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Biomedical subjects

M A Graham

Publications and source records attributed to M A Graham.

At least 19 recordsLinked to original sources
PubMed2002

Phase I study of weekly oxaliplatin plus irinotecan in previously treated patients with metastatic colorectal cancer.

BACKGROUND: In vitro synergy between Oxal (oxaliplatin) and CPT-11 (irinotecan) has been reported. Oxaliplatin exerts its antineoplastic activity through the formation of platinum-DNA adducts. Resistance to oxaliplatin is through repair of these adducts, which is inhibited by irinotecan. PATIENTS AND METHODS: Oxaliplatin and irinotecan were administered weekly for 4 weeks followed by a 2-week rest period. The dose of oxaliplatin was escalated first, starting at 30 mg/m(2). Once a dose of 60 mg/m(2) was attained, the weekly dose of irinotecan was escalated, from 40 mg/m(2) to 85 mg/m(2). A total of 49 previously treated patients with metastatic colorectal cancer were entered in order to establish the maximum tolerated dose. Pharmacokinetics of oxaliplatin and irinotecan were analyzed. RESULTS: Forty-nine patients were evaluable for toxicity. The recommended phase II doses for this combination are oxaliplatin 60 mg/m(2) and irinotecan 50 mg/m(2), weekly x 4 q 6 weeks. Diarrhea was the most common dose-limiting toxicity. No pharmacological interactions were noted between oxaliplatin and irinotecan. Twelve of the 47 evaluable patients (26%) achieved a partial response. CONCLUSION: Weekly combination of oxaliplatin and irinotecan appears to be a well tolerated and active regimen in patients previously treated for metastatic colorectal cancer. Further investigations of this regimen are warranted.

Adult↗
PubMed2001

Position paper on fatal abusive head injuries in infants and young children.

This article represents the work of the National Association of Medical Examiners Ad Hoc Committee on shaken baby syndrome. Abusive head injuries include injuries caused by shaking as well as impact to the head, either by directly striking the head or by causing the head to strike another object or surface. Because of anatomic and developmental differences in the brain and skull of the young child, the mechanisms and types of injuries that affect the head differ from those that affect the older child or adult. The mechanism of injury produced by inflicted head injuries in these children is most often rotational movement of the brain within the cranial cavity. Rotational movement of the brain damages the nervous system by creating shearing forces, which cause diffuse axonal injury with disruption of axons and tearing of bridging veins, which causes subdural and subarachnoid hemorrhages, and is very commonly associated with retinal schisis and hemorrhages. Recognition of this mechanism of injury may be helpful in severe acute rotational brain injuries because it facilitates understanding of such clinical features as the decrease in the level of consciousness and respiratory distress seen in these injured children. The pathologic findings of subdural hemorrhage, subarachnoid hemorrhage, and retinal hemorrhages are offered as "markers" to assist in the recognition of the presence of shearing brain injury in young children.

Battered Child Syndrome↗
PubMed2001

In-vivo phenotyping for CYP3A by a single-point determination of midazolam plasma concentration.

We investigated whether a single plasma midazolam concentration could serve as an accurate predictor of total midazolam clearance, an established in-vivo probe measure of cytochrome P450 3A (CYP3A) activity. In a retrospective analysis of data from 224 healthy volunteers, non-compartmental pharmacokinetic parameters were estimated from plasma concentration-time curves following intravenous (IV) and/or oral administration. Based on statistical moment theory, the concentration at the mean residence time (MRT) should be the best predictor of the total area under the curve (AUC). Following IV or oral midazolam administration, the average MRT was found to be approximately 3.5 h, suggesting that the optimal single sampling time to predict AUC was between 3 and 4 h. Since a 4-h data point was common to all studies incorporated into this analysis, we selected this time point for further investigation. The concentrations of midazolam measured 4 h after an IV or oral dose explained 80 and 91% of the constitutive interindividual variability in midazolam AUC, respectively. The 4-h midazolam measurement was also an excellent predictor of drug-drug interactions involving CYP3A induction and inhibition. Compared with baseline values, the direction and magnitude of change in midazolam AUC and the 4-h concentration were completely concordant for all study subjects. We conclude that a single 4-h midazolam concentration following IV or oral administration represents an accurate marker of CYP3A phenotype under constitutive and modified states. Moreover, the single-point approach offers an efficient means to phenotype and identify individuals with important genetic polymorphisms that affect CYP3A activity.

Administration, Oral↗
PubMed2001

Adolescents' hero identification and self-perception.

This study explored associations for having a hero with aspects of adolescents' self-concept for 168 high school students who completed Harter's Self-per ception Profile and questions about their heroes. Having a hero was related to having a stronger sense of social acceptance, romantic appeal, and athletic competence and a weaker sense of scholastic competence.

Achievement↗
PubMed2000

High-performance liquid chromatographic analysis of AQ4N, an alkylaminoanthraquinone N-oxide.

A simple, highly selective and reproducible reversed-phase high-performance liquid chromatography method has been developed for the analysis of the new anti-cancer pro-drug AQ4N. The sample pre-treatment involves a simple protein precipitation protocol, using methanol. Chromatographic separations were performed using a HiChrom HIRPB (25 cmX4.6 mm I.D.) column, with mobile phase of acetonitrile-ammonium formate buffer (0.05 M) (22:78, v/v), with final pH adjusted to 3.6 with formic acid. The flow-rate was maintained at 1.2 ml min(-1). Detection was via photodiode array performed in the UV range at 242 nm and, since the compounds are an intense blue colour, in the visible range at 612 nm. The structurally related compound mitoxantrone was used as internal standard. The validated quantification range of the method was 0.05-10.0 microg ml(-1) in mouse plasma. The inter-day relative standard deviations (RSDs) (n=5) ranged from 18.4% and 12.1% at 0.05 microg ml(-1) to 2.9% and 3.3% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The intra-day RSDs for supplemented mouse plasma (n=6) ranged from 8.2% and 14.2% at 0.05 microg ml(-1) to 7.6% and 11.5% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The overall recovery of the procedure for AQ4N was 89.4 +/- 1.77% and 76.1 +/- 7.26% for AQ4. The limit of detection was 50 ng ml(-1) with a 100 microl sample volume. The method described provides a suitable technique for the future analysis of low levels of AQ4N and AQ4 in clinical samples.

Animals↗
PubMed2000

Validation of a highly sensitive ICP-MS method for the determination of platinum in biofluids: application to clinical pharmacokinetic studies with oxaliplatin.

ELOXATIN (Oxaliplatin) is a novel platinum containing anti-cancer agent with a diaminocyclohexane carrier ligand which has been approved in several major European countries. Clinical studies have demonstrated that the compound exhibits marked activity against colorectal cancers in combination with 5-fluorouracil (5-FU). The aim of this work was to develop and validate a highly sensitive inductively coupled plasma mass spectrometry assay for the determination of oxaliplatin-derived platinum in plasma ultrafiltrate, plasma and whole blood and to apply this technique to clinical pharmacokinetic studies with oxaliplatin. Ultratrace detection of platinum in plasma ultrafiltrate was achieved using ultrasonic nebulisation combined with ICP-MS. This technique allows detection of platinum at the 0.001 microg Pt/ml level in only 100 microl of matrix. Assays in blood and plasma utilised a standard Meinhardt nebuliser and spray chamber, achieving detection limits of 0.1 microg Pt/ml in 100 and 200 microl of matrix, respectively. The assays were validated (accuracy and precision within +/- 15%) over the concentration ranges: 0.001-0.250 microg Pt/ml in plasma ultrafiltrate and 0.1-10 microg Pt/ml for plasma and whole blood. The effect of sample digestion. dilution, long term frozen storage and quantitation in the presence of 5-FU were also investigated and validated. The method was used to monitor platinum exposure following oxaliplatin administration (130 mg/m2) to cancer patients. Following a 2 h i.v. infusion, peak platinum levels declined in a triphasic manner in all blood compartments. Free platinum was detected in plasma ultrafiltrate at low levels (0.001 0.010 microg Pt/ml) for up to 3 weeks. In conclusion, a highly sensitive and specific assay has been developed for the determination of platinum in biofluids. This method enabled characterisation of the long term exposure to platinum in patients following oxaliplatin treatment.

Antineoplastic Agents↗
PubMed2000

Expression and genome organization of resistance gene analogs in soybean.

Sequence analysis of cloned plant disease-resistance genes reveals a number of conserved domains. Researchers have used these domains to amplify analogous sequences, resistance gene analogs (RGAs), from soybean and other crops. Many of these RGAs map in close proximity to known resistance genes. While this technique is useful in identifying potential disease resistance loci, identifying the functional resistance gene from a cluster of homologs requires sequence information from outside of these conserved domains. To study RGA expression and to determine the extent of their similarity to other plant resistance genes, two soybean cDNA libraries (root and epicotyl) were screened by hybridization with RGA class-specific probes. cDNAs hybridizing to RGA probes were detected in each library. Two types of cDNAs were identified. One type was full-length and contained several disease-resistance gene (R-gene) signatures. The other type contained several deletions within these signatures. Sequence analyses of the cDNA clones placed them in the Toll-Interleukin-1 receptor, nucleotide binding domain, and leucine-rich repeat family of disease-resistance genes. Using clone-specific primers from within the 3' end of the LRRs, we were able to map two cDNA clones (LM6 and MG13) to a BAC contig that is known to span a cluster of disease-resistance genes.

Amino Acid Sequence↗
PubMed2000

Unsafe sleep practices and an analysis of bedsharing among infants dying suddenly and unexpectedly: results of a four-year, population-based, death-scene investigation study of sudden infant death syndrome and related deaths.

BACKGROUND: Prone sleep and unsafe sleep surfaces increase the risk of sudden infant death. Recent epidemiologic studies also suggest that when an infant's head or face is covered by bedding, or when a sleep surface is shared with others, the risk of dying increases. The inference of a causal role for these risk factors is supported by physiologic studies and by the consistent finding that fewer infants die when risk factors are reduced. The prevalence of most of these risk factors in infant deaths in the United States is uncertain. OBJECTIVE: To describe the prevalence of several important risk factors related to sleep practices among a defined population of infants dying suddenly and unexpectedly. METHODS: In this population-based study, we retrospectively reviewed death-scene information and medical examiners' investigations of deaths in the city of St Louis and St Louis County between January 1, 1994 and December 31, 1997. Because of the potential for diagnostic overlap, all deaths involving infants <2 years old with the diagnoses of sudden infant death syndrome (SIDS), accidental suffocation, or cause undetermined were included. RESULTS: The deaths of 119 infants were studied. Their mean age was 109.3 days (range: 6-350). The diagnoses were SIDS in 88 deaths, accidental suffocation in 16, and undetermined in 15. Infants were found prone in 61.1% of cases and were found on a sleep surface not designed for infants in 75.9%. The head or face was covered by bedding in 29.4%. A shared sleep surface was the site of death in 47.1%. Only 8.4% of deaths involved infants found nonprone and alone, with head and face uncovered. CONCLUSIONS: Using detailed death-scene descriptions, we found that similar unsafe sleeping practices occurred in the large majority of cases diagnosed as SIDS, accidental suffocation, and cause undetermined. Considering these diagnoses together may be useful in public health campaigns during a time when there may be diagnostic overlap. Regardless of the diagnosis, recommendations that infants sleep supine on firm sleep surfaces that lessen the risk of entrapment or head covering have the potential to save many lives. Campaigns are needed to heighten awareness of these messages and of the risks of dangerous bedsharing.

Asphyxia↗
PubMed2000

Relationship among body image, sex, and popularity of high school students.

Body dissatisfaction and attempts to lose weight are increasingly common among adolescents. Research has identified a number of factors significantly associated with body image, including sex, media, parental relationship, and puberty as well as weight and popularity. It was hypothesized that popular adolescents would have greater body dissatisfaction, more body distortion, and lower body esteem. From a rural high school 116 10th and 12th grade students were surveyed. Two teachers from the school also completed a Body Image Figure scale for each student. Subjects rated each grade member on a 5-point Likert-type scale, indicating how much they liked the classmate. A Social Preference rating (Popularity) was calculated for each subject from these ratings. Each subject also completed a Body Image Figure scale and Body Esteem scale. Body distortion was calculated by comparing the teachers' and a student's responses. Significant sex differences were found for scores on body satisfaction, distortion, and esteem, but none for popularity with distortion and body esteem. A relationship between popularity and body satisfaction was found, with the most popular adolescents reporting the least discrepancy between their ideal body image and their current body image. Popular adolescents are most satisfied with their body type.

Adolescent↗
PubMed2000

Clinical pharmacokinetics of oxaliplatin: a critical review.

Oxaliplatin (cis-[(1R,2R)-1,2-cyclohexanediamine-N,N'] oxalato(2-)-O,O'] platinum; Eloxatine) is a novel platinum coordination complex used for the treatment of metastatic colorectal carcinoma in combination with fluoropyrimidines. The objective of this review is to integrate the key data from multiple studies into a single, comprehensive overview of oxaliplatin disposition in cancer patients. The pharmacokinetics (PKs) of unbound platinum in plasma ultrafiltrate after oxaliplatin administration was triphasic, characterized by a short initial distribution phase and a long terminal elimination phase (t1/2, 252-273 h). No accumulation was observed in plasma ultrafiltrate after 130 mg/m2 every 3 weeks or 85 mg/m2 every 2 weeks. Interpatient and intrapatient variability in platinum exposure (area under the curve(0-48)) is moderate to low (33 and 5% respectively). In the blood, platinum binds irreversibly to plasma proteins (predominantly serum albumin) and erythrocytes. Accumulation of platinum in blood cells is not considered to be clinically significant. Platinum is rapidly cleared from plasma by covalent binding to tissues and renal elimination. Urinary excretion (53.8 +/- 9.1%) was the predominant route of platinum elimination, with fecal excretion accounting for only 2.1 +/- 1.9% of the administered dose 5 days postadministration. Tissue binding and renal elimination contribute equally to the clearance of ultrafilterable platinum from plasma. Renal clearance of platinum significantly correlated with glomerular filtration rate, indicating that glomerular filtration is the principal mechanism of platinum elimination by the kidneys. Clearance of ultrafilterable platinum is lower in patients with moderate renal impairment; however, no marked increase in drug toxicity was reported. The effect of severe renal impairment on platinum clearance and toxicity is currently unknown. Covariates such as age, sex, and hepatic impairment had no significant effect on the clearance of ultrafilterable platinum, and dose adjustment due to these variables is not required. Oxaliplatin undergoes rapid and extensive nonenzymatic biotransformation and is not subjected to CYP450-mediated metabolism. Up to 17 platinum-containing products have been observed in plasma ultrafiltrate samples from patients. These include several proximate cytotoxic species, including the monochloro-, dichloro-, and diaquo-diaminocyclohexane platinum complexes, along with several other noncytotoxic products. Oxaliplatin does not inhibit CYP450 isoenzymes in vitro. Platinum was not displaced from plasma proteins by a variety of concomitant medications tested in vitro, and no marked PK interactions between oxaliplatin, 5-fluorouracil, and irinothecan have been observed. These results indicate that the additive/synergistic antitumor activity observed with these agents is not due to major alterations in drug exposure, and the enhanced efficacy is likely to be mechanistically based. Together, these PK, biotransformation, drug-drug interaction analyses and studies in special patient populations provide a firm scientific basis for the safe and effective use of oxaliplatin in the clinic. These analyses also reveal that the pharmacological activity of oxaliplatin may be attributable, at least in part, to the unique pattern of platinum disposition observed in patients.

Antineoplastic Agents↗
PubMed2000

Phase I pharmacokinetic study of the novel antitumor agent SR233377.

SR233377 is a novel thioxanthenone analogue that demonstrated solid tumor selectivity in vitro with activity confirmed in vivo against several murine tumors including those of colon, pancreas, and mammary origin. Its primary preclinical dose-limiting toxicities included myelosuppression and neurological toxicity. The neurological toxicity was acute and could be ameliorated in mice when the drug was administered as a 1-h infusion instead of rapid i.v. injection. As a result of its preclinical efficacy profile, SR233377 entered Phase I clinical investigation. The compound was administered i.v. over 2 h on day 1 repeated every 28 days. The starting dose was 33 mg/m2 (one-tenth the mouse LD10). Escalations continued to 445 mg/m2 (six escalations), where dose-limiting toxicity was observed. At this dose, acute ventricular arrhythmias, including one patient with torsades de pointes and transient cardiac arrest, occurred. Because this toxicity might have been related to the plasma peak, the protocol was amended to a 24-h infusion beginning at 225 mg/m2. With this dose, prolongation of the corrected QT interval (QTc) over the pretreatment levels resulted. Because prolonged QTc is a known forerunner to acute ventricular arrhythmias, clinical development of SR233377 was stopped. However, preclinical antitumor and toxicity studies with analogues are underway with hopes of identifying a new clinical candidate with similar antitumor effects that is devoid of cardiac toxic effects.

Adult↗
PubMed2000

Protein kinase C regulation of corneal endothelial cell proliferation and cell cycle.

PURPOSE: The purpose of this study was to determine the role of protein kinase C (PKC) in corneal endothelial cell proliferation. METHODS: Immunocytochemistry and Western blotting were used to define the PKC isoforms expressed in primary cultures of rat corneal endothelial cells. For proliferation studies, primary cultures of rat corneal endothelial cells were serum-starved for 48 hours and incubated for 2 hours with the PKC inhibitors staurosporine (10(-9) to 10(-7) M), chelerythrine (10(-9) to 5 x 10(-8) M), or calphostin C (10(-9) to 10(-7) M). Individual PKC isoforms were inhibited using PKCalpha antisense oligonucleotide transfection or exposure for 1 hour to myristoylated, pseudosubstrate-derived peptide inhibitors against PKCalpha, -alphassgamma, -epsilon, and -delta (10(-8) to 10(-6) M). Cells were then stimulated with 2.5% serum for 24 hours. Cell proliferation was measured with bromodeoxyuridine (BrDU) and Ki67 immunocytochemistry. Protein level of cyclin E was determined by Western blotting. RESULTS: PKCalpha, -ssII, -delta, -epsilon, -iota, -eta, -gamma, and -theta were detected in corneal endothelial cells. Maximum inhibition of PKC with staurosporine, calphostin C, and chelerythrine reduced cell proliferation to 7%, 31%, and 48% of control, respectively. Myristoylated peptide inhibition of PKCalpha and -epsilon reduced cell proliferation to 57% and 59% of control, respectively. PKCalpha antisense oligonucleotide reduced cell proliferation to 35% of control. Cyclin E protein level was decreased to 70%, 38%, 57%, and 43% of control in cells treated with calphostin C, staurosporine, chelerythrine, and PKCalpha antisense, respectively. CONCLUSIONS: PKC activity, in particular PKCalpha and -epsilon activity, is important in promoting corneal endothelial cell proliferation. Inhibition of PKC activity prohibits G1/S-phase progression and reduces cyclin E protein levels.

Animals↗
PubMed1999

Phase I/pharmacokinetic trial of the novel thioxanthone SR233377 (WIN33377) on a 5-day schedule.

PURPOSE: SR233377 (WIN33377) is a novel 4-aminomethyl thioxanthone derivative with promising preclinical activity against solid tumors at doses substantially below the MTD. We performed a phase I trial to determine a suitable phase II dose of SR233377 when administered as a 2-h intravenous infusion for five consecutive days. METHODS: A group of 25 patients with a range of solid tumor diagnoses and good performance status received SR233377 at eight dose levels ranging from 4.8 mg/m2 per day to 74.7 mg/m2 per day. Cycles were repeated every 35 days and patients were evaluated for response following two cycles of treatment. Doses were escalated in cohorts of three using a modified Fibonacci scheme. Pharmacokinetic sampling was performed during the first cycle in all patients. RESULTS: Toxicities of SR233377 on this schedule included neutropenia, fever, nausea, and dyspnea but all were mild and not dose-limiting. Asymptomatic prolongation of the corrected QT (QTc) interval during infusion in all patients monitored at the 74.7 mg/m2 dose level prompted closure of the study. QT lengthening correlated with increasing plasma concentrations of SR233377. SR233377 Cmax values increased linearly with dose, but substantial interpatient variability in SR233377 AUC, clearance, and half-life was noted. There was no evidence of drug accumulation when day 1 and day 5 AUC and Cmax values were compared. Seven patients displayed tumor growth inhibition lasting for 4 months or more. CONCLUSIONS: We conclude that SR233377 administered on a 5-day schedule is associated with tolerable clinical symptoms and some activity against a range of solid tumors but dosing is limited by QTc prolongation, a condition that predisposes to ventricular arrhythmias. Phase II development on this schedule is not recommended based on the occurrence of this concentration-dependent effect. Further investigation of alternative schedules of administration and of SR233377 analogues is warranted.

Adult↗
PubMed1998

Forensic pathology. Pulmonary disease.

Certain conditions in cases with pulmonary pathology such as thrombosis and embolism, pregnancy, asthma, drug abuse, Sudden Infant Death Syndrome (SIDS) and occupational exposures are particularly likely to come under critical scrutiny and may form the basis of allegations of medical negligence, wrongful death or product liability. Pathologists may play an important role in the resolution of these legal claims through the proper performance, interpretation and reporting of their examinations. Pathologists can also assist in the legal process by explaining pathologic findings and their significance, correlating them with the clinical course and addressing issues of causation.

Adult↗
PubMed1997

Preclinical evaluation of the fluorinated 2-nitroimidazole N-(2-hydroxy-3,3,3-trifluoropropyl)-2-(2-nitro-1-imidazolyl) acetamide (SR-4554) as a probe for the measurement of tumor hypoxia.

A novel probe, N-(2-hydroxy-3,3,3,-trifluoropropyl)-2-(2-nitro-1-imidazolyl) acetamide (SR-4554), has been used to detect tumor hypoxia noninvasively by 19F magnetic resonance spectroscopy (19F MRS). The compound was designed to undergo a hypoxia-dependent, one-electron reduction to metabolites that are selectively retained in tumors and has attractive pharmacokinetic, toxicological, and detection sensitivity properties. As a prelude to clinical studies, we report here for the first time on the ability to detect a MR signal following SR-4554 administration in various transplantable tumors and describe validation studies, consisting of a correlation between signal retention and radiobiological hypoxic fraction, and the effects of modulating the degree of hypoxia by hydralazine and carbogen breathing. SR-4554 was absorbed and then eliminated from EMT6 tumors with a half-life of 51 min following an injection of 180 mg/kg i.p. of SR-4554. Using a quantitative 19F MRS technique, the 19F retention index (19FRI; 19F signal level at 6 h/45 min) was determined for four commonly used murine tumors (EMT6, SCCVII, KHT, and RIF-1). The retention of high tumor concentrations of fluorinated probe at 6 h, despite the much lower (20-fold) concentration of parent SR-4554 detected by high-performance liquid chromatography, was consistent with the involvement of one or more nitroreduced metabolites and suggested that 19F MRS might give a quantitative measure of tumor hypoxia. In these murine tumors, 19FRI correlated with the reported radiobiological hypoxic fraction of the tumors (r = 0.988; P = 0.01). In addition, changes in tumor microenvironment were detected by 19F MRS. An increase in hypoxia induced by hydralazine treatment of RIF-1 tumor-bearing mice was associated with a 2.4-fold increase in 19FRI compared to untreated controls. In contrast, carbogen breathing by C3H mammary tumor-bearing mice produced a 6-fold decrease in the 19FRI compared to air-breathing mice. The data presented support the preclinical and clinical development of SR-4554 as a noninvasive probe for tumor hypoxia.

Animals↗
PubMed1997

Hyperintense subcortical brain alterations in anorexia nervosa.

OBJECTIVE: The results of past research have identified changes in brain structure in anorexia nervosa. We observed previously unreported MRI alterations in two cases of anorexia nervosa. METHOD: For both cases, we reviewed the clinical history, MRI scans and conducted a pertinent literature review. RESULTS: The MRI brain scans of two patients with the diagnosis of anorexia nervosa revealed evidence of subcortical hyperintense changes on T2-weighted images. DISCUSSION: No previous reports of these findings have been described in the literature on anorexia nervosa to date. Clinical and pathologic correlates associated with these brain observations in anorexia nervosa are discussed.

Adolescent↗
PubMed1997

Pharmacokinetics of the hypoxic cell cytotoxic agent tirapazamine and its major bioreductive metabolites in mice and humans: retrospective analysis of a pharmacokinetically guided dose-escalation strategy in a phase I trial.

Tirapazamine (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide; SR 259075) is a selective hypoxic cell cytotoxic agent that is bioreductively activated in tumours to a reactive-drug free radical. Preclinically the agent has been shown to possess additive and synergistic anti-tumour activity in combination with radiotherapy and chemotherapy regimens. In the present study the pharmacokinetics and metabolism of tirapazamine were investigated in mice and patients as part of pre-clinical and phase I investigations. The objectives of this work were twofold; firstly, to evaluate retrospectively the utility of a pharmacokinetically guided dose-escalation (PGDE) strategy for tirapazamine, and secondly, to investigate if pharmacologically relevant plasma concentrations could be achieved at tolerable doses. Pharmacokinetic studies for PGDE were conducted in mice at four dose levels ranging from one-tenth of the LD10 to the LD50. The AUC at the LD10 (2932 micrograms ml-1 min) was used to determine a target AUC value of 1173 micrograms ml-1 min (equivalent to 40% of the mouse LD10 AUC) for clinical studies. A phase I study to investigate the tolerance of a single i.v. infusion of tirapazamine (once every 3 weeks) was initiated with close pharmacokinetic monitoring. The starting dose (36 mg/m2) was based on toxicity data obtained in the mouse, rat and dog. Doses were escalated by increases in the volume and duration of infusion. A retrospective analysis of the pharmacokinetic and toxicity data was then made to determine the utility of a PGDE approach. The drug exhibited a steep dose-lethality relationship in mice (LD10 294 mg/m2, LD50 303 mg/m2). The major gross toxicities were body-weight loss (15-20%), pilo-erection and hypoactivity at all dose levels. Sporadic ptosis and conjunctivitis were observed at doses of > 300 mg/m2. The plasma elimination of tirapazamine fitted a monoexponential open model, with rapid elimination from the plasma (t1/2 = 36 +/- 0.65 min) occurring at the LD10 dose of 294 mg/m2. A 10.3-fold increase in dose resulted in a 25.0-fold increase in AUC. Clinically, doses were escalated over the range of 36-450 mg/m2. Ototoxicity (tinnitus and reversible hearing loss) was dose-limiting at 450 mg/m2 and the MTD was 390 mg/m2 for this schedule. Pharmacokinetic analyses in patients revealed that the elimination of tirapazamine in patients was generally bi-phasic, with low inter-patient variability being found in clearance. A 12.5-fold increase in dose resulted in a 19.0-fold increase in AUC. There was good quantitative agreement in metabolite formation between mice and humans with respect to the two- and four-electron bioreductive metabolites. AUC values recorded for tirapazamine at the MTD of 390 mg/m2 (range 1035-1611 micrograms ml-1 min) were similar to the target AUC in mice. Importantly, these levels are consistent with the levels required for radiation-dose enhancement and effective combination with cisplatin in mice. Given (a) the similarities in plasma pharmacokinetics and metabolism observed at the target AUC/MTD in mice, rats, dogs and humans, (b) the similar degree of plasma protein binding seen between species and (c) the relatively low inter-patient variability noted in drug clearance, a successful PGDE approach should have been feasible. The results also indicate that potentially therapeutic levels of tirapazamine are achievable in patients at tolerable doses.

Animals↗