Phase I and pharmacokinetic study of tiazofurin (TCAR,NSC 286193) administered by continuous infusion

Summary Tiazofurin (2--D-ribofuranosylthiazole-4-carboxamide, TCAR) is a synthetic C-nucleoside that demonstrated significant in vivo activity against a variety of animal tumors as well as in vitro activity against human tumor-derived cell lines. Thirteen patients were treated with TCAR administered as a 5-day continuous infusion in this Phase I trial. Seventeen complete cycles were administered in three dose levels ranging from 550 to 1450 mg/M². Dose-limiting toxicities were myelosuppression and neurotoxicity including severe lethargy. Other toxicities including superficial skin peeling, myalgias, and tearing were seen at all doses. One patient had chest pain on day 4 resulting in stopping the drug, however, there was no evidence of cardiac or pericardial disease. Uric acid levels rose within one day in the absence of allopurinol treatment. There were no treatment related deaths. HPLC measurement of drug levels demonstrated steady-state plasma levels during the infusion, and a half-life following the infusion of 7.7 ± 0.6 hours. Minor abnormalities in renal function were associated with dramatic changes in pharmacokinetics and toxicity. No clinical responses were observed in this trial.Abbreviations TCAR Tiazofurin - HPLC High performance liquid chromatography - IMPD Inosine monophosphate dehydrogenase - WBC white blood cell - CPK creatine phosphokinase - C_ss steady-state concentration     

THE ARDEN GRATINGS IN OPTOMETRIC PRACTICE

The use of the Arden gratings (AO contrast sensitivity system) in optometric practice is evaluated. A total of 320 patients presenting for eye examination were screened with the gratings. Sixty-four eyes (10%) gave abnormal grating scores although results from conventional examination techniques revealed no abnormality. Of the 110 abnormal eyes detected by routine examination techniques, 8 presented with normal grating scores, 6 with "borderline suspect" scores and 96 with abnormal scores. Used in isolation, the failure rate of the Arden gratings to detect ocular abnormality in the patient population was 1.3% and the "false positive" referral rate was 10%.     

High-dose induction chemotherapy of metastatic breast cancer in protected environment: a prospective randomized study

To test the hypothesis of whether high doses of chemotherapy in combination achieve higher response rates and longer durations of response and survival, we treated 33 pre- and perimenopausal patients with good performance status in a prospective trial with escalating doses of fluorouracil, doxorubicin and cyclophosphamide (FAC). Patients were randomly assigned to be treated within a protected environment (laminar air flow room), with prophylactic antibiotics, or in a standard hospital room. Important patient characteristics were equally distributed in the two treatment arms. A major objective response was observed in 27 of the 32 evaluable patients (84%), and 11 (34%) achieved a complete remission (CR). There was no significant difference in overall and complete response rates between the two treatment arms, nor was there a substantial difference in times to progression or survival between the groups treated in or out of the protected environment. Comparison of the results of this study with previously reported programs of FAC chemotherapy in patients with metastatic breast cancer shows that this study achieved higher overall and complete response rates. However, neither the time to progression, nor the survival of responders or the entire patient group was different from our previous experience with standard FAC chemotherapy. When the study was initiated in 1976, the proposed dose escalation represented high-dose chemotherapy. In retrospect, even the "high" doses used in this study represent only a modest increase over standard doses of chemotherapy. Much steeper dose escalations will be needed to evaluate the efficacy of high-dose chemotherapy in breast cancer, as well as the protective value of the protected environment and prophylactic antibiotics in metastatic breast cancer.     

Induction of rat liver microsomal epoxide hydrolase by thiazole and pyrazine: hydrolysis of 2-cyanoethylene oxide

Liver microsomal epoxide hydrolase (mEH) is active in the detoxificationof epoxide-containing carcinogens. The effects of thiazole andpyrazine, constituents of tobacco and tobacco smoke as wellas of a variety of foods, on the expression and regulation ofmEH were examined in rats (200 mg/kg body wt/day, i.p., 1/emdash3 days). Immunoblot analyses using rabbit anti-rat mEH antibodyrevealed a significant increase in mEH levels in hepatic microsomesisolated from either thiazole- or pyrazine-treated animals.Another protein (43 kd) cross-reacting with polyclonal mEH antibodywas found to be increased concomitantly following pyrazine treatment.Northern and slot blot analyses showed substantial increasesin mEH mRNA following either thiazole or pyrazine treatment.The level of mEH mRNA increased 17-fold at 24 h following thiazoletreatment, relative to control. Approximately 20- and 16-foldincreases in mEH mRNA were also observed at 48 and 72 h respectivelyfollowing treatment with pyrazine. The level of polymerase chainreaction (PCR)-amplified mEH DNA derived from poly(A)+ RNA wasclearly elevated following either thiazole or pyrazine treatmentrelative to that from untreated animals. Both sense and antisensestrands of PCR-amplified mEH DNA were cloned into an M13mpl9phage vector in order to examine the nucleotide sequences ofPCR-amplified mEH DNA derived from the poly(A)+ RNA isolatedfrom thiazole- or pyrazine-treated animals. Sequence analysesrevealed that the sequence of PCR-amplified DNA from the inducedmRNA was identical to that published for mEH cDNA. Epoxide hydrolaseactivity toward the hydrolysis of 2-cyanoethylene oxide (CEO),the epoxide metabolite of the rat carcinogen acrylonitrile,was not significant in hepatic microsomes from untreated rats,but was substantially induced by treatment with thiazole orpyrazine. Microsomal hydrolysis activity was heat-sensitiveand potently inhibited by l, l, l-trichloropropene-2, 3-oxide,indicating that mEH was the catalyst. The V_max for the hydrolysisof CEO by hepatic microsomes from thiazole-treated rats (13.4nmol/min/mg protein) was 1.5-fold greater than that with microsomesfrom pyrazine-treated rats, whereas similar K_m values ( 1 mM)were observed for both microsomal preparations. These kineticdata correlate well with the increases in mEH mRNA observedafter administration of thiazole or pyrazine to rats. Theseresults provide evidence that administration of thiazole orpyrazine induces mEH with a large increase in mEH mRNA, andthat the induced mEH catalyzes the hydrolysis of CEO.     

Telomerase and telomere inhibitors in preclinical development

Telomerase is an enzyme required by actively dividing cells to maintain the ends of chromosomes (telomeres). It is present in germline tissue, stem cells and cancer cells, but is repressed in somatic cells. Efforts are underway to exploit this selective expression of telomerase in cancer therapeutics. This review describes the status of telomerase research, which although at present predominantly preclinical, has the potential to enter clinical research.