Projects Area

Our approach against cancer

Three RAS isoforms, HRAS, NRAS and KRAS, are frequently mutated in cancer and major drivers of tumorigenesis. However, it is not understood, why certain RAS isoforms are more often associated with certain cancer types than others. For example, KRAS is highly mutated in pancreatic cancer, while HRAS is most often mutated in head and neck cancers.

We investigate the emergence of isoform specific activities of RAS at the plasma membrane, where RAS is organised into di- or oligomeric proteo-lipid complexes, called nanoclusters. Only nanoclustered RAS engages effectors and transmits specific signalling. Hence, RAS nanoclustering and other RAS isoform selective processes represent novel drug targeting opportunities.

Our core methodologies are:

  • quantitative fluorescence imaging (FRET, FRAP etc.), superresolution and confocal imaging
  • molecular cell biology (mammalian cell culture, proliferation, 3D sphere cultures, RNAi, CRISPR)
  • biochemistry (SPR, fluorescence polarization, protein interactions, structure)

Projects:

Development of an inhibitory peptide targeting the galectin-1/Raf interface

H-Ras is highly mutated in head and neck cancers, as well as bladder cancer. Nanoclustering of H-Ras is increased by galectin-1 (Gal1), a small lectin known for its lattice forming activity in the extracellular space. We have previously shown that Gal1 binds to the Ras binding domain (RBD) of Raf and needs to be a dimer in order to increase H-Ras nanoclustering (Blazevits 2016 Sci Rep, PMID 27087647). This suggests that stacked dimers of Raf and Gal1 stabilize H-Ras nanocluster. Moreover, the Gal1 high situation seems to increase cancer cell stemness promoting activities of H-Ras (Posada IMD 2017 Oncotarget, PMID 28562352)

In this project we will develop a peptidic inhibitor of the Gal1/Raf interface and explore its application to selectively treat H-Ras mutant cancers with high Gal1 levels.

PI: Daniel Abankwa

Funder: University of Luxembourg, 2018-2023 Postdoc project

Prototypic covalent inhibitors against CaM a target for K-Ras driven cancer cell stemness

K-Ras is more frequently mutated than H-Ras. In line with this, others recently showed that K-Ras has a greater potential than H-Ras to drive cancer cell stemness. We showed that targeting calmodulin (CaM) with the covalent inhibitor ophiobolin A (OphA), blocks selectively K-Ras membrane organisation and inhibits stemness features of cancer cells.

In this project, we aim at developing less toxic and more selective covalent CaM inhibitors and characterize their activity in K-Ras driven cancer cells.

PI: Daniel Abankwa

Funder: University of Luxembourg, 2018-2021 PhD project

Figure: A, Covalent adduct formation of Ophiobolin A or Benzazulenes with Lys residues of calmodulin (CaM). B, Derivatization option of Benzazulene parent 1. C, CaM bound to inhibitory small molecules. D, Growth of MDA-MB-231 3D spheroids is abrogated by CaM inhibitors and knockdown.

Establishing the K-Ras specific targeting mechanism of conglobatin A

We recently showed that conglobatin A selectively inhibits K-Ras, but not H-Ras membrane signalling complexes, thus blocking growth of cancer stem cells (Najumudeen 2016 Oncogene, PMID 26973241). Here we set out to establish the molecular mechanism of how conglobatin A selectively inhibits K-Ras.

Conglobatin A is known as a protein-protein interface inhibitor of Hsp90 and its co-chaperone Cdc37. It displays a strikingly low toxicity, suggesting that Hsp90/Cdc37 inhibitors may have an exciting drug development potential.

We will here establish the K-Ras directed mechanism and identify novel functional analogues of conglobatin A.

PI: Daniel Abankwa

Funder: University of Luxembourg, 2018-2023

Figure: A, Conglobatin A (purple) docked at the interface of Hsp90 (green, N-terminus) and Cdc37 (orange). Inset showing details of binding site. B, Cellular FRET data show selective disruption of K-Ras, but not H-Ras membrane organisation by conglobatins. C, Split-luciferase lysate assay sensitively detects inhibition of Hsp90 interaction with Cdc37 by conglobatin A. D, This assay was used to validate in silico hits using a compound library at FIMM. Green dots, significantly active compounds.

Evaluation of the biological activity of novel PDE6D inhibitors

We have developed Deltaflexins, novel inhibitors against PDE6D (Figure 7), a surrogate target of K-Ras. However, PDE6D is a general trafficking chaperone for prenylated proteins.

In this project we explore the anti-cancer effect of Deltaflexins e.g. via other clients of PDE6D. For example, INPP5E trafficking to the primary cilium is enabled by PDE6D. Primary cilia are implicated in stemness signalling that may be relevant in cancer.

PI: Daniel Abankwa

Funder: Luxembourg National Research Fund (FNR), 2020-2024 PhD project

Drugs against PDE6D for KRAS driven cancer therapy

K-Ras is highly mutated in >20% of cancers and a driver of cancer cell stemness. So far, no drug against K-Ras has been approved. PDE6D (or PDEdelta) is a trafficking chaperone of prenylated proteins and has been nominated as a surrogate target for K-Ras. We have developed novel inhibitors against PDE6D, the Deltaflexins, which overcome some limitations of previous generation (Figure 8).

In this project, we aim at improving our inhibitors up to the licensing-ready lead compound stage.

PI: Daniel Abankwa

Funder: Luxembourg National Research Fund (FNR), 2019

Analysis of the signal transduction network upstream of L-plastin Ser5 phosphorylation in breast cancer cells and tissues (PLASTIN)

In cancer research, the identification of predictive biomarkers represents an essential goal as it paves the way for patient-tailored treatment. The protein L-plastin is a cancer biomarker candidate and, not only L-plastin expression, but also L-plastin Ser5 phosphorylation have been described to be important for cancer progression. In this project, we aim at unravelling both the signalling network leading to Ser5 phosphorylation of L-plastin and the functional outcome of this phosphorylation in breast cancer.

PI: Elisabeth Schaffner-Reckinger

Funder: Fondation Cancer, 2016-2020 Postdoc project

Figure: L-plastin is recruited to invadopodia, which are structures that enable cancer cells to invade into the surrounding matrix. Shown is a merged maximum projection confocal image of MDA-MB-231 breast cancer cells transduced with L-plastin-GFP expressing lentivirus. In detail, enlarged high resolution stack with orthogonal views showing the colocalization of L-plastin (green), cortactin (blue) and F-actin (red), which is illustrated by the white dots resulting from the overlay of green, blue and red. Figure provided by Raquel Machado, the Postdoc of the project.