No abstract

The etiology of chemically induced cancer is thought to involve the covalent binding of carcinogens to DNA (adducts) leading to mutations in oncogenes or tumor suppressor genes, and ultimately to tumors. Thus, the DNA-carcinogen adduct has been used as a measurable biochemical endpoint in laboratory studies designed to assess carcinogen exposure, carcinogen metabolism, mutagenesis, and tumorigenesis. Unfortunately, the significance of adducts in the etiology of human cancer is still unclear. This is partially due to the difficulty detecting adducts at carcinogen exposures relevant to humans, which are often orders of magnitude lower than animal model exposures. The relationship between adducts and higher biological effects is also not known at low doses. We have been assessing the DNA damage caused by exposure to heterocyclic amine carcinogens in the diet.Using the technique of 32P-postlabeling in combination with accelerator mass spectrometry, we have determined that DNA adduction in rodents decreases linearly with decreasing dose from the high doses used in typical cancer bioassays to the low doses relevant to human exposures. For a given tissue, adduct levels are correlated with dose, but the level of DNA modification by carcinogens is tissue-specific and does not completely correlate with tumor site. This lack of correlation may be due to differences in adduct formation and repair rates among tissues. Comparison of carcinogen metabolism routes between rodents and humans also indicates that species differences could influence the amount and type of damage resulting from exposure to these carcinogens. The use of model systems to study dosimetry, species differences in adduction, and role of adducts in mutation will ultimately lead to a better understanding of the significance of adducts in human disease. This should eventually allow the use of adducts as biomarkers for estimating carcinogen exposure and individual SuScePtibilitY. We have used a number of models, including whole animals, tissue fractions, and bacterial assays, to study the mechanisms leading to DNA adduct formation, species differences in these mechanisms, and the dosimetry of DNA adduction. In particular, we have examined a group of dietary heterocyclic amine carcinogens that may be causative factors in the incidence of human colon cancer [a]. We have principally used the techniques of accelerator mass spectrometry (AMS) and "P-postlabeling. AMS is a low-energy nuclear physics technique for measuring isotopes, making it ideal for isotope tracer studies [3]; it isolates and counts specific nuclei particle by particle as opposed to measuring atomic decay. Depending on the isotope, AMS gives a lo3-to lO6-fold improvement in isotope detection efficiency relative to decay counting, allowing us to quantitatively measure DNA adduct levels on the order of one adduct per 1011-1012 nucleotides (1 adduct/100-1000 cells) [3,4]. This sensitivity has made possible studies on DNA adduction at doses of chemical carcinogens close to actual human exposur...

Calicheamicin antibody–drug conjugates (ADCs) are effective therapeutics for leukemias with two recently approved in the United States: Mylotarg (gemtuzumab ozogamicin) targeting CD33 for acute myeloid leukemia and Besponsa (inotuzumab ozogamicin) targeting CD22 for acute lymphocytic leukemia. Both of these calicheamicin ADCs are heterogeneous, aggregation-prone, and have a shortened half-life due to the instability of the acid-sensitive hydrazone linker in circulation. We hypothesized that we could improve upon the heterogeneity, aggregation, and circulation stability of calicheamicin ADCs by directly attaching the thiol of a reduced calicheamicin to an engineered cysteine on the antibody via a disulfide bond to generate a linkerless and traceless conjugate. We report herein that the resulting homogeneous conjugates possess minimal aggregation and display high in vivo stability with 50% of the drug remaining conjugated to the antibody after 21 days. Furthermore, these calicheamicin ADCs are highly efficacious in mouse models of both solid tumor (HER2+ breast cancer) and hematologic malignancies (CD22+ non-Hodgkin lymphoma). Safety studies in rats with this novel calicheamicin ADC revealed an increased tolerability compared with that reported for Mylotarg. Overall, we demonstrate that applying novel linker chemistry with site-specific conjugation affords an improved, next-generation calicheamicin ADC.

No abstract

The bioavailability and the bioreactivity of the carcinogenic heterocyclic amine [2-'4CJ2-amino-1-methyl-6phenyl-inidazo [4, have been investigted d a dose a in that likluy from thehuman diet by accelerator mass spectrometry (AMS). [2-_4CJPhIP mus administered to mice at a dose equivalent to the consumption of two 100 g beef patties (41 ng/kg). The biological halflife of PhIP was 1 hr, with 90% ofthe dose being excreted via the urine. Peak tissue PhEP concentrations were reached within 3 hr, with the highest levels in the tissues ofthe gastrointestil tract, followed by the liver, kidney, pancreas, and thymus. Since the detection limit by AMS is dependent on the natural abundance of 14C, we have achieved further increases in sensitivity by producing mice that have 20% ofthe naturl abundance of 14C. Use of these 14C-depleted aniS all Ms rementS to be made near the natural lvel ofexore for many environmental carcinogens. PhIP-DNA adduct levels havealso been measured by 32P-postlabeling at doses of 1.0 , and 20 mg/kg.The highest adduct levels were found in the pancreas, thynms, heart, and iver and increased linearly with dose. The principal adducts are derived from guanine.