An engineered chimeric toxin that cleaves activated mutant and wild-type RAS inhibits tumor growth

An enhanced intracellular delivery platform based on a distant diphtheria toxin homolog that evades pre-existing antitoxin antibodies

Targeted intracellular delivery of therapeutic proteins remains a significant unmet challenge in biotechnology. A promising approach is to leverage the intrinsic capabilities of bacterial toxins like diphtheria toxin (DT) to deliver a potent cytotoxic enzyme into cells with an associated membrane translocation moiety. Despite showing promising clinical efficacy, widespread deployment of DT-based therapeutics is complicated by the prevalence of pre-existing antibodies in the general population arising from childhood DT toxoid vaccinations, which impact the exposure, efficacy, and safety of these potent molecules. Here, we describe the discovery and characterization of a distant DT homolog from the ancient reptile pathogen Austwickia chelonae that we have dubbed chelona toxin (ACT). We show that ACT is comparable to DT structure and function in all respects except that it is not recognized by pre-existing anti-DT antibodies circulating in human sera. Furthermore, we demonstrate that ACT delivers heterologous therapeutic cargos into target cells more efficiently than DT. Our findings highlight ACT as a promising new chassis for building next-generation immunotoxins and targeted delivery platforms with improved pharmacokinetic and pharmacodynamic properties.

Therapeutic expression of RAS Degrader RRSP in Pancreatic Cancer via Nanocarrier-mediated mRNA delivery

About one-third of all human cancers encode abnormal RAS proteins locked in a constitutively activated state to drive malignant transformation and uncontrolled tumor growth. Despite progress in development of small molecules for treatment of mutant KRAS cancers, there is a need for a pan-RAS inhibitor that is effective against all RAS isoforms and variants and that avoids drug resistance. We have previously shown that the naturally occurring bacterial enzyme RAS/RAP1-specific endopeptidase (RRSP) is a potent RAS degrader that can be re-engineered as a biologic therapy to induce regression of colorectal, breast, and pancreatic tumors. Here, we have developed a strategy for in vivo expression of this RAS degrader via mRNA delivery using a synthetic nonviral gene delivery platform composed of the poly(ethylene glycol)-b-poly(propylene sulfide) (PEG-b-PPS) block copolymer conjugated to a dendritic cationic peptide (PPDP2). Using this strategy, PPDP2 is shown to deliver mRNA to both human and mouse pancreatic cells resulting in RRSP gene expression, activity, and loss of cell proliferation. Further, pancreatic tumors are reduced with residual tumors lacking detectable RAS and phosphorylated ERK. These data support that mRNA-loaded synthetic nanocarrier delivery of a RAS degrader can interrupt the RAS signaling system within pancreatic cancer cells while avoiding side effects during therapy.

Structural perspectives on recent breakthrough efforts toward direct drugging of RAS and acquired resistance

The Kirsten rat sarcoma viral oncoprotein homolog (KRAS) is currently a primary focus of oncologists and translational scientists, driven by exciting results with KRAS-targeted therapies for non-small cell lung cancer (NSCLC) patients. While KRAS mutations continue to drive high cancer diagnosis and death, researchers have developed unique strategies to target KRAS variations. Having been investigated over the past 40 years and considered "undruggable" due to the lack of pharmacological binding pockets, recent breakthroughs and accelerated FDA approval of the first covalent inhibitors targeting KRASG12C, have largely sparked further drug development. Small molecule development has targeted the previously identified primary location alterations such as G12, G13, Q61, and expanded to address the emerging secondary mutations and acquired resistance. Of interest, the non-covalent KRASG12D targeting inhibitor MRTX-1133 has shown promising results in humanized pancreatic cancer mouse models and is seemingly making its way from bench to bedside. While this manuscript was under review a novel class of first covalent inhibitors specific for G12D was published, These so-called malolactones can crosslink both GDP and GTP bound forms of G12D. Inhibition of the latter state suppressed downstream signaling and cancer cell proliferation in vitro and in mouse xenografts. Moreover, a non-covalent pan-KRAS inhibitor, BI-2865, reduced tumor proliferation in cell lines and mouse models. Finally, the next generation of KRAS mutant-specific and pan-RAS tri-complex inhibitors have revolutionized RAS drug discovery. This review will give a structural biology perspective on the current generation of KRAS inhibitors through the lens of emerging secondary mutations and acquired resistance.

Development of plug-and-deliverable intracellular protein delivery platforms based on botulinum neurotoxin

Intracellular protein delivery systems have great potential in the fields of therapeutics development and biomedical research. However, targeted delivery, passing through the cell membrane without damaging the cells, and escaping from endosomal entrapment of endocytosed molecular cargos are major challenges of the system. Here, we present a novel intracellular protein delivery system based on modularly engineered botulinum neurotoxin type A (BoNT/A). LHNA domain, consisting of light chain and endosomal escape machinery of BoNT/A, was genetically fused with SpyCatcher (SC) and EGFR targeting affibody (EGFRAfb) to create SC-LHNA-EGFRAfb, a target-specific and protein cargo-switchable BoNT/A-based intracellular protein delivery platform. SC-LHNA-EGFRAfb was purely purified in large quantities, efficiently ligated with multiple ST-fused protein cargos individually, generating a variety of protein cargo-containing intracellular delivery complexes, and successfully delivered ligated protein cargos into the cytosol of target cells via receptor-mediated endocytosis, followed by endosomal escape and subsequent cytosolic delivery. SC-LHNA-EGFRAfb enhanced intracellular delivery efficiency of protein toxin, gelonin, by approximately 100-fold, highlighting the crucial roles of EGFRAfb and LHNA domain as a targeting ligand and an endosomal escape machinery, respectively, in the delivery process. The BoNT-based plug-and-deliverable intracellular protein delivery system has the potential to expand its applications in protein therapeutics and manipulating cellular processes.

Biodegradable Hydrogen-Bonded Organic Framework for Cytosolic Protein Delivery

Hydrogen-bonded organic frameworks (HOFs) are a novel class of porous nanomaterials that show great potential for intracellular delivery of protein therapeutics. However, the inherent challenges in interfacing protein with HOFs, and the need for spatiotemporally controlling the release of protein within cells, have constrained their therapeutic potential. In this study, we report novel biodegradable hydrogen-bonded organic frameworks, termed DS-HOFs, specially designed for the cytosolic delivery of protein therapeutics in cancer cells. The synthesis of DS-HOFs involves the self-assembly of 4-[tris(4-carbamimidoylphenyl) methyl] benzenecarboximidamide (TAM) and 4,4'-dithiobisbenzoic acid (DTBA), governed by intermolecular hydrogen-bonding interactions. DS-HOFs exhibit high efficiency in encapsulating a diverse range of protein cargos, underpinned by the hydrogen-bonding interactions between the protein residue and DS-HOF subcomponents. Notably, DS-HOFs are selectively degraded in cancer cells triggered by the distinct intracellular reductive microenvironments, enabling an enhanced and selective release of protein inside cancer cells. Additionally, we demonstrate that the efficient delivery of bacterial effector protein DUF5 using DS-HOFs depletes the mutant RAS in cancer cells to prohibit tumor cell growth both in vitro and in vivo. The design of biodegradable HOFs for cytosolic protein delivery provides a powerful and promising strategy to expand the therapeutic potential of proteins for cancer therapy.

Histidine-Rich Protein Accelerates the Biomineralization of Zeolitic Imidazolate Frameworks for In Vivo Protein Delivery

Biomineralization of metal-organic frameworks (MOFs) provides a powerful approach for intracellular protein delivery, enabling the study of biological function and therapeutic potential of proteins. However, the potency of this approach is largely challenged by the low efficiency of current strategies for interfacing proteins with MOFs for biomineralization and intracellular delivery. Here, we report a versatile and convenient biomineralization strategy for the rapid encapsulation and enhanced delivery of proteins using MOFs, accelerated by histidine-rich proteins. We demonstrate that the histidine-rich green fluorescent protein (H39GFP) can accelerate the biomineralization of MOFs by promoting the coordination between proteins and metal ions, leading to enhanced protein delivery efficiency up to 15-fold. Moreover, we show that the delivery of H39GFP-fused cytotoxic ribonuclease and bacterial-derived RAS protease can effectively inhibit tumor cell growth. The strategy of promoting the biomineralization of MOFs via histidine-rich proteins for enhanced intracellular delivery could be expanded to other biomacromolecules, advancing their therapeutic potential and the biomedical scope of MOFs.

Potent and selective eradication of tumor cells by an EpCAM-targeted Ras-degrading enzyme

Despite decades of efforts, an urgent need remains to develop tumor cell-selective rat sarcoma (Ras)-targeting therapies that can treat patients with Ras-driven tumors. Here we report modular engineered proteins that degrade Ras selectively in tumor cells that overexpress the tumor cell marker epithelial cell adhesion molecule (EpCAM) by fusing the Ras degrader Ras-Rap1-specific endopeptidase with the translocation domain of the Pseudomonas aeruginosa exotoxin A (ETA) or diphtheria toxin (DT). Redirection to EpCAM is achieved by a designed ankyrin repeat protein. In two-dimensional tumor cell cultures, complete degradation of Ras proteins after 24 h was observed with EpCAM-targeted Ras degraders fused to ETA or DT in EpCAM-overexpressing MCF7 and HCT116 cells, with median inhibition concentration values at sub-nanomolar levels. The viability of EpCAM-low non-cancerous fibroblasts remained unaffected. In a three-dimensional (3D) tumor-on-a-chip system that mimics the natural tumor microenvironment, effective Ras degradation and selective toxicity toward tumor cells, particularly with the ETA-fused constructs, was determined on-chip. To conclude, we demonstrate the potential of modular engineered proteins to kill tumor cells highly selectively by simultaneously exploiting EpCAM as a tumor-specific cell surface molecule as well as Ras as an intracellular oncotarget in a 3D system mimicking the natural tumor microenvironment.

Small molecular inhibitors for KRAS-mutant cancers

Three rat sarcoma (RAS) gene isoforms, KRAS, NRAS, and HRAS, constitute the most mutated family of small GTPases in cancer. While the development of targeted immunotherapies has led to a substantial improvement in the overall survival of patients with non-KRAS-mutant cancer, patients with RAS-mutant cancers have an overall poorer prognosis owing to the high aggressiveness of RAS-mutant tumors. KRAS mutations are strongly implicated in lung, pancreatic, and colorectal cancers. However, RAS mutations exhibit diverse patterns of isoforms, substitutions, and positions in different types of cancers. Despite being considered "undruggable", recent advances in the use of allele-specific covalent inhibitors against the most common mutant form of RAS in non-small-cell lung cancer have led to the development of effective pharmacological interventions against RAS-mutant cancer. Sotorasib (AMG510) has been approved by the FDA as a second-line treatment for patients with KRAS-G12C mutant NSCLC who have received at least one prior systemic therapy. Other KRAS inhibitors are on the way to block KRAS-mutant cancers. In this review, we summarize the progress and promise of small-molecule inhibitors in clinical trials, including direct inhibitors of KRAS, pan-RAS inhibitors, inhibitors of RAS effector signaling, and immune checkpoint inhibitors or combinations with RAS inhibitors, to improve the prognosis of tumors with RAS mutations.

RAS degraders: The new frontier for RAS-driven cancers

The function and significance of RAS proteins in cancer have been widely studied for decades. In 2013, the National Cancer Institute established the RAS Initiative to explore innovative approaches for attacking the proteins encoded by mutant forms of RAS genes and to create effective therapies for RAS-driven cancers. This initiative spurred researchers to develop novel approaches and to discover small molecules targeting this protein that was at one time termed "undruggable." More recently, advanced efforts in RAS degraders including PROTACs, linker-based degraders, and direct proteolysis degraders have been explored as novel strategies to target RAS for cancer treatment. These RAS degraders present new opportunities for RAS therapies and may prove fruitful in understanding basic cell biology. Novel delivery strategies will further enhance the efficacy of these therapeutics. In this review, we summarize recent efforts to develop RAS degraders, including PROTACs and E3 adaptor and ligase fusions as cancer therapies. This review also details the direct RAS protease degrader, RAS/RAP1-specific endopeptidase that directly and specifically cleaves RAS.

Targeting Ras with protein engineering

Ras proteins are small GTPases that regulate cell growth and division. Mutations in Ras genes are associated with many types of cancer, making them attractive targets for cancer therapy. Despite extensive efforts, targeting Ras proteins with small molecules has been extremely challenging due to Ras's mostly flat surface and lack of small molecule-binding cavities. These challenges were recently overcome by the development of the first covalent small-molecule anti-Ras drug, sotorasib, highlighting the efficacy of Ras inhibition as a therapeutic strategy. However, this drug exclusively inhibits the Ras G12C mutant, which is not a prevalent mutation in most cancer types. Unlike the G12C variant, other Ras oncogenic mutants lack reactive cysteines, rendering them unsuitable for targeting via the same strategy. Protein engineering has emerged as a promising method to target Ras, as engineered proteins have the ability to recognize various surfaces with high affinity and specificity. Over the past few years, scientists have engineered antibodies, natural Ras effectors, and novel binding domains to bind to Ras and counteract its carcinogenic activities via a variety of strategies. These include inhibiting Ras-effector interactions, disrupting Ras dimerization, interrupting Ras nucleotide exchange, stimulating Ras interaction with tumor suppressor genes, and promoting Ras degradation. In parallel, significant advancements have been made in intracellular protein delivery, enabling the delivery of the engineered anti-Ras agents into the cellular cytoplasm. These advances offer a promising path for targeting Ras proteins and other challenging drug targets, opening up new opportunities for drug discovery and development.

Intracellular delivery of bacterial effectors for cancer therapy using biodegradable lipid nanoparticles

Bacterial effector proteins are virulence factors that are secreted and mediate orthogonal post-translational modifications of proteins that are not found naturally in mammalian systems. They hold great promise for developing biotherapeutics by regulating malignant cell signaling in a specific and targeted manner. However, delivering bacterial effectors into disease cells poses a significant challenge to their therapeutic potential. In this study, we report on the design of a combinatorial library of bioreducible lipid nanoparticles containing disulfide bonds for highly efficient bacterial effector delivery and potential cancer therapy. A leading lipid, PPPDA-O16B, identified from the library, can encapsulate and deliver DNA plasmids into cells. The gene cargo is released in response to the reductive cellular environment that is upregulated in cancer cells, leading to enhanced gene delivery and protein expression efficiency. Furthermore, we demonstrate that PPPDA-O16B can deliver the bacterial effector protein, DUF5, to degrade mutant RAS and inactivate downstream MAPK signaling cascades to suppress cancer cell growth in vitro and in tumor-bearing mouse xenografts. This strategy of delivering bacterial effectors using biodegradable lipid nanoparticles can be expanded for cancer cell signaling regulation and antitumor studies.

KRAS-Mutant Lung Cancer: Targeting Molecular and Immunologic Pathways, Therapeutic Advantages and Restrictions

RAS mutations are among the most common oncogenic mutations in human cancers. Among RAS mutations, KRAS has the highest frequency and is present in almost 30% of non-small-cell lung cancer (NSCLC) patients. Lung cancer is the number one cause of mortality among cancers as a consequence of outrageous aggressiveness and late diagnosis. High mortality rates have been the reason behind numerous investigations and clinical trials to discover proper therapeutic agents targeting KRAS. These approaches include the following: direct KRAS targeting; synthetic lethality partner inhibitors; targeting of KRAS membrane association and associated metabolic rewiring; autophagy inhibitors; downstream inhibitors; and immunotherapies and other immune-modalities such as modulating inflammatory signaling transcription factors (e.g., STAT3). The majority of these have unfortunately encountered limited therapeutic outcomes due to multiple restrictive mechanisms including the presence of co-mutations. In this review we plan to summarize the past and most recent therapies under investigation, along with their therapeutic success rate and potential restrictions. This will provide useful information to improve the design of novel agents for treatment of this deadly disease.

Bacteria-derived chimeric toxins as potential anticancer agents

Cancer is one of the major causes of death globally, requiring everlasting efforts to develop novel, specific, effective, and safe treatment strategies. Despite advances in recent years, chemotherapy, as the primary treatment for cancer, still faces limitations such as the lack of specificity, drug resistance, and treatment failure. Bacterial toxins have great potential to be used as anticancer agents and can boost the effectiveness of cancer chemotherapeutics. Bacterial toxins exert anticancer effects by affecting the cell cycle and apoptotic pathways and regulating tumorigenesis. Chimeric toxins, which are recombinant derivatives of bacterial toxins, have been developed to address the low specificity of their conventional peers. Through their targeting moieties, chimeric toxins can specifically and effectively detect and kill cancer cells. This review takes a comprehensive look at the anticancer properties of bacteria-derived toxins and discusses their potential applications as therapeutic options for integrative cancer treatment.

Identification of potential inhibitors, conformational dynamics, and mechanistic insights into mutant Kirsten rat sarcoma virus (G13D) driven cancers

The mutations at the hotspot region of K-Ras result in the progression of cancer types. Our study aimed to explore the small molecule inhibitors against the G13D mutant K-Ras model with anti-cancerous activity from food and drug administration (FDA)-approved drug compounds. We implemented several computational strategies such as pharmacophore-based virtual screening, molecular docking, absorption, distribution, metabolism and excretion features, and molecular simulation to ensure the identified hit compounds have potential efficacy against G13D K-Ras. We found that the FDA-approved compounds, namely, azelastine, dihydrocodeine, paroxetine, and tramadol, are potential candidates to inhibit the action of G13D mutant K-Ras. All four compounds exhibited similar binding patterns of sotorasib, and a structural binding mechanism with significant hydrophobic contacts. The descriptor features from the QikProp of all four compounds are within allowable limits compared to sotorasib drug. Consequently, a molecular simulation result emphasized that the dihydrocodeine and tramadol exhibited less fluctuation, minimal basin, significant h-bonds, and potent inhibition against G13D K-Ras. As a result, the current research identifies prospective K-Ras inhibitors that could be further improved with biochemical analysis for precision medicine against K-Ras-driven cancers.

Proteolytic pan-RAS Cleavage Leads to Tumor Regression in Patient-derived Pancreatic Cancer Xenografts

The lack of effective RAS inhibition represents a major unmet medical need in the treatment of pancreatic ductal adenocarcinoma (PDAC). Here, we investigate the anticancer activity of RRSP-DTB, an engineered biologic that cleaves the Switch I of all RAS isoforms, in KRAS-mutant PDAC cell lines and patient-derived xenografts (PDX). We first demonstrate that RRSP-DTB effectively engages RAS and impacts downstream ERK signaling in multiple KRAS-mutant PDAC cell lines inhibiting cell proliferation at picomolar concentrations. We next tested RRSP-DTB in immunodeficient mice bearing KRAS-mutant PDAC PDXs. Treatment with RRSP-DTB led to ≥95% tumor regression after 29 days. Residual tumors exhibited disrupted tissue architecture, increased fibrosis and fewer proliferating cells compared with controls. Intratumoral levels of phospho-ERK were also significantly lower, indicating in vivo target engagement. Importantly, tumors that started to regrow without RRSP-DTB shrank when treatment resumed, demonstrating resistance to RRSP-DTB had not developed. Tracking persistence of the toxin activity following intraperitoneal injection showed that RRSP-DTB is active in sera from immunocompetent mice for at least 1 hour, but absent after 16 hours, justifying use of daily dosing. Overall, we report that RRSP-DTB strongly regresses hard-to-treat KRAS-mutant PDX models of pancreatic cancer, warranting further development of this pan-RAS biologic for the management of RAS-addicted tumors.

Targeted intracellular delivery of Cas13 and Cas9 nucleases using bacterial toxin-based platforms

Targeted delivery of therapeutic proteins toward specific cells and across cell membranes remains major challenges. Here, we develop protein-based delivery systems utilizing detoxified single-chain bacterial toxins such as diphtheria toxin (DT) and botulinum neurotoxin (BoNT)-like toxin, BoNT/X, as carriers. The system can deliver large protein cargoes including Cas13a, CasRx, Cas9, and Cre recombinase into cells in a receptor-dependent manner, although delivery of ribonucleoproteins containing guide RNAs is not successful. Delivery of Cas13a and CasRx, together with guide RNA expression, reduces mRNAs encoding GFP, SARS-CoV-2 fragments, and endogenous proteins PPIB, KRAS, and CXCR4 in multiple cell lines. Delivery of Cre recombinase modifies the reporter loci in cells. Delivery of Cas9, together with guide RNA expression, generates mutations at the targeted genomic sites in cell lines and induced pluripotent stem cell (iPSC)-derived human neurons. These findings establish modular delivery systems based on single-chain bacterial toxins for delivery of membrane-impermeable therapeutics into targeted cells.

Bacterial Toxin and Effector Regulation of Intestinal Immune Signaling

The host immune response is highly effective to detect and clear infecting bacterial pathogens. Given the elaborate surveillance systems of the host, it is evident that in order to productively infect a host, the bacteria often coordinate virulence factors to fine-tune the host response during infection. These coordinated events can include either suppressing or activating the signaling pathways that control the immune response and thereby promote bacterial colonization and infection. This review will cover the surveillance and signaling systems for detection of bacteria in the intestine and a sample of the toxins and effectors that have been characterized that cirumvent these signaling pathways. These factors that promote infection and disease progression have also been redirected as tools or therapeutics. Thus, these toxins are enemies deployed to enhance infection, but can also be redeployed as allies to enable research and protect against infection.

RAS specific protease induces irreversible growth arrest via p27 in several KRAS mutant colorectal cancer cell lines

Ras-specific proteases to degrade RAS within cancer cells are under active development as an innovative strategy to treat tumorigenesis. The naturally occurring biological toxin effector called RAS/RAP1-specific endopeptidase (RRSP) is known to cleave all RAS within a cell, including HRAS, KRAS, NRAS and mutant KRAS G13D. Yet, our understanding of the mechanisms by which RRSP drives growth inhibition are unknown. Here, we demonstrate, using isogenic mouse fibroblasts expressing a single isoform of RAS or mutant KRAS, that RRSP equally inactivates all isoforms of RAS as well as the major oncogenic KRAS mutants. To investigate how RAS processing might lead to varying outcomes in cell fate within cancer cells, we tested RRSP against four colorectal cancer cell lines with a range of cell fates. While cell lines highly susceptible to RRSP (HCT116 and SW1463) undergo apoptosis, RRSP treatment of GP5d and SW620 cells induces G1 cell cycle arrest. In some cell lines, growth effects were dictated by rescued expression of the tumor suppressor protein p27 (Kip1). The ability of RRSP to irreversibly inhibit cancer cell growth highlights the antitumor potential of RRSP, and further warrants investigation as a potential anti-tumor therapeutic.

Translocation expands the scope of the large clostridial toxin family

Large clostridial toxins (LCTs) are a family of six homologous disease-causing proteins characterised by their large size (>200 kDa) and conserved multidomain architectures. Using their central translocation and receptor-binding domain (T domain), LCTs bind host cell receptors and translocate their upstream glycosyltransferase and cysteine protease domain across the endosomal membrane and into the cytosol. The recent discovery of hundreds of LCT-like T domains in diverse genomic contexts and domain architectures from bacteria other than clostridia has provided significant new insights into the enigmatic process of LCT translocation, but also has put the definition of what constitutes an LCT into question. In this opinion article, we discuss how these findings have expanded our understanding of LCT translocation and reshaped the scope of the LCT family.

Targeting the "undruggable" RAS with biologics

RAS proteins represent critical drivers of tumor development and thus are the focus of intense efforts to pharmacologically inhibit these proteins in human cancer. Although recent success has been attained in developing clinically efficacious inhibitors to KRASG12C, there remains a critical need for developing approaches to inhibit additional mutant RAS proteins. A number of anti-RAS biologics have been developed which reveal novel and potentially therapeutically targetable vulnerabilities in oncogenic RAS. This review will discuss the growing field of anti-RAS biologics and potential development of these reagents into new anti-RAS therapies.

A Computational Investigation of In Vivo Cytosolic Protein Delivery for Cancer Therapy

The ability to specifically block or degrade cytosolic targets using therapeutic proteins would bring tremendous therapeutic opportunities in cancer therapy. Over the last few years, significant progress has been made with respect to tissue targeting, cytosolic delivery, and catalytic inactivation of targets, placing this aim within reach. Here, we developed a mathematical model specifically built for the evaluation of approaches towards cytosolic protein delivery, involving all steps from systemic administration to translocation into the cytosol and target engagement. Focusing on solid cancer tissues, we utilized the model to investigate the effects of microvascular permeability, receptor affinity, the cellular density of targeted receptors, as well as the mode of activity (blocking/degradation) on therapeutic potential. Our analyses provide guidance for the rational optimization of protein design for enhanced activity and highlight the importance of tuning the receptor affinity as a function of receptor density as well as the receptor internalization rate. Furthermore, we provide quantitative insights into how enzymatic cargoes can enhance the distribution, extent, and duration of therapeutic activity, already at very low catalytic rates. Our results illustrate that with current protein engineering approaches, the goal of delivery of cytosolic delivery of proteins for therapeutic effects is well within reach.

Engineering subtilisin proteases that specifically degrade active RAS

We describe the design, kinetic properties, and structures of engineered subtilisin proteases that degrade the active form of RAS by cleaving a conserved sequence in switch 2. RAS is a signaling protein that, when mutated, drives a third of human cancers. To generate high specificity for the RAS target sequence, the active site was modified to be dependent on a cofactor (imidazole or nitrite) and protease sub-sites were engineered to create a linkage between substrate and cofactor binding. Selective proteolysis of active RAS arises from a 2-step process wherein sub-site interactions promote productive binding of the cofactor, enabling cleavage. Proteases engineered in this way specifically cleave active RAS in vitro, deplete the level of RAS in a bacterial reporter system, and also degrade RAS in human cell culture. Although these proteases target active RAS, the underlying design principles are fundamental and will be adaptable to many target proteins.

Therapeutic resistance of pancreatic cancer: Roadmap to its reversal

Pancreatic cancer is a lethal disease with limited opportunity for resectable surgery as the first choice for cure due to its late diagnosis and early metastasis. The desmoplastic stroma and cellular genetic or epigenetic alterations of pancreatic cancer impose physical and biological barriers to effective therapies, including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. Here, we review the current therapeutic options for pancreatic cancer, and underlying mechanisms and potential reversal of therapeutic resistance, a hallmark of this deadly disease.