Undruggable Targets Research Articles

Abstract SY17-03: Reimagining druggability using chemoproteomic platforms

Abstract The Nomura Research Group is focused on reimagining druggability using chemoproteomic platforms to develop transformative medicines. One of the greatest challenges that we face in discovering new disease therapies is that most proteins are considered “undruggable,” in that most proteins do not possess known binding pockets or “ligandable hotspots” that small-molecules can bind to modulate protein function. Our research group addresses this challenge by advancing and applying chemoproteomic platforms to discover and pharmacologically target unique and novel ligandable hotspots for disease therapy. We currently have three major research directions. Our first major focus is on developing and applying chemoproteomics-enabled covalent ligand discovery approaches to rapidly discover small-molecule therapeutic leads that target unique and novel ligandable hotspots for undruggable protein targets and pathways. Our second research area focuses on using chemoproteomic platforms to expand the scope of targeted protein degradation technologies. Our third research area focuses on using chemoproteomics-enabled covalent ligand discovery platforms to develop new induced proximity-based therapeutic modalities. Collectively, our lab is focused on developing next-generation transformative medicines through pioneering innovative chemical technologies to overcome challenges in drug discovery. Citation Format: Daniel K. Nomura. Reimagining druggability using chemoproteomic platforms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY17-03.

Structural and Functional Insights into GID/CTLH E3 Ligase Complexes.

Multi-subunit E3 ligases facilitate ubiquitin transfer by coordinating various substrate receptor subunits with a single catalytic center. Small molecules inducing targeted protein degradation have exploited such complexes, proving successful as therapeutics against previously undruggable targets. The C-terminal to LisH (CTLH) complex, also called the glucose-induced degradation deficient (GID) complex, is a multi-subunit E3 ligase complex highly conserved from Saccharomyces cerevisiae to humans, with roles in fundamental pathways controlling homeostasis and development in several species. However, we are only beginning to understand its mechanistic basis. Here, we review the literature of the CTLH complex from all organisms and place previous findings on individual subunits into context with recent breakthroughs on its structure and function.

A New Method for Undruggable Targets: Amino Acids as Fragments of Inhibitors

Over the last decade, protein‐protein interactions (PPIs) have emerged as promising targets in the precise treatment of serious diseases. Many essential cellular pathways that are implicated in human diseases are controlled by intracellular PPIs. Such PPIs could be potential drug targets, and thus the ability of molecules to inhibit specific PPIs has remarkable therapeutic value. Unfortunately, PPI interfaces are generally large and present great difficulty for small molecule inhibitor design. Alternate strategies are being developed towards drug design and discovery for this type of target. For example, the synthesis of unnatural amino acids allows production of extremely large libraries of highly modified peptides, which may be screened against a PPI target. Peptide hits are a potential source of lead compounds in the search for new pharmaceutical agents and are promising for PPI inhibition. It is in this context that selection of the right unnatural amino acid becomes crucial.For this reason, developing new strategies to solve this problem is a key factor to find more efficient and specific inhibitors to PPI’s.In this study, we introduce a simple, Nuclear Magnetic Resonance (NMR) based methodology that screens natural and unnatural amino acids as “fragments” for development of new peptide‐based inhibitors for specific PPI’s. We validate this new method against MDM2, a well‐characterized and important negative regulator of the p53 tumor suppressor with known small peptides that inhibit its interaction with p53. A central tryptophan is the largest contributor to binding in this interface, and the corresponding MDM2 binding pocket is where we focused our efforts. Using this methodology, we screened non‐natural tryptophan derivatives, and several displayed a better binding affinity compared with the natural counterpart. Our simplified method allows priority ranking of amino acids according to their affinity to the protein. The highest‐ranking amino acids will be incorporated into peptides synthetically to confirm that improved free amino acid affinity translates to enhanced peptide binding and inhibition. In addition, this serves as a convenient and robust method to ‘pre‐screen’ amino acids for incorporation into in vitro peptide selection via mRNA display.

A robust post-insertion method for the preparation of targeted siRNA LNPs

Targeted delivery of nucleic acids is gaining momentum due to improved efficacy, selectivity, increased circulation time and enhanced tissue retention in target cells. Using nucleic acid-based therapies previously undruggable targets have proven now to be amenable for treatment. Currently, several methods for preparing targeted or labelled delivery vehicles for nucleic acids are based on liposomal formulations. Lipid nanoparticles (LNPs) are structurally different from liposomes and these methods should therefore be evaluated before being translated to siRNA LNPs preparation protocols. Here, we describe a robust and facile method for the preparation of targeted or fluorescently labelled siRNA LNPs. Using a copper free strain-promoted azide-alkyne cycloaddition (SPAAC) we demonstrate that post-insertion of ligand-lipid conjugates into preformed LNPs is superior to direct-surface modification because it preserves the physicochemical parameters of the LNPs. We found that the time point of solvent removal by dialysis is critical and affects the hydrodynamic diameter of the LNPs; post-insertion after dialysis shows the smallest increase in hydrodynamic diameter and polydispersity index (PDI). The post-insertion of ligand-lipid conjugates also proceeded with rapid kinetics and high efficacy over a wide temperature range. Using this optimised protocol, we generated siRNA LNPs containing both targeting and fluorescent tracking ligands allowing us to monitor siRNA LNP uptake kinetics in dependence of the targeting ligand. In aggregate, we describe a robust approach for the generation of targeted and labelled siRNA LNPs that allows their controlled and facile decoration with ligand combinations.

Optimization of Cyclic Peptide Property Using Chromatographic Capacity Factor on Permeability of Passive Cell Membrane and Human Induced Pluripotent Stem Cell-Derived Intestinal Membrane

Cyclic peptides have attracted increasing attention as a privileged class of molecules addressing undruggable targets. Cell permeability of cyclic peptides has remained a challenging issue owing to their molecular properties. Various efficiency metrics have emerged to assess this issue. Among them, the lipophilic permeability efficiency (LPE) metric is the difference between an experimental 1,9-decadiene-water partition coefficient at pH 7.4 (log Ddec/w) and calculated octanol/water partition coefficients (ALogP). This metric provides insight into how structural changes affect permeability. Here, we demonstrate the chromatographic capacity factor (log k’) of cyclic peptides using reversed-phase liquid chromatography as an alternative to log Ddec/w, which enables efficient and reliable experimental lipophilicity for the adoption of LPE in early drug discovery. The log k’ indicates the passive membrane permeability of cyclic peptides and can be used to optimize passive membrane permeability in combination with other parameters. In addition, intestinal membrane permeability of cyclic peptides on human induced pluripotent stem cell-derived intestinal epithelial cells was achieved with log k’ and high passive membrane permeability, although cyclic peptides are P-glycoprotein substrates. These approaches could facilitate optimization of properties of cyclic peptides for oral administration and contribute to the successful discovery and development of cyclic peptides.

Targeting key proteins involved in transcriptional regulation for cancer therapy: Current strategies and future prospective.

The key proteins involved in transcriptional regulation play convergent roles in cellular homeostasis, and their dysfunction mediates aberrant gene expressions that underline the hallmarks of tumorigenesis. As tumor progression is dependent on such abnormal regulation of transcription, it is important to discover novel chemical entities as antitumor drugs that target key tumor-associated proteins involved in transcriptional regulation. Despite most key proteins (especially transcription factors) involved in transcriptional regulation are historically recognized as undruggable targets, multiple targeting approaches at diverse levels of transcriptional regulation, such as epigenetic intervention, inhibition of DNA-binding of transcriptional factors, and inhibition of the protein-protein interactions (PPIs), have been established in preclinically or clinically studies. In addition, several new approaches have recently been described, such as targeting proteasomal degradation and eliciting synthetic lethality. This review will emphasize on accentuating these developing therapeutic approaches and provide a thorough conspectus of the drug development to target key proteins involved in transcriptional regulation and their impact on future oncotherapy.

Targeted siRNA nanocarrier: a platform technology for cancer treatment

The small arginine-rich protein protamine condenses complete genomic DNA into the sperm head. Here, we applied its high RNA binding capacity for spontaneous electrostatic assembly of therapeutic nanoparticles decorated with tumour-cell-specific antibodies for efficiently targeting siRNA. Fluorescence microscopy and DLS measurements of these nanocarriers revealed the formation of a vesicular architecture that requires presence of antibody-protamine, defined excess of free SMCC-protamine, and anionic siRNA to form. Only these complex nanoparticles were efficient in the treatment of non-small-cell lung cancer (NSCLC) xenograft models, when the oncogene KRAS was targeted via EGFR-mediated delivery. To show general applicability, we used the modular platform for IGF1R-positive Ewing sarcomas. Anti-IGR1R-antibodies were integrated into an antibody-protamine nanoparticle with an siRNA specifically against the oncogenic translocation product EWS/FLI1. Using these nanoparticles, EWS/FLI1 knockdown blocked in vitro and in vivo growth of Ewing sarcoma cells. We conclude that these antibody-protamine-siRNA nanocarriers provide a novel platform technology to specifically target different cell types and yet undruggable targets in cancer therapy by RNAi.

Abstract OT1-12-02: Trial in progress: Phase 2, open-label study to evaluate the safety and efficacy of praluzatamab ravtansine in metastatic HER2 non-amplified breast cancer as monotherapy and combination with pacmilimab

Abstract Background: Probody® therapeutic candidates (Pb-Tx) are masked antibodies designed to be conditionally activated in the tumor microenvironment by tumor-associated proteases. This allows Pb-Tx to address previously undruggable targets that are highly expressed in both tumor and normal tissues. Praluzatamab ravtansine is a masked antibody-drug conjugate targeting CD166 with a DM4 payload. A phase 1 monotherapy study showed safety and durable clinical activity (clinical benefit rate at 24 weeks [CBR24] 28%) in patients (pts) with metastatic HR-positive/HER2 non–amplified breast cancer (mHR+/HER2− BC) or metastatic triple-negative breast cancer (mTNBC). Pacmilimab, a masked PD-L1 inhibitor, demonstrated monotherapy activity in pts with TNBC with an acceptable tolerability profile.Trial design: This phase 2, open-label study with 3 parallel arms (~40 evaluable/arm) will evaluate praluzatamab ravtansine monotherapy (7 mg/kg Q3W) in pts with mHR+/HER2− BC or mTNBC, and praluzatamab ravtansine (7 mg/kg Q3W) combined with pacmilimab (1200 mg Q3W) in pts with mTNBC. Adult pts with an ECOG PS 0–1, measurable disease, and willingness to receive ocular prophylaxis for DM4-related toxicities will be enrolled. Key eligibility criteria for the mHR+/HER2− BC cohort include 2–4 prior regimens in the metastatic setting (excluding single-agent endocrine therapy). No CD166 screening required for HR+/HER2− BC but mTNBC must be CD166+. Pts with mTNBC must have received 1–3 prior metastatic regimens. For mTNBC pts who receive the doublet, key exclusion criteria include known PDL1 negative tumor, history of autoimmune disease, and progression within 120 days of 1st dose of an immuno-oncology agent. Pts with corneal disorders will be excluded. Primary endpoint is overall response rate (ORR) assessed by an independent radiology committee per RECIST v1.1. Secondary endpoints include ORR by investigator, duration of response, CBR16 & 24, progression-free survival, and overall survival. This study will also evaluate safety and tolerability, pharmacokinetics, and antidrug antibodies with praluzatamab ravtansine as monotherapy and in combination with pacmilimab. This trial is enrolling (NCT04596150). Citation Format: Kathy Miller, Leisha A. Emens, Sara M. Tolaney, Sara A. Hurvitz, Erika Hamilton, Virginia Paton, Alison Hannah, Valentina Boni. Trial in progress: Phase 2, open-label study to evaluate the safety and efficacy of praluzatamab ravtansine in metastatic HER2 non-amplified breast cancer as monotherapy and combination with pacmilimab [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-12-02.

Perspective: It is time to consider new ways to attack unpesticidable (undruggable) target sites by designing peptide pesticides.

Evolved resistance and regulatory deregistration have severely limited farmers' pesticide options. Many potential new pesticide target sites have been elucidated using targeted gene suppression and mutational tools, but few small molecules could be found that inhibit the target enzymes; the targets were considered 'undruggable'. Some organisms from all biological kingdoms use toxic peptides to ward off or kill enemies, and the agrochemical industry has used a few peptide analogs (glufosinate and bialophos) for field application. Conversely, pharmaceutical scientists have been using three-dimensional target protein structure to discover and synthesize short peptides that bind tightly to the surfaces of, and inhibit previously undruggable targets. New computational tools to quickly elucidate 3-D protein structure from amino acid sequence have just emerged. They replace crystallizing target proteins and performing X-ray crystallography to elucidate 3-D structure. These new tools allow prediction of peptides that will bind to the target proteins. They have further modified such peptides to enhance penetration, translocation and temperature stability. There is reason to assume that the same pioneering techniques can be used to develop peptide pesticides as well as pesticide synergists that act against undruggable targets and have excellent environmental and toxicological profiles. © 2022 Society of Chemical Industry.

Delivery of Oligonucleotides: Efficiency with Lipid Conjugation and Clinical Outcome.

Oligonucleotides have shifted drug discovery into a new paradigm due to their ability to silence the genes and inhibit protein translation. Importantly, they can drug the un-druggable targets from the conventional small-molecule perspective. Unfortunately, poor cellular permeability and susceptibility to nuclease degradation remain as major hurdles for the development of oligonucleotide therapeutic agents. Studies of safe and effective delivery technique with lipid bioconjugates gains attention to resolve these issues. Our review article summarizes the physicochemical effect of well-studied hydrophobic moieties to enhance the cellular entry of oligonucleotides. The structural impacts of fatty acids, cholesterol, tocopherol, and squalene on cellular internalization and membrane penetration in vitro and in vivo were discussed first. The crucial assays for delivery evaluation within this section were analyzed sequentially. Next, we provided a few successful examples of lipid-conjugated oligonucleotides advanced into clinical studies for treating patients with different medical backgrounds. Finally, we pinpointed current limitations and outlooks in this research field along with opportunities to explore new modifications and efficacy studies.

PROTACs technology for treatment of Alzheimer's disease: Advances and perspectives.

Neurodegenerative diseases (NDs) are characteristic with progression of neuron degeneration, resulting in dysfunction of cognition and mobility. Many neurodegenerative diseases are because of proteinopathies that results from unusual protein accumulations and aggregations. The aggregation of misfolded proteins like β-amyloid, α-synuclein, tau, and polyglutamates are hallmarked in Alzheimer's disease (AD), which are undruggable targets, and usually do not respond to conventional small-molecule agents. Therefore, developing novel technology and strategy for reducing the levels of protein aggregates would be critical for treatment of AD. Recently, the emerging proteolysis targeting chimeras (PRPTACs) technology has been significantly considered for artificial and selective degradation of aberrant target proteins. These engineered bifunctional molecules engage target proteins to be degraded by either the cellular degradation machinery in the ubiquitin-proteasome system (UPS) or via the autophagy-lysosome degradation pathway. Although the application of PROTACs technology is preferable than oligonucleotide and antibodies for treatment of NDs, many limitations such as their pharmacokinetic properties, tissue distribution and cell permeabilities, still need to be corrected. Herein, we review the recent advances in PROTACs technology with their limitation for pharmaceutical targeting of aberrant proteins involved in Alzheimer's diseases. We also review therapeutic potential of dysregulated signaling such as PI3K/AKT/mTOR axis for the management of AD.

Drug-development Strategy for Undruggable Targets Using a Novel Target Degradation Technology CANDDY

Drug-development Strategy for Undruggable Targets Using a Novel Target Degradation Technology CANDDY

Modulating undruggable targets to overcome cancer therapy resistance

Many cancer patients frequently fail to respond to anti-cancer treatment due to therapy resistance which is the major obstacle towards curative cancer treatment. Therefore, identification of the molecular mechanisms underlying resistance is of paramount clinical and economic importance. The advent of targeted therapies based on a molecular understanding of cancer could serve as a model for strategies to overcome drug resistance. Accordingly, the identification and validation of proteins critically involved in resistance mechanisms represent a path towards innovative therapeutic strategies to improve the clinical outcome of cancer patients. In this review, we discuss emerging targets, small molecule therapeutics and drug delivery strategies to overcome therapy resistance. We focus on rational treatment strategies based on transcription factors, pseudokinases, nuclear export receptors and immunogenic cell death strategy. Historically, unliganded transcription factors and pseudokinases were considered undruggable while blocking the nuclear export e.g., through inhibition of the nuclear export receptor CRM1 was predicted as highly toxic. Recent success inhibiting Gli-1, HIF-1α, HIF-2α and reactivating the tumor suppressor transcription factors p53 and FOXO illustrates the feasibility and power of this targeting approach. Similarly, progress has been made in modulating the activity of pseudokinase proteins implicated in therapy resistance including members of the Tribbles protein family. On the other hand, the recent clinical approval of Selinexor, a specific inhibitor of CRM-1, a protein that mediates the transport of cargos with leucine-rich nuclear export signals and known to be a driver of drug resistance, represents the proof-of-concept for inhibiting the nuclear export as a feasible strategy to overcome therapy resistance. The ever-growing capacity to target resistance mechanisms with judiciously selected small molecules, some of which are being formulated within smart nanoparticles, will pave the way towards the improvement of the clinical outcome and realize the full potential of targeted therapies and immunotherapies.

Novel Small Molecules Capable of Blocking mtRAS-Signaling Pathway.

RAS mutants are involved in approximately 30% of all human cancers and have been regarded as undruggable targets owing to relatively smooth protein surface and obscure binding pockets. In our previous study, we have demonstrated that GNF-7, a multi-targeted kinase inhibitor, possesses potent anti-proliferative activity against Ba/F3 cells transformed with NRAS-G12D. Based on our further analysis using Ba/F3 cells transformed with mtRAS, we discovered a series of pyrimido[4,5-d]pyrimidin-2-one analogues as mtRAS-signaling pathway blockers. In addition, our efforts expanded the assessment to cancer cells with mtRAS, which revealed that these substances are also capable of strongly suppressing the proliferation of various cancer cells harboring KRAS-G12D (AsPC-1), KRAS-G12V (SW480, DU-145), KRAS-G12C (H358), KRAS-G13D (MDA-MB-231), KRAS-Q61L (HT-29), and NRAS-Q61L (OCI-AML3). We herein report novel and potent mtRAS-signaling pathway blockers, SIJ1795 and SIJ1772, possessing 2 to 10-fold increased anti-proliferative activities compared to those of GNF-7 on cancer cells harboring mtRAS as well as on Ba/F3 cells transformed with mtRAS. Both SIJ1795 and SIJ1772 attenuate phosphorylation of RAS downstream molecules (AKT and MEK) and induce apoptosis and G0/G1 cell cycle arrest on cancer cells with mtRAS. Moreover, both substances substantially suppress the migration, invasion, and colony formation of cancer cells harboring mtRAS. Taken together, this study led us to identification of SIJ1795 and SIJ1772 capable of strongly inhibiting mtRAS-signaling pathway on cancer cells harboring mtRAS.

Abstract LBA002: Targeting GSPT1 by a novel cereblon E3 ligase modulator for the treatment of Acute Lymphoblastic Leukemia

Abstract Acute Lymphoblastic Leukemia (ALL), the most common childhood cancer and the second most common acute leukemia in adults, arises from clonal expansion of undifferentiated lymphoid precursor cells in bone marrow. Although the majority of childhood ALL cases harbor clonal genetic alterations of transcription factor (TF) gene mutations or rearrangements, TF alterations remain difficult therapeutic targets. Small molecule induced protein degradation is a novel strategy that can be applied to currently undruggable targets such as TF and fusion oncoproteins. In this paradigm, small molecule degraders (either PROTAC or Molecular Glue (MG)) redirect the cell’s endogenous ubiquitin proteasome system and induce ubiquitination of the target protein or non-native substrate of an E3 ligase (neosubstrate) and its subsequent proteasomal degradation. Recently, the CRBN E3 ligase modulator, CC90009 was reported to show potent antitumor activity in acute myeloid leukemia, leading to the identification of GSPT1 (G1 to S phase transition factor) as a CRBN neosubstrate. These findings suggest the potential of MGs to target unanticipated vulnerabilities in different malignancies. Here, using a structurally diverse and unique set of MGs (Molecular Glue Library (MGL)) with confirmed CRBN binding affinity, we sought to identify novel CRBN modulators through phenotypic and proteomic methods. Our screening of the MGL in a panel of representative acute leukemia cell lines, including the CRLF2-rearranged ALL cell line MHH-CALL-4 identified several active MGs with EC50 <5 μM. A lenalidomide competition assay and MHH-CALL-4 CRBN knock down cells confirmed the CRBN dependency of these MGs. Among these compounds, SJ6986, a thalidomide-driven sulfonamide showed potent cytotoxicity in over 10 ALL cell lines tested in vitro. TMT-MS proteomic analyses identified GSPT1/2 as the primary targets for this compound with high selectivity. We next tested SJ6986 activity in a panel of patient derived ALL xenografts (PDX) harboring rearrangement of IGH-CRLF2, EPOR, ATF7IP-JAK2 ex vivo. All the tested tumors were highly sensitive to SJ6986 with IC50s at nanomolar range. PK analyses in NSG mice indicated rapid absorption and over 80% oral bioavailability for SJ6986. PD studies in an IGH-CRLF2 PDX showed dose-dependent degradation of GSPT1 within 48 hours of treatment. Finally, we examined the antitumor activity of SJ6986 in 6 different PDX representative of high-risk subtypes of ALL including near haploid, low-hypodiploid, CRLF2-rearranged and EPOR-rearranged, in vivo for 28 days. SJ6986 was able to dramatically decrease the tumor burden at 1 mg/kg dose in most of the tumor models. Collectively, these results affirm that SJ6986 is a novel CRBN modulator and a potential therapeutic agent by targeting GSPT1 protein with high selectivity and potency for the treatment of ALL. Citation Format: Fatemeh Keramatnia, Yunchao Chang, Gisele Nishiguchi, Jaeki Min, Charles Mullighan, Marcus Fischer, Zoran Rankovic, Fatemeh Keramatnia. Targeting GSPT1 by a novel cereblon E3 ligase modulator for the treatment of Acute Lymphoblastic Leukemia [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA002.

Abstract P140: Chromomycin A5, a marine-derived antibiotic, targets the oncogenic TBX2 in breast cancer

Abstract Breast cancer (BC) continues to pose a major health burden. In 2020 alone, over 2 million people were diagnosed with BC globally and of these 684 996 people succumbed to the disease. Cancer cell drug resistance and the notion of transcription factors as undruggable targets has slowed progress for novel BC therapies. The transcription factor, TBX2, is commonly over-expressed in breast cancer with various hormone receptor statuses where it functions as a powerful pro-proliferative factor by directly repressing p21, PTEN, CST-6, and NDGR1 expression. Furthermore, TBX2 mediates Cisplatin drug resistance by inducing an S-phase cell cycle arrest allowing for cisplatin-induced DNA damage repair and breast cancer cell survival. Targeting TBX2 with DNA-damaging chemotherapies therefore emerges as a promising anti-cancer strategy to treat BC. To this end, we performed a reverse affinity screen to fish for marine-derived compounds with DNA-damaging- and TBX2 binding- activity and identified the antibiotic Chromomycin A5 (CMA5) as a promising agent. This project confirms the binding affinity of CMA5 for TBX2 by thermophoresis and fully characterizes the in vitro anticancer activity of CMA5 in TBX2-driven BC cells. Short-term and long-term selective cytotoxicity of CMA5 were investigated in two TBX2-driven BC cell lines (MCF-7 and T47D) and a non-malignant breast epithelial cell line (MCF-12A) using MTT and clonogenic assays. Our results show that CMA5 exhibited potent (IC50 ≤6.5 nM) and selective (SI ~ 3.3 ) cytotoxicity against BC cells. Importantly, CMA5 inhibited TBX2 protein levels and co-treatment of the BC cells with CMA5 and the proteasome 26S inhibitor MG132 rescued TBX2 levels. These results show that CMA5 targets TBX2 for protein degradation. Furthermore, whereas knocking down TBX2 using shRNA blocked the cytotoxicity of CMA5 (IC50 increased by 5-fold), ectopically over-expressing TBX2 increased the cytotoxic activity of CMA5 (IC50 decreased by 1.2-fold). These results suggest that CMA5 cytotoxicity is dependent, in part, on the presence of TBX2. To further explore the significance of TBX2 inhibition by CMA5 we investigated the impact of CMA5 on expression levels of the TBX2 target genes p21, PTEN, CST-6 and NDGR1 by quantitative real-time PCR analyses. The results revealed that all four genes were upregulated in the presence of CMA5 treatment which suggested that CMA5 inhibits BC cell viability and survival by targeting TBX2 and thus releasing its ability to repress these tumor suppressors. To elucidate the mechanism(s) underpinning the cytotoxic activity of CMA5 we investigated its effects on several markers of DNA damage (yH2AX expression) and apoptosis (cleaved caspase 3, 7, 8, 9 and PARP) by western blotting and immunocytochemistry. Our results show that CMA5 induced DNA damage and killed cells, in part, by both the intrinsic and extrinsic apoptotic programmed cell death pathways. Overall, this study identifies CMA5 as a promising anti-breast cancer agent because of its capability to induce DNA damage and to inhibit the oncogenic TBX2. Citation Format: Claire Bellis, Suparna Chakraborty, Mihlali Mlaza, Bianca Del Bianco Sahm, Paula Rezende Teixeira, Leticia Costa-Lotufo, Sharon Prince. Chromomycin A5, a marine-derived antibiotic, targets the oncogenic TBX2 in breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P140.

Nucleic Acid Drugs-Current Status, Issues, and Expectations for Exosomes.

Simple SummaryNucleic acid drugs provide novel therapeutic modalities with characteristics that differ from those of small molecules and antibodies. In this review, I focus on the various mechanisms through which nucleic acid drugs act on, the status of their clinical development, and discuss several hurdles that need to be surmounted. In addition, by listing examples of how the progress in exosome biology can lead to the solution of problems in nucleic acid drug therapy, I hope that many more nucleic acid drugs including anticancer drugs will be developed in the future.Nucleic acid drugs are being developed as novel therapeutic modalities. They have great potential to treat human diseases such as cancers, viral infections, and genetic disorders due to unique characteristics that make it possible to approach undruggable targets using classical small molecule or protein/antibody-based biologics. In this review, I describe the advantages, classification, and clinical status of nucleic acid therapeutics. To date, more than 10 products have been launched, and many products have been tested in clinics. To promote the use of nucleic acid therapeutics such as antibodies, several hurdles need to be surmounted. The most important issue is the delivery of nucleic acids and several other challenges have been reported. Recent advanced delivery platforms are lipid nanoparticles and ligand conjugation approaches. With the progress of exosome biology, exosomes are expected to contribute to the solution of various problems associated with nucleic acid drugs.

Strategies for targeting undruggable targets

ABSTRACT Introduction Undruggable targets refer to clinically meaningful therapeutic targets that are ‘difficult to drug’ or ‘yet to be drugged’ via traditional approaches. Featuring characteristics of lacking defined ligand-binding pockets, non-catalytic protein–protein interaction functional modes and less-investigated 3D structures, these undruggable targets have been targeted with novel therapeutic entities developed with the progress of unconventional drug discovery approaches, such as targeted degradation molecules and display technologies. Area covered This review first presents the concept of ‘undruggable’ exemplified by RAS and other targets. Next, detailed strategies are illustrated in two aspects: innovation of therapeutic entities and development of unconventional drug discovery technologies. Finally, case studies covering typical undruggable targets (Bcl-2, p53, and RAS) are depicted to further demonstrate the feasibility of the strategies and entities above. Expert opinion Targeting the undruggable expands the scope of therapeutically reachable targets. Consequently, it represents the drug discovery frontier. Biomedical studies are capable of dissecting disease mechanisms, thus broadening the list of undruggable targets. Encouraged by the recent approval of the KRAS inhibitor Sotorasib, we believe that merging multiple discovery approaches and exploiting various novel therapeutic entities would pave the way for dealing with more ‘undruggable’ targets in the future.

The Future of Medicinal Chemistry, PROTAC, and Undruggable Drug Targets.

WRD5 is a promising target for anticancer drug discovery. In addition, it plays a vital role in epigenetic regulation. Since biological inactivation of WRD5 is difficult to reach via classical approach, PROTACs (Proteolysis Targeting Chimeras) are offering a new option. In a study, published in this journal, new WRD5 targeting PROTACS are introduced. These new compounds, which are also active in cells, make it possible to evaluate the value of WRD5 as a drug target.

Commentary: PROTACs make undruggable targets druggable: Challenge and opportunity

Commentary: PROTACs make undruggable targets druggable: Challenge and opportunity