Src-Family Protein Kinase Inhibitors Suppress MYB Activity in a p300-Dependent Manner

Emerging role of MYB transcription factors in cancer drug resistance

Decades ago, the viral myeloblastosis oncogene v-myb was identified as a gene responsible for the development of avian leukemia. However, the relevance of MYB proteins for human cancer diseases, in particular for solid tumors, remained basically unrecognized for a very long time. The human family of MYB transcription factors comprises MYB (c-MYB), MYBL2 (b-MYB), and MYBL1 (a-MYB), which are overexpressed in several cancers and are associated with cancer progression and resistance to anticancer drugs. In addition to overexpression, the presence of activated MYB-fusion proteins as tumor drivers was described in certain cancers. The identification of anticancer drug resistance mediated by MYB proteins and their underlying mechanisms are of great importance in understanding failures of current therapies and establishing new and more efficient therapy regimens. In addition, new drug candidates targeting MYB transcription factor activity and signaling have emerged as a promising class of potential anticancer therapeutics that could tackle MYB-dependent drug-resistant cancers in a more selective way. This review describes the correlation of MYB transcription factors with the formation and persistence of cancer resistance to various approved and investigational anticancer drugs.

MYB as a Critical Transcription Factor and Potential Therapeutic Target in AML

Myb was identified over four decades ago as the transforming component of acute leukemia viruses in chickens. Since then it has become increasingly apparent that dysregulated MYB activity characterizes many blood cancers, including acute myeloid leukemia, and that it represents the most "addictive" oncoprotein in many, if not all, such diseases. As a consequence of this tumor-specific dependency for MYB, it has become a major focus of efforts to develop specific antileukemia drugs. Much attention is being given to ways to interrupt the interaction between MYB and cooperating factors, in particular EP300/KAT3B and CBP/KAT3A. Aside from candidates identified through screening of small molecules, the most exciting prospect for novel drugs seems to be the design of peptide mimetics that interfere directly at the interface between MYB and its cofactors. Such peptides combine a high degree of target specificity with good efficacy including minimal effects on normal hematopoietic cells.

Synthetic oleanane triterpenoids suppress MYB oncogene activity and sensitize T-cell acute lymphoblastic leukemia cells to chemotherapy

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy with poor prognosis. The MYB oncogene encodes a master transcription factor that is activated in the majority of human T-ALLs. In the present study, we have performed a large-scale screening with small-molecule drugs to find clinically useful inhibitors of MYB gene expression in T-ALL. We identified several pharmacological agents that potentially could be used to treat MYB-driven malignancies. In particular, treatment with the synthetic oleanane triterpenoids (OTs) bardoxolone methyl and omaveloxolone decreased MYB gene activity and expression of MYB downstream target genes in T-ALL cells with constitutive MYB gene activation. Notably, treatment with bardoxolone methyl and omaveloxolone led to a dose-dependent reduction in cell viability and induction of apoptosis at low nanomolar concentrations. In contrast, normal bone marrow-derived cells were unaffected at these concentrations. Bardoxolone methyl and omaveloxolone treatment downregulated the expression of DNA repair genes and sensitized T-ALL cells to doxorubicin, a drug that is part of the standard therapy of T-ALL. OT treatment may thus potentiate DNA-damaging chemotherapy through attenuation of DNA repair. Taken together, our results indicate that synthetic OTs may be useful in the treatment of T-ALL and potentially also in other MYB-driven malignancies.

LIS1 interacts with CLIP170 to promote tumor growth and metastasis via the Cdc42 signaling pathway in salivary gland adenoid cystic carcinoma

Salivary gland adenoid cystic carcinoma (SACC) is one of the most common malignant tumors, with high aggressive potential in the oral and maxillofacial regions. Lissencephaly 1 (LIS1) is a microtubule-organizing center-associated protein that regulates the polymerization and stability of microtubules by mediating the motor function of dynein. Recent studies have suggested that LIS1 plays a potential role in the malignant development of tumors, such as in mitosis and migration. However, the role of LIS1 in SACC development and its related molecular mechanisms remain unclear. Thus, the effects of LIS1 on the proliferation, apoptosis, invasion and metastasis of SACC were studied, in vivo and in vitro. The results of immunohistochemical staining showed that LIS1 was highly expressed in SACC tissues, and its expression level was associated with malignant progression. In vitro, the results of CCK-8, TUNEL, wound healing and Transwell assays demonstrated that LIS1 promotes proliferation, inhibits apoptosis, and enhances the migration and invasion of SACC-LM cells. In vivo, knockdown of LIS1 effectively suppressed the growth of subcutaneous tumors in a mouse xenograft and distant metastasis of tumor cells in the metastasis model. The co-immunoprecipitation, immunofluorescence and western blot results also revealed that LIS1 binds to cytoplasmic linker protein 170 (CLIP170) to form a protein complex (LIS1/CLIP170), which activates the cell division control protein 42 homolog (Cdc42) signaling pathway to modulate the proliferation and anti-apoptosis of tumor cells, and enhanced invasion and metastasis by regulating the formation of invadopodia and the expression of MMPs in SACC-LM cells. Therefore, the present study demonstrated that LIS1 is a cancer promoter in SACC, and the molecular mechanism of the LIS1/CLIP170/Cdc42 signaling pathway is involved in the malignant progression, which offers a promising strategy for targeted therapy of SACC.