bims-pimaco 2023-06-18 papers

Issue of 2023‒06‒18
six papers selected by
Lucas B. Zeiger
Beatson Institute for Cancer Research

Sci Signal. 2023 Jun 13. 16(789): eadd3184

Modulation of the substrate specificity of the kinase PDK1 by distinct conformations of the full-length protein.

The activation of at least 23 different mammalian kinases requires the phosphorylation of their hydrophobic motifs by the kinase PDK1. A linker connects the phosphoinositide-binding PH domain to the catalytic domain, which contains a docking site for substrates called the PIF pocket. Here, we used a chemical biology approach to show that PDK1 existed in equilibrium between at least three distinct conformations with differing substrate specificities. The inositol polyphosphate derivative HYG8 bound to the PH domain and disrupted PDK1 dimerization by stabilizing a monomeric conformation in which the PH domain associated with the catalytic domain and the PIF pocket was accessible. In the absence of lipids, HYG8 potently inhibited the phosphorylation of Akt (also termed PKB) but did not affect the intrinsic activity of PDK1 or the phosphorylation of SGK, which requires docking to the PIF pocket. In contrast, the small-molecule valsartan bound to the PIF pocket and stabilized a second distinct monomeric conformation. Our study reveals dynamic conformations of full-length PDK1 in which the location of the linker and the PH domain relative to the catalytic domain determines the selective phosphorylation of PDK1 substrates. The study further suggests new approaches for the design of drugs to selectively modulate signaling downstream of PDK1.

DOI: https://doi.org/10.1126/scisignal.add3184

Mol Cancer Ther. 2023 Jun 13. pii: MCT-23-0110. [Epub ahead of print]

Vincristine Enhances the Efficacy of MEK Inhibitors in Preclinical Models of KRAS-mutant Colorectal Cancer.

Susmita Ghosh, Fan Fan, Reid T Powell, Jason Roszik, Yongsung Park, Clifford Stephan, Manu Sebastian, Lin Tan, Alexey V Sorokin, Philip L Lorenzi, Scott Kopetz, Lee M Ellis, Rajat Bhattacharya.

Mutations in KRAS are found in more than 50% of tumors from patients with metastatic colorectal cancer (mCRC). However, direct targeting of most KRAS mutations is difficult; even the recently developed KRASG12C inhibitors failed to show significant benefit in patients with mCRC. Single agents targeting MEK, a downstream mediator of RAS, have also been ineffective in CRC. To identify drugs that can enhance the efficacy of MEK inhibitors we performed unbiased high-throughput screening using CRC spheroids. We used trametinib as the anchor drug and examined combinations of trametinib with the National Cancer Institute Approved Oncology Library version 5. The initial screen, and following focused validation screens, identified vincristine as being strongly synergistic with trametinib. In vitro, the combination strongly inhibited cell growth, reduced clonogenic survival, and enhanced apoptosis compared to monotherapies in multiple KRAS-mutant CRC cell lines. Furthermore, this combination significantly inhibited tumor growth, reduced cell proliferation, and increased apoptosis in multiple KRAS-mutant patient-derived xenograft mouse models. In vivo studies using drug doses that reflect clinically achievable doses demonstrated that the combination was well tolerated by mice. We further determined that the mechanism underlying the synergistic effect of the combination was due to enhanced intracellular accumulation of vincristine associated with MEK inhibition. The combination also significantly decreased p-mTOR levels in vitro, indicating that it inhibits both RAS-RAF-MEK and PI3K-AKT-mTOR survival pathways. Our data thus provide strong evidence that the combination of trametinib and vincristine represents a novel therapeutic option to be studied in clinical trials for patients with KRAS-mutant mCRC.

DOI: https://doi.org/10.1158/1535-7163.MCT-23-0110

Cancer Biol Ther. 2023 Dec 31. 24(1): 2223388

Preclinical evaluation of the CDK4/6 inhibitor palbociclib in combination with a PI3K or MEK inhibitor in colorectal cancer.

Cha Len Lee, Mattia Cremona, Angela Farrelly, Julie A Workman, Sean Kennedy, Razia Aslam, Aoife Carr, Stephen Madden, Brian O'Neill, Bryan T Hennessy, Sinead Toomey.

BACKGROUND: Studies have demonstrated the efficacy of Palbociclib (CDK 4/6 inhibitor), Gedatolisib (PI3K/mTOR dual inhibitor) and PD0325901 (MEK1/2 inhibitor) in colorectal cancer (CRC), however single agent therapeutics are often limited by the development of resistance.METHODS: We compared the anti-proliferative effects of the combination of Gedatolisib and Palbociclib and Gedatolisib and PD0325901 in five CRC cell lines with varying mutational background and tested their combinations on total and phosphoprotein levels of signaling pathway proteins.
RESULTS: The combination of Palbociclib and Gedatolisib was superior to the combination of Palbociclib and PD0325901. The combination of Palbociclib and Gedatolisib had synergistic anti-proliferative effects in all cell lines tested [CI range: 0.11-0.69] and resulted in the suppression of S6rp (S240/244), without AKT reactivation. The combination of Palbociclib and Gedatolisib increased BAX and Bcl-2 levels in PIK3CA mutated cell lines. The combination of Palbociclib and Gedatolisib caused MAPK/ERK reactivation, as seen by an increase in expression of total EGFR, regardless of the mutational status of the cells.
CONCLUSION: This study shows that the combination of Palbociclib and Gedatolisib has synergistic anti-proliferative effects in both wild-type and mutated CRC cell lines. Separately, the phosphorylation of S6rp may be a promising biomarker of responsiveness to this combination.

Keywords: Colorectal cancer; Gedatolisib; S6rp (S240/244); drug combinations; palbociclib

DOI: https://doi.org/10.1080/15384047.2023.2223388

EMBO J. 2023 Jun 12. e113908

PERK signaling promotes mitochondrial elongation by remodeling membrane phosphatidic acid.

Valerie Perea, Christian Cole, Justine Lebeau, Vivian Dolina, Kelsey R Baron, Aparajita Madhavan, Jeffery W Kelly, Danielle A Grotjahn, R Luke Wiseman.

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are linked in the onset and pathogenesis of numerous diseases. This has led to considerable interest in defining the mechanisms responsible for regulating mitochondria during ER stress. The PERK signaling arm of the unfolded protein response (UPR) has emerged as a prominent ER stress-responsive signaling pathway that regulates diverse aspects of mitochondrial biology. Here, we show that PERK activity promotes adaptive remodeling of mitochondrial membrane phosphatidic acid (PA) to induce protective mitochondrial elongation during acute ER stress. We find that PERK activity is required for ER stress-dependent increases in both cellular PA and YME1L-dependent degradation of the intramitochondrial PA transporter PRELID1. These two processes lead to the accumulation of PA on the outer mitochondrial membrane where it can induce mitochondrial elongation by inhibiting mitochondrial fission. Our results establish a new role for PERK in the adaptive remodeling of mitochondrial phospholipids and demonstrate that PERK-dependent PA regulation adapts organellar shape in response to ER stress.

Keywords: endoplasmic reticulum (ER) stress; mitochondrial morphology; phosphatidic acid; unfolded protein response (UPR)

DOI: https://doi.org/10.15252/embj.2023113908

ACS Med Chem Lett. 2023 Jun 08. 14(6): 689-691

Discovery of Selective and Potent KRASG12D Inhibitors as Potential Therapy in Cancer.

Robert B Kargbo.

Recent studies reveal that nearly one in seven human cancers exhibit KRAS alterations, contributing to an estimated 19.3 million new cancer cases worldwide in 2020. To date, no marketed mutant-selective and potent KRASG12D inhibitors are available. The current Patent Highlight presents compounds that directly bind to KRASG12D, selectively inhibiting its activity. These compounds possess a favorable therapeutic index, stability, bioavailability, and toxicity profile, suggesting potential utility in cancer therapeutics.

DOI: https://doi.org/10.1021/acsmedchemlett.3c00167

Cell Stem Cell. 2023 Jun 12. pii: S1934-5909(23)00182-0. [Epub ahead of print]

Organoid cultures for cancer modeling.

Helen H N Yan, April S Chan, Frank Pui-Ling Lai, Suet Yi Leung.

Organoids derived from adult stem cells (ASCs) and pluripotent stem cells (PSCs) are important preclinical models for studying cancer and developing therapies. Here, we review primary tissue-derived and PSC-derived cancer organoid models and detail how they have the potential to inform personalized medical approaches in different organ contexts and contribute to the understanding of early carcinogenic steps, cancer genomes, and biology. We also compare the differences between ASC- and PSC-based cancer organoid systems, discuss their limitations, and highlight recent improvements to organoid culture approaches that have helped to make them an even better representation of human tumors.

Keywords: cancer; organoids

DOI: https://doi.org/10.1016/j.stem.2023.05.012