The role of protein kinase C in the synergistic interaction of safingol and irinotecan in colon cancer cells

Abstract

Abstract. Colon cancer represents one of the most common solid tumors in adults. Although 5-fluorouracil (5-FU) and irinotecan have been frequently administered in colon cancer patients, low response rates to these single drug therapies were reported. It is therefore imperative to search for new targeted combination therapies that are effective. In this study, we investigated the anti-cancer effect of safingol as a single agent or in combination with irinotecan using HT-29 and LS-174T colon cancer cells as our in vitro models. As a single agent, safingol was more potent than irinotecan and 5-FU, with IC 50 values of 2.5±1.1 μM and 3.4±1.0 μM achieved in HT-29 and LS-174T cells, respectively. However, protein kinase C (PKC) was not inhibited with concentrations of safingol which could induce substantial cell kill. The combination of safingol/irinotecan at 1:1 molar ratio was found to be additive in HT-29 cells (CI=0.94) and synergistic in LS-174T cells (CI=0.68), and resulted in concentration-and time-dependent down-regulation of p-PKC and p-MARCKS. The drug effect of the safingol/irinotecan combination was further modulated in the presence of a PKC stimulator (phorbol 12-myristate 13-acetate) or a PKC inhibitor (staurosporine). Furthermore, the 1:1 safingol/irinotecan combination inhibited the adhesion of colon cancer cells to the extracellular matrix 4-h post-treatment. Taken together, modulation of the PKC pathway could be a possible molecular basis for the observed synergism of the safingol/irinotecan combination, and these results demonstrate the therapeutic potential of this drug combination in colon cancer treatment.

Targeting Sphingolipids for Cancer Therapy

“…The inhibitory effects on signaling, particularly on PKCϵ and PI3k, concomitant with the presence of ROS ( 67 ) synergize to induce apoptosis (decreased Bcl-2 levels and increased caspase cleavage) ( 59 , 60 , 62 – 65 , 68 ) and/or autophagy ( 63 , 67 ) ( Figure 3 ). According to preclinical studies, the combination of safingol with conventional chemotherapy agents, such as doxorubicin ( 67 ), irinotecan ( 66 ), and mitomycin C ( 65 ), potentiates their effects, inducing apoptotic cell death and ROS production in different cell lines. Additionally, the administration of safingol in combination with bortezomib inhibits lung tumor growth and metastasis (through the modulation of NF-κB signaling) in orthotopic syngeneic mouse models ( 69 ).…”

Restoration of MARCK enhances chemosensitivity in cancer

“…Interestingly, recent publications provided evidence of reduced MARCKS activity in CRC being associated with increased malignancy (Bickeböller et al 2015;Chen et al 2014Chen et al , 2015Chiu 2009;Clarke et al 1993). In this context, either genetic deletion via frameshift mutations or a cytosolic retention via a hyperphosphorylation of MARCKS was found to correlate with a negative patient outcome (Bickeböller et al 2015;Chen et al 2015).…”

Sphingosine Kinase 1 Signaling in Breast Cancer: A Potential Target to Tackle Breast Cancer Stem Cells

“…Safingol is a sphingosine-competitive SPHK1 inhibitor ( Olivera et al, 1998 ). Pre-clinical studies have demonstrated that the anti-tumor activities of safingol and its prominent efficacy in synergizing the killing effects of chemotherapeutic agents such as cisplatin, doxorubicin and irinotecan ( Kedderis et al, 1995 ; Schwartz et al, 1995 ; Schwartz et al, 1997 ; Coward et al, 2009 ; Ling et al, 2009 ; Ling et al, 2011 ). However, it is important to note that the anti-cancer effects induced by safingol can also be attributable to its role as PKC inhibitor ( Kedderis et al, 1995 ; Schwartz et al, 1995 ; Schwartz et al, 1997 ; Coward et al, 2009 ; Ling et al, 2009 ).…”

“…Pre-clinical studies have demonstrated that the anti-tumor activities of safingol and its prominent efficacy in synergizing the killing effects of chemotherapeutic agents such as cisplatin, doxorubicin and irinotecan ( Kedderis et al, 1995 ; Schwartz et al, 1995 ; Schwartz et al, 1997 ; Coward et al, 2009 ; Ling et al, 2009 ; Ling et al, 2011 ). However, it is important to note that the anti-cancer effects induced by safingol can also be attributable to its role as PKC inhibitor ( Kedderis et al, 1995 ; Schwartz et al, 1995 ; Schwartz et al, 1997 ; Coward et al, 2009 ; Ling et al, 2009 ). Nevertheless, safingol is the first putative SPHK inhibitor that entered clinical trial as oncology therapeutic agent and it has completed its phase I trial as a combination therapy with cisplatin in patients with advanced stages of solid malignancies ( ClinicalTrials.gov Identifier: NCT00084812) ( Dickson et al, 2011 ).…”