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R Seshadri

Publications and source records attributed to R Seshadri.

At least 91 records · Page 5Linked to original sources
PubMed1992

Effects of mono-, di-, and triamines on the N-methyl-D-aspartate receptor complex: a model of the polyamine recognition site.

Systematic series of monoamines, diamines, and triamines were used to define the structural requirements for interaction at the polyamine recognition site of the N-methyl-D-aspartate receptor complex. Effects of amines on binding of [3H]MK-801 to washed synaptic plasma membranes were measured in the presence of L-glutamate and glycine (100 microM each), in the absence or presence of spermine (10 microM). Linear aliphatic monoamines of methylene chain length up to 12 (dodecylamine) did not interact with the polyamine recognition site. Nonspecific inhibition of binding was observed at high concentrations of the longer monoamines. alpha,omega-Diamines of methylene chain length 2 (1,2-diaminoethane, DA2) through 12 (1,12-diaminododecane, DA12) had varying actions, depending on chain length. The shortest diamines (DA2 and DA3) acted as weak partial agonists, enhancing the binding of [3H[MK-801. Intermediate-length diamines (DA4-DA7) were selective polyamine antagonists, having little or no effect on binding of [3H]MK-801 measured in the absence of spermine but inhibiting binding measured in the presence of spermine. The longest diamines tested (DA8-DA12) acted as inverse agonists; they inhibited binding in the absence or presence of spermine, and this inhibition was blocked by the selective polyamine antagonist diethylenetriamine. Computer modeling of conformations of the diamines quantitatively documented that 1) these molecules are flexible and 2) long diamines may easily adopt conformations with inter-nitrogen distances mimicking those of short diamines. The cis and trans isomers of 1,4-diaminocyclohexane are inflexible, conformationally restricted diamines with markedly different actions. The cis isomer was a partial agonist and the trans isomer was an antagonist at the polyamine recognition site. Triamines of general structure NH2(CH2)3NH(CH2)xNH2 (TRI[3,x]), in which x = 3-12, were synthesized and tested for activity at the polyamine recognition site. Despite the large range of size, TRI[3,3] through TRI[3,9] were all fully polyamine agonists of similar potency. TRI[3,10] was a partial agonist, whereas TRI[3,12] inhibited binding of [3H]MK-801. Diethylenetriamine did not attenuate the effect of TRI[3,12]. Based on the results of the radioligand binding studies and the computer analysis, a model of the polyamine recognition site is proposed.

Amines↗
PubMed1991

Molecular diagnosis of Philadelphia negative CML using the polymerase chain reaction and DNA analysis: clinical features and course of M-bcr negative and M-bcr positive CML.

The Philadelphia chromosome (Ph) is the cytogenetic hallmark of chronic myeloid leukemia (CML) and as such has been used to confirm the diagnosis of CML based on morphological and clinical criteria. We have investigated 12 patients who were considered to have clinical and morphological features of CML and who did not have detectable abnormalities of chromosomes 9q34 or 22q11. In six of the 12 patients, rearrangement within the 5.8 kb major breakpoint region (M-bcr) and amplification of CML specific M-bcr-ABL cDNA sequences by the polymerase chain reaction (PCR) was demonstrated. Six other CML patients did not have rearrangement of the M-bcr gene or amplification of BCR-ABL by PCR. These patients had atypical CML. They were significantly older, most had less than 10% immature granulocytic cells (metamyelocytes, myelocytes and promyelocytes) and had various degrees of marrow fibrosis. Three of these six patients died of blastic transformation at 4, 15 and 54 months from diagnosis.

Adult↗
PubMed1990

Inhibition of mitochondrial carnitine palmitoyltransferases by adriamycin and adriamycin analogues.

Adriamycin (ADR; doxorubicin) and its highly lipophilic, less toxic analogue N-benzyl-adriamycin-14-valerate (AD 198) were found to inhibit rat heart and liver carnitine palmitoyltransferases of both mitochondrial outer and inner membranes. The outer membrane enzyme was more sensitive to inhibition by these drugs than the inner membrane enzyme, and AD 198 was a more potent inhibitor of these enzymes than ADR. Other analogues of ADR, N-trifluoroacetyladriamycin-14-valerate (AD 32) and N-trifluoroacetyladriamycin-14-O-hemiadipate (AD 143), which are documented as being noncardiotoxic, were also more potent inhibitors of the mitochondrial carnitine palmitoyltransferases than ADR. Overall, the cardiac mitochondrial carnitine palmitoyltransferases seemed to be slightly more sensitive to the inhibitory effects of ADR and its analogues than the liver enzyme. ADR was an uncompetitive inhibitor with respect to palmitoyl-CoA and a noncompetitive inhibitor with respect to carnitine for both mitochondrial outer and inner membrane enzymes. Our data suggest that mitochondria can take up ADR and concentrate it within the matrix, as is known to happen with other positively-charged compounds. More ADR was found associated with the mitochondrial inner membrane than with the outer membrane; this could be due to the greater protein content of the inner membrane rather than drug binding to cardiolipin. Although inhibition of cardiac inner membrane carnitine palmitoyltransferase has been implicated previously as part of the cardiotoxicity mechanism of ADR, the present findings with ADR and its noncardiotoxic analogues do not support this view.

Animals↗
PubMed1990

Metabolism and elimination of rhodamine 123 in the rat.

Little is known of the pharmacology of rhodamine 123 (RH-123), an agent reported to have carcinoma-selective experimental antitumor activity. Accordingly, using a high-performance liquid chromatographic assay system with fluorescence detection, we examined the plasma decay and the biliary and urinary elimination of parent drug and metabolites in female Sprague-Dawley rats receiving RH-123 at an intravenous dose (5 mg/kg) equivalent to the therapeutic dose used in murine tumor models. Following drug administration to unconscious animals, plasma levels of drug-associated fluorescence fell in a triphasic manner (t1/2 alpha, 15 min; t1/2 beta, 1 h; t1/2 gamma, 4.7 h). In plasma, unchanged drug predominated but lower levels of the deacylated metabolite rhodamine 110 (RH-110) and two unknowns were also detectable throughout the study. Drug fluorescence was recovered extensively in both urine and bile. In unconscious animals with ureteral cannulae, urinary excretion (11.4% of the dose in 6 h) occurred predominantly as unchanged RH-123 (97% of the total), with low levels of RH-110 (2.4%) and two unknowns (less than 0.6% combined) also being present. Similarly dosed conscious animals (without surgical intervention) housed in metabolic cages showed a comparable pattern of urinary excretion, with 11.9% of the drug dose being recovered in 6 h and 21.9%, by 48 h. Biliary drug elimination accounted for 8% of the delivered dose in 6 h in unconscious animals and for 11% by 36 h in conscious animals fitted with biliary cannulae. In contrast to urinary excretion, in which unchanged drug predominated, only 50% of the fluorescence recovered in bile was attributable to RH-123. The remainder was due to a number of products that were detectable throughout the study. Of these, one present at significant levels was identified as a glucuronide conjugate of RH-123, based on the liberation of parent drug when the purified metabolite was incubated with beta-glucuronidase or hydrolyzed with 1 N hydrochloric acid. Further studies with a radiolabeled form of RH-123 are necessary to establish the identity of the remaining unknowns disclosed in this work.

Animals↗
PubMed1990

Conversion to estriol in "normal", benign and malignant human breast tissues.

Since there are controversial reports in the literature on 16 alpha-hydroxylase activity in human breast tumors, we have studied this enzyme activity in "normal", benign and malignant breast tissues by measuring the conversion of estradiol to estriol. Whereas 8 out of 14 (58%) malignant tumors showed positive activity, none of the other tissues had any detectable 16 alpha-hydroxylase activity. These preliminary results, when combined with reports in the literature on animal and human tissues, appear to indicate that more extensive studies on this enzyme could be useful as it could be an additional metabolic marker in human breast cancer.

Adult↗
PubMed1990

Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities in normal canine mammary gland and in mammary tumours and their correlation with oestrogen receptors.

Glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) activities were studied in 10 normal canine mammary glands and in 19 canine mammary tumours, which included seven benign and 12 malignant neoplasms. The malignant tumours were also examined for oestradiol receptors. The mean G-6-PD and 6-PGD activities were 5.17 +/- 1.84 and 1.65 +/- 0.64 IU per g protein in normal glands, 8.8 +/- 2.7 and 3.8 +/- 0.99 IU per g protein in benign and 19.6 +/- 5.2 and 8.5 +/- 2.1 IU per g protein in malignant mammary tumours. The enzyme activities were significantly higher in tumour tissue than in normal glands. Malignant tumours had much greater activity than benign. With the increasing anaplasia, there was a corresponding rise in the activity of the two enzymes. There was an inverse correlation between the oestrogen receptor (ER) status and the enzyme activity. The ER-positive tumours had low and ER-negative tumours had high enzyme activities.

Animals↗
PubMed1990

Steroid receptors in mammary glands and tumors of hysterectomised rats.

Epidemiological survey suggests that longer exposure of the breast to sex steroids may be one of the factors involved in increased risk for cancer. Using an experimental model of bilaterally hysterectomised rats, the sex steroid receptors in the mammary glands during growth as well as incidence and hormonal characteristics of chemically induced mammary tumors have been studied. Though steroid receptors were detectable in the mammary glands of the model earlier than in intact rats, the incidence or hormone dependency of the mammary tumors in the two groups were not considerably altered.

Animals↗
PubMed1990

Abrogation of the selectivity of adriamycin for negatively-charged phospholipids by 14-valerate side chain substitution.

The impressive affinity of Adriamycin and related anthracycline antibiotics for negatively-charged phospholipids has been implicated in the mechanism of the cardiac toxicity of these drugs. In this report we employ the method of fluorescence anisotropy titration to examine the manner in which 14-valerate side chain substitution modulates anthracycline drug associations with electroneutral vesicles composed of dimyristoyl phosphatidylcholine as well as negatively-charged vesicles composed of dimyristoyl phosphatidylglycerol or a binary mixture of dimyristoyl phosphatidylcholine and cardiolipin. Equilibrium binding data gathered on several anthracycline analogs indicate that incorporation of a hydrophobic valerate side chain abolished the high levels of preferential drug binding to negatively-charged membranes. Thus, we propose that 14-O-acyl substitution may prove to be a useful synthetic modification to prevent the selective accumulation of positively-charged anthracyclines in tissues or membrane domains rich in negatively-charged lipid.

Antibiotics, Antineoplastic↗
PubMed1989

DNA topoisomerase II-mediated interaction of doxorubicin and daunorubicin congeners with DNA.

Three groups of doxorubicin and daunorubicin analogues, differing by their substituents on the chromophore and sugar moieties, were used in this study. The 3'-N-unsubstituted (Group 1), 3'-N-acyl (Group 2), and 3'-N-alkyl (Group 3) analogues were tested for: (a) in vivo antitumor activity and in vitro cytotoxicity; (b) cellular or tissue uptake and metabolic conversion; (c) strength of DNA intercalation; and (d) interaction with DNA topoisomerase II (topo-II). Compounds of Group 1 were cytotoxic, were strongly intercalative, and, except for those with C-14 side chain substitution, induced the formation of topo-II-DNA cleavable complexes. As shown previously, esterolysis of C-14-acyl substituents was required to yield a metabolite which can interact with topo-II in the purified system. The C-14-substituted compounds of Group 2 and their C-14-unsubstituted metabolites were cytotoxic. These drugs were weak intercalators, and the C-14-unsubstituted cogeners induced cleavable complex formation in the purified system, but with reduced potency relative to doxorubicin. The type of the 3'-N-position substituent determined whether Group 3 analogues were cytotoxic and strong intercalators, or less active and nonintercalating. Although C-14-unsubstituted intercalators of Group 3 did not form cleavable complexes in the purified system, they were cytotoxic. The study shows that DNA intercalation is required but not sufficient for the activity by topo-II-targeted anthracyclines. In addition to the planar chromophore which is involved in intercalation, two other domains of the anthracycline molecule are important for the interaction with topo-II: (a) substitution of the C-14 position totally inhibits drug activity in the purified system, but enhances cytotoxicity by aiding drug uptake and presumably acting on other cellular targets; and (b) substitutions on the 3'-N position of the sugar ring can, depending on the nature of the substituent, inhibit intercalation and/or topo-II-targeting activity. These findings may provide guidance for the synthesis and development of new active analogues.

Animals↗
PubMed1989

A fluorescence study examining how 14-valerate side chain substitution modulates anthracycline binding to small unilamellar phospholipid vesicles.

The intrinsic fluorescence properties of the anthracycline antitumor antibiotics were studied in an effort to understand how 14-valerate side chain substitution modulates drug associations with small unilamellar phospholipid vesicles (SUVs) under near physiological conditions. Drug location and dynamics in fluid-phase dimyristoylphosphatidylcholine (DMPC) bilayers were evaluated for several analogs; accessibilities of bound fluorophores to membrane-impermeable iodide were evaluated in quenching experiments, while the diffusive motions of these agents were studied using lifetime-resolved anisotropy plots. The bulky and hydrophobic valerate substituent was found to further hinder the rotations experienced by a bound drug molecule, with apparent limiting anisotropy (a infinity) values showing increases of 13-82% upon valerate group substitution. In addition, the bimolecular quenching rate constants (unit, 10(9) M-1.s-1) for membrane-bound adriamycin (1.4), N-trifluoroacetyladriamycin (0.4), and their corresponding valerate-substituted analogs (kq values of 1.1 and 0.5, respectively) reveal that the side chain is a weak modulator of fluorophore penetration into the bilayer, with stronger modulation being achieved through amino group substitution. Similar results were obtained for drugs bound to negatively-charged dimyristoylphosphatidylglycerol (DMPG) bilayers. Finally, comparison of the equilibrium binding affinities of the various congeners for electroneutral DMPC versus negatively-charged DMPG bilayers demonstrate that positively-charged parent anthracyclines display high levels of selective binding to negatively-charged phospholipids, unlike valerate-substituted analogs which display no such selectivity. The modulation of anthracycline-membrane interactions achieved through valerate substitution offers potential explanations, at least in part, for some of the novel biological properties of valerate-containing anthracyclines.

Antibiotics, Antineoplastic↗
PubMed1989

The significance of oncogene amplification in primary breast cancer.

Alterations in the gene copy numbers of the proto-oncogenes HER2/neu and c-myc in primary human breast cancer investigated in 73 patients. We detected amplification of HER2/neu in 17 patient samples and amplification of c-myc in 11, while amplification of both was seen in 6 samples. There was no correlation of age, hormone receptor positivity or tumour size with amplification of either proto-oncogene. Amplification of HER2/neu was significantly correlated with the stage of the disease. HER2/neu amplification was observed in 18.5% and 38% of node-negative and node-positive patients, respectively; the association between HER2/neu amplification and advanced stage of the disease was statistically significant (p = 0.05). Since this is a prospective study, the clinical significance of oncogene amplification is not known. The relatively high frequency of HER2/neu amplification points to a functional role in human breast cancer, particularly in the progression of the disease. The method used in our study allows oncogene amplification to be studied in conjunction with hormone receptor determination and thus may be of value in large clinical trials to determine the significance of oncogene abnormalities in breast cancer.

Breast Neoplasms↗
PubMed1989

Comparative uptake and retention of adriamycin and N-benzyladriamycin-14-valerate in human CEM leukemic lymphocyte cell cultures.

N-Benzyladriamycin-14-valerate (AD 198) is a new lipophilic adriamycin (ADR) analogue that shows marked therapeutic superiority to ADR in murine tumor model systems yet differs mechanistically from ADR in a number of ways. Among its other properties, AD 198 produces a delayed but profound effect on cell-cycle progression and a pattern of continuing DNA damage in cultured cells briefly exposed to the drug. Using radiolabeled drug forms and radioassays combined with HPLC separation and fluorimetric detection techniques, aspects of drug accumulation, biotransformation, and retention in cultured human CEM leukemic lymphocytes were studied, in part to determine a possible pharmacologic basis for the latent effects seen with this drug. In addition, the cellular pharmacology of AD 198 and ADR were comparatively examined under identical experimental conditions. When CEM cells were incubated with drug at equi-growth inhibitory/minimally cytotoxic concentrations (AD 198, 1.0 microM; ADR, 0.1 microM), a number of differences were apparent. Under conditions of continuous 24-h drug exposure, a slow cellular accumulation and equilibration was observed with ADR (cell: medium equilibrium, 1:11 after 4-6 h), whereas the uptake of AD 198 was rapid and extensive (cell: medium equilibrium, 3:1 within 30 min). In drug-retention studies, when cells were pretreated at the same drug concentrations as before (AD 198 for 1 h; ADR for 4 h) and then transferred to drug-free media, both compounds re-equilibrated their intracellular drug content with the fresh media, losing about 50% of their respective anthracycline levels. Liquid chromatographic analysis of ADR-treated cultures under both sets of conditions showed the parent drug to be the only intracellular anthracycline species, whereas analysis of AD 198-treated cultures revealed two fluorescent signals corresponding to the parent drug and its 14-de-esterified biotransformation product, N-benzyladriamycin (AD 288). Levels of AD 288 rose from 2% of the total intracellular anthracycline content immediately on drug admixture to 61% following 24 h continuous drug exposure and to 69% at 24 h in cells exposed to drug for 1 h and then continued in drug-free media for 24 h. At all times, the balance of the intracellular anthracycline fluorescence was attributable to the parent drug; no ADR was detectable in AD 198-treated cells by either fluorescence detection or radioassay.(ABSTRACT TRUNCATED AT 400 WORDS)

Biotransformation↗
PubMed1989

Interaction of N-alkylanthracyclines with lipid bilayers: correlations between partition coefficients, lipid phase distributions and thermotropic behavior.

The thermotropic behavior of multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC), or of DPPC in admixture with cardiolipin or cholesterol, in the presence of various N-alkyl derivatives of both adriamycin and adriamycin-14-valerate has been investigated by high sensitivity differential scanning calorimetry. The analogues, particularly the 14-valerate derivatives, which were most lipophilic as judged by their lipid/buffer, and to a lesser extent by their octanol/buffer, partition coefficients, were the most effective in depressing the tm of the investigated lipids; correlations, however, were not absolute. Other factors, such as the distribution of the drugs between the solid and liquid-crystalline phases of the bilayer, were also important to the observed membrane perturbations. With all anthracyclines, however, no major changes in the transition enthalpy were observed. In the case of vesicles prepared from pure DPPC, curve fitting analysis based on ideal solution theory (J.M. Sturtevant (1984) Proc. Natl. Acad. Sci. USA 81, 1398-1400) applied at relatively low drug concentrations where single peak transitions were produced, adequately described the differential scanning calorimetric results. At high drug concentrations, however, the presence of multi-peak transitions were indicative of non-ideality.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

N-benzyladriamycin-14-valerate versus progressively doxorubicin-resistant murine tumours: cellular pharmacology and characterisation of cross-resistance in vitro and in vivo.

N-Benzyladriamycin-14-valerate (AD198) is a novel lipophilic anthracycline with greater in vivo antitumour activity than doxorubicin (DOX) in experimental model systems. Using sensitive and progressively DOX-resistant L1210 mouse leukaemia and B16-BL6 mouse melanoma lines, we have determined the cellular pharmacokinetics and cytotoxic response in vitro and in vivo of AD198. In the L1210 leukaemia model following 3 h drug exposure in vitro, the IC50 for AD198 was approximately 0.35 microgram ml-1 for the sensitive and 10-fold DOX resistant cells and 1.0 microgram ml-1 for the 40-fold DOX resistant cells. A similar pattern of cross-resistance to AD198 was also observed with the B16-BL6 melanoma, with and IC50 for AD198 with the sensitive and 10-fold DOX-resistant cells being similar, and about 2-fold higher with the 40-fold resistant cells. In the L1210 leukaemia model, cellular pharmacokinetics of AD198 revealed the following: (a) accumulation of AD198 was concentration but not time dependent, and cellular drug levels in the sensitive and resistant sublines were similar when treated with equimolar concentrations; (b) retention of AD 198 was 60% of the initial drug uptake and, in cells treated with the IC50 of AD198, cellular levels in the 40-fold DOX-resistant line were, as expected, 2-fold higher than in sensitive or 10-fold DOX-resistant cells; (c) in vitro biotransformation of AD 198 in the sensitive and resistant sublines was comparable. Studies in vivo with i.p. L1210 leukaemia (disseminating) and B16-BL6 melanoma (non-disseminating) tumour models evaluating therapeutic efficacy of DOX vs AD 198 in mice implanted with tumour i.p. on day 0 and treated i.p. on days 1-4 indicated: (a) DOX at 3 mg kg-1 administered once daily on days 1-4 resulted in a 55% ILS and 104% ILS with parent-sensitive B16-BL6 melanoma and L1210 leukaemia models respectively; however, similar doses of DOX in the resistant sublines were ineffective, with survival similar to the untreated control; (b) AD198 at 10-12.5 mg kg-1 day-1 for 4 days was extremely effective in the sensitive L1210 (189% ILS), and similar to DOX (61% ILS) in the sensitive B16-BL6; (c) AD198 (10-12.5 mg kg-1) was ineffective (survival similar to untreated control) in the 10-and 40-fold DOX-resistant L1210 leukaemia and 40-fold DOX resistant B16-BL6 melanoma, but produced a 76% ILS in the 10-fold DOX resistant B16-BL6 melanoma.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Bilateral testicular and adrenal malignant lymphoma of pre B-cell type.

A rare case of pre B-lymphoblastic lymphoma of the testes and adrenal glands is presented. No lymph node, central nervous system or bone marrow involvement was demonstrated at diagnosis. The primary presentation was of acute unilateral pain and swelling, mimicking simple orchitis. The diagnosis was made using aspiration cytology and the lymphoma characterized using immunohistochemical, electron microscopic and karyotype analysis techniques. Pre B-cell markers were clearly demonstrated by all criteria used. Monoclonal antibodies (FMC 29 and FMC 31) were used to define the early B-cell nature of the lymphoma. Confirmation using karyotype analysis in addition to immunoglobulin and T-cell beta-receptor gene rearrangement was obtained. Intrathecal chemotherapy was used prophylactically. Combination chemotherapy produced regression of the primary lymphomatous lesions, but subsequent bone marrow spread led to death.

Adrenal Gland Neoplasms↗
PubMed1989

Presence of calcitonin-like peptide in rat milk: possible physiological role in regulation of neonatal prolactin secretion.

Previous results have shown that salmon calcitonin (sCT), a peptide in rat brain and pituitary gland, inhibits basal and TRH-stimulated PRL release and reduces PRL mRNA levels in isolated anterior pituitary cells of adult rats in culture. Rat milk contains a variety of neuropeptides and hormones, some of which are absorbed in bioactive form to exert endocrine influences in the developing offspring. The present studies were undertaken to investigate whether a CT-like peptide is present in rat milk. Circulating PRL levels in neonatal rats are low, and there is an abrupt increase in the basal secretion of this hormone at weaning. A second objective was to examine whether CT plays a role in the regulation of PRL secretion in neonatal animals. A sensitive and specific RIA for sCT was developed and used to assay rat milk on various days of lactation for sCT-like immunoreactivity. sCT-like activity was present in the water-soluble (infranatant) fraction of milk throughout lactation in concentrations as high as 1589 pg/ml. There were no statistically significant differences in immunoreactive levels of the peptide in milk samples from different days of lactation. sCT-like immunoreactivity in rat milk infranatant coeluted with synthetic sCT on reverse phase HPLC, and these HPLC fractions inhibited basal PRL release when added to cultures of anterior pituitary cells. This inhibition of PRL release by the sCT-immunoreactive HPLC fractions was comparable to that exerted by equivalent concentrations of synthetic sCT. Newborn rats were injected sc with 10 microliters normal rabbit serum or anti-sCT serum from the day of birth until postpartum day 10. The rats were killed on day 11, and their sera were analyzed for PRL. Anti-sCT-injected rats showed a significant increase in serum PRL levels compared to those in untreated or normal serum-treated rats. These results demonstrate that a CT-like peptide, which is a potent inhibitor of PRL release, is present in rat milk throughout lactation, and that passive immunization with a highly specific anti-sCT serum leads to an increase in serum PRL levels in neonatal rats. CT, possibly of milk origin, may be a physiologically relevant PRL-inhibiting factor during the neonatal period.

Animals↗