Inflammatory cytokines, such as interleukin-6 (IL-6) and IL-11, activate the signal transducer and activator of transcription 3 (STAT3), which drives the gene transcription of cellular processes attributed as hallmarks of cancer. High levels of these cytokines, in combination with driver mutations, facilitate tumour growth and progression in preclinical models of colon cancer. Previous studies in our laboratory identified bazedoxifene (BZA), currently approved for the treatment of osteoporosis, as a small molecule inhibitor of GP130 (the receptor common to the IL-6 family of cytokines), selectively suppressing IL-6 and IL-11 signalling to reduce colon and gastric cancer growth in vivo (Thilakasiri et al. EMBO Mol Med 2019).
The specific aims of the current study are to determine (i) the effects of BZA in combination with chemotherapy on apoptotic pathways in colon cancer cells and early passage patient derived colon cancer cells; (ii) the effects of BZA in combination with chemotherapy on apoptotic body formation in colon cancer cells and (iii) identify new compounds that inhibit GP130 activity. The combined effect of BZA, fluorouracil and oxaliplatin on inducing apoptosis in LIM2405 colon cancer cells was analysed using flow cytometry. STAT3 expression and response to IL-11/STAT3 signalling was characterised by Western blotting. An in silico screen of GP130 using a small molecule library was conducted and compounds for effects on STAT3 transcriptional activity using cell-based assays.
Our results demonstrated that combination treatment with BZA, fluorouracil and oxaliplatin significantly increased apoptosis in LIM2405 cells. We have also identified novel analogues of our lead small molecule compound which decrease STAT3 transcriptional activity. Our data showed that BZA inhibited GP130-dependent STAT3 activity in the human colon cancer cell line LIM2405. BZA treatment sensitized cells to chemotherapy leading to increased apoptosis. The identification of novel compounds that target GP130 suggests a role for STAT3 inhibition in colon cancer as a treatment strategy.