A phase I study of flavopiridol using an alternative schedule in patients (pts) with advanced solid tumors

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Background: A phase I study of flavopiridol, a cyclin-dependent kinase inhibitor, using an alternative schedule was conducted in pts with solid tumors given its promising activity in pts with chronic lymphocytic leukemia (CLL). Methods: Using standard 3x3 ph I dose escalation design, NCI-sponsored trial was performed to determine the safety and dose-limiting toxicity (DLT) of flavopiridol given as a 30-min IV loading dose followed by a 4-hr infusion weekly for 4 wks repeated every 6 wks. DLT was defined as Gr 4 hematologic toxicity (HT) for > 7 days, > Gr 3 non-HT except Gr 3 fatigue or diarrhea resolving <4 days and cytokine release syndrome (CRS) > Gr 3 despite steroids. Blood samples were obtained at pre-dose and 0.5, 1, 3, 4.5, 6, 8, 24, and 48-hr after start of first bolus dose for pharmacokinetics (PK). Results: 26 pts with advanced solid tumors with a median age of 63 (44–75) yrs were enrolled. Median no. of doses was 7.5 (1–24). Table 1 outlines the PK parameters, DLTs and CRS. Due to a grade 5 CRS/death in cohort 3, the protocol was amended to include 20 mg IV dexamethasone prior to flavopiridol to prevent CRS (cohorts 2B, 1B). Of the 20 evaluable pts, 35% had stable- and 65% had progressive-disease. Results of serum cytokines (IL-2, IL-4, IL-6, TNF-a, IFN-g, IL-10) levels will be presented. Conclusions: There was a higher frequency of CRS, despite prophylactic steroids seen our pts with solid tumors compared to previous studies with CLL and this correlated with AUC. PK and toxicity profile in our pt population differs from pts with hematologic malignancies administered flavopiridol on the same schedule. Protein binding and serum albumin levels are under evaluation as potential contributors. This work is supported by NCI U01-CA76576.

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Significant clinical and biologic activity of RAF/VEGF-R kinase inhibitor BAY 43–9006 in patients with metastatic papillary thyroid carcinoma (PTC): Updated results of a phase II study

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Purpose: Oncogenic defects in the genes involving RAS-RAF-MAPK signaling pathway (RAS, BRAF, or RET/PTC) occur in ∼60% of PTC. VEGF also plays a critical role in thyroid cancer progression. Due to lack of effective treatment, systemic therapy for iodine-refractory PTC is desperately needed. Methods: The primary endpoint of this phase II trial was to assess the objective response rates of BAY 43–9006 in pts with metastatic PTC. Secondary endpoints included clinical response correlation with 1) serum thyroglobulin (Tg) levels; 2) functional imaging including FDG-PET, and DCE-MRI; and 3) tumor genotype and degree of signaling inhibition in tumor biopsies. Using a minimax 2-stage design, 16 or 25 chemo-naïve pts with iodine-refractory PTC were to be enrolled in Arm A (accessible tumor for biopsy). An exploratory Arm B was designed with a plan to halt accrual as soon as Arm A was fully accrued. Eligible pts for Arm B had other subtypes of thyroid cancer or prior chemo, and did not require tumor biopsies. Pts received BAY 43–9006 at the dose of 400 mg PO BID. Response was assessed every 8 wks using RECIST. Results: A total of 58 pts (Arm A = 20, Arm B = 38) were enrolled from October 2004 to August 2005. Median duration of follow-up is 36 weeks (range, 16–60). Of 56 pts assessable for toxicity, serious adverse events (AEs) included aspergillus infection (gr 5, n = 1), secondary AML (gr 5, n = 1) and diverticular rupture (gr 3, n = 1). Common Gr 3 AEs were hand-foot syndrome (n = 9) and musculoskeletal pain (n = 10). Two confirmed partial responses (PRs) and 6 minor responses (23–29% decrease in sum of the longest diameter) were observed in 16 evaluable pts on Arm A. In 10 Tg-response evaluable pts on Arm A, median decrease in Tg was 70% (range, 45–90). Significant decreases in tumor perfusion and SUVs were noted in such pts. In addition, one PR and one minor response (27% decrease in sum of longest diameter; 85% reduction in Tg) have been observed among 20 pts with PTC on Arm B. Data for functional imaging and tissue correlative studies will be presented. Conclusions: BAY 43–9006 is a well-tolerated targeted therapy that has significant clinical and biologic anti-tumor activity in pts with iodine-refractory metastatic PTC.

No significant financial relationships to disclose.

Neoplasia in zebrafish (Danio rerio) treated with N-methyl-N'-nitro-N-nitrosoguanidine by three exposure routes at different developmental stages

We exposed embryos (83 hours postfertilizaton) and fry (3 weeks posthatch) to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) by immersion in aqueous solutions of 0-10 ppm for 1 hour (embryo) or 0-2 ppm for 24 hours (fry). Zebrafish embryos were microinjected with MNNG at levels of 0 or 96 ng/egg. Diets containing 0-2,000 ppm MNNG were fed to juvenile zebrafish for 3 months beginning at 2 months posthatch. Fish were sampled for histopathologic study at 6-12 months after initiation of carcinogen exposure. Embryos and fry were both quite responsive to MNNG; however, juvenile zebrafish were remarkably refractory to MNNG-induced neoplasia. Principal target organs in zebrafish treated as embryos with MNNG were liver and testis, with hepatocellular adenoma the most prevalent hepatic neoplasm. A variety of mesenchymal neoplasms occurred in zebrafish following embryo exposure to MNNG, including chondroma, hemangioma, hemangiosarcoma, leiomyosarcoma, and rhabdomyosarcoma. Testis and blood vessels were primary target organs for MNNG following fry exposure, with seminoma, hemangioma, hemangiosarcoma, and various other epithelial and mesenchymal neoplasms occurring. The zebrafish is a responsive, cost-effective lower vertebrate model system in which to study mechanisms of carcinogenesis.

Neoplasia in zebrafish (Danio rerio) treated with 7,12-dimethylbenz[a]anthracene by two exposure routes at different developmental stages

Using zebrafish, Danio rerio, initial pioneering work in the 1960s revealed carcinogen responsiveness of fish, yet very few subsequent tumorigenesis investigations have utilized this species. We exposed embryos (60 hours postfertilization) and fry (3 week posthatch) to 7,12-dimethylbenz[a]anthracene (DMBA) by immersion in aqueous solutions for 24 hours, at concentrations of 0-1 or 0-5 ppm (mg/L), respectively. Juvenile zebrafish 2 months posthatch were fed a diet containing 0-1,000 ppm DMBA for 4 months. Fish were sampled for histologic evaluation at 7-12 months after the onset of carcinogen treatment. Fry were most responsive to DMBA and showed the widest diversity of target tissues and histologic types of neoplasia, having several types of epithelial, mesenchymal, and neural neoplasia. The principal target tissues for carcinogenic response were liver following embryo or fry exposure, with gill and blood vessel the second and third most responsive tissues in fry. Intestine was the primary target and gill a secondary target in fish that received dietary DMBA as juveniles. These studies indicate that young zebrafish are most responsive to DMBA, showing a greater diversity of neoplasm types than rainbow trout. Thus, zebrafish are a valuable model system in which to study mechanistic aspects of the carcinogenesis process.

Chlorophyllin chemoprevention in trout initiated by aflatoxin B(1) bath treatment: An evaluation of reduced bioavailability vs. target organ protective mechanisms

Chlorophyllin (CHL) is known to inhibit DNA adduction and hepatocarcinogenesis in trout when administered at doses up to 4000 ppm in the diet with aflatoxin B(1) (AFB(1)). The principal protective mechanism is believed to involve CHL:AFB(1) complex formation, which may reduce systemic carcinogen absorption. However, mechanisms operative within the target organ in situ have not been ruled out. The present study used alternative CHL and AFB(1) exposures as well as hepatic metabolism studies to distinguish these mechanisms. Duplicate lots of 150 rainbow trout each were initiated by brief water bath exposure to 0.1 ppm AFB(1), with or without 500 ppm CHL in the water. The addition of 500 ppm CHL to the water bath, under conditions where AFB(1) is calculated to be >99% sequestered as the CHL:AFB(1) complex, reduced hepatic AFB(1)-DNA adduction by 95% and reduced hepatocarcinogenesis from 20.5% to 2%, compared with exposure to AFB(1) alone. Inclusion of 500 ppm CHL in the water bath also significantly reduced total body burden and hepatic levels of AFB(1) as well as AFB(2), a structural analogue of AFB(1) unable to directly form the 8,9-epoxide proximate electrophile but equally capable of complexing with CHL. By contrast, internal target organ CHL loading by pretreatment of trout with 4000 ppm dietary CHL for 7 days prior to (and 2 days following) AFB(1) waterbath exposure had no effect on AFB(1)-DNA adduction or tumorigenicity. Dietary CHL up to 8000 ppm had no effect on hepatic CYP2K1, CYP1A, glutathione transferase, UDP-glucuronosyl transferase, or, with one exception, the relative ratios among hepatic AFB(1) metabolites in vivo. These results support the hypothesis that CHL:AFB(1) complex formation and reduced systemic AFB(1) bioavailability is a principal mechanism for CHL chemoprevention in this model and that in situ target organ inhibitory mechanisms are relatively insignificant.

Modulation of aflatoxin-B1 hepatocarcinogenesis in trout by dehydroepiandrosterone: initiation/post-initiation and latency effects

Previously, we demonstrated that dehydroepiandrosterone (DHEA) enhances aflatoxin B1 (AFB1) hepatocarcinogenesis in trout when administered following AFB1 exposure. This paper examines the effect of DHEA on tumor latency and the comparative potency for DHEA to modulate AFB1 carcinogenesis when administered prior to and concurrent with AFB1 compared with a post-initiation exposure. Trout were initiated by a 30 min water bath exposure to 10 p.p.b. AFB1. At 3 months post-initiation, animals were started on either control diet or a diet containing 444 p.p.m. dehydroepiandrosterone (DHEA). Fifty trout per treatment were sampled prior to the start of experimental diets, and then at monthly intervals for the next 7 months and examined for the presence of tumors. Tumors were not detected in initiated controls until 7 months after initiation. In initiated trout fed DHEA, the first tumor was detected 5 months after initiation (after just 2 months of dietary DHEA). At 6 months post-initiation, 20% of the AFB1-initiated trout fed DHEA had tumors, while no tumors were visible in either AFB1-initiated controls or noninitiated trout fed DHEA. A second experiment was designed to determine if the enhancing effect of DHEA on AFB1 carcinogenesis is dependent on the time of DHEA administration relative to the time of AFB1 exposure, and if DHEA could be chemopreventive if administered prior to and concurrent with AFB1. Trout were fed one of two levels of DHEA (888 or 1776 p.p.m.) either prior to and during a 4-week initiation period of dietary AFB1 administration, or for 8 weeks following initiation with AFB1. At 9 months after initiation the livers were examined for tumors. Neither exposure protocol provided protection towards AFB1 hepatocarcinogenesis. The strongest enhancement occurred when DHEA was fed during the post-initiation period. Levels of p53 and p34cdc2 were decreased by DHEA treatment, indicating that DHEA may act through alterations in cell-cycle control.

Modulation of N-methyl-N'-nitro-nitrosoguanidine multiorgan carcinogenesis by dehydroepiandrosterone in rainbow trout

Dehydroepiandrosterone (DHEA) and its sulfate conjugate are the major circulating steroids in human plasma. Low levels of these adrenal steroids are associated with a number of human diseases including certain cancers. In animal studies, DHEA is chemopreventive toward both spontaneous and chemically induced cancers. A potential concern for long-term usage of DHEA in humans is the finding that DHEA is hepatocarcinogenic in rats. The human health risk has been thought to be minimal, however, as the mechanism of DHEA hepatocarcinogenesis is assumed to be due to its properties as a peroxisome proliferator, a class of compounds to which humans are relatively insensitive. Recently, we have found DHEA to be a potent promoter of aflatoxin B1-initiation as well as a complete hepatocarcinogen in the rainbow trout, a species which is also insensitive to peroxisome proliferators. In order to determine the initiator- and tissue-specificity of DHEA promotion, we examined the effects of DHEA on N-methyl-N'-nitro-nitrosoguanidine (MNNG)-initiated carcinogenesis. Trout fry were initiated by a bath exposure (30 min at 35 ppm) to MNNG and then fed DHEA at levels of 0, 55, 111, 222, 444, or 888 ppm for 7 months. DHEA increased liver tumor incidence, multiplicity, and size in a dose-dependent manner. The liver tumor incidence ranged from 0 in the MNNG-initiated controls to 99% in initiated trout fed 888 ppm DHEA. The latter represents a potential synergistic interaction in liver between MNNG and DHEA, as tumor incidence in sham-initiated trout fed this level of DHEA was 41%. The kidney tumor incidence was also enhanced two- and threefold over initiated controls by 111 and 888 ppm DHEA, respectively. In contrast, the total number of stomach and swim bladder tumors was reduced by DHEA treatment. This study demonstrates differential effects of DHEA on MNNG-initiated carcinogenesis in liver, kidney, stomach, and swim bladder.

Dietary chlorophyllin is a potent inhibitor of aflatoxin B1 hepatocarcinogenesis in rainbow trout

Epidemiological and experimental evidence indicates a strong relationship between diet and cancer. The purpose of this study was to examine the potential of chlorophyllin (CHL), a food-grade derivative of the ubiquitous green plant pigment chlorophyll, to inhibit experimental carcinogenesis. We report that CHL is a potent, dose-responsive inhibitor of aflatoxin B1 DNA adduction and hepatocarcinogenesis in the rainbow trout model when fed with carcinogen. CHL neither promoted nor suppressed carcinogenesis with chronic postinitiation feeding. By molecular dosimetry analysis, reduced aflatoxin B1-DNA adduction accounted quantitatively for reduced tumor response up to 2000 ppm dietary CHL, but an additional protective mechanism was operative at 4000 ppm CHL. The finding of potent inhibition (up to 77%) at CHL levels well within the chlorophyll content of some green leafy vegetables may have important implications in intervention and dietary management of human cancer risks.

Localization of the gene encoding 3-hydroxy-3-methylglutaryl-coenzyme A synthase to human chromosome 5

A series of hybrids between primary human cells and a Chinese hamster somatic cell mutant (Mev-1), defective in expression of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase [(S)-3-hydroxy-3-methylglutaryl-CoA acetoacetyl-CoA-lyase (CoA-acetylating, EC 4.1.3.5], has been prepared that complements the mutant defect. A technique based on differential sensitivity of this enzyme activity to inhibition by magnesium ion is described that allows the discrimination of expression of human and hamster HMG-CoA synthase in these hybrids. The results indicate a structural gene defect in expression of HMG-CoA synthase activity in Mev-1 cells. Segregation of human chromosomes that do not possess the complementing marker have allowed the assignment of human HMG-CoA synthase activity to chromosome 5. This is the second demonstrably transcriptionally regulated enzyme of cholesterologenesis to be assigned to chromosome 5, the other being HMG-CoA reductase.