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Biomedical subjects

S B Howell

Publications and source records attributed to S B Howell.

At least 127 records · Page 7Linked to original sources
PubMed1992

Synergism between dipyridamole and cisplatin in human ovarian carcinoma cells in vitro.

Dipyridamole (DPM), a nucleoside membrane transport inhibitor, enhanced the cytotoxicity of cisplatin (DDP) for human ovarian carcinoma 2008 cells by a factor of 4.7 +/- 0.4-fold (mean +/- SD) and for the 10-fold DDP-resistant 2008/C13*5.25 subline by a factor of 5.8 +/- 2.7-fold. This interaction was shown to be truly synergistic by isobologram and median effect analysis. DPM enhancement of DDP cytotoxicity was schedule dependent; it was greatest when cells were exposed to DPM continuously during and following a 1-h exposure to DDP and less pronounced when DPM exposure was limited to pretreatment or concurrent treatment only. DPM increased DDP uptake in a concentration-dependent manner as measured with both [195mPt]-DDP and the DDP analogue [3H]-cis-dichloro(ethylenediamine) platinum. Nitrobenzylthioinosine, another nucleoside membrane transport inhibitor, did not enhance DDP cytotoxicity or uptake at concentrations that produced equivalent degrees of inhibition of [3H]uridine uptake. DPM did not interact synergistically through an increase in cellular cyclic AMP levels. DPM did not increase trypan blue or propidium iodide uptake, or change cell size, indicating that it did not nonspecifically increase membrane permeability. We conclude that DPM interacts synergistically with DDP and that, while an increase in DDP uptake is one component of the mechanism of this interaction, there are additional components since maximal effect was observed only with prolonged DDP exposure.

Carcinoma↗
PubMed1992

Increased gene-specific repair of cisplatin interstrand cross-links in cisplatin-resistant human ovarian cancer cell lines.

We have studied several aspects of DNA damage formation and repair in human ovarian cancer cell lines which have become resistant to cisplatin through continued exposure to the anticancer drug. The resistant cell lines A2780/cp70 and 2008/c13*5.25 were compared with their respective parental cell lines, A2780 and 2008. Cells in culture were treated with cisplatin, and the two main DNA lesions formed, intrastrand adducts and interstrand cross-links, were quantitated before and after repair incubation. This quantitation was done for total genomic lesions and at the level of individual genes. In the overall genome, the initial frequency of both cisplatin lesions assayed was higher in the parental than in the derivative resistant cell lines. Nonetheless, the total genomic repair of each of these lesions was not increased in the resistant cells. These differences in initial lesion frequency between parental and resistant cell lines were not observed at the gene level. Resistant and parental cells had similar initial frequencies of intrastrand adducts and interstrand cross-links in the dihydrofolate reductase (DHFR) gene and in several other genes after cisplatin treatment of the cells. There was no increase in the repair efficiency of intrastrand adducts in the DHFR gene in resistant cell lines compared with the parental partners. However, a marked and consistent repair difference between parental and resistant cells was observed for the gene-specific repair of cisplatin interstrand cross-links. DNA interstrand cross-links were removed from three genes, the DHFR, multidrug resistance (MDR1), and delta-globin genes, much more efficiently in the resistant cell lines than in the parental cell lines. Our findings suggest that acquired cellular resistance to cisplatin may be associated with increased gene-specific DNA repair efficiency of a specific lesion, the interstrand cross-link.

Blotting, Southern↗
PubMed1992

Modulation of cisplatin sensitivity and growth rate of an ovarian carcinoma cell line by bombesin and tumor necrosis factor-alpha.

A twofold change in the cisplatin (DDP) sensitivity of 2008 human ovarian carcinoma cells is sufficient to reduce tumor response in vivo. The DDP sensitivity of these cells can be enhanced by activation of the epidermal growth factor and protein kinase C signal transduction pathways. We report here that two endogenous growth factors, bombesin and tumor necrosis factor alpha (TNF alpha), enhanced DDP sensitivity by factors of 1.7 +/- 0.1 (SD)-fold and 1.8 +/- 0.1 (SD)-fold, respectively. Both agents also produced sensitization in an 11-fold DDP-resistant 2008 subline. Neither bombesin nor TNF alpha changed the accumulation of DDP, glutathione content, or glutathione-S-transferase activity in 2008 cells. However, a 2-h exposure to both bombesin and TNF alpha was sufficient to increase 2008 cloning efficiency by up to 2.6 +/- 0.1 (SD)-fold and 2.2 +/- 0.1 (SD)-fold, and it increased average colony size by 1.35 +/- 0.1 (SD)-fold and 1.55 +/- 0.1 (SD)-fold, respectively. Bombesin increased intracellular free calcium, and this was blocked by the bombesin receptor-specific antagonist SC196, demonstrating that 2008 cells have functional bombesin receptors. These results indicate that bombesin and TNF alpha can enhance sensitivity to DDP in both DDP sensitive and resistant variants of a human ovarian carcinoma and that both agents serve as growth factors for this tumor.

Bombesin↗
PubMed1992

Intraperitoneal therapy in the management of patients with ovarian cancer.

Basic pharmacologic principles support the concept that more drugs can be delivered to the tumor when it is delivered through the intraperitoneal route. Pharmacokinetic studies have confirmed that for many chemotherapeutic agents a substantial pharmacologic advantage can be achieved using this approach. Preliminary studies have suggested that intraperitoneal chemotherapy may be especially advantageous in patients with small-volume disease or in patients who have a negative second-look laparotomy. Clinical studies are ongoing to further define the role intraperitoneal therapy will play in the management of patients with ovarian cancer.

Antineoplastic Agents↗
PubMed1992

Enhancement of the loss of multiple drug resistance by hydroxyurea.

Gene amplification is one mechanism whereby tumor cells can become resistant to antineoplastic agents. Unstably amplified genes occur either on submicroscopic circular pieces of extrachromosomal DNA called episomes or on small acentric chromosomes called double minutes. Double minutes are frequently associated with cells containing amplified drug-resistance genes. Human epidermoid carcinoma KBV1 cells contain unstably amplified mdr1 genes and overexpress P glycoprotein, resulting in decreased intracellular drug accumulation. In this cell line, a nonlethal concentration of hydroxyurea accelerated the rate of loss of vinblastine resistance once vinblastine had been removed from the culture medium. After removal of vinblastine, KBV1 cells exposed to hydroxyurea for the time required to complete 12 cell doublings accumulated more vinblastine than control cells grown in the absence of hydroxyurea. In contrast, hydroxyurea had no effect on vinblastine sensitivity and accumulation in parental drug-sensitive KB-3-1 cells. Hydroxyurea also had no effect on sensitivity to cisplatin in cisplatin-resistant human ovarian carcinoma 2008/C13* cells, indicating that hydroxyurea's effect on drug sensitivity was specific for a drug-resistance phenotype associated with unstably amplified drug-resistance genes. These results indicate that, after removing selective pressure, hydroxyurea accelerates loss of resistance to vinblastine and increases accumulation of vinblastine in KBV1 cells, presumably by accelerating loss of amplified mdr1 genes and thus P glycoprotein.

Carcinoma, Squamous Cell↗
PubMed1991

Expression of the c-Ha-ras oncogene in mouse NIH 3T3 cells induces resistance to cisplatin.

The effect of expression of the c-Ha-ras oncogene on cisplatin (DDP) sensitivity was examined in murine NIH 3T3 cells transfected with the dexamethasone (DEX)-inducible mouse mammary tumor virus promoter linked to an activated c-Ha-ras gene [LTR H-ras(A) cells]. Treatment of these cells with 5 microM DEX for 24 h induced c-Ha-ras expression and produced an 8.2 +/- 1.3-fold (SD) increase in DDP resistance as quantitated by clonogenic assay. Induction of the c-Ha-ras oncogene reduced DDP accumulation by 40% and intrastrand adduct formation by 17%. In nontransfected wild-type NIH 3T3 cells, DEX did not induce DDP resistance nor did it decrease DDP accumulation. Induction of c-Ha-ras expression did not alter cellular glutathione content or the activity of glutathione-S-transferase in the LTR H-ras(A) cells. DEX increased cellular metallothionein content by 1.6-fold in NIH 3T3 cells and 3.3-fold in LTR H-ras(A) cells. We conclude that DEX-induced overexpression of a mutant c-Ha-ras gene confers DDP resistance and that this resistance is associated with an impairment of cellular drug accumulation and an increase in metallothionein content.

3T3 Cells↗
PubMed1991

Modulation of cis-diamminedichloroplatinum(II) accumulation and sensitivity by forskolin and 3-isobutyl-1-methylxanthine in sensitive and resistant human ovarian carcinoma cells.

We have determined the effect of forskolin, an adenyl cyclase agonist, and 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, on the accumulation and cytotoxicity of cisplatin (DDP) in 2008 human ovarian carcinoma cells. In DDP-sensitive 2008 cells, forskolin and IBMX caused 2.1-fold and 2.3-fold increases, respectively, in the short-term accumulation of DDP relative to untreated cells. The inactive analogue, 1,9-dideoxyforskolin, decreased DDP accumulation. Forskolin and IBMX also increased accumulation in A2780 cells. Neither forskolin nor IBMX had any effect on DDP accumulation in DDP-resistant 2008 cells. The effects were detectable as early as 1 min and persisted at 60 min. The concentrations for half-maximal stimulation of DDP accumulation were approximately 0.2 microM for forskolin and 0.2 mM for IBMX. Forskolin caused marked increases in cAMP levels in both sensitive and resistant 2008 cells within 1 min, although there were differences in the subsequent time-courses of the response. Both 2008 cell types had identical cAMP-dependent protein kinase (PKA) activity. These results suggest that there is a target downstream of PKA that is an important participant in DDP accumulation, and that this target is defective or missing in DDP-resistant cells. Following a 1-hr exposure to drugs, forskolin and IBMX at concentrations that were by themselves completely non-toxic increased the slopes of the clonogenic survival vs. DDP concentration curves in 2008 cells 1.9-fold and 3.3-fold, respectively. In DDP-resistant 2008 cells, however, forskolin and IBMX increased the slopes only 1.2 and 2.6-fold, respectively. These effects of forskolin and IBMX on DDP cytotoxicity did not directly correlate with the effects on the 1-hr DDP accumulation which suggested that, in addition to modulating DDP accumulation, these agents increase the cytotoxicity of the intracellular platinum. The results indicate that modulation of cAMP levels can have important effects on DDP accumulation and cytotoxicity in 2008 cells and that these effects are significantly diminished in DDP-resistant cells.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Phase I and pharmacokinetic trial of intraperitoneal etoposide in combination with the multidrug-resistance-modulating agent dipyridamole.

Dipyridamole synergistically enhances the sensitivity of human ovarian carcinoma cells to etoposide in vitro. We conducted a phase I trial to investigate the feasibility of using dipyridamole to selectively increase the sensitivity to etoposide of tumors confined to the peritoneal cavity. Etoposide and dipyridamole were administered as a continuous 72-hour intraperitoneal infusion to 16 patients. The maximum tolerated dose of etoposide was 175 mg/m2 per day when administered with dipyridamole at a fixed dose of 24 mg/m2 per day. Dose-limiting toxic effects were leukopenia and thrombocytopenia. No other major toxic effects were observed. The free peritoneal etoposide and dipyridamole concentrations varied with the etoposide dose rate, reaching 218.9 and 25.3 microM, respectively, at an etoposide dose rate of 175 mg/m2 per day. The free etoposide and dipyridamole concentrations attained were well within the range needed for synergistic interaction.

Adult↗
PubMed1991

Modulation of vinblastine sensitivity by dipyridamole in multidrug resistant fibrosarcoma cells lacking mdr1 expression.

We examined the ability of dipyridamole (DPM) to act synergistically with vinblastine (VBL) in HT1080 fibrosarcoma cells and a drug-resistant variant, HT1080/DR4, which lacks mdr1 expression, in order to determine whether DPM requires P-glycoprotein to modulate drug sensitivity. Median effect analysis of clonogenic assay was used to produce the combination index (CI50, values less than 1 indicate synergy). DPM was mildly synergistic with VBL producing a CI50 of 0.83 +/- 0.13 for HT1080 cells and 0.80 +/- 0.16 for HT1080/DR4 cells. HT1080 and HT1080/DR4 cells accumulated 6.7 +/- 0.7 and 5.6 +/- 0.9 pmol 3H-VBL mg cells-1 at steady state (Css) and 20 microM DPM elevated the Css by 1.8 and 2.9-fold, respectively. In comparison, the CI50 was 1.1 +/- 0.2 in parental KB-3-1 cells and 0.1 +/- 0.1 in mdr1-expressing KB-GRC1 cells. The KB-3-1 and KB-GRC1 cells had a Css of 3.8 +/- 0.8 and 0.7 +/- 0.2 pmol 3H-VBL mg cells-1, respectively, and DPM elevated the Css by 9.2-fold in KB-GRC1 cells. These studies demonstrate that DPM can produce synergy independently of mdr1 expression but that much greater levels of synergy are achievable in mdr1-expressing tumour cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

A phase II trial of intraperitoneal cisplatin and etoposide as salvage treatment for minimal residual ovarian carcinoma.

We conducted a phase II study of intraperitoneal (IP) cisplatin (CDDP) and etoposide (VP-16) as salvage therapy in patients with ovarian cancer who had persistent disease or who had relapsed after primary systemic chemotherapy and had residual disease of less than 2 cm. Two hundred eleven courses of IP chemotherapy consisting of CDDP 200 mg/m2 and VP-16 350 mg/m2 were administered. All patients received intravenous (IV) thiosulfate protection. Treatment was given once every 4 weeks for a median of six cycles. Twenty-four of 37 assessable patients were clinically free of disease at the end of treatment (normal physical exam, computed tomographic [CT] scan, CA-125 and peritoneal cytology); one patient had a partial response. Ten of these 24 patients consented to reexploration at the end of treatment, and nine were in pathologic complete remission, while one patient had positive peritoneal washings as her only evidence of persistent disease. The median survival of the 37 patients was 26 months from the first day of IP treatment and 51 months from diagnosis. The major toxicity was myelosuppression, with median nadir WBC, granulocyte, and platelet counts of 2,400, 684, and 134,000/mm3, respectively. There was no cumulative renal damage, hypomagnesemia, or chemical peritonitis. We conclude that IP CDDP and VP-16 can produce pathologic complete remissions when used as a second-line regimen for patients with ovarian cancer who have received systemic cisplatin-based therapy and have less than 2 cm disease.

Adult↗
PubMed1991

Intraperitoneal cisplatin-based chemotherapy for ovarian carcinoma.

Ovarian carcinoma demonstrates a steep dose-response curve for cisplatin, but even very small levels of acquired resistance at the cellular level are sufficient to block the efficacy of intravenous (IV) cisplatin. The intraperitoneal (IP) route of administration produces a 12-fold to 15-fold greater exposure for the peritoneal cavity, and concurrent use of IV thiosulfate permits the safe IP injection of 200 mg/m2 cisplatin. In this study, two phase II trials of an IP regimen containing cisplatin 200 mg/m2 and etoposide 350 mg/m2 with IV thiosulfate were conducted; the first trial enrolled patients with residual disease less than 2 cm who had failed primary cisplatin-based IV chemotherapy and the second trial newly diagnosed ovarian carcinoma patients irrespective of the size of residual disease after primary surgery. As salvage therapy, the IP cisplatin/etoposide regimen produced a median survival of 26 months from the start of IP therapy and 51 months from diagnosis. As first-line therapy, the median survival has not yet been reached; projected survival is 68% at 27 months. In both studies the major toxicity was myelosuppression; the use of concurrent thiosulfate almost completely eliminated serious nephrotoxicity and neurotoxicity. The size of the largest tumor mass was an important determinant of efficacy in both settings. The results of these trials are consistent with the hypothesis that increased drug delivery will result in higher response rates and improved survival. Data are sufficiently encouraging to mandate phase III randomized trials of this program.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1990

Modulation of drug sensitivity by dipyridamole in multidrug resistant tumor cells in vitro.

The concept of overcoming multidrug resistance using modulators is based on the hypothesis that there will be a synergistic interaction between the modulator and the cytotoxic agent. We examined the ability of dipyridamole (DPM) to synergistically enhance drug sensitivity in drug-sensitive KB-3-1 cells and their drug-resistant variants, KB-GRC1 and KBV1 cells, using median effect analysis to produce a quantitative measure of the extent of synergy. The drug-resistant variants were resistant to vinblastine (VBL), colchicine (COL), and etoposide (VP-16) in the order VBL greater than COL greater than VP-16 on the basis of 50% inhibitory concentration values obtained by clonogenic assay with continuous drug exposure. The extent of staining with the monoclonal antibody HYB-241, directed at a Mr 180,000 form of the mdrI gene product, correlated with drug resistance for all three drugs (r greater than or equal to 0.92). DPM and verapamil elevated the steady state content (Css) of VBL, but there was no correlation between elevation of Css and the extent of synergy observed. DPM enhanced the cytotoxicity of VBL and COL in a synergistic manner in KB-GRC1 cells, and in KBV1 cells DPM interacted synergistically with VBL. VPL was synergistic with VBL only in KB-GRC1 cells. No synergy was observed in the parental KB-3-1 line. These data indicate that, although both DPM and verapamil can increase Css in cells not expressing P-glycoprotein, such an increase was not associated with synergy. In cells expressing mdrl, synergy was observed, and it was greatest for the cytotoxic agent for which expression of mdrl produced the greatest fold-resistance and enhancement of Css. However, neither the level of resistance, the level of expression of mdrl, nor the ability of the modulator to alter Css accurately predicted whether the interaction would be truly synergistic. We conclude that additional factors determine the nature of the drug interaction.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Increased sensitivity to cis-diamminedichloroplatinum(II) in human ovarian carcinoma cells in response to treatment with 12-O-tetradecanoylphorbol 13-acetate.

The tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) enhanced sensitivity to cis-diamminedichloroplatinum(II) (DPP) in human ovarina carcinoma 2008 cells by a factor of 2.53 +/- 0.74 fold (S.D.). Sensitization was maximum 3 h after a 1-h exposure to TPA and had disappeared completely by 7 h after treatment. An equivalent degree of sensitization was produced in a 2008 variant selected for 10-fold resistance to DDP. TPA neither increased nor decreased cellular accumulation of DDP. Phorbol, a TPA analog which does not activate protein kinase C, did not cause sensitization. This synergistic interaction between TPA and DDP was completely inhibited by pretreatment with staurosporine, a protein kinase C inhibitor. Cellular cAMP was not altered by TPA stimulation. Furthermore, cycloheximide, a potent protein synthesis inhibitor, did not block the TPA-induced enhancement of drug sensitivity. These results strongly suggest that DDP sensitivity can be modulated by protein kinase C and regulated by phosphorylation of a protein kinase C substrate in both intrinsically sensitive and DDP-resistant cells.

Alkaloids↗
PubMed1990

Short-term cis-diamminedichloroplatinum(II) accumulation in sensitive and resistant human ovarian carcinoma cells.

We examined the short-term accumulation of cisplatin (DDP) in sensitive 2008 human ovarian carcinoma cells and in a 2- to 3-fold DDP-resistant and accumulation-deficient variant. During the 1st min of exposure to 500 microM DDP, sensitive cells accumulated platinum at a rate of 187 +/- 63 pmol/mg protein per min, whereas resistant cells accumulated platinum at 123 +/- 85 pmol/mg protein per min, a rate that was 66% that of sensitive cells. From 2-10 min of exposure, sensitive and resistant cells accumulated the drug at rates of 51.4 +/- 21.5 and 34.0 +/- 9.70 pmol/mg protein per min, respectively. In resistant cells, this rate again represented 66% that of sensitive cells. For each cell line, the DDP accumulation was 3.6 times faster during the 1st min than it was over 2-10 min. Initial DDP accumulation was linear with drug concentration in each cell line. Efflux measurements were made over a 50-min period after a 10-min load in 500 microM DDP. The loss of platinum was biphasic in each cell line, with an initial, rapidly effluxing component being lost within 10 min in each cell line. The rate constant for loss of platinum from this rapidly effluxing pool, measured after a 10-min loading period in 500 microM DDP, was 0.67 +/- 0.09 s-1 in sensitive cells and 1.03 +/- 0.15 s-1 (a 53% increase) in resistant cells. Between 5 and 50 min of an accumulation time course in 500 microM DDP, the size of the rapidly effluxing platinum pool remained relatively constant in each cell line, with the major contribution to the increase in total platinum over time coming from growth of the slowly effluxing platinum pool. We conclude that diminished retention of platinum in the rapidly effluxing pool of resistant cells is a major determinant of decreased DDP accumulation in these cells.

Cisplatin↗
PubMed1990

Extremely prolonged continuous intraperitoneal infusion of cytosine arabinoside.

Intraperitoneal administration of ara-C produces a peritoneal/plasma concentration ratio of 330-1,000: In principle, optimal tumor-cell kill should be obtained when high ara-C concentrations ar maintained in the environment of the tumor for very long periods of time. A phase 1 study was undertaken to determine the maximum tolerated dose of ara-C that could be given as a continuous i.p. infusion for 3 weeks. A total of 14 patients with refractory malignancies were given 28 courses in the outpatient setting. Ara-C infusions were given using a portable programmable pump (Pancreatec Provider Model 2000). No significant side effects were observed in patients receiving 30 mg/m2 per day (five courses) or 40 mg/m2 per day x 21 days (seven courses). However, at a dose of 60 mg/m2 per day, although 10/16 courses were tolerated for at least 1 week, only 3/16 attempted courses could be continued for the full 3 weeks. The dose-limiting toxicity was chemical peritonitis, which occurred during 7/16 courses at this dose level and required termination of therapy in 4 courses. Myelosuppression was also observed at this dose. There was a large variation in the ara-C and ara-U peritoneal concentrations both within and between patients. The mean peritoneal ara-C concentration increased nonlinearly with ara-C dose whereas the mean ara-U concentration decreased. This study establishes the feasibility and safety of giving a cell-cycle-specific drug intraperitoneally over an extremely prolonged period. For subsequent studies a dose of 40 mg/m2 per day for 21 days is recommended.

Adult↗
PubMed1990

A review: intraperitoneal cisplatin in the management of patients with ovarian cancer.

Since ovarian cancer remains confined to the peritoneal cavity for the majority of its natural history, it provides us with a unique opportunity to explore the possibility of administering chemotherapeutic agents in direct contact with the tumor. Sound pharmacologic principles have been developed that allow us to predict with accuracy agents that should be useful in this approach. The peritoneal pharmacokinetics of a number of active chemotherapeutic agents have been investigated and several effective agents have been identified. Cisplatin has been extensively investigated and has demonstrated excellent activity when used in this fashion. The recognition of sodium thiosulfate as a renal protective agent, against cisplatin-induced nephrotoxicity, has allowed for significant dose escalation of cisplatin. The favorable pharmacokinetic profile and clinical activity of cisplatin render it an important component of intraperitoneal chemotherapy regimens.

Antineoplastic Combined Chemotherapy Protocols↗