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Biomedical subjects

S B Howell

Publications and source records attributed to S B Howell.

At least 217 records · Page 12Linked to original sources
PubMed1984

Kinetics of sodium thiosulfate, a cisplatin neutralizer.

Sodium thiosulfate kinetics were studied in eight subjects, six of whom were given the drug as a cisplatin neutralizer. Thiosulfate at a dose of 12 gm/m2 was injected by continuous intravenous infusion over 6 hr. Under these conditions, steady-state plasma concentrations were not achieved and apparent volume of distribution could not be calculated. The drug was eliminated from plasma by first-order kinetics, and the data best fit a one-compartment kinetic model with a t1/2 (mean +/- SD) of 80 +/- 38 min. Total body thiosulfate clearance was 190 +/- 76 ml/min/m2 and renal clearance was 50 +/- 11 ml/min/m2. The plasma elimination t1/2 and renal thiosulfate clearance correlated poorly with clearance of endogenous creatinine. Only 28.5% +/- 9.4% of the thiosulfate was recovered unchanged in the urine. Urinary excretion was rapid, with approximately 95% of recoverable drug eliminated within 4 hr after termination of the infusion. No toxic effects of thiosulfate were observed. These data provide the basis for the rational development of dose schedules when sodium thiosulfate is used as a cisplatin neutralizer.

Adult↗
PubMed1984

Combination intracavitary chemotherapy for malignant pleural disease.

Seven previously heavily pretreated patients with malignant pleural disease and effusions were treated with 12 courses of combination intrapleural chemotherapy with cisplatin, cytarabine, and doxorubicin. Two patients with ovarian cancer metastatic to the pleura demonstrated dramatic clinical improvement following therapy. Local pain, nephrotoxicity, or bone marrow suppression were not observed during this trial. Further investigation of intrapleural therapy utilizing an escalated dose of cytarabine is warranted.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

Totally implantable system for peritoneal access.

A totally implantable system for providing access to the peritoneal cavity was evaluated. Fifty-six Port-A-Cath (Pharmacia Nu Tech, Piscataway, NJ) peritoneal access systems were implanted in 54 cancer patients receiving intraperitoneal chemotherapy. The catheters are accessed by transcutaneous placement of a Huber point needle through a silicone septum at the top of the portal. A total of 32 patient years of experience are reported. The Port-A-Caths have been in place for a median of 22 weeks (range, one to 85). A total of 401 entries have been made for paracentesis, chemotherapy administration, antibiotic administration, peritoneal lavage for cytology, and catheter flushing. There have been six episodes of peritonitis (five Staphylococcus epidermidis, one S aureus) in three patients. There have been no mechanical failures of the Port-A-Caths. Loss of bidirectional flow through the catheter due to fibrin deposition about the catheter has been the major cause of catheter failure. Patient acceptance of the Port-A-Cath has been excellent.

Antineoplastic Agents↗
PubMed1984

Combination intraperitoneal chemotherapy with cisplatin, cytarabine, and doxorubicin for refractory ovarian carcinoma and other malignancies principally confined to the peritoneal cavity.

Thirty-one patients with refractory ovarian cancer and other malignancies principally confined to the abdominal cavity were treated with an intraperitoneal combination-chemotherapy regimen consisting of cisplatin (100 to 200 mg/m2), cytosine arabinoside (10(-4) to 10(-3) mol/L) and doxorubicin (2 to 18 mumol/L). Sodium thiosulfate was simultaneously administered intravenously to prevent cisplatin-induced nephrotoxicity. Eight of 26 evaluable patients demonstrated clinical response including seven of 17 (41%) with ovarian cancer refractory to frontline chemotherapy. Systemic toxicity was mild except for nausea and vomiting. Abdominal pain secondary to doxorubicin was the major complication of therapy. We conclude that combination intraperitoneal therapy with cisplatin, cytosine arabinoside, and doxorubicin can be safely administered with objective tumor responses observed in patients with ovarian cancer heavily pretreated and in individuals with other malignancies involving the peritoneal cavity. Doxorubicin-induced local pain limits the ability to administer multiple courses of this treatment regimen.

Adult↗
PubMed1984

Intraperitoneal cytosine arabinoside therapy in ovarian carcinoma.

Previous pharmacokinetic modeling has suggested that cytosine arabinoside (ara-C) may be an ideal agent for peritoneal administration in the treatment of intraabdominal neoplasms. In vitro drug sensitivity testing with clonogenic assays demonstrated sensitivity to the high concentrations of ara-C potentially achievable by intraperitoneal (IP) administration in five of nine patients with ovarian carcinoma. The kinetics of IP ara-C were then studied in three patients, and a 2 to 3 log concentration gradient was observed between the peritoneal compartment and plasma. Subsequently, the clinical efficacy of IP ara-C given for a five-day course every four weeks was evaluated in 10 patients with ovarian carcinoma who had failed systemic chemotherapy. Chemical peritonitis did not occur and systemic toxicity was minimal. Two patients were rendered free of disease and are alive without disease 14+ and 15+ months since therapy was discontinued. These results demonstrate that there is a very large pharmacologic advantage to the IP route of administration for ara-C, that ara-C is active against advanced ovarian carcinoma, and that the IP route of administration permits the cytokinetically rational use of very long durations of exposure for this cell-cycle phase-specific agent.

Adult↗
PubMed1984

Intraperitoneal chemotherapy with melphalan.

We administered melphalan by the intraperitoneal route to investigate its toxicity and pharmacokinetics. The drug was instilled with 2 litres of fluid and allowed to dwell in the peritoneal cavity for 4 hours. No local toxicity was detected by clinical examination, laboratory tests, or histologic examination. The intraperitoneal route allowed the dose to be increased to approximately three times the maximum dose tolerated intravenously before drug leaking into the systemic circulation produced dose-limiting myelosuppression. The peak peritoneal concentration averaged 93-fold greater than the plasma concentration, and total drug exposure for the peritoneal cavity averaged 63-fold greater than that for plasma. Tumor regressions were observed in patients with ovarian carcinoma and gastrointestinal adenocarcinomas. This study shows that from the pharmacologic point of view, if any portion of the tumor can be reached by intraperitoneal instillation, then there is a very strong rationale for the administration of melphalan by the intraperitoneal route, rather than the oral or intravenous route, for the treatment of tumors confined to the peritoneal cavity.

Adult↗
PubMed1984

Hypoxanthine concentrations in normal subjects and patients with solid tumors and leukemia.

Mean plasma hypoxanthine (Hyp) concentrations determined by high-pressure liquid chromatography were 0.56 microM (range, 0.2 to 1.9 microM) in 16 normal subjects, 0.68 microM (range, 0.1 to 1.1 microM) in 10 untreated acute leukemic subjects, and 0.89 microM (range, 0.3 to 2.6 microM) in 14 solid tumor patients. Despite large differences in Hyp concentration between patients, every 4-hr sampling, indicated that diurnal variation in individual patients was small (maximum, 2.3-fold). While the mean plasma and malignant effusion Hyp concentrations did not differ significantly, bone marrow plasma Hyp concentration averaged 4.0-fold greater than that of simultaneously drawn venous plasma. Allopurinol 300 mg p.o. caused a mean 1.5-fold increase in plasma Hyp within 3 hr. In 17 patients with acute leukemia, treatment with allopurinol at 300 mg daily plus initiation of chemotherapy caused a mean 7-fold increase in plasma Hyp to 4.6 microM (range, 1 to 12 microM). The ability of Hyp to modulate the toxicity of antimetabolites affecting purine synthesis (6- diazao -5- oxonorleucine , 6-methylmercaptopurine riboside, 6-mercaptopurine, and 6-thioguanine) was determined in vitro using human B-lymphoblast (WI-L2) and promyelocytic leukemia (HL-60) cell lines. Hyp permitted growth of both cell lines in the presence of clinically achievable concentrations of all 4 drugs, but the initial culture concentrations of Hyp required were above those found in patients. Since Hyp was consumed rapidly during the culture period, the average Hyp concentrations required for the protection of cells were actually much lower. We conclude that, in patients with acute leukemia receiving allopurinol during chemotherapy, plasma Hyp concentrations are significantly elevated; the potential for antagonism of antimetabolite activity is uncertain.

Acute Disease↗
PubMed1984

Modulation of cytarabine uptake and toxicity by dipyridamole.

The effect of dipyridamole, an inhibitor of membrane nucleoside transport, on the uptake and toxicity of cytarabine was examined in normal and malignant tissues. Preliminary pharmacokinetic data were obtained in mice and humans to determine appropriate dipyridamole dosage ranges for in vitro testing. At concentrations achievable in man, dipyridamole produced 75% and 94% reductions in cytarabine uptake in freshly harvested normal mouse and human bone marrow cells, respectively. Under the same conditions, greater than 90% reductions in cytarabine uptake were also seen in both L1210 murine leukemia and HL-60 human leukemia cells. In addition, treatment with dipyridamole also reduced the growth inhibitory effects of cytarabine on HL-60 cells in culture and protected mice from toxic doses of this antimetabolite. These results demonstrate the ability of dipyridamole to modulate the activity of cytarabine in both murine and human cells.

Animals↗
PubMed1983

Effect of allopurinol on the toxicity of high-dose 5-fluorouracil administered by intermittent bolus injection.

The effect of allopurinol pretreatment on the toxicity of 5-fluorouracil (5-FU) was examined in a clinical trial. Twenty-three patients were given bolus infusions of 5-FU every two weeks in doses that produced mild toxicity (0.8-1.9 g/m2). On alternate courses patients were pretreated with allopurinol either 300 mg two hours prior to and 10 hours after 5-FU, or 300 mg every 8 hours for 4 doses starting 24 hours before 5-FU. Seventeen and 20 pairs of courses were evaluable from the 2- and 24-hour pretreatment groups, respectively. Allopurinol did not produce a significant degree of protection against 5-FU-induced myelosuppression or mucositis on either dose schedule. Neurotoxicity manifesting as both cerebellar and encephalopathic signs and symptoms was the most important toxicity encountered and was dose-limiting for 5-FU on this schedule. Mean oxipurinol serum concentrations at the time of 5-FU administration were 24 microM and 104 microM for the 2- and 24-hour allopurinol pretreatment schedules respectively. Allopurinol increased the T 1/2 of 5-FU by a mean of 67% in three of the four patients studied. Pretreatment with allopurinol did not reduce the toxicity of 5-FU administered as an intravenous bolus.

Allopurinol↗
PubMed1983

Modulation of plasma cyst(e)ine by cisplatin.

Some types of human malignant cells are cyst(e)ine auxotrophs. In 8 cancer patients given 10 courses of treatment cisplatin caused a mean (+/- S.D.) 83 +/- 17% decrease in plasma cyst(e)ine when measured before and 6 hr after drug infusion. The magnitude of the decrease correlated with peak plasma cisplatin concentration, and serial measurements demonstrated that in some patients plasma cyst(e)ine was still decreasing at 6 hr. The mean 6-hr plasma cyst(e)ine was low enough (9 +/- 9 microM) to prevent the proliferation of human promyelocytic (HL-60) cells in culture.

Cell Division↗
PubMed1983

Regulation of de novo purine synthesis in human bone marrow mononuclear cells by hypoxanthine.

In previous studies from this laboratory, human bone marrow hypoxanthine concentrations were found to average 7.1 microM, three times higher than plasma hypoxanthine concentrations measured simultaneously. To assess the significance of this finding, the relationship between hypoxanthine concentration and the rate of purine nucleotide synthesis by the de novo pathway was studied in normal human bone marrow mononuclear cells and in the human promyelocytic cell line, HL-60, in vitro. Utilizing a [14C]formate incorporation technique, rates of total cellular de novo purine synthesis as well as rates of de novo adenine, de novo guanine, and thymine synthesis and incorporation into RNA and DNA were measured as a function of hypoxanthine concentration. In normal human marrow cells, the rate of total de novo purine synthesis declined by 81%, while the rate of de novo adenine and de novo guanine synthesis and incorporation into macromolecules declined by 89 and 75%, respectively, when media hypoxanthine was increased from 0 to 10 microM. Similar results were seen in the HL-60 cell line. In contrast, rates of thymine synthesis and incorporation into DNA as well as overall rates of RNA and DNA synthesis did not change with varying media hypoxanthine concentrations. In addition, hypoxanthine salvage and incorporation into RNA and DNA was shown to progressively increase with increasing media hypoxanthine concentrations. These results indicate that physiologic concentrations of hypoxanthine are sufficient to regulate the rate of de novo purine synthesis in human bone marrow in vivo.

Adenine↗
PubMed1983

Clinical pharmacokinetics of intraarterial cisplatin in humans.

The pharmacokinetics of intraarterially administered cisplatin (DDP) were studied in three patients with large hepatic tumors, and one patient with a fibrous histiocytoma in the thigh, using an assay sensitive to only those forms of non-protein bound DDP capable of reacting with the nucleophilic ligand diethyldithiocarbamate. Each patient received continuous intravenous and intraarterial infusions at various dose rates, with and without concurrent infusion of the neutralizing agent sodium thiosulfate. Steady-state DDP concentrations were achieved within two hours, and the mean (+/- SEM) plasma clearance at infusion rates of 5-15 mg/m2 per hour was 345 +/- 45 mL/m2 per minute. Apparent plasma clearance did not vary significantly with route of infusion. Based on the plasma clearance, predicted values for the relative advantage of an intraarterial infusion (Rt) were less than two for hepatic infusion; observed values averaged 1.9 +/- 0.5 (+/- SEM). The infusion of thiosulfate did not significantly increase plasma clearance. The mean (+/- SEM) extraction ratio for hepatic infusions was 0.24 +/- 0.09, and for infusion of the peripheral soft tissue sarcoma it was 0.27 +/- 0.03. These data indicate that from the point of view of both the tumor and the systemic circulation there is only a limited pharmacologic advantage for intraarterial infusion of DDP into organs with plasma flows of greater than 350 mL/m2 per minute.

Adult↗
PubMed1983

Pharmacokinetics of intraarterial mitomycin C in humans.

The pharmacological advantage of mitomycin C (MMC) given by intraarterial infusion as compared to i.v. infusion was studied in seven patients with cancer metastatic to the liver. Hepatic artery, hepatic vein, and peripheral vein catheters were placed, and then each patient received constant infusions of MMC via the intraarterial and peripheral i.v. routes at 0.4, 1.2, and 4.0 mg/sq m/hr. MMC concentrations were measured in the hepatic artery, hepatic vein, and a peripheral vein by high-pressure liquid chromatography after steady state had been reached at 2 hr. Mean plasma clearance increased significantly with infusion rate from 0.6 liter/min at 0.4 mg/sq m/hr to 1.1 liters/min at 4.0 mg/sq m/hr. The calculated relative advantage of treating hepatic tumors via the intraarterial route (Rt) was found to be 2.5- to 3.6-fold at a plasma flow rate of 0.4 liter/sq m and MMC infusion rates of 0.4 to 4.0 mg/sq m/hr. The hepatic vein MMC concentration averaged 30% higher during intraarterial than during i.v. infusion. Hepatic extraction of MMC averaged only 23%, so that the intraarterial route offered little advantage with respect to reduced systemic toxicity. These data suggest a limited pharmacological rationale for the selection of the intraarterial route for the treatment of hepatic tumors with MMC.

Aged↗
PubMed1983

Phase I trial of cytarabine and hydroxyurea.

A combination of hydroxyurea (HU) and cytarabine (ara-C) can overcome ara-C resistance in vitro. To determine the pattern of toxicity of this combination, 22 patients with refractory leukemia and lymphoma were treated for 5 days with ara-C (100 mg/m2/day by constant infusion) and escalating doses of HU (0.375-1.77 g/m2 every 6 hours). Hematologic toxicity was severe even at the lowest HU dose level. Skin and mucosal toxic effects were frequent but not dose-limiting. No novel types of toxic effects were observed.

Adolescent↗
PubMed1983

Intraperitoneal cis-diamminedichloroplatinum with systemic thiosulfate protection.

The toxicity and pharmacokinetics of cis-diamminedichloroplatinum (cisplatin) (90 mg/sq m) administered as a single 4-hr peritoneal dialysis, with or without concurrent i.v. infusion of sodium thiosulfate, 0.43 or 2.13 g/sq m/hr for 12 hr, were studied on 20 courses of treatment. When given without thiosulfate, the toxicity of cisplatin was systemic rather than local, and the peritoneal cavity/plasma ratio of the area under the curve was 12. Addition of i.v. thiosulfate significantly reduced the nephrotoxicity. The concentration of cisplatin in the peritoneal cavity was sufficiently greater than that in the plasma to prevent thiosulfate, which equilibrated into the cavity, from interfering with the antitumor activity of cisplatin in the peritoneum. This study demonstrates a pharmacokinetic advantage of i.p. chemotherapy with cisplatin.

Adult↗
PubMed1983

Preclinical re-evaluation of benzaldehyde as a chemotherapeutic agent.

Benzaldehyde (BA), an agent extracted from figs, is reported to have antitumor activity in vitro against a variety of experimental tumors and in vivo against refractory human neoplasms. We employed recently developed in vitro techniques to examine the effect of BA on growth of malignant human cells, and examined its effects in vivo against two human tumor xenografts established from primary specimens. BA showed dose-dependent inhibition of HL60 promyelocytic leukemia cells and normal human granulocyte/macrophage colonies. It showed no in vitro activity against either KG-1 myeloid leukemia cells or chronic lymphocytic leukemia cells grown in colony culture. BA failed to inhibit growth of either HL60 or KG-1 cells in liquid culture, and did not induce differentiation of HL60 cells. When tested against human tumor colony-forming cells from 30 patients with solid tumors, inhibition of colony growth greater than 70% was seen in six patients (20%). BA failed to inhibit the in vivo growth of either the T222 epidermoid carcinoma xenograft or the T380 ovarian carcinoma xenograft. We conclude that BA lacks significant activity against most human tumors tested in these experimental systems.

Animals↗
PubMed1982

Comparison of the activity of doxorubicin analogues using colony-forming assays and human xenografts.

The potential use of nude mouse xenografts as a source of human tumor tissue for preclinical assessment of drug activity was examined by a comparison of in vitro sensitivity to four anthracycline derivatives of eight xenografts maintained in nude mice and tumor colony-forming units (CFU) from the xenografts grown in agar. Results obtained in the two systems with doxorubicin (Dx) and a new, closely related derivative (epi-doxorubicin, epi-Dx) correlated well. In vivo tumor growth delay and maximum in vitro tumor CFU kill for these two drugs showed a significant correlation (r = 0.64, P less than .01). Separation of tumors into "sensitive" and "insensitive" tumor populations on the basis of maximum in vitro CFU kill also predicted the in vivo response to these two drugs in 88% of cases. Similar analyses performed on in vitro and in vivo results with two other new anthracyclines (4'-deoxy-doxorubicin, deoxy-Dx and 4'-O-methyl-doxorubicin, O-Me-Dx) showed a significant negative correlation between in vivo and in vitro results; the in vitro system failed to predict in vivo activity of these two drugs. No significant differences in in vitro activity against normal, granulocyte/macrophage progenitors (CFU-GM) or against various tumor CFUs were detected. Thus, the selectivity (activity against normal tissue compared with that against tumor) of the four drugs appeared equal. These data suggest that in vitro screening of drugs using tumor CFUs from nude mouse xenografts may predict the in vivo activity of drugs for which pharmacologic data are available, but illustrate the difficulties in attempting to predict the in vivo activity of new drugs for which no such data are available.

Animals↗