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M Hinds

Publications and source records attributed to M Hinds.

At least 19 recordsLinked to original sources
PubMed1995

The pumping and left ventricular unloading capabilities of the ventricular synchronous skeletal-muscle ventricle.

The pumping and left ventricular unloading capabilities of the left ventricular, ventricular synchronous skeletal-muscle ventricle were determined in nine anesthetized dogs ranging in weight from 20.7 to 31.8 kg. The ventricular synchronous skeletal-muscle ventricle consists of the left rectus abdominis muscle wrapped around a 4-mil-thick polyethylene pouch (wrapped volume 80 to 100 ml) connected to the left ventricular apex with no valve and to the aorta via a prosthetic heart valve. The rectus muscle is timed to contract tetanically and relax during left ventricular ejection. This arrangement provides a high precontraction pressure for the rectus muscle and a high muscle capillary blood flow during skeletal muscle relaxation. The timing signal for initiation of the train of stimulating pulses (40/sec) was derived from the ventricular electrogram. The delay for the stimulus train determines the preload for the rectus muscle and along with the stimulus train duration determines ventricular synchronous skeletal-muscle ventricle stroke volume, which was measured by electric impedance. With unconditioned rectus muscles (70 to 120 gm) and with a pumping ratio of 1:3, ventricular synchronous skeletal-muscle ventricle stroke volume average 26.1 ml, which provided an average output of 876 ml/min. The normalized ventricular synchronous skeletal-muscle ventricle output was 35.6 ml/min per kilogram of body weight. In a typical resting dog (and man), the normalized cardiac output is 70 ml/min per kilogram. Therefore the ventricular synchronous skeletal-muscle ventricle is capable of pumping 52% of the cardiac output (with a pumping ratio of 1:3). The optimum train delay from the apex of the ventricular electrogram ranged from 10 to 100 msec. The left ventricular ejection period averaged 309 msec, and this determines the time available for the rectus muscle to contract and relax. Evidence for unloading the left ventricle is shown by the reduced left ventricular diastolic pressure and stroke volume for the postassisted beats.

Animals↗
PubMed1993

The ventricular-synchronous, skeletal-muscle ventricle: preliminary feasibility studies.

The two requirements for the optimal use of skeletal muscle wrapped around a pouch used to pump blood are:(1) a low pouch diastolic pressure (to assure a high muscle capillary blood flow; and (2) a high pouch precontraction pressure (PCP) (to assure a forceful muscle contraction). Both requirements are satisfied with the pumping method described herein. This new type of skeletal-muscle ventricle (SMV) consists of a rectus abdominis muscle wrapped around a pouch connected to the left ventricular apex (with no valve) and to the aorta via a one-way valve. Consequently, the pressure in the SMV pouch is always equal to left ventricular pressure. The high PCP is obtained by stimulating the rectus muscle to contract at the desired left ventricular pressure. The R (or P) wave of the cardiac electrogram initiates a delayed train of stimuli to cause the rectus muscle to contract tetanically and expel blood from the pouch. We have designated this pumping configuration the ventricular-synchronous SMV (VS-SMV). In this study, eight acute anesthetized dogs were used. The muscles were unconditioned and among the items investigated were the importance of the delay (d) between the R (or P) wave and the onset of the stimulus train, the optimal stimulus frequency and train duration, the VS-SMV output with different ratios of VS-SMV to left ventricular contractions, unloading of the left ventricle, Frank-Starling curves for the VS-SMV, pressure-volume loops for the VS-SMV with and without contraction of the rectus muscle, and washout characteristics of the VS-SMV. It was found that a stimulus frequency of 40/sec, and a train duration of 250 msec is optimal. It was also found that choice of the proper delay from the R or P wave provided maximal augmentation in stroke volume, typically 20 to 40 mL. Pumping with a ratio of 1:2 provided VS-SMV outputs ranging from 20 to 140 mL/min per kg of body weight. With this same pumping ratio, cardiac output increased by 28% and the post-VS-SMV contraction, left ventricular stroke volume was reduced. The Frank-Starling curves showed that PCPs on the order of aortic pressure are needed for the most forceful muscle contraction. With this new pumping configuration, the left ventricle resembles an atrium which delivers blood to the VS-SMV that is stimulated to contract when the desired PCP is reached. Studies were also conducted in which the VS-SMV outlet (valve end) was closed and filling and emptying occurred through the left ventricle.(ABSTRACT TRUNCATED AT 400 WORDS)

Abdominal Muscles↗
PubMed1993

The importance of timing muscle contraction in dynamic cardiomyoplasty.

This acute dynamic cardiomyoplasty (CMP) study used ten dogs (weight range 21-32 kg) and was designed to determine the importance of the train of stimuli initiation time when applied to the thoracodorsal nerve, which innervates the latissimus dorsi (LD) muscle that is wrapped around the ventricles. Using the P wave of the cardiac electrogram to trigger a special delay circuit, the stimulus train could be initiated from the apex of the R wave to any time throughout and at the end of the isovolumic period, signaled by opening of the aortic valve. The cardiac electrogram (which contained the R wave), left ventricular pressure (LVP), aortic flow velocity (AFV), beat-by-beat stroke volume (SV), femoral artery pressure, and the envelope of the stimulus train were recorded as the onset of the stimulus train was varied from the R wave to the end of the isovolumic period with a pumping ratio of one LD contraction for every seven ventricular contractions. In four dogs there was a pronounced increase in the augmentation in LVP, AFV, and SV when the stimulus train was initiated later than 40 msec after the first peak of the R wave. In five dogs the augmentation in LVP, AFV, and SV was not as clearly apparent, although all of these dogs exhibited an optimal train delay. Data were not obtained on one dog due to an anomalous LD muscle blood supply. For all of the dogs, the optimum train delay from the R wave averaged 58 msec (range 40-80 msec). The average augmentation in SV was 26% (range 13%-45%). The same muscle-wrap tightness was used in all dogs. In one dog, the muscle-wrap tightness was varied, and by tightening the wrap the SV augmentation increased from 17% to 27%. For all dogs the range of augmentation in SV (13%-45%) perhaps represents variations in muscle-wrap tightness, which may be a major uncontrolled factor in dynamic CMP.

Animals↗
PubMed1992

Components of intrinsic drug resistance in the rat hepatoma.

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin and daunorubicin, and to the demethylepipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m-AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m-AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m-AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.

Animals↗
PubMed1992

Relative activity of structural analogues of amsacrine against human leukemia cell lines containing amsacrine-sensitive or -resistant forms of topoisomerase II: use of computer simulations in new drug development.

Anilino analogues of amsacrine showed increased activity against amsacrine (AMSA)-resistant cell lines when compared with the parent compound, but the mechanisms of amsacrine resistance in these lines were unknown (Finlay, G. J., Baguley, B. C., Snow, K., and Judd, W., J. Natl. Cancer Inst., 82: 662-667, 1990). We tested the cytotoxic and DNA-cleaving activities of two amsacrine analogues which were derivatives of 9-anilinoacridine (1'-methylcarbamate and 1'-benzenesulfonamide) against an amsacrine-resistant human leukemia cell line (HL-60/AMSA) whose resistance is due to an amsacrine-resistant topoisomerase II. Neither agent could overcome the amsacrine resistance of HL-60/AMSA. Neither agent could induce HL-60/AMSA topoisomerase II-mediated cleavage of DNA in an isolated biochemical system, although at high concentrations the two analogues could inhibit HL-60/AMSA topoisomerase II-mediated DNA strand passage. Both analogues were at least as active, if not more active, than amsacrine against amsacrine-sensitive HL-60 and its topoisomerase II. Comparison of the cellular and biochemical results with those from computer simulation of the energy-minimized structures of amsacrine, its inactive isomer o-AMSA, and the two new active analogues suggests the following possibilities: (a) the positioning of the potential topoisomerase II-binding site (1'-anilino group) of the two new drugs resembles the positioning of this site in amsacrine; (b) the HL-60 topoisomerase II has a binding site which interacts with amsacrine and the two anilino analogues but not with o-AMSA, an analogue with altered positioning of the methoxy group; (c) the HL-60/AMSA topoisomerase II interacts with reduced affinity with amsacrine and the two anilino analogues, although HL-60/AMSA topoisomerase II still interacts with the structurally distinct topoisomerase II-reactive nonintercalator, etoposide; (d) because of their higher DNA binding affinity or the greater possible positions of their side groups in comparison to amsacrine, the two analogues can, at high concentrations, inhibit the strand-passing activity of HL-60/AMSA topoisomerase II.

Amsacrine↗
PubMed1992

The chronaxie for myocardium and motor nerve in the dog with chest-surface electrodes.

The chronaxie (i.e., the duration for a stimulating current having twice the rheobasic, or minimum, value) was determined for ventricular myocardium in 12 pentobarbital-anesthetized dogs. Current was applied transthoracically via chest-surface electrodes located at the optimal axillary site for producing inspiration by stimulation of the phrenic nerve (electroventilation). In four dogs the chronaxie for motor-nerve was determined using electrodes at the same location. After using hand-held electrodes to identify the optimal stimulation site for electroventilation, 4.1 cm diameter electrodes were applied bilaterally to the optimal site on the thorax. In 12 dogs, the threshold current for producing ventricular ectopic beats was determined for single rectangular current pulses ranging from 0.1-10 ms in duration. From these data, strength-duration curves were determined and the average chronaxie for ventricular myocardium was found to be 1.82 ms. In four dogs the relationship between inspired volume and maximum stimulus intensity was determined using a 0.8 s burst of stimuli (60/s) with pulse durations ranging from 20-500 microseconds. From these data, strength-duration curves for current were constructed and the average chronaxie for motor-nerve was found to be 0.17 ms. The results of this study show that, because of the differing chronaxies, the current required to produce inspiration with short-duration stimuli is much less than that required to evoke an ectopic heart beat.

Animals↗
PubMed1992

Ventricular fibrillation produced by stimulation of external transthoracic electrodes--an experimental study.

The threshold for ventricular fibrillation was determined in 12 pentobarbital anesthetized dogs using transthoracic electrodes located at the optimal axillary electroventilation sites. Electroventilation is the name used to designate inspiration produced by stimuli applied to body surface electrodes. The optimal stimulation site for electroventilation was first determined using hand-held electrodes. Then electrodes, 4.1 cm in diameter, were sutured bilaterally to the optimal anterior axillary stimulation site. The threshold current for producing ventricular fibrillation was determined using single pulses ranging from 0.1-10 msec in duration delivered during the vulnerable period of the cardiac cycle. Fibrillation was produced in all dogs with the 10- and 5-msec pulse durations, in 11 dogs with 0.3-msec, in 6 dogs with 0.2-msec, and in 1 dog with 0.1-msec pulse duration. In all dogs, the current required to produce ventricular fibrillation increased greatly as the pulse duration was decreased. The current required for fibrillation was much in excess of that required to produce one tidal volume. With the longer duration pulses, the ratio was about 80. With the 8 microseconds duration pulses used for electroventilation the estimated ratio is about 800.

Animals↗
PubMed1991

Identification of a point mutation in the topoisomerase II gene from a human leukemia cell line containing an amsacrine-resistant form of topoisomerase II.

HL-60/AMSA is a human leukemia cell line that is 50- to 100-fold more resistant to the cytotoxic actions of the topoisomerase II-reactive intercalator amsacrine than is its drug-sensitive HL-60 parent line. Previously, we have shown that the topoisomerase II from HL-60/AMSA is also resistant to inhibition by amsacrine and other intercalating agents. We therefore sought the molecular basis for the resistance of the topoisomerase II of HL-60/AMSA and, by inference, of the HL-60/AMSA line itself. We report the cloning and sequencing of the topoisomerase II genes from both the sensitive and resistant leukemia cell lines using polymerase chain reaction technology. We have identified a single base change associated with the drug-resistant form of topoisomerase II. This mutation is present in both cloned HL-60/AMSA complementary DNA and extracted HL-60/AMSA genomic DNA. A rapid assay for this mutation in clinical samples has been developed and applied to the DNA of cells from both normal volunteers and leukemia patients. Thus far, the HL-60/AMSA genotype has not been identified in the cells from any individual, suggesting that this genotype is indeed a mutation and not an allelic form of topoisomerase II. The novel assay developed will allow a rapid search for the prevalence of this mutation in clinical samples from patients with leukemia who have relapsed following intercalator therapy.

Amino Acid Sequence↗
PubMed1991

Cross-resistance of an amsacrine-resistant human leukemia line to topoisomerase II reactive DNA intercalating agents. Evidence for two topoisomerase II directed drug actions.

HL-60/AMSA is a human leukemia cell line that is 50-100-fold more resistant than its drug-sensitive HL-60 parent line to the cytotoxic actions of the DNA intercalator amsacrine (m-AMSA). HL-60/AMSA topoisomerase II is also resistant to the inhibitory actions of m-AMSA. HL-60/AMSA cells and topoisomerase II are cross-resistant to anthracycline and ellipticine intercalators but relatively sensitive to the nonintercalating topoisomerase II reactive epipodophyllotoxin etoposide. We now demonstrate that HL-60/AMSA and its topoisomerase II are cross-resistant to the DNA intercalators mitoxantrone and amonafide, thus strongly indicating that HL-60/AMSA and its topoisomerase II are resistant to topoisomerase II reactive intercalators but not to nonintercalators. At high concentrations, mitoxantrone and amonafide were also found to inhibit their own, m-AMSA's, and etoposide's abilities to stabilize topoisomerase II-DNA complexes. This appears to be due to the ability of these concentrations of mitoxantrone and amonafide to inhibit topoisomerase II mediated DNA strand passage at a point in the topoisomerization cycle prior to the acquisition of the enzyme-DNA configuration that yields DNA cleavage and topoisomerase II-DNA cross-links. In addition, amonafide can inhibit the cytotoxic actions of m-AMSA and etoposide. Taken together, these results suggest that the cytotoxicity of m-AMSA and etoposide is initiated primarily by the stabilization of the topoisomerase II-DNA complex. Other topoisomerase II reactive drugs may inhibit the enzyme at other steps in the topoisomerization cycle, particularly at elevated concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Amsacrine↗
PubMed1991

The effect of staurosporine on drug-induced, topoisomerase II-mediated DNA cleavage in human leukemia cells.

Phorbol-12-myristate 13-acetate (PMA), a stimulator of protein kinase C, dramatically decreased topoisomerase II-reactive drug-induced DNA cleavage in HL-60 human leukemia cells. The effect of staurosporine, an inhibitor of protein kinase C, on drug-induced, topoisomerase II-mediated DNA cleavage was quantified in the same cells. Staurosporine decreased the magnitude of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA)- and etoposide-induced DNA cleavage in a dose- and time-dependent fashion. Measurement of several parameters of cell proliferation revealed no clear and uniform correlation between staurosporine's inhibition of these parameters and its effects on drug-induced DNA cleavage. A direct comparison with PMA's effects on drug-induced DNA cleavage showed that whereas PMA's inhibition of etoposide-induced cleavage was much greater than its inhibition of m-AMSA-induced cleavage, the magnitude of staurosporine's effect on the cleavage produced by the two topoisomerase II-reactive drugs was similar. Thus, although PMA stimulates protein kinase C and staurosporine inhibits this enzyme, it is unlikely that the actions of either on topoisomerase II-reactive, drug-induced DNA cleavage are mediated directly via protein kinase C. Furthermore, it is likely that the mechanisms by which PMA and staurosporine inhibit topoisomerase II-reactive drug-induced cleavage are different.

Alkaloids↗
PubMed1990

Phorbol ester effects on topoisomerase II activity and gene expression in HL-60 human leukemia cells with different proclivities toward monocytoid differentiation.

We examined the effects of phorbol ester treatment on topoisomerase II-mediated events in two human leukemia cell lines with different proclivities toward phorbol ester-induced monocytoid differentiation. HL-60 is the parent line that will terminally differentiate; 1E3 is a derived line that will not terminally differentiate. Within 24 h of phorbol ester treatment, etoposide-induced, topoisomerase II-mediated DNA cleavage declined 10-fold, whereas 4'-(9-acridinylamino)-methanesulfon-m-anisidide- induced DNA cleavage declined 3-fold in HL-60. In phorbol-treated 1E3, etoposide-induced DNA cleavage declined only 2-fold, whereas 4'-(9-acridinylamino)methanesulfon-m-anisidide-induced cleavage was barely affected. There was a 2- to 3-fold decline in topoisomerase II activity within the nuclear extracts from phorbol-treated HL-60 cells but not from phorbol-treated 1E3 cells. Immunoblotting experiments with anti-topoisomerase II antibodies indicated that phorbol treatment produced a structural change in the immunoreactive topiosomerase II in HL-60 nuclear extracts but produced no change in 1E3 topoisomerase II. Phorbol ester treatment also produced a decline in the level of topoisomerase II gene expression in HL-60 but not in 1E3 cells. By contrast, the cytotoxicity of etoposide in both lines was decreased following phorbol treatment. Thus, phorbols may uncouple the mechanisms linking drug-induced, topoisomerase II-DNA cleavable complex stabilization with drug-induced cytotoxicity, particularly in 1E3.

Amsacrine↗
PubMed1990

HT1080/DR4: a P-glycoprotein-negative human fibrosarcoma cell line exhibiting resistance to topoisomerase II-reactive drugs despite the presence of a drug-sensitive topoisomerase II.

HT1080/DR4 (DR4) is a doxorubicin-resistant human fibrosarcoma line that exhibits 150-fold cross-resistance to etoposide but does not overexpress P-glycoprotein (one mechanism of multiple drug resistance). We examined another possible mechanism that could explain resistance to both doxorubicin and etoposide: a quantitative or qualitative alteration in topoisomerase II, the putative nuclear target of these agents. The amount of immunoreactive topoisomerase II present in whole-cell lysates and nuclear extracts was three- to 10-fold lower in DR4 than in HT1080 cells. However, the topoisomerase II in nuclear extracts from both lines was sensitive to the effects of amsacrine (AMSA) and etoposide. Following treatment with AMSA, etoposide, and 5-iminodaunorubicin, topoisomerase II-mediated DNA cleavage in DR4 cells and nuclei was reduced compared with cleavage in HT1080 parent cells and nuclei. The difference between the HT1080 and DR4 lines in AMSA- and 5-iminodaunorubicin-induced cleavage was similar in cells and nuclei and could be due to the lower amount of DR4 topoisomerase II. By contrast, the difference between the HT1080 and DR4 lines in etoposide-induced DNA cleavage was much greater in cells than in nuclei. This finding suggested that cytosolic factors, removed from isolated nuclei, could influence the susceptibility of intact cells to the cytotoxic and DNA-cleaving actions of etoposide. The specific activities of several antioxidant enzymes, components of the cell's defense against free-radical damage that may be produced by doxorubicin or etoposide, were significantly different in HT1080 and DR4 cytosolic extracts. These differences may constitute an additional mechanism of resistance. Regardless, the magnitude of the resistance of DR4 to doxorubicin and etoposide cannot be explained solely on the basis of a topoisomerase II-related mechanism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Comparison of three methods of electrical stimulation for converting skeletal muscle to a fatigue resistant power source suitable for cardiac assistance.

Twelve dogs were sorted into 3 equal groups, and the in-situ right latissimus dorsi muscle of each dog was stimulated via its motor nerve for a period of 6 weeks. The resulting isotonic contractions were used to pump fluid in an implanted, 2-chambered, compressible pouch system. Three methods of electrical stimulation were used: (a) continuous 2 sec-1 single pulses that caused muscle twitching, (b) a 250 msec train of pulses (36 sec-1) that caused tetanic muscle contractions and was repeated every 2 sec for 15 min followed by a 15 min period of rest, and (c) alternating 15 min periods of the above 2 stimulation methods to cause alternating twitch and tetanic contractions. The 2 sec-1 twitch stimulation and the combined twitch/tetanic stimulation methods resulted in a 100% conversion to fatigue-resistant fibers within 6 weeks. Standardized muscle function tests were performed weekly. With the twitch stimulation (Method 1), the time to fatigue increased from 9 to 116 min (p less than 0.001), but fluid pumping ability of the muscle decreased substantially from 0.25 to 0.14 liters min-1 (p less than 0.05). With the intermittent tetanic stimulation (Method 2), the fatigue resistance increased only slightly from 7 to 11 minutes (p = NS), and pumping ability was unchanged. With the combined (twitch-tetanic) stimulation (Method 3), the time to fatigue increased from 9 to 107 min (p less than 0.001), and the pumping ability did not significantly change from 0.20 to 0.22 liters min-1 (p = NS). These results suggest that a combined electrical stimulation method which produces both twitches and tetanic contractions can achieve rapid fiber conversion and increased fatigue resistance without loss of muscle strength.

Adaptation, Physiological↗
PubMed1990

A restriction fragment length polymorphism for human topoisomerase II: possible relationship to drug-resistance.

In previous studies we used Southern blotting to examine the topoisomerase II locus (on chromosome 17) in human leukemia cell lines and noted a difference in the XmnI restriction endonuclease digestion pattern between an m-AMSA-resistant line and its m-AMSA-sensitive parent line (Zwelling, L. A.; Hinds, M,; Chan, D.; Mayes, J.; Sie, K. L.; Parker, E.; Silberman, L.; Radcliffe, A.; Beran, M.; Blick, M. Characterization of an amsacrine-resistant line of human leukemia cells. Evidence for a drug-resistant form of topoisomerase II. Journal of Biological Chemistry 264:16411-16420; 1989). We now demonstrate that the variable XmnI digestion pattern represents a normal restriction fragment length polymorphism (RFLP) which is observed in subjects without malignant disease and exhibits an autosomal pattern of inheritance. These data suggest that the previously described deviation in the genomic structure of topoisomerase II in the m-AMSA-resistant cell line did not reflect a new mutation, but rather a reduction to homozygosity at the topoisomerase II locus. This reduction to homozygosity is not due to chromosomal loss, as chromosome 17-specific gene probes clearly identify two chromosome 17's in the sensitive line and four in the resistant line, using chromosome painting with a chromosome 17-specific library. Some other genetic change must be the cause of the resistance of HL-60/AMSA and its topoisomerase II to the inhibiting actions of m-AMSA.

Alleles↗
PubMed1989

Characterization of an amsacrine-resistant line of human leukemia cells. Evidence for a drug-resistant form of topoisomerase II.

HL-60/AMSA is a human leukemia cell line that is 100 times more resistant to the cytotoxic actions of the antineoplastic, topoisomerase II-reactive DNA intercalating acridine derivative amsacrine (m-AMSA) than is its parent HL-60 line. HL-60/AMSA cells are minimally resistant to etoposide, a topoisomerase II-reactive drug that does not intercalate. Previously we showed that HL-60 topoisomerase II activity in cells, nuclei, or nuclear extracts was sensitive to m-AMSA and etoposide, while HL-60/AMSA topoisomerase II was resistant to m-AMSA but sensitive to etoposide. Now we show that purified topoisomerase II from the two cell lines exhibits the same drug sensitivity or resistance as that in the nuclear extracts although the magnitude of the m-AMSA resistance of HL-60/AMSA topoisomerase II in vitro is not as great as the resistance of the intact HL-60/AMSA cells. In addition HL-60/AMSA cells are cross-resistant to topoisomerase II-reactive intercalators from the anthracycline and ellipticine families and the pattern of sensitivity or resistance to the cytotoxic actions of the various topoisomerase II-reactive drugs is paralleled by topoisomerase II-reactive drug-induced DNA cleavage and protein cross-link production in cells and the production of drug-induced, topoisomerase II-mediated DNA cleavage and protein cross-linking in isolated biochemical systems. In addition to its lowered sensitivity to intercalators, HL-60/AMSA differed from HL-60 in 1) the susceptibility of its topoisomerase II to stimulation of DNA topoisomerase II complex formation by ATP, 2) the catalytic activity of its topoisomerase II in an ionic environment chosen to reproduce the environment found within the living cell, and 3) the observed restriction enzyme pattern on a Southern blot probed with a cDNA for human topoisomerase II. These data indicate that an m-AMSA-resistant form of topoisomerase II contributes to the resistance of HL-60/AMSA to m-AMSA and to other topoisomerase II-reactive DNA intercalating agents. The drug resistance is associated with additional biochemical and molecular alterations that may be important determinants of cellular sensitivity or resistance to topoisomerase II-reactive drugs.

Adenosine Triphosphate↗
PubMed1989

The safety factor for electroventilation measured by production of cardiac ectopy in the anesthetized dog.

The safety factor of electroventilation (ie, the ratio of the current required to produce an ectopic beat to the current required to produce an inspired volume of 225 ml, which is approximately twice tidal volume) was determined in 12 pentobarbital-anesthetized dogs using transthoracic electrodes positioned at the optimal electroventilation site. The optimal stimulation site for electroventilation was first determined using hand-held, stimulating electrodes. Then electrodes, 4.1 cm in diameter, were sutured bilaterally to the optimal stimulation site. The relationship between inspired volume and stimulus intensity was determined using a 0.8-s burst of stimuli (60/s) with a pulse duration of 0.1 ms. Using the same electrodes, the threshold current for producing ectopic beats was determined for single pulses ranging from 0.1 to 10 ms duration. In all dogs, the current required to produce an ectopic beat increased greatly as the pulse duration decreased. At 0.1 ms, the safety factor for electroventilation was calculated to be 25.8.

Anesthesia↗
PubMed1988

Effect of phorbol ester treatment on drug-induced, topoisomerase II-mediated DNA cleavage in human leukemia cells.

Tumor-promoting phorbol esters such as phorbol 12-myristate 13-acetate (PMA) induce the monocytoid differentiation of HL-60 human leukemia cells. The cellular receptor for PMA is protein kinase C. However, cellular events distal to protein kinase C phosphorylation are also critical steps toward differentiation. These events may include specific programs of oncogene transcription that have been associated with phorbol ester-induced leukemic cell differentiation. Recently, it has been found that topoisomerase II could be activated by protein kinase C-mediated serine phosphorylation and that PMA treatment of HL-60 cells enhanced extractable topoisomerase II from these cells. Additionally, topoisomerase II-reactive antineoplastic drugs could block PMA-induced differentiation of HL-60. This enzyme has been implicated in gene regulation, and drug-induced, topoisomerase II-mediated DNA cleavage sites have been identified within cellular oncogenes. Thus, topoisomerase II could play a critical role in the signal transduction cascade leading from PMA-protein kinase interaction to monocytoid differentiation. We have examined this relationship between topoisomerase II and PMA-induced differentiation through measurements of drug-induced, topoisomerase II-mediated DNA cleavage (via alkaline elution) in PMA-treated HL-60 cells. Etoposide-induced DNA cleavage was reduced 10-fold in HL-60 cells treated with 10 nM PMA for 24 h. Neither dimethyl sulfoxide (which produces granulocytoid differentiation) nor non-differentiation-inducing phorbol esters could produce this effect. The decreased cleavage was not due to a PMA-induced inhibition of cell-associated etoposide and was demonstrable in nuclei isolated from PMA-treated cells. The decrease was not simply related to decreased cellular proliferation rate as reflected in the inhibition of DNA synthesis because conditions leading to marked inhibition of DNA synthesis did not necessarily inhibit etoposide-induced DNA cleavage. By contrast, lower concentrations of PMA inhibited etoposide-mediated DNA cleavage disproportionately compared with PMA effects on DNA synthesis. Interestingly, PMA reduced cleavage induced by the topoisomerase II-reactive DNA intercalator 4'-(9-acridinylamino)methanesulfon-m-anisidide by 2-fold, suggesting that specific drug-DNA interactions could partially overcome the PMA-induced effect that resulted in decreased etoposide-induced, topoisomerase II-mediated DNA cleavage. Nuclear proteins in 0.35 M NaCl extracts from untreated or PMA-treated HL-60 cells were virtually identical in topoisomerase II activity and in topoisomerase II-associated drug sensitivity.(ABSTRACT TRUNCATED AT 400 WORDS)

Amsacrine↗