Biomedical subjects

F M Balis

Publications and source records attributed to F M Balis.

At least 55 records · Page 3Linked to original sources

PubMed1998

Pharmacokinetics of O6-benzylguanine and its active metabolite 8-oxo-O6-benzylguanine in plasma and cerebrospinal fluid after intrathecal administration of O6-benzylguanine in the nonhuman primate.

O6-Benzylguanine (O6BG) irreversibly inactivates the single-turnover DNA repair protein alkylguanine-alkyltransferase. Thus, O6BG increases tumor-cell sensitivity to alkylating agents such as carmustine, lomustine, procarbazine, and temozolomide. We investigated the pharmacokinetic behavior of O6BG and O6-benzyl-8-oxoguanine (8-oxo-O6BG) in cerebrospinal fluid (CSF) and plasma after intraventricular administration of O6BG in a nonhuman primate model. In our study, three animals received a single 1-mg dose of O6BG into the lateral ventricle. CSF from the 4th ventricle and plasma samples were collected after administration, and O6BG and 8-oxo-O6BG concentrations were measured by high-performance liquid chromatography. Four additional animals received 1 mg of O6BG via the intralumbar route weekly for 6 weeks to assess the feasibility and toxicity of this route of administration. The peak O6BG CSF concentration was 412+/-86 microM, the t1/2 was 0.52+/-0.02 h, the clearance was 0.22+/-0.01 ml/min, and the area under the concentration-time curve was 319+/-15 microM x h in 4th ventricular CSF. The peak CSF concentration of 8-oxo-O6BG in CSF was 1.9+/-0.4 microM, the t1/2 was 0.76+/-0.03 h, and the area under the concentration-time curve was 5.0+/-1.1 microM x h. Both O6BG and 8-oxo-O6BG were detected in the plasma 0.5-3 h after intraventricular O6BG administration. The plasma peak concentration of O6BG was 0.4 microM at 30 min, and the concentration was <0.1 microM by 3 h. The plasma concentration of 8-oxo-O6BG was 0.2 microM at 30 min and 0.6 microM at 3 h. The animals tolerated the single intraventricular dose and 6 weekly intralumbar doses of O6BG without toxicity. We concluded that intrathecal administration of O6BG is well tolerated in the nonhuman primate and seems to have a substantial pharmacokinetic advantage over systemic administration for meningeal tumors.

Animals↗

PubMed1997

Fluorescence properties of pteridine nucleoside analogs as monomers and incorporated into oligonucleotides.

Eighteen fluorescent pteridine-based nucleoside analogs have been prepared that are suitable for synthesis as phosphormidites and site-specific incorporation into oligonucleotides. Their quantum yields ranged from < or = 0.03 to 0.88. The maximum excitation and emission wavelenghts of seven selected probes with quantum yields > 0.15 ranged from 334 to 358 and 400 to 444 nm, respectively. Fluorescence decay curves of the seven probes were biexponential, and the mean intensity-weighted lifetimes ranged from 0.87 to 6.54 ns. Incorporation of probes 4 and 17 (3-methylisoxanthopterin and 6-methylisoxanthopterin) into oligonucleotides significantly quenched their fluorescence signal, and the degree of quench correlated with the number and proximity of purines in the oligonucleotide. Incorporation also resulted in a shift in absorbance-, emission-, and decay-associated spectra for 6-methylisoxanthopterin. An increase in the complexity of the decay curve and a decrease in the mean lifetime occurred for both probes. Formation of double-stranded oligonucleotides did not substantially increase the degree of quenching but generally increased the complexity of decay curves and decreased the mean lifetimes. Melting temperature, Tm, depression equivalent to that of a single base pair mismatch was observed in 3-methylisoxanthopterin-containing double-stranded oligonucleotides, while the Tm of 6-methylisoxanthopterin-containing double-stranded oligonucleotides were unperturbed, e.g., equivalent to unlabeled double-stranded oligonucleotides. This new class of fluorophore yields promising probes for the study of protein/DNA interactions.

Fluorescent Dyes↗

PubMed1997

Fluorescence properties of a new guanosine analog incorporated into small oligonucleotides.

The fluorescence properties of 3-methyl-isoxanthopterin (3-MI) incorporated into different oligonucleotides have been determined. This highly fluorescent guanosine analog has its absorption and fluorescence spectra well resolved from those of the normal nucleotides and the aromatic amino acids. The small shifts observed in absorption and fluorescence emission spectra upon incorporation of 3-MI into these oligonucleotides are consistent with a general solvent effect and do not suggest any contribution from the position of the probe from the 5' end, the sequence of nucleotides immediately 5' or 3' to the probe, or the single- or double-stranded nature of the oligomer. However, steady-state and time-resolved fluorescence studies indicate that the presence of a purine immediately 5' or 3' to the probe results in some dynamic but mostly static quenching in the single-stranded oligomer. Furthermore, a 3' purine is more effective than a 5' purine, and an adenine appears to be more effective than a guanine for these static quenching interactions. Formation of the double-stranded oligomer leads to an additional loss of quantum yield, which can also be ascribed primarily to static quenching. These results show that this new class of spectrally enhanced fluorescent purine analogs will be able to provide useful information concerning the perturbation of nucleic acid structures.

Base Sequence↗

PubMed1997

Phase I trial and pharmacokinetic study of all-trans-retinoic acid administered on an intermittent schedule in combination with interferon-alpha2a in pediatric patients with refractory cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) of all-trans-retinoic acid (ATRA) administered on an intermittent oral schedule with interferon-alpha2a (IFN-alpha2a) in children with refractory cancer, and whether the marked reduction in plasma ATRA concentrations observed with chronic daily oral dosing could be circumvented with an intermittent dosing schedule. PATIENTS AND METHODS: Thirty-three children with refractory cancer (stratified by age, < or = 12 and > 12 years) were treated with ATRA 3 consecutive days per week and IFN-alpha2a 3 x 10(6) U/m2 5 consecutive days per week, both repeated weekly. The starting dose of ATRA was 60 mg/m2/d divided into three doses, with planned escalations to 90 and 120 mg/m2/d. Because severe headaches have been noted to occur on the initial day of ATRA administration, only two of three doses of ATRA were administered on day 1 of each week. RESULTS: Pseudotumor cerebri or dose-limiting headache was observed in two of five patients older than 12 years treated at the 120-mg/m2/d dose level and in one of six < or = 12 years at the 90-mg/m2/d level. Other non-dose-limiting toxicities of ATRA included reversible elevations in hepatic transaminases and triglycerides, dry skin, cheilitis, and nausea/vomiting. One child with recurrent neuroblastoma had an objective response of 6 months' duration, and one with recurrent Wilms' tumor had histologic maturation of multiple tumors. This intermittent schedule allowed for exposure to relatively high plasma concentrations of ATRA on a repetitive basis. Following 30-mg/m2 doses, the ATRA area under the concentration-time curve (AUC) decreased from 96 +/- 14 micromol/L/min on day 1 to 26 +/- 24 micromol/L/min by day 3 of drug administration, but on day 1 of the fourth consecutive week of therapy, the AUC averaged 110 +/- 16 micromol/L/min. The recommended pediatric phase II dose of ATRA administered on this schedule is 90 mg/m2/d. CONCLUSION: An intermittent schedule of ATRA administration appears to circumvent the low plasma drug exposure that is a result of the sustained upregulation of metabolism when this drug is administered on a chronic daily schedule. Based on the results of this trial, a phase II trial of ATRA/IFN-alpha2a in neuroblastoma and Wilms' tumor using this schedule is in progress.

Adolescent↗

PubMed1997

Phase I trial of docetaxel administered as a 1-hour infusion in children with refractory solid tumors: a collaborative pediatric branch, National Cancer Institute and Children's Cancer Group trial.

PURPOSE: A phase I trial of docetaxel was performed to determine the maximum-tolerated dose (MTD), the dose-limiting toxicities, and the incidence and severity of other toxicities in children with refractory solid tumors. PATIENTS AND METHODS: Forty-four children received 103 courses of docetaxel administered as a 1-hour intravenous infusion every 21 days. Doses ranged from 55 to 150 mg/m2, MTD was defined in heavily pretreated and less heavily pretreated (< or = 2 prior chemotherapy regimens, no prior bone marrow transplantation [BMT], and no radiation to the spine, skull, ribs, or pelvic bones) patients. RESULTS: Dose-related neutropenia was the primary dose-limiting toxicity. The MTD in the heavily pretreated patient group was 65 mg/m2, but the less heavily pretreated patients tolerated a significantly higher dose of docetaxel (maximum-tolerated dose, 125 mg/m2). Neutropenia and constitutional symptoms consisting of malaise, myalgias, and anorexia were the dose-limiting toxicities at 150 mg/m2 in the less heavily pretreated patients. Thrombocytopenia was not prominent, even in patients who experienced dose-limiting neutropenia. Common nonhematologic toxicities of docetaxel included skin rashes, mucositis, and mild elevations of serum transaminases. Neuropathy was uncommon. Peripheral edema and weight gain were observed in two of five patients who received more than three cycles of docetaxel. A complete response (CR) was observed in one patient with rhabdomyosarcoma, a partial response (PR) in one patient with peripheral primitive neuroectodermal tumor (PPNET), and a minimal response (MR) in two patients with PPNET. Three of the four responding patients were treated at doses > or = 100 mg/m2. CONCLUSION: The recommended phase II dose of docetaxel administered as a 1-hour intravenous infusion in children with solid tumors in 125 mg/m2. Because neutropenia was the dose-limiting toxicity and thrombocytopenia was mild, further escalation of the dose should be attempted with granulocyte colony-stimulating factor (G-CSF) support.

Adolescent↗

PubMed1997

Carboxypeptidase-G2, thymidine, and leucovorin rescue in cancer patients with methotrexate-induced renal dysfunction.

PURPOSE: Methotrexate nephrotoxicity can lead to delayed methotrexate elimination and the development of life-threatening toxicity, which may not be preventable with the standard rescue agent leucovorin. In preclinical studies, we previously demonstrated that carboxypetidase-G2 (CPDG2) rapidly hydrolyzes methotrexate to nontoxic metabolites. A protocol for the compassionate use of CPDG2 in patients who develop nephrotoxicity while receiving high-dose methotrexate was therefore developed. The pharmacologic and clinical outcome of CPDG2 rescue administered with thymidine and leucovorin in 20 patients is presented here. METHODS: Patients with high-dose methotrexate-induced renal dysfunction received one to three doses of CPDG2, 50 U/kg body weight intravenously (i.v.), thymidine 8 g/m2/d by continuous i.v. infusion, and standard pharmacokinetically guided leucovorin rescue. Plasma concentrations of methotrexate and its inactive metabolite 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA) were measured before and after CPDG2 using high-pressure liquid chromatography (HPLC). Tolerance of CPDG2 and thymidine, development of methotrexate toxicities, and recovery of renal function were monitored. RESULTS: Twenty patients who received high-dose methotrexate for osteosarcoma (n = 11), lymphoid cancers (n = 8), and gastric cancer (n = 1) developed nephrotoxicity (median serum creatinine, 3.2 mg/dL) and elevated plasma methotrexate concentrations (median, 201 mumol/L at hour 46). CPDG2 and thymidine rescue was well tolerated and resulted in a rapid 95.6% to 99.6% reduction in the plasma methotrexate concentration. Methotrexate-related toxicity was mild to moderate. Serum creatinine returned to normal values at a median of 22 days. CONCLUSION: CPDG2, thymidine, and leucovorin rescue was highly effective in 20 patients at high risk for developing life-threatening methotrexate toxicity after the onset of methotrexate-induced nephrotoxicity and delayed methotrexate excretion.

Adolescent↗

PubMed1997

A pediatric phase I trial and pharmacokinetic study of thioguanine administered by continuous i.v. infusion.

Although mercaptopurine is the thiopurine antimetabolite predominantly used in the treatment of childhood acute lymphoblastic leukemia (ALL), thioguanine (TG) is more potent than mercaptopurine in in vitro cytotoxicity studies in human leukemic cell lines and leukemic cells from patients with ALL. We conducted a pediatric Phase I trial of TG administered as a continuous i.v. infusion (CIV). A pharmacokinetically guided dose escalation was performed to define the dose rate of TG required to achieve a steady-state plasma concentration (Css) exceeding the target concentration of 1 microM, and then the maximum tolerated duration of infusion of TG at this dose rate was defined. Eighteen patients (median age, 18 years; range, 4-25 years) with refractory malignancies (16 solid tumors and 2 ALL) were enrolled in this study. The starting dose rate of 10 mg/m2/h administered for 24 h achieved an average Css of 0.9 microM (range, 0.7-1.2 microM). Therefore, the dose rate was escalated to 20 mg/m2/h, which achieved an average Css of 4.1 microM (range, 1. 0-8.3 microM). This disproportionate increase in the Css of TG suggested a capacity-limited (saturable) elimination process, and a pharmacokinetic model incorporating two compartments with capacity-limited elimination from the central compartment was developed to describe the disposition of TG. The TG clearances (derived from model parameters) at the 10- and 20-mg/m2/h dose rates were 987 and 608 ml/min/m2, respectively. Dose-limiting myelosuppression (absolute granulocyte count < 500/mm3 and platelet count < 25,000/mm3) was observed in two of three patients treated with a dose rate of 20 mg/m2/h administered for 36 h. Administration of CIV of TG at 20 mg/m2/h for 24 h was well tolerated in nine patients. Nonhematological toxicities included nonneutropenic infections and mild, reversible changes in hepatic function tests. The recommended dose rate and duration for CIV of TG is 20 mg/m2/h for 24 h.

Adolescent↗

PubMed1997

A pilot study of gamma-1b-interferon in combination with fluorouracil, leucovorin, and alpha-2a-interferon.

The combination of IFN-alpha-2a (IFN-alpha) and IFN-gamma-1b (IFN-gamma) has been found to produce more than additive cytotoxicity with fluorouracil (5-FU) in HT 29 colon cancer cells due to enhanced DNA-directed effects. We therefore studied the combination of IFN-gamma with IFN-alpha, 5-FU, and leucovorin (LV) in a clinical trial. Fifty-three patients received an initial cycle of 5 million units (MU)/m2 IFN-alpha s.c. on days 1-7 with 500 mg/m2 LV and 370 mg/m2 5-FU i.v. on days 2-6. IFN-gamma was then added once tolerable doses of 5-FU and IFN-alpha were established for each patient. IFN-gamma was administered at one of six dose levels between 0.3-4.8 MU/m2 s.c. on days 1-7. This design permitted comparison of the clinical toxicity and pharmacokinetics of 5-FU in two consecutive cycles in an individual treated with the same doses of 5-FU/LV/IFN-alpha in the absence and presence of IFN-gamma. In 43 matched patient cycles, the addition of IFN-gamma did not seem to worsen gastrointestinal toxicity, and skin toxicity tended to be milder. 5-FU clearance was higher in 14 cycles with IFN-gamma compared to the patient's prior cycle with the same doses of 5-FU/LV/IFN-alpha: 798 +/- 309 versus 601 +/- 250 ml/min/m2 (mean +/- SD; P = 0.04). In these 28 cycles, the median 5-FU clearance was significantly lower in 11 cycles that were complicated by more severe diarrhea: 524 versus 798 ml/min/m2 (grade 2 versus 0-1; P = 0. 0032). Overall, 38% and 26% of patients had grade 3-4 diarrhea and mucositis. Dose reductions of IFN-gamma for chronic fatigue, malaise, or anorexia were ultimately required more frequently with >/=2.4 MU/m2 (P = 0.018), and the maximum tolerated dose of IFN-gamma was considered to be 1.2 MU/m2/ day. Objective responses were seen in 41% of 29 measurable colorectal cancer patients. Compared to our previous experience with 5-FU/LV/IFN-alpha, IFN-gamma and IFN-alpha appeared to have opposite effects on 5-FU clearance. These results suggest that any potential benefit of adding IFN-alpha to 5-FU/LV on this schedule may not depend solely on alterations in 5-FU clearance.

Adult↗

PubMed1996

Ifosfamide and etoposide plus vincristine, doxorubicin, and cyclophosphamide for newly diagnosed Ewing's sarcoma family of tumors.

BACKGROUND: This study was conducted to determine the feasibility of, and improve outcome by, incorporating ifosfamide and etoposide (IE) into the therapy of newly diagnosed patients with Ewing's sarcoma family of tumors of bone and soft tissue. METHODS: Fifty-four newly diagnosed patients received 7 cycles of vincristine, doxorubicin, and cyclophosphamide (VAdriaC) and 11 cycles of IE. Radiation therapy after the fifth chemotherapy cycle was the primary approach to local control. RESULTS: Actuarial 5-year event-free survival (EFS) and overall survival rates were 42% and 45%, respectively, with a median duration of potential follow-up of 6.8 years. EFS was significantly better for patients with localized tumors than for those with metastatic lesions (64% v. 13%, P < 0.0001). Actuarial local progression-free survival at 5 years was 74%, and did not correlate with primary tumor size or site, histologic subtype, or the presence of metastases. Febrile neutropenia developed after 49% of cycles, and clinical or sub-clinical cardiac dysfunction was common (7% and 40% respectively). There were four toxic deaths and one case of secondary myelodysplastic syndrome. CONCLUSIONS: Despite substantial toxicity, the integration of IE into the front-line, VAdriaC-based therapy of patients with Ewing's sarcoma family of tumors is feasible and appeared to significantly improve the outcome for patients with high risk localized tumors, but had no impact on the poor prognosis of patients with metastatic tumors. Local control can be achieved in the vast majority of patients using radiotherapy exclusively, even among patients with bulky, central axis tumors. Longer follow-up is needed to evaluate the late effects of this intensive therapy.

Adolescent↗

PubMed1996

Phase II evaluation of topotecan for pediatric central nervous system tumors.

BACKGROUND: Topotecan is a topoisomerase I inhibitor that has good penetration across the blood-brain barrier and significant antitumor activity against human brain tumor xenografts. In a Phase I trial in children with refractory cancer, topotecan was well tolerated when administered as a 24-hour infusion. The maximum tolerated dose was 5.5 mg/m2 and the dose-limiting toxicity was myelosuppression. This Phase II study of topotecan was performed to assess the activity of topotecan against childhood brain tumors. METHODS: Forty-five children with either a previously treated primary brain tumor that was refractory to standard therapy, or an untreated brain stem glioma or glioblastoma multiforme, received topotecan administered as a 24-hour intravenous infusion every 21 days. The initial dose was 5.5 mg/m2 with escalation to 7.5 mg/m2 on the second and subsequent doses in patients who did not experience dose-limiting toxicity. RESULTS: There were no complete or partial responses in the patients with high grade glioma (n=9), medulloblastoma (n=9), or brain stem glioma (n=14). One of 2 patients with a low grade glioma had a partial response lasting more than 17 months; 3 patients with a brain stem glioma had stable disease for 12 to 28 weeks; and 1 patient with a malignant neuroepithelial tumor and 1 patient with an optic glioma had stable disease for 41 weeks and 22 weeks, respectively. Dose escalation from 5.5 mg/m2 to 7.5 mg/m2 was well tolerated in the first 11 patients enrolled on this study who had not received prior craniospinal radiation therapy. The starting dose was subsequently increased to 7.5 mg/m2 for patients without prior craniospinal radiation. CONCLUSIONS: Topotecan administered as a 24-hour infusion every 21 days is inactive in high grade gliomas, medulloblastomas, and brain stem tumors.

Adolescent↗

PubMed1996

Cytotoxicity and DNA damage associated with pyrazoloacridine in MCF-7 breast cancer cells.

We examined the effects of pyrazoloacridine (PZA), an investigational anticancer agent in clinical trials, on cytotoxicity, DNA synthesis, and DNA damage in MCF-7 human breast carcinoma cells. With PZA concentrations ranging from 0.5 to 50 microM for durations of 3-72 hr, cytotoxicity increased in proportion to the total PZA exposure (concentration x time). Inhibition of DNA and RNA syntheses increased with increasing PZA concentration x time (microM.hr). A 24-hr exposure to 1 and 10 microM PZA reduced DNA synthesis to 62 and 5% of control, respectively, decreased the proportion of cells in S phase with accumulation of cells in G2 + M phase, and inhibited cell growth at 72 hr by 68 and 100%. Newly synthesized DNA was more susceptible to damage during PZA exposure, with subsequent induction of parental DNA damage. Significant damage to newly synthesized DNA as monitored by alkaline elution was evident after a 3-hr exposure to > or = 5 microM PZA. Longer PZA exposures (> or = 10 microM for 16 hr) were required to elicit damage to parental DNA. Induction of single-strand breaks in parental DNA correlated closely with induction of double-strand breaks and detachment of cells from the monolayer. PZA-mediated DNA fragmentation was not accompanied by the generation of oligonucleosomal laddering in MCF-7 cells, but induction of very high molecular weight DNA fragmentation (0.5 to 1 Mb) was detected by pulsed-field gel electrophoresis. In vitro binding of PZA to linear duplex DNA (1 kb DNA ladder) and closed, circular plasmid DNA was demonstrated by a shift in migration during agarose electrophoresis. PZA interfered with topoisomerase I- and II-mediated relaxation of plasmid DNA in a cell-free system, but the cytotoxic effects of PZA did not appear to involve a direct interaction with topoisomerase I or II (stabilization of the topoisomerase I- or II-DNA cleavable complex). PZA-mediated cytotoxicity correlated strongly with inhibition of DNA and RNA syntheses, and damage to both nascent and parental DNA. Neither the cytotoxicity of PZA nor induction of double-stranded DNA fragmentation was prevented by aphidicolin, indicating that PZA-mediated lethality occurred in the absence of DNA replication. Since free radical formation was not detected, induction of nascent and parental DNA damage appeared to be a consequence of the avid binding of PZA to DNA, presumably by interfering with the access of replication, repair, and transcription enzyme complexes.

Acridines↗

PubMed1996

A phase II study of thioTEPA in children with recurrent solid tumor malignancies: a Children's Cancer Group study.

A Phase II study of thioTEPA was performed by the Children's Cancer Group. ThioTEPA was administered intravenously every three weeks, at a dose of 65 mg/m2. Pediatric patients with recurrent sarcomas were targeted, but patients with other tumor diagnoses were also eligible. Toxicity was primarily hematopoietic, with thrombocytopenia being predominant. ThioTEPA did not demonstrate significant activity in the target tumor groups evaluated.

Adolescent↗

PubMed1996

Randomized trial of the cardioprotective agent ICRF-187 in pediatric sarcoma patients treated with doxorubicin.

PURPOSE: We conducted an open-label, randomized trial to determine whether ICRF-187 would reduce doxorubicin-induced cardiotoxicity in pediatric sarcoma patients. METHODS: Thirty-eight patients were randomized to receive doxorubicin-containing chemotherapy (given as an intravenous bolus) with or without ICRF-187. Resting left ventricular ejection fraction (LVEF) was monitored serially with multigated radionuclide angiography (MUGA) scan. The two groups were compared for incidence and degree of cardiotoxicity, response rates to four cycles of chemotherapy, event-free and overall survival, and incidence and severity of noncardiac toxicities. RESULTS: Eighteen ICRF-187-treated and 15 control patients were assessable for cardiac toxicity. ICRF-187-treated patients were less likely to develop subclinical cardiotoxicity (22% v 67%, P < .01), had a smaller decline in LVEF per 100 mg/m2 of doxorubicin (1.0 v 2.7 percentage points, P = .02), and received a higher median cumulative dose of doxorubicin (410 v 310 mg/m2, P < .05) than did control patients. Objective response rates were identical in the two groups, with no significant differences seen in event-free or overall survival. ICRF-187-treated patients had a significantly higher incidence of transient grade 1 serum transaminase elevations and a trend toward increased hematologic toxicity. CONCLUSION: ICRF-187 reduces the risk of developing short-term subclinical cardiotoxicity in pediatric sarcoma patients who receive up to 410 mg/m2 of doxorubicin. Response rates to chemotherapy, event-free and overall survival, and noncardiac toxicities appear to be unaffected by the use of ICRF-187. Additional clinical trials with larger numbers of patients are needed to determine if the short-term cardioprotection afforded by ICRF-187 will reduce the incidence of late cardiac complications in long-term survivors of childhood cancer.

Adolescent↗

PubMed1996

Phase I crossover study of paclitaxel with r-verapamil in patients with metastatic breast cancer.

PURPOSE: We conducted a phase I crossover study of escalating doses of both paclitaxel (Taxol; Bristol-Myers, Squibb, Princeton, NJ) and r-verapamil, the less cardiotoxic stereoisomer, in heavily pretreated patients with metastatic breast cancer. PATIENTS AND METHODS: Twenty-nine patients refractory to paclitaxel by 3-hour infusion were treated orally with r-verapamil every 4 hours starting 24 hours before the same-dose 3-hour paclitaxel infusion and continuing for a total of 12 doses. Once the maximum-tolerated dose (MTD) of the combination was determined, seven additional patients who had not been treated with either drug were evaluated to determine whether the addition of r-verapamil altered the pharmacokinetics of paclitaxel. Consenting patients had tumor biopsies for P-glycoprotein (Pgp) expression before receiving paclitaxel and after becoming refractory to paclitaxel therapy. RESULTS: The MTD of the combination was 225 mg/m2 of r-verapamil every 4 hours with paclitaxel 200 mg/m2 by 3-hour infusion. Dose-limiting hypotension and bradycardia were observed in three of five patients treated at 250 mg/m2 r-verapamil. Fourteen patients received 32 cycles of r-verapamil at the MTD as outpatient therapy without developing cardiac toxicity. The median peak and trough serum verapamil concentrations at the MTD were 5.1 micromol/L (range, 1.9 to 6.3), respectively, which are within the range necessary for in vitro modulation of Pgp-mediated multidrug resistance (MDR). Increased serum verapamil concentrations and cardiac toxicity were observed more frequently in patients with elevated hepatic transaminases and bilirubin levels. Hematologic toxicity from combined paclitaxel and r-verapamil was significantly worse compared with the previous cycle of paclitxel without r-verapamil. In the pharmacokinetic analysis, r-verapamil delayed mean paclitaxel clearance and increased mean peak paclitaxel concentrations. CONCLUSION: r-Verapamil at 225 mg/m2 orally every 4 hours can be given safely with paclitaxel 200 mg/m2 by 3-hour infusion as outpatient therapy and is associated with serum levels considered active for Pgp inhibition. The addition of r-verapamil significantly alters the toxicity and pharmacokinetics of paclitaxel.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1995

A prospective evaluation of ifosfamide-related nephrotoxicity in children and young adults.

BACKGROUND: Ifosfamide has been associated with proximal renal tubular dysfunction resembling Fanconi-like syndrome and leading to rickets in young children. The characteristic manifestations of this nephrotoxicity include phosphaturia and hypophosphatemia, glycosuria, aminoaciduria, renal tubular acidosis, and urinary loss of low molecular weight serum proteins. However, the relationship between acute ifosfamide nephrotoxicity, which is frequently subclinical, and long term renal damage is unclear. In this prospective study, the laboratory features of ifosfamide-induced acute nephrotoxicity were characterized further and correlated with the development of chronic nephropathy. METHODS: The renal function of newly diagnosed children and young adults with high risk sarcomas was followed during therapy with a high dose ifosfamide-containing regimen. Serum and urine were collected regularly immediately before and after 5-day cycles of ifosfamide throughout treatment for determination of the fractional excretion of electrolytes (sodium, potassium, phosphate, magnesium, calcium) and glucose and urinary excretion of amino acids and beta 2-microglobulin. RESULTS: Significant changes in the renal threshold of phosphate excretion, the fractional excretion of calcium and glucose, and the urinary excretion of beta 2-microglobulin were observed when comparing pretreatment values with those at the end of a 5-day treatment cycle. The median renal threshold of phosphate excretion decreased from 1.22 to 0.82 mmol/L (P < 0.0001). The median fractional excretions of calcium and glucose increased from 1.05% to 1.68% (P < 0.0001) and 0.05% to 0.08% (P = 0.0006), respectively. Beta 2-microglobulin excretion increased by 70-fold from 0.02 to 1.42 mg/mmol (P < 0.0001). Except for glucose and beta 2-microglobulin excretion, renal parameters returned to baseline before the next ifosfamide treatment cycle. Acute aminoaciduria was observed in 21 of 23 patients. Chronic nephrotoxicity, as defined by the development of a Fanconi-like syndrome or chronic tubular electrolyte loss requiring oral supplementation, developed in the three patients with the highest urinary excretion of beta 2-microglobulin after ifosfamide therapy. CONCLUSIONS: Prospectively, high dose ifosfamide was associated with a 4% incidence of Fanconi-like syndrome; however, evidence of acute reversible subclinical nephrotoxicity was observed for all patients. Severe beta 2-microglobulinuria appeared to be a prognostic laboratory indicator for the development of chronic nephrotoxicity.

Adolescent↗

PubMed1995

Plasma and cerebrospinal fluid pharmacokinetics of O6-benzylguanine and time course of peripheral blood mononuclear cell O6-methylguanine-DNA methyltransferase inhibition in the nonhuman primate.

O6-Benzylguanine (O6BG) enhances the cytotoxicity of the nitrosoureas by irreversibly binding and inhibiting the DNA repair enzyme O6-methyl-guanine-DNA methyltransferase (MGMT). The plasma and cerebrospinal fluid (CSF) pharmacokinetics of O6BG and its active metabolite, O6-benzyl-8-oxoguanine, were studied in a nonhuman primate model after 200 mg/m2 had been injected i.v. The parent drug and the metabolite were measured with a reverse-phase HPLC assay. A pharmacokinetic model incorporating separate compartments for O6BG and the O6-benzyl-8-oxoguanine metabolite, first-order conversion of O6BG to the metabolite, and additional first-order elimination rate constants for each compound, was simultaneously fitted to the parent drug and metabolite plasma concentration time data. Elimination of O6BG from plasma was rapid; it had a half-life of 1.6 h and a clearance of 68 ml/min/m2. On the basis of the pharmacokinetic model, essentially all of the O6BG was converted to O6-benzyl-8-oxoguanine. The plasma pharmacokinetic profile of the metabolite differed considerably from that the parent drug. The half-life (14 h) was 10-fold longer and the area under the curve (2420 microM/h) was 11-fold higher than that of O6BG (212 microM/h). The clearance rate of O6-benzyl-8-oxoguanine was 6.4 ml/min/m2. The CSF:plasma ratio was 4.3% for O6BG and 36% for O6-benzyl-8-oxoguanine, and the metabolite area under the curve was 90-fold higher than that of O6BG in CSF. The excellent CSF penetration of the active metabolite provides a rationale for the use of O6BG as a chemosensitizing agent for brain tumors. We also studied the duration of MGMT inhibition in peripheral blood mononuclear cells. By 2 h after a 200 mg/m2 dose of O6BG, > 98% of MGMT activity was suppressed, and > 95% suppression of enzyme activity persisted at 18 and 48 h after the dose. By 2 weeks after the treatment, MGMT levels had returned to baseline. Persistent high concentrations of the active metabolite appear to provide a pharmacological explanation for the prolonged suppression of MGMT activity.

Animals↗

PubMed1995

A phase I trial of amifostine (WR-2721) and melphalan in children with refractory cancer.

Melphalan has a steep dose-response curve, but the use of high doses results in unacceptable myelosuppression. Strategies to circumvent this dose-limiting myelosuppression would allow for the administration of higher, more effective doses of melphalan. Amifostine (WR-2721) has been shown in preclinical studies to protect the bone marrow from the myelotoxicity of melphalan, and in clinical trials, to protect from the myelotoxicity of other alkylating agents. A Phase I trial of the combination of amifostine and melphalan was performed in children with refractory cancers to: (a) define the acute toxicities of amifostine and its maximum tolerated dose (MTD); and (b) to determine whether the dose of melphalan could be safely escalated when administered in combination with amifostine. Amifostine was administered i.v. as a 15-min infusion 30 min before melphalan. The starting dose of amifostine was 750 mg/m2, with planned dose escalations in 30% increments. Melphalan was administered as a 5-min infusion using the previously defined MTD in heavily pretreated patients, 35 mg/m2, as the starting dose. The dose of melphalan was escalated by 30% increments. Nineteen patients, ranging in age from 3 to 24 years (median, 15 years), were entered on trial. The dose of amifostine was escalated to 2700 mg/m2, which is approximately 3-fold higher than the adult recommended dose, without reaching a MTD. Fifteen patients experienced nondose-limiting (< 25%), transient decreases in blood pressure after the amifostine infusion. Other nondose-limiting toxicities of amifostine included mild nausea and vomiting, flushing, anxiety, diarrhea, and urinary retention. Six patients, three each at the 2100 and 2700 mg/m2 amifostine dose levels were treated with an escalated dose of melphalan (45 mg/m2). All of these patients experienced grade 4 neutropenia (< 500/mm3), and five of six patients had grade 4 thrombocytopenia. The duration of this dose-limiting myelosuppression exceeded 7 days in four of six patients. Although no dose-limiting (grade 3 or 4) toxicity was attributed to amifostine, significant anxiety and reversible urinary retention occurred at the two highest amifostine dose levels. A dose of 1650 mg/m2 for pediatric Phase II trials is recommended. High doses of amifostine, however, do not appear to allow for escalation of melphalan beyond its single agent MTD of 35 mg/m2.

Adolescent↗

PubMed1995

Incorporation of a fluorescent guanosine analog into oligonucleotides and its application to a real time assay for the HIV-1 integrase 3'-processing reaction.

We have synthesized a highly fluorescent (quantum yield 0.88) guanosine analog, (3-methyl-8-(2-deoxy-beta-D-ribofuranosyl) isoxanthopterin (3-Mi) in a dimethoxytrityl, phosphoramidite protected form, which can be site-specifically inserted into oligonucleotides through a 3',5'-phosphodiester linkage using an automated DNA synthesizer. Fluorescence is partially quenched within an oligonucleotide and the degree of quench is a function of the fluorophore's proximity to purines and its position in the oligonucleotide. As an example of the potential utility of this class of fluorophores, we developed a continuous assay for HIV-1 integrase 3'-processing reaction by incorporating 3-MI at the cleavage site in a double-stranded oligonucleotide identical to the U5 terminal sequence of the HIV genome. Integrase cleaves the 3'-terminal dinucleotide containing the fluorophore, resulting in an increase in fluorescence which can be monitored on a spectrofluorometer. Substitution of the fluorophore for guanosine at the cleavage site does not inhibit integrase activity. This assay is specific for the 3'-processing reaction. The change in fluorescence intensity is linear over time and proportional to the rate of the reaction. This assay demonstrates the potential utility of this new class of fluorophore for continuous monitoring of protein/DNA interactions.

Base Sequence↗