IRAK4 mediates colitis-induced tumorigenesis and IRAK4 mediates colitis-induced tumorigenesis and chemoresistance in colorectal cancer chemoresistance in colorectal cancer IRAK4 mediates colitis-induced tumorigenesis and chemoresistance in colorectal cancer IRAK4 mediates colitis-induced tumorigenes

cells during neoplastic progression. and phospho-IRAK4 or is associated with significantly worse survival in CRC patients. Our results support targeting IRAK4 to improve the effects of chemotherapy and outcomes in CRC. In epithelial cells, the IKK/NF- κ B axis can be activated by the Toll-like receptor/IL-1 receptor (TIR) superfamily members, which consist of the Toll-like receptor (TLR) and IL-1 receptor (IL-1R) families Ligation of these receptors results in recruitment and assembly of the adaptor protein MyD88 and IL-1 receptor–associated kinase (IRAK) isoforms 1, 2, and 4, leading to activation of TAK1 kinase and subsequently the IKK complex and NF- κ B (18). Therapeutic value of targeting the IRAK members, specifically the IRAK1 and IRAK4 isoforms, has been elucidated in several cancer types, including diffuse large B cell lymphoma (DLBCL) (19, 20), myelodysplastic syndrome (21), T cell acute lymphoblastic leukemia (22), melanoma (23), breast cancer (24), and head and neck cancer (25), and in pancreatic cancer by our group (26, 27). In pancreatic cancer, IL-1 β secreted by both neoplastic cells and fibroblasts activates the IRAK4/ NF- κ B axis to foster tumor fibrosis, which contributes to chemoresistance. Notably, we showed that the kinase activity of IRAK4, but not IRAK1, is essential in driving NF- κ B activity in pancreatic cancer cells (27). Contribution of the TIR receptors and IRAK4 to the progression and treatment resistance of CRC has not been investigated in detail. In an elegant study, KRAS -dependent colon cancer cells stimulate BMP-7 secretion to autologously activate BMP receptor, TAK1 kinase, and the NF- κ B transcription factors (28). safe and TAK1 inhibitors elusive. TAK1 deletion to massive bone marrow and liver failure in mice, again raising for toxicities TAK1 inhibition CRC in The actual role of MyD88, the critical adaptor that recruits and activates IRAK4, during different stages of colitis-induced CRC development is divergent, largely dependent on mouse models and experimental conditions (49). We showed that IRAK4i is highly effective in blocking DSS-induced neoplastic progression in APC Min/+ mice but has no effect on tumorigenic growth of established CRC tumors in vivo. To clearly determine the role of epithelial IRAK4 during neoplastic progression, we pretreated APC Min/+ mice with DSS to allow enough time for inflammation to occur before introduction of IRAK4i, which is known to have antiin-flammatory effect. The near-complete obliteration of tumor formation in IRAK4i-treated mice suggests epithelial IRAK4 to be required in neoplastic transformation, which was further supported by the requirement of IRAK4 in the MC38 model. These results are in agreement with work by others that showed an essential cell-intrinsic role of MyD88 in spontaneous intestinal and azoxymethane-induced (AOM-induced) colon cancer formation in APC Min/+ mice (50–52). As opposed to the MyD88 –/– APC Min/+ model, MyD88 –/– C57BL/6 mice develop more severe colitis upon acute AOM and/or DSS treatment, leading to more DNA damage and higher incidence of CRC development (50, 53, 54). On the contrary, in a chronic oxazolone-induced colitis model, MyD88 –/– mice develop robust inflammation but not colon cancer, largely because of loss of MyD88-dependent protumorigenic M2 macrophages in enhanced survival, which enables CRC cells to evade chemotherapy-induced apoptosis. neoplastic progression. Generation of conditional IRAK4 -null mice will be essential in dissecting the role of IRAK4 in various subsets of hematopoietic cells during CRC development and to definitively address these possibilities. Nonetheless, our results suggest that systemic inhibition of IRAK4 appears to be an effective strategy in curbing CRC development. While various combinations markers have developed to aid and selection for enhanc-ing the effect of chemotherapy, as can be achieved by cotargeting of IRAK4 and IKK–NF- κ B, represents an equally important endeavor to improve overall patient outcome. In summary, our study provides preclinical rationale for testing IRAK4 inhibitors in combination with chemotherapy in CRC. We demonstrate that chemotherapy can induce IKK–NF- κ B and sustain CRC cell survival by upregulating TLR9/IRAK4 signaling, providing justification for targeting IRAK4. Further work is needed to potential resistance mechanisms and to enable development of more effective and durable combinatorial regimens for this promising treatment paradigm. USA). SW620, SW620-L1, and SW620-L2 were gifts Mien-Chie and were used as previously described (60) and were not further authenticated. All cells were cultured in DMEM/10% FBS/1% peni-cillin-streptomycin at 5% CO 2 , 37°C incubators. Mycoplasma testing was performed every 6 months using MycoSEQ Detection kit (Applied Biosystems). All cell lines were used for less than 6 months after receipt or resuscitation from cryopreservation. Statistics . All results, when applicable, were expressed as the means ± SEM. Statistical analysis was performed using the Prism 6 software program. Unpaired Student’s 2-tailed t tests were used to compare 2 groups when appropriate. For multiple groups, 1-way ANOVA with Tukey’s post-test was used. P values less than 0.05 were considered as statistically significant. Cox proportional hazards models were used to evaluate the relationships between clinical characteristics and overall survival. The upper quantile of p-IRAK4 H score in TMA and IRAK4 mRNA in TCGA was used as cut point. Survival probabilities were calculated using Kaplan-Meier method. Differences between strata of p-IRAK4 H score and IRAK4 mRNA were determined by log-rank tests. All statistical tests were 2-sided using an α = 0.05 level of signif-icance. SAS version 9.4 was used to perform all survival analyses.