Design of Small Molecules That Compete with Nucleotide Binding to an Engineered Oncogenic KRAS Allele

Proteolysis targeting chimeras in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) has very poor prognosis in advanced stages. Discovery and application of therapies targeting specific oncogenic driver mutations has greatly improved overall survival. However, targeted therapies are limited in their efficacy due to resistance mutations that may arise with long term use. Proteolysis targeting Chimeras (PROTACs) are a promising approach to combating resistance mutations. PROTACs commandeer innate ubiquitination machinery to degrade oncogenic proteins. Here we review the PROTACs that have been developed for targeting common EGFR, KRAS, and ALK mutations.

NMR in integrated biophysical drug discovery for RAS: past, present, and future

Mutations in RAS oncogenes occur in ~ 30% of human cancers, with KRAS being the most frequently altered isoform. RAS proteins comprise a conserved GTPase domain and a C-terminal lipid-modified tail that is unique to each isoform. The GTPase domain is a 'switch' that regulates multiple signaling cascades that drive cell growth and proliferation when activated by binding GTP, and the signal is terminated by GTP hydrolysis. Oncogenic RAS mutations disrupt the GTPase cycle, leading to accumulation of the activated GTP-bound state and promoting proliferation. RAS is a key target in oncology, however it lacks classic druggable pockets and has been extremely challenging to target. RAS signaling has thus been targeted indirectly, by harnessing key downstream effectors as well as upstream regulators, or disrupting the proper membrane localization required for signaling, by inhibiting either lipid modification or 'carrier' proteins. As a small (20 kDa) protein with multiple conformers in dynamic equilibrium, RAS is an excellent candidate for NMR-driven characterization and screening for direct inhibitors. Several molecules have been discovered that bind RAS and stabilize shallow pockets through conformational selection, and recent compounds have achieved substantial improvements in affinity. NMR-derived insight into targeting the RAS-membrane interface has revealed a new strategy to enhance the potency of small molecules, while another approach has been development of peptidyl inhibitors that bind through large interfaces rather than deep pockets. Remarkable progress has been made with mutation-specific covalent inhibitors that target the thiol of a G12C mutant, and these are now in clinical trials. Here we review the history of RAS inhibitor development and highlight the utility of NMR and integrated biophysical approaches in RAS drug discovery.

Overcoming Resistance to Drugs Targeting KRASG12C Mutation

Activating KRAS mutations are present in 25% of human cancer. Although oncogenic Ras was deemed “undruggable” in the past, recent efforts led to the development of pharmacological inhibitors targeting the KRAS^G12C mutant, which have shown promise in early clinical trials. The development of allele-specific K-Ras^G12C inhibitors marked a new chapter in targeting oncogenic KRAS mutant in cancer. However, drug resistance against these new drugs will likely limit their efficacy in the clinic. Genome-wide approaches have been used to interrogate the mechanisms of resistance to K-Ras^G12C inhibitors, which would facilitate the development of therapeutics overcoming drug resistance. This article reviews the latest progress in resistance to K-Ras^G12C-targeted therapies and aims to provide insight in future research targeting drug resistance in cancer.

•

Clinical grade K-Ras^G12C inhibitor marks a new chapter in targeted drug discovery

•

Resistance to K-Ras^G12C inhibitors is driven by intrinsic or acquired mechanisms

•

Co-targeting vertical Ras signaling overcomes resistance to K-Ras^G12C inhibition

•

Standard-of-care chemo- and immunotherapies synergize with K-Ras^G12C inhibition

Selective binding of a bioactive porphyrin-based photosensitizer to the G-quadruplex from the KRAS oncogene promoter

BACKGROUND

The G-quadruplex-forming sequence within the KRAS proto-oncogene P1 promoter is a promising target for anticancer therapy. Porphyrin derivatives are among the most rewarding G-quadruplex binders. They can also behave as photosensitizers.

METHODS

Three water-soluble, positively charged porphyrin-like compounds were synthesized and tested for their interaction with the KRAS G-quadruplex by circular dichroism, fluorescence, and molecular docking calculations. For a comparison of ligands binding affinity and selectivity, TMPyP4 was taken as a reference.

RESULTS

One out of the three tested compounds proved biological activity and selectivity for G-quadruplex over duplex DNA. It also showed to discriminate between different G-quadruplex topologies, with a preference for the parallel over antiparallel conformation. Molecular docking studies suggested a preferential binding to the 3'-end of the KRAS G-quadruplex driven through π-π stacking interactions. Biological assays also revealed a good photodynamic-induced cytotoxicity on HeLa cells.

CONCLUSIONS

The reported results show that these porphyrin-like compounds could actually give the basis for the development of G-quadruplex ligands with effective photodynamic-induced cytotoxicity on cancer cells.

GENERAL SIGNIFICANCE

The possibility of obtaining photosensitizers with improved physico-chemical features and able to selectively target G-quadruplexes is a very interesting perspective to develop new therapeutic agents.

K-RasG12D Has a Potential Allosteric Small Molecule Binding Site

KRAS is the most commonly mutated oncogene in human cancer, with particularly high mutation frequencies in pancreatic cancers, colorectal cancers, and lung cancers [Ostrem, J. M., and Shokat, K. M. (2016) Nat. Rev. Drug Discovery 15, 771-785]. The high prevalence of KRAS mutations and its essential role in many cancers make it a potentially attractive drug target; however, it has been difficult to create small molecule inhibitors of mutant K-Ras proteins. Here, we identified a putative small molecule binding site on K-Ras^G12D using computational analyses of the protein structure and then used a combination of computational and biochemical approaches to discover small molecules that may bind to this pocket, which we have termed the P110 site, due to its adjacency to proline 110. We confirmed that one compound, named K-Ras allosteric ligand KAL-21404358, bound to K-Ras^G12D, as measured by microscale thermophoresis, a thermal shift assay, and nuclear magnetic resonance spectroscopy. KAL-21404358 did not bind to four mutants in the P110 site, supporting our hypothesis that KAL-21404358 binds to the P110 site of K-Ras^G12D. This compound impaired the interaction of K-Ras^G12D with B-Raf and disrupted the RAF-MEK-ERK and PI3K-AKT signaling pathways. We synthesized additional compounds, based on the KAL-21404358 scaffold with more potent binding and greater aqueous solubility. In summary, these findings suggest that the P110 site is a potential site for binding of small molecule allosteric inhibitors of K-Ras^G12D.

Novel Targets in Pancreatic Cancer Therapy - Current Status and Ongoing Translational Efforts

Pancreatic ductal adenocarcinoma (PDAC, pancreatic cancer) carries one of the poorest overall prognoses of all human malignancies known to date. Despite the introduction of novel therapeutic regimens, the outcome has not markedly improved over the past decades, the incidence rates are almost identical to the mortality rates, and PDAC is projected to soon become the second most common cause of cancer-related mortality in Western countries. Despite this clear medical need to develop novel therapeutic strategies against this dire malady, this need has so far not been addressed with sufficient institutional attention and support in terms of research funding and strategical programs. Given the still growing life expectancy and projected demographic changes with a growing proportion of senior citizens in many European societies, this discrepancy is likely to become even more pressing in the future. This article provides a brief overview of ongoing preclinical efforts to identify novel targets and, based on this, to develop novel strategies to treat advanced pancreatic cancer and improve survival and the quality of life of patients suffering from this malignancy.