By serving as intermediaries between cellular metabolism and the bioenergetic demands of proliferation, endolysosomes allow cancer cells to thrive under normally detrimental conditions. Here, we show that an endolysosomal TRP channel, TRPML1, is necessary for the proliferation of cancer cells that bear activating mutations in HRAS. Expression of MCOLN1, which encodes TRPML1, is significantly elevated in HRAS‐positive tumors and inversely correlated with patient prognosis. Concordantly, MCOLN1 knockdown or TRPML1 inhibition selectively reduces the proliferation of cancer cells that express oncogenic, but not wild‐type, HRAS. Mechanistically, TRPML1 maintains oncogenic HRAS in signaling‐competent nanoclusters at the plasma membrane by mediating cholesterol de‐esterification and transport. TRPML1 inhibition disrupts the distribution and levels of cholesterol and thereby attenuates HRAS nanoclustering and plasma membrane abundance, ERK phosphorylation, and cell proliferation. These findings reveal a selective vulnerability of HRAS‐driven cancers to TRPML1 inhibition, which may be leveraged as an actionable therapeutic strategy.

f K-Ras must localize to the plasma membrane and be arrayed in nanoclusters for biological activity. We show here that K-Ras is a substrate for cyclic GMP-dependent protein kinases (PKGs). In intact cells, activated PKG2 selectively colocalizes with K-Ras on the plasma membrane and phosphorylates K-Ras at Ser181 in the C-terminal polybasic domain. K-Ras phosphorylation by PKG2 is triggered by activation of AMP-activated protein kinase (AMPK) and requires endothelial nitric oxide synthase and soluble guanylyl cyclase. Phosphorylated K-Ras reorganizes into distinct nanoclusters that retune the signal output. Phosphorylation acutely enhances K-Ras plasma membrane affinity, but phosphorylated K-Ras is progressively lost from the plasma membrane via endocytic recycling. Concordantly, chronic pharmacological activation of AMPK ¡ PKG2 signaling with mitochondrial inhibitors, nitric oxide, or sildenafil inhibits proliferation of K-Ras-positive non-small cell lung cancer cells. The study shows that K-Ras is a target of a metabolic stress-signaling pathway that can be leveraged to inhibit oncogenic K-Ras function. Ras proteins are small GTPases that regulate important cellular signaling cascades to control cell growth, proliferation, and differentiation (1). The three Ras isoforms, H-, N-, and K-Ras4B (here, K-Ras), are ubiquitously expressed in mammalian cells. Ras proteins must be localized to the inner leaflet of the plasma membrane (PM) by a C-terminal membrane anchor for biological activity. In the case of K-Ras, the anchor comprises a posttranslationally attached C-terminal cysteine farnesyl-methyl ester operating in concert with a polybasic motif of 6 lysine residues (2, 3). Electrostatic interactions between the K-Ras C-terminal polybasic domain and the negatively charged inner leaflet of the PM provide membrane affinity (2, 4-9). Maintenance of K-Ras on the PM also requires the chaperone protein PDE␦ (10). Cytosolic PDE␦ binds K-Ras released from the PM as a result of endocytosis and unloads K-Ras in the perinuclear region in response to Arl2/3 binding, whence K-Ras translocates to the recycling endosome (RE) for redelivery to the PM by vesicular transport (11). Ras proteins on the PM are spatially organized into nanodomains, called nanoclusters, that are required for high-fidelity signal transduction by the Ras/mitogen-activated protein kinase (MAPK) pathway (12-14). Ras GTP nanoclusters contain ϳ6 to 7 Ras proteins, are Ͻ20 nm in diameter, and are exclusive platforms for Raf recruitment and MEK/extracellular signal-regulated kinase (ERK) activation. Perturbation of the spatiotemporal dynamics of Ras nanoclustering disrupts cellular signaling (15, 16).We have used a high-content cell-based screen (HCS) to identify multiple chemical compounds that mislocalize K-Ras from the PM and abrogate K-Ras signal transmission (17,18). One group of compounds disrupts the cellular phosphatidylserine (PtdSer) distribution or PtdSer levels with a consequent reduction in the PtdSer content of the inner leaflet of the PM (18-21)....

During a search for inhibitors of oncogenic K-Ras, we detected two known and two new examples of the rare neoantimycin structure class from a liquid cultivation of Streptomyces orinoci, and reassigned/assigned structures to all based on detailed spectroscopic analysis and microscale C3 Marfey’s and C3 Mosher chemical degradation/derivatization/analysis. SAR investigations inclusive of the biosynthetically related antimycins and respirantin, and synthetic benzoxazolone, documented a unique N-formyl amino-salicylamide pharmacophore as a potent inhibitor of oncogenic K-Ras.

Frequently present in pancreatic, colorectal and non-small cell lung carcinomas, oncogenic mutant K-Ras must be localised to the plasma membrane (PM) to be functional. Inhibitors of K-Ras PM localisation are therefore putative cancer chemotherapeutics. By screening a microbial extract library in a high content cell-based assay we detected the rare oligomycin class of Streptomyces polyketides as inhibitors of K-Ras PM localisation. Cultivation and fractionation of three unique oligomycin producing Streptomyces strains yielded oligomycins A–E (1–5) and 21-hydroxy-oligomycin A (6), together with the new 21-hydroxy-oligomycin C (7) and 40-hydroxy-oligomycin B (8). Structures for 1–8 were assigned by detailed spectroscopic analysis. Cancer cell viability screening confirmed 1–8 were cytotoxic to human colorectal carcinoma cells (IC50 >3 μM), and were inhibitors of the ABC transporter efflux pump P-glycoprotein (P-gp), with 5 being comparable in potency to the positive control verapamil. Significantly, oligomycins 1–8 proved to be exceptionally potent inhibitors of K-Ras PM localisation (Emax 0.67–0.75 with an IC50 ~1.5–14 nM).

Oncogenic RAS proteins are commonly expressed in human cancer. To be functional, RAS proteins must undergo post-translational modification and localize to the plasma membrane (PM). Therefore, compounds that prevent RAS PM targeting have potential as putative RAS inhibitors. Here we examine the mechanism of action of oxanthroquinone G01 (G01), a recently described inhibitor of KRAS PM localization. We show that G01 mislocalizes HRAS and KRAS from the PM with similar potency and disrupts the spatial organization of RAS proteins remaining on the PM. G01 also inhibited recycling of epidermal growth factor receptor and transferrin receptor, but did not impair internalization of cholera toxin, indicating suppression of recycling endosome function. In searching for the mechanism of impaired endosomal recycling we observed that G01 also enhanced cellular sphingomyelin (SM) and ceramide levels and disrupted the localization of several lipid and cholesterol reporters, suggesting that the G01 molecular target may involve SM metabolism. Indeed, G01 exhibited potent synergy with other compounds that target SM metabolism in KRAS localization assays. Furthermore, G01 significantly abrogated RAS-RAF-MAPK signaling in Madin-Darby canine kidney (MDCK) cells expressing constitutively activated, oncogenic mutant RASG12V. G01 also inhibited the proliferation of RAS-less mouse embryo fibroblasts expressing oncogenic mutant KRASG12V or KRASG12D but not RAS-less mouse embryo fibroblasts expressing oncogenic mutant BRAFV600E. Consistent with these effects, G01 selectively inhibited the proliferation of KRAS-transformed pancreatic, colon, and endometrial cancer cells. Taken together, these results suggest that G01 should undergo further evaluation as a potential anti-RAS therapeutic.

The primary site for KRAS signaling is the inner leaflet of the plasma membrane (PM). We previously reported that oxanthroquinone G01 (G01) inhibited KRAS PM localization and blocked KRAS signaling. In this study, we identified acylpeptide hydrolase (APEH) as a molecular target of G01. APEH formed a stable complex with biotinylated G01, and the enzymatic activity of APEH was inhibited by G01. APEH knockdown caused profound mislocalization of KRAS and reduced clustering of KRAS that remained PM localized. APEH knockdown also disrupted the PM localization of phosphatidylserine (PtdSer), a lipid critical for KRAS PM binding and clustering. The mislocalization of KRAS was fully rescued by ectopic expression of APEH in knockdown cells. APEH knockdown disrupted the endocytic recycling of epidermal growth factor receptor and transferrin receptor, suggesting that abrogation of recycling endosome function was mechanistically linked to the loss of KRAS and PtdSer from the PM. APEH knockdown abrogated RAS-RAF-MAPK signaling in cells expressing the constitutively active (oncogenic) mutant of KRAS (KRASG12V), and selectively inhibited the proliferation of KRAStransformed pancreatic cancer cells. Taken together, these results identify APEH as a novel drug target for a potential anti-KRAS therapeutic.

The current immune checkpoint blockade therapy has been successful in treating some cancers but not others. New molecular targets and therapeutic approaches of cancer immunology need to be identified. Leukocyte associated immunoglobulin like receptor 1 (LAIR1) is an immune inhibitory receptor expressing on most immune cell types. However, it remains a question whether we can specifically and actively block LAIR1 signaling to activate immune responses for cancer treatment. Here we report the development of specific antagonistic anti-LAIR1 monoclonal antibodies and studied the effects of LAIR1 blockade on the anti-tumor immune functions. The anti-LAIR1 antagonistic antibody stimulated the activities of T cells, natural killer cells, macrophages, and dendritic cells in vitro. The single-cell RNA sequencing analysis of intratumoral immune cells in syngeneic human LAIR1 transgenic mice treated with control or anti-LAIR1 antagonist antibodies indicates that LAIR1 signaling blockade increased the numbers of CD4 memory T cells and inflammatory macrophages, but decreased those of pro-tumor macrophages, regulatory T cells, and plasmacytoid dendritic cells. Importantly, the LAIR1 blockade by the antagonistic antibody inhibited the activity of immunosuppressive myeloid cells and reactivated T cells from cancer patients in vitro and impeded tumor metastasis in a humanized mouse model. Blocking LAIR1 signaling in immune cells represents a promising strategy for development of anti-cancer immunotherapy.

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