Abstract Gain-of-function mutations in RAS genes are the most prevalent oncogenic mutations responsible for about one-third of all human malignancies. Despite decades of research, direct targeting of RAS remains a major clinical challenge as RAS inhibitors recently FDA-approved or in clinical trials appear to have limited efficacy due to the emergence of acquired resistance. We recently described a mechanistically distinct pan-RAS inhibitor, ADT-007, that selectively kills cancer cells harboring activated RAS, whether driven by oncogenic mutations or activation by upstream receptor tyrosine kinase signaling. ADT-007 potently inhibited the growth of an array of cancer cell lines harboring various RAS mutations or activated RAS with low nM IC50 values. In contrast, cancer cells with downstream RAF mutations or cells of normal tissues were essentially insensitive. Cellular, biochemical, and biophysical studies demonstrated that ADT-007 binds nucleotide-free RAS to block GTP loading and activation of the MAPK/AKT signaling pathway, resulting in mitotic arrest and apoptosis. ADT-007’s unique selectivity was attributed to metabolic detoxification by glucuronidation from UDP-glucuronosyltransferases (UGTs), which we found to be enriched in normal cells compared with RAS-mutant cancer cells. Notably, ADT-007 induced apoptosis and caused nearly complete inhibition of colony formation of Mia-PaCa-2 human pancreatic cell line, while the pan-KRAS inhibitor, BI-2865, and the pan-RAS inhibitor, RMC-6236, did not induce apoptosis, but only suppressed proliferation and marginally inhibited colony formation under the same conditions. Furthermore, RAS mutant colon and pancreatic cancer cells did not develop resistance to ADT-007 under chronic exposure, in contrast to sotorasib, BI-2865, and RMC-6236, which readily produced cultures that were essentially unresponsive to the inhibitor they were exposed to. Moreover, the resistant cell lines exhibited cross-resistance to mechanistically distinct classes of RAS inhibitors, including pan-KRAS, pan-RAS, and allele-specific KRAS inhibitors, but not to ADT-007 or a second-generation inhibitor, ADT-030. These observations suggest a shared mechanism of acquired resistance that may limit the efficacy of currently known RAS inhibitors (approved or in development). An orally bioavailable prodrug of ADT-007, ADT-1004, demonstrated favorable tolerability and suppressed tumor growth in orthotopic and patient-derived xenograft models of pancreatic cancer, accompanied by reductions in activated RAS and p-ERK levels. Consistent with resistance experiments, ADT-1004 displayed superior efficacy than sotorasib or adagrasib in a xenograft model using a resistant MIA-PaCa-2. These findings support further development of ADT-1004 that holds promise for broad and durable efficacy against RAS-driven cancers. Citation Format: Junwei Wang, Xi Chen, Sindhu Ramesh, Jeremy B. Foote, Chung-Hui Huang, Kristy L. Berry, Khalda Fadlalla, Dhana Sekhar Reddy Bandi, Purnachandra Ganji, Elmar Nurmemmedov, Ivan Babic, Donald Buchsbaum, Asfar S. Azmi, Yulia Y. Maxuitenko, Adam B Keeton, Bassel El-Rayes, Gary A. Piazza. ADT-007: A mechanistically distinct Pan-RAS inhibitor with capacity to escape acquired resistance common to other RAS inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 413.

Integrating quantitative cellular target engagement measurements into drug discovery remains challenging, particularly for structurally dynamic protein targets. Here, we present a practical, real-time MICRO-TAG temperature-series assay for quantitative measurement of cellular target engagement. Computational prediction of target thermal stability serves as an auxiliary tool to guide initial assay configuration, including selection of temperature range and resolution. Using three mechanistically distinct target classes—PLK1, cMYC, and β2AR—we demonstrate robust detection of ligand-induced stabilization and destabilization events across target-specific thermal windows. Continuous ramp–hold–detect temperature cycling on a standard real-time qPCR instrument captures dynamic engagement signatures, enabling quantitative comparison of compounds and determination of target engagement potency. The workflow eliminates the need for prior melting-point scouting while supporting reproducible temperature-series interrogation within a single experimental run. These studies establish a practical analytical framework for quantitative measurement of ligand–target interactions across diverse target classes, with computational thermal-stability prediction providing an optional starting point for experimental assay configuration.

Abstract Resistance to mutant or isoform-specific KRAS inhibitors from compensatory activation of MAPK/AKT signaling by unchecked non-mutant RAS isoforms supports the development of pan-RAS inhibitors. However, secondary mutations or aberrant activation of other oncogenic pathways (e.g., Wnt/APC/β-catenin) may cause resistance to pan-RAS inhibitors. We and others have reported that the cyclic nucleotide-phosphodiesterase 10A (PDE10) isozyme is overexpressed in cancer cell lines and tumors but has low expression and no known function in tissues outside the CNS. PDE10-specific inhibitors and gene silencing were found to selectively inhibit the growth of cancer cells. PDE10 inhibitors developed to treat CNS disorders achieve high brain levels but low levels in peripheral tissues. Thus, we designed a novel, orally bioavailable PDE10 inhibitor, ADT-030, that achieves high systemic levels exceeding those required to inhibit recombinant PDE10 but lacks the major side effect (sedation) caused by conventional PDE10 inhibitors. ADT-030 bound to PDE10 and activated protein kinase G in cancer cells within the same concentration range that inhibited proliferation and induced apoptosis of a large panel of histologically diverse cancer cell lines. These effects also occurred within the same concentration range at which ADT-030 inhibited RAS-mediated MAPK/AKT signaling and selectively degraded the oncogenic (transcriptionally active) pool of β-catenin. Notably, cancer cell lines that developed resistance to pan-RAS, pan-KRAS, or mutant-specific KRAS inhibitors retained full sensitivity to ADT-030. ADT-030 strongly inhibited tumor growth in mouse models of colon, lung, breast, and pancreatic cancer at dosages that were well tolerated. Pancreatic cancer models were particularly sensitive to ADT-030, resulting in tumor regression, inhibition of metastasis, and prolonged survival. ADT-030 also increased survival and inhibited metastasis in mouse models of lung cancer with a durable response that persisted well beyond the treatment period, resulting in cures. ADT-030 also enhanced the antitumor activity of chemotherapy (paclitaxel) and immune checkpoint inhibitors in mouse models of lung, colon, and breast cancer. Deep immunophenotyping studies revealed a significant impact of ADT-030 treatment on the tumor immune microenvironment, characterized by the selective induction of apoptosis in myeloid-derived suppressor cells (MDSC), while increasing tumor infiltration by CD8+ T cells and natural killer cells. These results show that ADT-030 has potential advantages over direct-acting RAS inhibitors, supporting clinical trials of ADT-030 as a monotherapy or in combination with chemotherapy or immunotherapy for a broad range of RAS-driven cancers. Citation Format: Gary A. Piazza, Dhana Sekhar Reddy Bandi, Veronica Ramirez Alcantara, Ganji Purnachandra Nagaraju, Junwei Wang, Sindhu Ramesh, Kristy Berry, Khalda Fadlalla, Elmar Nurmemmedov, Ivan Babic, Md Yeashin Gazi, Xi Chen, Jeremy B Foote, Adam B Keeton, Yulia Y. Maxuitenko, Donald Buchsbaum, Fokhrul Hossain, Gang Zhou, Bassel F. El-Rayes. Robust and durable antitumor activity of a novel PDE10 inhibitor, ADT-030, that enhances the efficacy of chemotherapy and immunotherapy by blocking RAS and β-catenin signaling and overcoming resistance to RAS-selective inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3046.

Abstract G protein-coupled receptors (GPCRs) form the largest and most pharmacologically important family of membrane proteins, translating extracellular cues into intracellular signaling cascades. As master regulators of cell metabolism, differentiation, growth, neurotransmission, and sensory perception, GPCRs remain among the most valuable yet technically challenging therapeutic targets. Discovery of drugs targeting these receptors is a challenge in early drug discovery. Conventional biophysical methods that rely on recombinant or purified proteins have achieved limited success, as they poorly capture the structural and functional relevance of GPCRs outside of their native cellular context. Here, we present the MICRO-TAG® Cell Target Engagement platform as a cellular and translatable assay system capable of identifying and functionally validating compounds that directly bind GPCRs in their native membrane environment. Using GPR75 — a receptor implicated in obesity, cancer, and metabolic syndrome—as a model, we demonstrate the ability of MICRO-TAG® to: (1) detect direct ligand-receptor binding, (2) monitor downstream GPCR signaling, and (3) provide sensitive reporter-based readouts of agonist or antagonist activity. By integrating direct target engagement with functional pathway interrogation in a cellular environment, MICRO-TAG® enables scalable and physiologically relevant drug discovery for some of the most challenging drug target classes in biology. Citation Format: Ivan Babic, Elmar Nurmemmedov. MICRO-TAG® cell target engagement redefines GPCR drug discovery with functional relevance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6424.

Phosphodiesterase 10 (PDE10) was previously reported to be overexpressed in various cancers and essential for cancer cell proliferation and survival. Here, we studied a novel PDE10 inhibitor, ADT-030, and found it to potently and selectively inhibit KRAS mutant PDAC cell proliferation and clonogenicity by inducing G2/M arrest and apoptosis. ADT-030 also inhibited motility of PDAC cells in vitro. These effects were mediated by increased cAMP/cGMP levels and activation of PKA/PKG. The growth inhibitory activity of ADT-030 was associated with reduced β-catenin and RAS signaling. Notably, ADT-030 also inhibited the growth of KRASG12D and KRASG12C mutant PDAC cells resistant to allele-specific KRAS inhibitors. Oral administration of ADT-030 significantly suppressed tumor growth, reduced lung and liver metastasis, and increased survival without systemic toxicity in syngeneic and patient-derived xenograft (PDX) PDAC models. ADT-030 also increased chemotherapy response in orthotopic PDAC models. Immune phenotyping and single-cell RNA sequencing revealed remodeling of the tumor microenvironment by ADT-030 with a more favorable immune suppressive profile to activate anti-tumor immunity. These results show that ADT-030 is a promising drug development candidate for the treatment of KRAS-mutant PDAC capable of simultaneously targeting key oncogenic signaling pathways, resulting in tumor-intrinsic and immunomodulatory effects.

Abstract Transcription factors are challenging drug targets that require the native cellular environment for interrogation of direct engagement with potential therapeutic candidates. The transcription factor β-catenin is a therapeutically valuable yet challenging drug target, serving as signaling hub of the complex and highly interconnected WNT signaling network. Its central role and extensive pathway crosstalk have complicated efforts to distinguish effectors that bind β-catenin directly from those acting indirectly through upstream WNT components. This mechanistic distinction is critical for guiding rational drug discovery. We applied the MICRO-TAG® Cell Target Engagement technology to interrogate 25 reported β-catenin/WNT effectors. Using a novel direct target engagement system employing real-time temperature series, we quantified ligand-dependent stabilization of β-catenin across multiple doses, profiling their cellular target engagement potencies, under cellular conditions. Parallel functional assays, including TOPFlash reporter activity and WNT-responsive surface markers, integrated direct binding with downstream signaling readouts. This integrated approach distinguished direct β-catenin binders from effectors acting indirectly through upstream pathway components. By coupling cellular target engagement with functional readout, the MICRO-TAG® system enables scalable, mechanism-resolved drug discovery system for complex signaling pathways. This approach establishes a new paradigm for functionally interrogating therapeutic candidates through integrated target engagement and functional readout, within a unified, quantitative, and biologically relevant framework that is readily translatable to other challenging drug targets. Citation Format: Ivan Babic, Elmar Nurmemmedov. MICRO-TAG® cell target engagement dissects direct and indirect effectors of β-catenin with functional readout [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6413.

Little is known about why Foxp3⁺ regulatory T (Treg) cells require at least three HDAC1/HDAC2-containing chromatin-remodeling complexes (NuRD, Sin3 and CoREST), or whether selective disruption of these complexes can be exploited to enhance antitumor immunity. Here, we investigated the role of chromodomain helicase DNA-binding protein 4 (CHD4), the ATP-dependent remodeling subunit of the NuRD complex, in Treg biology. Conditional deletion of Chd4 in Foxp3⁺ Tregs resulted in severe systemic autoimmunity and early lethality, accompanied by reduced Foxp3 expression, impaired Treg suppressive function, and loss of Treg lineage stability. Transcriptomic analyses demonstrated that CHD4 deficiency closely phenocopied Hdac2 deletion, whereas quantitative proteomic analyses revealed that CHD4 assembles into highly conserved NuRD complexes in both Treg and conventional CD4⁺ T cells. These findings indicate that the selective dependence of Tregs on CHD4 does not arise from the formation of lineage-specific protein complexes but rather from the unique epigenetic program maintained by CHD4-containing chromatin-remodeling complexes that is required for Treg differentiation and stability. Using a novel cellular target-engagement platform, we identified CH41, a potent small-molecule inhibitor of CHD4 that recapitulated the effects of genetic CHD4 ablation on Treg function. Pharmacological inhibition of CHD4 impaired intratumoral Treg accumulation and function and significantly inhibited the growth of lung and hepatocellular carcinomas in immunocompetent, but not immunodeficient, mice, without inducing systemic autoimmunity. Collectively, our findings identify CHD4 as a critical epigenetic regulator of Treg lineage stability and establish pharmacological targeting of the CHD4/NuRD axis as a promising strategy to selectively disrupt tumor-associated Tregs and enhance antitumor immunity.

Abstract CHD4, the catalytic core of the NuRD complex, regulates chromatin remodeling, transcriptional repression, and DNA repair. Its overexpression in glioblastoma correlates with poor prognosis, yet CHD4 has remained undruggable. Employing a novel cell target engagement strategy, we identified CH41, a first-in-class small molecule that covalently engages cystine residues in the CHD4 chromodomain. The compound stabilizes CHD4 on chromatin, blocks its remodeling activity, and induces NuRD complex dissociation and proteasomal degradation. MICRO-TAG® cellular target engagement assay system applied in both discovery and validation stages, confirms direct CHD4 binding and real-time intracellular stabilization consistent with mechanistic trapping. CH41 disrupts CHD4 interaction with ZMYND8 and RBBP4/7, represses RAD51 expression, and impairs homologous-recombination repair, leading to reduced RAD51 foci and increased γH2AX and 53BP1 accumulation. Functionally, CH41 disables CHD4-dependent DNA repair and transcriptional control, re-sensitizing temozolomide-resistant glioblastoma cells. The data establishes CH41 as the first selective CHD4 inhibitor and illustrates how advances in cellular biophysics and cellular target engagement profiling are transforming the discovery of small molecule modulators of challenging transcription factor targets, such as chromatin remodelers. Citation Format: Anthony Sanchez, Minkyu Kim, Ivan Babic, Kyle Miller, Elmar Nurmemmedov. First-in-class stabilizing inhibitor of CHD4 that traps and disassembles the NuRD complex [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2415.

Smartly designed drug discovery programs can amplify the success rate and accelerate the progress from hit discovery to optimization. Drug discovery for challenging or “undruggable” drug targets such as transcription factors necessitates the proteomic complexities of the cellular milieu for proper folding and function. Therefore, conventional drug discovery methods are not sufficient for most of these proteins. The incorporation of recent cell target engagement methodologies has helped improve drug discovery efforts. However, currently available high throughput cell target engagement methods are limited to measurement of end-point signal, poor utility across multiple challenging target families and insufficient resolution for kinetic and mechanistic readouts. Here we present MICRO-TAGTM cell target engagement platform for challenging drug targets. We provide data demonstrating utility of MICRO-TAG platform for rapid discovery of novel interacting drug molecules to several challenging drug targets. The platform enables cross experimentation with the same cell reporter system for comprehensive hit identification, validation, lead identification and optimization employing several experimental strategies. Ivan Babic, Elmar Nurmemmedov. Micro-TagTM cell target engagement platform - From discovery to optimization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3164.

Drug discovery for challenging drug targets necessitates the proteomic complexities of the cellular milieu for proper folding and function. Therefore, the conventional biophysical methods are not sufficient due to the artificial acellular environment they impose on the target. Cell target engagement is a powerful paradigm in drug discovery, as measures transitions in the thermodynamic state of target protein during engagement with drug molecules. The currently available luminescence-based cell target engagement methods are limited to measurement of end-point signal, poor utility across multiple challenging target families and insufficient resolution and integration for kinetic and mechanistic readouts. We have developed a highly sensitive and versatile fluorescence-based cell target engagement strategy designed for challenging drug targets. The technology enables interrogation of drug targets without interfering with folding, localization and function - all within the physiological milieu of the cell. Importantly, this new method allows for quantitation and monitoring of cell target engagement in real time using live cells. The system seamlessly integrates with readily available real-time systems such as QuantStudio, thus making it highly sensitive and scalable. We share data on challenging drug targets such as Myc, MAPK1, UBE2N and KRAS, and we demonstrate utility of this new methodology for future drug discovery. Ivan Babic, Nikolas Bryan, Claire Cunningham, Avery Sampson, Daniel Starczynowski, Elmar Nurmemmedov. Live cell real-time quantification of drug-target engagement for rapid drug discovery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5480.

MYC overexpression is a well-established cancer vulnerability, yet direct therapeutic targeting of Myc remains a challenge. Here, we identify DL78 as a potent antimitotic agent with selective anticancer activity through its regulation of Myc. DL78 demonstrated broad efficacy by inhibiting growth across nine cancer types and significantly reducing tumor burden in an in vivo model of platinum-resistant high-grade serous ovarian cancer, with no overt toxicity. DL78 preferentially targets chromosomally unstable, MYC-overexpressing cancer cells, a hallmark of high-grade serous ovarian cancer. Mechanistically, DL78 exploits Myc’s role in mitotic entry by disrupting its interaction with α-tubulin, leading to sustained mitotic arrest, mitotic catastrophe, and apoptosis while sparing nonmalignant cells. This study establishes a novel paradigm for Myc-targeted therapy by introducing DL78, which induces cancer-selective mitotic catastrophe by disrupting Myc’s interaction with α-tubulin rather than its transcriptional activity.

Drug discovery for challenging drug targets necessitates the proteomic complexities of the cellular milieu for contextual target folding and function. Conventional biophysical methods for assessing drug interaction with a target are often not sufficiently suited for drug discovery as they impose acellular environment on the target and rely on recombinant purified protein material. In contrast, cell target engagement offers a powerful paradigm for drug discovery, through measurement of transitions in the thermodynamic state of a target protein, as it engages with drug molecules in the cell. Split-enzyme cell target engagement methods offer scaled utility during early drug discovery. Here, we describe a novel highly sensitive and scalable fluorescence-based cell target engagement method that leverages complementation of split-RNase S. This offers a unique combination of procedural and biophysical advantages, enabling its seamless integration with various instruments and applications designed for fluorescence detection. Most importantly, this new method allows for quantitation of cell target engagement in programmable temperature series format, consistent with conventional thermal shift assays, rather than at a single melting temperature. We demonstrate the sensitivity and versatility of this approach for drug discovery using targets MAPK1, KRAS, and UBE2N.

Chromatin remodeling enzymes, which reposition nucleosomes throughout the genome to regulate transcription and other processes, include 4 families: chromodomain helicase DNA-binding (CHD), switch/sucrose non-fermentable (SWI/SNF), imitation switch (ISWI), and inositol requiring 80 (INO80). CHD4, a ubiquitous and abundant chromatin remodeling enzyme essential for normal development across a range of tissues, and that is overexpressed in various cancers, is a core member of the nucleosome remodeling and deacetylase (NuRD) complex. Though originally described as a transcriptional repressor, the NuRD complex is now regarded as able to ‘fine-tune’ gene expression, acting as both an activator and a repressor of transcription. CHD4 is important to the development of lymphocytes but has not been studied in the context of Foxp3+ T-regulatory (Treg) cells. Our work involved genetic deletion of Foxp3 in Treg cells and use of a pharmacologic inhibitor of CHD4 (CHD4i) in studies with WT mice. In basic studies, Foxp3 co-immunoprecipitated with CHD4 and deletion of CHD4 led to decreased Foxp3+ Treg production in the thymus. In the periphery, CHD4-/- Tregs showed decreased Foxp3 expression and suppressive function in vitro and in vivo, with resultant severe autoimmunity and death by 3 weeks of life. These events were associated with an absence of CNS2 demethylation in the Foxp3 locus and hierarchical clustering map for differentially expressed genes included cytokines and chemokines, leukocyte antigens, transcription factors and genes associated with apoptosis, as well as enrichment of genes associated with regulation of the cell cycle and DNA damage and repair. Thereafter, a DEL screen involving cell target engagement led to discovery of a compound CH41, binding to the CHD4 chromodomain. CH41 impaired Treg suppressive function in vitro and when used in syngeneic tumor models led to inhibition of tumor growth in lung and liver carcinoma models but was ineffective in immunodeficient mice. Efficacy was associated with increased CD4 (IL-2) and CD8 (IFN-g) infiltration and effector cytokine production. Importantly, neither WT tumor bearing mice nor their immunodeficient partners developed evidence of autoimmunity under CHD4i therapy, consistent with our previous data that tumor-associated Tregs have distinctive properties rendering them especially susceptible to immunotherapy versus their peripheral counterparts. We conclude that CHD4 targeting has interesting immunologic effects that include preferentially inhibiting Treg vs. conventional T cell responses, leading to significantly increased anti-tumor immunity. Wayne W. Hancock, Yan Xiong, Liqing Wang, Martina Minisini, Fanhua Kong, Eros di Giorgio, Tatiana Akimova, Ivan Babic, Elmar Nurmemmedov. Targeting the NuRD component, CHD4, impairs Foxp3+ Treg cell production and function and promotes anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6041.

Background:This phase 1 (NCT04396717) open-label, multicenter study, evaluated Pritumumab, a IgG1 monoclonal antibody, in patients with gliomas and brain metastases. The primary objective was to evaluate the safety and/or tolerability and to identify a recommended phase 2 dose (RP2D) of Pritumumab. Methods:Adult patients with recurrent gliomas or brain metastases were enrolled in the dose cohort that was open at the time of their consent. Study treatment consisted of pritumumab administered intravenously weekly on days 1, 8, 15, and 22 in 28-day cycles. Safety, pharmacokinetics (PK), pharmacodynamics (PD), and clinical activity were evaluated. Results:Fifteen patients received Pritumumab in the recurrent setting. Pritumumab was well tolerated, with no serious adverse events related to Pritumumab reported. The most common drug-related toxicities were constipation and fatigue. There were no dose-limiting toxicities observed, and a maximum tolerable dose was not reached. Thus, the maximum feasible dose and recommended phase 2 dose of Pritumumab was established at 16.2 mg/kg weekly. Out of eleven patients evaluated for efficacy, one patient (9.1%) demonstrated partial response based on response assessment in neuro-oncology criteria, and disease stabilization was seen in 3 patients (27.3%). Conclusions:Pritumumab was well tolerated with no DLTs observed up to 16.2 mg/kg weekly. Further studies are warranted to determine clinical benefit in patients.

Abstract Triple Negative Breast Cancer (TNBC) is a highly aggressive breast cancer subtype, disproportionately affecting young and African American populations. TNBC constitutes up to 15% of breast cancers that lack effective targeted therapy. The Nucleosome Remodeling and Deacetylase (NuRD) complex, a pivotal chromatin remodeling entity, plays a crucial role in cancer development and progression. Specifically, the NuRD complex associates with SALL4 in cancer cells, contributing to the silencing of tumor-suppressor genes like PTEN. In this study, we discover R9, a novel small-molecule nucleotide analog, a first-in-class NuRD inhibitor. Utilizing computational and cellular methods, R9 demonstrated selective engagement with RBBP4, a key NuRD complex subunit. Cellular target engagement technology has been utilized to verify direct interaction of R9 with NuRD complex as well as to guide medicinal chemistry efforts. Mass spectrometry thermal proteome profiling (TPP) affirmed RBBP4 as the primary target of R9 with minimal off-target effects. In vitro studies reveal R9 displaying robust toxicity in TNBC cells, while sparing normal tissue derived cells. Encouragingly, R9 effectively impeded TNBC tumors growth in mice without inducing toxicity. Mechanistically, we demonstrate R9 induces DNA damage in sensitive TNBC cells, and the sensitivity correlates to DNA damage-vulnerable cancer cells, indicating DNA damage is a major effector of NuRD complex inhibition in TNBCs. We further demonstrate that R9 induces DNA damage through a c-MYC dependent manner. Ongoing studies aim to elucidate key transcription factors involved in NuRD complex inhibition and the role of MYC and DNA damage in response to NuRD complex inhibition. This research positions R9 as a promising candidate for targeted therapy in TNBC, offering potential insights into the intricate molecular pathways involved in TNBC tumor progression. Citation Format: Kun Zhang, Sheeba Jacob, Mikhail Dozmorov, Ivan Babic, Elmar Nurmemmedov, Anthony C. Faber. R9: A novel NuRD complex inhibitor for targeted therapy in triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5976.

2053 Background: Pritumumab, a fully human IgG1 (kappa) monoclonal antibody (mAb), was originally isolated from a patient with cervical carcinoma. This classical example of a natural human anti-cancer antibody recognizes an altered form of the cytoskeletal protein vimentin, referred to as ectodomain vimentin (EDV). EDV is an ideal target for immunotherapy as it is expressed on the surface of tumor cells and is significantly overexpressed in glioblastomas (GBM). A multi-center phase 1 study was performed to assess the safety and pharmacokinetics of Pritumumab (NCT04396717). Methods: Eligible patients included age ≥18 years, histologically confirmed diagnosis of a central nervous system cancer, and have failed prior standard therapy. Exclusion criteria included insufficient time from prior therapy characterized as less than 28 days from cytotoxic therapy, less than 14 days from non-cytotoxic investigational agent, and less than 7 days for non-cytotoxic or immunotherapy agent. Dose Escalation Schema: Five cohort arms with up to 6 patients at each dose level included Cohort 1 (1.6 mg/kg), Cohort 2 (4.8 mg/kg), Cohort 3 (8.0 mg/kg), Cohort 4 (12.0 mg/kg), and Cohort 5 (16.2 mg/kg) on weekly 3+3 dosing schedule. Dose escalation was based on the dose-limiting toxicities (DLT) encountered through Day 28 of treatment. Pharmacokinetics:Blood and CSF samples were collected for pharmacokinetic (PK) analysis both pre- and post-dose. Results: 24 patients provided informed consent and 9 were excluded for not meeting eligibility. 15 patients received the investigational agent and were evaluable for safety and efficacy analyses. 12/15 patients had a diagnosis of glioblastoma and one patient each had anaplastic astrocytoma, oligodendroglioma, and non-small lung cancer with brain metastases. 13 patients discontinued treatment due to disease progression, one due to PI discretion for an unrelated CNS infection, and one withdrew for personal reasons. One partial response showed nearly a 98.0% and 40.8% reduction in 2 tumor lesions for 17 months on study. There were no dose-limiting toxicities to this natural human IgG mAb. The most common adverse events at least possibly attributed to Pritumumab were fatigue (53.3%) and constipation (33.3%). Other rare side effects, possibly related to Pritumumab, occurred at 6.7% were nausea, joint tenderness, dehydration, hypomagnesemia, neuropathy, pruritus, scalp dryness, dry skin (face), and depression. There were no Grade 3, 4, or 5 adverse events attributed to pritumumab. Preliminary pharmacokinetic (PK) data shows volume of distribution as 38.36 mL/kg and clearance of Pritumumab as 0.1305 mL/h/kg. The half-life of Pritumumab was found to be 12.5 days. Conclusions: Single agent Pritumumab is safe up to a dose of 16.2 mg/kg every 7 days in brain tumor patients. A phase 2 study is being planned as single agent and in combination with checkpoint inhibitors in both recurrent gliomas and upfront with chemoradiation in newly diagnosed gliomas. Clinical trial information: NCT04396717 .

mp3 file (9.8 MB). In the November edition of the Cancer Discovery podcast, Executive Editor Mark Landis talks with Paul S. Mischel about his paper, which identifies mTORC2 as a novel mediator of drug resistance and regulator of NF-κB signaling in glioblastoma.