Erythrofordins D and E, two new cassaine-type diterpenes from Erythrophleum suaveolens.

Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroon collection of Erythrophleum suaveolens were isolated and assessed for anti-tumor activity. In the NCI-60 cancer cell assay, erythrofordins D (1) and E (2) were found to be cytotoxic in the low micro molar ranges with a mean GI50 value of 2.45 and 0.71 µM, mean TGI value of 9.77 and 2.29 µM, and a mean LC50 of 26.92 and 11.48 µM for 1 and 2 respectively. Using the COMPARE algorithm, the new compounds were found to have similar NCI-60 response profiles to the known cardiac glycosides hyrcanoside and strophanthin. In addition, in an assay examining the viability and contractile function in human cardiomyocytes derived from induced pluripotent stem-cells, erythrofordins showed cardiotoxicity effects at concentrations as low as 0.03 µg/mL.

A case report of typhlitis during novel use of ropidoxuridine-capecitabine-radiotherapy for treatment-naïve rectal cancer.

BACKGROUND: Rectal carcinomas are tumors that arise from the last 12 cm of the large intestine closest to the anus. They generally have a modest prognosis exacerbated by a high local recurrence rate if radiosensitizing chemotherapy is not given during radiotherapy. This case report discusses the clinical trial treatment of a patient with rectal adenocarcinoma by a new ropidoxuridine-capecitabine-radiotherapy combination. This case report is novel due to the patient's participation in an accelerated titration phase I clinical trial and the resultant rare adverse event of treatment-related sigmoid typhlitis. CASE PRESENTATION: The patient was an 82-year-old female who noticed hematochezia and change in stool caliber over a period of 3 months. A rectal mass was identified by biopsy as a microsatellite stable adenocarcinoma. A planned total neoadjuvant treatment involved eight cycles of leucovorin calcium (folinic acid)-fluorouracil-oxaliplatin (mFOLFOX6) chemotherapy, followed by a clinical trial combination of ropidoxuridine-capecitabine-radiotherapy, prior to definitive surgery. The patient began daily intensity modulated pelvic radiotherapy with concurrent twice-daily oral ropidoxuridine and twice-daily oral capecitabine to be given over 6 weeks. After 14 days of ropidoxuridine-capecitabine-radiotherapy, the patient developed sigmoid typhlitis requiring a 10-day hospitalization and 14-day disruption of treatment. The patient died 27 days after the start of ropidoxuridine-capecitabine-radiotherapy. This adverse event was listed as a definite attribution to the ropidoxuridine-capecitabine treatment; pharmacokinetic and pharmacodynamic data showed low ropidoxuridine metabolite DNA incorporation and high capecitabine metabolite concentration. The accelerated titration phase I clinical trial has been subsequently closed to accrual (NCT04406857). CONCLUSIONS: We believe this case report demonstrates the decision-making process for terminating a phase I accelerated titration designed clinical trial. The report also presents the rare complication of sigmoid typhlitis as a treatment-attributed adverse event. In this case, a ropidoxuridine-capecitabine combination was used as an investigational radiosensitizing treatment now with a narrower future clinical development pathway.

Targeted Investigational Oncology Agents in the NCI-60: A Phenotypic Systems-based Resource.

The NCI-60 human tumor cell line panel has proved to be a useful tool for the global cancer research community in the search for novel chemotherapeutics. The publicly available cell line characterization and compound screening data from the NCI-60 assay have significantly contributed to the understanding of cellular mechanisms targeted by new oncology agents. Signature sensitivity/resistance patterns generated for a given chemotherapeutic agent against the NCI-60 panel have long served as fingerprint presentations that encompass target information and the mechanism of action associated with the tested agent. We report the establishment of a new public NCI-60 resource based on the cell line screening of a large and growing set of 175 FDA-approved oncology drugs (AOD) plus >825 clinical and investigational oncology agents (IOA), representing a diverse set (>250) of therapeutic targets and mechanisms. This data resource is available to the public (https://ioa.cancer.gov) and includes the raw data from the screening of the IOA and AOD collection along with an extensive set of visualization and analysis tools to allow for comparative study of individual test compounds and multiple compound sets.

ROADMAPS: An Online Database of Response Data, Dosing Regimens, and Toxicities of Approved Oncology Drugs as Single Agents to Guide Preclinical In Vivo Studies.

Preclinical studies provide valuable data in the early development of novel drugs for patients with cancer. Many cancer treatment regimens now utilize multiple agents with different targets to delay the emergence of drug-resistant tumor cells, and experimental agents are often evaluated in combination with FDA-approved drugs. The Biological Testing Branch (BTB) of the U.S. NCI has evaluated more than 70 FDA-approved oncology drugs to date in human xenograft models. Here, we report the first release of a publicly available, downloadable spreadsheet, ROADMAPS (Responses to Oncology Agents and Dosing in Models to Aid Preclinical Studies, dtp.cancer.gov/databases_tools/roadmaps.htm), that provides data filterable by agent, dose, dosing schedule, route of administration, tumor models tested, responses, host mouse strain, maximum weight loss, drug-related deaths, and vehicle formulation for preclinical experiments conducted by the BTB. Data from 70 different single targeted and cytotoxic agents and 140 different xenograft models were included. Multiple xenograft models were tested in immunocompromised mice for many cancer histologies, with lung cancer as the most broadly tested (24 models). Many of the dose levels and schedules used in these experiments were comparable with those tolerated in humans. Targeted and cytotoxic single agents were included. The online spreadsheet will be updated periodically as additional agent/dose/model combinations are evaluated. ROADMAPS is intended to serve as a publicly available resource for the research community to inform the design of clinically relevant, tolerable single and combinatorial regimens in preclinical mouse models. SIGNIFICANCE: ROADMAPS includes data that can be used to identify tolerable dosing regimens with activity against a variety of human tumors in different mouse strains, providing a resource for planning preclinical studies.

F-aza-T-dCyd (NSC801845), a Novel Cytidine Analog, in Comparative Cell Culture and Xenograft Studies with the Clinical Candidates T-dCyd, F-T-dCyd, and Aza-T-dCyd.

In this article, 5-aza-4'-thio-2'-ß-fluoro-2'-deoxycytidine (F-aza-T-dCyd, NSC801845), a novel cytidine analog, is first disclosed and compared with T-dCyd, F-T-dCyd, and aza-T-dCyd in cell culture and mouse xenograft studies in HCT-116 human colon carcinoma, OVCAR3 human ovarian carcinoma, NCI-H23 human NSCLC carcinoma, HL-60 human leukemia, and the PDX BL0382 bladder carcinoma. In three of five xenograft lines (HCT-116, HL-60, and BL-0382), F-aza-T-dCyd was more efficacious than aza-T-dCyd. Comparable activity was observed for these two agents against the NCI-H23 and OVCAR3 xenografts. In the HCT-116 study, F-aza-T-dCyd [10 mg/kg intraperitoneal (i.p.), QDx5 for four cycles], produced complete regression of the tumors in all mice with a response that proved durable beyond postimplant day 150 (129 days after the last dose). Similarly, complete tumor regression was observed in the HL-60 leukemia xenograft when mice were dosed with F-aza-T-dCyd (10 mg/kg i.p., QDx5 for three cycles). In the PDX BL-0382 bladder study, both oral and i.p. dosing of F-aza-T-dCyd (8 mg/kg QDx5 for three cycles) produced regressions that showed tumor regrowth beginning 13 days after dosing. These findings indicate that further development of F-aza-T-dCyd (NSC801845) is warranted. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/20/4/625/F1.large.jpg.

Targeting Protein Translation by Rocaglamide and Didesmethylrocaglamide to Treat MPNST and Other Sarcomas.

Malignant peripheral nerve sheath tumors (MPNST) frequently overexpress eukaryotic initiation factor 4F components, and the eIF4A inhibitor silvestrol potently suppresses MPNST growth. However, silvestrol has suboptimal drug-like properties, including a bulky structure, poor oral bioavailability (<2%), sensitivity to MDR1 efflux, and pulmonary toxicity in dogs. We compared ten silvestrol-related rocaglates lacking the dioxanyl ring and found that didesmethylrocaglamide (DDR) and rocaglamide (Roc) had growth-inhibitory activity comparable with silvestrol. Structure-activity relationship analysis revealed that the dioxanyl ring present in silvestrol was dispensable for, but may enhance, cytotoxicity. Both DDR and Roc arrested MPNST cells at G2-M, increased the sub-G1 population, induced cleavage of caspases and PARP, and elevated the levels of the DNA-damage response marker γH2A.X, while decreasing the expression of AKT and ERK1/2, consistent with translation inhibition. Unlike silvestrol, DDR and Roc were not sensitive to MDR1 inhibition. Pharmacokinetic analysis confirmed that Roc had 50% oral bioavailability. Importantly, Roc, when administered intraperitoneally or orally, showed potent antitumor effects in an orthotopic MPNST mouse model and did not induce pulmonary toxicity in dogs as found with silvestrol. Treated tumors displayed degenerative changes and had more cleaved caspase-3-positive cells, indicative of increased apoptosis. Furthermore, Roc effectively suppressed the growth of osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma cells and patient-derived xenografts. Both Roc- and DDR-treated sarcoma cells showed decreased levels of multiple oncogenic kinases, including insulin-like growth factor-1 receptor. The more favorable drug-like properties of DDR and Roc and the potent antitumor activity of Roc suggest that these rocaglamides could become viable treatments for MPNST and other sarcomas.

Phase I trial of TRC102 (methoxyamine HCl) in combination with temozolomide in patients with relapsed solid tumors and lymphomas.

BACKGROUND: TRC102 inhibits base excision repair by binding abasic sites and preventing AP endonuclease processing; it potentiates the activity of alkylating agents, including temozolomide, in murine models. In published xenograft studies, TRC102 enhanced the antitumor effect of temozolomide regardless of cell line genetic characteristics, e.g., O6-methylguanine DNA methyltransferase (MGMT), mismatch repair (MMR), or p53 status. MATERIALS AND METHODS: We conducted a phase 1 trial of TRC102 with temozolomide given orally on days 1-5 of 28-day cycles in adult patients with refractory solid tumors that had progressed on standard therapy. Tumor induction of nuclear biomarkers of DNA damage response (DDR) γH2AX, pNBs1, and Rad51 was assessed in the context of MGMT and MMR protein expression for expansion cohort patients. RESULTS: Fifty-two patients were enrolled (37 escalation, 15 expansion) with 51 evaluable for response. The recommended phase 2 dose was 125 mg TRC102, 150 mg/m2 temozolomide QDx5. Common adverse events (grade 3/4) included anemia (19%), lymphopenia (12%), and neutropenia (10%). Four patients achieved partial responses (1 non-small cell lung cancer, 2 granulosa cell ovarian cancer, and 1 colon cancer) and 13 patients had a best response of stable disease. Retrospective analysis of 15 expansion cohort patients did not demonstrate a correlation between low tumor MGMT expression and patient response, but treatment induced nuclear Rad51 responses in 6 of 12 patients. CONCLUSIONS: The combination of TRC 102 with temozolomide is active, with 4 of 51 patients experiencing a partial response and 13 of 51 experiencing stable disease, and the side effect profile is manageable.

Phase I and Pharmacology Study of Ropidoxuridine (IPdR) as Prodrug for Iododeoxyuridine-Mediated Tumor Radiosensitization in Advanced GI Cancer Undergoing Radiation.

PURPOSE: Iododeoxyuridine (IUdR) is a potent radiosensitizer; however, its clinical utility is limited by dose-limiting systemic toxicities and the need for prolonged continuous infusion. 5-Iodo-2-pyrimidinone-2'-deoxyribose (IPdR) is an oral prodrug of IUdR that, compared with IUdR, is easier to administer and less toxic, with a more favorable therapeutic index in preclinical studies. Here, we report the clinical and pharmacologic results of a first-in-human phase I dose escalation study of IPdR + concurrent radiation therapy (RT) in patients with advanced metastatic gastrointestinal (GI) cancers. PATIENTS AND METHODS: Adult patients with metastatic GI cancers referred for palliative RT to the chest, abdomen, or pelvis were eligible for study. Patients received IPdR orally once every day × 28 days beginning 7 days before the initiation of RT (37.5 Gy in 2.5 Gy × 15 fractions). A 2-part dose escalation scheme was used, pharmacokinetic studies were performed at multiple time points, and all patients were assessed for toxicity and response to Day 56. RESULTS: Nineteen patients were entered on study. Dose-limiting toxicity was encountered at 1,800 mg every day, and the recommended phase II dose is 1,200 mg every day. Pharmacokinetic analyses demonstrated achievable and sustainable levels of plasma IUdR ≥1 µmol/L (levels previously shown to mediate radiosensitization). Two complete, 3 partial, and 9 stable responses were achieved in target lesions. CONCLUSIONS: Administration of IPdR orally every day × 28 days with RT is feasible and tolerable at doses that produce plasma IUdR levels ≥1 µmol/L. These results support the investigation of IPdR + RT in phase II studies.

The National Cancer Institute ALMANAC: A Comprehensive Screening Resource for the Detection of Anticancer Drug Pairs with Enhanced Therapeutic Activity.

To date, over 100 small-molecule oncology drugs have been approved by the FDA. Because of the inherent heterogeneity of tumors, these small molecules are often administered in combination to prevent emergence of resistant cell subpopulations. Therefore, new combination strategies to overcome drug resistance in patients with advanced cancer are needed. In this study, we performed a systematic evaluation of the therapeutic activity of over 5,000 pairs of FDA-approved cancer drugs against a panel of 60 well-characterized human tumor cell lines (NCI-60) to uncover combinations with greater than additive growth-inhibitory activity. Screening results were compiled into a database, termed the NCI-ALMANAC (A Large Matrix of Anti-Neoplastic Agent Combinations), publicly available at https://dtp.cancer.gov/ncialmanac Subsequent in vivo experiments in mouse xenograft models of human cancer confirmed combinations with greater than single-agent efficacy. Concomitant detection of mechanistic biomarkers for these combinations in vivo supported the initiation of two phase I clinical trials at the NCI to evaluate clofarabine with bortezomib and nilotinib with paclitaxel in patients with advanced cancer. Consequently, the hypothesis-generating NCI-ALMANAC web-based resource has demonstrated value in identifying promising combinations of approved drugs with potent anticancer activity for further mechanistic study and translation to clinical trials. Cancer Res; 77(13); 3564-76. ©2017 AACR.

First-in-Human Phase I Study of the Tamoxifen Metabolite Z-Endoxifen in Women With Endocrine-Refractory Metastatic Breast Cancer.

Purpose Endoxifen is a tamoxifen metabolite with potent antiestrogenic activity. Patients and Methods We performed a phase I study of oral Z-endoxifen to determine its toxicities, maximum tolerated dose (MTD), pharmacokinetics, and clinical activity. Eligibility included endocrine-refractory, estrogen receptor-positive metastatic breast cancer. An accelerated titration schedule was applied until moderate or dose-limiting toxicity occurred, followed by a 3+3 design and expansion at 40, 80, and 100 mg per day. Tumor DNA from serum (circulating cell free [cf); all patients] and biopsies [160 mg/day and expansion]) was sequenced. Results Of 41 enrolled patients, 38 were evaluable for MTD determination. Prior endocrine regimens during which progression occurred included aromatase inhibitor (n = 36), fulvestrant (n = 21), and tamoxifen (n = 15). Patients received endoxifen once daily at seven dose levels (20 to 160 mg). Dose escalation ceased at 160 mg per day given lack of MTD and endoxifen concentrations > 1,900 ng/mL. Endoxifen clearance was unaffected by CYP2D6 genotype. One patient (60 mg) had cycle 1 dose-limiting toxicity (pulmonary embolus). Overall clinical benefit rate (stable > 6 months [n = 7] or partial response by RECIST criteria [n = 3]) was 26.3% (95% CI, 13.4% to 43.1%) including prior tamoxifen progression (n = 3). cfDNA mutations were observed in 13 patients ( PIK3CA [n = 8], ESR1 [n = 5], TP53 [n = 4], and AKT [n = 1]) with shorter progression-free survival ( v those without cfDNA mutations; median, 61 v 132 days; log-rank P = .046). Clinical benefit was observed in those with ESR1 amplification (tumor; 80 mg/day) and ESR1 mutation (cfDNA; 160 mg/day). Comparing tumor biopsies and cfDNA, some mutations ( PIK3CA, TP53, and AKT) were undetected by cfDNA, whereas cfDNA mutations ( ESR1, TP53, and AKT) were undetected by biopsy. Conclusion In endocrine-refractory metastatic breast cancer, Z-endoxifen provides substantial drug exposure unaffected by CYP2D6 metabolism, acceptable toxicity, and promising antitumor activity.

Imaging the pharmacokinetics of [F-18]FAU in patients with tumors: PET studies.

PURPOSE: FAU (1-(2'-deoxy-2'-fluoro-beta-D: -arabinofuranosyl) uracil) can be phosphorylated by thymidine kinase, methylated by thymidylate synthase, followed by DNA incorporation and thus functions as a DNA synthesis inhibitor. This first-in-human study of [F-18]FAU was conducted in cancer patients to determine its suitability for imaging and also to understand its pharmacokinetics as a potential antineoplastic agent. METHODS: Six patients with colorectal (n = 3) or breast cancer (n = 3) were imaged with [F-18]FAU. Serial blood and urine samples were analyzed using HPLC to determine the clearance and metabolites. RESULTS: Imaging showed that [F-18]FAU was concentrated in breast tumors and a lymph node metastasis (tumor-to-normal-breast-tissue-ratio 3.7-4.7). FAU retention in breast tumors was significantly higher than in normal breast tissues at 60 min and retained in tumor over 2.5 h post-injection. FAU was not retained above background in colorectal tumors. Increased activity was seen in the kidney and urinary bladder due to excretion. Decreased activity was seen in the bone marrow with a mean SUV 0.6. Over 95% of activity in the blood and urine was present as intact [F-18]FAU at the end of the study. CONCLUSIONS: Increased [F-18]FAU retention was shown in the breast tumors but not in colorectal tumors. The increased retention of FAU in the breast compared to bone marrow indicates that FAU may be useful as an unlabeled antineoplastic agent. The low retention in the marrow indicates that unlabeled FAU might lead to little marrow toxicity; however, the images were not of high contrast to consider FAU for diagnostic clinical imaging.

Effects of capecitabine treatment on the uptake of thymidine analogs using exploratory PET imaging agents: 18F-FAU, 18F-FMAU, and 18F-FLT.

BACKGROUND: A principal goal for the use of positron emission tomography (PET) in oncology is for real-time evaluation of tumor response to chemotherapy. Given that many contemporary anti-neoplastic agents function by impairing cellular proliferation, it is of interest to develop imaging modalities to monitor these pathways. Here we examined the effect of capecitabine on the uptake of thymidine analogs used with PET: 3'-deoxy-3'-[18F]fluorothymidine (18F-FLT), 1-(2'-deoxy-2'-[18F]fluoro-ß-D-arabinofuranosyl) thymidine (18F-FMAU), and 1-(2'-deoxy-2'-[18F]fluoro-ß-D-arabinofuranosyl) uracil (18F-FAU) in patients with advanced cancer. METHODS: Fifteen patients were imaged, five with each imaging agent. Patients had been previously diagnosed with breast, colorectal, gastric, and esophageal cancers and had not received therapy for at least 4 weeks prior to the first scan, and had not been treated with any prior fluoropyrimidines. Subjects were imaged within a week before the start of capecitabine and on the second day of treatment, after the third dose of capecitabine. Tracer uptake was quantified by mean standard uptake value (SUVmean) and using kinetic analysis. RESULTS: Patients imaged with 18F-FLT showed variable changes in retention and two patients exhibited an increase in SUVmean of 172.3 and 89.9 %, while the other patients had changes ranging from +19.4 to -25.4 %. The average change in 18F-FMAU retention was 0.2 % (range -24.4 to 23.1) and 18F-FAU was -10.2 % (range -40.3 to 19.2). Observed changes correlated strongly with SUVmax but not kinetic measurements. CONCLUSIONS: This pilot study demonstrates that patients treated with capecitabine can produce a marked increase in 18F-FLT retention in some patients, which will require further study to determine if this flare is predictive of therapeutic response. 18F-FAU and 18F-FMAU showed little change, on average, after treatment.

Imaging DNA synthesis in vivo with 18F-FMAU and PET.

UNLABELLED: We imaged DNA synthesis in vivo with PET and (18)F-1-(2'-deoxy-2'-fluoro-beta-d-arabinofuranosyl)thymine (FMAU), which is phosphorylated by thymidine kinases and incorporated into DNA. METHODS: We produced (18)F-FMAU and injected the tracer into 5 normal dogs and studied them by imaging or biodistribution for up to 2.5 h. The pharmacokinetics of FMAU in blood and urine were determined using high-performance liquid chromatography analysis. At the end of each study, selected tissues were removed to measure the total activity retained in these tissues. In addition, the selected tissues were extracted by acid precipitation, by which the macromolecules can be precipitated to determine the radioactivity of (18)F-FMAU incorporated into DNA. RESULTS: Imaging and tissue analysis showed increased activity in the lymph nodes, stomach, small intestine, and bone marrow, with mean standardized uptake values of 1.4, 1.6, 2.3, and 3.9, respectively, because of varying degrees of increased cell proliferation. In contrast, (18)F-FMAU was distributed with tissue-to-muscle ratios of approximately 1.0 in nonproliferative organs such as lung, liver, and kidneys. Analysis of the tissue extracts using acid precipitation demonstrated that 88% of activity in marrow and 65% of activity in small intestine was acid precipitated. However, more than 90% of activity in the nonproliferating tissues such as heart and lungs was in the supernatant. Increased activity was seen in the heart because of a high level of thymidine kinase 2 and in the gallbladder because of excretion. Analysis of blood and urine demonstrated that more than 95% of activity was present as intact (18)F-FMAU at the end of the studies. CONCLUSION: The results showed that (18)F-FMAU was selectively retained in DNA of the proliferating tissues and was resistant to degradation. These features indicate that (18)F-FMAU might be an alternative to (11)C-thymidine for imaging DNA synthesis in normal tissues and tumors.

Biodistribution and radiation dosimetry estimates of 1-(2'-deoxy-2'-(18)F-Fluoro-1-beta-D-arabinofuranosyl)-5-bromouracil: PET imaging studies in dogs.

UNLABELLED: This study reports on the biodistribution and radiation estimates of 1-(2'-deoxy-2'-(18)F-fluoro-1-beta-d-arabinofuranosyl)-5-bromouracil ((18)F-FBAU), a potential tracer for imaging DNA synthesis. METHODS: Three normal dogs were intravenously administered (18)F-FBAU and a dynamic PET scan was performed for 60 min over the upper abdomen followed by a whole-body scan for a total of 150 min. Blood samples were collected at stipulated time intervals to evaluate tracer clearance and metabolism. Tissue samples of various organs were analyzed for tracer uptake and DNA incorporation. Dynamic accumulation of the tracer in different organs was derived from reconstructed PET images. The radiation dosimetry of (18)F-FBAU was evaluated using the MIRD method. RESULTS: At 60 min after injection, blood analysis found >90% of the activity in unmetabolized form. At 2 h after injection, (18)F-FBAU uptake was highest in proliferating tissues (mean SUVs: marrow, 2.6; small intestine, 4.0), whereas nonproliferative tissues showed little uptake (mean SUVs: muscle, 0.75; lung, 0.70; heart, 0.85; liver, 1.28). Dynamic image analysis over 60 min showed progressive uptake of the tracer in marrow. Extraction studies demonstrated that most of the activity in proliferative tissues was in the acid-insoluble fraction (marrow, 83%; small intestine, 73%), consistent with incorporation into DNA. In nonproliferative tissue, most of the activity was not found in the acid-insoluble fraction (>84% for heart, muscle, and liver). CONCLUSION: These results demonstrate that (18)F-FBAU was resistant to metabolism, readily incorporated into DNA in proliferating tissues, and showed good contrast between organs of variable DNA synthesis. These findings indicate that (18)F-FBAU may find use in measuring DNA synthesis with PET.

Metabolic profile of XK469 (2(R)-[4-(7-chloro-2-quinoxalinyl)oxyphenoxy]-propionic acid; NSC698215) in patients and in vitro: low potential for active or toxic metabolites or for drug-drug interactions.

As part of an ongoing phase 1 study, we studied the excretion of XK469 and its metabolism in patients and in vitro. Five primary metabolites were identified by HPLC/MS/MS. An oxidized product formed by cytosolic aldehyde oxidase was the predominant species both in urine and human hepatocytes in vitro. Conjugates of XK469 with glycine, taurine, and glucuronic acid, as well as the microsomal product, 4-oxo-XK469, were also found in urine and in vitro, but none were major contributors to the mass balance for XK469 elimination. Based upon the relative concentrations circulating in plasma, systemic exposure to parent drug was 100-fold higher than for the metabolites. Thus, both toxicity and efficacy of XK469 are most likely to be produced by the parent molecule, rather than the metabolites. Urinary recovery of parent drug was low (2% of dose in 24 h), partly because of the long half-life of XK469 (approximately 3 days). In addition, the metabolite profile in urine indicates that only 25% of the XK469-derived material was unchanged drug. Thus, urinary excretion was not a major factor in XK469 elimination. Variations in systemic exposure to XK469 will be strongly influenced by factors that alter the activity of aldehyde oxidase, including pharmacogenetics, enzyme inhibition, and enzyme induction, but no specific modifiers have been reported. The multiday half-life of XK469 hampered our ability to obtain a complete mass balance, and the possibility exists that other routes, such as biliary excretion, may also play a substantial role in XK469 disposition.

Distribution of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) uracil in mice bearing colorectal cancer xenografts: rationale for therapeutic use and as a positron emission tomography probe for thymidylate synthase.

PURPOSE: In colorectal, breast, and head and neck cancers, response to 5-fluorouracil is associated with low expression of thymidylate synthase. In contrast, tumors with high expression of thymidylate synthase may be more sensitive to prodrugs such as 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) uracil (FAU) that are activated by thymidylate synthase. These studies were designed to evaluate FAU as a potential therapeutic and diagnostic probe. EXPERIMENTAL DESIGN: [18F]-FAU and [3H]-FAU were synthesized with >97% radiochemical purity. [3H]-FAU or [18F]-FAU was administered intravenously to severe combined immunodeficient mice bearing either HT29 (low thymidylate synthase) or LS174T (high thymidylate synthase) human colon cancer xenografts. Four hours after [3H]-FAU dosing, tissue distribution of total radioactivity and incorporation of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) 5-methyluracil (FMAU), derived from thymidylate synthase activation of FAU, into tumor DNA was measured. Positron emission tomography (PET) images were obtained for 90 minutes after injection of [18F]-FAU. Thymidylate synthase activity was determined in vitro in tumors from untreated mice by [3H] release from [3H]dUMP. Each cell line was incubated in vitro with [3H]-FAU or [3H]-FMAU in the absence or presence of 5-fluoro-2'-deoxyuridine (FdUrd) and then was analyzed for incorporation of radiolabel into DNA. RESULTS: Thymidylate synthase enzymatic activity in LS174T xenografts was approximately 3.5-fold higher than in HT29 xenografts, and incorporation of radioactivity derived from [3H]-FAU into LS174T DNA was approximately 2-fold higher than into HT29 DNA. At 240 minutes, radioactivity derived from [3H]-FAU was approximately 2-fold higher in tumors than in skeletal muscle. At times up to 90 minutes, PET imaging detected only small differences in uptake of [18F]-FAU between the tumor types. Fluorine-18 in skeletal muscle was higher than in tumor for the first 90 minutes and plateaued earlier, whereas [18F] in tumor continued to increase during the 90-minute imaging period. For both cell lines in vitro, FdUrd decreased the rate of incorporation of [3H]-FAU into DNA, whereas the incorporation of [3H]-FMAU was increased. CONCLUSIONS: These results for FAU incorporation into DNA in vitro and in vivo further support clinical evaluation of FAU as a therapeutic agent in tumors with high concentrations of thymidylate synthase that are less likely to respond to 5-fluorouracil treatment. The high circulating concentrations of thymidine reported in mice may limit their utility in evaluating FAU as a PET probe.

Review of microdialysis in brain tumors, from concept to application: first annual Carolyn Frye-Halloran symposium.

In individuals with brain tumors, pharmacodynamic and pharmacokinetic studies of therapeutic agents have historically used analyses of drug concentrations in serum or cerebrospinal fluid, which unfortunately do not necessarily reflect concentrations within the tumor and adjacent brain. This review article introduces to neurological and medical oncologists, as well as pharmacologists, the application of microdialysis in monitoring drug metabolism and delivery within the fluid of the interstitial space of brain tumor and its surroundings. Microdialysis samples soluble molecules from the extracellular fluid via a semipermeable membrane at the tip of a probe. In the past decade, it has been used predominantly in neurointensive care in the setting of brain trauma, vasospasm, epilepsy,and intracerebral hemorrhage. At the first Carolyn Frye-Halloran Symposium held at Massachusetts General Hospital in March 2002, the concept of microdialysis was extended to specifically address its possible use in treating brain tumor patients. In doing so we provide a rationale for the use of this technology by a National Cancer Institute consortium, New Approaches to Brain Tumor Therapy, to measure levels of drugs in brain tissue as part of phase 1 trials.

Evaluation of highly bound drugs: interspecies, intersubject, and related comparisons.

Free (unbound) drug is generally the pharmacologically relevant parameter for drug exposure. Thus, comparisons among species, among individuals, and in other situations such as cell culture or drug metabolism experiments in vitro should be based on free drug. Although the traditional focus has been on the absolute value for free drug, the applications for the data in this study are primarily comparative. Therefore, the authors evaluated direct dialysis of one plasma sample versus another. At equilibrium, the total concentration of valproate in human plasma was 3-fold higher than in rat plasma. The total concentration of monoacetyl dapsone was 10-fold higher in human plasma than in rat plasma and 18-fold higher in human plasma than in dog plasma. These results confirm predictions derived from conventional dialysis of each plasma sample separately versus buffer. These data can be interpreted directly, without interspecies correction factors for binding, especially for the most important cases--drugs that are highly protein-bound.

Metabolism by N-acetyltransferase 1 in vitro and in healthy volunteers: a prototype for targeted inhibition.

Inhibition of drug metabolism is generally avoided but can be useful in limited circumstances, such as reducing the formation of toxic metabolites. Acetylation is a major pathway for drug elimination that can also convert substrates into toxic species, including carcinogens. Sulfamethoxazole, a widely used antibiotic, is metabolized via arylamine N-acetyltransferase 1. p-Aminosalicylate, used for antitubercular treatment, is also metabolized by N-acetyltransferase 1 and could potentially inhibit sulfamethoxazole metabolism. Human hepatocytes from 4 donors were incubated in vitro with sulfamethoxazole and paminosalicylate at clinically achievable concentrations. p-Aminosalicylate competitively reduced the acetylation of sulfamethoxazole in vitro by 61% to 83% at 200 microM. Four healthy volunteers were studied following doses of 500 mg sulfamethoxazole either alone or during administration of paminosalicylate (4 g ter in die). Plasma concentrations of paminosalicylate exceeded 100 microM. With each subject as his or her own control, p-aminosalicylate reduced by 5-fold the ratio of plasma concentrations of acetylsulfamethoxazole relative to parent drug (P < .001). Metabolic drug-drug interaction studies in vitro successfully predicted inhibition of acetylation via N-acetyltransferase 1 in vivo. Although no specific toxic species was investigated in this work, the potential was demonstrated for improving the therapeutic index of drugs that have toxic metabolites.

Imaging [18F]FAU [1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl) uracil] in dogs.

We have studied the biodistribution of [(18)F]FAU [(1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)uracil], which previous work has shown is incorporated into DNA and functions as an inhibitor of DNA synthesis. It is being tested as a potential antineoplastic agent and imaging agent for PET. We have produced [(18)F]FAU and injected the tracer into 3 normal dogs and imaged them for up to 4 hours and removed tissues along with blood and urine samples for HPLC and activity analysis. The results showed that [(18)F]FAU evenly distributed to most of organs. In sharp contrast to our prior experience with thymidine and its analogs, marrow had less retention of [(18)F]FAU than the non-proliferating tissues.