Therapeutic strategies to target RAS-mutant cancers

KRAS inhibitor-resistance in MET-amplified KRAS G12C non-small cell lung cancer induced by RAS- and non-RAS-mediated cell signaling mechanisms

PURPOSE

Treatment with KRAS ^G12C inhibitors such as sotorasib can produce substantial regression of tumors in some patients with non-small cell lung cancer (NSCLC). These patients require alternative treatment after acquiring resistance to the inhibitor. The mechanisms underlying this acquired resistance are unclear. The purpose of this study was to identify the mechanisms underlying acquired sotorasib resistance, and to explore potential treatments for rescuing patients with sotorasib-resistant KRAS ^G12C NSCLC cells.

EXPERIMENTAL DESIGN

Clones of sotorasib-sensitive KRAS ^G12C NSCLC H23 cells exposed to different concentrations of sotorasib were examined using whole-genomic transcriptome analysis, multiple receptor kinase phosphorylation analysis, and gene copy number evaluation. The underlying mechanisms of resistance were investigated using immunological examination, and a treatment aimed at overcoming resistance was tested in vitro and in vivo Results: Unbiased screening detected subclonal evolution of MET amplification in KRAS ^G12C NSCLC cells that had developed resistance to sotorasib in vitro MET knockdown using siRNA restored susceptibility to sotorasib in these resistant cells. MET activation by its amplification reinforced RAS cycling from its inactive form to its active form. In addition to RAS-mediated MEK-ERK induction, MET induced AKT activation independently of RAS. Crizotinib, a MET inhibitor, restored sensitivity to sotorasib by eliminating RAS-MEK-ERK as well as AKT signaling. MET/KRAS ^G12C dual inhibition led to tumor shrinkage in sotorasib-resistant xenograft mice.

CONCLUSIONS

MET amplification leads to the development of resistance to KRAS ^G12C inhibitors in NSCLC. Dual blockade of MET and KRAS ^G12C could be a treatment option for MET amplified, KRAS ^G12C-mutated NSCLC.

Small molecule Son of Sevenless 1 (SOS1) inhibitors: a review of the patent literature

Introduction: Up to 30% of all human cancers are driven by the overactivation of RAS signaling. Son of Sevenless 1 (SOS1) is a central node in RAS signaling pathways and modulation of SOS1-mediated RAS activation represents a unique opportunity for treating RAS-addicted cancers. Several recent publications and patent documents have demonstrated the ability of small molecules to affect the activation of RAS by SOS1 and have shown their potential for the treatment of cancers driven by RAS mutants.Areas covered: Documents focusing on both small-molecule inhibitors and activators of the SOS1:RAS interaction and their potential use as cancer therapeutics are covered. A total of 10 documents from 4 applicants are evaluated with discussion focusing on structural modifications of these compounds as well as relevant preclinical data.Expert opinion: The last decade has seen a significant increase in research and disclosures in the development of small-molecule SOS1 inhibitors. Considering the promising data that have been disclosed, interest in this area of research will likely remain strong for the foreseeable future. With the first SOS1 inhibitor currently in phase I clinical trials, the outcome of these trials will likely influence future development of SOS1 inhibitors for treatment of RAS-driven cancers.

ABHD17 regulation of plasma membrane palmitoylation and N-Ras-dependent cancer growth

Multiple Ras proteins, including N-Ras, depend on a palmitoylation/depalmitoylation cycle to regulate their subcellular trafficking and oncogenicity. General lipase inhibitors such as Palmostatin M (Palm M) block N-Ras depalmitoylation, but lack specificity and target several enzymes displaying depalmitoylase activity. Here, we describe ABD957, a potent and selective covalent inhibitor of the ABHD17 family of depalmitoylases, and show that this compound impairs N-Ras depalmitoylation in human acute myeloid leukemia (AML) cells. ABD957 produced partial effects on N-Ras palmitoylation compared with Palm M, but was much more selective across the proteome, reflecting a plasma membrane-delineated action on dynamically palmitoylated proteins. Finally, ABD957 impaired N-Ras signaling and the growth of NRAS-mutant AML cells in a manner that synergizes with MAP kinase kinase (MEK) inhibition. Our findings uncover a surprisingly restricted role for ABHD17 enzymes as regulators of the N-Ras palmitoylation cycle and suggest that ABHD17 inhibitors may have value as targeted therapies for NRAS-mutant cancers.

DHA exhibits synergistic therapeutic efficacy with cisplatin to induce ferroptosis in pancreatic ductal adenocarcinoma via modulation of iron metabolism

Pancreatic ductal adenocarcinoma (PDAC) is an extremely lethal cancer with limited treatment options. Cisplatin (DDP) is used as a mainstay of chemotherapeutic agents in combination with other drugs or radiotherapy for PDAC therapy. However, DDP exhibits severe side-effects that can lead to discontinuation of therapy, and the acquired drug resistance of tumor cells presents serious clinical obstacles. Therefore, it is imperative to develop a more effective and less toxic therapeutic strategy. We and others have previously discovered that dihydroartemisinin (DHA) represents a safe and promising therapeutic agent to preferentially induce cancer cell ferroptosis. In the present study, we find that DHA could intensively strengthen the cytotoxicity of DDP and significantly reduce its effective concentrations both in vitro and in vivo. Combination of DHA and DDP synergistically inhibits the proliferation and induces DNA damage of PDAC cells. Mechanically, the combinative treatment impairs mitochondrial homeostasis, characterized by destroyed mitochondrial morphology, decreased respiratory capacity, reduced ATP production, and accumulated mitochondria-derived ROS. Further studies show that ferroptosis contributes to the cytotoxic effects in PDAC cells under the challenge of DHA and DDP, together with catastrophic accumulation of free iron and unrestricted lipid peroxidation. Moreover, pharmacologic depleting of the free iron reservoir or reconstituted expression of FTH contributes to the tolerance of DHA/DDP-induced ferroptosis, while iron addition accelerates the ferroptotic cell death. In summary, these results provide experimental evidence that DHA acts synergistically with DDP and renders PDAC cells vulnerable to ferroptosis, which may act as a promising therapeutic strategy.

Targeting KRAS4A splicing through the RBM39/DCAF15 pathway inhibits cancer stem cells

The commonly mutated human KRAS oncogene encodes two distinct KRAS4A and KRAS4B proteins generated by differential splicing. We demonstrate here that coordinated regulation of both isoforms through control of splicing is essential for development of Kras mutant tumors. The minor KRAS4A isoform is enriched in cancer stem-like cells, where it responds to hypoxia, while the major KRAS4B is induced by ER stress. KRAS4A splicing is controlled by the DCAF15/RBM39 pathway, and deletion of KRAS4A or pharmacological inhibition of RBM39 using Indisulam leads to inhibition of cancer stem cells. Our data identify existing clinical drugs that target KRAS4A splicing, and suggest that levels of the minor KRAS4A isoform in human tumors can be a biomarker of sensitivity to some existing cancer therapeutics.

Ferroptosis: an iron-dependent cell death form linking metabolism, diseases, immune cell and targeted therapy

Compared with the traditional forms of cell death-apoptosis, necrosis and autophagy, ferroptosis is a novel form of iron-dependent programmed cell death forms which is different from the above traditional forms of cell death. Brent R Stockwell, a Professor of Columbia University, firstly proposed that this from of cell death was named ferroptosis in 2012. The main characteristics of ferroptosis is increasing iron loading and driving a lot of lipid peroxide generated and ultimately lead to cell death. In this paper, the mechanism of ferroptosis, relationship between ferroptosis and common diseases and immune state of body are reviewed, and the inhibitors and inducers related to ferroptosis that have been found are summarized to provide medicine exploration targeted of ferroptosis and reference for the research in the future.

Strategies to tackle RAS-mutated metastatic colorectal cancer

The RAS oncogene is among the most commonly mutated in cancer. RAS mutations are identified in about half of patients diagnosed with metastatic colorectal cancer (mCRC), conferring poor prognosis and lack of response to anti-epidermal growth factor receptor (EGFR) antibodies. In the last decades, several investigational attempts failed in directly targeting RAS mutations, thus RAS was historically regarded as 'undruggable'. Recently, novel specific KRASG12C inhibitors showed promising results in different solid tumors, including mCRC, renewing interest in this biomarker as a target. In this review, we discuss different strategies of RAS targeting in mCRC, according to literature data in both clinical and preclinical settings. We recognized five main strategies focusing on those more promising: direct RAS targeting, targeting the mitogen-activated protein kinase (MAPK) pathway, harnessing RAS through immunotherapy combinations, RAS targeting through metabolic pathways, and finally other miscellaneous approaches. Direct KRASG12C inhibition is emerging as the most promising strategy in mCRC as well as in other solid malignancies. However, despite good disease control rates, tumor response and duration of response are still limited in mCRC. At this regard, combinational approaches with anti-epidermal growth factor receptor drugs or checkpoint inhibitors have been proposed to enhance treatment efficacy, based on encouraging results achieved in preclinical studies. Besides, concomitant therapies increasing metabolic stress are currently under evaluation and expected to also provide remarkable results in RAS codon mutations apart from KRASG12C. In conclusion, based on hereby reported efforts of translational research, RAS mutations should no longer be regarded as 'undruggable' and future avenues are now opening for translation in the clinic in mCRC.

Characterization of genetically defined sporadic and hereditary type 1 papillary renal cell carcinoma cell lines

Renal cell carcinoma (RCC) is not a single disease but is made up of several different histologically defined subtypes that are associated with distinct genetic alterations which require subtype specific management and treatment. Papillary renal cell carcinoma (pRCC) is the second most common subtype after conventional/clear cell RCC (ccRCC), representing ~20% of cases, and is subcategorized into type 1 and type 2 pRCC. It is important for preclinical studies to have cell lines that accurately represent each specific RCC subtype. This study characterizes seven cell lines derived from both primary and metastatic sites of type 1 pRCC, including the first cell line derived from a hereditary papillary renal carcinoma (HPRC)-associated tumor. Complete or partial gain of chromosome 7 was observed in all cell lines and other common gains of chromosomes 16, 17, or 20 were seen in several cell lines. Activating mutations of MET were present in three cell lines that all demonstrated increased MET phosphorylation in response to HGF and abrogation of MET phosphorylation in response to MET inhibitors. CDKN2A loss due to mutation or gene deletion, associated with poor outcomes in type 1 pRCC patients, was observed in all cell line models. Six cell lines formed tumor xenografts in athymic nude mice and thus provide in vivo models of type 1 pRCC. These type 1 pRCC cell lines provide a comprehensive representation of the genetic alterations associated with pRCC that will give insight into the biology of this disease and be ideal preclinical models for therapeutic studies.

Targeting p130Cas- and microtubule-dependent MYC regulation sensitizes pancreatic cancer to ERK MAPK inhibition

To identify therapeutic targets for KRAS mutant pancreatic cancer, we conduct a druggable genome small interfering RNA (siRNA) screen and determine that suppression of BCAR1 sensitizes pancreatic cancer cells to ERK inhibition. Integrative analysis of genome-scale CRISPR-Cas9 screens also identify BCAR1 as a top synthetic lethal interactor with mutant KRAS. BCAR1 encodes the SRC substrate p130Cas. We determine that SRC-inhibitor-mediated suppression of p130Cas phosphorylation impairs MYC transcription through a DOCK1-RAC1-β-catenin-dependent mechanism. Additionally, genetic suppression of TUBB3, encoding the βIII-tubulin subunit of microtubules, or pharmacological inhibition of microtubule function decreases levels of MYC protein in a calpain-dependent manner and potently sensitizes pancreatic cancer cells to ERK inhibition. Accordingly, the combination of a dual SRC/tubulin inhibitor with an ERK inhibitor cooperates to reduce MYC protein and synergistically suppress the growth of KRAS mutant pancreatic cancer. Thus, we demonstrate that mechanistically diverse combinations with ERK inhibition suppress MYC to impair pancreatic cancer proliferation.

NRAS mutant melanoma: Towards better therapies

Genetic alterations affecting RAS proteins are commonly found in human cancers. Roughly a fourth of melanoma patients carry activating NRAS mutations, rendering this malignancy particularly challenging to treat. Although the development of targeted as well as immunotherapies led to a substantial improvement in the overall survival of non-NRAS^mut melanoma patients (e.g. BRAF^mut), patients with NRAS^mut melanomas have an overall poorer prognosis due to the high aggressiveness of RAS^mut tumors, lack of efficient targeted therapies or rapidly emerging resistance to existing treatments. Understanding how NRAS-driven melanomas develop therapy resistance by maintaining cell cycle progression and survival is crucial to develop more effective and specific treatments for this group of melanoma patients. In this review, we provide an updated summary of currently available therapeutic options for NRAS^mut melanoma patients with a focus on combined inhibition of MAPK signaling and CDK4/6-driven cell cycle progression and mechanisms of the inevitably developing resistance to these treatments. We conclude with an outlook on the most promising novel therapeutic approaches for melanoma patients with constitutively active NRAS. STATEMENT OF SIGNIFICANCE: An estimated 75000 patients are affected by NRAS^mut melanoma each year and these patients still have a shorter progression-free survival than BRAF^mut melanomas. Both intrinsic and acquired resistance occur in NRAS-driven melanomas once treated with single or combined targeted therapies involving MAPK and CDK4/6 inhibitors and/or checkpoint inhibiting immunotherapy. Oncolytic viruses, mRNA-based vaccinations, as well as targeted triple-agent therapy are promising alternatives, which could soon contribute to improved progression-free survival of the NRAS^mut melanoma patient group.

RAF-MEK-ERK pathway in cancer evolution and treatment

The RAF-MEK-ERK signaling cascade is a well-characterized MAPK pathway involved in cell proliferation and survival. The three-layered MAPK signaling cascade is initiated upon RTK and RAS activation. Three RAF isoforms ARAF, BRAF and CRAF, and their downstream MEK1/2 and ERK1/2 kinases constitute a coherently orchestrated signaling module that directs a range of physiological functions. Genetic alterations in this pathway are among the most prevalent in human cancers, which consist of numerous hot-spot mutations such as BRAF^V600E. Oncogenic mutations in this pathway often override otherwise tightly regulated checkpoints to open the door for uncontrolled cell growth and neoplasia. The crosstalk between the RAF-MEK-ERK axis and other signaling pathways further extends the proliferative potential of this pathway in human cancers. In this review, we summarize the molecular architecture and physiological functions of the RAF-MEK-ERK pathway with emphasis on its dysregulations in human cancers, as well as the efforts made to target the RAF-MEK-ERK module using small molecule inhibitors.

Recurrent Somatic MAP2K1 Mutations in Papillary Thyroid Cancer and Colorectal Cancer

Mitogen-activated protein kinase kinase 1 (MAP2K1) is a dual specificity protein kinase that phosphorylates both threonine and tyrosine residues in ERK. MAP2K1 mutations have been identified in several cancers. However, their role in Middle Eastern papillary thyroid cancer (PTC) and colorectal cancer (CRC) is lacking. In this study, we evaluated the prevalence of MAP2K1 mutations in a large cohort of Middle Eastern PTC and CRC using whole-exome and Sanger sequencing technology. In the discovery cohort of 100 PTC and 100 CRC cases (comprising 50 MAPK mutant and 50 MAPK wildtype cases each), we found one MAP2K1 mutation each in PTC and CRC, both of which were MAPK wildtype. We further analyzed 286 PTC and 289 CRC MAPK wildtype cases and found three MAP2K1 mutant PTC cases and two MAP2K1 mutant CRC cases. Thus, the overall prevalence of MAP2K1 mutation in MAPK wildtype cases was 1.1% (4/336) in PTC and 0.9% (3/339) in CRC. Histopathologically, three of the four MAP2K1 mutant PTC cases were follicular variant and all four tumors were unifocal with absence of extra-thyroidal extension. All the three CRC cases harboring MAP2K1 mutation were of older age (> 50 years) and had moderately differentiated stage II/III tumors located in the left colon. In conclusion, this is the first comprehensive report of MAP2K1 somatic mutations prevalence in PTC and CRC from this ethnicity. The mutually exclusive nature of MAP2K1 and MAPK mutations suggests that each of these mutation may function as an initiating mutation driving tumorigenesis through MAPK signaling pathway.

The Role of Wild-Type RAS in Oncogenic RAS Transformation

The RAS family of oncogenes (HRAS, NRAS, and KRAS) are among the most frequently mutated protein families in cancers. RAS-mutated tumors were originally thought to proliferate independently of upstream signaling inputs, but we now know that non-mutated wild-type (WT) RAS proteins play an important role in modulating downstream effector signaling and driving therapeutic resistance in RAS-mutated cancers. This modulation is complex as different WT RAS family members have opposing functions. The protein product of the WT RAS allele of the same isoform as mutated RAS is often tumor-suppressive and lost during tumor progression. In contrast, RTK-dependent activation of the WT RAS proteins from the two non-mutated WT RAS family members is tumor-promoting. Further, rebound activation of RTK–WT RAS signaling underlies therapeutic resistance to targeted therapeutics in RAS-mutated cancers. The contributions of WT RAS to proliferation and transformation in RAS-mutated cancer cells places renewed interest in upstream signaling molecules, including the phosphatase/adaptor SHP2 and the RasGEFs SOS1 and SOS2, as potential therapeutic targets in RAS-mutated cancers.

A Phase 2 Clinical Trial of Trametinib and Low-Dose Dabrafenib in Patients with Advanced Pretreated NRASQ61R/K/L Mutant Melanoma (TraMel-WT)

BACKGROUND

MEK-inhibitor monotherapy has activity in advanced NRAS^Q61R/K/L mutant melanoma but is associated with dose-limiting cutaneous toxicity. The combination of a BRAF- with a MEK-inhibitor at their full dose (as in BRAF^V600E/K mutant melanoma) has low cutaneous toxicity. It is unknown whether a low dose of BRAF-inhibitor can mitigate the skin toxicity associated with full-dose MEK-inhibitor treatment in patients with advanced NRAS^Q61R/K/L mutant melanoma.

METHODS

This two-stage phase 2 clinical trial investigated trametinib 2 mg once daily in patients with advanced NRAS^Q61R/K/L mutant melanoma who were pretreated with immune checkpoint inhibitors. In case of trametinib-related cutaneous toxicity, low-dose dabrafenib (50 mg twice daily) was added to prevent recurrent cutaneous toxicity (pre-amendment). Following an amendment, trametinib was combined upfront with low-dose dabrafenib (post-amendment). Objective response rate (ORR) served as the primary endpoint.

RESULTS

All 6 patients enrolled pre-amendment developed trametinib-related cutaneous toxicity, necessitating treatment interruption. Combining trametinib with low-dose dabrafenib prevented recurrent skin toxicity thereafter. Trametinib-related skin toxicity was effectively mitigated in all 10 patients post-amendment. In all 16 included patients, the ORR and disease control rate was 6.3% (1 partial response) and 50.0%, respectively. The trial was halted after the first stage.

CONCLUSIONS

Combining full-dose trametinib with low-dose dabrafenib can mitigate MEK-inhibitor-related skin toxicity but was insufficiently active in this patient population. This combination can be of further interest for the treatment of MEK-inhibitor-sensitive tumors.

Development of a single-chain fragment variable fused-mutant HALT-1 recombinant immunotoxin against G12V mutated KRAS colorectal cancer cells

Background

KRAS oncogenes harboring codon G12 and G13 substitutions are considered gatekeeper mutations which drive oncogenesis in many cancers. To date, there are still no target-specific vaccines or drugs available against this genotype, thus reinforcing the need towards the development of targeted therapies such as immunotoxins.

Methods

This study aims to develop a recombinant anti-mKRAS scFv-fused mutant Hydra actinoporin-like-toxin-1 (mHALT-1) immunotoxin that is capable of recognizing and eradicating codon-12 mutated k-ras antigen abnormal cells. One G13D peptide mimotope (164-D) and one G12V peptide mimotope (68-V) were designed to elicit antigen specific IgG titres against mutated K-ras antigens in immunised Balb/c mice. The RNA was extracted from splenocytes following ELISA confirmation on post-immunized mice sera and was reverse transcribed into cDNA. The scFv combinatorial library was constructed from cDNA repertoire of variable regions of heavy chain (V_H) and light chain (V_L) fusions connected by a flexible glycine-serine linker, using splicing by overlap extension PCR (SOE-PCR). Anti-mKRAS G12V and G13D scFvs were cloned in pCANTAB5E phagemid and superinfected with helper phage. After few rounds of bio-panning, a specific mKRAS G12V and G13D scFv antibody against G12V and G13D control mimotope was identified and confirmed using ELISA without any cross-reactivity with other mimotopes or controls. Subsequently, the anti-mKRAS scFv was fused to mHALT-1 using SOE-PCR and cloned in pET22b vector. Expressed recombinant immunotoxins were analyzed for their effects on cell proliferation by the MTT assay and targeted specificity by cell-based ELISA on KRAS-positive and KRAS-negative cancer cells.

Results

The V_H and V_L genes from spleen RNA of mice immunized with 164-D and 68-V were amplified and randomly linked together, using SOE-PCR producing band sizes about 750 bp. Anti-mKRAS G12V and G13D scFvs were constructed in phagemid pCANTAB5E vectors with a library containing 3.4 × 10⁶ and 2.9 × 10⁶ individual clones, respectively. After three rounds of bio-panning, the anti-mKRAS G12V-34 scFv antibody against G12V control mimotope was identified and confirmed without any cross-reactivity with other controls using ELISA. Anti-mKRAS G12V-34 scFv fragment was fused to mHALT-1 toxin and cloned in pET22b vector with expression as inclusion bodies in E. coli BL21(DE3) (molecular weight of ~46.8 kDa). After successful solubilization and refolding, the mHALT-1-scFv immunotoxin exhibited cytotoxic effects on SW-480 colorectal cancer cells with IC₅₀ of 25.39 μg/mL, with minimal cytotoxicity effect on NHDF cells.

Discussion

These results suggested that the development of such immunotoxins is potentially useful as an immunotherapeutic application against KRAS-positive malignancies.

Sensitivity and Resistance of Oncogenic RAS-Driven Tumors to Dual MEK and ERK Inhibition

Simple Summary

Mutations in RAS-family genes frequently cause different types of human cancers. Inhibitors of the MEK (mitogen-activated protein kinase) and ERK (extracellular signal-regulated kinase) protein kinases that function downstream of RAS proteins have shown some clinical benefits when used for the treatment of these cancers, but drug resistance frequently emerges. Here we show that combined treatment with MEK and ERK inhibitors blocks the emergence of resistance to either drug alone. However, if cancer cells have already developed resistance to MEK inhibitors or to ERK inhibitors, the combined therapy is frequently ineffective. These findings imply that these inhibitors should be used together for cancer therapy. We also show that drug resistance involves complex patterns of rewiring of cellular kinase signaling networks that do not overlap between each different cancer cell line. Nonetheless, we show that MAP4K4 is required for efficient cell proliferation in several different MEK/ERK inhibitor resistant cancer cell lines, uncovering a potential new therapeutic target.

Abstract

Oncogenic mutations in RAS family genes arise frequently in metastatic human cancers. Here we developed new mouse and cellular models of oncogenic Hras^G12V-driven undifferentiated pleomorphic sarcoma metastasis and of Kras^G12D-driven pancreatic ductal adenocarcinoma metastasis. Through analyses of these cells and of human oncogenic KRAS-, NRAS- and BRAF-driven cancer cell lines we identified that resistance to single MEK inhibitor and ERK inhibitor treatments arise rapidly but combination therapy completely blocks the emergence of resistance. The prior evolution of resistance to either single agent frequently leads to resistance to dual treatment. Dual MEK inhibitor plus ERK inhibitor therapy shows anti-tumor efficacy in an Hras^G12V-driven autochthonous sarcoma model but features of drug resistance in vivo were also evident. Array-based kinome activity profiling revealed an absence of common patterns of signaling rewiring in single or double MEK and ERK inhibitor resistant cells, showing that the development of resistance to downstream signaling inhibition in oncogenic RAS-driven tumors represents a heterogeneous process. Nonetheless, in some single and double MEK and ERK inhibitor resistant cell lines we identified newly acquired drug sensitivities. These may represent additional therapeutic targets in oncogenic RAS-driven tumors and provide general proof-of-principle that therapeutic vulnerabilities of drug resistant cells can be identified.

A Historic Perspective and Overview of H-Ras Structure, Oncogenicity, and Targeting

H-Ras is a unique isoform of the Ras GTPase family, one of the most prominently mutated oncogene families across the cancer landscape. Relative to other isoforms, though, mutations of H-Ras account for the smallest proportion of mutant Ras cancers. Yet, in recent years, there have been renewed efforts to study this isoform, especially as certain H-Ras-driven cancers, like those of the head and neck, have become more prominent. Important advances have therefore been made not only in the understanding of H-Ras structural biology but also in approaches designed to inhibit and impair its signaling activity. In this review, we outline historic and present initiatives to elucidate the mechanisms of H-Ras-dependent tumorigenesis as well as highlight ongoing developments in the quest to target this critical oncogene.

Mechanisms of Resistance to KRASG12C-Targeted Therapy

KRAS mutations are among the most common drivers of human carcinogenesis, and are associated with poor prognosis and an aggressive disease course. With the advent of KRAS^G12C inhibitors, the RAS protein is now targetable, with such inhibitors showing marked clinical responses across multiple tumor types. However, these responses are short-lived due to the development of resistance. Preclinical studies now suggest MAPK reactivation, stimulation of CDK4/6-dependent cell-cycle transition, and immune defects as possible mechanisms of resistance. Devising strategies to overcome such resistance mechanisms, which are a barrier to long-term clinical response, remain an active area of research. SIGNIFICANCE: Although KRAS-targeted cancer therapy is revolutionary, tumors rapidly develop resistance. Understanding the mechanisms driving this resistance and designing combination strategies to overcome it are integral to achieving long-term disease control.

Quantifying single-cell ERK dynamics in colorectal cancer organoids reveals EGFR as an amplifier of oncogenic MAPK pathway signalling

Direct targeting of the downstream mitogen-activated protein kinase (MAPK) pathway to suppress extracellular-regulated kinase (ERK) activation in KRAS and BRAF mutant colorectal cancer (CRC) has proven clinically unsuccessful, but promising results have been obtained with combination therapies including epidermal growth factor receptor (EGFR) inhibition. To elucidate the interplay between EGF signalling and ERK activation in tumours, we used patient-derived organoids (PDOs) from KRAS and BRAF mutant CRCs. PDOs resemble in vivo tumours, model treatment response and are compatible with live-cell microscopy. We established real-time, quantitative drug response assessment in PDOs with single-cell resolution, using our improved fluorescence resonance energy transfer (FRET)-based ERK biosensor EKAREN5. We show that oncogene-driven signalling is strikingly limited without EGFR activity and insufficient to sustain full proliferative potential. In PDOs and in vivo, upstream EGFR activity rigorously amplifies signal transduction efficiency in KRAS or BRAF mutant MAPK pathways. Our data provide a mechanistic understanding of the effectivity of EGFR inhibitors within combination therapies against KRAS and BRAF mutant CRC.

KRAS G12C inhibition and innate immune targeting

INTRODUCTION

KRAS mutations drive tumorigenesis by altering cell signaling and the tumor immune microenvironment. Recent studies have shown promise for KRAS-G12C covalent inhibitors, which are advancing rapidly through clinical trials. The sequencing and combination of these agents with other therapies including immune checkpoint blockade (ICB) will benefit from strategies that also address the immune microenvironment to improve durability of response.

AREAS COVERED

This paper reviews KRAS signaling and discusses downstream effects on cytokine production and the tumor immune microenvironment. RAS targeted therapy is introduced and perspectives on therapeutic targeting of KRAS-G12C and its immunosuppressive tumor microenvironment are offered.

EXPERT OPINION

The availability of KRAS-G12C covalent inhibitors raises hopes for targeting this pervasive oncogene and designing better therapeutic combinations to promote anti-tumor immunity. A comprehensive mechanistic understanding of KRAS immunosuppression is required in order to prioritize agents for clinical trials.

Targeting loss of heterozygosity for cancer-specific immunotherapy

Developing therapeutic agents with potent antitumor activity that spare normal tissues remains a significant challenge. Clonal loss of heterozygosity (LOH) is a widespread and irreversible genetic alteration that is exquisitely specific to cancer cells. We hypothesized that LOH events can be therapeutically targeted by "inverting" the loss of an allele in cancer cells into an activating signal. Here we describe a proof-of-concept approach utilizing engineered T cells approximating NOT-gate Boolean logic to target counterexpressed antigens resulting from LOH events in cancer. The NOT gate comprises a chimeric antigen receptor (CAR) targeting the allele of human leukocyte antigen (HLA) that is retained in the cancer cells and an inhibitory CAR (iCAR) targeting the HLA allele that is lost in the cancer cells. We demonstrate that engineered T cells incorporating such NOT-gate logic can be activated in a genetically predictable manner in vitro and in mice to kill relevant cancer cells. This therapeutic approach, termed NASCAR (Neoplasm-targeting Allele-Sensing CAR), could, in theory, be extended to LOH of other polymorphic genes that result in altered cell surface antigens in cancers.

Targeting KRAS: The Elephant in the Room of Epithelial Cancers

Mutations of the proto-oncogene KRAS are the most frequent gain-of-function alterations found in cancer. KRAS is mutated in about 30% of all human tumors, but it could reach more than 90% in certain cancer types such as pancreatic adenocarcinoma. Although historically considered to be undruggable, a particular KRAS mutation, the G12C variant, has recently emerged as an actionable alteration especially in non-small cell lung cancer (NSCLC). KRASG12C and pan-KRAS inhibitors are being tested in clinical trials and have recently shown promising activity. Due to the difficulties in direct targeting of KRAS, other approaches are being explored. The inhibition of target upstream activators or downstream effectors of KRAS pathway has shown to be moderately effective given the evidence of emerging mechanisms of resistance. Various synthetic lethal partners of KRAS have recently being identified and the inhibition of some of those might prove to be successful in the future. The study of escape mechanisms to KRAS inhibition could support the utility of combination strategies in overcoming intrinsic and adaptive resistance and enhancing clinical benefit of KRASG12C inhibitors. Considering the role of the microenvironment in influencing tumor initiation and promotion, the immune tumor niche of KRAS mutant tumors has been deeply explored and characterized for its unique immunosuppressive skewing. However, a number of aspects remains to be fully understood, and modulating this tumor niche might revert the immunoresistance of KRAS mutant tumors. Synergistic associations of KRASG12C and immune checkpoint inhibitors are being tested.

The evolving landscape of biomarker testing for non-small cell lung cancer in Europe

The discovery of oncogenic driver mutations rendering non-small cell lung cancer (NSCLC) targetable by small-molecule inhibitors, and the development of immunotherapies, have revolutionised NSCLC treatment. Today, instead of non-selective chemotherapies, all patients with advanced NSCLC eligible for treatment (and increasing numbers with earlier, less extensive disease) require fast and comprehensive screening of biomarkers for first-line patient selection for targeted therapy, chemotherapy, or immunotherapy (with or without chemotherapy). To avoid unnecessary re-biopsies, biomarker screening before first-line treatment should also include markers that are actionable from second-line onwards; PD-L1 expression testing is also mandatory before initiating treatment. Population differences exist in the frequency of oncogenic driver mutations: EGFR mutations are more frequent in Asia than Europe, whereas the converse is true for KRAS mutations. In addition to approved first-line therapies, a number of emerging therapies are being investigated in clinical trials. Guidelines for biomarker testing vary by country, with the number of actionable targets and the requirement for extensive molecular screening strategies expected to increase. To meet diagnostic demands, rapid screening technologies for single-driver mutations have been implemented. Improvements in DNA- and RNA-based next-generation sequencing technologies enable analysis of a group of genes in one assay; however, turnaround times remain relatively long. Consequently, rapid screening technologies are being implemented alongside next-generation sequencing. Further challenges in the evolving landscape of biomarker testing in NSCLC are actionable primary and secondary resistance mechanisms to targeted therapies. Therefore, comprehensive testing on re-biopsies, collected at the time of disease progression, in combination with testing of circulating tumour DNA may provide important information to guide second- or third-line therapies. Furthermore, longitudinal biomarker testing can provide insights into tumour evolution and heterogeneity during the course of the disease. We summarise best practice strategies for Europe in the changing landscape of biomarker testing at diagnosis and during treatment.

KRAS G12C-Mutant Non-Small Cell Lung Cancer: Biology, Developmental Therapeutics, and Molecular Testing

Mutation in the gene that encodes Kirsten rat sarcoma viral oncogene homolog (KRAS) is the most common oncogenic driver in advanced non-small cell lung cancer, occurring in approximately 30% of lung adenocarcinomas. Over 80% of oncogenic KRAS mutations occur at codon 12, where the glycine residue is substituted by different amino acids, leading to genomic heterogeneity of KRas-mutant tumors. The KRAS glycine-to-cysteine mutation (G12C) composes approximately 44% of KRAS mutations in non-small cell lung cancer, with mutant KRas^G12C present in approximately 13% of all patients with lung adenocarcinoma. Mutant KRas has been an oncogenic target for decades, but no viable therapeutic agents were developed until recently. However, advances in KRas molecular modeling have led to the development and clinical testing of agents that directly inhibit mutant KRas^G12C. These agents include sotorasib (AMG-510), adagrasib (MRTX-849), and JNJ-74699157. In addition to testing for known actionable oncogenic driver alterations in EGFR, ALK, ROS1, BRAF, MET exon 14 skipping, RET, and NTRK and for the expression of programmed cell-death protein ligand 1, pathologists, medical oncologists, and community practitioners will need to incorporate routine testing for emerging biomarkers such as MET amplification, ERBB2 (alias HER2), and KRAS mutations, particularly KRAS G12C, considering the promising development of direct inhibitors of KRas^G12C protein.

Clinicopathological Features and Prognostic Value of KRAS/NRAS/BRAF Mutations in Colorectal Cancer Patients of Central China

The incidence of colorectal cancer (CRC) is increasing in China, with high mortality. Here, we aimed to evaluate the latest clinicopathological features and prognostic value of the KRAS/NRAS/BRAF mutation status in CRC patients in Central China. The clinical data of 1549 CRC patients with stage I-IV disease diagnosed at Union Hospital, Tongji Medical College of Huazhong University of Science and Technology from 2015 to 2017 were collected and analyzed retrospectively. KRAS/NRAS/BRAF mutations were detected by real-time quantitative polymerase chain reaction (q-PCR) in 410 CRC patients, with mutation frequencies of KRAS, NRAS and BRAF of 47.56%, 2.93% and 4.15%, respectively. The gene mutation status and clinicopathological characteristics of 410 patients with CRC who underwent qPCR were analyzed. The KRAS and BRAF gene mutations were related to the pathological differentiation and number of metastatic lymph nodes. The BRAF gene mutation was also associated with cancer thrombosis in blood vessels. Cox regression analysis showed that there was no statistically significant difference in the overall survival (OS) between patients with KRAS, NRAS mutants and wild-type CRC patients, while the BRAF gene mutation was negatively correlated with the OS rate of CRC patients. It is suggested that the BRAF gene mutation may be an independent risk factor for the prognosis of CRC.

Two Targets, One Hit: new Anticancer Therapeutics to Prevent Tumorigenesis Without Cardiotoxicity

A serious adverse effect of cancer therapies is cardiovascular toxicity, which significantly limits the widespread use of antineoplastic agents. The promising new field of cardio-oncology offers the identification of potent anti-cancer therapeutics that effectively inhibit cancer cell proliferation without causing cardiotoxicity. Future introduction of recently identified cardio-safe compounds into clinical practice (including ERK dimerization inhibitors or BAX allosteric inhibitors) is expected to help oncologists avoid unwanted cardiological complications associated with therapeutic interventions.

Matched Targeted Therapy for Pediatric Patients with Relapsed, Refractory, or High-Risk Leukemias: A Report from the LEAP Consortium

Despite a remarkable increase in the genomic profiling of cancer, integration of genomic discoveries into clinical care has lagged behind. We report the feasibility of rapid identification of targetable mutations in 153 pediatric patients with relapsed/refractory or high-risk leukemias enrolled on a prospective clinical trial conducted by the LEAP Consortium. Eighteen percent of patients had a high confidence Tier 1 or 2 recommendation. We describe clinical responses in the 14% of patients with relapsed/refractory leukemia who received the matched targeted therapy. Further, in order to inform future targeted therapy for patients, we validated variants of uncertain significance, performed ex vivo drug-sensitivity testing in patient leukemia samples, and identified new combinations of targeted therapies in cell lines and patient-derived xenograft models. These data and our collaborative approach should inform the design of future precision medicine trials. SIGNIFICANCE: Patients with relapsed/refractory leukemias face limited treatment options. Systematic integration of precision medicine efforts can inform therapy. We report the feasibility of identifying targetable mutations in children with leukemia and describe correlative biology studies validating therapeutic hypotheses and novel mutations.See related commentary by Bornhauser and Bourquin, p. 1322.This article is highlighted in the In This Issue feature, p. 1307.

Mechanistic insights into the effect of phosphorylation on Ras conformational dynamics and its interactions with cell signaling proteins

Ras undergoes interconversion between the active GTP-bound state and the inactive GDP-bound state. This GTPase cycle, which controls the activities of Ras, is accelerated by Ras GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (SOS). Oncogenic Ras mutations could affect the GTPase cycle and impair Ras functions. Additionally, Src-induced K-Ras Y32/64 dual phosphorylation has been reported to disrupt GTPase cycle and hinder Ras downstream signaling. However, the underlying mechanisms remain unclear. To address this, we performed molecular dynamics simulations (~30 μs in total) on unphosphorylated and phosphorylated K-Ras4B in GTP- and GDP-bound states, and on their complexes with GTPase cycle regulators (GAP and SOS) and the effector protein Raf. We found that K-Ras4B dual phosphorylation mainly alters the conformation at the nucleotide binding site and creates disorder at the catalytic site, resulting in the enlargement of GDP binding pocket and the retard of Ras-GTP intrinsic hydrolysis. We observed phosphorylation-induced shift in the distribution of Ras-GTP inactive-active sub-states and recognized potential druggable pockets in the phosphorylated Ras-GTP. Moreover, decreased catalytic competence or signal delivery abilities due to reduced binding affinities and/or distorted catalytic conformations of GAP, SOS and Raf were observed. In addition, the allosteric pathway from Ras/Raf interface to the distal Raf L4 loop was compromised by Ras phosphorylation. These results reveal the mechanisms by which phosphorylation influences the intrinsic or GAP/SOS catalyzed transformations between GTP- and GDP-bound states of Ras and its signal transduction to Raf. Our findings project Ras phosphorylation as a target for cancer drug discovery.

The ERK mitogen-activated protein kinase signaling network: the final frontier in RAS signal transduction

The RAF-MEK-ERK mitogen-activated protein kinase (MAPK) cascade is aberrantly activated in a diverse set of human cancers and the RASopathy group of genetic developmental disorders. This protein kinase cascade is one of the most intensely studied cellular signaling networks and has been frequently targeted by the pharmaceutical industry, with more than 30 inhibitors either approved or under clinical evaluation. The ERK-MAPK cascade was originally depicted as a serial and linear, unidirectional pathway that relays extracellular signals, such as mitogenic stimuli, through the cytoplasm to the nucleus. However, we now appreciate that this three-tiered protein kinase cascade is a central core of a complex network with dynamic signaling inputs and outputs and autoregulatory loops. Despite our considerable advances in understanding the ERK-MAPK network, the ability of cancer cells to adapt to the inhibition of key nodes reveals a level of complexity that remains to be fully understood. In this review, we summarize important developments in our understanding of the ERK-MAPK network and identify unresolved issues for ongoing and future study.

The State-of-the-Art of Phase II/III Clinical Trials for Targeted Pancreatic Cancer Therapies

Pancreatic cancer is a devastating disease with very poor prognosis. Currently, surgery followed by adjuvant chemotherapy represents the only curative option which, unfortunately, is only available for a small group of patients. The majority of pancreatic cancer cases are diagnosed at advanced or metastatic stage when surgical resection is not possible and treatment options are limited. Thus, novel and more effective therapeutic strategies are urgently needed. Molecular profiling together with targeted therapies against key hallmarks of pancreatic cancer appear as a promising approach that could overcome the limitations of conventional chemo- and radio-therapy. In this review, we focus on the latest personalised and multimodal targeted therapies currently undergoing phase II or III clinical trials. We discuss the most promising findings of agents targeting surface receptors, angiogenesis, DNA damage and cell cycle arrest, key signalling pathways, immunotherapies, and the tumour microenvironment.

Tumor Burden and Immunotherapy: Impact on Immune Infiltration and Therapeutic Outcomes

Cancer immunotherapy has revolutionized the treatment landscape in medical oncology, but its efficacy has been variable across patients. Biomarkers to predict such differential response to immunotherapy include cytotoxic T lymphocyte infiltration, tumor mutational burden, and microsatellite instability. A growing number of studies also suggest that baseline tumor burden, or tumor size, predicts response to immunotherapy. In this review, we discuss the changes in immune profile and therapeutic responses that occur with increasing tumor size. We also overview therapeutic approaches to reduce tumor burden and favorably modulate the immune microenvironment of larger tumors.

The level of oncogenic Ras determines the malignant transformation of Lkb1 mutant tissue in vivo

The genetic and metabolic heterogeneity of RAS-driven cancers has confounded therapeutic strategies in the clinic. To address this, rapid and genetically tractable animal models are needed that recapitulate the heterogeneity of RAS-driven cancers in vivo. Here, we generate a Drosophila melanogaster model of Ras/Lkb1 mutant carcinoma. We show that low-level expression of oncogenic Ras (RasLow) promotes the survival of Lkb1 mutant tissue, but results in autonomous cell cycle arrest and non-autonomous overgrowth of wild-type tissue. In contrast, high-level expression of oncogenic Ras (RasHigh) transforms Lkb1 mutant tissue resulting in lethal malignant tumors. Using simultaneous multiview light-sheet microcopy, we have characterized invasion phenotypes of Ras/Lkb1 tumors in living larvae. Our molecular analysis reveals sustained activation of the AMPK pathway in malignant Ras/Lkb1 tumors, and demonstrate the genetic and pharmacologic dependence of these tumors on CaMK-activated Ampk. We further show that LKB1 mutant human lung adenocarcinoma patients with high levels of oncogenic KRAS exhibit worse overall survival and increased AMPK activation. Our results suggest that high levels of oncogenic KRAS is a driving event in the malignant transformation of LKB1 mutant tissue, and uncovers a vulnerability that may be used to target this aggressive genetic subset of RAS-driven tumors.

Broadening horizons: the role of ferroptosis in cancer

The discovery of regulated cell death processes has enabled advances in cancer treatment. In the past decade, ferroptosis, an iron-dependent form of regulated cell death driven by excessive lipid peroxidation, has been implicated in the development and therapeutic responses of various types of tumours. Experimental reagents (such as erastin and RSL3), approved drugs (for example, sorafenib, sulfasalazine, statins and artemisinin), ionizing radiation and cytokines (such as IFNγ and TGFβ1) can induce ferroptosis and suppress tumour growth. However, ferroptotic damage can trigger inflammation-associated immunosuppression in the tumour microenvironment, thus favouring tumour growth. The extent to which ferroptosis affects tumour biology is unclear, although several studies have found important correlations between mutations in cancer-relevant genes (for example, RAS and TP53), in genes encoding proteins involved in stress response pathways (such as NFE2L2 signalling, autophagy and hypoxia) and the epithelial-to-mesenchymal transition, and responses to treatments that activate ferroptosis. Herein, we present the key molecular mechanisms of ferroptosis, describe the crosstalk between ferroptosis and tumour-associated signalling pathways, and discuss the potential applications of ferroptosis in the context of systemic therapy, radiotherapy and immunotherapy.

New advances in the clinical management of RAS and BRAF mutant colorectal cancer patients

INTRODUCTION

In colorectal carcinogenesis, genetic alterations in RAS and BRAF oncogenes play an important role for cancer initiation and/or progression and represent a key focus in the search for targeted therapies. Despite many years of research and a great amount of studies, until very recently this pathway was considered extremely hard to downregulate to obtain a significant clinical impact in colorectal cancer patients. But better times are coming with the advent of new promising drugs and combinations strategies.

AREAS COVERED

In this review, we go over the biological characteristics of the MAPK pathway in colorectal tumors, while illustrating the clinical correlation of RAS and BRAF mutations, particularly its prognostic and predictive value. We also present newly data about recent improvements in the treatment strategy for patients harboring these types of tumors.

EXPERT COMMENTARY

With great advances in the knowledge of molecular basis of RAS and BRAF mutant colorectal cancer in conjunction with biotechnology development and the constant effort for improvement, in the near future many new therapeutic options would be available for the management of this group of patient with dismal prognosis.

Affinity maturation of the RLIP76 Ral binding domain to inform the design of stapled peptides targeting the Ral GTPases

Ral GTPases have been implicated as critical drivers of cell growth and metastasis in numerous Ras-driven cancers. We have previously reported stapled peptides, based on the Ral effector RLIP76, that can disrupt Ral signaling. Stapled peptides are short peptides that are locked into their bioactive form using a synthetic brace. Here, using an affinity maturation of the RLIP76 Ral-binding domain, we identified several sequence substitutions that together improve binding to Ral proteins by more than 20-fold. Hits from the selection were rigorously analyzed to determine the contributions of individual residues and two 1.5 Å cocrystal structures of the tightest-binding mutants in complex with RalB revealed key interactions. Insights gained from this maturation were used to design second-generation stapled peptides based on RLIP76 that exhibited vastly improved selectivity for Ral GTPases when compared with the first-generation lead peptide. The binding of second-generation peptides to Ral proteins was quantified and the binding site of the lead peptide on RalB was determined by NMR. Stapled peptides successfully competed with multiple Ral-effector interactions in cellular lysates. Our findings demonstrate how manipulation of a native binding partner can assist in the rational design of stapled peptide inhibitors targeting a protein-protein interaction.

Combined blockade of polo-like kinase and pan-RAF is effective against NRAS-mutant non-small cell lung cancer cells

NRAS mutation is rarely observed in non-small cell lung cancer (NSCLC) patients, and there are no approved treatments for NRAS-mutant NSCLC. Here, we evaluated the effect of pan-RAF inhibitors on human NRAS-mutant NSCLC cell lines and performed high-throughput screening using human kinome small interfering (si)RNA or CRISPR/Cas9 libraries to identify new targets for combination NSCLC treatment. Our results indicate that human NRAS-mutant NSCLC cells are moderately sensitive to pan-RAF inhibitors. High-throughput kinome screenings further showed that G2/M arrest, particularly following knockdown of polo-like kinase 1 (PLK1), can inhibit the growth of human NRAS-mutant NSCLC cells and those treated with the type II pan-RAF inhibitor LXH254. In addition, treatment with volasertib plus LXH254, resulting in dual blockade of PLK1 and pan-RAF, was found to be more effective than LXH254 monotherapy for inhibiting long-term cell viability, suggesting that this combination therapeutic strategy may lead to promising results in the clinic.

The novel rexinoid MSU-42011 is effective for the treatment of preclinical Kras-driven lung cancer

Effective drugs are needed for lung cancer, as this disease remains the leading cause of cancer-related deaths. Rexinoids are promising drug candidates for cancer therapy because of their ability to modulate genes involved in inflammation, cell proliferation or differentiation, and apoptosis through activation of the retinoid X receptor (RXR). The only currently FDA-approved rexinoid, bexarotene, is ineffective as a single agent for treating epithelial cancers and induces hypertriglyceridemia. Here, we used a previously validated screening paradigm to evaluate 23 novel rexinoids for biomarkers related to efficacy and safety. These biomarkers include suppression of inducible nitric oxide synthase (iNOS) and induction of sterol regulatory element-binding protein (SREBP). Because of its potent iNOS suppression, low SREBP induction, and activation of RXR, MSU-42011 was selected as our lead compound. We next used MSU-42011 to treat established tumors in a clinically relevant Kras-driven mouse model of lung cancer. KRAS is one of the most common driver mutations in human lung cancer and correlates with aggressive disease progression and poor patient prognosis. Ultrasound imaging was used to detect and monitor tumor development and growth over time in the lungs of the A/J mice. MSU-42011 markedly decreased the tumor number, size, and histopathology of lung tumors compared to the control and bexarotene groups. Histological sections of lung tumors in mice treated with MSU-42011 exhibited reduced cell density and fewer actively proliferating cells compared to the control and bexarotene-treated tumors. Although bexarotene significantly (p < 0.01) elevated plasma triglycerides and cholesterol, treatment with MSU-42011 did not increase these biomarkers, demonstrating a more favorable toxicity profile in vivo. The combination of MSU-42011 and carboplatin and paclitaxel reduced macrophages in the lung and increased activation markers of CD8+T cells compared to the control groups. Our results validate our screening paradigm for in vitro testing of novel rexinoids and demonstrate the potential for MSU-42011 to be developed for the treatment of KRAS-driven lung cancer.

Small-Molecule Inhibitors Directly Targeting KRAS as Anticancer Therapeutics

KRAS, the most frequently mutated oncogene, plays a predominant role in driving initiation and progression of cancers. Decades of effort to target KRAS using small molecules has been unsuccessful, causing KRAS to be considered an "undruggable" cancer target. However, this view began to change recently, as drug discovery techniques have developed several KRAS G12C allosteric inhibitors that are currently being evaluated in clinical trials. Herein we provide an in-depth analysis of the structure and binding pockets of KRAS, medicinal chemistry optimization processes, and the biological characterization of small-molecule inhibitors that directly target KRAS, including covalent allosteric inhibitors specific for the G12C mutant, GTP-competitive inhibitors targeting the nucleotide-binding site, and protein-protein interaction inhibitors that bind in the switch I/II pocket or the A59 site. Additionally, we propose potential challenges faced by these new classes of KRAS inhibitors under clinical evaluation.

Nanoformulation of Apolipoprotein E3-Tagged Liposomal Nanoparticles for the co-Delivery of KRAS-siRNA and Gemcitabine for Pancreatic Cancer Treatment

PURPOSE

KRAS is the most frequently mutated gene in human cancers, and ~ 90% of pancreatic cancers exhibit KRAS mutations. Despite the well-known role of KRAS in malignancies, directly inhibiting KRAS is challenging.

METHODS

In this study, we successfully synthesized apolipoprotein E3-based liposomes for the co-delivery of gemcitabine (GEM) and a small interfering RNA targeting KRAS (KRAS-siRNA) to improve the efficacy of pancreatic cancer treatment.

RESULTS

Apolipoprotein E3 self-assembly on the liposome surface led to a substantial increase in its internalization in PANC1 human pancreatic cancer cells. KRAS-siRNA led to downregulated KRAS protein expression and KRAS-dependent carcinogenic pathways, resulting in the inhibition of cell proliferation, cell cycle arrest, increased apoptosis, and suppression of tumor progression. The combination of KRAS-siRNA and GEM induced a synergistic improvement in cell apoptosis and significantly lower cell viability compared with single-agent therapy. The low IC₅₀ value of A3-SGLP might be attributed to potentiation of the anticancer effect of GEM by siRNA-mediated silencing of KRAS mutations, thereby inducing synergistic effects on cancer cells.

CONCLUSION

A3-SGLP led to a marked decrease in the overall tumor burden and did not show any signs of toxicity. Therefore, the combination of KRAS-siRNA and GEM holds great potential for the treatment of pancreatic cancer.

Structure of two G-quadruplexes in equilibrium in the KRAS promoter

KRAS is one of the most mutated oncogenes and still considered an undruggable target. An alternative strategy would consist in targeting its gene rather than the protein, specifically the formation of G-quadruplexes (G4) in its promoter. G4 are secondary structures implicated in biological processes, which can be formed among G-rich DNA (or RNA) sequences. Here we have studied the major conformations of the commonly known KRAS 32R, or simply 32R, a 32 residue sequence within the KRAS Nuclease Hypersensitive Element (NHE) region. We have determined the structure of the two major stable conformers that 32R can adopt and which display slow equilibrium (>ms) with each other. By using different biophysical methods, we found that the nucleotides G9, G25, G28 and G32 are particularly implicated in the exchange between these two conformations. We also showed that a triad at the 3' end further stabilizes one of the G4 conformations, while the second conformer remains more flexible and less stable.

Tumor regression and resistance mechanisms upon CDK4 and RAF1 inactivation in KRAS/P53 mutant lung adenocarcinomas

KRAS mutant lung adenocarcinomas remain intractable for targeted therapies. Genetic interrogation of KRAS downstream effectors, including the MAPK pathway and the interphase CDKs, identified CDK4 and RAF1 as the only targets whose genetic inactivation induces therapeutic responses without causing unacceptable toxicities. Concomitant CDK4 inactivation and RAF1 ablation prevented tumor progression and induced complete regression in 25% of KRAS/p53-driven advanced lung tumors, yet a significant percentage of those tumors that underwent partial regression retained a population of CDK4/RAF1-resistant cells. Characterization of these cells revealed two independent resistance mechanisms implicating hypermethylation of several tumor suppressors and increased PI3K activity. Importantly, these CDK4/RAF1-resistant cells can be pharmacologically controlled. These studies open the door to new therapeutic strategies to treat KRAS mutant lung cancer, including resistant tumors.

Regulation of CD47 expression in cancer cells

CD47 is overexpressed in various types of cancers and it can directly bind with SIRPα, which is mainly located on macrophages. The binding of CD47-SIRPα transmits a “don't eat me” signal, which can prevent cancer cells from immune clearance. Targeting the phagocytosis checkpoint of CD47-SIRPα axis has shown remarkable anticancer effect in preclinical and clinical research, which indicates the potential application of CD47-SIRPα blockade for cancer treatment. In this case, the comprehensive description of the regulation of CD47 in different types of cancer cells has significant implications for furthering our understanding of the role of CD47 in cancer. Based on the current reports, we summarized the regulatory factors, i.e., cytokines, oncogenes, microRNAs as well as enzymes, of CD47 expression in cancer cells. Accordingly, we also proposed several points needing further research, hoping to provide useful insights for the future investigation on the regulation of CD47 in cancers.

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Cytokines, oncogenes, microRNAs and enzymes regulate CD47 expression in cancer.

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CD47 expression could be regulated at the transcriptional, post-transcriptional and post-translational modification level.

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Further studies are required to determine other factors that regulate CD47 expression.

The Emerging Role of Ras Pathway Signaling in Pediatric Cancer

As genomic sequencing has become more widely available, the high prevalence of Ras pathway mutations in pediatric diseases has begun to emerge. Germline Ras-activating mutations have been known to contribute to cancer predisposition in a group of disorders known as the RASopathies, and now large pediatric sequencing studies have identified frequent somatic Ras pathway alterations across a diverse group of pediatric malignancies. These include glial brain tumors, relapsed high-risk neuroblastoma, embryonal rhabdomyosarcoma, acute myeloid leukemia, and relapsed acute lymphoblastic leukemia, and their prognostic impact is becoming increasingly better understood. Clinically, there has been success in targeting the Ras pathway in pediatric diseases, including the use of MEK inhibitors in plexiform neurofibromas associated with neurofibromatosis type 1 and the use of Ras pathway inhibitors in low-grade gliomas. Given the importance of this pathway in pediatric cancer, it is imperative that future studies strive to better understand the functional significance of these mutations, including their role in tumor growth and treatment resistance and how they can be better targeted to improve outcomes.

Tailored Chemodynamic Nanomedicine Improves Pancreatic Cancer Treatment via Controllable Damaging Neoplastic Cells and Reprogramming Tumor Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) strongly resists standard therapies since KRAS-mutated cancer cells harbor endogenous resistance toward chemotherapy-induced apoptosis and tumor-associated macrophages (TAMs) activate stroma cells to create the nearly impenetrable matrix. Herein, we developed a tailored nanocomplex through the self-assembly of synthetic 4-(phosphonooxy)phenyl-2,4-dinitrobenzenesulfonate and Fe³⁺ followed by hyaluronic acid decoration, realizing chemodynamic therapy (CDT) to combat PDAC. By controllably releasing its components in a GSH-sensitive manner under the distinctive redox homeostasis in cancer cells and TAMs, the nanocomplex selectively triggered a Fenton reaction to induce oxidative damage in cancer cells and simultaneously repolarized TAMs to deactivate stromal cells and thus attenuate stroma. Compared to gemcitabine, CDT remarkably inhibited tumor growth and prolonged animal survival in orthotopic PDAC models without noticeable side effects. This study provides a promising strategy to improve the treatment of PDAC through CDT-mediated controlled cancer cells damage and reprogramming of the stromal microenvironment.

Revisiting cancer hallmarks: insights from the interplay between oxidative stress and non-coding RNAs

Cancer is one of the most common disease worldwide, with complex changes and certain traits which have been described as “The Hallmarks of Cancer.” Despite increasing studies on in-depth investigation of these hallmarks, the molecular mechanisms associated with tumorigenesis have still not yet been fully defined. Recently, accumulating evidence supports the observation that microRNAs and long noncoding RNAs (lncRNAs), two main classes of noncoding RNAs (ncRNAs), regulate most cancer hallmarks through their binding with DNA, RNA or proteins, or encoding small peptides. Reactive oxygen species (ROS), the byproducts generated during metabolic processes, are known to regulate every step of tumorigenesis by acting as second messengers in cancer cells. The disturbance in ROS homeostasis leads to a specific pathological state termed “oxidative stress”, which plays essential roles in regulation of cancer progression. In addition, the interplay between oxidative stress and ncRNAs is found to regulate the expression of multiple genes and the activation of several signaling pathways involved in cancer hallmarks, revealing a potential mechanistic relationship involving ncRNAs, oxidative stress and cancer. In this review, we provide evidence that shows the essential role of ncRNAs and the interplay between oxidative stress and ncRNAs in regulating cancer hallmarks, which may expand our understanding of ncRNAs in the cancer development from the new perspective.

A novel targeted delivery system for drug-resistant hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC) is a severe malignant disease threatening human life. Current chemotherapy methods usually result in poor prognosis with low treatment efficacy and high side effects because of weak targeting specificity and fast acquisition of multidrug resistance (MDR). HCSP4 is a 12-aa peptide previously identified to specifically and sensitively bind to HCC cells and tissues. In this study, a novel class of HCC-targeting doxorubicin (DOX) delivery system, named HCSP4-Lipo-DOX-miR101, was synthesized and investigated for anticancer activity. HCSP4-Lipo-DOX-miR101 exhibited specific HCC targeting characteristics and satisfactory anticancer potency against HepG2 and HepG2/ADR cells, particularly HepG2/ADR cells. Moreover, the expression levels of genes closely related to membrane transport and cancer growth were significantly suppressed. This finding suggests that HCSP4-Lipo-DOX-miR101 can cause DOX-resistant HCC cell death and growth inhibition based on the targeting of MDR-related genes by miR-101. In conclusion, the findings of this study suggest that HCSP4-Lipo-DOX-miR101 may serve as a promising novel targeted delivery system for improving the therapeutic efficiency of drug-resistant hepatocellular carcinoma.

Rapid Improvement of the Performance Status and Reduction of the Tumor Size in KRAS-Mutated Colorectal Cancer Patient Receiving Binimetinib, Hydroxychloroquine, and Bevacizumab

Activating RAS mutations occur in more than a half of colorectal cancers (CRCs). RAS-mutated CRCs are notoriously difficult to treat given that they are characterized by the aggressive disease course and the lack of appropriate targeted therapies. Recent preclinical studies demonstrated that RAS-mutated cells escape from therapeutic MEK inhibition by the development of autophagy, and this escape may be prevented by the administration of an antimalarial drug, hydroxychloroquine. The available clinical data are limited to a single case observation involving a patient with KRAS-mutated pancreatic cancer. Here, we report a woman with KRAS G12D-mutated CRC, whose tumor did not respond to conventional therapy. The combination of binimetinib, hydroxychloroquine, and bevacizumab was administered as a last-hope option. The patient experienced rapid improvement of the performance status. The tumor lumps demonstrated 17% reduction in the size within the first 6 weeks of the therapy. This report calls for evaluation of the efficacy of a combination of MEK inhibitors and hydroxychloroquine, possibly with the addition of bevacizumab, in chemotherapy-resistant patients with RAS-mutated cancers.