Clinical benefit of continuing ALK inhibition with crizotinib beyond initial disease progression in patients with advanced ALK-positive NSCLC

BACKGROUND

Crizotinib is approved to treat advanced ALK-positive non-small-cell lung cancer (NSCLC), but most patients ultimately develop progressive disease (PD). We investigated whether continuing ALK inhibition with crizotinib beyond PD (CBPD) is clinically beneficial and attempted to identify clinicopathologic characteristics associated with patients who experience clinical benefit.

PATIENTS AND METHODS

Patients with advanced ALK-positive NSCLC enrolled in two ongoing multicenter, single-arm trials who developed RECIST-defined PD were allowed to continue crizotinib if they were deriving ongoing clinical benefit. In the present retrospective analysis, continuation of CBPD was defined as >3 weeks of crizotinib treatment after PD documentation. Patients who had PD as best response to initial crizotinib treatment were excluded. Baseline and post-progression characteristics, sites of PD, and overall survival (OS) were compared in patients who continued CBPD versus those who did not. The impact of continuing CBPD on OS after adjusting for potential confounding factors was assessed.

RESULTS

Among 194 crizotinib-treated patients with RECIST-defined PD, 120 (62%) continued CBPD. A significantly higher proportion of patients who continued CBPD than patients who did not had an ECOG performance status (PS) of 0/1 at PD (96% versus 82%; P=0.02). CBPD patients had significantly longer OS from the time of PD [median 16.4 versus 3.9 months; hazards ratio (HR) 0.27, 95% confidence interval (CI): 0.17-0.42; P<0.0001] and from the time of initial crizotinib treatment (median 29.6 versus 10.8 months; HR 0.30, 95% CI: 0.19-0.46; P<0.0001). The multiple-covariate Cox regression analysis revealed that CBPD remained significantly associated with improved OS after adjusting for relevant factors.

CONCLUSIONS

Patients who continued CBPD were more likely to have good ECOG PS (0/1) at the time of PD. Continuing ALK inhibition with crizotinib after PD may provide survival benefit to patients with advanced ALK-positive NSCLC.

Hypertension as a potential biomarker of efficacy in patients with gastrointestinal stromal tumor treated with sunitinib

BACKGROUND

Reliable biomarkers of sunitinib response in gastrointestinal stromal tumor (GIST) are lacking. Hypertension (HTN), an on-target class effect of vascular endothelial growth factor signaling-pathway inhibitors, has been shown to correlate with clinical outcome in advanced renal cell carcinoma treated with sunitinib.

PATIENTS AND METHODS

This retrospective analysis examined correlations between sunitinib-associated HTN and antitumor efficacy (N = 319) and safety (N = 1565) across three advanced GIST studies. Blood pressure (BP) was measured on days 1 and 28 of each treatment cycle at a minimum. Time-to-event endpoints were estimated using Kaplan-Meier methods, and patient subgroups with and without HTN (maximum systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg) were compared using Cox proportional hazards models. Landmark analyses evaluated associations between early HTN and efficacy endpoints. Adverse events (AEs) were compared between groups.

RESULTS

Sunitinib-associated HTN correlated with improved objective response rates, time to tumor progression, progression-free survival, and overall survival. Almost all benefits remained significant in multivariate and landmark analyses. Overall incidences of HTN-related AEs were low and similar between groups; incidences of cardiovascular AEs were somewhat higher in patients with HTN.

CONCLUSION

Sunitinib-associated HTN appeared to correlate with improved clinical outcomes in GIST, while incidences of HTN-associated AEs were generally low and manageable.

Clinical evaluation of continuous daily dosing of sunitinib malate in patients with advanced gastrointestinal stromal tumour after imatinib failure

AIMS

To assess the antitumour activity, safety, pharmacokinetics and pharmacodynamics of continuous daily sunitinib dosing in patients with imatinib-resistant/intolerant gastrointestinal stromal tumour (GIST) and to assess morning dosing versus evening dosing.

PATIENTS AND METHODS

In this open-label phase II study, patients were randomised to receive morning or evening dosing of sunitinib 37.5mg/day. The primary end-point was clinical benefit rate (CBR; percent complete responses+partial responses [PRs]+stable disease [SD] 24 weeks). Secondary end-points included progression-free survival (PFS), overall survival (OS), safety, pharmacokinetic parameters and plasma biomarker levels.

RESULTS

Sixty of 61 planned patients received treatment (30 per dosing group); 26 completed the study. Overall, the CBR was 53% (95% exact CI, 40-66): eight patients (13%) achieved objective PRs; 24 (40%) achieved SD 24 weeks. Median PFS was 34 weeks (95% CI, 24-49); median OS was 107 weeks (95% CI, 72 - not yet calculable). Most adverse events (AEs) were of grade 1 or 2 in severity, and were manageable through dose modification or standard interventions. No new AEs were apparent compared with the approved intermittent dosing schedule. Antitumour activity and safety were generally similar with morning and evening dosing. Continuous daily sunitinib dosing achieved and sustained effective drug concentrations without additional accumulation across cycles. Decreases from baseline in plasma levels of soluble KIT after 20 and 24 weeks of dosing correlated with longer OS.

CONCLUSION

For patients with imatinib-resistant/intolerant GIST, continuous daily sunitinib dosing appears to be an active alternative dosing strategy with acceptable safety.

Clinical phenotype and infertility treatment in a male with hypogonadotropic hypogonadism due to mutations Ala129Asp/Arg262Gln of the gonadotropin-releasing hormone receptor

OBJECTIVE

To characterize the genotype and phenotype of a man with idiopathic hypogonadism with infertility.

DESIGN

Molecular analysis and clinical description.

SETTING

Medical school laboratory and reproductive endocrine clinic.A 40-year-old male with idiopathic hypogonadotropic hypogonadism.

INTERVENTION(S)

Denaturing gradient gel electrophoresis analysis and DNA sequencing of the gonadotropin-releasing hormone receptor (GNRHR) gene were performed. The patient was treated with hCG and FSH.

MAIN OUTCOME MEASURE(S)

GNRHR mutation detection, genotype/phenotype correlation, and testicular response to exogenous gonadotropin therapy.

RESULT(S)

The proband demonstrated compound heterozygosity for Ala129Asp/Arg262Gln GNRHR mutations. He had a complete form of idiopathic hypogonadotropic hypogonadism, with descended testes and severe oligospermia but little response to exogenous gonadotropins.

CONCLUSION(S)

The phenotype of this patient differs from the one other family described with the same mutations. Exogenous gonadotropin therapy may not be as beneficial for increasing sperm concentration in older men with idiopathic hypogonadotropic hypogonadism.

Estrogens and hormone replacement therapy: is there a role in the preservation of cognitive function?

Alzheimer's disease affects as many as 40% of Americans over the age of 80 and, as such, is a major public health issue. Interestingly, there is a two- to threefold greater prevalence in women than in men. It has been estimated that the prevalence of Alzheimer's disease will quadruple over the next half century. There have been implications of an effect of estrogen on neurological function for many years. As long as 50 years ago a study published in the gerontology literature suggested that the administration of i.m. estrogen in a nursing home population was associated with improvement in memory and a delay in progression of memory loss. Most recently there has been great interest in the effect of estrogen on both neurons and the CNS vasculature. A study evaluating verbal memory and abstract reasoning in over 700 women without dementia demonstrated that women who had used estrogen for as little as 1 year had significant improvements in baseline cognitive testing. The pathogenesis of Alzheimer's disease and neurodementia is better understood today but remains incompletely elucidated. It has been suggested that inflammation exists both within the neurovasculature and the stroma and that beta-amyloid creates an inflammatory reaction. In Alzheimer's patients there are abnormal deposits of proteins such as beta-amyloid, presenelin, and apolipoprotein E-4. Estrogen may act as a protectant against these inflammatory mediating proteins. While a recent trial demonstrated no impact of estrogen in patients diagnosed with mild to moderate Alzheimer's, other studies have suggested that estrogen use significantly delays disease onset. One study followed over 1,100 subjects who were free of disease at trial initiation over a period of 1 to 5 years. Even short-term use of estrogen imparted protection, although longer-term estrogen use was associated with greater protection. Unfortunately, most women are unaware of the potential beneficial effect of estrogen on cognitive function. Prospective studies are under way to try to delineate how estrogen impacts Alzheimer's disease.

Familial gonadotropin-releasing hormone resistance and hypogonadotropic hypogonadism in a family with multiple affected individuals

OBJECTIVE

To characterize the phenotype of idiopathic hypogonadotropic hypogonadism due to compound heterozygous GnRHR gene mutations (Arg262Gln/Tyr284Cys).

DESIGN

Retrospective review.

SETTING

Tertiary medical center.

PATIENT(S)

Family containing four siblings (three female and one male) with complete idiopathic hypogonadotropic hypogonadism.

INTERVENTION(S)

Baseline and stimulated laboratory studies. One patient received GnRH treatment and one received human menopausal gonadotropins.

MAIN OUTCOME MEASURE(S)

Clinical phenotype vs. genotype is assessed by endocrine studies, karyotype, pedigree, and review of pathology slides of ovarian neoplasm.

RESULT(S)

With GnRH stimulation, two patients with idiopathic hypogonadotropic hypogonadism had maximum LH < 10 mIU/mL, and two others had peak LH > 10 mIU/mL. With repeated GnRH stimulation 24 hours later, gonadotropin levels in all patients were increased. Stimulation of thyroid-releasing hormone and tests for insulin-induced hypoglycemia were normal. One affected patient did not ovulate after GnRH treatment, but her sister ovulated with gonadotropin treatment. Another affected sibling had bilateral oophorectomy for seromucinous cystadenomas, and her hypogonadotropic state remained after castration. The man with idiopathic hypogonadotropic hypogonadism and his unaffected brother had a ring chromosome 21.

CONCLUSION(S)

All patients with complete idiopathic hypogonadotropic hypogonadism had the same GnRHR mutations, but clinical presentations and endocrinologic responses were heterogeneous. Gonadotropin levels remained low in patients with idiopathic hypogonadotropic hypogonadism after castration, and ring chromosome 21 was present, suggesting that sequences from this chromosome could affect the idiopathic hypogonadotropic hypogonadism phenotype.

Molecular evaluation of the gonadotropin-releasing hormone receptor

The gonadotropin-releasing hormone receptor (GnRHR) is a guanine nucleotide-binding protein-coupled receptor with a characteristic seven transmembrane domain motif. It transduces the hypothalamic message carried by the decapeptide gonadotropin-releasing hormone. At the gonadotrope cell surface the hormone binds to the receptor, leading to pituitary synthesis and secretion of gonadotropins. These glycoprotein hormones, in turn, modulate folliculogenesis and ovulation in the ovary. Failure of the GnRHR to respond appropriately to its cognate ligand has been demonstrated in humans. These patients have genomic mutations in the gene for the GnRHR and represent the first individuals with hypogonadotropic hypogonadism of autosomal inheritance. The mutant receptors are poorly expressed at the cell surface and have a diminished capacity to transduce the hypothalamic message efficiently. To date, no mutations have been identified that lead to constitutively active receptors and autonomous gonadotropin function. This article identifies the mutations in the GnRHR reported to date and reviews how these abnormal receptors help us to better understand the biology of this interesting molecule.

Pre-clinical evaluation of SN-38 and novel camptothecin analogs against human chronic B-cell lymphocytic leukemia lymphocytes

The topoisomerase I inhibitor camptothecin and its analogs have potent activity against a wide range of solid tumors and several hematologic malignancies. Previous studies with these compounds using the MTT metabolic inhibition assay have shown significant cytotoxicity against lymphocytes from patients with chronic B-cell lymphocytic leukemia (B-CLL). Yet the water soluble analogue, topotecan, which was inhibitory at > 1 microM in vitro, had no clinical activity in vivo. In the present study, we evaluated the in vitro cytotoxicities of SN-38, the active form of irinotecan, and two newer water soluble camptothecin derivatives 10,11-methylenedioxy-20(S)-camptothecin glycinate (MDCG) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin glycinate (CMMDCG). These two glycinate esters are prodrugs for 10,11-methylenedioxy-20(S)-camptothecin (MDC) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC), respectively. Effects on cellular metabolism, induction of apoptosis, and overall cell survival were used to evaluate chemosensitivity. We report that the relative cytotoxic potency for these compounds is MDC > or = CMMDC > or = SN-38 >> TPT > CPT-11, where MDC, CMMDC, and SN-38 were over an order of magnitude more cytotoxic than TPT and CPT-11. We also investigated potential mechanisms underlying the unexpected cytotoxicity of these camptothecin derivatives in B-CLL cells that are known to be arrested in G0/G1 of the cell cycle, and found that this class of compounds inhibited [3H]uridine incorporation. We therefore postulate that the inhibition of RNA rather than DNA synthesis may be responsible for the observed cytotoxicity in non-cycling B-CLL cells.

Molecular analysis of the gonadotropin-releasing hormone receptor in patients with polycystic ovary syndrome

OBJECTIVE

To determine whether a mutation in the GnRH receptor gene is responsible for polycystic ovary syndrome (PCOS).

DESIGN

Molecular analysis of human genomic DNA.

SETTING

Academic research environment.

PATIENT(S)

Eighty patients with PCOS.

INTERVENTION(S)

Extraction and polymerase chain reaction (PCR) analysis of genomic DNA, confirmation of PCR products by ethidium bromide staining of agarose gels after electrophoresis, denaturing gradient gel electrophoresis of PCR products, and photography.

MAIN OUTCOME MEASURE(S)

Mutations in the GnRH receptor of women with PCOS.

RESULT(S)

Denaturing gradient gel electrophoresis revealed no mutations in the exonic sequence encoding the open reading frame of the GnRH receptor.

CONCLUSION(S)

A mutation in the GnRH receptor gene is unlikely to be the underlying cause of PCOS in most patients. The molecular basis of this disorder remains unknown.

The Finnish follicle-stimulating hormone receptor gene mutation is rare in North American women with 46,XX ovarian failure

OBJECTIVE

To determine whether FSH receptor gene missense mutation in Finnish women with premature ovarian failure (POF) is present in North American women with POF.

DESIGN

Analysis of DNA from patients and controls.

PATIENT(S)

Thirty-five women with POF and ten normal controls.

INTERVENTION(S)

Extraction of DNA with subsequent digestion by the enzyme BsmI, polyacrylamide gel electrophoresis, ethidium bromide staining, and photography.

MAIN OUTCOME MEASURE(S)

After restriction enzyme digestion, the frequencies of the normal allele (two fragments of 51 and 27 base pairs) and the mutant allele (a single 78-base pair fragment) were determined.

RESULT(S)

BsmI digestion was noted for all 35 affected individuals and 10 controls, thus demonstrating homozygosity for the normal FSH receptor allele. No patient or control was heterozygous or homozygous for the mutant allele.

CONCLUSION(S)

The missense mutation in the human FSH receptor gene in Finnish women with POF is uncommon in North American women with POF. The molecular basis of ovarian failure for most patients remains unknown.

Human calcitonin receptors exhibit agonist-independent (constitutive) signaling activity

The human CT receptor (hCTR), which is found as three isoforms, belongs to a small, recently described subfamily of G protein-coupled receptors (GPCRs). Several mutant GPCRs have been shown to exhibit constitutive (or agonist-independent) signaling activity and cause disease in humans, but only a few GPCRs have been identified with agonist-independent activity in the wild-type (or native) form. In the hCTR subfamily, no wild-type receptor has been shown to exhibit constitutive activity and only one, a mutated receptor for PTH/PTH-related peptide, has been found with constitutive activity to cause disease in humans. We demonstrate that two wild-type isoforms of hCTR, hCTR-1 and hCTR-2, exhibit constitutive activity by showing that they cause elevation of cAMP and induction of a cAMP-responsive gene in two cell types in culture in the absence of agonist. The identical mutation that caused the PTH/PTH-related peptide receptor to be constitutively active was made in hCTR-2 and shown to have no effect on signaling. We suggest that constitutive activity of wild-type hCTR-1 and hCTR-2 may reflect an adaptation of their signaling properties to exert their regulatory function in the absence of agonist in some cell types.

Relevance of molecular medicine to clinical obstetrics and gynecology

Understanding molecular biology can improve the clinical acumen of the practicing obstetrician/gynecologist. An area of basic research now becoming clinically relevant involves the G proteins and G protein-coupled receptors. Clinicians already manipulate G protein-coupled receptors in their daily practice. Examples include the administration of oxytocin (oxytocin receptors), beta-2 tocolytic agents (beta 2-adrenergic receptors), GnRH agonists (GnRH receptors), exogenous gonadotropins (FSH and LH receptors), and bromocriptine (dopamine receptor). Clinically important disorders presenting to the obstetrician/gynecologist include some forms of precocious puberty, delayed puberty, premature ovarian failure, and pituitary adenomas which are due to mutations of G proteins and G protein-coupled receptors. The importance of these proteins is demonstrated by the fact that G protein-related genes comprise about 1 percent of the human genome. Additionally, the knowledge that some G protein gene mutations are present in the germ line, and others are somatic cell in origin (and not heritable), aids in more accurate genetic counseling to patients.

Intracellular retention and rapid degradation of human calcitonin receptors overexpressed in COS cells

Overexpression of native and epitope-tagged human calcitonin (CT) receptors (hCTR-2) in COS-1 cells was performed to permit identification of the receptor protein and begin studies of receptor turnover. Data obtained with immunological techniques and cross-linking of radiolabeled salmon CT ([125I]sCT) revealed two forms of hCTR-2 in transfected cells: a larger, mature cell surface receptor (apparent size, 81 kDa) and a smaller, intracellular form (apparent size, 66 kDa). These conclusions are based on the following observations. 1) Only the larger hCTR-2 was visualized by cell surface [125I]sCT binding, whereas both species were identified by [125I]sCT binding to cell lysates. 2) Immunofluorescence studies with antibodies directed against the epitope confirmed the presence of cell surface and intracellular hCTR-2s; there were apparently many more receptors intracellularly than on the cell surface. 3) Both hCTR-2 forms were changed to a similar size of approximately 57-60 kDa by deglycosylation with endoglycosidase F; this size is consistent with that predicted by the amino acid sequence. Metabolic studies with radioactive amino acids labeled only the intracellular form. This immature form exhibited a rapid half-life of 30 min. We conclude that overexpression of native and epitope-tagged hCTR-2s in COS-1 cells leads to their intracellular retention and rapid degradation.

Neuropeptide Y and calcitonin gene-related peptide modulate voltage-gated Ca2+ channels in mature female rat paracervical ganglion neurons

OBJECTIVE

To assess the predominant subtype of calcium channel present in neurons of the paracervical ganglia (PG) of the female rat and the ability of neuroactive peptide to modulate total calcium current.

METHODS

Whole-cell patch clamp techniques were used on isolated PG neurons to assess calcium current modulation in the presence and absence of selective calcium channel subtype inhibitors and neuropeptides. Digital imaging analysis of cells was used to determine neuronal cell size distributions within the ganglia.

RESULTS

Average PG cell diameter was 28.1 microns. Most PG neurons (64%) had an N-type calcium current that contributed 41% of the total calcium current. The low voltage-activated or T-type current was not present. Very few neurons (22%) were sensitive to the P-type calcium channel blocker omega-agatoxin IVA, and in only 10% of neurons was the calcium current sensitive to the L-type channel blocker nimodipine. Neuropeptide Y (NPY) inhibited the calcium current by 41% in 79% of the neurons, but vasoactive intestinal peptide (VIP) had no effect. Calcitonin gene-related peptide (CGRP) both increased and decreased the calcium current in separate cell populations.

CONCLUSIONS

Calcium currents in female rat PG neurons are carried primarily through N-type calcium channels with a small contribution from L- and P-type channels. An unidentified calcium channel type is also present. Modulation of the calcium current by NPY is demonstrated, and support for the presence of a local, CGRP-mediated circuit is presented.

Iodocalcitonin binds to human calcitonin receptors with higher affinity than calcitonin

The reported binding affinities of cloned human calcitonin receptors (hCTRs) for salmon calcitonin (sCT) vary over a wide range. Because the greatest differences were between values estimated in association binding versus competition binding experiments, we considered the possibility that this variation was due to differences in the affinities of hCTRs for moniodinated sCT (I-sCT) and sCT. We found that I-sCT competed with 125I-sCT for binding with 9.3 +/- 0.58 times the apparent affinity of sCT in COS-1 and Madin Darby canine kidney (MDCK) cells expressing cloned hCTRs. I-sCT was 25 times more potent than sCT in stimulating cAMP formation in MDCK cells expressing hCTRs. These data demonstrate that monoiodinated sCT interacts more avidly with hCTRs than sCT with a consequent enhanced potency in stimulating second messenger formation. Therefore, as I-sCT (or 125I-sCT) binds with different affinity to hCTRs than sCT, affinity measurements must be performed with I-sCT (or 125I-sCT) alone.

Induction of phorbol ester responsiveness in conventional B cells after activation via surface Ig

The signals required to induce S phase entry in murine splenic B cells were found to be altered by prolonged treatment with low doses of anti-Ig antibody. Whereas fresh splenic B cells are stimulated by the combination of a phorbol ester protein kinase C agonist plus a calcium ionophore, anti-Ig-treated splenic B cells were stimulated by phorbol ester alone, in the absence of a comitogen. The majority of these phorbol ester responsive B cells expressed CD5. The phorbol ester responses of anti-Ig-treated splenic B cells paralleled those previously reported for untreated peritoneal CD5+ B cells in a number of respects: responses were not idiosyncratic to phorbol esters but occurred with nonphorbol protein kinase C agonists; phorbol ester responses were enhanced by IL-4; and, phorbol ester responses occurred rapidly and were greater at 24 than at 48 h. However, the effect of agents that act to raise intracellular levels of cAMP distinguished between anti-Ig-treated splenic B cells and untreated peritoneal B cells in that the phorbol ester responses of the former were enhanced whereas the responses of the latter were inhibited. The present results add a functional dimension to the phenotypic similarity between splenic B cells treated with anti-Ig and resident peritoneal B cells that constitutively express CD5; however, some differences in behavior were noted.

Induction of phorbol ester responsiveness in conventional B cells after activation via surface Ig

The signals required to induce S phase entry in murine splenic B cells were found to be altered by prolonged treatment with low doses of anti-Ig antibody. Whereas fresh splenic B cells are stimulated by the combination of a phorbol ester protein kinase C agonist plus a calcium ionophore, anti-Ig-treated splenic B cells were stimulated by phorbol ester alone, in the absence of a comitogen. The majority of these phorbol ester responsive B cells expressed CD5. The phorbol ester responses of anti-Ig-treated splenic B cells paralleled those previously reported for untreated peritoneal CD5+ B cells in a number of respects: responses were not idiosyncratic to phorbol esters but occurred with nonphorbol protein kinase C agonists; phorbol ester responses were enhanced by IL-4; and, phorbol ester responses occurred rapidly and were greater at 24 than at 48 h. However, the effect of agents that act to raise intracellular levels of cAMP distinguished between anti-Ig-treated splenic B cells and untreated peritoneal B cells in that the phorbol ester responses of the former were enhanced whereas the responses of the latter were inhibited. The present results add a functional dimension to the phenotypic similarity between splenic B cells treated with anti-Ig and resident peritoneal B cells that constitutively express CD5; however, some differences in behavior were noted.

Elevated levels of protein kinase C activity and alpha-isoenzyme expression in murine peritoneal B cells

Conventional murine splenic B cells are stimulated to initiate DNA synthesis by the combination of a phorbol ester protein kinase C (PKC) agonist, and a calcium ionophore; in contrast, recent work from this laboratory has shown that peritoneal B cells, enriched for the Ly-1+ B cell subset, differ in that they proliferate in response to the single signal provided by phorbol ester, acting alone. To elucidate the mechanism responsible for the abbreviated signaling requirement of peritoneal B cells, studies of intracellular Ca2+ and PKC were carried out. Measurements using the calcium sensitive dye, Indo-1, showed that base line levels of intracellular Ca2+ in peritoneal B cells were similar to those of splenic B cells, and that there was no change as a result of phorbol ester treatment. However, measurements of PKC based on the phosphorylation of histone showed enzymatic activity in peritoneal B cells to be about 60% greater than that of splenic B cells on a per microgram protein basis. Furthermore, this difference was accentuated by phorbol ester treatment, so that after 4 h, membrane and cytosol fractions from peritoneal B cells contained more than 5 times the PKC activity of the corresponding splenic B cell fractions because the down-regulation of PKC was relatively delayed in peritoneal B cells. This could not be accounted for by the onset of new PKC synthesis, but may relate to the finding that peritoneal B cells express more of the alpha-isoenzyme of PKC than splenic B cells, as shown by immunoblot analysis. Together with data from experiments using the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride(H7), these results suggest that PKC activity remaining hours after phorbol ester treatment may contribute to the unusual phorbol ester responsiveness of peritoneal B cells, and indicate that B cells from separate anatomic locations differ in terms of several parameters relating to the activity and behavior of PKC.

Elevated levels of protein kinase C activity and alpha-isoenzyme expression in murine peritoneal B cells

Conventional murine splenic B cells are stimulated to initiate DNA synthesis by the combination of a phorbol ester protein kinase C (PKC) agonist, and a calcium ionophore; in contrast, recent work from this laboratory has shown that peritoneal B cells, enriched for the Ly-1+ B cell subset, differ in that they proliferate in response to the single signal provided by phorbol ester, acting alone. To elucidate the mechanism responsible for the abbreviated signaling requirement of peritoneal B cells, studies of intracellular Ca2+ and PKC were carried out. Measurements using the calcium sensitive dye, Indo-1, showed that base line levels of intracellular Ca2+ in peritoneal B cells were similar to those of splenic B cells, and that there was no change as a result of phorbol ester treatment. However, measurements of PKC based on the phosphorylation of histone showed enzymatic activity in peritoneal B cells to be about 60% greater than that of splenic B cells on a per microgram protein basis. Furthermore, this difference was accentuated by phorbol ester treatment, so that after 4 h, membrane and cytosol fractions from peritoneal B cells contained more than 5 times the PKC activity of the corresponding splenic B cell fractions because the down-regulation of PKC was relatively delayed in peritoneal B cells. This could not be accounted for by the onset of new PKC synthesis, but may relate to the finding that peritoneal B cells express more of the alpha-isoenzyme of PKC than splenic B cells, as shown by immunoblot analysis. Together with data from experiments using the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride(H7), these results suggest that PKC activity remaining hours after phorbol ester treatment may contribute to the unusual phorbol ester responsiveness of peritoneal B cells, and indicate that B cells from separate anatomic locations differ in terms of several parameters relating to the activity and behavior of PKC.

Adenosine 3',5'-cyclic monophosphate modulates the mitogenic responses of murine B lymphocytes

Adenosine 3',5'-cyclic monophosphate (cAMP) acts to inhibit a number of lymphocyte activities. The extent of this inhibition was tested by evaluating the effects of two cAMP-raising agents on B cell S phase entry induced by several different mitogenic regimens. It was found that both dibutyryl cAMP (dbcAMP) and isobutylmethylxanthine (IBMX) enhanced S phase entry induced by some regimens but inhibited S phase entry induced by others. The observed enhancing activity stands in contrast to the general notion of cAMP as being a "negative regulator," and it confirms that the observed inhibiting activity does not simply reflect cytotoxicity. Mitogenic regimens that appear to mimic each other, such as F(ab')2 fragments of goat anti-mouse immunoglobulin and the combination of a calcium ionophore and a phorbol ester, were distinguished by their responses to the addition of the two cAMP-raising agents. B cell responses were enhanced or inhibited even when dbcAMP was added 18-24 hr after the establishment of cultures. Cyclic AMP may regulate in a complex fashion S phase entry in cells of the immune system.

Host responses to Borrelia burgdorferi in dogs and horses

By using paired sera the IgM and IgG host responses were analyzed in dogs with ELISA and Western blot techniques. Antibodies in clinical seropositive dogs bound to 4-25 IgM and up to 40 or more IgG antigenic determinants. Early IgM response to the 41-kDa flagellin persisted for at least 9 months and involved as many as seven other peptides. IgG response expanded later in the disease and involved more immunogens than are currently recognized in late human disease. A percentage of asymptomatic dogs that later developed clinical symptoms were seropositive. Immunoblot studies suggested that B. burgdorferi is persistent in both asymptomatic and weakly reactive animals and if untreated could lead to disease expression. Clinical seropositive, asymptomatic seronegative, and experimentally infected horses were similarly studied. In experimentally inoculated animals IgG antibodies were initially bound to flagellin and later to the 34- and 31-kDa polypeptides, even though ELISA values were considered only slightly reactive.

Catechol estrogens and thrombosis: lack of a direct effect of 2-hydroxyestradiol on platelets

Women who use the oral contraceptive pill are at risk for a variety of thromboembolic complications, but the precise mechanism is unclear. Since 2-hydroxyestradiol is a major metabolite of estradiol and possesses some of the structural and functional properties of catecholamines, we examined whether this compound might influence thrombogenesis, in particular whether it would exert an epinephrine-like effect on the platelet. In vitro, 2-hydroxyestradiol does not cause or potentiate aggregation or thromboxane release, nor does it prevent the rise in cyclic AMP caused by anti-aggregatory prostaglandins. While 2-hydroxyestradiol does not exert a direct effect on the platelet in vitro, it may play a role in thrombosis in women who take oral contraceptives through another mechanism.