MITOMYCIN C RESISTANCEMODELS IN HUMAN COLON CANCER

We have developed a series of human colon carcinoma cell lines with
different biological properties which include responsive to mitomycin C
(MMC) and "naturally" refractory (NR) to MMC. We have also selected
sublines of MMC-resistant cells (SR) from the sensitive parental
subpopulations. Naturally refractory and MMC selected cell lines will be
compared to define the spectrum of mechanisms of MMC resistance that are
encountered and to determine whether particular mechanisms of resistance
are associated with either selected resistance or "natural resistance".
Cell lines will be identified as responsive or refractory by challenge of
cells with MMC as cell cultures and as xenografts in athymic mice.
Possible mechanisms of MMC resistance include MMC influx and efflux
alterations, lack of MMC activation by microsomal enzymes, enhanced repair
of MMC-DNA adducts, and MMC inactivation reactions. Differences in these
properties between sensitive and resistant cells will be explored. MMC
influx, efflux, and deactivation reactions will be studied using
radioactive MMC, MMC activation will be compared using spectrophotometric
methods, and DNA interstrand crosslink formation and repair will be
followed by alkaline elution methods. MMC analogs that have superior
activity to MMC in murine test systems will be evaluated for their efficacy
against MMC refractory colon cancer cell lines. Finally, we will
characterize the mechanisms of MMC resistance and the efficacy of MMC
analogs to circumvent this resistance among human colon cancer cells cloned
from early passage cultures of clinical colon cancer specimens. The
identification of specific mechanisms of resistance and development of
model systems reflecting these mechanisms will have impact on the clinical
utilization of MMC, the future clinical development of new MMC analogs, and
the development of in vitro and in vivo models for the evaluation of new
anticancer drugs and analogs of existing drugs.