Development of novel therapies for colorectal carcinoma using dietary indoles
2014-12-08T11:42:45Z (GMT) by
Colorectal carcinoma is the third commonest cancer in the UK and is the second commonest cause of cancer related death. There is a need for efficacious chemotherapeutic and chemopreventative agents against colorectal carcinogenesis. Indole-3-carbinol and its acid condensation product, 3,3 diindolylmethane (DIM), exhibit anti-tumourigenic activity in preclinical models. This study investigated their therapeutic potential in colorectal carcinoma. A panel of four colorectal carcinoma cell lines (HT29, HCT116, SW480 and SW620) was used to compare effects of DIM and I3C on cell viability, induction of apoptosis and cell cycle arrest. Treatment with DIM or I3C resulted in dose-dependent reductions in cell viability. Cell lines were sensitive to 25–75 μM DIM (GI[subscript 50] = 45 μM), but not to 200 μM I3C. DIM (40 μM) induced apoptosis in all cell lines. This was associated with downregulation of survivin and appeared to be independent of p53. Furthermore it induced G[subscript 1] arrest in HCT116, SW480 and SW620 and G[subscript 2]/M arrest in HT29. DIM induced activatory phosphorylation of Chk2 in HT29 but not in HCT116. DIM downregulated cell cycle proteins: PLK1, cdc25C, cdc2 and cyclins B1, D1 and E. Since all colon cancer cell lines expressed significant levels of Src, their response to Src inhibition was investigated. Colon cancer cells were modestly sensitive to AZD0530 (AstraZeneca), but combination with indoles reduced viability to a greater extent than single agent treatment. Combining 40 μM DIM with 1 μM AZD0530 was particularly effective, reducing viability by half after 48 hours on average. Decreases were sustained and progressive over extended timepoints. Attempts were made to establish primary cultures from resected hepatic metastases however issues were identified with cell death, fibroblast overgrowth and slow cell turnover. Potential changes to address these were identified. These data suggest chemotherapeutic potential of DIM in colon cancer, particularly in combination with Src inhibition.