Chemical remodeling of a cellular chaperone to target the active state of mutant KRAS

Synthetic approaches and clinical application of KRAS inhibitors for cancer therapy

Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations are among the most common oncogenic alterations in various cancers, including pancreatic, colorectal, and non-small cell lung cancer (NSCLC). Targeting KRAS has long been considered a difficult challenge due to its high affinity for guanosine triphosphate (GTP) and the lack of a druggable binding site. However, recent advancements in small-molecule inhibitor design have led to the development of targeted therapies aimed at KRAS mutations, particularly the KRASG12C mutation. Inhibitors such as Sotorasib and Adagrasib have shown promise in preclinical and clinical studies by irreversibly binding to the mutant KRAS protein, locking it in an inactive state and disrupting downstream signaling pathways critical for tumor growth and survival. These inhibitors have demonstrated clinical efficacy in treating patients with KRASG12C-mutated cancers, leading to tumor regression, prolonged progression-free survival, and improved patient outcomes. This review discusses the synthetic strategies employed to develop these KRAS inhibitor and also examines the clinical application of these inhibitors, highlighting the challenges and successes encountered during clinical trials. Ultimately, KRAS inhibitors represent a breakthrough in cancer therapy, offering a promising new treatment option for patients with KRAS-driven tumors.

Small molecules for Kirsten rat sarcoma viral oncogene homolog mutant cancers: Past, present, and future

Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations have been identified in more than 20% of human cancers as one of the most common oncogenes, especially in non-small cell lung, colorectal, and pancreatic cancers. KRAS regulates the activation of multiple proteins involved in cell growth and proliferation, such as extracellular regulated protein kinases and mammalian target of rapamycin, as a hub between the epidermal growth factor receptor (EGFR) and downstream MAPK and AKT pathways. However, due to the lack of a binding pocket, KRAS has long been considered an undruggable target in recent decades until the discovery of Sotorasib (AMG510). With the approval of Glecirasib (JAB-21822), there are three approved small molecule inhibitors of KRAS, all of which are KRAS G12C inhibitors. At the same time, the limited clinical benefits and rapid emergence of drug resistance to the approved inhibitors have also promoted the emergence of more therapeutics, such as tri-complexes and proteolysis-targeting chimeras (PROTAC). In this paper, we summarize the development of KRAS inhibitors (KRASG12C, KRASG12D, and KRASmulti inhibitors, PROTAC, and tri-complex) and discuss the challenges and opportunities in the discovery of KRAS inhibitors in the hope of providing insights into the development of novel medications for KRAS.

Dealing with KRAS G12C inhibition in non-small cell lung cancer (NSCLC) - biology, clinical results and future directions

KRAS G12C mutation occurs in ∼ 14 % of non-small cell lung cancer (NSCLC) patients and has been historically deemed undruggable, with immune-checkpoint inhibitors (ICIs) and platinum-based chemotherapy (PBC) representing the standard-of-care in the advanced setting. First-in-class, covalent KRAS G12C OFF-inhibitors sotorasib and adagrasib have revolutionized the therapeutic landscape and recently entered clinical practice. However, limited efficacy alongside toxicity profiles strengthen the need to design novel molecules and to optimize therapeutic strategies to address and overcome intrinsic and acquired resistance mechanisms. Moreover, KRAS G12C frequently co-occurs with STK11/KEAP1 mutations, that represent a negative prognostic factor, being associated with increased metastatic potential and reduced overall survival and poorer outcomes with ICIs. Furthermore, the high incidence of brain metastases is common in KRAS G12C-mutant NSCLC, and the efficacy of standard therapies and KRAS G12C inhibitors in treating or preventing central nervous system involvement is still suboptimal. In this context, novel inhibitors, such as broad-spectrum inhibitors targeting the active GTP-bound ON-state, pan-RAS ON inhibitors and allele-selective tricomplex inhibitors, have showed promising early clinical activity although their clinical utility needs to be further elucidated. In addition, targeting upstream, downstream and parallel signaling pathways through combination strategies might enhance the activity of KRAS G12C inhibitors and eventually improve clinical outcomes in this subset of NSCLC patients. Several combinations are currently under clinical investigation and promising approaches include combinations of KRAS G12C inhibitors with ICIs, SOS1, SHP2 inhibitors and PBC. Notwithstanding the potential improved efficacy of combination strategies, tolerability remains a critical challenge that must be carefully assessed and managed.

Nondegradative Synthetic Molecular Glues Enter the Clinic

Molecular glues are small molecules that can induce or stabilize protein-protein interactions between proteins inside cells. Unlike classical small molecule drugs, molecular glues can target challenging disease-causing proteins lacking well-defined binding pockets. Nature has repeatedly used this mode of action, but identifying molecular glues for new target proteins has been a major challenge. Recently, manmade molecular glues, inspired by natural products, for KRas, entered clinical trials although KRas is a major cancer target long thought to be undruggable. Here, how these molecules are initially discovered and optimized to provide several advanced drug candidates for various KRas-dependent cancer types are outlined. The major insights obtained for this new class of drug modalities are further summarized. These results showcase how molecular glues that do not rely on protein degradation can provide clinical benefits for challenging drug targets.

Identification and characterization of ternary complexes consisting of FKBP12, MAPRE1 and macrocyclic molecular glues

Many disease-relevant and functionally well-validated targets are difficult to drug. Their poorly defined 3D structure without deep hydrophobic pockets makes the development of ligands with low molecular weight and high affinity almost impossible. For these targets, incorporation into a ternary complex may be a viable alternative to modulate and in most cases inhibit their function. Therefore, we are interested in methods to identify and characterize molecular glues. In a protein array screen of 50 different macrocyclic FKBP12 ligands against 2500 different randomly selected proteins, a molecular glue compound was found to recruit a dimeric protein called MAPRE1 to FKBP12 in a compound-dependent manner. The corresponding ternary complex was characterized by TR-FRET proximity assay and native MS spectroscopy. Insights into the 3D structure of the ternary complex were obtained by 2D protein NMR spectroscopy and finally by an X-ray structure, which revealed the ternary complex as a 2 : 2 : 2 FKBP12 : molecular glue : MAPRE1 complex exhibiting multiple interactions that occur exclusively in the ternary complex and lead to significant cooperativity α. Using the X-ray structure, rationally guided synthesis of a series of analogues led to the cooperativity driven improvement in the stability of the ternary complex. Furthermore, the ternary complex formation of the series was confirmed by cellular NanoBiT assays, whose A max values correlate with those from the TR-FRET proximity assay. Furthermore, NanoBiT experiments showed the functional impact (inhibition) of these molecular glues on the interaction of MAPRE1 with its intracellular native partners.

Broad Target Screening Reveals Abundance of FKBP12-Based Molecular Glues in Focused Libraries

Competitive (nondegradative) molecular glues represent a promising drug modality that remains underexplored primarily due to the lack of adequate hit identification approaches. In this study, we screened our historically grown FKBP-focused library containing >1000 drug-like molecules to identify FKBP-assisted molecular glues targeting a diverse panel of 57 proteins. In addition to establishing a robust and generalizable screening approach, we discovered three novel FKBP-dependent molecular glues targeting PTPRN, BRD4BD2, and STAT4. Our results demonstrate that molecular glues are more common than previously thought and that they can be identified by repurposing existing focused libraries. An optimized, highly cooperative FKBP12-BRD4BD2 glue demonstrated the involvement of the BD2 pocket and exhibited selectivity over the closely related BD1 domain. Our results underscore the value of FKBP12-assisted molecular glues to target challenging proteins with the potential for high selectivity.

Design, synthesis and biological evaluation of pyrrolopyrimidine urea derivatives as novel KRASG12C inhibitors for the treatment of cancer

The KRASG12C mutation, which occurs in approximately 14 % of lung adenocarcinomas, has recently become a crucial target for therapy via small molecules that covalently bind to the mutated cysteine. In this study, a novel series of pyrrolopyrimidine derivatives was rationally designed and synthesized, employing a structure-based drug design strategy. Through structure-activity relationship (SAR) analysis, compound SK-17 emerged as a direct and highly potent inhibitor of KRASG12C. Cellular assays illustrated that SK-17 exhibits potent antiproliferative effects, induces apoptosis, possesses anti-tumor metastasis properties, and effectively inhibits the downstream KRAS pathway in a dose-dependent manner. Moreover, the synergistic enhancement observed when SK-17 is combined with SHP2 inhibitors in vitro underscores its innovative potential in combinatorial therapies. In the xenograft mouse model, SK-17 demonstrated outstanding tumor growth suppression with good safety. Importantly, the in vivo test results show that compound SK-17 has a superior PK profile and lower toxicity in zebrafish test. These results demonstrated the potential of SK-17 with novel scaffold as a promising lead compound targeting KRASG12C to guide in-depth structural optimization.

KRASG12C/mTORC1 inhibition: a powerful duo in NSCLC therapeutics

In a recent report in Nature Communications, Kitai et al. designed a combinational treatment based on targeting the active-state KRASG12C-mutant variant that characterizes a substantial subset of non-small-cell lung cancer (NSCLC) cases. The authors highlighted that dual targeting with KRASG12C (ON) and mammalian target of rapamycin (mTOR) complex (mTORC)-1-selective inhibition potentially provides a new strategy to overcome drug resistance.

Glecirasib, a Potent and Selective Covalent KRAS G12C Inhibitor Exhibiting Synergism with Cetuximab or SHP2 Inhibitor JAB-3312

SIGNIFICANCE

Glecirasib potently and selectively inhibits KRAS G12C and reduces ERK and AKT phosphorylation in KRAS G12C-mutant cancer cells, further inducing cell-cycle arrest and apoptosis. Glecirasib monotherapy leads to tumor regression in KRAS G12C-mutant animal models and shows synergistic effects with cetuximab or JAB-3312 (sitneprotafib).

Targeted protein degradation for cancer therapy

Targeted protein degradation (TPD) aims at reprogramming the target specificity of the ubiquitin-proteasome system, the major cellular protein disposal machinery, to induce selective ubiquitination and degradation of therapeutically relevant proteins. Since its conception over 20 years ago, TPD has gained a lot of attention mainly due to improvements in the design of bifunctional proteolysis targeting chimeras (PROTACs) and understanding the mechanisms underlying molecular glue degraders. Today, PROTACs are on the verge of a first clinical approval and recent structural and mechanistic insights combined with technological leaps promise to unlock the rational design of protein degraders, following the lead of lenalidomide and related clinically approved analogues. At the same time, the TPD universe is expanding at a record speed with the discovery of novel modalities beyond molecular glue degraders and PROTACs. Here we review the recent progress in the field, focusing on newly discovered degrader modalities, the current state of clinical degrader candidates for cancer therapy and upcoming design approaches.

Ginger extract inhibits c-MET activation and suppresses osteosarcoma in vitro and in vivo

BACKGROUND

Osteosarcoma (OS) as an invasive and lethal malignancy showing a low 5-year survival rate requires novel therapeutic targets and their suppressors to improve prevention and treatment strategies.

METHODS

Our research served to clarify the therapeutic potential of ginger extract and its underlying antineoplastic mechanisms in OS. In vitro studies were used to detect the anti-proliferation ability of ginger extract towards OS cells. Patient-derived xenograft (PDX) was performed to confirm whether ginger extract suppressed tumor growth. Cancer Heat Shock Protein (HSP) database was utilized to identify the potential target of ginger extract, which was subsequently validated through a computational docking model screening method, molecular dynamics simulations and pull-down assay. Analysis of the Gene Expression Omnibus (GEO) database revealed the c-MET expression among OS samples as well as the potential mechanism. Immunohistochemistry (IHC) staining corroborated the c-MET expression level among OS tissues relative to the controls. Functional studies involving c-MET knockdown among OS cell lines were produced to elucidate the functional role of c-MET in OS cellular processes.

RESULTS

In vitro studies demonstrated that ginger extract administration impeded OS cell progress while inducing apoptosis and inhibiting migration. Moreover, in vivo tests unveiled that ginger extract prominently inhibited patient-derived xenograft (PDX) tumor development. Cancer HSP database analysis recognized c-MET as an underlying target of ginger extract, which was subsequently validated through a computational docking model screening, molecular dynamics simulations and pull-down assay. Analysis of the Gene Expression Omnibus (GEO) database combined with immunohistochemistry (IHC) staining corroborated the c-MET overexpression among OS tissues in contrast with the controls. Next, our study confirmed the significant suppression of cell progress and anchorage-independent growth, while concomitantly inducing apoptosis after c-MET knockdown, underscoring its prospect for a therapeutic target.

CONCLUSION

Collectively, our findings show that c-MET is a prospective therapeutic target for OS. Ginger extract, a natural c-MET inhibitor, exhibits potent antineoplastic effects by suppressing OS growth both in vitro and in vivo, highlighting its prospect for a new therapeutic agent of this aggressive malignancy.

Pan-KRAS Inhibitors BI-2493 and BI-2865 Display Potent Antitumor Activity in Tumors with KRAS Wild-type Allele Amplification

KRASG12C selective inhibitors, such as sotorasib and adagrasib, have raised hopes of targeting other KRAS-mutant alleles in patients with cancer. We report that KRAS wild-type (WT)-amplified tumor models are sensitive to treatment with the small-molecule KRAS inhibitors BI-2493 and BI-2865. These pan-KRAS inhibitors directly target the "OFF" state of KRAS and result in potent antitumor activity in preclinical models of cancers driven by KRAS-mutant proteins. In this study, we used the high-throughput cellular viability Profiling Relative Inhibition Simultaneously in Mixtures assay to assess the antiproliferative activity of BI-2493 in a 900+ cancer cell line panel, expanding on our previous work. KRAS WT-amplified cancer cell lines, with a copy number >7, were identified as the most sensitive, across cell lines with any KRAS alterations, to our pan-KRAS inhibitors. Importantly, our data suggest that a KRAS "OFF" inhibitor is better suited to treat KRAS WT-amplified tumors than a KRAS "ON" inhibitor. KRAS WT amplification is common in patients with gastroesophageal cancers in which it has been shown to act as a unique cancer driver with little overlap to other actionable mutations. The pan-KRAS inhibitors BI-2493 and BI-2865 show potent antitumor activity in vitro and in vivo in KRAS WT-amplified cell lines from this and other tumor types. In conclusion, this is the first study to demonstrate that direct pharmacologic inhibition of KRAS shows antitumor activity in preclinical models of cancer with KRAS WT amplification, suggesting a novel therapeutic concept for patients with cancers bearing this KRAS alteration.

The "three body solution": Structural insights into molecular glues

Molecular glues are small molecules that nucleate novel or stabilize natural, protein-protein interactions resulting in a ternary complex. Their success in targeting difficult to drug proteins of interest has led to ever-increasing interest in their use as therapeutics and research tools. While molecular glues and their targets vary in structure, inspection of diverse ternary complexes reveals commonalities. Whether of high or low molecular weight, molecular glues are often rigid and form direct hydrophobic interactions with their target protein. There is growing evidence that these hotspots can accommodate multiple ternary complex binding modes and enable targeting of traditionally undruggable targets. Advances in screening from the molecular glue degrader literature and insights in structure-based drug design, especially from the non-degrading tri-complex work, are likely intersectional.

Discovery of Daraxonrasib (RMC-6236), a Potent and Orally Bioavailable RAS(ON) Multi-selective, Noncovalent Tri-complex Inhibitor for the Treatment of Patients with Multiple RAS-Addicted Cancers

Oncogenic RAS mutations are among the most common in human cancers. To target the active, GTP-bound state of RAS(ON) directly, we employed an innovative tri-complex inhibitor (TCI) modality. Formation of a complex with an intracellular chaperone protein CypA, an inhibitor, and a target protein RAS blocks effector binding, inhibiting downstream RAS signaling and tumor cell proliferation. Herein, we describe the structure-guided SAR journey that led to the discovery of daraxonrasib (RMC-6236), a noncovalent, potent tri-complex inhibitor of multiple RAS mutant and wild-type (WT) variants. This orally bioavailable bRo5 macrocyclic molecule occupies a unique composite binding pocket comprising CypA and SWI/SWII regions of RAS(ON). To achieve broad-spectrum RAS isoform activity, we deployed an SAR campaign that focused on interactions with residues conserved between mutants and WT RAS isoforms. Concurrent optimization of potency and drug-like properties led to the discovery of daraxonrasib (RMC-6236), currently in clinical evaluation in RAS mutant advanced solid tumors (NCT05379985; NCT06040541; NCT06162221; NCT06445062; NCT06128551).

Discovery of Elironrasib (RMC-6291), a Potent and Orally Bioavailable, RAS(ON) G12C-Selective, Covalent Tricomplex Inhibitor for the Treatment of Patients with RAS G12C-Addicted Cancers

The discovery of elironrasib (RMC-6291) represents a significant breakthrough in targeting the previously deemed undruggable GTP-bound, active KRASG12C. To target the active state of RAS (RAS(ON)) directly, we have employed an innovative tri-complex inhibitor (TCI) modality involving formation of a complex with an inhibitor, the intracellular chaperone protein CypA, and the target protein KRASG12C in its GTP-bound form. The resulting tri-complex inhibits oncogenic signaling, inducing tumor regressions across various preclinical models of KRASG12C mutant human cancers. Here we report structure-guided medicinal chemistry efforts that led to the discovery of elironrasib, a potent, orally bioavailable, RAS(ON) G12C-selective, covalent, tri-complex inhibitor. The investigational agent elironrasib is currently undergoing phase 1 clinical trials (NCT05462717, NCT06128551, NCT06162221), with preliminary data indicating clinical activity in patients who had progressed on first-generation inactive state-selective KRASG12C inhibitors.

In Situ RAS:RAF Binding Correlates with Response to KRASG12C Inhibitors in KRASG12C-Mutant Non-Small Cell Lung Cancer

PURPOSE

Therapeutic efficacy of KRASG12C(OFF) inhibitors (KRASG12Ci) in KRASG12C-mutant non-small cell lung cancer (NSCLC) varies widely. The activation status of RAS signaling in tumors with KRASG12C mutation remains unclear, as its ability to cycle between the active GTP-bound and inactive GDP-bound states may influence downstream pathway activation and therapeutic responses. We hypothesized that the interaction between RAS and its downstream effector RAF in tumors may serve as indicators of RAS activity, rendering NSCLC tumors with a high degree of RAS engagement and downstream effects more responsive to KRASG12Ci compared with tumors with lower RAS-RAF interactions.

EXPERIMENTAL DESIGN

We developed a method for measuring in situ RAS binding to RAF in cancer samples using proximity ligation assays (PLA) designed to detect panRAS-CRAF interactions.

RESULTS

The panRAS-CRAF PLA signal correlated with levels of both RAS-GTP and phosphorylated ERK protein, suggesting that this assay can effectively assess active RAS signaling. We found that elevated panRAS-CRAF PLA signals were associated with increased sensitivity to KRASG12Ci in KRASG12C-mutant NSCLC cell lines, xenograft models, and patient samples. Applying a similar PLA approach to measure the interactions between EGFR and its adapter protein growth factor receptor-bound protein 2 as a surrogate for EGFR activity, we found no relationship between EGFR activity and response to KRASG12Ci in the same samples.

CONCLUSIONS

Our study highlights the importance of evaluating in situ RAS-RAF interactions as a potential predictive biomarker for identifying patients with NSCLC most likely to benefit from KRASG12Ci. The PLA developed for quantifying these interactions represents a valuable tool for guiding treatment strategies.

Genetically encoding ε-N-methacryllysine into proteins in live cells

Lysine acylation is a ubiquitous post-translational modification (PTM) that plays pivotal roles in various cellular processes, such as transcription, metabolism, protein localization and folding. Thousands of lysine acylation sites have been identified based on advances in antibody enrichment strategies, highly sensitive analysis by mass spectrometry (MS), and bioinformatics. However, only 27 lysine methacrylation (Kmea) sites have been identified exclusively in histone proteins. It is hard to separate, purify and differentiate the Kmea modification from its structural isomer lysine crotonylation (Kcr) using general biochemical approaches. Here, we identify Kmea sites on a non-histone protein, Cyclophillin A (CypA). To investigate the functions of Kmea in CypA, we develop a general genetic code expansion approach to incorporate a non-canonical amino acid (ncAA) ε-N-Methacryllysine (MeaK) into target proteins and identify interacting proteins of methacrylated CypA using affinity-purification MS. We find that Kmea at CypA site 125 regulates cellular redox homeostasis, and HDAC1 is the regulator of Kmea on CypA. Moreover, we discover that genetically encode Kmea can be further methylated to ε-N-methyl-ε-N-methacrylation (Kmemea) in live cells.

Impact of Co-mutations and Transcriptional Signatures in Non-Small Cell Lung Cancer Patients Treated with Adagrasib in the KRYSTAL-1 Trial

PURPOSE

KRAS inhibitors are revolutionizing the treatment of non-small cell lung cancer (NSCLC), but clinico-genomic determinants of treatment efficacy warrant continued exploration.

EXPERIMENTAL DESIGN

Patients with advanced KRASG12C-mutant NSCLC treated with adagrasib [KRYSTAL-1 (NCT03785249)] were included in the analysis. Pretreatment next-generation sequencing data were collected per protocol. HTG EdgeSeq Transcriptome Panel was used for gene expression profiling. Clinical endpoints included objective response, progression-free survival (PFS), and overall survival (OS). KRASG12C-mutant NSCLC cell lines and xenograft models were used for sensitivity analyses and combination drug screens.

RESULTS

KEAP1 MUT and STK11MUT were associated with shorter survival to adagrasib [KEAP1: PFS 4.1 vs. 9.9 months, HR 2.7, P < 0.01; OS 5.4 vs. 19.0 months, HR 3.6, P < 0.01; STK11: PFS 4.2 vs. 11.0 months, HR 2.2, P < 0.01; OS 9.8 months vs. not reached (NR), HR 2.6, P < 0.01]. KEAP1WT/STK11WT status identified adagrasib-treated patients with significantly longer PFS (16.9 months) and OS (NR). Preclinical analyses further validate the association between KEAP1 loss of function and adagrasib resistance. Adagrasib and mTOR inhibitor combinations produced higher treatment efficacy in NSCLC models harboring STK11 and KEAP1 co-mutations. NRF2HIGH signaling was associated with shorter survival to adagrasib (PFS: 4.2 vs. 8.4 months, HR 2.0, P = 0.02; OS: 6.5 vs. 19.0 months, HR 2.8, P < 0.01) even in patients with KEAP1WT NSCLC. KEAP1WT/STK11WT/NRF2LOW status identified patients-32%-with longer survival to adagrasib (PFS 12.0 vs. 4.2 months, HR 0.2, P < 0.01; OS NR vs. 8.0 months, HR 0.1, P < 0.01).

CONCLUSIONS

KEAP1, STK11, and NRF2 status define patients with KRASG12C-mutant NSCLC with markedly distinct outcomes to adagrasib. These results further support the use of genomic features-mutational and nonmutational-for the treatment selection of patients with KRASG12C-mutant NSCLC.

Discovery of Novel Oxazolo[4,3-f]purine Derivatives as Antitumor Agents through PPIA Interaction

54 novel oxazolo [4,3-f]purine derivatives were designed, synthesized, and evaluated for antitumor activity, among which compound 20b exhibited potent activity against several cancer cell lines. Compound 20b inhibited cell metastasis, arrested the cell cycle in the G0/G1 phase, and induced apoptosis in HCT116 cells. Mechanistic studies revealed that 20b increased ROS levels and led to DNA damage, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction in HCT116 cells. Limited proteolysis-small molecule mapping (LiP-SMap), drug affinity responsive target stability (DARTS) assay, cellular thermal shift assay (CETSA), and surface plasmon resonance (SPR) experiments provided evidence that compound 20b bound to PPIA with a KD value of 0.52 μM. siRNA assay indicated that 20b-mediated antiproliferative and antimigration activities were abolished and that the PPIA/MAPK signaling pathway was inhibited when PPIA was silenced in HCT116 cells. Significantly, compound 20b presented significant anticolorectal cancer efficacy in vivo without obvious toxicity. These results indicate that 20b may serve as a novel anticancer agent targeting PPIA, meriting further attention in antitumor drug research.

Overcoming cancer therapy resistance: From drug innovation to therapeutics

One of the major limitations of cancer therapy is the emergence of drug resistance. This review amis to provide a focused analysis of the multifactorial mechanisms underlying therapy resistance,with an emphasis on actionable insights for developing novel therapeutic strategies. It concisely outlines key factors contributing to therapy resistance, including drug delivery barriers, cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), cancer heterogeneity, tumor microenvironment (TME), genetic mutations, and alterlations in gene expression. Additionally, we explore how tumors evade targeted therapies through pathway-specific mechanisms that restore disrupted signaling pathways. The review critically evaluates innovative strategies designed to sensitize resistant tumor cells, such as targeted protein dedgradation, antibody-drug conjugates, structure-based drug design, allosteric drugs, multitarget drugs, nanomedicine and others We also highlight the importance of understanding the pharmacological actions of these agents and their integration into treatment regimens. By synthesizing current knowledge and identifying gaps in our understanding, this review aims to guide future research and improve patient outcomes in cancer therapy.

Chemical Synthesis, Refolding, and Characterization of Mirror-Image Cyclophilin A

The chemical synthesis of proteins (CSP) has been an essential tool in studying and understanding the role of these biological polymers and in enabling the discovery of novel classes of inhibitors. However, CSP with commercially available synthesizers is typically limited to producing polypeptides of about 50 to 70 amino acids in length. Consequently, a wide range of protein targets have been inaccessible using these technologies, or they require cumbersome synthesis and purification of multiple peptide fragments. In this report, we employed a powerful combination of automated fast-flow peptide synthesis (AFPS), native chemical ligation (NCL), and high-throughput evaluation of refolding conditions to achieve the first chemical synthesis of both the wild-type and mirror-image forms of functional full-length cyclophilin A, which plays a vital role in proline cis-trans isomerization and other important processes. Functional assays confirmed that the chemically synthesized proteins retained their biological properties.

Structural insights, regulation, and recent advances of RAS inhibitors in the MAPK signaling cascade: a medicinal chemistry perspective

The MAPK pathway has four main components: RAS, RAF, MEK, and ERK. Among these, RAS is the most frequently mutated protein and the leading cause of cancer. The three isoforms of the RAS gene are HRAS, NRAS, and KRAS. The KRAS gene is characterized by two splice variants, K-Ras4A and K-Ras4B. The occurrence of cancer often involves a mutation in both KRAS4A and KRAS4B. In this study, we have elucidated the mechanism of the RAS protein complex and the movement of switches I and II. Only two RAS inhibitors, sotorasib and adagrasib, have been approved by the FDA, and several are in clinical trials. This review comprises recent developments in synthetic RAS inhibitors, their unique properties, their importance in inhibiting RAS mutations, and the current challenges in developing new RAS inhibitors. This review will undoubtedly help researchers design novel RAS inhibitors.

Discovery of BBO-8520, a First-In-Class Direct and Covalent Dual Inhibitor of GTP-Bound (ON) and GDP-Bound (OFF) KRASG12C

Approved inhibitors of KRASG12C prevent oncogenic activation by sequestering the inactive, GDP-bound (OFF) form rather than directly binding and inhibiting the active, GTP-bound (ON) form. This approach provides no direct target coverage of the active protein. Expectedly, adaptive resistance to KRASG12C (OFF)-only inhibitors is observed in association with increased expression and activity of KRASG12C(ON). To provide optimal KRASG12C target coverage, we have developed BBO-8520, a first-in-class, direct dual inhibitor of KRASG12C(ON) and (OFF) forms. BBO-8520 binds in the Switch-II/Helix3 pocket, covalently modifies the target cysteine, and disables effector binding to KRASG12C(ON). BBO-8520 exhibits potent signaling inhibition in growth factor-activated states, in which current (OFF)-only inhibitors demonstrate little measurable activity. In vivo, BBO-8520 demonstrates rapid target engagement and inhibition of signaling, resulting in durable tumor regression in multiple models, including those resistant to KRASG12C(OFF)-only inhibitors. BBO-8520 is in phase 1 clinical trials in patients with KRASG12C non-small cell lung cancer. Significance: BBO-8520 is a first-in-class direct, small molecule covalent dual inhibitor that engages KRASG12C in the active (ON) and inactive (OFF) conformations. BBO-8520 represents a novel mechanism of action that allows for optimal target coverage and delays the emergence of adaptive resistance seen with (OFF)-only inhibitors in the clinic. See related commentary by Zhou and Westover, p. 455.

Decoding the functional impact of the cancer genome through protein-protein interactions

Acquisition of genomic mutations enables cancer cells to gain fitness advantages under selective pressure and, ultimately, leads to oncogenic transformation. Interestingly, driver mutations, even within the same gene, can yield distinct phenotypes and clinical outcomes, necessitating a mutation-focused approach. Conversely, cellular functions are governed by molecular machines and signalling networks that are mostly controlled by protein-protein interactions (PPIs). The functional impact of individual genomic alterations could be transmitted through regulated nodes and hubs of PPIs. Oncogenic mutations may lead to modified residues of proteins, enabling interactions with other proteins that the wild-type protein does not typically interact with, or preventing interactions with proteins that the wild-type protein usually interacts with. This can result in the rewiring of molecular signalling cascades and the acquisition of an oncogenic phenotype. Here, we review the altered PPIs driven by oncogenic mutations, discuss technologies for monitoring PPIs and provide a functional analysis of mutation-directed PPIs. These driver mutation-enabled PPIs and mutation-perturbed PPIs present a new paradigm for the development of tumour-specific therapeutics. The intersection of cancer variants and altered PPI interfaces represents a new frontier for understanding oncogenic rewiring and developing tumour-selective therapeutic strategies.

Mechanisms of Resistance to KRAS Inhibitors: Cancer Cells' Strategic Use of Normal Cellular Mechanisms to Adapt

KRAS was long deemed undruggable until the discovery of the switch-II pocket facilitated the development of specific KRAS inhibitors. Despite their introduction into clinical practice, resistance mechanisms can limit their effectiveness. Initially, tumors rely on mutant KRAS, but as they progress, they may shift to alternative pathways, resulting in intrinsic resistance. This resistance can stem from mechanisms like epithelial-to-mesenchymal transition (EMT), YAP activation, or KEAP1 mutations. KRAS inhibition often triggers cellular rewiring to counteract therapeutic pressure. For instance, feedback reactivation of signaling pathways such as MAPK, mediated by receptor tyrosine kinases, supports tumor cell survival. Inhibiting KRAS disrupts protein homeostasis, but reactivation of MAPK or AKT can restore it, aiding tumor cell survival. KRAS inhibition also causes metabolic reprogramming and protein re-localization. The re-localization of E-cadherin and Scribble from the membrane to the cytosol causes YAP to translocate to the nucleus, where it drives MRAS transcription, leading to MAPK reactivation. Emerging evidence indicates that changes in cell identity, such as mucinous differentiation, shifts from alveolar type 2 to type 1 cells, or lineage switching from adenocarcinoma to squamous cell carcinoma, also contribute to resistance. In addition to these nongenetic mechanisms, secondary mutations in KRAS or alterations in upstream/downstream signaling proteins can cause acquired resistance. Secondary mutations in the switch-II pocket disrupt drug binding, and known oncogenic mutations affect drug efficacy. Overcoming these resistance mechanisms involves enhancing the efficacy of drugs targeting mutant KRAS, developing broad-spectrum inhibitors, combining therapies targeting multiple pathways, and integrating immune checkpoint inhibitors.

Glecirasib in KRASG12C-mutated nonsmall-cell lung cancer: a phase 2b trial

Glecirasib (JAB-21822) is a new covalent oral KRAS-G12C inhibitor. This multicenter, single-arm phase 2b study assessed the efficacy and safety of glecirasib administered orally at 800 mg daily in patients with locally advanced or metastatic KRASG12C-mutated nonsmall-cell lung cancer. The primary endpoint was the objective response rate (ORR) assessed by an independent review committee (IRC). Between 15 September 2022 and 28 September 2023, 119 patients with a median age of 62 years were enrolled. As of the data cut-off date on 28 March 2024, the ORR assessed by IRC was 47.9% (56/117; 95% confidence interval: 38.5-57.3%). The incidence of treatment-related adverse events (TRAEs) of any grade was 97.5% (116/119). The incidence of grades 3 and 4 TRAEs was 38.7% (46/119). A total of 5.0% (6/119) of patients discontinued the treatment due to TRAEs. No treatment-related deaths occurred. Glecirasib exhibited promising clinical efficacy and manageable safety profiles in these patient populations. ClinicalTrials.gov identifier: NCT05009329 .

Next steps for targeted protein degradation

Targeted protein degradation (TPD) has greatly advanced as a therapeutic strategy in the past two decades, and we are on the cusp of rationally designed protein degraders reaching clinical approval. Offering pharmacological advantages relative to occupancy-driven protein inhibition, chemical methods for regulating biomolecular proximity have provided opportunities to tackle disease-related targets that were undruggable. Despite the pre-clinical success of designed degraders and existence of clinical therapies that serendipitously utilize TPD, expansion of the TPD toolbox is necessary to identify and characterize the next generation of molecular degraders. Here we highlight three areas for continued growth in the field that should be prioritized: expansion of TPD platform with greater spatiotemporal precision, increased throughput of degrader synthesis, and optimization of cooperativity in chemically induced protein complexes. The future is bright for TPD in medicine, and we expect that innovative approaches will increase therapeutic applications of proximity-induced pharmacology.

KRAS mutants confer platinum resistance by regulating ALKBH5 posttranslational modifications in lung cancer

Constitutively active mutations of KRAS are prevalent in non-small cell lung cancer (NSCLC). However, the relationship between these mutations and resistance to platinum-based chemotherapy and the underlying mechanisms remain elusive. In this study, we demonstrate that KRAS mutants confer resistance to platinum in NSCLC. Mechanistically, KRAS mutants mediate platinum resistance in NSCLC cells by activating ERK/JNK signaling, which inhibits AlkB homolog 5 (ALKBH5) N6-methyladenosine (m6A) demethylase activity by regulating posttranslational modifications (PTMs) of ALKBH5. Consequently, the KRAS mutant leads to a global increase in m6A methylation of mRNAs, particularly damage-specific DNA-binding protein 2 (DDB2) and XPC, which are essential for nucleotide excision repair. This methylation stabilized the mRNA of these 2 genes, thus enhancing NSCLC cells' capability to repair platinum-induced DNA damage and avoid apoptosis, thereby contributing to drug resistance. Furthermore, blocking KRAS-mutant-induced m6A methylation, either by overexpressing a SUMOylation-deficient mutant of ALKBH5 or by inhibiting methyltransferase-like 3 (METTL3) pharmacologically, significantly sensitizes KRAS-mutant NSCLC cells to platinum drugs in vitro and in vivo. Collectively, our study uncovers a mechanism that mediates KRAS-mutant-induced chemoresistance in NSCLC cells by activating DNA repair through the modulation of the ERK/JNK/ALKBH5 PTM-induced m6A modification in DNA damage repair-related genes.

Natural products targeting RAS by multiple mechanisms and its therapeutic potential in cancer: An update since 2020

RAS proteins, as pivotal signal transduction molecules, are frequently mutated and hyperactivated in various human cancers, closely associated with tumor cell proliferation, survival, and metastasis. Despite extensive research on RAS targeted therapies, developing effective RAS inhibitors remains a significant challenge. Natural products, endowed with unique chemical structures and diverse biological activities through long-term natural selection, have emerged as a vital resource for discovering novel RAS-targeted therapeutic drugs. This review focuses on the latest advancements in targeting RAS with natural products and categorizes these natural products based on their mechanisms of action. Additionally, we discuss the challenges faced by these natural products during clinical translation, including issues related to pharmacokinetics. Strategies such as combination therapy, structural optimization, and drug delivery systems are anticipated to enhance efficacy and overcome these challenges.

Current Strategies and Future Dimensions in the Development of KRAS Inhibitors for Targeted Anticancer Therapy

KRAS is a proto-oncogene that is found to be mutated in 15% of all metastatic cancers with high prevalence in pancreatic, lung, and colorectal cancers. Additionally, patients harboring KRAS mutations respond poorly to standard cancer therapy. As a result, KRAS is seen as an attractive target for targeted anticancer therapy. Over the last decade, this protein has evolved from being termed "undruggable" to producing two clinically approved drugs along with several more in clinical development, and many under preclinical investigations. This review details the development of various KRAS-targeted molecules with emphasis on the different drug design strategies employed by examining the following areas: (1) Direct inhibition of KRAS mutants using small molecule binders, (2) Inhibiting the activated state of KRAS mutants using a binary complex of small molecule binders and cyclophilin A, and (3) Targeted degradation of KRAS mutants using the PROTAC approach. We assess the pharmacological attributes and possible clinical benefits of the different molecules and look to the next frontiers in the application of KRAS inhibitors as anticancer agents.

KRAS inhibitors: resistance drivers and combinatorial strategies

In 1982, the RAS genes HRAS and KRAS were discovered as the first human cancer genes, with KRAS later identified as one of the most frequently mutated oncogenes. Yet, it took nearly 40 years to develop clinically effective inhibitors for RAS-mutant cancers. The discovery in 2013 by Shokat and colleagues of a druggable pocket in KRAS paved the way to FDA approval of the first covalently binding KRASG12C inhibitors, sotorasib and adagrasib, in 2021 and 2022, respectively. However, rather than marking the end of a successful assault on the Mount Everest of cancer research, this landmark only revealed new challenges in RAS drug discovery. In this review, we highlight the progress on defining resistance mechanisms and developing combination treatment strategies to improve patient responses to KRAS therapies.

Digestive cancers: mechanisms, therapeutics and management

Cancers of the digestive system are major contributors to global cancer-associated morbidity and mortality, accounting for 35% of annual cases of cancer deaths. The etiologies, molecular features, and therapeutic management of these cancer entities are highly heterogeneous and complex. Over the last decade, genomic and functional studies have provided unprecedented insights into the biology of digestive cancers, identifying genetic drivers of tumor progression and key interaction points of tumor cells with the immune system. This knowledge is continuously translated into novel treatment concepts and targets, which are dynamically reshaping the therapeutic landscape of these tumors. In this review, we provide a concise overview of the etiology and molecular pathology of the six most common cancers of the digestive system, including esophageal, gastric, biliary tract, pancreatic, hepatocellular, and colorectal cancers. We comprehensively describe the current stage-dependent pharmacological management of these malignancies, including chemo-, targeted, and immunotherapy. For each cancer entity, we provide an overview of recent therapeutic advancements and research progress. Finally, we describe how novel insights into tumor heterogeneity and immune evasion deepen our understanding of therapy resistance and provide an outlook on innovative therapeutic strategies that will shape the future management of digestive cancers, including CAR-T cell therapy, novel antibody-drug conjugates and targeted therapies.

Discovery of fully synthetic FKBP12-mTOR molecular glues

Molecular glues are a new drug modality with the potential to engage otherwise undruggable targets. However, the rational discovery of molecular glues for desired targets is a major challenge and most known molecular glues have been discovered by serendipity. Here we present the first fully synthetic FKBP12-mTOR molecular glues, which were discovered from a FKBP-focused, target-unbiased ligand library. Our biochemical screening of >1000 in-house FKBP ligands yielded one hit that induced dimerization of FKBP12 and the FRB domain of mTOR. The crystal structure of the ternary complex revealed that the hit targeted a similar surface on the FRB domain compared to natural product rapamycin but with a radically different interaction pattern. Structure-guided optimization improved potency 500-fold, and led to compounds which initiate FKBP12-FRB complex formation in cells. Our results show that molecular glues targeting flat surfaces can be discovered by focused screening and support the use of FKBP12 as a versatile presenter protein for molecular glues.

Covalent Proximity Inducers

Molecules that are able to induce proximity between two proteins are finding ever increasing applications in chemical biology and drug discovery. The ability to introduce an electrophile and make such proximity inducers covalent can offer improved properties such as selectivity, potency, duration of action, and reduced molecular size. This concept has been heavily explored in the context of targeted degradation in particular for bivalent molecules, but recently, additional applications are reported in other contexts, as well as for monovalent molecular glues. This is a comprehensive review of reported covalent proximity inducers, aiming to identify common trends and current gaps in their discovery and application.

Programming the Kinetics of Chemical Communication: Induced Fit vs Conformational Selection

Life on Earth depends on chemical communication and the ability of biomolecular switches to integrate various chemical signals that trigger their activation or deactivation over time scales ranging from microseconds to days. The ability to similarly program and control the kinetics of artificial switches would greatly assist the design and optimization of future chemical and nanotechnological systems. Two distinct structure-switching mechanisms are typically employed by biomolecular switches: induced fit (IF) and conformational selection (CS). Despite 60 years of experimental and theoretical investigations, the kinetic and evolutive advantages of these two mechanisms remain unclear. Here, we have created a simple modular DNA switch that can operate through both mechanisms and be easily tuned and adapted to characterize its thermodynamic and kinetic parameters. We show that the fastest activation rate of a switch occurs when the ligand is able to bind its inactive conformation (IF). In contrast, we show that when the ligand can only bind the active conformation of the switch (CS), its activation rate can be easily programmed over many orders of magnitude by a simple tuning of its conformational equilibrium. We demonstrate the programming ability of both these mechanisms by designing a drug delivery vessel that can be programmed to release a drug over different time scales (>1000-fold). Overall, these findings provide a programmable strategy to optimize the kinetics of molecular systems and nanomachines while also illustrating how evolution may have taken advantage of IF and CS mechanisms to optimize the kinetics of biomolecular switches.

"Undruggable KRAS": druggable after all

The three RAS genes (HRAS, KRAS, and NRAS) comprise the most frequently mutated oncogene family in cancer. KRAS is the predominant isoform mutated in cancer and is most prevalently mutated in major causes of cancer deaths including lung, colorectal, and pancreatic cancers. Despite extensive academic and industry efforts to target KRAS, it would take nearly four decades before approval of the first clinically effective KRAS inhibitors for the treatment of KRAS mutant lung cancer. We revisit past anti-KRAS strategies and painful lessons learned and then focus on the rapidly evolving landscape of direct RAS inhibitors, resistance mechanisms, and potential combination treatments.

Advances in Novel Targeted Therapies for Pancreatic Adenocarcinoma

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with limited therapeutic options and poor prognosis. Recent advances in targeted therapies have opened new avenues for intervention in PDAC, focusing on key genetic and molecular pathways that drive tumor progression.

METHODS

In this review, we provide an overview on advances in novel targeted therapies in pancreatic adenocarcinoma.

RESULTS

Here, we explore the latest development in targeting the KRAS pathway, a historically "undruggable" target crucial to PDAC pathogenesis. Strategies to inhibit KRAS include direct KRAS-targeted therapies, modulation of upstream and downstream signaling, KRAS-specific siRNA, and novel combination therapies integrating KRAS inhibitors with immune checkpoint blockade, PARP inhibitors, chemotherapy, CDK4/6 inhibitors, and autophagy modulators. Beyond KRAS, emerging targets such as NRG1 fusions, NTRK/ROS1 fusions, RET alterations, and the PRMT5/CDKN2A/MAT2A axis, along with EGFR and Claudin18.2 inhibitors, are also discussed as promising therapeutic strategies. Additionally, the review highlights novel approaches for microsatellite instability-high (MSIH) PDAC and emerging therapies, including adoptive cell therapies (CAR-T, TCR, TIL), cancer vaccines, and strategies to modify the tumor microenvironment.

CONCLUSION

Overall, the rapid evolution of targeted therapies offers renewed optimism in the fight against pancreatic cancer, a malignancy with historically poor outcomes.

Dynamic conformational equilibria in the active states of KRAS and NRAS

The design of potent RAS inhibitors benefits from a molecular understanding of the dynamics in KRAS and NRAS and their oncogenic mutants. Here we characterize switch-1 dynamics in GTP-state KRAS and NRAS by 31P NMR, by 15N relaxation dispersion NMR, hydrogen-deuterium exchange mass spectrometry (HDX-MS), and molecular dynamics simulations. In GMPPNP-bound KRAS and NRAS, we see the co-existence of two conformational states, corresponding to an "inactive" state-1 and an "active" state-2, as previously reported. The KRAS oncogenic mutations G12D, G12C and G12V only slightly affect this equilibrium towards the "inactive" state-1, with rank order wt < G12C < G12D < G12V. In contrast, the NRAS Q61R oncogenic mutation shifts the equilibrium fully towards the "active" state-2. Our molecular dynamics simulations explain this by the observation of a transient hydrogen bond between the Arg61 side chain and the Thr35 backbone carbonyl oxygen. NMR relaxation dispersion experiments with GTP-bound KRAS Q61R confirm a drastic decrease in the population of state-1, but still detect a small residual population (1.8%) of this conformer. HDX-MS indicates that higher populations of state-1 correspond to increased hydrogen-deuterium exchange rates in some regions and increased flexibility, whereas low state-1 populations are associated with KRAS rigidification. We elucidated the mechanism of action of a potent KRAS G12D inhibitor, MRTX1133. Binding of this inhibitor to the switch-2 pocket causes a complete shift of KRAS G12D towards the "inactive" conformation and prevents binding of effector RAS-binding domain (RBD) at physiological concentrations, by signaling through an allosteric network.

Advances and Challenges in RAS Signaling Targeted Therapy in Leukemia

RAS mutations are prevalent in leukemia, including mutations at G12, G13, T58, Q61, K117, and A146. These mutations are often crucial for tumor initiation, maintenance, and recurrence. Although much is known about RAS function in the last 40 years, a substantial knowledge gap remains in understanding the mutation-specific biological activities of RAS in cancer and the approaches needed to target specific RAS mutants effectively. The recent approval of KRASG12C inhibitors, adagrasib and sotorasib, has validated KRAS as a direct therapeutic target and demonstrated the feasibility of selectively targeting specific RAS mutants. Nevertheless, KRASG12C remains the only RAS mutant successfully targeted with FDA-approved inhibitors for cancer treatment in patients, limiting its applicability for other oncogenic RAS mutants, such as G12D, in leukemia. Despite these challenges, new approaches have generated optimism about targeting specific RAS mutations in an allele-dependent manner for cancer therapy, supported by compelling biochemical and structural evidence, which inspires further exploration of RAS allele-specific vulnerabilities. This review will discuss the recent advances and challenges in the development of therapies targeting RAS signaling, highlight emerging therapeutic strategies, and emphasize the importance of allele-specific approaches for leukemia treatment.

Single-cell sensor analyses reveal signaling programs enabling Ras-G12C drug resistance

Clinical resistance to rat sarcoma virus (Ras)-G12C inhibitors is a challenge. A subpopulation of cancer cells has been shown to undergo genomic and transcriptional alterations to facilitate drug resistance but the immediate adaptive effects on Ras signaling in response to these drugs at the single-cell level is not well understood. Here, we used Ras biosensors to profile the activity and signaling environment of endogenous Ras at the single-cell level. We found that a subpopulation of KRas-G12C cells treated with Ras-G12C-guanosine-diphosphate inhibitors underwent adaptive signaling and metabolic changes driven by wild-type Ras at the Golgi and mutant KRas at the mitochondria, respectively. Our Ras biosensors identified major vault protein as a mediator of Ras activation through its scaffolding of Ras signaling pathway components and metabolite channels. Overall, methods including ours that facilitate direct analysis on the single-cell level can report the adaptations that subpopulations of cells adopt in response to cancer therapies, thus providing insight into drug resistance.

Pharmacological restoration of GTP hydrolysis by mutant RAS

Approximately 3.4 million patients worldwide are diagnosed each year with cancers that have pathogenic mutations in one of three RAS proto-oncogenes (KRAS, NRAS and HRAS)1,2. These mutations impair the GTPase activity of RAS, leading to activation of downstream signalling and proliferation3-6. Long-standing efforts to restore the hydrolase activity of RAS mutants have been unsuccessful, extinguishing any consideration towards a viable therapeutic strategy7. Here we show that tri-complex inhibitors-that is, molecular glues with the ability to recruit cyclophilin A (CYPA) to the active state of RAS-have a dual mechanism of action: not only do they prevent activated RAS from binding to its effectors, but they also stimulate GTP hydrolysis. Drug-bound CYPA complexes modulate residues in the switch II motif of RAS to coordinate the nucleophilic attack on the γ-phosphate of GTP in a mutation-specific manner. RAS mutants that were most sensitive to stimulation of GTPase activity were more susceptible to treatment than mutants in which the hydrolysis could not be enhanced, suggesting that pharmacological stimulation of hydrolysis potentiates the therapeutic effects of tri-complex inhibitors for specific RAS mutants. This study lays the foundation for developing a class of therapeutics that inhibit cancer growth by stimulating mutant GTPase activity.

KRAS mutations in advanced non-small cell lung cancer: From biology to novel therapeutic strategies

Kristen rat sarcoma viral oncogene homolog (KRAS) mutations play a major role in the carcinogenesis of many types of solid tumors including non-small cell lung cancer (NSCLC). Among KRAS mutations, p.G12C single-nucleotide variant (KRASG12C) is the most frequently reported in NSCLC patients, with a prevalence of about 12-13 %. For many decades, KRAS mutations including KRASG12C were considered "undruggable" because of the lack of effective and well-tolerated selective therapies. Noteworthy, CodeBreaK100 and KRYSTAL-1 clinical trials have recently demonstrated that sotorasib and adagrasib, two novel selective KRASG12C inhibitors, have clinical activity with acceptable adverse-event profile for the treatment of advanced NSCLC patients with KRASG12C mutation. On the other hand, no selective therapies are approved for the treatment of advanced NSCLC patients with non-G12C KRAS mutations. As a result, these patients receive the same treatments as those without KRAS mutations. In this paper, we describe the role of KRAS mutations in NSCLC focusing on the clinical and molecular characteristics which potentially identify specific subtypes of NSCLC patients based on different KRAS mutations. We also provide an overview of the main clinical trials testing novel selective KRASG12C inhibitors as well as novel potential therapeutic strategies for NSCLC patients with non-G12C KRAS mutations.

Targeted degradation of oncogenic KRASG12V triggers antitumor immunity in lung cancer models

Kirsten rat sarcoma viral oncogene homolog (KRAS) is the most frequently mutated oncogene in lung adenocarcinoma, with G12C and G12V being the most predominant forms. Recent breakthroughs in KRASG12C inhibitors have transformed the clinical management of patients with the G12C mutation and advanced our understanding of the function of this mutation. However, little is known about the targeted disruption of KRASG12V, partly due to a lack of specific inhibitors. Here, we leverage the degradation tag (dTAG) system to develop a KRASG12V-transgenic mouse model. We explored the therapeutic potential of KRASG12V degradation and characterized its effect on the tumor microenvironment (TME). Our study reveals that degradation of KRASG12V abolished lung and pancreatic tumors in mice and caused a robust inhibition of KRAS-regulated cancer-intrinsic signaling. Importantly, targeted degradation of KRASG12V reprogrammed the TME toward a stimulatory milieu and drove antitumor immunity, elicited mainly by effector and cytotoxic CD8+ T cells. Our work provides insights into the effect of KRASG12V degradation on both tumor progression and the immune response, highlighting degraders as a powerful strategy for targeting KRAS-mutant cancers.

Structure-Based Design of "Head-to-Tail" Macrocyclic PROTACs

Macrocyclization is a compelling strategy for conventional drug design for improving biological activity, target specificity, and metabolic stability, but it was rarely applied to the design of PROTACs possibly due to the mechanism and structural complexity. Herein, we report the rational design of the first series of "Head-to-Tail" macrocyclic PROTACs. The resulting molecule SHD913 exhibited pronounced Brd4 protein degradation with low nM DC50 values while almost totally dismissing the "hook effect", which is a general character and common concern of a PROTAC, in multiple cancer cell lines. Further biological evaluation revealed that the compound exhibited positive cooperativity and induced de novo protein-protein interactions (PPIs) in both biophysical and cellular NanoBRET assays and outperformed macroPROTAC-1 that is the first reported macrocyclic Brd4 PROTAC, in cellular assays. In vitro liver microsomal stability evaluation suggested that SHD913 demonstrated improved metabolic stability in different species compared with the linear counterpart. The co-crystal structure of Brd4BD2: SHD913: VCB (VHL, Elongin C and Elongin B) complex determination and molecular dynamics (MD) simulation also elucidated details of the chemical-induced PPIs and highlighted the crucial contribution of restricted conformation of SHD913 to the ternary complex formation. These results collectively support that macrocyclization could be an attractive and feasible strategy for a new PROTAC design.

Ringing medicinal chemistry: The importance of 3-membered rings in drug discovery

Scaffold-based drug design has become increasingly prominent in the pharmaceutical field due to the systematic and effective approach through which it facilitates the development of novel drugs. The identification of key scaffolds provides medicinal chemists with a fundamental framework for subsequent research. With mounting evidence suggesting that increased aromaticity could impede the chances of developmental success for oral drug candidates, there is an imperative need for a more thorough exploration of alternative ring systems to mitigate attrition risks. The unique characteristics exhibited by three-membered rings have led to their application in medicinal chemistry. This review explores the use of cyclopropane-, aziridine-, thiirane-, and epoxide-containing compounds in drug discovery, focusing on their roles in approved medicines and drug candidates. Specifically, the importance of the three-membered ring systems in rending biological activity for each drug molecule was highlighted. The undeniable therapeutic value and intriguing features presented by these compounds suggest significant pharmacological potential, providing justification for their incorporation into the design of novel drug candidates.

Molecular glue degrader for tumor treatment

Targeted Protein Degradation (TPD) represented by Proteolysis-Targeting Chimeras (PROTAC) is the frontier field in the research and development of antitumor therapy, in which oral drug HP518 Receives FDA Proceed Authorization for its IND Application for Prostate Cancer Treatment. Recently, molecular glue, functioning via degradation of the target protein is emerging as a promising modality for the development of therapeutic agents, while exhibits greater advantages over PROTAC, including improved efficiency, resistance-free properties, and the capacity to selectively target "undruggable" proteins. This marks a revolutionary advancement in the landscape of small molecule drugs. Given that molecular glue research is still in its early stage, we summarized the mechanisms of molecular glue, the promising drugs in clinical trials and diverse feasible design strategies for molecular glue therapeutics.

RAS-mutant leukaemia stem cells drive clinical resistance to venetoclax

Cancer driver mutations often show distinct temporal acquisition patterns, but the biological basis for this, if any, remains unknown. RAS mutations occur invariably late in the course of acute myeloid leukaemia, upon progression or relapsed/refractory disease1-6. Here, by using human leukaemogenesis models, we first show that RAS mutations are obligatory late events that need to succeed earlier cooperating mutations. We provide the mechanistic explanation for this in a requirement for mutant RAS to specifically transform committed progenitors of the myelomonocytic lineage (granulocyte-monocyte progenitors) harbouring previously acquired driver mutations, showing that advanced leukaemic clones can originate from a different cell type in the haematopoietic hierarchy than ancestral clones. Furthermore, we demonstrate that RAS-mutant leukaemia stem cells (LSCs) give rise to monocytic disease, as observed frequently in patients with poor responses to treatment with the BCL2 inhibitor venetoclax. We show that this is because RAS-mutant LSCs, in contrast to RAS-wild-type LSCs, have altered BCL2 family gene expression and are resistant to venetoclax, driving clinical resistance and relapse with monocytic features. Our findings demonstrate that a specific genetic driver shapes the non-genetic cellular hierarchy of acute myeloid leukaemia by imposing a specific LSC target cell restriction and critically affects therapeutic outcomes in patients.

Toward Dual Targeting of Catalytic and Gatekeeper Pockets in Cyclophilins Using a Macrocyclic Scaffold

Cyclophilins, especially cyclophilin A, are involved in a variety of diseases, including the life cycle of many viruses. An advanced macrocyclic inhibitor of cyclophilin was reported to bind the catalytic pocket but not the neighboring gatekeeper pocket. Here we describe macrocyclic cyclophilin inhibitors bearing side chains designed to reach out to the gatekeeper pocket. After establishing a suitable synthesis allowing for late-stage modification of the relevant positions, we explored this exit vector. This culminated in a rigid ornithine-resembling analogue as a versatile building block, which was also incorporated into the macrocyclic scaffold. The use of amines as the gatekeeper-engaging modality was invalidated, but the exit vector was successfully established as a promising position for future modifications. Further work is needed to identify suitable motifs to simultaneously engage the catalytic and gatekeeper pockets in this highly developed macrocyclic scaffold.

Advances in molecular glues: exploring chemical space and design principles for targeted protein degradation

The discovery of the E3 ligase cereblon (CRBN) as the target of thalidomide and its analogs revolutionized the field of targeted protein degradation (TPD). This ubiquitin-mediated degradation pathway was first harnessed by bivalent degraders. Recently, the emergence of low-molecular-weight molecular glue degraders (MGDs) has expanded the TPD landscape, because MGDs operate via the same mechanism while offering attractive physicochemical properties that are consistent with small-molecule therapeutics. This review delves into the discovery and advancement of MGDs, with case studies on cyclin K and the zinc finger protein IKZF2, highlighting the design principles, biological assays and therapeutic applications. Additionally, it examines the chemical space of molecular glues and outlines the collaborative efforts that are fueling innovation in this field.

Mechanisms of Resistance to Oncogenic KRAS Inhibition in Pancreatic Cancer

KRAS inhibitors demonstrate clinical efficacy in pancreatic ductal adenocarcinoma (PDAC); however, resistance is common. Among patients with KRASG12C-mutant PDAC treated with adagrasib or sotorasib, mutations in PIK3CA and KRAS, and amplifications of KRASG12C, MYC, MET, EGFR, and CDK6 emerged at acquired resistance. In PDAC cell lines and organoid models treated with the KRASG12D inhibitor MRTX1133, epithelial-to-mesenchymal transition and PI3K-AKT-mTOR signaling associate with resistance to therapy. MRTX1133 treatment of the KrasLSL-G12D/+; Trp53LSL-R172H/+; p48-Cre (KPC) mouse model yielded deep tumor regressions, but drug resistance ultimately emerged, accompanied by amplifications of Kras, Yap1, Myc, Cdk6, and Abcb1a/b, and co-evolution of drug-resistant transcriptional programs. Moreover, in KPC and PDX models, mesenchymal and basal-like cell states displayed increased response to KRAS inhibition compared to the classical state. Combination treatment with KRASG12D inhibition and chemotherapy significantly improved tumor control in PDAC mouse models. Collectively, these data elucidate co-evolving resistance mechanisms to KRAS inhibition and support multiple combination therapy strategies. Significance: Acquired resistance may limit the impact of KRAS inhibition in patients with PDAC. Using clinical samples and multiple preclinical models, we define heterogeneous genetic and non-genetic mechanisms of resistance to KRAS inhibition that may guide combination therapy approaches to improve the efficacy and durability of these promising therapies for patients. See related commentary by Marasco and Misale, p. 2018.