Oncogenes and human neoplasia

Genes whose products are directly involved in the transformation of a normal to a neoplastic cell are present in most but not all oncogenic RNA viruses (retroviruses) have genes found in oncogenic RNA viruses (retroviruses) have also been found in normal cells, their coding sequences highly conserved in evolution. Such viral genes (v-onc) are expressed at high levels in infected cells. "Activation" of cellular homologues of v-onc genes (c-onc) may occur by a variety of mechanisms leading to an abnormal and/or increased expression of such activated c-onc genes in malignant cells. Although oncogene activation appears to be a critical step in the neoplastic transformation induced by oncogenic viruses, the role of this process in the development of chemical and radiation-induced neoplasia is not yet clear.     

Application of quantitative stereology to the evaluation of phenotypically heterogeneous enzyme-altered foci in the rat liver

Quantitative stereologic relationships are applied in this report to the evaluation of F344 rat liver foci where the tissue sections exhibit congruent enzyme-altered areas of the several different phenotypes as well as enzyme-altered areas within a larger area of another enzyme alteration, that is, a "focus within a focus.' Quantitation of both the numbers and volume occupied by each of the phenotypes of the enzyme-altered foci was accomplished by the unique logic described in this report. The application of this logic to four representative experimental protocols with the use of three phenotypic markers demonstrated all possible congruent phenotypes as well as a small number of "foci within foci.' The variance of the quantitation of the experimental data was shown to depend on the number of focal transections identified in the sections, the number of sections examined, and the distribution of phenotypic alterations among foci.     

The aryl hydrocarbon receptor is required for developmental closure of the ductus venosus in the neonatal mouse

A developmental role for the Ahr locus has been indicated by the observation that mice harboring a null allele display a portocaval vascular shunt throughout life. To define the ontogeny and determine the identity of this shunt, we developed a visualization approach in which three-dimensional (3D) images of the developing liver vasculature are generated from serial sections. Applying this 3D visualization approach at multiple developmental times allowed us to demonstrate that the portocaval shunt observed in Ahr-null mice is the remnant of an embryonic structure and is not acquired after birth. We observed that the shunt is found in late-stage wild-type embryos but closes during the first 48 h of postnatal life. In contrast, the same structure fails to close in Ahr-null mice and remains open throughout adulthood. The ontogeny of this shunt, along with its 3D position, allowed us to conclude that this shunt is a patent developmental structure known as the ductus venosus (DV). Upon searching for a physiological cause of the patent DV, we observed that during the first 48 h, most major hepatic veins, such as the portal and umbilical veins, normally decrease in diameter but do not change in Ahr-null mice. This observation suggests that failure of the DV to close may be the consequence of increased blood pressure or a failure in vasoconstriction in the developing liver.     

A phase I and pharmacokinetic study of a powder-filled capsule formulation of oral irinotecan (CPT-11) given daily for 5 days every 3 weeks in patients with advanced solid tumors

Purpose: Intravenous (i.v.) irinotecan is a cytotoxic topoisomerase I inhibitor with broad clinical activity in metastatic colorectal cancer and other tumors. The development of an oral formulation of irinotecan could enhance convenience and lessen the expense of palliative irinotecan delivery. This phase I study evaluated the dose-limiting toxicities (DLT), maximum tolerated dose (MTD), and pharmacokinetics (PK) of irinotecan given as a powder-filled capsule (PFC) daily for 5 days every 3 weeks. Patients and methods: Patients with advanced solid tumors received escalating doses of oral irinotecan daily for 5 days every 3 weeks. Plasma samples were collected following the first and fifth doses of irinotecan during Cycle 1 to determine the PK of irinotecan and its major circulating metabolites: SN-38, SN-38G, and APC. Results: 20 patients (median age 61.5 years, range 40–75; M/F 12/8; ECOG PS 0=5, 1=11, 2=4) received oral irinotecan at dose levels of 30 (n=3), 40 (n=3), 50 (n=6), and 60 (n=8) mg/m²/day. Of the eight patients enrolled at 60 mg/m², three patients experienced DLT (≥ grade 3) consisting of nausea (three patients), vomiting (three patients), diarrhea (two patients), and febrile neutropenia (two patients) for which all the three patients required hospitalization. Treatment of six patients at the 50-mg/m² dose level resulted in no DLT. Other toxicities observed include abdominal pain, alopecia, anorexia, and asthenia. After oral administration, irinotecan was rapidly absorbed into systemic circulation and converted to the active metabolite SN-38. Increasing dose levels resulted in a dose-dependent increase in mean exposure parameters (Cmax and AUC) of irinotecan and metabolites. Systemic exposure parameters (Cmax and AUC_0-24) of irinotecan and SN-38 were comparable between days 1 and 5. The extent of conversion from irinotecan to SN-38 was approximately threefold higher after the oral administration compared to that previously observed after i.v. administration. The exposure parameters of irinotecan or SN-38 are of limited value in predicting severity of Cycle 1 toxicities in the twofold dose range evaluated. Conclusion: Daily oral administration of irinotecan as the PFC formulation for 5 days every 3 weeks can safely deliver protracted exposure to SN-38, with the MTD of 50 mg/m²/d.Supported in part by Pharmacia and National Cancer Institute Grants U01-CA69912, M01-RR00585, and CA15083-26     

Urokinase receptor antagonists: discovery and application to in vivo models of tumor growth

Urokinase receptor antagonists based on the growth factor domains of both human and murine urokinase which show sub-nanomolar affinities for their homologous receptors have been expressed as recombinant proteins. Further modification of these molecules by preparing fusions with the constant region of human IgG has led to molecules with high affinities and long in vivo half-lives. Smaller peptidic inhibitors have been obtained by a combination of bacteriophage display and peptide analog synthesis. All of these molecules inhibit the binding of the growth factor domain of uPA to the uPA receptor and enhance binding of the uPA receptor to vitronectin. Protein uPA receptor antagonists were tested in an in vivo tumor model using the human breast carcinoma MDAmb231 in immunodeficient mice. Both human and murine receptor antagonists showed significant inhibition of primary tumor growth, demonstrating that in vivo, both tumor and stromal cell uPA receptor dependent plasminogen activation can modulate tumor growth.     

Effect of Chronic Administration of Mestranol, Tamoxifen, and Toremifene on Hepatic Ploidy in Rats

The nonsteroidal antiestrogen tamoxifen increases the incidenceof rat liver cancer through a variety of mechanisms. To comparethe effects of tamoxifen (TAM) and a structurally similar analogtoremifene (TOR) on rat liver, we determined the ploidy distributionfor hepatocytes isolated from rats treated for 18 months withthese antiestrogens or the estrogenic compound mestranol (MS).Female Sprague-Dawley rats were subjected to a 70% partial hepatectomyand administered the solvent, trioctanoin, or diethyhiitrosamine(10 mg DEN/kg). After a 2-week recovery from the surgery, therats were administered a basal diet or one containing TAM (250or 500 ppm), TOR (250, 500, or 750 ppm), or MS (0.2 ppm) for18 months. Pathologic changes in the liver were examined inthe 15–22 rats per treatment group at the 18-month timepoint. An increased incidence of hepatocellular carcinomas (HCC)was detected in the 500 ppm TAM group, but not with the othertreatments that did not include DEN. Both TOR and TAM promotedformation of DEN-initiated HCCs. At sacrifice, four to fiverats per group were perfused and the hepatocytes isolated andcultured. Karyotypic analysis was performed on colcemid-blockedcells after 2 days in culture. The hepatic ploidy distributionwas characterized in Giemsa-stained metaphase spreads. Thesestudies indicated that chronic treatment with TAM alone resultedin a shift from tetraploid to diploid, as was also observedfor rats treated once with DEN. TOR and MS alone did not causethis change in hepatic ploidy at the doses examined. A shifttoward an increased content of diploid hepatocytes occurredin all rats treated once with DEN followed by TAM, TOR, or MS.These results indicate that tamoxifen administration resultsin a shift toward growth of diploid hepatocytes, thus contributingto its carcinogenic action in the rat liver.