IC50 values of sotorasib, adagrasib and RMC-6236 in the GTP binding assay (µM)

MST raw data for the tested proteins from the Ras superfamily of small GTPases

Compounds SHY-855 and SHY-867 have no effects on cellular levels of cAMP

Compound SHY-867 inhibits K-Ras downstream signaling.

kon values (M-1s-1) for members of the Ras super family of small GTPases

Abstract New antimalarial drugs are needed to combat the current emergence and spread of Plasmodium falciparum parasite resistance to artemisinin-based combination therapies. Here, we characterize ZY19489, a triaminopyrimidine presently in a Phase Ib clinical trial. Asexual blood-stage parasites pressured with ZY19489 acquire low-grade resistance, mediated by a novel mutation in the P. falciparum chloroquine resistance transporter (PfCRT) that causes slow growth rates and a substantial fitness cost. ZY19489-resistant parasites lose their chloroquine resistance status and become hypersusceptible to piperaquine (PPQ), an artemisinin-based combination partner drug. Uptake studies in proteoliposomes loaded with drug-resistant PfCRT isoforms demonstrate that ZY19489 can block mutant PfCRT-mediated PPQ and chloroquine transport. In parasites, PfCRT mutant variants can mediate PPQ and chloroquine resistance via their efflux out of the digestive vacuole. Our findings evoke a scenario of an evolutionary trap whereby resistance to ZY19489 can block PPQ and chloroquine efflux and thereby restore their activity. Metabolomic studies show that ZY19489 leads to significantly reduced intracellular levels of short hemoglobin-derived peptides (a natural substrate of PfCRT) and accumulation of pyrimidine deoxynucleotides. Our results present a possible marker for tracking the evolution of clinical resistance to ZY19489 and a rationale for pairing this molecule with PPQ to generate a resistance-refractory combination.

Stability of recombinant K-Ras wild type and mutants

The genetic basis of Plasmodium falciparum resistance to quinine, a drug used to treat severe malaria, has long been unclear. To investigate this, here we used a human liver-chimaeric mouse model to conduct a P. falciparum genetic cross between quinine-partially resistant and quinine-sensitive parasites. Drug profiling and quantitative trait loci analyses of 120 unique recombinant progeny mapped resistance to segments on chromosomes 7 and 12, indicating a polygenic basis. The chloroquine resistance transporter PfCRT and a structurally similar putative drug/metabolite transporter, DMT1, were identified as primary chromosome 7 candidates based on gene-editing studies. In a proteoliposome assay, both mutant DMT1 and PfCRT transported more quinine than their wild-type isoforms. DMT1 localized to the P. falciparum digestive vacuole, lipid bodies, parasitophorous vacuolar membrane and structures associated with vesicular trafficking. An ATP-dependent zinc metalloprotease (FtsH1) on chromosome 12 also modulated quinine and chloroquine resistance. We suggest that genotypic surveillance of these markers should be performed in clinical settings of quinine use.

Combination studies on cell proliferation of SHY-855 and SHY-867 in combination with adagrasib

RAS genes encode small GTPases essential for mammalian cell proliferation, differentiation, and survival. RAS gene mutations are associated with 20% to 30% of all human cancers. Based on earlier reports of extremely high Ras binding affinities for GTP, Ras proteins were previously considered undruggable. Using three independent techniques, we report binding affinities of K-Ras and several K-Ras mutants for GTP in the 250 to 400 nmol/L range, orders of magnitude lower than previously reported (∼10 pmol/L). This discovery suggests that K-Ras and other small-GTPase proteins may indeed be druggable targets. We identified more than 400 small molecules that compete non-covalently with GTP binding to K-Ras. Focusing on two inhibitors, we demonstrate the inhibition of K-Ras in downstream signaling and cellular proliferation in human pancreatic and non-small cell lung cancer cells expressing wild-type or mutant K-Ras. These two compounds represent novel pan-Ras superfamily inhibitors as they also inhibited GTP binding to other members such as RAB5A and RAB35.

New antimalarial drugs are essential to combat the current emergence and spread of Plasmodium falciparum parasite resistance to first-line artemisinin-based combination therapies. Here, we identify a mechanism of parasite resistance to ZY19489, a triaminopyrimidine currently in a Phase IIb clinical trial. Low-grade resistance was mediated by a novel mutation in the P. falciparum chloroquine resistance transporter PfCRT, which caused a major reduction in asexual blood stage parasite growth rates and a substantial fitness cost. Parasites resistant to ZY19489 lost their chloroquine resistance status and became hypersusceptible to the artemisinin-based combination partner drug piperaquine. All three agents were shown to interfere with parasite-mediated catabolism of host hemoglobin. Uptake studies in PfCRT-containing proteoliposomes provide evidence that ZY19489 can block mutant PfCRT-mediated efflux of piperaquine and chloroquine, creating a scenario of an evolutionary trap whereby resistance to ZY19489 blocks PfCRT efflux-mediated resistance and restores susceptibility to piperaquine and chloroquine. Metabolomic studies revealed that ZY19489 significantly reduces intracellular levels of short hemoglobin-derived peptides (a natural substrate of PfCRT) and leads to higher accumulation of pyrimidine deoxynucleotides. Our data present a marker for tracking the evolution of clinical resistance to ZY19489 and a rationale for pairing this with piperaquine to generate a novel resistance-refractory combination.

Ion translocation is an essential process in all living cells. Most traditional approaches studying ion-translocating systems have employed cellular systems replete with native proteins that potentially interfere with the functional assessment of the protein of interest. The reconstitution of purified functional target proteins into proteoliposomes (PLs), artificial membrane systems of defined lipid composition, allows for their characterization without these intricacies. Targeting three distinct proteins, NhaA, pendrin, and the Plasmodium falciparum chloroquine resistance transporter (PfCRT), upon their reconstitution into PLs with a combined array of experimental approaches centered around solid-supported membrane electrophysiology, we show the advantage of the PL study system over cell-based approaches to assess protein-specific functional features. Using NhaA, the well-characterized archetype of Na+/H+ antiporters (exchangers), as a molecular ruler, our studies reveal that pendrin, a clinically relevant anion transporter in the thyroid, ear, kidney, and lungs, catalyzes the electrogenic exchange of its transported anions, opposing a long-standing dogma of the electroneutral activity of pendrin. We also provide direct evidence that PfCRT-a key contributor in multidrug resistance that thwarts efforts to combat malaria-mediates H+-coupled drug transport.

Anion Exchanger 1 (AE1) is an elevator-type transporter that plays a key role in acid-base homeostasis of erythrocytes. Here, we report three high-resolution cryo-electron microscopy (cryo-EM) structures of distinct states of AE1: two inward-facing (IF1 and IF2) and one outward-facing (OF). Uptake assay revealed the modulatory effect of phosphatidylinositol 4,5-bisphosphate (PIP2) lipids on AE1. Molecular dynamics simulations are conducted on these structures to determine the anion binding sites in AE1. We then use advanced enhanced sampling to study the OF⇌IF transition in AE1 in three systems: apo, HCO3--bound, and an AE1 system in which cryo-EM-determined PIP2 lipids had been removed. The transition pathways were then used to calculate the free energy of the OF⇌IF transition in AE1 under different conditions. The results show how substrate reduces the transition barrier against transport. Furthermore, they capture the inhibitory effect of PIP2 lipids and provide a molecular mechanism for this inhibitory effect.

The genetic basis of Plasmodium falciparum resistance to quinine (QN), a drug used to treat severe malaria, has long been enigmatic. To gain further insight, we used FRG-NOD human liver-chimeric mice to conduct a P. falciparum genetic cross between QN-resistant (Cam3.II) and QN-sensitive (NF54) parasites, which also differ in their susceptibility to chloroquine (CQ). By applying different selective conditions to progeny pools prior to cloning, we recovered 120 unique recombinant progeny. Drug profiling and quantitative trait loci analyses of the progeny revealed predominant peaks on chromosomes 7 and 12 associated with CQ and QN resistance, that is consistent with a multifactorial mechanism of resistance for these compounds. CQ and monodesethyl-CQ (md-CQ) resistance mapped to a chromosome 7 region harboring pfcrt as expected. However, for QN, resistance mapped to a dominant chromosome 7 peak centered 295 kb downstream of pfcrt, with pfcrt showing a smaller peak. We identified the drug/metabolite transporter 1 (DMT1) as the top chromosome 7 candidate due to its structural similarity to PfCRT and proximity to the peak. Deleting DMT1 in QN-resistant Cam3.II parasites significantly sensitized the parasite to QN but not to the other drugs tested, suggesting that DMT1 mediates QN response specifically. We localized DMT1 to structures associated with vesicular trafficking, as well as the parasitophorous vacuolar membrane, lipid bodies, and the digestive vacuole. We also observed that mutant DMT1 transports more QN than the wild-type isoform in vitro. Gene editing confirmed an additional role for mutant PfCRT in mediating QN resistance. In addition, we identified an ATP-dependent zinc metalloprotease (FtsH1) as one of the top candidates in the chromosome 12 locus and confirmed its role as a potential mediator of QN resistance and a modulator of md-CQ resistance using CRISPR/Cas9 SNP-edited lines. Interestingly, this chromosome 12 region mapped to resistance to both CQ and QN and was preferentially co-inherited with pfcrt. Our study demonstrates that DMT1 is a novel marker of QN resistance and that a new chromosome 12 locus associates with CQ and QN response, with ftsh1 as a potential candidate, suggesting these genes in addition to pfcrt should be genotyped in surveillance and clinical settings.