Reversal of adriamycin resistance by verapamil in human ovarian cancer.

The effectiveness of adriamycin in the treatment of ovarian cancer and other human tumors has been limited by the development of drug resistance. Verapamil, a calcium channel blocking agent, completely reversed adriamycin resistance in human ovarian cancer cells with moderate (three- to sixfold) degrees of resistance and partially reversed resistance in highly (150-fold) resistant cells. The potentiating effect of verapamil was due to inhibition of adriamycin efflux in the resistant cells. These results have led to a clinical trial of adriamycin and verapamil in refractory ovarian cancer patients.

Phase I-phase II trial of N-phosphonacetyl-L-aspartic acid given by intravenous infusion and 5-fluorouracil given by bolus injection.

A phase I clinical trial of N-phosphonacetyl-L-aspartic acid (PALA) and 5-fluorouracil (FUra) was performed on 30 patients. PALA was given as a 15-minute iv infusion once daily for 5 days, and FUra was given as a bolus injection on days 2, 3, 4, and 5. Cycles of treatment were repeated every 3 weeks. Dose-limiting toxicity was manifested by stomatitis and diarrhea. Skin rash was observed also but was not dose limiting. No consistent hematopoietic or renal toxicity was observed. Seventeen patients with disseminated metastatic melanoma and measurable disease were evaluated for response. One partial response was seen; however, the response was associated with significant toxicity, and the treatment could not be repeated. Stable disease was observed in 3 patients with melanoma, 1 patient with colon carcinoma, and 1 patient with ovarian carcinoma. Our findings suggest that the clinical activity of PALA and FUra given according to the above schedule for melanoma is less than 25% (P less than 0.05). Pharmacokinetic studies of FUra revealed no consistent effect of PALA pretreatment on FUra disappearance in plasma. The mean FUra elimination half-line in plasma was 7.11 +/- 0.84 minutes (SEM), which is no different from that reported for FUra alone. The recommended doses on this schedule for phase II studies are 1,000 mg PALA/m2/day iv daily for 5 days and 200 mg FUra/m2/day iv on days 2, 3, 4, and 5.

Selenium-induced cytotoxicity of human leukemia cells: interaction with reduced glutathione.

Selenium exists in a number of forms with differing valence states, some of which have shown antitumor activity. We studied the tumoricidal activity of four currently available selenium forms against a human leukemia cell line and exploited the differences among them to investigate the mechanism of antitumor action. Only selenocystine and sodium selenite showed antitumor activity, and these were also the only compounds which demonstrated significant redox chemistry, including depletion of cellular glutathione, stimulation of glutathione reductase, and stimulation of oxygen consumption. The interaction of these two compounds with glutathione suggests an intriguing potential role for them in cancer therapy.

Incorporation of iododeoxyuridine into DNA of granulocytes in patients.

Iododeoxyuridine (IdUrd) competes with thymidine for incorporation into DNA. In order to measure the incorporation of the drug in vivo, granulocytes were isolated from peripheral blood of patients at various times during and after 9- to 14-day IdUrd i.v. continuous infusions. DNA was extracted and enzymatically hydrolyzed. Both thymidine and IdUrd were separated and measured by high-performance liquid chromatography. Thymidine substitution by IdUrd was less than 1% prior to the fifth day of infusion and then increased rapidly to achieve a maximal value between 7 and 17% at the end of the infusion. In our protocol, thrombocytopenia was the most frequent dose-limiting systemic toxicity. For our group of patients, there was a clear overall relationship between the extent of substitution by IdUrd and the hematological toxicity. To our knowledge, these data provide the first direct quantitative determination of substitution by a drug into DNA in vivo without the use of radiolabeled compounds. The ability to directly monitor drug incorporation into DNA may provide the basis for monitoring and improving the selectivity of therapy.

Fluorodeoxyuridine modulation of the incorporation of iododeoxyuridine into DNA of granulocytes: a phase I and clinical pharmacological study.

The amount of iododeoxyuridine (IdUrd) incorporated into DNA determines the degree of radiosensitization. Fluorodeoxyuridine (FdUrd) has been shown to biochemically modulate IdUrd incorporation into DNA in vitro and in vivo. In this Phase I study, these drugs were coadministered to patients during 14-day continuous i.v. infusion periods in order to investigate whether the incorporation of IdUrd into DNA in vivo could be increased without increasing the dose of IdUrd. IdUrd plasma concentrations and incorporation of IdUrd into DNA of granulocytes were measured by high-performance liquid chromatography. Up to 8.8% substitution of thymidine by IdUrd was observed. Even at 3.5 mg/m2/day FdUrd for 14 days (78% of the maximum-tolerated dose as a single agent), no clinically relevant enhancement of incorporation of IdUrd into DNA of granulocytes was observed. Also, no changes in plasma levels of IdUrd were observed with escalating doses of FdUrd. Toxicity patterns (stomatitis, diarrhea, and bone marrow depression) and isobologram analysis suggested that IdUrd and FdUrd had additive, rather than synergistic, effects.

Pharmacological evaluation of intravenous delivery of 5-bromodeoxyuridine to patients with brain tumors.

Previously, 5-bromodeoxyuridine (BrdUrd) has been shown to be an effective radiosensitizing agent in rapidly dividing cells. As part of a Phase I/II study to evaluate BrdUrd as a radiosensitizer in gliomas, the pharmacology was studied in eight patients. BrdUrd was infused using an i.v. route as a 12-hr constant infusion each day for as long as 14 days. BrdUrd steady-state arterial levels are described for three different infusional rates: 1.6 mumol/sq m/min (350 mg/sq m/12 hr) produced a steady-state arterial level of 0.7 microM; 3.2 mumol/sq m/min (700 mg/sq m/12 hr) resulted in 2.1 microM; 5.9 mumol/sq m/min (650 mg/sq m/6 hr) showed a level of 3.9 microM. Because of myelosuppression, the highest tolerable dose for this intermittent long-term infusional therapy with BrdUrd appears to be 700 mg/sq m/12 hr. Contrary to the nonlinear pharmacokinetics of thymidine, 5-fluorouracil, and 5-fluorodeoxyuridine described previously, BrdUrd shows linear behavior in the range studied. BrdUrd still has promise as a radiosensitizer for gliomas in humans, but an alternative means of safe delivery into the carotid artery is needed. Because of an estimated 11- to 16-fold-higher local concentration, use of the intraarterial route could deliver optimum levels of BrdUrd to the tumor with minimal systemic toxicity.

Portal levels and hepatic clearance of 5-fluorouracil after intraperitoneal administration in humans.

Intrahepatic tumor is a major problem in clinical oncology. While direct intravascular infusions provide high local drug concentrations and variable rates of tumor response, they are limited by technical considerations and complications. In this study, we have tested whether high portal venous and hepatic arterial concentrations of 5-fluorouracil (5-FUra) can be achieved by administering drug via peritoneal dialysis. Four patients with metastatic colon carcinoma had a Tenckhoff catheter surgically implanted. During dialysis therapy with 4 mM 5-FUra, simultaneous samples of peritoneal fluid and of portal venous, hepatic venous, and peripheral venous, and arterial blood were obtained, and 5-FUra concentrations were determined. Mean peak portal vein drug concentrations were 60 microM and exceeded the measured concentrations in the other vessels. Total drug exposures as measured by concentration x time (mM x min) during Exchange 1 were: portal, 3.8 +/- 0.65; hepatic vein, 0.97 +/- 0.44; peripheral vein, 0.90 +/- 0.32; and arterial, 1.1 +/- 0.26. During Exchange 7, total drug exposures were: portal, 6.3 +/- 1.4; hepatic vein, 2.5 +/- 1.3; peripheral vein, 2.3 +/- 1.1; and arterial, 2.7 +/- .85. The fraction of i.p. drug that exited the peritoneal cavity through the portal venous system ranged from 0.29 to 1.0. This variation resulted in part from uncertainty in estimating portal blood flow and gastrointestinal drug elimination. Calculated hepatic extraction was 67% (range, 0.23 to 0.89). Extrahepatic metabolism was demonstrated. Measured 5-FUra concentrations compared favorably to values predicted by a pharmacokinetic model for 5-FUra. Dialysis therapy (i.p.) with 5-FUra provides a means of achieving high drug concentrations for treating both i.p. and intrahepatic tumor. Further clinical testing of this route of administration is warranted.

Pharmacology and phase I/II study of continuous intravenous infusions of iododeoxyuridine and hyperfractionated radiotherapy in patients with glioblastoma multiforme.

Forty-seven adult patients with glioblastoma multiforme (GBM) were treated in a phase I/II study combining continuous intravenous (IV) infusions of iododeoxyuridine (IdUrd) and hyperfractionated radiation therapy. IdUrd was administered as a continuous infusion (24 h/d) for two separate 14-day infusion periods. The dose of IdUrd was escalated from 500 to 1,200 mg/m2/d. The initial wide-field tumor volume was treated to 45 Gy at 1.5 Gy fractions twice daily over 3 weeks. Following a planned 2-week break, a reduced-field boost of 25 Gy was delivered using 1.25 Gy fractions twice daily over 2 weeks (total dose, 70 Gy over 9 weeks). The IdUrd infusion preceded both the wide-field and reduced-field irradiation by 1 week. All treatment was performed on an outpatient basis. Dose-limiting systemic toxicity to the bone marrow (primarily thrombocytopenia) and gastrointestinal (GI) tract (both stomatitis and diarrhea) established the maximum tolerable dose (MTD) at 1,000 mg/m2/d for a 14-day infusion. Significant local toxicity (within the radiation field) was not seen. The kinetics of IdUrd were linear with dose escalation and reached steady-state plasma concentrations of 1.3 to 3.4 mumol/L. The total body clearance of IdUrd was .82 L/min/m2. The primary metabolite, 5-iodouracil (IUra) approached steady state by day 6 of the infusion when plasma levels were 60 times higher than IdUrd. Plasma levels of uracil and thymine, but not thymidine, were elevated throughout the infusion. With a minimum follow-up of 1 year, ten patients remain alive, while 33 patients died of progressive disease, and four patients died of other causes (including one treatment-related death). The median survival for all 47 patient and for the 40 patients receiving the MTD was 45 and 47 weeks, respectively, with 12% and 14% survivals at 24 months. Using a Cox regression analysis, age (less than or equal to 50 years v greater than 50 years) and pretreatment performance status (PS) (Eastern Cooperative Oncology Group [ECOG]-PS 0 to 1 v PS 2 to 3) were independent, statistically significant (P2 less than .05) predictors of survival, with the ECOG status being a better predictor. Patients with a PS 0 to 1 (28 patients) had a median survival of 64 weeks with 21% survival at 24 months, compared with a median survival of 29 weeks and 0% survival at 12 months in the 19 patients with PS 2 to 3. The overall and subgroup survival data are at least comparable to other combined modality treatment approaches in patients with GBM.

Verapamil and adriamycin in the treatment of drug-resistant ovarian cancer patients.

Eight patients with refractory ovarian cancer were treated on a pilot protocol of verapamil plus Adriamycin (Adria Laboratories, Columbus, OH). This trial was based on our previous laboratory studies which demonstrated that Adriamycin resistance in human ovarian cancer cell lines could be partially reversed by exposure of the cells to high concentrations of verapamil (3,000 ng/mL). Patients were treated in an intensive care unit with continuous cardiovascular monitoring. The dose of verapamil was escalated in each patient until hypotension or heart block developed, and this dose was maintained for 72 hours. Adriamycin (50 mg/m2) was infused over 24 hours during the second day of the verapamil infusion and verapamil alone was administered on the third day in an effort to block efflux from drug-resistant cells. This intensive approach led to a median plasma verapamil level of 1,273 ng/mL (range, 720 to 2,767). However, the high infusion rates of verapamil (9 micrograms/kg/min) required to achieve these plasma levels produced an unacceptable degree of cardiac toxicity. Two patients developed transient atropine-responsive complete heart block and four patients developed transient congestive heart failure with increases in pulmonary capillary wedge pressure. There was no evidence that the noncardiac toxicities of Adriamycin were enhanced by verapamil. There were no objective responses to therapy. Future studies should use less cardiotoxic calcium channel blockers that can be safely administered to produce the plasma levels required for in vitro sensitization of drug resistant cells.

Phase I and pharmacokinetic study of the multidrug resistance modulator dexverapamil with EPOCH chemotherapy.

PURPOSE: Dexverapamil is a competitive inhibitor of the P-glycoprotein (Pgp) efflux pump, a potent mechanism of multidrug resistance (mdr-1) in vitro. We performed a phase I study to determine the maximum-tolerated dose (MTD) and pharmacokinetics of dexverapamil with etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (EPOCH) chemotherapy. PATIENTS AND METHODS: Eligible patients had relapsed or refractory lymphoma or sarcoma. Patients initially received EPOCH alone, and those with stable or progressive disease were crossed-over to received dexverapamil on subsequent cycles of EPOCH. Dexverapamil was administered orally for 6 days and escalated over eight dose levels ranging from 240 to 1,200 mg/m2/d. Pharmacokinetics of dexverapamil and its active metabolite, nor-dexverapamil, were obtained in most patients. In seven patients, pharmacokinetics of doxorubicin, doxorubicinol, and etoposide were determined on paired cycles of EPOCH with or without dexverapamil. RESULTS: Sixty-five patients received 130 cycles of dexverapamil/EPOCH chemotherapy. The MTD of dexverapamil was 150 mg/m2 every 4 hours (900 mg/m2/d), and hypotension was the principal dose-limiting toxicity. The dexverapamil area under the curve (AUC) increased proportionally with dexverapamil dose, but significant interpatient variation occurred. At the MTD, the median plasma average concentrations of dexverapamil and nor-dexverapamil were 1.2 and 1.4 mumol/L, respectively. Dexverapamil did not affect the steady-state concentration (Css) of etoposide, but increased the Css of doxorubicin and doxorubicinol nearly twofold. The absolute neutrophil and platelet nadirs were significantly lower on the dexverapamil cycles compared with cycles of EPOCH alone, but other chemotherapy-related toxicities did not change. CONCLUSION: The phase II recommended dose of dexverapamil with EPOCH is 150 mg/m2 every 4 hours. This dose was well tolerated on an outpatient basis and achieved plasma concentrations of dexverapamil and nor-dexverapamil within the effective range for Pgp inhibition in vitro. Although dexverapamil increased the hematopoietic toxicity of EPOCH, it was mild, readily reversible, and offset by EPOCH dose reductions. Dexverapamil should be considered for further study.

Suicide prodrugs activated by thymidylate synthase: rationale for treatment and noninvasive imaging of tumors with deoxyuridine analogues.

Most tumors are resistant to therapy by thymidylate synthase (TS) inhibitors due to their high levels of TS. Instead of inhibiting TS, we hypothesized that it was possible to use this enzyme to activate suicide prodrugs (deoxyuridine analogues) to more toxic species (thymidine analogues). Tumors with high levels of TS could be particularly sensitive to deoxyuridine analogues because they would be more efficient in producing the toxic methylated species. Furthermore, the accumulation of methylated species within tumors could be visualized externally if a tracer dose of the deoxyuridine analogue was tagged with an isotope, preferably a positron emitter, such as 18F. Higher accumulation of isotope indicates higher activity of TS and lower sensitivity of the tumor to TS inhibitors, but perhaps more sensitivity to therapy with deoxyuridine analogues as suicide prodrugs. 2'-F-ara-deoxyuridine (FAU) was used as a prototype to demonstrate these concepts experimentally. FAU readily entered cells and was phosphorylated, methylated, and subsequently incorporated into cellular DNA. Among different cell lines, FAU produced varying degrees of growth inhibition. Greater DNA incorporation (e.g., for CEM and U-937 cells) was reflected as increased toxicity. FAU produced less DNA incorporation in Raji or L1210 cells, and growth rate was minimally decreased. As the first demonstration that cells with high levels of TS activity can be more vulnerable to therapy than cells with low TS activity, this preliminary work suggests a new therapeutic approach for common human tumors that were previously resistant. Furthermore, it appears that the TS activity of tumors could be noninvasively imaged in situ by tracer doses of [18F]FAU and that this phenotypic information could guide patient therapy.

Selective incorporation of iododeoxyuridine into DNA of hepatic metastases versus normal human liver.

Fourteen patients received 5-iodo-2(1)-deoxyuridine (IdUrd) before surgery for placement of a hepatic arterial catheter. Biopsy specimens were obtained at the time of surgery and incorporation of IdUrd into deoxyribonucleic acid (DNA) in tumor and normal hepatic tissue was measured by HPLC and used as an index of drug selectivity. Over a 3-day intravenous infusion of IdUrd at 1000 mg/m2/day, substitution for thymidine in tumor DNA averaged 3.1%. Normal hepatic DNA contained less than 1% substitution by IdUrd. Arterial delivery of IdUrd increased levels in DNA, whereas modulation with fluorodeoxyuridine produced mixed results. In six patients, flow cytometric analysis showed that the tumor contained a median of 32% of tumor cells that had incorporated IdUrd in 3 days, corresponding to a potential doubling time of only 10 days. Thymidylate synthetase activity in tumors was 20-fold greater than in normal liver tissue, whereas thymidine kinase activity was twofold greater in tumors. These pharmacologic studies encourage further clinical trials of IdUrd as a cytotoxic agent or radiosensitizer.

Clinical pharmacology of 5-iodo-2'-deoxyuridine and 5-iodouracil and endogenous pyrimidine modulation.

We describe the clinical pharmacology and metabolism of 5-iodo-2'-deoxyuridine (IdUrd) during and after a 12-hour infusion. The kinetics of IdUrd were linear between 250 and 1200 mg/m2. The plasma IdUrd concentration reached steady state in less than 1 hour. Total body clearance of IdUrd was 750 ml/min/m2 and the disappearance t1/2 at the end of the infusion was less than 5 minutes. The primary metabolite, 5-iodouracil (IUra), did not reach steady state during the infusion. At the end of the 1200 mg/m2 infusion, the maximum plasma IUra concentration was 100 mumol/L, or about 10 times the simultaneous IdUrd plasma concentration. During the infusion there was at least a fifty- to 100-fold increase in uracil and thymine plasma concentrations. After the infusion, IUra disappearance from plasma was nonlinear, with an apparent Michaelis constant of 30 mumol/L. Plasma uracil and thymine levels slowly decreased after the IdUrd infusion until IUra fell to less than 30 mumol/L. There was subsequently a parallel and more rapid decrease in the plasma concentrations of uracil and thymine. Uridine, 2'-deoxyuridine, and thymidine plasma levels did not change significantly as a result of IdUrd therapy. These changes in endogenous pyrimidine pools are consistent with competitive inhibition of dihydrouracil dehydrogenase by IUra. An in vitro human bone marrow assay was used to determine the relative toxicity of IdUrd and IUra. Although exposure to IUra was tenfold higher than that to IdUrd, IdUrd was at least 100 times more cytotoxic to marrow cells.

Plasma and cerebrospinal fluid pharmacokinetics of 3'-azido-3'-deoxythymidine: a novel pyrimidine analog with potential application for the treatment of patients with AIDS and related diseases.

We investigated the clinical pharmacokinetics of azidothymidine (N3TdR) as part of a phase I/II trial in the treatment of acquired immunodeficiency syndrome and related diseases. During the 6-week course of therapy, drug levels in plasma, cerebrospinal fluid, and urine were determined by HLPC. The plasma half-life of N3TdR was 1.1 hour. The total body clearance was 1.3 L/kg/hr. At intravenous doses of 5 mg/kg or oral doses of 10 mg/kg, plasma levels were continuously maintained above the target level of 1 mumol/L. Oral bioavailability was 63% +/- 13%. Substantial penetration of N3TdR into cerebrospinal fluid was demonstrated. At doses of 5 mg/kg intravenously or 10 mg/kg orally, cerebrospinal fluid drug levels exceeded and were maintained close to 1 mumol/L. Nineteen percent of the administered dose was excreted unchanged into the urine. Renal clearance was 0.23 L/kg/hr. N3TdR possesses pharmacokinetic properties that would facilitate the long-term treatment of patients with acquired immunodeficiency syndrome: it can be given orally and it penetrates the central nervous system.

Iododeoxyuridine (IdUrd) incorporation into DNA of human hematopoietic cells, normal liver and hepatic metastases in man: as a radiosensitizer and as a marker for cell kinetic studies.

Iododeoxyuridine (IdUrd) was administered as a continuous infusion for 14 days to patients with glioblastoma and sarcoma, and for 3 days to patients with metastatic colorectal carcinoma. In the first group, the maximum incorporation of IdUrd into DNA was determined, taking granulocytes as parameter. In the second group, selective incorporation into DNA of normal liver and hepatic metastases of colorectal cancer was investigated. The highest dose of 675 mg/sq.m./day for 14 days produced IdUrd plasma concentrations of 1.8 +/- 0.3 microM, and a substitution of dThd by IdUrd in the range of 7.1-11.7%. Coadministration of fluorodeoxyuridine did not show significant enhancement of IdUrd-incorporation in granulocytes. Three-day intravenous infusions of IdUrd 1000 mg/sq.m./day produced 1.7-4.5% IdUrd-incorporation in hepatic metastases. Three-day intraarterial infusions (hepatic artery) produced 3.8-10.5% dThd-replacement, whereas, in 9/10 patients this was less than 1% in normal liver. In tumor tissue there was a trend towards FdUrd-modulated enhancement of IdUrd-incorporation, although there was considerable scatter. Cell kinetic studies revealed that IdUrd-incorporation in monocytes and granulocytes was very similar. In lymphocytes, a much lower fraction incorporated IdUrd. Liver tumor contained a considerably higher fraction of IdUrd-labeled cells, compared with normal liver. Potential doubling times for the tumors were estimated to be 10 days.

Adriamycin accumulation and metabolism in adriamycin-sensitive and -resistant human ovarian cancer cell lines.

Adriamycin accumulation and metabolism were studied in three distinct groups of human ovarian cancer cell lines: those derived from previously untreated patients, those from clinically refractory (relapsed) patients, and those with induced resistance to adriamycin in vitro. The 2-hr [14C] adriamycin accumulation in cell lines from previously untreated patients (A2780 and A1847 [Eva et al., Nature, Lond. 295, 116 (1982)] and OVCAR-5 [National Institutes of Health human OVarian CAR-cinoma cell line no. 5]) was 11-14 ng/10(6) cells. 2780AD and 1847AD (variants with in vitro induced resistance to adriamycin) accumulated one-third as much adriamycin after 2 hr (4 ng/10(6) cells). However, three cell lines derived from clinically refractory patients accumulated the same amount of adriamycin as cell lines from untreated patients (8-13 ng/10(6) cells). A high-performance liquid chromatography (HPLC) assay for adriamycin and its analogs confirmed these results and demonstrated only parent drug (no metabolites) in any of the cell lines tested. These results demonstrate that the primary mechanism of adriamycin resistance in some ovarian cancer cells from clinically refractory patients is not enhanced metabolism of drug or a transport defect leading to a decreased net accumulation such as has been described for cells with in vitro induced resistance to adriamycin.

Pharmacokinetics of 2',3'-dideoxycytidine in patients with AIDS and related disorders.

The clinical pharmacokinetics of 2',3'-dideoxycytidine (DDC) were determined after oral and intravenous administration in ten patients with AIDS or AIDS-related complex. A high performance liquid chromatography (HPLC) analysis procedure using cation exchange extraction columns was used to measure DDC levels as low as 0.1 microM (21 ng/mL) in plasma and urine. The kinetics of DDC were linear over the dose range of 0.03 to 0.5 mg/kg. Total body clearance was 227 mL/min/m2 and did not change after 6 to 14 days of dosing. The volume of distribution at steady state was 0.54 L/kg. Plasma half-life was 1.2 hours, and bioavailability was 88%. Most (75%) of the parent drug was found unchanged in the urine. As a result, renal function could play a role in dose adjustment of DDC. Comparison is made between the kinetics of DDC and 3'-azido-2',3'-dideoxythymidine (AZT). Similarities are noted in half-life and bioavailability. However, differences are observed for total body clearance, cerebrospinal fluid penetration, volume of distribution, metabolism, and recovery in urine.

Clinical pharmacokinetics of suramin in patients with HTLV-III/LAV infection.

Suramin has been reported to inhibit the reverse transcriptase activity of a number of retroviruses and to reduce the in vitro infectivity and cytopathic effect of HTLV-III/LAV, the etiologic agent of acquired immune deficiency syndrome (AIDS). The clinical pharmacokinetics of suramin were investigated as part of a pilot study to evaluate the safety and efficacy of this drug for the treatment of patients with diseases caused by HTLV-III/LAV. A dose of suramin 6.2 g was given intravenously over a five-week period to four patients. After the last dose, the plasma half-life of suramin was 44 to 54 days. This is among the longest half-lives reported for any therapeutic substance given to humans. Total plasma levels of suramin were greater than 100 micrograms/mL for several weeks. In vitro activity of suramin was found at concentrations as low as 50 micrograms/mL. Metabolites were not found in plasma, and urinary excretion accounts for elimination of most of the drug. Suramin is approximately 99.7% bound to plasma proteins. The results from these initial clinical pharmacokinetic studies might assist the design of further therapeutic trials of suramin, especially the selection of frequency of dosing and adjustments for renal impairment.

Thymidine phosphorylase as a target for imaging and therapy with thymine analogs.

PURPOSE: Thymidine phosphorylase (TPase; platelet-derived endothelial cell growth factor) is an attractive target for imaging and therapy because of the strong relationship between its expression in tumor biopsies and clinical outcome in many tumor types. Although the mechanism has yet to be explained, expression of TPase is highly associated with angiogenesis. METHODS: Tumor cells were phenotyped for TPase activity, and incubated with thymine or its analogs (5-X-Ura). After intracellular conversion to thymidine analogs via the reverse reaction for TPase, these molecules were phosphorylated and incorporated into DNA. RESULTS: Preferential localization was found in cells with high TPase, e.g. U937. Incorporation was enhanced in cells with high TPase by coincubation with modulators such as deoxyuridine. CONCLUSIONS: 5-X-Ura molecules can be readily labeled with positron emitters, and this finding provides support for further evaluation in vivo of their potential as probes for noninvasive external imaging of TPase, both at the time of diagnosis and during maneuvers intended to manipulate TPase. If the 5-X-Ura molecules were labeled with a therapeutic isotope, e.g. 125I or 211At, selective cytotoxicity would be expected in cells with high TPase expression. However, direct evaluation of the safety in vivo of the therapeutic approach is required. The 5-X-Ura compounds constitute a novel approach to both imaging and therapy directed towards TPase. Further, there are distinct advantages to using the imaging mode to identify tumors likely to benefit from therapy with the same set of molecules.

Steady-state plasma concentrations and effects of taxol for a 250 mg/m2 dose in combination with granulocyte-colony stimulating factor in patients with ovarian cancer.

Taxol, a natural product initially isolated from the stem bark of the western yew Taxus brevifolia, is undergoing phase II and III evaluation due to its reported activity against a variety of tumors. Previous studies have described correlations between plasma concentrations and toxicity when taxol is given (a) at lower doses, (b) for shorter infusion times, and (c) without granulocyte-colony-stimulating factor. Because the 24-h infusion schedule is most commonly used in current clinical trials, we attempted to correlate steady-state plasma concentrations of taxol achieved with a 24-h continuous i.v. infusion with toxicities and responses. Plasma samples from 48 refractory ovarian cancer patients were obtained 1-2 h prior to the end of the first taxol infusion. Taxol concentrations were measured by high-performance liquid chromatography (HPLC). Interpatient variation of taxol plasma concentrations was small (mean +/- SD, 0.85 +/- 0.21 microM. Total taxol body clearance was 256 +/- 72 ml min-1 m-2 (mean +/- SD). Taxol plasma protein binding was 88.4% +/- 1.3% (mean +/- SD, n = 9). Grade 3-4 hematologic toxicity, mainly leukopenia, occurred in 92% of the patients. The leukopenia was transient and did not warrant a reduction in the dose of taxol. Grade 3-4 nonhematologic toxicity occurred in 8% of the patients. No severe hypersensitivity reaction or grade 3-4 neurotoxicity was observed. Correlations of plasma concentrations and toxicities were not feasible due to the high frequency of hematologic effects and the low frequency of nonhematologic toxicity. The low degree of interpatient variation in plasma concentrations hindered the development of correlations with response.