International Variation in Criteria for Internal Mammary Chain Radiotherapy

AIMS

Evidence has emerged that internal mammary chain (IMC) radiotherapy reduces breast cancer mortality, leading to changes in treatment guidelines. This study investigated current IMC radiotherapy criteria and the percentages of patients irradiated for breast cancer in England who fulfilled them.

MATERIALS AND METHODS

A systematic search was undertaken for national guidelines published in English during 2013-2018 presenting criteria for 'consideration of' or 'recommendation for' IMC radiotherapy. Patient and tumour variables were collected for patients who received breast cancer radiotherapy in England during 2012-2016. The percentages of patients fulfilling criteria stipulated in each set of guidelines were calculated.

RESULTS

In total, 111 729 women were recorded as receiving adjuvant breast cancer radiotherapy in England during 2012-2016 and full data were available on 48 095 of them. Percentages of patients fulfilling IMC radiotherapy criteria in various national guidelines were: UK Royal College of Radiologists 13% (6035/48 095), UK National Institute for Health and Care Excellence 18% (8816/48 095), Germany 32% (15 646/48 095), Ireland 56% (26 846/48 095) and USA 59% (28 373/48 095). Differences between countries occurred because in Ireland and the USA, treatment may be considered in some node-negative patients, whereas in the UK, treatment is considered if at least four axillary nodes are involved or for high-risk patients with one to three positive nodes. In Germany, treatment may be considered for all node-positive patients.

CONCLUSIONS

There is substantial variability between countries in criteria for consideration of IMC radiotherapy, despite guidelines being based on the same evidence. This will probably lead to large variations in practice and resource needs worldwide.

Use of lipid composition and metabolism to examine structure and activity of estuarine detrital microflora

Earlier studies have shown that the activity of the estuarine detrital microflora measured by various enzyme activities, muramic acid and adenosine 5'-triphosphate (ATP) content, heterotrophic potentials, and respiratory activities correlates with the incorporation of C and P into the microbial lipids. In this study, these lipids were reproducibly fractionated into neutral lipid, glycolipid, and phospholipid classes. Distinct differences between the active microflora of oak leaves, sweet gum leaves, and pine needles were evidenced both in the rate of lipid synthesis and in the proportions of neutral lipids, glycolipids, and phospholipids. Successional changes in the microflora of leaves incubated in a semitropical estuary, previously suggested by ATP-to-muramic acid ratios and scanning electron micrography, were reflected in changes in the proportions of C in major lipid classes when analyzed from the same type of detritus. Short incubation times with C gave lipid compositions rich in phospholipids that are typical for the faster-growing bacterial populations; longer incubation with C gave lipid compositions richer in neutral and glycolipids, more characteristic of slower-growing eukaryotes or morphologically more complex prokaryotes. The metabolism of the lipids of the estuarine detrital microflora was examined by a pulse-chase experiment with C. Glycolipids lost C at a rate equal to the loss of C of the slow component of muramic acid. Individual phospholipids lost C from their backbone glycerol esters at different rates.

Plasma membrane IP3 receptors

IP3Rs (inositol 1,4,5-trisphosphate receptors) are expressed in the membranes of non-mitochondrial organelles in most animal cells, but their presence and role within the plasma membrane are unclear. Whole-cell patch-clamp recording from DT40 cells expressing native or mutated IP3Rs has established that each cell expresses just two or three functional IP3Rs in its plasma membrane. Only approx. 50% of the Ca2+ entry evoked by stimulation of the B-cell receptor is mediated by store-operated Ca2+ entry, the remainder appears to be carried by the IP3Rs expressed in the plasma membrane. Ca2+ entering the cell via just two large-conductance IP3Rs is likely to have very different functional consequences from the comparable amount of Ca2+ that enters through the several thousand low-conductance store-operated channels.

Signalling from parathyroid hormone

PTH (parathyroid hormone), acting via type 1 PTH receptors, is a major regulator of plasma [Ca(2+)]. The G-protein, G(s), is an essential component of the sequence linking PTH to plasma Ca(2+) regulation, but the relative importance of intracellular signals, including Ca(2+) and cAMP, that lie downstream of G(s) is not resolved.

Cardiac Risks of Breast-cancer Radiotherapy: A Contemporary View

For some time, there has been compelling evidence both from randomised-controlled trials and from observational studies, that some of the breast-cancer radiotherapy regimens used in the past have led to increased risk of mortality from heart disease. There is also some evidence that the more recent regimens used in the USA are associated with lower risks than previous ones, but it is not clear whether current regimens are free from cardiac risk, especially in the light of recent evidence from the survivors of the bombings of Hiroshima and Nagasaki, in whom a clear relationship was observed between the risk of mortality from heart disease and radiation dose for doses in the range 0-4 Gy. Mortality from radiation-induced heart disease usually occurs at least a decade after irradiation. Symptomatic heart disease might have a much shorter induction period, but little information about it is available at present. Subclinical vascular abnormalities have been observed within months of irradiation, via myocardial perfusion imaging studies, but little is known about the relationship between these and later overt heart disease. At present, few data relate heart dose and other specific characteristics of breast radiotherapy to cardiac outcome. Further information on these topics is needed to enable estimation of the cardiac risk, that is likely to arise from radiotherapy regimens in current use and from those being considered for future use. Such knowledge would facilitate radiotherapy treatment planning and enable a reduction in cardiac risk while maintaining the known benefit in terms of breast cancer mortality.

Leukemic infiltration of the orbit: report of three cases and literature review

Orbital infiltration by acute lymphoblastic leukemia is rare. The authors present 3 patients, 2 with optic nerve involvement and 1 with anterior chamber infiltration, treated by chemotherapy and radiotherapy. Two are in continuous remission at 64 and 59 months and 1 relapsed in the central nervous system 35 months after ocular relapse. Visual deterioration was prevented in two. Early diagnosis and treatment are important for preservation of vision.

Oncological aspects of breast reconstruction

Breast reconstruction has become increasingly popular over the past 20 years. There is concern that it may mask locoregional recurrence or that immediate reconstruction may compromise adjuvant treatments. We review available evidence regarding its oncological safety. The literature consists almost entirely of single institution, small retrospective reviews with variable follow-up and varying conclusions. Most reviews suggest that breast reconstruction does not adversely affect disease-free or overall survival and that there is no significant delay in presentation with recurrent disease. Three retrospective series compared chemotherapy delivery after immediate breast reconstruction with controls having mastectomy alone. No delay in chemotherapy delivery or effect on dose intensity was demonstrated. Irradiation of a prosthetic implant has been shown to increase the rate of capsular contracture; irradiation of autogenous tissue reconstruction is usually well tolerated.

The effect of immediate breast reconstruction on adjuvant chemotherapy

Immediate breast reconstruction is being increasingly offered to patients requiring mastectomy for breast cancer. An audit was carried out to determine whether it affected time to initiation of chemotherapy, delays during chemotherapy, percentage intended dose and need for support with antibiotics or granulocyte-colony stimulating factor. A total of 44 patients undergoing a variety of reconstructive procedures followed by chemotherapy were identified and patient records were reviewed. These were compared with a control group of 49 patients undergoing mastectomy alone and chemotherapy in the same 4-year period and institution. Patients undergoing transverse rectus abdominis myocutaneous flap reconstruction experienced an average of 5 more days delay to chemotherapy initiation than controls with the commonest reason being poor wound healing. Percentage intended dose, delays during chemotherapy and need for support with granulocyte-colony stimulating factor or antibiotics were comparable in all groups.

IP3 receptors and their regulation by calmodulin and cytosolic Ca2+

Inositol 1,4,5-trisphosphate (IP(3)) receptors are tetrameric intracellular Ca(2+) channels, the opening of which is regulated by both IP(3) and Ca(2+). We suggest that all IP(3) receptors are biphasically regulated by cytosolic Ca(2+), which binds to two distinct sites. IP(3) promotes channel opening by controlling whether Ca(2+) binds to the stimulatory or inhibitory sites. The stimulatory site is probably an integral part of the receptor lying just upstream of the pore region. Inhibition of IP(3) receptors by Ca(2+) probably requires an accessory protein, which has not yet been unequivocally identified, but calmodulin is a prime candidate. We speculate that one lobe of calmodulin tethers it to the IP(3) receptor, while the other lobe can bind Ca(2+) and then interact with a second site on the receptor to cause inhibition.

T-level downstaging and complete pathologic response after preoperative chemoradiation for advanced rectal cancer result in decreased recurrence and improved disease-free survival

PURPOSE

Preoperative chemoradiation therapy is used widely in the treatment of rectal cancer. The predictive value of response to neoadjuvant remains uncertain. We retrospectively evaluated the impact of response to preoperative and, specifically, of T-level downstaging, nodal downstaging, and complete pathologic response after chemoradiation therapy on oncologic outcome of patients with locally advanced rectal cancer.

METHODS

There were 88 patients with ultrasound Stage T3/T4 midrectal (n = 37) and low rectal (n = 51) cancers (63 males; mean age 62.6 years). All patients were treated by preoperative 5-fluorouracil-based chemotherapy and pelvic radiation followed by surgical resection in six weeks or longer (56 sphincter-preserving resections).

RESULTS

T-level downstaging after neoadjuvant treatment was demonstrated in 36 (41 percent) of 88 patients, and complete pathologic response was observed in 16 (18 percent) of the 88. Of the 42 patients with ultrasound-positive nodes, 27 had no evidence of nodal involvement on pathologic evaluation (64 percent). The overall response rate (T-level downstaging or nodal downstaging) was 51 percent. At a median follow-up of 33 months, 86.4 percent of patients were alive. The overall recurrence rate was 10.2 percent (three patients had local and six had metastatic recurrences). Patients with T-level downstaging and complete pathologic response were characterized by significantly better disease-free survival (P = 0.03, P = 0.04) and better overall survival (P = 0.07, P = 0.08), according to Wilcoxon's test comparing Kaplan-Meier survival curves. None of the patients with complete pathologic response developed recurrence or died during the follow-up period.

CONCLUSION

T-level downstaging and complete pathologic response after preoperative chemoradiation therapy followed by definitive surgical resection for advanced rectal cancer resulted in decreased recurrence and improved disease-free survival. Advanced rectal cancers that undergo T-level downstaging and complete pathologic response after chemoradiation therapy may represent subgroups that are characterized by better biologic behavior.

Functional properties of Drosophila inositol trisphosphate receptors

The functional properties of the only inositol trisphosphate (IP(3)) receptor subtype expressed in Drosophila were examined in permeabilized S2 cells. The IP(3) receptors of S2 cells bound (1,4,5)IP(3) with high affinity (K(d)=8.5+/-1.1 nM), mediated positively co-operative Ca(2+) release from a thapsigargin-sensitive Ca(2+) store (EC(50)=75+/-4 nM, Hill coefficient=2.1+/-0.2), and they were recognized by an antiserum to a peptide conserved in all IP(3) receptor subtypes in the same way as mammalian IP(3) receptors. As with mammalian IP(3) receptors, (2,4,5)IP(3) (EC(50)=2.3+/-0.3 microM) and (4,5)IP(2) (EC(50) approx. 10 microM) were approx. 20- and 100-fold less potent than (1,4,5)IP(3). Adenophostin A, which is typically approx. 10-fold more potent than IP(3) at mammalian IP(3) receptors, was 46-fold more potent than IP(3) in S2 cells (EC(50)=1.67+/-0.07 nM). Responses to submaximal concentrations of IP(3) were quantal and IP(3)-evoked Ca(2+) release was biphasically regulated by cytosolic Ca(2+). Using rapid superfusion to examine the kinetics of IP(3)-evoked Ca(2+) release from S2 cells, we established that IP(3) (10 microM) maximally activated Drosophila IP(3) receptors within 400 ms. The activity of the receptors then slowly decayed (t(1/2)=2.03+/-0.07 s) to a stable state which had 47+/-1% of the activity of the maximally active state. We conclude that the single subtype of IP(3) receptor expressed in Drosophila has similar functional properties to mammalian IP(3) receptors and that analyses of IP(3) receptor function in this genetically tractable organism are therefore likely to contribute to understanding the roles of mammalian IP(3) receptors.

Calcium signalling: IP3 rises again...and again

Recent results indicate that 'regulators of G-protein signalling' may contribute to the generation of receptor-specific patterns of cytosolic Ca2+ oscillations by associating with specific receptors, accelerating G-protein inactivation and responding to changes in cytosolic Ca2+.

Destabilization of steroid receptors by heat shock protein 90-binding drugs: a ligand-independent approach to hormonal therapy of breast cancer

Steroid hormone receptors have become an important target in the management of breast cancers. Despite a good initial response rate, however, most tumors become refractory to current hormonal therapies within a year of starting treatment. To address this problem, we evaluated the effects of agents that bind the molecular chaperone heat shock protein 90 (Hsp90) on estrogen receptor function in breast cancer. Unstimulated estrogen and progesterone receptors exist as multimolecular complexes consisting of the hormone-binding protein itself and several essential molecular chaperones including Hsp90. We found that interaction of the Hsp90-binding drugs geldanamycin and radicicol with the chaperone destabilizes these hormone receptors in a ligand-independent manner, leading to profound and prolonged depletion of their levels in breast cancer cells cultured in vitro. Consistent with these findings, in vivo administration of the geldanamycin derivative 17-allylaminogeldanamycin (17AAG; NSC330507) to estrogen-supplemented, tumor-bearing SCID mice resulted in marked depletion of progesterone receptor levels in both uterus and tumor. Drug administration also delayed the growth of established, hormone-responsive MCF-7 and T47D human tumor xenografts for up to 3 weeks after the initiation of therapy. We conclude that in light of their novel mechanism of anti-hormone action, consideration should be given to examining the activity of 17AAG and other Hsp90-binding agents in patients with refractory breast cancer in future clinical trials, either alone or in combination with conventional hormone antagonists.

Bicyclic analogues of D-myo-inositol 1,4,5-trisphosphate related to adenophostin A: synthesis and biological activity

The high affinity of adenophostin A for 1D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] receptors may be related to an alteration in the position of its 2'-phosphate group relative to the corresponding 1-phosphate group in Ins(1,4,5)P(3). To investigate this possibility, two bicyclic trisphosphates 9 and 10, designed to explore the effect of relocating the 1-phosphate group of Ins(1,4,5)P(3) using a novel fused-ring system, were synthesized from myo-inositol. Biological evaluation of 9 and 10 at the Ins(1,4,5)P(3) receptors of hepatocytes showed that both were recognized by hepatic Ins(1,4,5)P(3) receptors and both stimulated release of Ca(2+) from intracellular stores, but they had lower affinity than Ins(1,4,5)P(3). This finding may be explained by considering the three-dimensional structures of 9 and 10 in light of recent studies on the conformation of adenophostin A.

Xylopyranoside-based agonists of D-myo-inositol 1,4,5-trisphosphate receptors: synthesis and effect of stereochemistry on biological activity

The synthesis of a series of tetrahydrofuranyl alpha- and beta-xylopyranoside trisphosphates, designed by excision of three motifs of adenophostin A is reported. The synthetic route features improved preparations of allyl alpha-D-xylopyranoside and its 2-O-benzyl ether, and gives access to four diastereoisomeric trisphosphates, which show a range of abilities to mobilise Ca2+ from the intracellular stores of hepatocytes. A comparison of the potencies of the four trisphosphates provides useful information relating to the effects of stereochemical variation on the recognition of carbohydrate-based trisphosphates by D-myo-inositol 1,4,5-trisphosphate receptors. 1-O-[(3'S,4'R)-3-hydroxytetrahydrofuran-4-yl] alpha-D-xylopyranoside 3,4,3'-trisphosphate (8) is the most active member of the series with a potency close to Ins(1,4,5)P3; a beta-linked analogue, 1-O-[(3'R,4'S)-3-hydroxytetrahydrofuran-4-yl] beta-D-xylopyranoside 3,4,3'-trisphosphate, is ca. 20-fold weaker than Ins(1,4,5)P3, and the other compounds are much less active. While no compound attained a potency close to that of adenophostin A, we believe that 8 represents the minimal structure for potent Ca2+-releasing activity in this type of carbohydrate-based analogue.

Structural determinants of adenophostin A activity at inositol trisphosphate receptors

Adenophostin A is the most potent known agonist of inositol 1,4,5-trisphosphate (InsP(3)) receptors. Ca(2+) release from permeabilized hepatocytes was 9.9 +/- 1.6-fold more sensitive to adenophostin A (EC(50), 14.7 +/- 2.4 nM) than to InsP(3) (145 +/- 10 nM), consistent with the greater affinity of adenophostin A for hepatic InsP(3) receptors (K(d) = 0.48 +/- 0.06 and 3.09 +/- 0.33 nM, respectively). Here, we systematically modify the structures of the glucose, ribose, and adenine moieties of adenophostin A and use Ca(2+) release and binding assays to define their contributions to high-affinity binding. Progressive trimming of the adenine of adenophostin A reduced potency, but it fell below that of InsP(3) only after complete removal of the adenine. Even after substantial modifications of the adenine (to uracil or even unrelated aromatic rings, retaining the beta-orientation), the analogs were more potent than InsP(3). The only analog with an alpha-ribosyl linkage had massively decreased potency. The 2'-phosphate on the ribose ring of adenophostin A was essential and optimally active when present on a five-membered ring in a position stereochemically equivalent to its location in adenophostin A. Xylo-adenophostin, where xylose replaces the glucose ring of adenophostin A, was only slightly less potent than adenophostin A, whereas manno-adenophostin (mannose replacing glucose) had similar potency to InsP(3). These results are consistent with the relatively minor role of the 3-hydroxyl of InsP(3) (the equivalent is absent from xylo-adenophostin) and greater role of the equatorial 6-hydroxyl (the equivalent is axial in manno-adenophostin). This is the first comprehensive analysis of all the key structural elements of adenophostin A, and it provides a working model for the design of related high-affinity ligands of InsP(3) receptors.

Dysphagia and thoracoabdominal aneurysm

Two elderly patients who presented with gradually progressive dysphagia are described. Investigations excluded an intraluminal obstruction and showed extrinsic compression of the oesophagus by an aneurysmal aorta. Surgery was not performed and they were successfully managed with a liquid diet.

Selective recognition of inositol phosphates by subtypes of the inositol trisphosphate receptor

Synthetic analogues of inositol trisphosphate (IP(3)), all of which included structures equivalent to the 4,5-bisphosphate of (1,4,5)IP(3), were used to probe the recognition properties of rat full-length type 1, 2 and 3 IP(3) receptors expressed in insect Spodoptera frugiperda 9 cells. Using equilibrium competition binding with [(3)H](1,4,5)IP(3) in Ca(2+)-free cytosol-like medium, the relative affinities of the receptor subtypes for (1,4,5)IP(3) were type 3 (K(d)=11+/-2 nM)>type 2 (K(d)=17+/-2 nM)>type 1 (K(d)=24+/-4 nM). (1,4,5)IP(3) binding was reversibly stimulated by increased pH, but the subtypes differed in their sensitivity to pH (type 1>type 2>type 3). For all three subtypes, the equatorial 6-hydroxy group of (1,4,5)IP(3) was essential for high-affinity binding, the equatorial 3-hydroxy group significantly improved affinity, and the axial 2-hydroxy group was insignificant; a 1-phosphate (or in its absence, a 2-phosphate) improved binding affinity. The subtypes differed in the extents to which they tolerated inversion of the 3-hydroxy group of (1,4,5)IP(3) (type 1>type 2>type 3), and this probably accounts for the selectivity of (1,4,6)IP(3) for type 1 receptors. They also differed in their tolerance of inversion, removal or substitution (by phosphate) of the 2-hydroxy group (types 2 and 3>type 1), hence the selectivity of (1,2,4,5)IP(4) for type 2 and 3 receptors. Removal of the 3-hydroxy group or its replacement by fluorine or CH(2)OH was best tolerated by type 3 receptors, and accounts for the selectivity of 3-deoxy(1,4,5)IP(3) for type 3 receptors. Our results provide the first systematic analysis of the recognition properties of IP(3) receptor subtypes and have identified the 2- and 3-positions of (1,4,5)IP(3) as key determinants of subtype selectivity.

Single umbilical artery is associated with an increased incidence of structural and chromosomal anomalies and growth restriction

The objective to characterize neonatal outcome associated with ultrasonographic identification of a single umbilical artery. Pregnancies diagnosed with single umbilical artery antenatally were identified. All prenatal/antenatal and pediatric records were reviewed for maternal demographics, associated anomalies, karyotypic analysis, pregnancy complications, and neonatal outcome. Twenty-seven pregnancies complicated by fetal single umbilical artery were identified. Of the 27 pregnancies, 5 (18.5%) underwent pregnancy termination and 1 (3.7%) experienced fetal demise. Of the 21 liveborn infants, 4 (19%) died within the first year of life. Sixty-seven percent of fetuses had an associated structural anomaly. Sixteen of the 27 pregnancies underwent amniocentesis and 7 of these were chromosomally abnormal. All of the karyotypically abnormal fetuses had a structural defect in addition to the single umbilical artery. Of the six fetuses without any associated structural or chromosomal anomalies, three (50%) demonstrated growth restriction. Single umbilical artery is relatively rare finding. When a single umbilical artery is identified, a vigilant search for associated anomalies should be undertaken. Pregnancies identified as having fetuses with associated structural anomalies should be offered amniocentesis. Pregnancies with isolated single umbilical artery should be carefully monitored for evidence of fetal growth restriction.

A phase I and pharmacodynamic evaluation of polyethylene glycol-conjugated L-asparaginase in patients with advanced solid tumors

PURPOSE

To evaluate the in vitro activity of polyethylene glycol-conjugated L-asparaginase (PEG-Lasparaginase) against fresh human tumor specimens, using the human tumor clonogenic assay (HTCA), and to perform a phase I dose-escalation clinical trial of PEG-L-asparaginase. The goal of the clinical study was to determine the toxicity and optimum biologic dose of PEG-L-asparaginase based on depletion of serum L-asparagine in patients with advanced solid tumors.

METHODS

A modified method for determination of serum L-asparagine is described. PEG-L-asparaginase was administered by intramuscular injection every 2 weeks to 28 patients with various types of advanced solid tumor malignancies. At least 3 patients were evaluated at each dose level: 250 IU/m2, 500 IU/m2, 1,000 IU/m2, 1,500 IU/m2, 2,000 IU/m2.

RESULTS

The in vitro HTCA studies suggested good antitumor activity against malignant melanoma and multiple myeloma. Serum L-asparagine was most consistently and profoundly depleted (up to 4 weeks) in patients treated with 2,000 IU/m2. Patients receiving this dose level also showed more frequent grade 1, grade 2, and occasional grade 3 toxicities of fatigue/weakness, nausea/vomiting, and anorexia/ weight loss. Three patients developed hypersensitivity reactions, but these were not dose related. Two patients developed deep vein thromboses. We saw no episodes of clinical pancreatitis, but there were minor fluctuations of serum amylase and lipase. We saw no partial or complete responses in patients treated in this study, including 11 patients with malignant melanoma.

CONCLUSIONS

We conclude that PEG-L-asparaginase is generally well tolerated in patients with advanced solid tumors, and a dosage of 2,000 IU/m2 by intramuscular injection every 2 weeks results in significant depletion of serum L-asparagine.

Crucial role of type 1, but not type 3, inositol 1,4,5-trisphosphate (IP(3)) receptors in IP(3)-induced Ca(2+) release, capacitative Ca(2+) entry, and proliferation of A7r5 vascular smooth muscle cells

Stimulation of G protein- or tyrosine kinase-coupled receptors regulates cell proliferation through intracellular Ca(2+) ([Ca(2+)](i)) signaling. In A7r5 cells, we confirmed that inositol 1,4,5-trisphosphate (IP(3)) mediates vasopressin (VP)-evoked Ca(2+) release from intracellular stores and showed that types 1 (IP(3)R(1)) and 3 (IP(3)R(3)) IP(3) receptors were expressed. Using antisera selective for IP(3)R(1) or IP(3)R(3) and another that interacted equally well with both subtypes, together with membranes from SF:9 cells expressing only single IP(3)R subtypes to calibrate immunoblotting, we established that A7r5 cells express 81% IP(3)R(1) and 19% IP(3)R(3). To elucidate the contributions of IP(3)R(1) and IP(3)R(3) to Ca(2+) signaling and proliferation, stable clones expressing promoter-inducible antisense cDNA fragments (-90 to +9) corresponding to the two IP(3)R subtypes were selected. Mild inhibition of IP(3)R(1) (71+/-8% of control level) slightly attenuated the IP(3)-evoked Ca(2+) release (IICR) induced by VP but significantly decreased the subsequent capacitative Ca(2+) entry (CCE) and proliferation. Moderate inhibition (34+/-6%) strongly decreased both IICR and CCE and further blocked proliferation. Complete inhibition almost abolished IICR and CCE and arrested proliferation entirely. Complete inhibition of IP(3)R(3) expression slightly attenuated IICR without affecting CCE or proliferation. In cells microinjected with a low dose of heparin, VP-induced CCE was more susceptible than IICR to mild inhibition of both IP(3)R(1) and IP(3)R(3). A high dose of heparin had a similar effect to complete inhibition of IP(3)R(1) expression: it blocked VP-evoked IICR entirely and CCE by 90%. We conclude that IP(3)R(1), but not IP(3)R(3), is crucial for IICR, CCE, and proliferation of vascular smooth muscle cells.

Rapid activation and partial inactivation of inositol trisphosphate receptors by adenophostin A

Adenophostin A, the most potent known agonist of inositol 1,4, 5-trisphosphate (InsP(3)) receptors, stimulated (45)Ca(2+) release from the intracellular stores of permeabilized hepatocytes. The concentration of adenophostin A causing the half-maximal effect (EC(50)) was 7.1+/-0.5 nM, whereas the EC(50) for InsP(3) was 177+/-26 nM; both responses were positively co-operative. In rapid superfusion analyses of (45)Ca(2+) release from the intracellular stores of immobilized hepatocytes, maximal concentrations of adenophostin A or InsP(3) evoked indistinguishable patterns of Ca(2+) release. The Ca(2+) release evoked by both agonists peaked at the same maximal rate after about 375 ms and the activity of the receptors then decayed to a stable, partially (60%) inactivated state with a half-time (t(1/2)) of 318+/-29 ms for adenophostin A and 321+/-22 ms for InsP(3). Dissociation rates were measured by recording rates of InsP(3)-receptor channel closure after rapid removal of agonist. The rate of adenophostin A dissociation (t(1/2), 840+/-195 ms) was only 2-fold slower than that of InsP(3) (t(1/2), 436+/-48 ms). We conclude that slow dissociation of adenophostin A from InsP(3) receptors does not underlie either its high-affinity binding or the reported differences in the Ca(2+) signals evoked by InsP(3) and adenophostin A in intact cells.

Contribution of the adenine base to the activity of adenophostin A investigated using a base replacement strategy

Syntheses of 3'-O-alpha-D-glucopyranosyl-1-beta-D-ribofuranosidoimidazole 2',3'', 4''-trisphosphate (7) and 3'-O-alpha-D-glucopyranosyl-9-beta-D-ribofuranosidopurine 2',3'',4''- trisphosphate (8), two analogues of the superpotent 1D-myo-inositol 1,4,5-trisphosphate receptor agonist adenophostin A (2), are described. 5-O-Benzyl-1, 2-O-isopropylidene-alpha-D-ribofuranose was prepared by an improved route from 1,2-O-isopropylidene-alpha-D-xylofuranose and was coupled with 3,4-di-O-acetyl-2,6-di-O-benzyl-D-glucopyranosyl dimethyl phosphite to give 3',4'-di-O-acetyl-2',5, 6'-tri-O-benzyl-3-O-alpha-D-glucopyranosyl-1, 2-O-isopropylidene-alpha-D-ribofuranose. Removal of the isopropylidene acetal and subsequent acetylation gave the central disaccharide 1,2,3',4'-tetra-O-acetyl-2',5, 6'-tri-O-benzyl-3-O-alpha-D-glucopyranosyl-D-ribofuranose. Vorbrüggen condensation with activated imidazole or purine gave the required beta-substituted derivatives which were further elaborated to 7 and 8, respectively. Radioligand binding assays to hepatic InsP(3) receptors and functional assays of Ca(2+) release from permeabilized hepatocytes gave a rank order of potency of the ligands 2 approximately 8 > 7 approximately Ins(1,4,5)P(3) indicating that the N(6)-amino group of 2 is of little importance for activity and that a minimum of a two-fused-ring nucleobase is required for activity to exceed that of Ins(1,4,5)P(3). The role of the adenine base in the activity of the adenophostins is discussed. This general method should facilitate ready access to nucleobase-modified adenophostin analogues for SAR studies.

Different receptors use inositol trisphosphate to mobilize Ca(2+) from different intracellular pools

In cells expressing different receptors linked to Ins(1,4,5)P(3) formation, maximal stimulation of any one of them often releases all the Ins(1,4,5)P(3)-sensitive Ca(2+) stores, suggesting that Ins(1,4, 5)P(3) is used similarly by many receptors. In single HEK-293 cells, ATP and carbamylcholine (CCh) stimulated Ca(2+) release from intracellular stores via a pathway that was entirely dependent on Ins(1,4,5)P(3). After stimulation with maximal concentrations of ATP or CCh in Ca(2+)-free medium, there was no response to a second stimulation with the same agonist, indicating that each agonist had emptied the Ins(1,4,5)P(3)-sensitive stores to which it had access. However, the Ca(2+) release evoked by the second agonist was unaffected by prior stimulation with the first. We conclude that Ins(1,4,5)P(3) mediates the effects of both receptors, but Ins(1,4, 5)P(3) is more versatile than hitherto supposed, because the spatial organization of the signalling pathways apparently allows Ins(1,4, 5)P(3) made in response to each agonist to interact with different Ins(1,4,5)P(3) receptors.

C-glycoside based mimics of D-myo-inositol 1,4,5-trisphosphate

Epimeric C-glycoside based polyphosphates, alpha- and beta-D-glucopyranosylmethanol 3,4,1'-trisphosphates (8 and 9) were prepared from D-glucose. The key intermediate, allyl 2,6-di-O-benzyl-alpha-D-glucopyranoside, was prepared in five steps (67% yield) from allyl alpha-D-glucopyranoside without the need for chromatography. Compounds 8 and 9 were shown to be full agonists at the Ins(1,4,5)P3 receptors of permeabilised hepatocytes, but with markedly different potencies. Such C-glycoside analogues are worthy of further development as Ins(1,4,5)P, receptor ligands.

Phase II evaluation of interleukin-4 in patients with non-Hodgkin's lymphoma: a Southwest Oncology Group trial

We performed a phase II, Southwest Oncology Group (SWOG) clinical trial of recombinant human interleukin-4 (rhuIL-4) in patients with previously treated non-Hodgkin's lymphoma (NHL). We studied 18 eligible patients with low-grade and 21 patients with intermediate- or high-grade NHL. All patients had received prior chemotherapy. A protocol amendment after the first four patients reduced the frequency of s.c. rhuIL-4 administration from daily to 3 times per week at 3 microg/kg and limited the number of prior chemotherapy regimens allowed. We documented no complete or partial responses in the low-grade NHL group [0%; 95% confidence interval (CI) 0-19%]. One patient in the intermediate/high-grade NHL group developed a partial response lasting longer than 15 months (5%; 95% CI 0-24%). Median survivals for the low- and intermediate/high-grade NHL groups were 15 and 13 months, respectively. Common toxicities included: arhralgia/myalgia, fatigue/malaise/lethargy, fever, headache, nausea and rigors/chills. Cardiac toxicity, gastrointestinal ulceration and nasal congestion due to rhuIL-4 were not prominent toxicities in our patients. Our previously treated NHL patients tolerated s.c. rhuIL-4 at a dose of 3 microg/kg given 3 times per week, but objective response rarely occurred. Further evaluation of rhuIL-4 in these patient populations does not appear warranted.

Synthesis of potent agonists of the D-myo-inositol 1,4, 5-trisphosphate receptor based on clustered disaccharide polyphosphate analogues of adenophostin A

Clustered disaccharide analogues of adenophostin A (2), i.e. mono-, di-, and tetravalent derivatives 6-8, respectively, were synthesized and evaluated as novel ligands for the tetrameric D-myo-inositol 1,4, 5-trisphosphate receptor (IP(3)R). The synthesis was accomplished via Sonogashira coupling of propargyl 2-O-acetyl-5-O-benzyl-3-O-(3, 4-di-O-acetyl-2, 6-di-O-benzyl-alpha-D-glucopyranosyl)-beta-D-ribofuranoside (16) with iodobenzene 18, 22, or 25, followed by deacetylation, phosphorylation, and deprotection. The abilities of the target compounds 6-8, as well as ribophostin 4, propylphostin 5, and IP(3) (1), to evoke Ca(2+) release from permeabilized hepatocytes or displacement of [(3)H]IP(3) from its receptor in hepatic membranes were compared. Although the binding affinities of 4-8 were similar, there were modest though significant differences in their potencies in Ca(2+) release assays: tetraphostin 8 > IP(3) approximately diphostin 7 > phenylphostin 6 > ribophostin 4 approximately propylphostin 5.

Induction of a heat shock factor 1-dependent stress response alters the cytotoxic activity of hsp90-binding agents

In addition to its classic role in the cellular stress response, heat shock protein 90 (Hsp90) plays a critical but less well appreciated role in regulating signal transduction pathways that control cell growth and survival under basal, nonstress conditions. Over the past 5 years, the antitumor antibiotics geldanamycin and radicicol have become recognized as selective Hsp90-binding agents (HBA) with a novel ability to alter the activity of many of the receptors, kinases, and transcription factors involved in these cancer-associated pathways. As a consequence of their interaction with Hsp90, however, these agents also induce a marked cellular heat shock response. To study the mechanism of this response and assess its relevance to the anticancer action of the HBA, we verified that the compounds could activate a reporter construct containing consensus binding sites for heat shock factor 1 (HSF1), the major transcriptional regulator of the vertebrate heat shock response. We then used transformed fibroblasts derived from HSF1 knock-out mice to show that unlike conventional chemotherapeutics, HBA increased the synthesis and cellular levels of heat shock proteins in an HSF1-dependent manner. Compared with transformed fibroblasts derived from wild-type mice, HSF1 knock-out cells were significantly more sensitive to the cytotoxic effects of HBA but not to doxorubicin or cisplatin. Consistent with these in vitro data, we found that systemic administration of an HBA led to marked increases in the level of Hsp72 in both normal mouse tissues and human tumor xenografts. We conclude that HBA are useful probes for studying molecular mechanisms regulating the heat shock response both in cells and in whole animals. Moreover, induction of the heat shock response by HBA will be an important consideration in the clinical application of these drugs, both in terms of modulating their cytotoxic activity as well as monitoring their biological activity in individual patients.

Expression and distribution of InsP(3) receptor subtypes in proliferating vascular smooth muscle cells

The expression and distribution of types 1, 2, and 3 inositol 1,4, 5-trisphosphate receptor (InsP(3)R) in proliferating, primary cultures of rat aortic smooth muscle were compared to fully developed and differentiated rat aortic smooth muscle. Subtype-specific InsP(3)R antibodies revealed that the expression of type 1 InsP(3)R was similar in cultured aortic cells and aorta homogenate but expression of type 2 and 3 InsP(3)R subtypes was increased 3-fold in cultured aortic cells. The distribution of the type 1 InsP(3)R was located throughout the cytoplasm; type 2 InsP(3)R was found closely associated with the nucleus and at the plasma membrane; type 3 InsP(3)R was distributed predominantly around the nucleus. Alterations in InsP(3)R subtype expression and localization may have important functions in regulating intracellular calcium release around the nucleus when vascular smooth muscle cells switch to a more proliferating phenotype.

Parathyroid hormone controls the size of the intracellular Ca(2+) stores available to receptors linked to inositol trisphosphate formation

In HEK 293 cells stably expressing type 1 parathyroid (PTH) receptors, PTH stimulated release of intracellular Ca(2+) stores in only 27% of cells, whereas 96% of cells responded to carbachol. However, in almost all cells PTH potentiated the response to carbachol by about 3-fold. Responses to carbachol did not desensitize, but only the first challenge in Ca(2+)-free medium caused an increase in [Ca(2+)](i), indicating that the carbachol-sensitive Ca(2+) stores had been emptied. Subsequent addition of PTH also failed to increase [Ca(2+)](i), but when it was followed by carbachol there was a substantial increase in [Ca(2+)](i). A similar potentiation was observed between ATP and PTH but not between carbachol and ATP. Intracellular heparin inhibited responses to carbachol and PTH, and pretreatment with ATP and carbachol abolished responses to PTH, suggesting that the effects of PTH involve inositol trisphosphate (IP(3)) receptors. PTH neither stimulated detectable IP(3) formation nor affected the amount formed in response to ATP or carbachol. PTH stimulated cyclic AMP formation, but this was not the means whereby PTH potentiated Ca(2+) signals. We suggest that PTH may regulate Ca(2+) mobilization by facilitating translocation of Ca(2+) between discrete intracellular stores and that it thereby regulates the size of the Ca(2+) pool available to receptors linked to IP(3) formation.

Ca2+-calmodulin inhibits Ca2+ release mediated by type-1, -2 and -3 inositol trisphosphate receptors

InsP(3) binding to type-1, but not type-3, InsP(3) receptors is inhibited by calmodulin in a Ca(2+)-independent fashion [Cardy and Taylor (1998) Biochem. J. 334, 447-455], and Ca(2+) mobilization by type-1 InsP(3) receptors of cerebellum is inhibited by calmodulin [Patel, Morris, Adkins, O'Beirne and Taylor (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 11627-11632]. Using cell types expressing predominantly type-1, -2 or -3 InsP(3) receptors, we show that InsP(3)-evoked Ca(2+) mobilization from each is similarly inhibited by calmodulin. In SH-SY5Y cells, which express largely type-1 receptors, calmodulin (IC(50) approximately 15 microM) inhibited InsP(3)-evoked Ca(2+) release only in the presence of Ca(2+). The inhibition was unaffected by calcineurin inhibitors. The effect of calmodulin did not result from enhanced metabolism of InsP(3) because calmodulin also decreased the sensitivity of the Ca(2+) stores to adenophostin A, a non-metabolizable InsP(3)-receptor agonist. Protein kinase A-catalysed phosphorylation of type-1 InsP(3) receptors was unaffected by Ca(2+)-calmodulin. Using a scintillation proximity assay to measure (125)I-calmodulin binding to glutathione S-transferase-fusion proteins, we identified two regions of the type-1 InsP(3) receptor (cyt1, residues -6 to 159; and cyt11, residues 1499-1649) that bound (125)I-calmodulin. The higher-affinity site (cyt11) was also photoaffinity labelled with N-hydroxysuccinimidyl-4-azidobenzoate (HSAB)-calmodulin. We speculate that Ca(2+)-independent binding of calmodulin to a site within the first 159 residues of the type-1 InsP(3) receptor inhibits InsP(3) binding and may thereby regulate the kinetics of Ca(2+) release. Ca(2+)-dependent inhibition of Ca(2+) release by calmodulin is mediated by a different site: it may reside on an accessory protein that associates with all three receptor subtypes, or Ca(2+)-calmodulin binding to a site lying between residues 1499 and 1649 of the type-1 receptor may inhibit Ca(2+) release from any tetrameric receptor that includes a type-1 subunit.

Type 3 inositol trisphosphate receptors in RINm5F cells are biphasically regulated by cytosolic Ca2+ and mediate quantal Ca2+ mobilization

There are three subtypes of mammalian Ins(1,4,5)P(3) (InsP(3)) receptor, each of which forms an intracellular Ca(2+) channel. Biphasic regulation of InsP(3) receptors by cytosolic Ca(2+) is well documented in cells expressing predominantly type 1 or type 2 InsP(3) receptors and might contribute to the regenerative recruitment of Ca(2+) release events and to limiting their duration in intact cells. The properties of type 3 receptors are less clear. Bilayer recording from InsP(3) receptors of RIN-5F cells, cells in which the InsP(3) receptors are likely to be largely type 3, recently suggested that the receptors are not inhibited by Ca(2+) [Hagar, Burgstahler, Nathanson and Ehrlich (1998) Nature (London) 296, 81-84]. By using antipeptide antisera that either selectively recognized each InsP(3) receptor subtype or interacted equally well with all subtypes, together with membranes from Spodoptera frugiperda (Sf9) cells expressing only single receptor subtypes to calibrate the immunoblotting, we quantified the relative levels of expression of type 1 (17%) and type 3 (77%) InsP(3) receptors in RINm5F cells. In unidirectional (45)Ca(2+) efflux experiments from permeabilized RINm5F cells, submaximal concentrations of InsP(3) released only a fraction of the InsP(3)-sensitive Ca(2+) stores, indicating that responses to InsP(3) are quantal. Increasing the cytosolic free [Ca(2+)] ([Ca(2+)](i)) from approx. 4 to 186 nM increased the sensitivity of the Ca(2+) stores to InsP(3): the EC(50) decreased from 281+/-15 to 82+/-2 nM. Further increases in [Ca(2+)](i) massively decreased the sensitivity of the stores to InsP(3), by almost 10-fold when [Ca(2+)](i) was 2.4 microM, and by more than 3000-fold when it was 100 microM. The inhibition caused by 100 microM Ca(2+) was fully reversed within 60 s of the restoration of [Ca(2+)](i) to 186 nM. The effect of submaximal InsP(3) concentrations on Ca(2+) mobilization from permeabilized RINm5F cells is therefore biphasically regulated by cytosolic Ca(2+). We conclude that type 3 InsP(3) receptors of RINm5F cells mediate quantal Ca(2+) release and they are biphasically regulated by cytosolic Ca(2+), either because a single type 1 subunit within the tetrameric receptor confers the Ca(2+) inhibition or because the type 3 subtype is itself directly inhibited by Ca(2+).

Wortmannin inhibits the growth of mammary tumors despite the existence of a novel wortmannin-insensitive phosphatidylinositol-3-kinase

PURPOSE

Phosphatidylinositol (PtdIns) 3-kinase is an important mediator of many cellular functions. The study of PtdIns 3-kinase has been facilitated by the existence of the potent irreversible inhibitor of p110 PtdIns 3-kinase, wortmannin. The purpose of the study was to investigate the relationship between the cell growth inhibitory activity and antitumor activity of wortmannin and inhibition of PtdIns 3-kinase.

METHODS

PtdIns 3-kinase activity was measured in cells and tumors and the effects of wortmannin investigated.

RESULTS

Wortmannin inhibited the growth of murine C3H and human MCF-7 mammary tumors in vivo. However, the ability of wortmannin to inhibit C3H tumor growth was not related to inhibition of tumor PtdIns 3-kinase activity. The existence of wortmannin-insensitive PtdIns 3-kinase activity was demonstrated in C3H and MCF-7 cell culture lysates and solid tumors, and normal mouse tissue homogenates. In addition to being resistant to inhibition by wortmannin, MCF-7 cell lysate total PtdIns 3-kinase activity was also resistant to five additional known inhibitors of p110 PtdIns 3-kinase. Partial purification of wortmannin-insensitive PtdIns 3-kinase from MCF-7 cell lysate showed the activity to be independent of the PtdIns 3-kinase p85 regulatory subunit.

CONCLUSION

The results of the current study demonstrate that wortmannin can inhibit the growth of murine and human mammary tumors despite the presence of novel wortmannin-insensitive PtdIns 3-kinases in these tissues suggesting that some other target is responsible for wortmannin's antitumor activity.

Lateral inhibition of inositol 1,4,5-trisphosphate receptors by cytosolic Ca(2+)

Ryanodine and inositol 1,4,5-trisphosphate (IP(3)) receptors - two related families of Ca(2+) channels responsible for release of Ca(2+) from intracellular stores [1] - are biphasically regulated by cytosolic Ca(2+) [2] [3] [4]. It is thought that the resulting positive feedback allows localised Ca(2+)-release events to propagate regeneratively, and that the negative feedback limits the amplitude of individual events [5] [6]. Stimulation of IP(3) receptors by Ca(2+) occurs through a Ca(2+)-binding site that becomes exposed only after IP(3) has bound to its receptor [7] [8]. Here, we report that rapid inhibition of IP(3) receptors by Ca(2+) occurs only if the receptor has not bound IP(3). The IP(3) therefore switches its receptor from a state in which only an inhibitory Ca(2+)-binding site is accessible to one in which only a stimulatory site is available. This regulation ensures that Ca(2+) released by an active IP(3) receptor may rapidly inhibit its unliganded neighbours, but it cannot terminate the activity of a receptor with IP(3) bound. Such lateral inhibition, which is a universal feature of sensory systems where it improves contrast and dynamic range, may fulfil similar roles in intracellular Ca(2+) signalling by providing increased sensitivity to IP(3) and allowing rapid graded recruitment of IP(3) receptors.

Receptors linked to polyphosphoinositide hydrolysis stimulate Ca2+ extrusion by a phospholipase C-independent mechanism

In A7r5 cells with empty intracellular Ca(2+) stores in which the cytosolic free Ca(2+) concentration ([Ca(2+)](i)) had been increased by capacitative Ca(2+) entry, stimulation of receptors linked to phospholipase C (PLC), including those for Arg(8)-vasopressin (AVP) and platelet-derived growth factor (PDGF), caused a decrease in [Ca(2+)](i.) This effect was further examined in a stable variant of the A7r5 cell line in which the usual ability of hormones to stimulate non-capacitative Ca(2+) entry is not expresssed. In thapsigargin-treated cells, neither AVP nor PDGF affected capacitative Mn(2+) or Ba(2+) entry, but both stimulated the rate of Ca(2+) extrusion, and their abilities to decrease [Ca(2+)](i) were only partially inhibited by removal of extracellular Na(+). These results suggest that receptors linked to PLC also stimulate plasma membrane Ca(2+) pumps. Activation of protein kinase C by phorbol 12, 13-dibutyrate (PDBu, 1 microM) also caused a decrease in [Ca(2+)](i) by accelerating Ca(2+) removal from the cytosol; the effect was again only partially inhibited by removal of extracellular Na(+). An inhibitor of PKC, Ro31-8220 (10 microM), abolished the ability of PDBu to decrease [Ca(2+)](i), without affecting the response to maximal or submaximal concentrations of AVP. Similar experiments with PDGF were impracticable because Ro31-8220, presumably by inhibiting the tyrosine kinase activity of the PDGF receptor, abolished all responses to PDGF. U73122 (10 microM), an inhibitor of PLC, completely inhibited PDGF- or AVP-evoked Ca(2+) mobilization, without preventing either stimulus from causing a decrease in [Ca(2+)](i). We conclude that receptors coupled to PLC, whether via G-proteins or protein tyrosine kinase activity, also share an ability to stimulate the plasma membrane Ca(2+) pump via a mechanism that does not require PLC activity.

Early increases in breast tumor xenograft water mobility in response to paclitaxel therapy detected by non-invasive diffusion magnetic resonance imaging

An important goal in cancer chemotherapy is to sensitively and quantitatively monitor the response of individual patients' tumors to successful, or unsuccessful, therapy so that regimens can be altered iteratively. Currently, tumor response is monitored by frank changes in tumor morphology, yet these markers take long to manifest and are not quantitative. Recent studies suggest that the apparent diffusion coefficient of water (ADCw), measured noninvasively with magnetic resonance imaging, is sensitively and reliably increased in response to successful CTx. In the present study, we investigate the combination chemotherapy response of human breast cancer tumor xenografts sensitive or resistant to Paclitaxel by monitoring changes in the ADCw. Our results indicate that there is a clear, substantial, and early increase in the ADCw after successful therapy in drug sensitive tumors and that there is no change in the ADCw in p-glycoprotein-positive tumors, which are resistant to Paclitaxel. The mechanism underlying these changes is unknown yet is consistent with apoptotic cell shrinkage and a concomitant increase in the extracellular water fraction.

Overshooting cytosolic Ca2+ signals evoked by capacitative Ca2+ entry result from delayed stimulation of a plasma membrane Ca2+ pump

The effect of capacitative Ca2+ entry on cytosolic free Ca2+ concentration ([Ca2+]c) was examined in calf pulmonary artery endothelial cells treated with thapsigargin. Restoration of extracellular Ca2+ evoked an overshoot in [Ca2+]c: the initial rate of Ca2+ influx was 12.4 +/- 0.5 nM/s as [Ca2+]c rose monoexponentially (time constant, tau = 36 +/- 2 s) to a peak (322 +/- 16 nM) before declining to 109 +/- 14 nM after 2000 s. Rates of Ca2+ removal from the cytosol were measured throughout the overshoot by recording the monoexponential decrease in [Ca2+]c after rapid removal of extracellular Ca2+. The time constant for recovery (tau rec decreased from 54 +/- 4 s when Ca2+ was removed after 10 s to its limiting value of 8.8 +/- 1.0 s when it was removed after 2000 s. The time dependence of the changes in tau rec indicate that an increase in [Ca2+]c is followed by a delayed (tau = 408 s) stimulation of Ca2+ removal, which fully reverses (tau approximately 185 s) after Ca2+ entry ceases. Numerical simulation indicated that the changes in Ca2+ removal were largely responsible for the overshooting pattern of [Ca2+]c. Because prolonged (30 min) Ca2+ entry did not increase the total 45Ca2+ content of the cells, an increased rate of Ca2+ extrusion across the plasma membrane most likely mediates the Ca2+ removal, and since it persists in the absence of extracellular Na+, it probably results from stimulation of a plasma membrane Ca2+ pump. We conclude that delayed stimulation of a plasma membrane Ca2+ pump by capacitative Ca2+ entry may protect cells from excessive increases in [Ca2+]c and contribute to oscillatory changes in [Ca2+]c.

Enhancement of chemotherapy by manipulation of tumour pH

The extracellular (interstitial) pH (pHe) of solid tumours is significantly more acidic compared to normal tissues. In-vitro, low pH reduces the uptake of weakly basic chemotherapeutic drugs and, hence, reduces their cytotoxicity. This phenomenon has been postulated to contribute to a 'physiological' resistance to weakly basic drugs in vivo. Doxorubicin is a weak base chemotherapeutic agent that is commonly used in combination chemotherapy to clinically treat breast cancers. This report demonstrates that MCF-7 human breast cancer cells in vitro are more susceptible to doxorubicin toxicity at pH 7.4, compared to pH 6.8. Furthermore 31P-magnetic resonance spectroscopy (MRS) has shown that the pHe of MCF-7 human breast cancer xenografts can be effectively and significantly raised with sodium bicarbonate in drinking water. The bicarbonate-induced extracellular alkalinization leads to significant improvements in the therapeutic effectiveness of doxorubicin against MCF-7 xenografts in vivo. Although physiological resistance to weakly basic chemotherapeutics is well-documented in vitro and in theory, these data represent the first in vivo demonstration of this important phenomenon.

A non-capacitative pathway activated by arachidonic acid is the major Ca2+ entry mechanism in rat A7r5 smooth muscle cells stimulated with low concentrations of vasopressin

1. Depletion of the Ca2+ stores of A7r5 cells stimulated Ca2+, though not Sr2+, entry. Vasopressin (AVP) or platelet-derived growth factor (PDGF) stimulated Sr2+ entry. The cells therefore express a capacitative pathway activated by empty stores and a non-capacitative pathway stimulated by receptors; only the former is permeable to Mn2+ and only the latter to Sr2+. 2. Neither empty stores nor inositol 1,4,5-trisphosphate (InsP3) binding to its receptors are required for activation of the non-capacitative pathway, because microinjection of cells with heparin prevented PDGF-evoked Ca2+ mobilization but not Sr2+ entry. 3. Low concentrations of Gd3+ irreversibly blocked capacitative Ca2+ entry without affecting AVP-evoked Sr2+ entry. After inhibition of the capacitative pathway with Gd3+, AVP evoked a substantial increase in cytosolic [Ca2+], confirming that the non-capacitative pathway can evoke a significant increase in cytosolic [Ca2+]. 4. Arachidonic acid mimicked the effect of AVP on Sr2+ entry without stimulating Mn2+ entry; the Sr2+ entry was inhibited by 100 microM Gd3+, but not by 1 microM Gd3+ which completely inhibited capacitative Ca2+ entry. The effects of arachidonic acid did not require its metabolism. 5. AVP-evoked Sr2+ entry was unaffected by isotetrandrine, an inhibitor of G protein-coupled phospholipase A2. U73122, an inhibitor of phosphoinositidase C, inhibited AVP-evoked formation of inositol phosphates and Sr2+ entry. The effects of phorbol esters and Ro31-8220 (a protein kinase C inhibitor) established that protein kinase C did not mediate the effects of AVP on the non-capacitative pathway. An inhibitor of diacylglycerol lipase, RHC-80267, inhibited AVP-evoked Sr2+ entry without affecting capacitative Ca2+ entry or release of Ca2+ stores. 6. Selective inhibition of capacitative Ca2+ entry with Gd3+ revealed that the non-capacitative pathway is the major route for the Ca2+ entry evoked by low AVP concentrations. 7. We conclude that in A7r5 cells, the Ca2+ entry evoked by low concentrations of AVP is mediated largely by a non-capacitative pathway directly regulated by arachidonic acid produced by the sequential activities of phosphoinositidase C and diacylglycerol lipase.

Extracellular heavy-metal ions stimulate Ca2+ mobilization in hepatocytes

Populations of hepatocytes in primary culture were loaded with fura 2 and the effects of extracellular heavy-metal ions were examined under conditions that allowed changes in fura 2 fluorescence (R340/360, the ratio of fluorescence recorded at 340 and 360 nm) to be directly attributed to changes in cytosolic free [Ca2+] ([Ca2+]i). In Ca2+-free media, Ni2+ [EC50 (concentration causing 50% stimulation) approximately 24+/-9 microM] caused reversible increases in [Ca2+]i that resulted from mobilization of the same intracellular Ca2+ stores as were released by [Arg8]vasopressin. The effects of Ni2+ were not mimicked by increasing the extracellular [Mg2+], by addition of MnCl2, CoCl2 or CdCl2 or by decreasing the extracellular pH from 7.3 to 6.0; nor were they observed in cultures of smooth muscle, endothelial cells or pituitary cells. CuCl2 (80 microM), ZnCl2 (80 microM) and LaCl3 (5 mM) mimicked the ability of Ni2+ to evoke Ca2+ mobilization. The response to La3+ was sustained even in the absence of extracellular Ca2+, probably because La3+ also inhibited Ca2+ extrusion. Although Ni2+ entered hepatocytes, from the extent to which it quenched fura 2 fluorescence the free cytosolic [Ni2+] ([Ni2+]i) was estimated to be <5 nM at the peak of the maximal Ni2+-evoked Ca2+ signals and there was no correlation between [Ni2+]i and the amplitude of the evoked increases in [Ca2+]i. We conclude that extracellular Ni2+, Zn2+, Cu2+ and La3+, but not all heavy-metal ions, evoke an increase in [Ca2+]i in hepatocytes by stimulating release of the hormone-sensitive intracellular Ca2+ stores and that they may do so by interacting with a specific cell-surface ion receptor. This putative ion receptor may be important in allowing hepatocytes to contribute to regulation of plasma heavy-metal ions and may mediate responses to Zn2+ released into the portal circulation with insulin.

Simplification of adenophostin A defines a minimal structure for potent glucopyranoside-based mimics of D-myo-inositol 1,4,5-trisphosphate

The synthesis of 1-O-[(3S,4R)-3-hydroxytetrahydrofuran-4-yl]-alpha-D-glucopyranosid e 3,4,3'-trisphosphate (7), a novel Ca2+ mobilising agonist at the Ins(1,4,5)P3 receptor, designed by excision of two motifs of adenophostin A is reported, defining a potential minimal structure for potent glucopyranoside-based agonists of Ins(1,4,5)P3 receptors.

Plasmalemmal pH-gradients in drug-sensitive and drug-resistant MCF-7 human breast carcinoma xenografts measured by 31P magnetic resonance spectroscopy

31p Magnetic resonance spectroscopy (MRS) was employed to investigate tumor pH in xenografts of drug-sensitive and drug-resistant MCF-7 human breast carcinoma cells. Measured extracellular pH values were found to be lower than the intracellular pH in all three tumor types investigated. The magnitude of this acid-outside plasmalemmal pH gradient increased with increasing tumor size in tumors of two drug-resistant variants of MCF-7 cells, but not in tumors of the parent (drug-sensitive) cells. The partitioning of weak-base or weak-acid drug molecules across the plasma membrane of a tumor cell is dependent upon the acid-dissociation constant (pKa) of the drug as well as the plasmalemmal pH gradient. A large acid-outside pH gradient, such as those seen in MCF-7 xenografts, can exert a protective effect on the cell from weak-base drugs such as anthracyclines and Vinca alkaloids, which have pKa values of 7.5 to 9.5. The possibility of enhancing the therapeutic efficacy of weak-base drugs by dietary or metabolic manipulation of the extracellular pH, in order to reduce or reverse the plasmalemmal pH gradient, deserves investigation.

Oxytocin increases the [Ca2+]i sensitivity of human myometrium during the falling phase of phasic contractions

Oxytocin is commonly used to induce or augment labor, but its mode of action is uncertain. To address the issue, isometric tension and the intracellular free Ca2+ concentration ([Ca2+]i) were simultaneously recorded from isolated strips of pregnant human myometrium loaded with fura 2. The changes in [Ca2+]i and tension during phasic contractions were indistinguishable in myometrium taken before or after the onset of labor, enabling samples to be pooled. Oxytocin (10 nM) had no effect on basal [Ca2+]i or tension, but it increased both the [Ca2+]i and the tension recorded during phasic contractions. Analysis of the [Ca2+]i-tension relationship revealed that during the falling (relaxation) phase of the contractile response, oxytocin increased the tension recorded at each [Ca2+]i. By manipulating extracellular Ca2+ during phasic contractions, it was possible to ensure that the [Ca2+]i signals were similar in the presence and absence of oxytocin, yet oxytocin still improved the [Ca2+]i-tension relationship. We conclude that 10 nM oxytocin increases the [Ca2+]i sensitivity of the contractile proteins only after a contraction has begun, possibly by causing inhibition of myosin light chain phosphatase.

Interactions between inositol trisphosphate receptors and fluorescent Ca2+ indicators

Fura-2 and BAPTA were previously shown to be competitive antagonists of inositol trisphosphate (InsP3) receptors, but for practical reasons the analyses were performed at pH 8.3. We recently developed a scintillation proximity assay (SPA) for pure cerebellar InsP3 receptors which allows low affinity interactions to be characterized and is readily applicable to scarce or expensive ligands. In the present study, we use SPA to demonstrate that at pH 7.2, many of the commonly used fluorescent Ca2+ indicators reversibly displace 3H-InsP3 from its receptor and that they differ substantially in their affinities for the InsP3 receptor (IC50 = 6.5-137 microM). Recombinant type 1 InsP3 receptors expressed in Sf9 cells were used to examine 3H-InsP3 binding in cytosol-like medium: both fura-2 (IC50 = 796 +/- 86 microM) and Ca Green-5N (IC50 = 62 +/- 7 microM) completely inhibited the binding, but only in their Ca(2+)-free forms. Similar results were obtained with type 3 InsP3 receptors. We conclude that many Ca2+ indicators in their Ca(2+)-free forms compete with InsP3 for binding to its receptor, and that for Ca Green-5N the interaction occurs with sufficient affinity to significantly perturb physiological responses.

Acyclophostin: a ribose-modified analog of adenophostin A with high affinity for inositol 1,4,5-trisphosphate receptors and pH-dependent efficacy

Adenophostin A is the most potent known agonist of D-myo-inositol 1, 4,5-trisphosphate [Ins(1,4,5)P3] receptors. Equilibrium competition binding studies with 3H-Ins(1,4,5)P3 showed that the interaction of a totally synthetic adenophostin A with both hepatic and cerebellar Ins(1,4,5)P3 receptors was indistinguishable from that of the natural product. At pH 8.3, a synthetic analog of adenophostin A (which we named acyclophostin), in which most elements of the ribose ring have been removed, bound with substantially higher affinity (Kd = 2.76 +/- 0.26 nM) than Ins(1,4,5)P3 (Kd = 7.96 +/- 1.02 nM) to the 3H-Ins(1,4,5)P3-binding sites of hepatic membranes. At pH 7, acyclophostin (EC50 = 209 +/- 12 nM) and Ins(1,4,5)P3 (EC50 = 153 +/- 11 nM) stimulated 45Ca++ release to the same maximal extent and from the same intracellular stores of permeabilized hepatocytes. Comparison of the affinities of a range of Ins(1,4,5)P3 and adenophostin analogs with their abilities to stimulate Ca++ release revealed that although all other agonists had similar EC50/Kd ratios, that for acyclophostin was significantly higher. Similar results were obtained with cerebellar membranes, which express almost entirely type 1 InsP3 receptors. When the radioligand binding and functional assays of hepatocytes were performed under identical conditions, the higher EC50/Kd ratio for acyclophostin was retained at pH 8.3, but it was similar to that for Ins(1,4,5)P3 when the assays were performed at pH 7. To directly assess whether acyclophostin was a partial agonist of hepatic Ins(1,4,5)P3 receptors, the kinetics of 45Ca++ efflux from permeabilized hepatocytes was measured with a temporal resolution of 80 ms using rapid superfusion. At pH 7, the kinetics of 45Ca++ release, including the maximal rate of release, evoked by maximal concentrations of acyclophostin or Ins(1,4,5)P3 were indistinguishable. At pH 8.3, however, the maximal rate of 45Ca++ release evoked by a supramaximal concentration of acyclophostin was only 69 +/- 7% of that evoked by Ins(1,4,5)P3. We conclude that acyclophostin is the highest affinity ribose-modified analog of adenophostin so far synthesized, that at high pH it is a partial agonist of inositol trisphosphate receptors, and that it may provide a structure from which to develop high-affinity antagonists of inositol trisphosphate receptors.