Repressing DNA repair to enhance chemotherapy: targeting MyD88 in colon cancer

Colorectal cancer occurrence and treatment based on changes in intestinal flora

Colorectal cancer (CRC) is the most common cancer in the world, and its incidence has been increasing in recent years. The occurrence of CRC is believed to be related to a variety of factors. Epidemiological data indicate that CRC is mainly affected by environmental factors, eating habits, physical activity and genetic factors. As a newly recognized functional component, the intestinal microbiota plays important roles in preventing CRC formation and maintaining intestinal immunity. In this review, we summarize the mechanisms by which the gut microbiota causes CRC through alterations to immune function, focusing on the mechanisms by which intestinal microbial dysfunction promotes CRC. Furthermore, we describe the changes in the intestinal flora observed in CRC and their potential for CRC treatment with the goal of facilitating future research on the roles of the intestinal flora.

The Role of TLRs in Anti-cancer Immunity and Tumor Rejection

In recent years, a lot of scientific interest has focused on cancer immunotherapy. Although chronic inflammation has been described as one of the hallmarks of cancer, acute inflammation can actually trigger the immune system to fight diseases, including cancer. Toll-like receptor (TLR) ligands have long been used as adjuvants for traditional vaccines and it seems they may also play a role enhancing efficiency of tumor immunotherapy. The aim of this perspective is to discuss the effects of TLR stimulation in cancer, expression of various TLRs in different types of tumors, and finally the role of TLRs in anti-cancer immunity and tumor rejection.

Implication of myeloid differentiation factor 88 inhibitor TJ-M2010-5 for therapeutic intervention of hepatocellular carcinoma

AIM

Myeloid differentiation factor 88 (MyD88) plays a key role in tumor proliferation and metastasis. Targeting MyD88 is a potent strategy in tumor therapy. TJ-M2010-5 is a small molecule derivative of aminothiazole and could inhibit dimer formation of MyD88. To explore the potential of TJ-M2010-5 in tumor therapy, we determined its antitumor effect and correlate mechanisms of TJ-M2010-5 in hepatocellular carcinoma (HCC).

METHODS

The antitumor effect of intratumoral injection of TJ-M2010-5 to H22 tumor-bearing BALB/c mice was observed. Tumor growth was monitored. The expression of MyD88 and Ki-67 were detected by immunofluorescence. In vitro, the impacts of TJ-M2010-5 on proliferation, cell cycle, necrosis, and apoptosis of H22 cells were evaluated. The direct and indirect effects of TJ-M2010-5 on macrophages were evaluated using flow cytometry.

RESULTS

TJ-M2010-5 induced both G₀ /G₁ and G₁ /S phase arrests in HCC cells. Mechanically, downstream activation of MyD88 was suppressed by TJ-M2010-5 through the extracellular regulated protein kinase-1/2/p90 ribosomal S6 kinase/glycogen synthase kinase-3β signaling pathway. In turn, cyclin-dependent kinase (CDK)6/cyclin D1 and CDK2/cyclin E complexes were downregulated. More importantly, TJ-M2010-5 significantly inhibited tumor growth in mice. Additionally, the portion of antitumor M1 macrophages (F4/80⁺ CD11c⁺ ) in the tumor microenvironment were increased after TJ-M2010-5 treatment. Together, these data indicate that TJ-M2010-5 is a promising therapeutic drug for HCC.

CONCLUSIONS

These results indicate that MyD88 is a feasible target for antitumor treatment and TJ-M2010-5 is a qualified candidate for HCC therapy.

Dual functional roles of the MyD88 signaling in colorectal cancer development

The myeloid differentiation factor 88 (MyD88), an adaptor protein in regulation of the innate immunity, functions to regulate immune responses against viral and bacterial infections in the human body. Toll-like receptors (TLRs) and interleukin 1 receptors (IL-1R) can recognize microbes or endogenous ligands and then recruit MyD88 to activate the MyD88-dependent pathway, while MyD88 mutation associated with lymphoma development and altered MyD88 signaling also involved in cancer-associated cell intrinsic and extrinsic inflammation progression and carcinogenesis. Detection of MyD88 expression was to predict prognosis of various human cancers, e.g., lymphoid, liver, and colorectal cancers. In human cancers, MyD88 protein acts as a bridge between the inflammatory signaling from the TLR/IL-1R and Ras oncogenic signaling pathway. However, the MyD88 signaling played dual functional roles in colorectal cancer, i.e., the tumor-promoting role that enhances cancer inflammation and intestinal flora imbalance to induce tumor invasion and tumor cell self-renewal, and the anti-tumor role that helps to maintain the host-microbiota homeostasis to induce tumor cell cycle arrest and immune responses against cancer cells. This review precisely discusses the up to date literature for these contrasting effects of MyD88 signaling on colorectal cancer development and progression.

A preclinical study combining the DNA repair inhibitor Dbait with radiotherapy for the treatment of melanoma

Melanomas are highly radioresistant tumors, mainly due to efficient DNA double-strand break (DSB) repair. Dbait (which stands for DNA strand break bait) molecules mimic DSBs and trap DNA repair proteins, thereby inhibiting repair of DNA damage induced by radiation therapy (RT). First, the cytotoxic efficacy of Dbait in combination with RT was evaluated in vitro in SK28 and 501mel human melanoma cell lines. Though the extent of RT-induced damage was not increased by Dbait, it persisted for longer revealing a repair defect. Dbait enhanced RT efficacy independently of RT doses. We further assayed the capacity of DT01 (clinical form of Dbait) to enhance efficacy of “palliative” RT (10 × 3 Gy) or “radical” RT (20 × 3 Gy), in an SK28 xenografted model. Inhibition of repair of RT-induced DSB by DT01 was revealed by the significant increase of micronuclei in tumors treated with combined treatment. Mice treated with DT01 and RT combination had significantly better tumor growth control and longer survival compared to RT alone with the “palliative” protocol [tumor growth delay (TGD) by 5.7-fold; median survival: 119 vs 67 days] or the “radical” protocol (TGD by 3.2-fold; median survival: 221 vs 109 days). Only animals that received the combined treatment showed complete responses. No additional toxicity was observed in any DT01-treated groups. This preclinical study provides encouraging results for a combination of a new DNA repair inhibitor, DT01, with RT, in the absence of toxicity. A first-in-human phase I study is currently under way in the palliative management of melanoma in-transit metastases (DRIIM trial).