Targeting the oncogenic TBX3:nucleolin complex to treat multiple sarcoma subtypes

Sarcomas are diverse cancers of mesenchymal origin, with compromised clinical management caused by insufficient diagnostic biomarkers and limited treatment options. The transcription factor TBX3 is upregulated in a diverse range of sarcoma subtypes, where it plays a direct oncogenic role, and it may thus represent a novel therapeutic target. To identify versatile ways to target TBX3, we performed affinity purification coupled by mass spectrometry to identify putative TBX3 protein cofactors that regulate its oncogenic activity in sarcomas. Here we identify and validate the multifunctional phosphoprotein nucleolin as a TBX3 cofactor. We show that nucleolin is co-expressed with TBX3 in several sarcoma subtypes and their expression levels positively correlate in sarcoma patients which are associated with poor prognosis. Furthermore, we demonstrate that nucleolin and TBX3 interact in chondrosarcoma, liposarcoma and rhabdomyosarcoma cells where they act together to enhance proliferation and migration and regulate a common set of tumor suppressor genes. Importantly, the nucleolin targeting aptamer, AS1411, exhibits selective anti-cancer activity in these cells and mislocalizes TBX3 and nucleolin to the cytoplasm which correlates with the re-expression of the TBX3/nucleolin target tumor suppressors CDKN1A (p21^CIP1) and CDKN2A (p14^ARF). Our findings provide the first evidence that TBX3 requires nucleolin to promote features of sarcomagenesis and that disruption of the oncogenic TBX3-nucleolin interaction by AS1411 may be a novel approach for treating sarcomas.

Selective Inhibition of the C-Domain of ACE (Angiotensin-Converting Enzyme) Combined With Inhibition of NEP (Neprilysin): A Potential New Therapy for Hypertension

[Figure: see text].

Investigating the antifibrotic potential of N-acetyl seryl-aspartyl-lysyl-proline sequence peptides

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a physiological antifibrotic peptide that is hydrolysed by angiotensin I-converting enzyme (ACE). The beneficial antifibrotic effects of ACE inhibitors have been attributed, in part, to its inhibition of Ac-SDKP cleavage. There is indirect evidence that the SDK fragment of Ac-SDKP is the main component required for its antiproliferative action. However, the exact component of the physiological peptide that is responsible for its antifibrotic effect has yet to be determined. Ac-SDKP-derived analogues that are resistant to ACE degradation may provide a new avenue for fibrosis therapy. We tested the antifibrotic potential of various Ac-SDKP peptide sequences and an analogue resistant to ACE degradation in lung fibroblasts. We investigated the contribution and molecular mechanism of action of the amino acid residues in the Ac-SDKP sequence to its antifibrotic effects, and the effects of Ac-SDKP peptides in the prevention of collagen deposition in cells. The Ac-DKP fragment moderately inhibited endothelin-1 (ET-1) mediated transforming growth factor-β (TGF- β) expression, and could be slowly cleaved by ACE, revealing a different sequence requirement for the antifibrotic action of Ac-SDKP. The Ac-SDψKP analogue (where the peptide bond between the aspartate and lysine is reduced) inhibited TGF-β/small mother against decapentaplegic (Smad)-3 signalling and collagen deposition. The Ac-SDKP peptide, in combination with ACEi, demonstrated a greater inhibition of hydroxyproline as compared to Ac-SDKP alone.

Abstract C130: The oncogenic transcription factors TBX2 and TBX3 as attractive targets for anticancer drug development

TBX2 and TBX3 are transcription factors that play critical roles in embryonic development but have no known function in adult tissue, and their overexpression has been associated with a growing list of cancers including melanoma, sarcomas, breast, pancreatic, liver and bladder cancers (1). Previous studies in our laboratory have shown that TBX2 and TBX3 play central but different roles in oncogenesis, where TBX2 functions as a potent growth promoting factor and TBX3 contributes to tumour formation, metastasis and invasion (2-4). Additionally, our data have demonstrated that TBX2 confers resistance to cisplatin by promoting DNA repair and may also promote oncogenesis through inappropriate survival of cells with damaged DNA (5).

Recent work from our group has provided strong in vitro and in vivo biological evidence that TBX2 and TBX3 are novel targets for development of anti-cancer drugs for cancers where they are overexpressed. Knocking down TBX2 by shRNA induces senescence in advanced melanoma cells, and it results in profound inhibition of proliferation of several metastatic breast cancer cell lines (2,6). Furthermore, depleting TBX2 in metastatic melanoma and cisplatin-resistant breast cancer cells leads to their sensitization to this widely used chemotherapeutic drug, suggesting that targeting TBX2 in combination with currently used therapies could improve their efficacy (5). On the other hand, when TBX3 is depleted by shRNA in some breast cancers and melanomas, cells display reduced anchorage independence, cell migration, colony forming ability and a less aggressive phenotype (2).

We are in the process of exploring ways of identifying potential inhibitors of TBX2/TBX3 oncogenic activity by combining a structure-based approach that focuses on molecular recognition and interaction of TBX2/TBX3 with their target genes, and a medium throughput approach involving screening of small molecule libraries.

References

[1] Wansleben S, Peres J, Hare S, Goding CR, Prince S (2014) BBA - Reviews on Cancer, 1846, 380-391.

[2] Peres J, Davis E, Mowla S, Bennet DC, Li JA, Wansleben S and Prince S (2010) Genes & Cancer, 1(3):272-282.

[3] Mowla S, Pinnock R, Leaner VD, Goding CR, Prince S (2010) The Biochemical journal, 433(1): 145-53.

[4] Peres J, Prince S (2013) Molecular cancer, 12:117.DOI: 10.1186/1476-4598-12-117.

[5] Wansleben S, Davis E, Peres J, Prince S (2013) Cell Death and Disease, 4, e846; doi:10.1038/cddis.2013.365.

[6] Redmond, K.L., Crawford, N.T., Farmer, H., D'Costa, Z.C., O'Brien, G.J., Buckley, N.E., Kennedy, R.D., Johnston, P.G., Harkin, D.P., and Mullan, P.B. (2010) Oncogene 29, 3252-3262.

Citation Format: Serah Kimani, Deeya Ballim, Trevor Sewell, Edward Sturrock, Sharon Prince. The oncogenic transcription factors TBX2 and TBX3 as attractive targets for anticancer drug development. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C130.

Characterisation of the flavin adenine dinucleotide binding region of Myxococcus xanthus protoporphyrinogen oxidase

Protoporphyrinogen oxidase (PPOX), the penultimate enzyme in the haem biosynthetic pathway catalysers the six electron oxidation of protoporphyrinogen-IX to protoporphyrin-IX, in the presence of flavin adenine dinucleotide (FAD) and oxygen. In humans, partial defects in PPOX result in variegate porphyria. In this study, the FAD binding region in Myxococcus xanthus PPOX was analysed by engineering and characterising a selection of mutant proteins. Amino acid residues which interact with FAD via their side chains were selected for study. Mutants were characterised and compared with wild type protein. Characterisation included FAD quantitation, analysis of FAD spectra and kinetic assay. Results revealed that Serine 20 mutants could still bind FAD, but polarity in this position is favourable, yet not essential for the integrity of FAD binding. Study of Glutamate 39 mutants suggest that a negative charge at position 39 is clearly favoured for interaction with the ribose ring of FAD, as all non-conservative replacements could not bind sufficient FAD. Asparagine 441 appears not to be directly involved in FAD binding but rather in stabilizing the FAD, and polarity in this position appears important. Tryptophan 408 may play a role in orientating or stabilizing the bound substrate during catalysis, and a non-polar (or slightly polar) residue is favoured at this position; however, aromaticity in this position appears not to be critical. Overall this study sheds further light on how M. xanthus PPOX interacts with FAD.