title: The distribution and retention of paclitaxel and doxorubicin in multicellular             layer cultures.
abstract: Limited distribution of anticancer drugs has been recognized as a significant hurdle to efficacy. We investigated a detailed penetration/distribution profile of paclitaxel-rhodamine (PTX-rd) and doxorubicin (DOX) in multicellular layer (MCL) cultures of human cancer cells as an in vitro model for avascular regions of solid tumors. MCLs were exposed to drugs and fluorescent images of frozen sections were acquired for determination of drug penetration into MCL under various exposure conditions. PTX-rd and DOX showed drastically different profiles of penetration. DOX showed full penetration after 1 h and accumulation over 3 h, whereas PTX-rd showed slow and limited penetration, with accumulation only within the top 20% of layers by 2 h and insignificant penetration even at 72 h. Drug retention in MCL was more dependent on drug concentration, rather than exposure time, i.e., drug distribution increased by 6.3- and 2.5-fold for PTX-rd and DOX, respectively, when exposed to higher concentrations under comparable AUC exposure (1 µM x 24 h vs. 50 µM x 0.5 h). Anti-proliferative activity of PTX and DOX in MCL, as determined by cell cycle analysis, was minimal and may be attributed, at least in part, to their limited distribution in multicellular cultures. Overall, we demonstrated that penetration and retention of PTX and DOX in MCL was not only concentration- and time-dependent, but also schedule-dependent. It is suggested that slow releasing formulations or a slow infusion regimen may not necessarily be desirable, especially for PTX, due to insufficient penetration and accumulation which may result from a low local concentration at the target site.
authors.affiliation: Department of Medical Life Science, College of Medicine, The                     Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Joo-Ho
authors.initials: JH
authors.lastname: Lee
authors.forename: Kun
authors.initials: K
authors.lastname: Na
authors.forename: Soo-Chang
authors.initials: SC
authors.lastname: Song
authors.forename: Jaehwi
authors.initials: J
authors.lastname: Lee
authors.forename: Hyo-Jeong
authors.initials: HJ
authors.lastname: Kuh
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000378:metabolism* / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport; D018929:Cell Culture Techniques; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D003692:Delayed-Action Preparations; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008856:Microscopy, Fluorescence; D017239:Paclitaxel / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000903:Antibiotics, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D003692:Delayed-Action Preparations; D004317:Doxorubicin; D017239:Paclitaxel