C6-ceramide's effect on KRAS-defined colorectal cancer cells treated with oxaliplatin, 5-fluoruracil with and without cetuximab.

Abstract

619 Background: Cetuximab (Cet) is beneficial for patients with metastatic KRAS Wild type (WT) colorectal cancer (mCRC) only. C6-Ceramide (C6-Cer) can act synergistically with chemotherapy to induce cancer cell death. The aim of this study was to compare growth inhibition percentage (GIP) of cytostatics 5-fluoruracil (5-FU), oxaliplatin (Ox) and Cet with or without C6-Cer in KRAS WT and KRAS mutant (KRAS Mut) CRC cell lines (SW48 and SW480, respectively). Methods: Both cell lines were incubated with IC50 concentrations of test drugs. Drug concentrations included 0.8µM for 5-FU, 0.04µM for Ox, 25 µg/mL for Cet, and C6-Cer concentrations ranged from 5 to 10 µM. Cell survival was assessed 72h after using 0.4% Trypan Blue. Results: With above mentioned concentrations, C6-Cer’s GIP was 78.3% for SW-480 (vs. 33.33% for SW-48). It was also noted that the addition of C6-Cer to a combination of steady concentrations of Ox, Cet and 5-FU increased GIP with an especially significant effect on SW-480. Addition of 5 and 7.5µM resulted in doubling of GIP (75% and 86.25%, respectively, vs 32.5% of 5-FU + Ox + Cet). The greatest effect was seen when 10µM of C6-Cer was added to the IC50 concentrations of chemotherapeutic agents (using the 25µg/mL concentration of Cet), where GIP increased from 32.5% to 92.5% in SW-480. Same concentration of drugs increased GIP for SW-48 to a similar 93.5%. Conclusions: C6-Cer appears to have direct inhibitory properties, especially on KRAS Mut cells. Additionally when added to Ox, 5-FU and Cet, C6-Cer reversed the apparent insensitivity of KRAS Mut to Cet. Also, the study showed C6-Cer can provide additional synergism to their cytostatic properties in KRAS WT CRC cell lines. The true mechanism of these observations is still undergoing analysis, however the effect of isolated C6-Cer on KRAS Mut raises possibility of a different pathway that could bypass EFGR pathway. We believe the results of this study provide a starting point for clinical studies with C6-Ceramide in patients with relapsing or metastatic KRAS Mut CRC in combination with standard chemotherapy plus molecular target agents hoping they will translate into clinical benefit for this difficult to treat patient population.