Abstract P3-09-07: The role of MLK4 amplification in progression of triple negative breast cancer

Mixed Lineage Kinase 4 (MLK4) is a serine/threonine kinase that plays a role in a variety of cellular processes, including migration, apoptosis and proliferation. It belongs to the family of MAP3 kinases, which regulate the activity of specific MAPKs (mitogen-activated protein kinases). MLK4 is the least described member of the family and it was proved to act as a functional MAP3 kinase that activates the JNK, ERK and NFκB pathways. The rationale of this project is based on the recent data showing gene amplification and mRNA upregulation of MLK4 in invasive breast carcinoma at the frequency of 23%. Here, we performed a series of experiments aiming to characterize the role of MLK4 in breast cancer development and progression. We started from identification of breast cancer cell lines that express high endogenous level of MLK4. Since clinical data indicated that MLK4 expression was higher in triple-negative breast cancer (TNBC), comparing to other breast cancer subtypes, we decided to further study the role of MLK4 in TNBC. We have generated cell lines with doxycycline-inducible knock-down of MLK4, HCC1806 and HCC1599, and we found that MLK4 depletion resulted in reduced cell proliferation. We also observed that the knock-down of MLK4 in these conditions caused the reduction in size of the spheroids. Moreover, we noticed that when MLK4 is depleted in HCC1806 cells, the migration and invasion was significantly impaired. Lastly, our results of immunohistochemistry in samples from breast cancer patients showed that higher levels of MLK4 in TNBC samples significantly correlated with the occurrence of lymph node metastasis. Currently, we are investigating molecular pathways such as JNK, MEK/ERK and NF-κB, that might be affected by knock-down of MLK4. Collectively, our findings indicate that high levels of MLK4 promote aggressive phenotype of breast cancer cells, by increasing their migratory and invasive potential.

Citation Format: Prelowska MK, Mehlich D, Lazniewski M, Kaminska K, Gorczynski AS, Korwat A, Sokolowska O, Golab J, Biernat W, Plewczynski D, Brognard J, Nowis D, Marusiak AA. The role of MLK4 amplification in progression of triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-09-07.

Co-delivery of indoleamine 2,3-dioxygenase prevents loss of expression of an antigenic transgene in dystrophic mouse muscles

A significant problem affecting gene therapy approaches aiming at achieving long-term transgene expression is the immune response against the protein product of the therapeutic gene, which can reduce or eliminate the therapeutic effect. The problem is further exacerbated when therapy involves targeting an immunogenic tissue and/or one with a pre-existing inflammatory phenotype, such as dystrophic muscles. In this proof-of-principle study, we co-expressed a model antigen, bacterial β-galactosidase, with an immunosuppressive factor, indoleamine 2,3-dioxygenase 1 (IDO1), in muscles of the mdx mouse model of Duchenne muscular dystrophy. This treatment prevented loss of expression of the transgene concomitant with significantly elevated expression of T-regulatory (Treg) markers in the IDO1-expressing muscles. Moreover, co-expression of IDO1 resulted in reduced serum levels of anti-β-gal antibodies. These data indicate that co-expression of genes encoding immunomodulatory enzymes controlling kynurenine pathways provide a viable strategy for preventing loss of transgenes targeted into dystrophic muscles with pre-existing inflammation.

Heme oxygenase-1 protects tumor cells against photodynamic therapy-mediated cytotoxicity

Photodynamic therapy is a promising antitumor treatment modality approved for the management of both early and advanced tumors. The mechanisms of its antitumor action include generation of singlet oxygen and reactive oxygen species that directly damage tumor cells and tumor vasculature. A number of mechanisms seem to be involved in the protective responses to PDT that include activation of transcription factors, heat shock proteins, antioxidant enzymes and antiapoptotic pathways. Elucidation of these mechanisms might result in the design of more effective combination strategies to improve the antitumor efficacy of PDT. Using DNA microarray analysis to identify stress-related genes induced by Photofrin-mediated PDT in colon adenocarcinoma C-26 cells, we observed a marked induction of heme oxygenase-1 (HO-1). Induction of HO-1 with hemin or stable transfection of C-26 with a plasmid vector encoding HO-1 increased resistance of tumor cells to PDT-mediated cytotoxicity. On the other hand, zinc (II) protoporphyrin IX, an HO-1 inhibitor, markedly augmented PDT-mediated cytotoxicity towards C-26 and human ovarian carcinoma MDAH2774 cells. Neither bilirubin, biliverdin nor carbon monoxide, direct products of HO-1 catalysed heme degradation, was responsible for cytoprotection. Importantly, desferrioxamine, a potent iron chelator significantly potentiated cytotoxic effects of PDT. Altogether our results indicate that HO-1 is involved in an important protective mechanism against PDT-mediated phototoxicity and administration of HO-1 inhibitors might be an effective way to potentiate antitumor effectiveness of PDT.

Butyric acid enhances in vivo expression of hTNF-alpha in transduced melanoma cell line

Butyric acid (NaBut) and its derivatives are well-known agents eliciting tumor cell differentiation and apoptosis. In experimental models, NaBut is also used to enhance the efficacy of viral vectors. With the use of B78 murine melanoma cells transduced with the retroviral vector containing human tumor necrosis factor alpha (hTNF-alpha) gene, we investigated the ability of NaBut to increase the cytokine expression. We observed an increase in hTNF-alpha expression in vitro after incubation with NaBut. We also describe that the NaBut pro-drug tributyrin is able to increase hTNF-alpha expression in transduced B78 cells in a tumor vaccination model in mice. This observation strongly suggests a novel potential role for NaBut and its derivatives in tumor therapy. It could be used not only as a therapeutic directly acting on tumor cells but, in parallel, as a genetic vaccine "enhancer".

Antitumor activity of tributyrin in murine melanoma model

Butyric acid has been known to inhibit growth and to induce differentiation of a variety of tumor cells. Butyrate-treated tumor cells have also been observed to undergo apoptosis. Although butyrate compounds have demonstrated antitumor activity in murine tumor models and have already been admitted to clinical trials in tumor patients, the exact mechanism of their antitumor effects has not been elucidated. The results of our study showed antitumor activity of tributyrin, a butyric acid prodrug, in murine melanoma model and are strongly suggestive that antiangiogenic effects could participate in antitumor effects of butyrate compounds in vivo.