title: Styrene maleic acid copolymer-pirarubicin induces tumor-selective oxidative stress and decreases tumor hypoxia as possible treatment of colorectal cancer liver metastases.
abstract: BACKGROUND
  Pirarubicin, a derivative of doxorubicin, induces tumor destruction via the production of reactive oxygen species (ROS) but is associated with cardiotoxicity. As a macromolecule (conjugated to styrene-maleic acid [SMA]), SMA-pirarubicin is selective to tumors resulting in improved survival with decreased systemic toxicity. Tumor destruction is, however incomplete, and resistant cells at the periphery of the tumor contribute to recurrence. Tumor hypoxia is a major factor in tumor resistance. Understanding the effect of oxidative stress induced by SMA-pirarubicin on the tumor microenvironment may be key to overcoming resistance. This study investigated the pattern of ROS production and tumor hypoxia after treatment with SMA-pirarubicin in a murine model of colorectal liver metastases.
  
  
  METHODS
  Liver metastases were induced in male, CBA mice using a murine-derived colon cancer cell line. SMA-pirarubicin (maximum tolerated dose, 100 mg/kg) or pirarubicin, (maximum tolerated dose, 10 mg/kg) were administered intravenously 14 days after tumor induction. Systemic oxidative stress in serum, liver, and cardiac tissue was quantified using the thiobarbituric acid reactive substances assay. Flow cytometry and fluorescence microscopy were used to assess ROS production for 48 hours after treatment. Tumor hypoxia was quantified using immunohistochemistry for pimonidazole adducts.
  
  
  RESULTS
  SMA-pirarubicin (100 mg/kg) induced ROS exclusively in tumors with minimal levels in serum and cardiac tissue. ROS levels were induced in a time-dependent and dose-dependent manner optimal between 4 and 24 hours after drug administration. Although tumor hypoxia was decreased overall, residual tumor cells adjacent to patent vessels were hypoxic.
  
  
  CONCLUSIONS
  This study provides insight into the tumor microenvironment after chemotherapy. SMA-pirarubicin inhibits the growth of colorectal liver metastases by inducing ROS, which seems to be largely tumor selective. The temporal pattern of ROS production can be used to improve future dosing regimens. Furthermore, the observation that residual tumor cells are hypoxic clarifies the need for a multimodal approach with agents that can alter the hypoxic state to effect complete tumor destruction.
authors.affiliation: Department of Surgery, University of Melbourne, Austin Health, Victoria, Australia. Electronic address: jurstinedaruwalla@gmail.com.
authors.forename: Jurstine
authors.initials: J
authors.lastname: Daruwalla
authors.affiliation: Department of Pharmacology and Toxicology, University of Otago, Dunedin, New Zealand; Department of Oncology, Suez Canal University, Ismaïlia, Egypt.
authors.forename: Khaled
authors.initials: K
authors.lastname: Greish
authors.affiliation: Department of Surgery, University of Melbourne, Austin Health, Victoria, Australia.
authors.forename: Cathy
authors.initials: C
authors.lastname: Malcontenti-Wilson
authors.affiliation: Department of Surgery, University of Melbourne, Austin Health, Victoria, Australia.
authors.forename: Vijayaragavan
authors.initials: V
authors.lastname: Muralidharan
authors.affiliation: Institute of Drug Delivery Science, Sojo University, Kumamoto, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Maeda
authors.affiliation: Department of Surgery, University of Melbourne, Austin Health, Victoria, Australia.
authors.forename: Chris
authors.initials: C
authors.lastname: Christophi
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage*; D015687:Cell Hypoxia / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D004317:Doxorubicin / Q000008:administration & dosage / Q000031:analogs & derivatives; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000556:secondary; D008297:Male; D008298:Maleates / Q000008:administration & dosage; D051379:Mice; D008808:Mice, Inbred CBA; D018384:Oxidative Stress / Q000187:drug effects*; D011137:Polystyrenes / Q000008:administration & dosage; D017382:Reactive Oxygen Species / Q000378:metabolism; D059016:Tumor Microenvironment / Q000187:drug effects
chemical_list: D008298:Maleates; D011137:Polystyrenes; D017382:Reactive Oxygen Species; D004317:Doxorubicin; C024075:styrofoam; C030272:maleic acid; C027260:pirarubicin