomarker studies at baseline and over time were collected to evaluate potential mechanism-based correlates with tasquinimod efficacy including progression-free survival (PFS) and overall survival (OS).

RESULTS

With 111 mortality events, median OS was 33.4 months for tasquinimod versus 30.4 months for placebo overall, and 34.2 versus 27.1 months in men with bone metastases (n = 136), respectively. Multivariable analysis demonstrated an adjusted HR of 0.52 [95% confidence interval (CI), 0.35-0.78; P = 0.001] for PFS and 0.64 (95% CI, 0.42-0.97; P = 0.034) for OS, favoring tasquinimod. Time-to-symptomatic progression was improved with tasquinimod (P = 0.039, HR = 0.42). Toxicities tended to be mild in nature and improved over time. Biomarker analyses suggested a favorable impact on bone alkaline phosphatase and lactate dehydrogenase (LDH) over time and a transient induction of inflammatory biomarkers, VEGF-A, and thrombospondin-1 levels with tasquinimod. Baseline levels of thrombospondin-1 less than the median were predictive of treatment benefit.

CONCLUSIONS

The survival observed in this trial of men with minimally symptomatic mCRPC suggests that the prolongation in PFS with tasquinimod may lead to a survival advantage in this setting, particularly among men with skeletal metastases, and has a favorable risk:benefit ratio.

Phase II study of tasquinimod in chemotherapy-naive patients with metastatic castrate-resistant prostate cancer (CRPC): Safety and efficacy analysis including subgroups

126

Background: Tasquinimod (TASQ) is an oral quinoline-3-carboxamide derivative that binds to S100A9 and displays anti-angiogenic and anti-tumor activity in prostate cancer (PC) models. In a randomized blinded phase II study, 206 (136 TASQ, 70 placebo [P]) men with metastatic castrate resistant (CRPC) were assigned to TASQ/P once-daily at an initial dose level of 0.25 mg/day escalating to 1.0 mg/day over 4 weeks. The primary endpoint to demonstrate an improvement in PCWG2 criteria-defined progression at 6 months was met and presented at ASCO 2010. This abstract provides an update on safety and efficacy including CRPC subgroups.

Methods: Subgroups of patients based on baseline criteria were investigated for safety using NCI CTC v 3.0 criteria, PK and efficacy.

Results: 201 (134 TASQ, 67 P) pts with a median age of 72.6 years received treatment and were evaluable for efficacy and safety. The updated analysis based on 5 additional PFS events confirmed an improved PFS of 7.6 vs. 3.3 months for pts on TASQ vs. P. Most progression events in both arms were radiological, but more pts progressed on bone scan in the P group. Radiographic PFS was 8.8 vs 4.4 months. Significant PFS improvements were observed in the PCWG2 risk groups with bone metastatic and visceral disease. TASQ treatment led to a transient increase in inflammatory lab markers such as CRP and fibrinogen, as well as asymptomatic increases in amylase/lipase. CRP increase was associated with adverse events (AEs) such as muscle and joint pain, while increased amylase was associated with a lower risk for gastrointestinal AEs. TASQ treatment was associated with anaemia, but did not affect CV risk factors such as hypertension or QTc prolongation, and the rate of composite cardiac events was acceptably low. Clearance of TASQ is decreased with age (1.4 % per year) and patients over 80 often required dose reduction due to increased exposure and toxicities.

Conclusions: TASQ improved PFS in men with metastatic CRPC. Side effects are manageable and seem to correlate with laboratory markers. Individualized dosing based on tolerability is recommended and a phase III placebo-controlled study is being initiated.

[Table: see text]

Aberrant extrathymic T cell receptor gene rearrangement in the small intestinal mucosa: a risk factor for coeliac disease?

BACKGROUND

Coeliac disease is a small intestine enteropathy caused by permanent intolerance to wheat gluten. Gluten intake by patients with coeliac disease provokes a strong reaction by intestinal intraepithelial lymphocytes (IELs), which normalises on a gluten-free diet.

AIM

To investigate whether impaired extrathymic T cell maturation and/or secondary T cell receptor (TCR) gene recombination in IELs are features of coeliac disease which could contribute to the failure of establishing tolerance to gluten.

METHODS

Expression levels of the four splice-forms of recombination activating gene-1 (RAG1) mRNA and preT alpha-chain (preTalpha) mRNA were determined in IEL-subsets of children with coeliac disease and controls. Frequencies of RAG1 expressing IELs were determined by immunomorphometry.

RESULTS

In controls, the RAG1-1A/2 splice-form selectively expressed outside the thymus, was dominant and expressed in both mature (TCR(+)) and immature (CD2(+)CD7(+)TCR(-)) IELs ( approximately 8 mRNA copies/18S rRNA U). PreTalpha was expressed almost exclusively in CD2(+)CD7(+)TCR(-) IELs ( approximately 40 mRNA copies/18S rRNA U). By contrast, RAG1 and preTalpha mRNA levels were low in patients with coeliac disease compared to controls, both with active disease and with inactive, symptom-free disease on a gluten-free diet (p values <0.01 for mature and <0.05 for immature IELs). Similarly, the frequencies of RAG1+ IELs were significantly lower in patients with coeliac disease compared to controls (p<0.001).

CONCLUSIONS

Patients with coeliac disease appear to have an impaired capacity for extrathymic TCR gene rearrangement. This is an inherent feature, which probably plays a pivotal role in the failure to efficiently downregulate the T cell response to gluten.

A phase II study of a 5T4 oncofoetal antigen tumour-targeted superantigen (ABR-214936) therapy in patients with advanced renal cell carcinoma

In a phase II study, 43 renal cell carcinoma patients were treated with individualised doses of ABR-214936; a fusion of a Fab recognising the antigen 5T4, and Staphylococcal enterotoxin A. Drug was given intravenously on 4 consecutive days, treatment was repeated 1 month later. Treatment was associated with moderate fever and nausea, but well tolerated. Of 40 evaluable patients, 28 had disease control at 2 months, and at 4 months, one patient showed partial response (PR) and 16 patients stable disease. Median survival, with minimum follow-up of 26 months was 19.7 months with 13 patients alive to date. Stratification by the Motzer's prognostic criteria highlights prolonged survival compared to published expectation. Patients receiving higher drug exposure had greater disease control and lived almost twice as long as expected, whereas the low-exposure patients survived as expected. Sustained interleukin-2 (IL-2) production after a repeated injection appears to be a biomarker for clinical effect, as the induced-IL-2 level on the day 2 of treatment correlated with survival. The high degree of disease control and the prolonged survival suggest that this treatment can be effective. These findings will be used in the trial design for the next generation of drug, with reduced antigenicity and toxicity.

IGF-I and IGFBP-3 augment transforming growth factor-beta actions in human renal carcinoma cells

Renal cell carcinoma (RCC) is the most prevalent cancer of the kidney. In human RCC cells, we recently showed that insulin-like growth factor I (IGF-I) has growth-promoting effects regulated by IGF-binding protein 3 (IGFBP-3). In this study, the analysis was expanded to include the interaction between the IGF and transforming growth factor-beta (TGF-beta) systems in the human RCC cells Caki-2 (from a primary tumor) and SK-RC-52 (from a metastasis). Functional effects such as cell proliferation, TGF-beta receptor (TbetaR) signaling, and IGFBP-3 levels were monitored after stimulation with various concentrations of IGF-I, TGF-beta, and IGFBP-3. In addition, human RCC tissues as well as experimental human RCC tumors were analyzed for cellular expression of phosphorylated Smad2 by immunohistochemistry. TGF-beta regulated the endogenous IGFBP-3 levels in these RCC cells as neutralizing anti-TGF-beta(1-3) antibodies strongly reduced the basal IGFBP-3 level. In addition, IGF-I increased the IGFBP-3 levels five- to eightfold with TGF-beta acting in synergy to enhance the IGFBP-3 levels 12- to 17-fold. Neutralizing TGF-beta(1-3) activity circumvented the growth inhibitory effects of IGFBP-3 seen in SK-RC-52, whereas it inhibited the growth-promoting effects of IGFBP-3 in Caki-2. Moreover, IGF-I interacted directly with TGF-beta activation of the TbetaR complex by enhancing phosphorylation and nuclear translocation of Smad2. This study demonstrates a direct interaction of the IGF and TGF-beta systems in human renal carcinoma cells. The observations that IGF-I enhances the TGF-beta signaling and that TGF-beta promotes IGFBP-3 production and thus influence the biological activity of IGF may be of importance for future therapeutic options.

An open label phase I study of ABR-217620, a fusion protein of the 5T4 antibody moiety and an engineered superantigen, in patients with non-small cell lung, renal cell or pancreatic cancer

3083

Background: ABR-217620 (naptumomab estafenatox) is a recombinant fusion protein that consists of the 5T4Fab moiety genetically fused to the engineered superantigen variant SEA/E-120. This fusion protein is a new generation tumor-targeted superantigen based on the previously described ABR-214936 (anatumomab mafenatox). ABR-217620 was designed to reduce antigenicity and toxicity. The 5T4 antigen is expressed on more than 95 % of tumors from patients with non-small cell lung (NSCLC), renal cell (RCC) and pancreatic cancer (PC). In clinical PET studies 124I-labeled ABR-217620 has been shown to localize to 5T4 positive tumors. Methods: The compound was administered as a 5 min bolus infusion for 5 consecutive days. Patients with disease control at day 28 were offered a second cycle of therapy. Dose escalation has been performed using a Bayesian model starting at 0.5 μg/kg/day. The primary endpoint is determination of MTD. Secondary endpoints include characterization of side effects, immunological response, efficacy and pharmacokinetics. Results: 31 patients to date have been treated (19 NSCLC, 8 RCC, 4 PC). 3 patients have had dose limiting toxicities (fever, hypotension and nausea, grade 3) at doses between 23 and 28 μg/kg/day. The side effects were resolved quickly. Based on the experience from ABR-214936, these side effects were expected, but the MTD is ∼ 200 times higher. ABR-217620 leads to a dose dependent systemic increase of cytokines including IL-2 and IFN-γ after infusion. It also leads to an expansion of the superantigen reactive T cell population. 16/29 evaluable patients investigated had SD while 13 patients had PD. In contrast to ABR-214936, the first cycle of ABR-217620 treatment can be given without factoring in the titer of preformed anti-superantigen antibodies. Conclusions: ABR-217620 treatment had predicted and manageable side effects with fever, hypotension and nausea being dose limiting toxicities. Treatment with ABR-217620 resulted in a restricted systemic activation of the immune system. A large fraction of the patients have had stable disease.

[Table: see text]

Utility of the Housekeeping Genes 18S rRNA, beta-Actin and Glyceraldehyde-3-Phosphate-Dehydrogenase for Normalization in Real-Time Quantitative Reverse Transcriptase-Polymerase Chain Reaction Analysis of Gene Expression in Human T Lymphocytes

The accuracy of 18S rRNA, beta-actin mRNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA as indicators of cell number when used for normalization in gene expression analysis of T lymphocytes at different activation stages was investigated. Quantitative real-time reverse transcriptase-polymerase chain reaction was used to determine the expression level of 18S rRNA, beta-actin mRNA, GAPDH mRNA and mRNA for six cytokines in carefully counted samples of resting human peripheral blood mononuclear cells (PBMCs), intestinal lymphocytes and PBMCs subjected to polyclonal T-cell activation. The 18S rRNA level in activated and resting PBMCs and intestinal lymphocytes was essentially the same, while the levels of beta-actin and GAPDH mRNAs fluctuated markedly upon activation. When isolated gammadeltaTCR(+), CD4(+) and CD8(+) subpopulations were studied, 18S rRNA levels remained unchanged after 21 h of activation but increased slightly after 96 h. In contrast, there was a 30-70-fold increase of GAPDH mRNA/cell in these cell populations upon activation. Cytokine analysis revealed that only normalization to 18S rRNA gave a result that satisfactorily reflected their mRNA expression levels per cell. In conclusion, 18S rRNA was the most stable housekeeping gene and hence superior for normalization in comparative analyses of mRNA expression levels in human T lymphocytes.

Interplay Between Superantigens and Immunoreceptors

Superantigens (SAGs) cause a massive T-cell proliferation by simultaneously binding to major histocompatibility complex (MHC) class II on antigen-presenting cells and T-cell receptors (TCRs) on T cells. These T-cell mitogens can cause disease in host, such as food poisoning or toxic shock. The best characterized groups of SAGs are the bacterial SAGs secreted by Staphylococcus aureus and Streptococcus pyogenes. Despite a common overall three-dimensional fold of these SAGs, they have been shown to bind to MHC class II in different ways. Recently, it has also been shown that SAGs have individual preferences in their binding to the TCRs. They can interact with various regions of the variable beta-chain of TCRs and at least one SAG seems to bind to the alpha-chain of TCRs. In this review, different subclasses of SAGs are classified based upon their binding mode to MHC class II, and models of trimolecular complexes of MHC-SAG-TCR molecules are described in order to reveal and understand the complexity of SAG-mediated T-cell activation.

Linomide and Antibody-Targeted Superantigen Therapy Abolishes Formation of Liver Metastases in Mice

Hematogenous spread of tumor cells and metastasis formation in the liver are insidious aspects of cancer progression and are not frequently amenable to curative treatment. We examined the effect of Linomide and antibody-targeted therapy against the formation of hepatic metastases in vivo. For this purpose, syngenic B16 melanoma cells transfected with GA733-2 (a human colon cancer cell surface antigen) were injected into a mesenteric vein of C57/Bl6 mice. To test bacterial superantigen (Sag) targeting for immunotherapy of liver metastases, we used genetically fused proteins consisting of SEA and a Fab moiety of a GA733-2 tumor-reactive antibody (C215Fab-SEA). Linomide dose-dependently reduced hepatic metastases, and at 300 mg/kg this reduction was more than 80%. Treatment with C215Fab-SEA decreased metastases formation by 49% and the combination of Linomide and C215Fab-SEA was found to completely abolish liver metastases (>99% reduction). Taken together, our novel data suggest that Linomide and antibody-targeted superantigen therapy individually markedly reduce and together abolish liver metastases. Considering that current therapy of hepatic metastases is mainly limited to surgical resection in a subgroup of patients, these findings indicate that Linomide alone or in combination with antibody-targeted superantigen may provide a novel approach against liver metastases.

Over-expression of interleukin 10 in mucosal T cells of patients with active ulcerative colitis

Ulcerative colitis (UC), a chronic inflammatory bowel disease, exhibits pronounced increase of T lymphocytes in the inflamed mucosa. To understand the role of intestinal T lymphocytes in the pathogenesis of UC their cytokine production in the mucosa was analysed. Intestinal T lymphocytes of UC, Crohn's disease and control patients were analysed for cytokine mRNA levels by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) directly after isolation without in vitro stimulation. Frequencies of cytokine positive cells were determined in UC and control colon by immunomorphometry. T lymphocytes in normal colon expressed interleukin (IL)-2, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta1, but not IL-4, IL-5 or IL-10. In UC, a highly significant increase in IL-10 mRNA levels in T lymphocytes and an increased frequency of IL-10 positive cells was seen in colon. IL-10 mRNA levels were also elevated in T lymphocytes of the non-inflamed ileum and correlated with disease activity at both locations. CD4+ T lymphocytes were the major source of IL-10 mRNA. IL-2, IFN-gamma and TNF-alpha mRNA levels were decreased in colonic T lymphocytes, and virtually no IL-2, IFN-gamma, TNF-alpha or TGF-beta positive cells were detected in basal lymphoid aggregates. However, scattered IL-10 positive cells were found here. Lamina propria outside the aggregates contained IL-10-, IFN-gamma, TNF-alpha and TGF-beta but not IL-2 positive cells. T cells of UC patients did not express IL-4 or IL-5. Taken, together the data suggest a generalized activation of IL-10 producing CD4+ T cells along the intestine of UC patients. The local environment seems to determine the biological consequences of elevated IL-10.

Inhibition of the CD28-CD80 co-stimulation signal by a CD28-binding affibody ligand developed by combinatorial protein engineering

CD28 is one of the key molecules for co-stimulatory signalling in T cells. Here, novel ligands (affibodies) showing selective binding to human CD28 (hCD28) have been selected by phage display technology from a protein library constructed through combinatorial mutagenesis of a 58-residue three-helix bundle domain derived from staphylococcal protein A. Analysis of selected affibodies showed a marked sequence homology and biosensor analyses showed that all investigated affibodies bound to hCD28 with micromolar affinities (KD). No cross-reactivity towards the related protein human CTLA-4 could be observed. This lack of cross-reactivity to hCTLA-4 suggests that the recognition site on hCD28 for the affibodies resides outside the conserved MYPPPYY motif. The apparent binding affinity for hCD28 could be improved through fusion to an Fc fragment fusion partner, resulting in a divalent presentation of the affibody ligand. For the majority of selected anti-CD28 affibodies, in co-culture experiments involving Jurkat T-cells and CHO cell lines transfected to express human CD80 (hCD80) or LFA-3 (hLFA-3) on the cell surface, respectively, pre-incubation of Jurkat cells with affibodies resulted in inhibition of IL-2 production when they were co-cultured with CHO (hCD80+) cells, but not with CHO (hLFA-3+) cells. For one affibody variant denoted Z(CD28:5) a clear concentration-dependent inhibition was seen, indicating that this affibody binds hCD28 and specifically interferes in the interaction between hCD28 and hCD80.

Therapy of human non-small-cell lung carcinoma using antibody targeting of a modified superantigen

Superantigens activate T-cells by linking the T-cell receptor to MHC class II on antigen-presenting cells, and novel reactivity can be introduced by fusing the superantigen to a targeting molecule. Thus, an antibody-targeted superantigen, which activates T cells to destroy tumour cells, might be used as cancer therapy. A suitable target is the 5T4 oncofetal antigen, which is expressed on many carcinomas. We constructed a fusion protein from a Fab of a monoclonal antibody recognizing the 5T4 antigen, and an engineered superantigen. The recombinant product 5T4FabV13-SEA(D227A)bound the 5T4 antigen expressed on the human non-small-cell lung cancer cell line Calu-1 with a Kd of 1.2 nM while the substitution of Asp227 to Ala in the superantigen moiety reduced binding activity to MHC class II. 5T4FabV13-SEA(D227A)tumour reactivity was demonstrated in 7/7 NSCLC samples by immunohistochemistry, while normal tissue reactivity was low to moderate. 5T4FabV13-SEA(D227A)induced significant T-cell-dependent in vitro killing of sensitive 5T4 bearing Calu-1 cells, with maximum lysis at 10(-10)M, while the capacity to lyse MHC class II expressing cells was approximately 1000 times less effective. Immunotherapy of 5T4FabV13-SEA(D227A)against human NSCLC was investigated in SCID mice reconstituted with human peripheral blood mononuclear cells. Mice carrying intreperitoneally growing Calu-1 cells showed significant reduction in tumour mass and number after intravenous therapy with 5T4FabV13-SEA(D227A). Thus, 5T4FabV13-SEA(D227A)has highly attractive properties for therapy of human NSCLC.

Comparison of the cost-effectiveness of budesonide and sodium cromoglycate in the management of childhood asthma in everyday clinical practice

BACKGROUND

Budesonide and sodium cromoglycate are both recommended as maintenance therapy for childhood asthma.

OBJECTIVE

To compare the cost-effectiveness of these two treatment strategies in clinical practice, in an open-label, pharmacoeconomic clinical trial.

METHODS

Health economics were evaluated in 138 children, ages 5 to 11 years, with unstable asthma not previously treated with corticosteroids or cromones. The asthma was stabilized during 4 to 6 weeks with budesonide 200 to 400 microg twice daily. The children were then randomly allocated to one of the two treatment strategies aiming at maintaining asthma control for 12 months; budesonide 400 microg/day (N = 69) or sodium cromoglycate 60 mg/day (N = 69). If asthma control was judged unsatisfactory, the doses were increased or the children were switched to the alternate treatment.

RESULTS

In children continuing on the same treatment, the degree of asthma control was similar in the two groups at study end. To maintain asthma control, 42% of cromoglycate children switched to budesonide, and then experienced a 14% increase in symptom-free days. No budesonide patient had to switch therapy because of lack of asthma control. Although not statistically significant, total annual cost per patient was 24% (Swedish kronor 4195; US $487; Euro 485) lower in the budesonide than the cromoglycate group, mainly due to a lower cost for asthma medication.

CONCLUSIONS

A budesonide strategy for continued maintenance treatment, after an initial period of stabilizing treatment with budesonide, resulted in lower costs and less drug switches than did a strategy with sodium cromoglycate.

The crystal structure of staphylococcal enterotoxin H: implications for binding properties to MHC class II and TcR molecules

The X-ray structure of the superantigen staphylococcal enterotoxin H (SEH) has been determined at 1.69 A resolution. In this paper we present two structures of zinc-free SEH (apoSEH) and one zinc-loaded form of SEH (ZnSEH). SEH exhibits the conventional superantigen (SAg) fold with two characteristic domains. In ZnSEH one zinc ion per SEH molecule is bound to the C-terminal beta-sheet in the region implicated for major histocompatibility complex class II (MHC class II) binding in SEA, SED and SEE. Surprisingly, the zinc ion has only two ligating amino acid residues His206 and Asp208. The other ligands to the zinc ion are two water molecules. An extensive packing interaction between two symmetry-related molecules in the crystal, 834 A(2)/molecule, forms a cavity that buries the zinc ions of the molecules. This dimer-like interaction is found in two crystal forms. Nevertheless, zinc-dependent dimerisation is not observed in solution, as seen in the case of SED. A unique feature of SEH as compared to other staphylococcal enterotoxins is a large negatively charged surface close to the Zn(2+) site. The interaction of SEH with MHC class II is the strongest known among the staphylococcal enterotoxins. However, SEH seems to lack a SEB-like MHC class II binding site, since the side-chain properties of structurally equivalent amino acid residues in SEH and those in SEB-binding MHC class II differ dramatically. There is also a structural flexibility between the domains of SEH. The domains of two apoSEH structures are related by a 5 degrees rotation leading to at most 3 A difference in C(alpha) positions. Since the T-cell receptor probably interacts with both domains, SEH by this rotation may modulate its binding to different TcR Vbeta-chains.

The spectral and thermodynamic properties of staphylococcal enterotoxin A, E, and variants suggest that structural modifications are important to control their function

The superantigens staphylococcal enterotoxin A and E (SEA and SEE) can activate a large number of T-cells. SEA and SEE have approximately 80% sequence identity but show some differences in their biological function. Here, the two superantigens and analogues were characterized biophysically. SEE was shown to have a substantially higher thermal stability than SEA. Both SEA and SEE were thermally stabilized by 0.1 mM Zn(2+) compared with Zn(2+)-reduced conditions achieved using 1 mM EDTA or specific replacements that affect Zn(2+) coordination. The higher stability of SEE was only partly caused by the T-cell receptor (TCR) binding regions, whereas regions in the vicinity of the major histocompatibility complex class II binding sites affected the stability to a greater extent. SEE exhibited a biphasic denaturation between pH 5.0-6.5, influenced by residues in the TCR binding regions. Interestingly, enzyme-linked immunosorbent assay, isoelectric focusing, and circular dichroism analysis indicated that conformational changes had occurred in the SEA/E chimerical constructs relative to SEA and SEE. Thus, it is proposed that the Zn(2+) binding site is very important for the stability and potency of SEA and SEE, whereas residues in the TCR binding site have a substantial influence on the molecular conformation to control specificity and function.

Treatment with tumor-reactive Fab-IL-2 and Fab-staphylococcal enterotoxin A fusion proteins leads to sustained T cell activation, and long-term survival of mice with established tumors

C215Fab-IL-2 fusion protein, with full IL-2 and antigen binding activity, was produced in E. coli at high level (>50 mg/l). When co-administered with Fab-superantigen fusion protein (C215Fab-SEA) in mice strong and sustained T cell activation was observed. Combination treatment of mice carrying B16 melanoma transfected with C215 antigen was also more efficient than using C215Fab-SEA (p<0.01) or C215Fab-IL-2 alone (p<0.001). In a long-term survival experiment 5/12 mice having received combination treatment 5 days after i.v. inoculation of B16 cells survived >85 days. Improved therapeutic efficacy correlated with increased tumor infiltration by activated CD25+ T cells, indicating a T cell mediated mechanism.

Secretion in Escherichia coli and phage-display of recombinant insulin-like growth factor binding protein-2

Insulin-like growth factors (IGFs) promote cell growth and differentiation. Their actions are regulated by six different, but related, binding proteins (IGFBPs). To investigate the molecular interactions between IGFs and IGFBPs, an Escherichia coli based production method and a phage display system has been developed. The cDNA for bovine IGFBP-2 was inserted between regions coding for the pelB signal sequence and geneIII product, g3p, of bacteriophage fd in a phagemid vector to generate pGF14. The coding sequences of IGFBP-2 and g3p were separated by an amber stop codon and a flexible linker containing the cleavage recognition site for H64A subtilisin. Using this system in BL21, a non-supE strain lacking ompT, most product, approximately 4 mg 1(-1) of IGFBP-2, was obtained in the growth medium. The bacterially derived IGFBP-2 had a correct N-terminal sequence, molecular mass on SDS-PAGE and the same affinity for IGF-1 and IGF-II as IGFBP-2 from mammalian cells. In a supE strain of E. coli, IGFBP-2 was produced as an IGF-binding fusion to g3p. Procedures for display and approximately 10000 fold enrichment of IGFBP-2 bearing phage using adsorption to IGF-II coated microtitre plates were developed. Thus IGFBP-2 can be secreted in E. coli and displayed on filamentous phage. These can be selectively enriched by binding to immobilised IGF-II.

Localization of an insulin-like growth factor (IGF) binding site of bovine IGF binding protein-2 using disulfide mapping and deletion mutation analysis of the C-terminal domain

We have investigated which region(s) of bovine insulin-like growth factor binding protein-2 (bIGFBP-2) interact with insulin-like growth factors (IGFs) using C-terminally truncated forms of bIGFBP-2. Initially to aid in mutant design, we defined the disulfide bonding pattern of bIGFBP-2 C-terminal region using enzymatic digestion. The pattern is Cys186-Cys220, Cys231-Cys242, and Cys244-Cys265. In addition, cyanogen bromide cleavage of bIGFBP-2 revealed that the N- and C-terminal cysteine-rich domains were not linked by disulfide bonds. Taking the disulfide bonding pattern into consideration, C-terminal truncation mutants were designed and expressed in COS-1 mammalian cells. Following IGF binding assays, a region between residues 222 and 236 was identified as important in IGF binding. Specifically, mutants truncated by 14, 36, and 48 residues from the C terminus bound IGFs to the same extent as wild type (WT) bIGFBP-2. Removal of 63 residues resulted in a greatly reduced (up to 80-fold) ability to bind IGF compared with WT bIGFBP-2. Interestingly this mutant lacked the IGF-II binding preference of WT bIGFBP-2. Residues 236-270 also appeared to play a role in determining IGF binding specificity as their removal resulted in mutants with higher IGF-II binding affinity.

[Report of a case. Inhalation steroids caused adrenal cortex suppression]

In one of two cases of systemic effects of high-dose inhaled corticosteroid treatment with fluticasone propionate, adrenal suppression was demonstrated in a young man, and in the other retarded growth and severe general effects were observed in connection with infection in a child. These cases illustrate the risk of systemic effects of inhaled corticosteroids, and the importance of using the lowest possible maintenance dose.

Introduction of spacer peptides N-terminal to a cleavage recognition motif in recombinant fusion proteins can improve site-specific cleavage

To improve site-specific cleavage of a methionyl porcine growth hormone [[Met1]-pGH(1-46)-IGF-II] fusion protein by the enzyme H64A subtilisin, a series of flexible, unstructured spacer peptides were introduced N-terminal to the cleavage site. When enzymatic digestion preceded refolding of the fusion proteins, IGF-II could only be liberated from substrates which contained spacer peptides. Compared with the parent construct, the yield of IGF-II from refolded fusion proteins containing spacers was improved up to two-fold. Furthermore, this cleavage rate was improved by removing a competing protease recognition motif from the fusion partner. These data show that fusion partners can influence site-specific proteolysis of fusion proteins. Introduction of flexible spacers between the moieties can alleviate these interactions.

Identification of framework residues in a secreted recombinant antibody fragment that control production level and localization in Escherichia coli

The monoclonal antibody 5T4, directed against a human tumor-associated antigen, was expressed as a secreted Fab superantigen fusion protein in Escherichia coli. The product is a putative agent for immunotherapy of non-small cell lung cancer. During fermentation, most of the fusion protein leaked out from the periplasm to the growth medium at a level of approximately 40 mg/liter. This level was notably low compared with similar products containing identical CH1, CL, and superantigen moieties, and the Fv framework was therefore engineered. Using hybrid molecules, the light chain was found to limit high expression levels. Substituting five residues in VL increased the level almost 15 times, exceeding 500 mg/liter in the growth medium. Here, the substitutions Phe-10 --> Ser, Thr-45 --> Lys, Thr-77 --> Ser, and Leu-78 --> Val were most powerful. In addition, replacing four VH residues diminished cell lysis during fermentation. Thereby the product was preferentially located in the periplasm instead of the growth medium, and the total yield was more than 700 mg/liter. All engineered products retained a high affinity for the tumor-associated antigen. It is suggested that at least some of the identified framework residues generally have to be replaced to obtain high level production of recombinant Fab products in E. coli.

Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion

Site-directed mutagenesis was used to construct pepsin-resistant, single-point mutations of the N-terminal extended IGF-I analogue, long-R3-IGF-I. In order to identify the most susceptible sites, the kinetics of long-R3-IGF-I digestion by purified porcine pepsin were determined. Pepsin initially cleaved the Leu10-Phe11 bond in the N-terminal extension peptide to generate FVN-R3-IGF-I, followed in rapid succession by cleavage at Gln15-Phe16, Tyr24-Phe25, Leu10-Val11 and Met59-Tyr60 in the IGF-I moiety. Single-point mutations at these sites were designed on the basis of the preferred cleavage bonds for pepsin, as well as amino acid substitutions less likely to disturb protein structure. These included Leu10Val, Phe16Ala, Phe25Leu, Asp53Glu and Met59Gln. All five muteins retained growth-promoting activity equivalent to or higher than that of IGF-I. In terms of pepsin susceptibility, Leu10Val and Asp53Glu were degraded as rapidly as the parent long-R3-IGF-I, Met59Gln and Phe25Leu were partially stabilised, and Phe16Ala showed a marked improvement in stability over a wide range of pepsin:substrate ratios. Accordingly, the Phe16Ala mutein, long-R3A16-IGF-I, has potential for oral applications to enhance gastric growth and repair.

Increased cerebrospinal fluid concentration of nitrite in Parkinson's disease

The concentration of nitrite, a metabolite of nitric oxide (NO), was increased in the cerebrospinal fluid (CSF) of untreated patients with Parkinson's disease and in patients treated with L-DOPA in comparison with a group of patients without dopaminergic dysfunction. There was no difference in the concentration of L-arginine (ARG), a precursor of NO, between the groups. There was a highly significant, linear relationship between the concentration of nitrite and ARG in the CSF suggesting that the production of NO is dependent on the availability of ARG. The results support the possibility that production of NO is increased in the brain in Parkinson's disease.

Monoclonal antibody-superantigen fusion proteins: tumor-specific agents for T-cell-based tumor therapy

The bacterial superantigen staphylococcal enterotoxin A (SEA) is an extremely potent activator of T lymphocytes when presented on major histocompatibility complex (MHC) class II molecules. To develop a tumor-specific superantigen for cancer therapy, we have made a recombinant fusion protein of SEA and the Fab region of the C215 monoclonal antibody specific for human colon carcinoma cells. SEA as part of a fusion protein showed a > 10-fold reduction in MHC class II binding compared to native SEA, and accordingly, the affinity of the FabC215-SEA fusion protein for the C215 tumor antigen was approximately 100-fold stronger than to MHC class II molecules. The FabC215-SEA fusion protein efficiently targeted T cells to lyse C215+ MHC class II- human colon carcinoma cells, which demonstrates functional substitution of the MHC class II-dependent presentation of SEA with tumor specificity. Treatment of mice carrying B16 melanoma cells expressing a transfected C215 antigen resulted in 85-99% inhibition of tumor growth and allowed long-term survival of animals. The therapeutic effect was dependent on antigen-specific targeting of the FabC215-SEA fusion protein, since native SEA and an antigen-irrelevant FabC242-SEA fusion protein did not influence tumor growth. The results suggest that Fab-SEA fusion proteins convey superantigenicity on tumor cells, which evokes T cells to suppress tumor growth.

Effect of recombinant IGF binding protein-1 on primary cultures of human keratinocytes and fibroblasts: selective enhancement of IGF-1 but not IGF-2-induced cell proliferation

The present report describes the mitogenic effect of recombinant IGF-2 on cultured human keratinocytes and fibroblasts compared to that of IGF-1. Furthermore, the modulating effect of a recently expressed recombinant form of placental-derived IGF-binding protein 1 (IGFBP-1) on IGF-induced proliferation was examined. A dose-dependent increase, up to 100%, in cell proliferation was seen in cultured human keratinocytes with IGF-2 and -1 and the proliferative response was comparable to the effect of epidermal growth factor (EGF). In human fibroblasts, IGF-1 stimulated DNA synthesis up to 300% for IGF-1 and up to 200% for IGF-2. The mitogenic effect of IGF-1 was enhanced by IGFBP-1 in both cell types. In contrast, the IGF-2-induced mitogenic effect was unperturbed. These findings indicate that the interaction between IGFs and their binding proteins may induce different responses depending upon the ligand and the target cell.

Fusion proteins in biotechnology

Gene fusion techniques allow the production of recombinant proteins featuring the combined characteristics of the parental products. Originally, these techniques were used to probe transcriptional and translational activity, to translocate proteins across cell membranes, and to facilitate the recovery of proteins. Recently, new applications have emerged in areas such as protein refolding, immunology, drug targeting and protein display. A slightly modified version of this review is also published in Current Opinion in Structural Biology 1992, 2:569-575.

An evaluation of different enzymatic cleavage methods for recombinant fusion proteins, applied on des(1-3)insulin-like growth factor I

Different enzymatic methods for cleavage of recombinant fusion proteins were compared. To find an efficient cleavage method, five different fusion proteins were produced. The fusion proteins differed only in the linker region between the fusion partner and the desired product, human des(1-3)insulin-like growth factor I. A cleavage study was performed with enterokinase, plasmin, thrombin, urokinase, and recombinant H64A subtilisin. Significant cleavage was obtained using thrombin, H64A subtilisin, and enterokinase. Thrombin cleavage was studied on a larger scale and des(1-3)IGF-I was recovered at a final yield of 3 mg/L growth medium. Thrombin and enterokinase were also studied as immobilized proteases and they cleaved the fusion proteins with retained activity. To further improve thrombin cleavage, a continuous reactor was constructed, consisting of a closed system with a thrombin column and an ion exchange column in series. Here, the fusion protein circulated while free des(1-3)IGF-I was bound to the ion exchange column after release from the fusion protein. In the reactor, thrombin was as efficient as the free enzyme but gave a diminished rate of product degradation.

Disulfide exchange folding of insulin-like growth factor I

The disulfide exchange folding properties of insulin-like growth factor I (IGF-I) have been analyzed in a redox buffer containing reduced (10 mM) and oxidized (1 mM) glutathione. Under these conditions, the 3 disulfide bridges of the 70 amino acid peptide were not quantitatively formed. Instead, five major forms of IGF-I were detected, and these components were concluded to be in equilibrium as their relative amounts were similar starting from either reduced, native, or a mismatched variant of IGF-I containing two non-native disulfides. The different components in the mixtures were trapped by thiol alkylation using vinylpyridine and subsequently isolated by reverse-phase HPLC. The purified variants were further characterized using plasma desorption mass spectrometry and peptide mapping. Two of the five different forms were identified as native and mismatched IGF-I. One form was a variant with only one disulfide bond, and the other two major components had two disulfides formed. In a separate experiment, early refolding intermediates were trapped by pyridylethylation after only 90 s of refolding in the glutathione buffer, starting from reduced IGF-I. The intermediates were identical to the components observed at equilibrium, but at different relative concentrations. On the basis of the disulfide bond patterns of the different components in the equilibrium mixtures, we conclude that the disulfide between cysteines-47 and -52 in IGF-I is an unfavorable high-energy bond that may exist in the native molecule in a strained configuration.

Thrombin and H64A subtilisin cleavage of fusion proteins for preparation of human recombinant parathyroid hormone

Human parathyroid hormone, hPTH, an 84 amino acid polypeptide, was produced intracellularly in Escherichia coli as a fusion protein, linked to the C-terminus of a 15 kD IgG-binding protein. Approximately 100 mg fusion protein was obtained per liter fermentation medium. To test the efficiency of two alternative enzymatic cleavage methods, two fusion proteins differing only in the linker region were constructed. Cleavage of a Phe-Phe-Pro-Arg linker was obtained with bovine thrombin and cleavage of a Phe-Ala-His-Tyr linker with recombinant H64A subtilisin. Both enzymes yielded the correct N-terminus and cleaved their respective linkers quantitatively, although additional internal cleavage sites in hPTH were detected and characterized. The linker cleavage conditions were optimized and hPTH was purified to homogeneity. Thrombin cleavage resulted in a final yield of 5 mg hPTH/L, while H64A subtilisin cleavage was more specific and gave 8 mg/L. The purified recombinant product was identical to native hPTH and exhibited full biological activity in an adenylate cyclase assay.

Involvement of dopamine in inhibition of food intake by cholecystokinin octapeptide in male rats

Abstract Deprivation of food reduced the level of dopamine in the cerebrospinal fluid of male rats and subsequent ingestion of food or intraperitoneal injection of Cholecystokinin octapeptide restored the level. Injection of a dopamine receptor agonist (apomorphine) or Cholecystokinin octapeptide inhibited food intake and these effects were reversed by pretreatment with a dopamine receptor antagonist (cis-flupentixol). Blockade of cholecystokinin-A receptors, by treatment with L-364,718, but not cholecystokinin-B receptors, by treatment with L-365,260, blocked the inhibitory effect of Cholecystokinin octapeptide on food intake but did not affect the inhibitory effect of apomorphine. It is suggested that Cholecystokinin interacts with dopamine in the control of food intake.

Determination of Enkephalins in Rat Cerebrospinal Fluid with High-Performance Liquid Chromatography-Electrochemical Detection: Increased Concentrations During Lactation are Controlled by Sucking

Abstract Methionine- and leucine-enkephalin were measured in the cerebrospinal fluid of lactating rats by high-performance liquid chromatography and electrochemical detection. The concentration of both peptides was high while the rats were nursing their litter. The concentration of methionine-enkephalin decreased rapidly when the mother left her litter and increased equally rapidly after mother-young reunion, provided the pups were allowed direct contact with the nipples of the mother. The level of leucine-enkephalin did not change during the period of time the lactating rat normally stayed away from its litter but decreased after prolonged (12 h) mother-pup separation. These results show that the concentration of methionine-, but not leucine-enkephalin in the cerebrospinal fluid fluctuates as the lactating rat interacts with its litter and is directly dependent upon the suckling stimulus. Although methionine-enkephalin may contribute to the inhibition of sexual behaviour which occurs during lactation, the role of the enkephalins in the other behavioural and endocrine adaptations of lactation is unknown.

Involvement of Cholecystokinin in Food Intake: II. Lactational Hyperphagia in the Rat

Abstract The role of Cholecystokinin in the hyperphagia of lactation was studied by measuring the concentration of this hormone in plasma and cerebrospinal fluid in relation to food intake in lactating rats. Cholecystokinin was measured by high-performance liquid chromatography and radioimmunoassay in plasma and by radioimmunoassay in cerebrospinal fluid. Plasma concentrations of Cholecystokinin were increased in freely-fed lactating rats compared with non-lactating, regularly cycling rats. However, after 24 h of food deprivation the concentration of plasma Cholecystokinin was markedly decreased in the lactating rats to levels which were lower than those of non-lactating animals. Furthermore, plasma levels of Cholecystokinin did not increase in response to 1 h of feeding in lactating rats, whereas in non-lactating rats they did. In contrast, the concentration of cholecystokinin-like immunoreactivity in the cerebrospinal fluid was the same in freely-fed lactating and non-lactating rats. As in plasma, food deprivation markedly decreased the levels of cholecystokinin-like immunoreactivity in the cerebrospinal fluid of lactating rats but unlike in plasma, the levels were restored by feeding. The levels of cholecystokinin-like immunoreactivity were not changed under these conditions in the non-lactating rats. These results show that there is no correlation between the concentration of Cholecystokinin in plasma and cerebrospinal fluid, which supports the suggestion that the cholecystokinin-like immunoreactivity in the cerebrospinal fluid is derived from the brain. Removal of the litter from lactating rats deprived of food for 24 h reduced food intake and increased the concentration of cholecystokinin-like immunoreactivity in the cerebrospinal fluid, but not in plasma. The inhibition of food intake caused by an intraperitoneal injection of Cholecystokinin octapeptide increased after litter removal. It is suggested that hunger in the lactating rat is reflected by a decrease in the levels of cholecystokinin-like immunoreactivity in the cerebrospinal fluid and satiety by the restoration of these levels.

Involvement of Cholecystokinin in Food Intake: III. Oestradiol Potentiates the Inhibitory Effect of Cholecystokinin Octapeptide on Food Intake in Ovariectomized Rats

Abstract The role of Cholecystokinin in a model of hypophagia, oestradiol-treated Ovariectomized rats, was investigated. Implantation of oestradiol-filled constant-release implants in rats made obese by ovariectomy potentiated the inhibitory effect of intraperitoneal injection of Cholecystokinin octapeptide on food intake after 24 h of food deprivation. The alterations in the concentration of Cholecystokinin in pjasma and of cholecystokinin-like immunoreactivity in cerebrospinal fluid produced by deprivation of food for 24 h and subsequent food intake for 1 h were unaffected by the oestradiol treatment as was the amount of food consumed during 1 h. Oestradiol-treated rats deprived of food for 6 h, however, consumed less food during a 15-min test than controls. Treatment with oestradiol blunted the decrease in the concentration of cholecystokinin-like immunoreactivity in the cerebrospinal fluid in response to 6 h of food deprivation. No alterations in the concentration of Cholecystokinin in plasma occurred after this period of food deprivation and subsequent feeding during 15 min in either oestradiol-treated or control rats. Thus, treatment with oestradiol enhances responsivity to exogenous Cholecystokinin octapeptide and changes the response of endogenous levels of cholecystokinin-like immunoreactivity in the cerebrospinal fluid to a short period of food deprivation. It is suggested that these effects are caused by an action of oestradiol on Cholecystokinin pathways in the brain. The results support the suggestion that hunger in the rat is inversely related to the decrease in the concentration of cholecystokinin-like immunoreactivity in the cerebrospinal fluid.

Separation and characterization of modified variants of recombinant human insulin-like growth factor I derived from a fusion protein secreted from Escherichia coli

Human insulin-like growth factor I, IGF-I, was produced in Escherichia coli fused to a synthetic IgG-binding peptide The fusion protein is secreted into the medium during fermentation and was initially purified on an IgG-Sepharose column. After hydroxylamine cleavage, IGF-I was purified to homogeneity. During purification, impurities in the form of modified variants of IGF-I were detected and characterized. The closely related impurities were identified to be a misfolded form of IGF-I, having mismatched disulphide bonds, a form with the single methionine residue in IGF-I oxidized to methionine sulphoxide and a variant in which the methionine residue was substituted by a norleucine residue during protein synthesis. A form proteolytically cleaved between two arginine residue was also detected. These impurities were separated from the major component, native IGF-I, by using reverse-phase h.p.l.c. The modified molecules as well as native IGF-I were characterized both as intact molecules and as fragments, after pepsin digestion, using the techniques of plasma desorption m.s., N-terminal sequencing and amino acid analysis. The oxidized form was 90%, and the norleucine analogue was 70%, as potent as native IGF-I in a biological radioreceptor assay, and the form having mismatched disulphides lacked receptor affinity.

beta-Endorphin acts on the reproductive tract of female rats to suppress sexual receptivity

Sexual receptivity was suppressed in female rats immediately after the male had ejaculated. The inhibition was prevented by intravaginal injection of naloxone (100 micrograms) before testing and intravaginal injection of beta-endorphin (1.0 micrograms) inhibited sexual behavior in female rats in a manner comparable to that of ejaculation by the male. beta-Endorphin was present in ejaculatory plugs collected from the vagina of female rats (8.2 +/- 0.6 pM) and in seminal fluid collected from male rats (7.7 +/- 0.2 pM). The results suggest that beta-endorphin in the ejaculate of the male rat can act on the reproductive tract of the female rat to suppress her sexual behavior.

Comparison of two chemical cleavage methods for preparation of a truncated form of recombinant human insulin-like growth factor I from a secreted fusion protein

We have produced a naturally occurring variant of human insulin-like growth factor I, truncated by three amino acids at the amino terminus. The polypeptide is obtained as a fusion protein in Escherichia coli. The fusion partner is a synthetic IgG-binding peptide. During fermentation the fusion protein is secreted into the medium, and is purified on IgG--Sepharose prior to cleavage. Two different genes for the fusion protein were used, allowing chemical cleavage at either a tryptophan linker or a methionine linker between the fusion partner and the growth factor, using N-chlorosuccinimide (NCS) or cyanogen bromide (CNBr) respectively. A partial CNBr cleavage yielded the native peptide, whereas the NCS cleavage yielded a product in which the single methionine had been oxidized to the sulfoxide. The forms from both cleavage methods exhibited biological activity and were characterized after purification to homogeneity. Both cleavage methods gave products having correct N- and C-terminal ends. The purified product had a biological activity equal to that of corresponding material from natural sources, 15 000 U/mg. Modified forms of truncated IGF-I were also identified, purified and characterized. Modifications such as proteolysis and misincorporation of norleucine for methionine occurred during biosynthesis, while oxidation of methionine took place during both fermentation and chemical cleavage.

Plasma concentrations of cholecystokinin octapeptide and food intake in male rats treated with cholecystokinin octapeptide

Intraperitoneal injection of 5 micrograms cholecystokinin octapeptide (CCK-8) into male rats deprived of food for 48 h produced a transient (less than 15 min) increase in plasma levels of CCK-8 but suppressed food intake for an extended period (45 min). Plasma concentrations of CCK-8 after i.p. injection of CCK-8 were raised to levels which were fairly comparable to those after feeding. Intracerebroventricular (i.c.v.) injection of the CCK antagonist proglumide (100 micrograms) reversed the effect of CCK-8 on food intake, while i.p. injection of proglumide (100 micrograms) did not have this effect. Feeding increased the plasma concentrations of somatostatin and gastrin but not of oxytocin, and somatostatin and oxytocin but not gastrin were released in response to i.p. injection of CCK-8. However, neither somatostatin nor oxytocin affected food intake, and their release in response to CCK-8 was unaffected by i.c.v. injection of proglumide. These results support the suggestion that CCK-8 is a physiological 'satiety' peptide, which can affect food intake in rats by mechanisms involving both peripheral and central CCK receptors.

Tryptophan, 5-HTP, 5-HT and 5-HIAA in the cerebrospinal fluid and sexual behavior in male rats

No changes were found in the concentration of tryptophan (Trp), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT) or 5-hydroxyindole acetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of male rats either before sexual activity, immediately after ejaculation of after the postejaculatory refractory period (PEI). Injection of the Trp hydroxylase inhibitor p-chlorophenylalanine (PCPA, 25 or 100 mg/kg i.p. for 3 days) in combination with an injection of the monoamine oxidase inhibitor pargyline (100 mg/kg i.p.) increased the concentration of Trp while decreasing the concentration of 5-HTP, 5-HT and 5-HIAA in the CSF. Furthermore 100 (but not 25) mg/kg PCPA in combination with pargyline caused a significant reduction in the latency to ejaculation. Injection of probenecid (200 mg/kg i.p.), an inhibitor of the transport of 5-HIAA from the CSF, increased the concentration of 5-HIAA in the CSF and slightly prolonged the latency to ejaculation. Sexual activity caused no further increase in CSF 5-HIAA levels in the probenecid-treated rats. Since drug-induced changes in sexual behavior are associated with marked alterations in 5-HT metabolism in the CSF, whereas the changes in the behavior which occur normally are not, these results question the physiological significance of the proposed inhibitory role of 5-HT in male rat sexual behavior.

Sexual behavior induces naloxone-reversible hypoalgesia in male rats

The sensitivity to painful and sexual stimuli in male rats was markedly suppressed immediately after ejaculation and enhanced after the postejaculatory refractory period. The suppression of pain sensitivity induced by sexual activity was reversed, but sexual behavior was only slightly affected by intraperitoneal (i.p.) injection of the opioid antagonist naloxone (5 mg). Plasma concentrations of beta-endorphin-like immunoreactivity were unaffected by sexual activity. Injection of beta-endorphin (10 micrograms s.c.) markedly raised plasma concentrations of beta-endorphin-like immunoreactivity within 1 min of injection but did not affect the sensitivity to painful stimulation or the display of sexual behavior. It is suggested that while ejaculation may activate opioid receptor mechanisms, which affect the sensitivity to painful, but not sexual, stimuli, elevation of beta-endorphin in the blood does not affect the sensitivity to either sexual or painful stimuli in male rats.

Sexual activity increases plasma concentrations of cholecystokinin octapeptide and offsets hunger in male rats

Male rats deprived of food for 48 h ignored food pellets immediately after ejaculating with a sexually receptive female rat as did males tested 5 min after i.p. injection of 5 micrograms cholecystokinin octapeptide (CCK-8) or males which had consumed food pellets for 1 h. The concentration of CCK-8 in plasma was increased to comparable levels (10.1 +/- 3.8 (S.E.M.); 11.3 +/- 3.7 and 7.2 +/- 0.5 pmol/l respectively, compared with 1.2 +/- 0.3 pmol/l for NaCl-injected controls) under each of these conditions, whereas the concentration of gastrin increased only after food consumption (18.4 +/- 3.8; 17.7 +/- 5.4 and 54.3 +/- 7.0 pmol/l respectively, compared with 21.5 +/- 2.1 pmol/l for NaCl-injected controls). The effect of ejaculation on the latency to starting to eat was partially reversed by i.p. injection of 50 mg of the CCK-8 antagonist proglumide, but neither treatment with proglumide or CCK-8 nor consumption of food affected the display of sexual behaviour. The results support the suggestion that CCK-8 is a 'satiety peptide' in the rat.

Inhibition of sexual behavior in female rats by intracerebral injections of Met-enkephalin in combination with an inhibitor of enkephalin degrading enzymes

Injection of Met-enkephalin, either subcutaneously (10 or 100 microgram, s.c.), intracerebroventricularly (100 ng or 1 microgram, i.c.v.) or into the mesencephalic central gray (100 ng), had no inhibitory effect on sexual behavior in female rats. If combined with [(R)-3-(N-hydroxy)-carboxamido-2-benzylpropanoyl]-L-alanine (kelatorphan, 5 micrograms i.c.v.; 1.5 micrograms in the central gray; 200 micrograms s.c.), an inhibitor of enkephalin degrading enzymes, however, i.c.v. or central gray (100 ng), but not s.c. (100 micrograms), injection of Met-enkephalin suppressed the behavior. Injection of Leu-enkephalin, s.c. or i.c.v. alone or in combination with kelatorphan, had no inhibitory effect. Peptidases may rapidly inactivate Met-enkephalin after intracerebral injection and prevent the behavioral effect. Inhibition of sexual behavior by Met-enkephalin may occur during lactation, a physiological state when the behavior is suppressed by an opioid peptide.

Naloxone reverses post-ejaculatory inhibition of sexual behaviour in female rats

Sexual receptivity was inhibited in ovariectomized rats treated with oestradiol benzoate (OB: two injections of 2 micrograms) and progesterone (0.5 mg) immediately after ejaculation by the male and restored after the end of the post-ejaculatory refractory period in the male. The post-ejaculatory inhibition of sexual receptivity was reversed by i.p. (5 mg), intracerebroventricular (50 micrograms) or intrathecal (50 micrograms) injection of the opioid peptide receptor antagonist naloxone. The concentration of serum beta-endorphin-like immunoreactivity in ovariectomized rats treated with OB plus progesterone was unaltered by sexual interactions with males (18.3 +/- 6.0 (S.E.M.), 26.4 +/- 2.1 and 21.8 +/- 6.1 pmol/l before sexual activity, after ejaculation and after the end of the post-ejaculatory interval) but reduced to non-detectable by hypophysectomy. Subcutaneous injection of 10 micrograms beta-endorphin raised serum concentrations of beta-endorphin-like immunoreactivity but did not affect the display of sexual behaviour. The behaviour was also unaffected by intracerebroventricular injection of 0.1, 0.2 or 1.0 microgram beta-endorphin or by injections of 0.25 microgram beta-endorphin in the periaqueductal central grey of the mesencephalon. The results show that ejaculation by male rats causes a transient inhibition of sexual receptivity in the female which may be dependent upon opioid peptide receptor mechanisms in the brain and spinal cord. It is unlikely that the peptide is beta-endorphin.

Naloxone stimulates sexual behaviour in lactating rats

During lactation the display of sexual receptivity in response to treatment with oestradiol benzoate (OB; 2 or 10 micrograms) and progesterone (0.5 mg) was inhibited, but the behaviour could be activated by i.p. (5 mg) or intracerebroventricular (i.c.v.; 100 micrograms) but not intrathecal (i.t.; 100 or 500 micrograms) injections of the opioid peptide receptor antagonist naloxone. The behaviour was also inhibited in ovariectomized rats in which serum progesterone and prolactin levels had been raised by treatment with progesterone implants and the dopamine receptor antagonist domperidone, and the uterine cervix had been stimulated. Intraperitoneal injections of naloxone (1 mg) reactivated the behaviour of cervically stimulated rats. The concentration of beta-endorphin-like immunoreactivity in the serum of lactating rats (42.8 +/- 9.2 pmol/l) was not raised above that of ovariectomized rats (35.8 +/- 8.4 pmol/l) nor was the concentration of beta-endorphin-like immunoreactivity altered in the pituitary gland (22.5 +/- 2.5 pmol/l), midbrain central grey (6.3 +/- 2.2 pmol/l) or hypothalamus (5.6 +/- 2.6 pmol/l) of lactating rats in comparison with ovariectomized rats (24.8 +/- 4.4, 4.0 +/- 2.0 and 4.7 +/- 1.4 pmol/l respectively). Adrenalectomy facilitated the display of sexual behaviour in lactating rats treated with OB plus progesterone and caused a slight increase in serum beta-endorphin-like immunoreactivity (30.5 +/- 2.7 pmol/l) compared with that in non-adrenalectomized lactating rats (26.1 +/- 2.1 pmol/l). It is suggested that an opioid peptide, but probably not beta-endorphin, inhibits sexual behaviour during lactation and after cervical stimulation.

The effect of naloxone on sexual behavior in female rats depends on the site of injection

Intraperitoneal injections of the opiate receptor antagonist naloxone (0.1, 1, 5 or 10 mg) had no effects on sexual behavior in ovariectomized female rats made either partially or fully receptive by injections of ovarian hormones. Intracerebroventricular (i.c.v.) injections of naloxone (10, 50 or 100 micrograms) had no effects on the behavior of partially receptive rats and in fully receptive rats an i.c.v. injection of a high dose of naloxone (100 micrograms) inhibited the behavior. Intrathecal (i.t.) injections of naloxone (50 or 100 micrograms) facilitated sexual behavior in partially receptive rats while i.t. injections of even very high doses of naloxone (500 micrograms) had no behavioral effects in fully receptive rats. Thus, the effects of naloxone on female sexual behavior depend on the site of injection.

Role of the uterine cervix in inhibition of sexual behaviour in lactating rats

Treatment of ovariectomized rats with progesterone-filled constant-release implants, which increased serum progesterone concentrations to 99.4 +/- 5.0 nmol/l, facilitated the induction of lordosis behaviour by subsequent treatment with oestradiol benzoate (OB, 10 micrograms). Concurrent treatment with the dopamine receptor antagonist domperidone (two daily injections of 2.5 mg/rat), which increased serum prolactin concentrations, did not inhibit the behavioural response of ovariectomized progesterone-treated rats to OB. If the treatment was combined with stimulation of the uterine cervix it inhibited lordosis to a level which was comparable with that of progesterone-domperidone-treated rats, which had been ovariectomized and from which the pups had been removed on the day of parturition. The cervical stimulation did not increase the amount of prolactin secreted by the pituitary gland in response to an injection of domperidone. The behavioural effect of cervical stimulation was blocked by injecting an anaesthetic paste (0.1 ml lidocain-prilocain) intravaginally against the cervix. The effect of cervical stimulation, or of parturition, lasted only for a few days and sexual behaviour was inhibited during a prolonged period of lactation. Sucking by the pups on the nipples of the mother may be required for preventing sexual behaviour during the entire period of lactation.