Treatment of ras-induced cancers by the F-actin-bundling drug MKT-077

A rhodacyanine dye called MKT-077 has shown a highly selective toxicity tow ard several distinct human malignant cell lines, including bladder carcinom a 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 mo nkey 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 ms-trans formed 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 spec ific ligand. We have found that v-Ha-ras is responsible for the selective toxicity of MK T-077 in both in vitro and in vivo. Furthermore, we have identified and aff inity 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 nor mal cells. Microsequencing analysis has revealed that the p45 is a mixture of beta- and gamma-actin, whereas the p75 is HSC70, a constitutive member o f the Hsp70 heat shack adenosine triphosphatase family, which inactivates t he tumor suppressor p53. MKT-077 binds actin directly, bundles actin filame nts by cross-linking, and blocks membrane ruffling. Like a few F-actin-bundling proteins such as HS1, alpha-actinin, and vincul in 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 me mbrane ruffling. These findings suggest that other selective F-actin-bundli ng/capping compounds are also potentially useful for the chemotherapy of ra s-associated cancers.