A
rhodacyanine dye called
MKT-077 has shown a highly selective toxicity toward several distinct human malignant cell lines, including bladder
carcinoma EJ, and has been subjected to clinical trials for
cancer therapy. In the
pancreatic carcinoma cell line CRL-1420, but not in normal African green monkey kidney cell line
CV-1, it is selectively accumulated in mitochondria. However, both the specific oncogenes responsible for its selective toxicity toward
cancer cells, and its target
proteins in these
cancer cells, still remain to be determined. This study was conducted using normal and ras-transformed NIH 3T3 fibroblasts to determine whether oncogenic ras mutants such as v-Ha-ras are responsible for the selective toxicity of
MKT-077 and also to identify its targets, using its derivative called "compound 1" as a specific
ligand. We have found that v-Ha-ras is responsible for the selective toxicity of
MKT-077 in both in vitro and in vivo. Furthermore, we have identified and affinity purified at least two distinct
proteins of 45 kD (p45) and 75 kD (p75), which bind
MKT-077 in v-Ha-ras-transformed cells but not in parental normal cells. Microsequencing analysis has revealed that the p45 is a mixture of beta- and
gamma-actin, whereas the p75 is HSC70, a constitutive member of the Hsp70 heat shock
adenosine triphosphatase family, which inactivates the
tumor suppressor p53.
MKT-077 binds actin directly, bundles actin filaments by cross-linking, and blocks membrane ruffling. Like a few
F-actin-bundling
proteins such as HS1,
alpha-actinin, and
vinculin as well as
F-actin cappers such as
tensin and
chaetoglobosin K (CK), the
F-actin-bundling
drug MKT-077 suppresses ras transformation by blocking membrane ruffling. These findings suggest that other selective
F-actin-bundling/capping compounds are also potentially useful for the
chemotherapy of ras-associated
cancers.