Mutant Cell Lines Research Articles

Abstract LB220: Farnesyltransferase inhibitors show synergistic anticancer effects in combination with novel KRAS G12C inhibitors

Abstract Background. Farnesyltransferase inhibitors (FTI) failed as monotherapies for various cancer types until the discovery of their potency in HRAS mutant human head and neck and bladder cancers. On the other hand, RAS mutant cancers have been a great challenge for cancer research until the discoveries and approvals of several KRAS-G12C allele specific inhibitors. However, G12C inhibitors were effective mainly in lung cancer and de novo and acquired resistance prompted the development of various combinational modalities including immunotherapy as well as SOS- and SHP2-inhibitors. Based on in-silico analysis of drug sensitivities of KRAS mutant cancer cell lines treated with various drugs including FTIs, we have explored the possibility of the combination of FTIs with KRAS inhibitors.Methods. Clinically approved farnesyl-transferase inhibitors (tipifarnib and lonafarnib) were combined with, novel KRAS G12C inhibitors (sotorasib and adagrasib) using human lung-, pancreatic and colorectal- adenocarcinoma cells in vitro and in vivo. Antitumoral effects were evaluated for cell proliferation, apoptosis and migratory activity. Mechanisms of action were investigated by immunoblot analyzes of various farnesylated proteins, RAS activation and signaling, videomicroscopy and also by histopathology of xenograft tumors. Results. Synergistic anticancer effects were observed upon the combination of FTIs with G12C inhibitors in KRAS G12C mutant human cancer cell lines in vitro. We found that the combination interfered with the compensatory re-activation of HRAS, farnesylation of RHEB in the PI3K/mTOR pathway and lamin. Furthermore, we observed enhanced efficacy of sotorasib upon combination with tipifarnib in the xenograft models of lung adenocarcinoma affecting mitotic- and apoptotic rates and inducing necrosis.Discussion. Our findings suggest the potential clinical applicability of the combination of KRAS-G12C inhibitors and farnesyl-transferase inhibitors. Furthermore, our preliminary data suggest that the synergistic effect of FTIs on KRAS-G12C inhibitors can be projected to G12D inhibitors as well. Citation Format: Jozsef Timar, Marcell Baranyi, Eszter Molnar, Ivan Randelovic, Mihaly Cserepes, Jozsef Tovari, Balazs Hegedus. Farnesyltransferase inhibitors show synergistic anticancer effects in combination with novel KRAS G12C inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB220.

Abstract LB175: Discovery of HP567, a highly potent, brain-penetrating, and H1047R-selective PI3Kα inhibitor for the treatment of tumors bearing H1047R mutation

Abstract The phosphoinositide 3 kinase (PI3K)-protein kinase B (PKB/AKT) is one of the most altered pathways in human cancer and its hyperactivation promotes tumor growth and survival. H1047R increases kinase activity and is the most common PI3Kα mutation with a mutation rate of 7.8% in all cancers, and 21%, 5% and 3% in breast cancer, endometrium, and ovarian cancer, respectively. Alpelisib is an FDA approved PI3Kα inhibitor targeting both wild-type (WT) and mutant PI3Kα, yet its clinical benefit is limited by the toxicities including hyperglycemia and rash (which are considered on target effects of WT- PI3Kα inhibition). Here, we report an allosteric and brain-penetrating PI3Kα inhibitor, HP567 that is 14-fold selective for PI3Kα H1047R over PI3Kα WT and is 80-fold selective over other PI3K isoforms. HP567 strongly inhibits proliferation and p-AKT (S473) in H1047R mutant cell lines with an average IC50 of 138 nM and 8 nM, respectively, and has no activity against PI3Kα WT cell lines. HP567 strongly inhibits growth of tumors bearing H1047R in multiple CDX models including breast cancers (MDA-MB-453, T47D, and CAL-148), ovarian cancer (SK-OV-3), tongue squamous cell carcinoma (CAL-33), and a brain-metastatic breast cancer (MDA-MB-453), without causing hyperglycemia or increases in plasma insulin levels. In conclusion, HP567 is a novel, potent, and brain-penetrating PI3Kα H1047R selective inhibitor. The pre-clinical data supports the clinical development of HP567 for the treatment of tumors bearing PI3Kα H1047R mutations. Structure of HP567 will not be disclosed. Citation Format: Jing Li, Lei Fan, Chengcheng Liu, Yao Luo, Xiaohui Chu, Hua Yu, Fei Wang, Xinghai Li. Discovery of HP567, a highly potent, brain-penetrating, and H1047R-selective PI3Kα inhibitor for the treatment of tumors bearing H1047R mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB175.

Abstract ND07: BBO-8520, a first-in-class, direct inhibitor of KRASG12C (ON), locks GTP-bound KRASG12C in the state 1 conformation resulting in rapid and complete blockade of effector binding

Abstract The glycine to cysteine mutation on codon 12 of KRAS (KRASG12C) is found in ~15% of non-small cell lung cancers and in a low percentage of colorectal and pancreatic adenocarcinomas. This activating mutation pushes the balance of cellular KRAS towards its active, GTP-bound (ON) state that signals downstream and drives cellular proliferation. Recently approved inhibitors of KRASG12C that bind and sequester the oncogenic protein in its inactive GDP-bound (OFF) state, have demonstrated clinical efficacy; however, median duration of response has been < 9 months. Rapid tumor cell adaptation to KRASG12C (OFF)-only inhibitors like sotorasib and adagrasib has been attributed to reactivation of MAPK signaling through increased RTK flux and KRASG12C gene amplification that result in increased KRASG12C (ON) presence and activity. To block rapid KRASG12C (ON)-driven adaptation to KRASG12C (OFF) inhibitors, we have developed a first-in-class, direct, small molecule covalent inhibitor of both KRASG12C (ON) and (OFF) states. BBO-8520 binds in the switch II pocket and covalently modifies both the (ON) and (OFF) forms of KRASG12C independently of any other partner proteins. Mass spectrometry analysis of KRASG12C covalent engagement by BBO-8520 shows complete modification of both KRASG12C states within 15 minutes, while sotorasib and adagrasib, only modify the (OFF) state. 31P NMR studies demonstrate that BBO-8520 inhibits KRASG12C (ON) by locking the GTP-bound protein in state 1, a conformation where it is unable to bind effectors. The ability to directly bind KRASG12C (ON) leads to potent (~30 nM) inhibition in an effector (Raf1) binding assay where inactive (OFF) inhibitors demonstrate no measurable potency. BBO-8520 displays highly significant binding to KRASG12C in a global cysteine proteome analysis and is 100x more selective for KRASG12C than for WT KRAS and other mutant isoforms, with no measurable activity against N- or H-RAS. Cellular signaling and viability assays show that BBO-8520 has sub-nanomolar potency against KRASG12C mutant cell lines. In effector binding assays, BBO-8520 rapidly and completely blocks the RAS-RAF1 interaction, clearly differentiating it from inactive (OFF) inhibitors that require longer times to allow for cycling to the inactive (OFF) state. Additionally, long-term clonogenic assays that detect the emergence of resistance in the presence of inhibitors show that BBO-8520 is at least 30x more potent than sotorasib and adagrasib at preventing outgrowth. Importantly, the presence of growth factors (e.g., EGF) that push KRASG12C into its (ON) state, and significantly lower the potency of inactive (OFF) inhibitors (>20x), have only minor effects on BBO-8520’s potency. Drug-like pharmacokinetic properties allow BBO-8520 to achieve strong dose- and time-dependent pharmacodynamic effects (>80% inhibition of pERK) following a single, oral dose in KRASG12C mutant tumor bearing mice. In vivo target engagement and pERK inhibition in the MIAPaCa-2 and H358 KRASG12C mutant tumor models resulted in durable tumor regressions at 10 mg/kg. Similarly, daily dosing of 10 mg/kg of BBO-8520 in the KrasG12C-p53 driven GEMM model for 6 weeks resulted in better than 50% lung tumor volume regression. BBO-8520’s potent activity against KRASG12C (ON) presents, for the first time, the potential opportunity to directly target all mutant KRASG12C in cells, including the active form of KRASG12C, enabling efficacy following complete or near-complete target inhibition. Citation Format: Anna E. Maciag, James Stice, Bin Wang, Alok Sharma, Albert Chan, Ken Lin, Devansh Singh, Marcin Dyba, Yue Yang, Saman Setoodeh, Brian P. Smith, Dana Rabara, Zuhui Zhang, Erik K. Larsen, Dom Esposito, John Paul Denson, Michela Ranieri, Mary Meynardie, Sadaf Mehdizadeh, Patrick Alexander, Maria Abreu Blanco, David Turner, Rui Xu, Felice C. Lightstone, Kwok Kin Wong, Dhirendra Simanshu, Keshi Wang, Andrew G. Stephen, Kerstin Sinkevicius, Dwight V. Nissley, Eli Wallace, Frank McCormick, Pedro J. Beltran. BBO-8520, a first-in-class, direct inhibitor of KRASG12C (ON), locks GTP-bound KRASG12C in the state 1 conformation resulting in rapid and complete blockade of effector binding [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr ND07.

Abstract LB169: Using a global reporter on transcript abundance to identify a selective inhibitor of Nrf2 signaling in KEAP1-mutant non small cell lung cancer

Abstract Loss-of-function mutations in Kelch-like ECH-associated protein 1 (KEAP1) are common in non-small cell lung cancer (NSLC) and result in particularly poor prognosis. Such mutations activate the transcription factor Nrf2, leading to aberrant expression of chemoprotective genes and rendering cells resistant to chemotherapy. We used our chemo-transcriptomic platform, termed GRETA, for Global Reporter on Transcript Abundance, to identify compounds that inhibit Nrf2 transcription factor activity in KEAP1-mutant NSCLC cell lines. After defining the transcriptomic signature imparted by constitutive activation of Nrf2 in a KEAP1 KO NCI-H1975 cell line, we generated over 10,000 transcriptomes to identify compounds that dampen the Nrf2-overactive transcriptional signature. One such compound, ARP-4316, displays selectivity for KEAP1-mutant cell lines, reduces nuclear Nrf2 protein levels, and reduces Nrf2 transcriptional activity in an ARE reporter assay. Furthermore, ARP-4316 synergizes with 5-fluorouracil in two KEAP1-mutant cell models, A549 and NCI-H2122, suggesting that ARP-4316 may sensitize KEAP1 mutant cell lines to chemotherapy by inhibiting Nrf2 transcriptional activity. Efforts to identify the cellular target and mechanism of action of ARP-4316 are underway. Citation Format: Timothy J. Read, Leah Damon, Reo Yoo, Carter Grochala, Cole Liechty, Christy Rhine, Jenna Rimel, David Simpson, Riley Lundblad, Casey Pham, Richard Steel, Joey Azofeifa. Using a global reporter on transcript abundance to identify a selective inhibitor of Nrf2 signaling in KEAP1-mutant non small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB169.

Abstract CT154: Phase 1/2 clinical trial of JIN-A02, a 4th generation EGFR-TKI, in patients with 3rd generation EGFR-TKI resistance in EGFR mutated advanced/metastatic non-small cell lung cancer (NSCLC)

Abstract Background: Epidermal growth factor receptor (EGFR) mutations are the most common driver mutations in NSCLC. EGFR tyrosine kinase inhibitors (TKIs) are the recommended front-line option for EGFR-mutant advanced NSCLC patients, but patients invariably develop acquired resistance and face disease progression. JIN-A02, a 4th generation EGFR-TKI intended for oral administration, selectively and reversibly binds to EGFR mutations, including the C797S and/or T790M mutation that causes resistance to 3rd generation of EGFR-TKIs. Pre-clinical studies with EGFR C797S and/or T790M mutated cell lines showed that JIN-A02 can inhibit cell growth in a dose dependent manner and has a high degree of selectivity over wild-type EGFR. In vivo studies showed that administration of JIN-A02 dose-dependently inhibited tumor growth in the C797S+ xenograft mice model. Moreover, JIN-A02 shown to penetrate blood-brain barrier and exhibit anti-tumor activity in an intracranial tumor model. The strong potency and high selectivity of JIN-A02 for mutant EGFR may offer improved therapeutic window in the clinical setting vs available EGFR-TKIs. Methods: JIN-A02 is being evaluated in this Phase 1/2, multicenter, an open-label trial (NCT05394831) for subjects with advanced NSCLC harboring C797S and/or T790M mutation as a monotherapy. The primary object of this study is to assess safety, tolerability, pharmacokinetics, and anti-tumor effect for determining the recommended phase 2 dose (RP2D) of JIN-A02. The inclusion criteria are that the subject (≥ 18 years) must have an advanced or metastatic NSCLC showed progress disease (PD) after receiving approved standard EGFR-TKI therapies and/or platinum-based anticancer chemotherapy is allowed up to 1 time after using EGFR-TKI treatment with ECOG status 0 or 1. Before enrollment in the study, the EGFR mutation status is determined using either tumor tissue and/or plasma ctDNA. This study comprises three parts, dose escalation (Part A), dose exploration (Part B), and dose expansion (Part C). In Part A, dose escalation, comprised of 5 cohorts ranged from a starting dose of 12.5 mg P.O, QD to a top dose of 150 mg P.O, QD with every three subjects, is carried out where the maximum tolerated dose (MTD) is evaluated in subjects with 28-day cycles. Dose-limiting toxicities (DLT) are evaluated for 21 days. In Part B, dose exploration is carried out to evaluate the safety of JIN-A02 further and to determine the RP2D using 2 preliminary effective dose levels from Part A in subjects. In Part C dose-expansion study, subjects (n=36 for each cohort) are divided into 5 different cohorts based on the EGFR mutation (both or single positive of C797S and T790M), and the anti-tumor activity of JIN-A02 is evaluated according to RECIST v1.1 at RP2D. Citation Format: Sun Min Lim, Byoung Chul Cho, Ji Youn Han, Sang We Kim, Ki Hyeong Lee, Misako Nagasaka, Anna Jo, Ethan Seah, Choonok Kim, Thanyanan Reungwetwattana. Phase 1/2 clinical trial of JIN-A02, a 4th generation EGFR-TKI, in patients with 3rd generation EGFR-TKI resistance in EGFR mutated advanced/metastatic non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT154.

Crispr-Based Editing of Human Pluripotent Stem Cells for Disease Modeling.

The CRISPR system, as an effective genome editing technology, has been extensively utilized for the construction of disease models in human pluripotent stem cells. Establishment of a gene mutant or knockout stem cell line typically relies on Cas nuclease-generated double-stranded DNA breaks and exogenous templates, which can produce uncontrollable editing byproducts and toxicity. The recently developed adenine base editors (ABE) have greatly facilitated related research by introducing A/T > G/C mutations in the coding regions or splitting sites (AG-GT) of genes, enabling mutant gene knock-in or knock-out without introducing DNA breaks. In this study, we edit the AG bases in exons anterior to achieve gene knockout via the ABE8e-SpRY, which recognizes most expanded protospacer adjacent motif to target the genome. Except for gene-knockout, ABE8e-SpRY can also efficiently establish disease-related A/T-to-G/C variation cell lines by targeting coding sequences. The method we generated is simple and time-saving, and it only takes two weeks to obtain the desired cell line. This protocol provides operating instructions step-by-step for constructing knockout and point mutation cell lines.

Deafness-associated tRNAPhe mutation impaired mitochondrial and cellular integrity

Defects in mitochondrial RNA metabolism have been linked to sensorineural deafness that often occurs as a consequence of damaged or deficient inner ear hair cells. In this report, we investigated the molecular mechanism underlying a deafness-associated tRNAPhe 593T > C mutation that changed a highly conserved uracil to cytosine at position 17 of the DHU-loop. The m.593T > C mutation altered tRNAPhe structure and function, including increased melting temperature, resistance to S1 nuclease-mediated digestion, and conformational changes. The aberrant tRNA metabolism impaired mitochondrial translation, which was especially pronounced by decreases in levels of ND1, ND5, CYTB, CO1, and CO3 harboring higher numbers of phenylalanine. These alterations resulted in aberrant assembly, instability, and reduced activities of respiratory chain enzyme complexes I, III, IV, and intact supercomplexes overall. Furthermore, we found that the m.593T > C mutation caused markedly diminished membrane potential, and increased the production of reactive oxygen species in the mutant cell lines carrying the m.593T > C mutation. These mitochondrial dysfunctions led to the mitochondrial dynamic imbalance via increasing fission with abnormal mitochondrial morphology. Excessive fission impaired the process of autophagy including the initiation phase, formation, and maturation of the autophagosome. In particular, the m.593T > C mutation upregulated the PARKIN-dependent mitophagy pathway. These alterations promoted an intrinsic apoptotic process for the removal of damaged cells. Our findings provide critical insights into the pathophysiology of maternally inherited deafness arising from tRNA mutation-induced defects in mitochondrial and cellular integrity.

Porcine reproductive and respiratory syndrome virus infection activates ADAM17 to induce inflammatory responses

Porcine reproductive and respiratory syndrome (PRRS), which has posed substantial threats to the swine industry worldwide, is primarily characterized by interstitial pneumonia. A disintegrin and metalloproteinase 17 (ADAM17) is a multifunctional sheddase involved in various inflammatory diseases. Herein, our study showed that PRRS virus (PRRSV) infection elevated ADAM17 activity, as demonstrated in primary porcine alveolar macrophages (PAMs), an immortalized PAM cell line (IPAM cells), and the lung tissues of PRRSV-infected piglets. We found that PRRSV infection promoted ADAM17 translocation from the endoplasmic reticulum to the Golgi by enhancing its interaction with inactive rhomboid protein 2 (iRhom2), a newly identified ADAM17 regulator, which in turn elevated ADAM17 activity. By screening for PRRSV-encoded structural proteins, viral envelope (E) and nucleocapsid (N) proteins were identified as the predominant ADAM17 activators. E and N proteins bind with both ADAM17 and iRhom2 to form ternary protein complexes, ultimately strengthening their interactions. Additionally, we demonstrated, using an ADAM17-knockout cell line, that ADAM17 augmented the shedding of soluble TNF-α, a pivotal inflammatory mediator. We also discovered that ADAM17-mediated cleavage of porcine TNF-α occurred between Arg-78 and Ser-79. By constructing a precision mutant cell line with Arg-78-Glu/Ser-79-Glu substitution mutations in TNF-α, we further revealed that the ADAM17-mediated production of soluble TNF-α contributed to the induction of inflammatory responses by PRRSV and its E and N proteins. Taken together, our results elucidate the mechanism by which PRRSV infection activates the iRhom2/ADAM17/TNF-α axis to enhance inflammatory responses, providing valuable insights into the elucidation of PRRSV pathogenesis.

Identification of P21 (CDKN1A) Activated Kinase 4 as a Susceptibility Gene for Familial Non-Medullary Thyroid Carcinoma.

Background: Familial non-medullary thyroid carcinoma (FNMTC) is a genetically predisposed disease with unclear genetic mechanisms. This makes research on susceptibility genes important for the diagnosis and treatment options. Methods: This study included a five-member family affected by papillary thyroid carcinoma. The candidate genes were identified through whole-exome sequencing and Sanger sequencing in family members, other FNMTC patients, and sporadic non-medullary thyroid carcinoma patients. The pathogenicity of the mutation was predicted using in silico tools. Cell phenotype experiments in vitro and models of lung distant metastasis in vivo were conducted to confirm the characteristics of the mutation. Transcriptome sequencing and mechanistic validation were employed to compare the disparities between PAK4 wild-type (WT) and PAK4 mutant (MUT) cell lines. Results: This mutation alters the protein structure, potentially increasing instability by affecting hydrophobicity, intra-molecular hydrogen bonding, and phosphorylation sites. It specifically promotes phosphorylated PAK4 nuclear translocation and expression in thyroid tissue and cell lines. Compared with the WT cells line, PAK4 I417T demonstrates enhanced proliferation, invasiveness, accelerated cell division, and inhibition of cell apoptosis in vitro. In addition, it exhibits a significant propensity for metastasis in vivo. It activates tumor necrosis factor signaling through increased phosphorylation of PAK4, JNK, NFκB, and c-Jun, unlike the WT that activates it via the PAK4-NFκ-MMP9 axis. In addition, PAK4 MUT protein interacts with matrix metalloproteinase (MMP)3 and regulates MMP3 promoter activity, which is not observed in the WT. Conclusions: Our study identified PAK4: c.T1250C: p.I417T as a potential susceptibility gene for FNMTC. The study concludes that the mutant form of PAK4 exhibits oncogenic function, suggesting its potential as a novel diagnostic molecular marker for FNMTC.

Abstract 3022: GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells

Abstract Chemical carcinogens or xenobiotics present in the diet play a significant role in colon cancer (CC) formation. p53, a tumor suppressor and multi-functional protein, provides an important barrier against the initiation and maintenance of CC. p53 mutation or inactivation is observed in about 60% of CCs and about 90% of all cancers. Therefore, therapeutic avenues that will rejuvenate wild-type p53 or target mutant p53 should have a significant impact on the prevention and treatment of CC. GPR109A, a G-protein coupled receptor for the FDA-approved lipid-lowering drug Niacin (NA), bacterial metabolite Butyrate (BTR), and ketone body β-hydroxybutyrate (BHB), functions as a novel tumor suppressor in the colon by providing the molecular link between colonic bacteria and p53 function. GPR109A activation limits cAMP by inhibiting adenylate cyclase (AC), which induces RAS and its downstream growth-promoting signaling. cAMP also enhances the binding of MDM2 to p53 and induces the proteasomal degradation of p53. p53 is an NAD+-dependent molecule and deficiency of NA, the precursor of NAD+, impairs p53 function. We tested the role of GPR109A and its agonists (NA, BTR, and BHB) in normal immortalized colon epithelial cell lines (CCD33 and CCD81) and various CC lines such as HCT116-p53+/+, HCT116-p53−/−, DLD1 (p53 point mutation), VACO4A (p53 insertion mutation), and SW498 (p53 deletion) and measured cell proliferation, cell cycle, apoptosis, and analyzed the expression of GPR109A and p53 (total, phosphorylated, and acetylated), MDM2, p21, Bax, and Puma in the presence and absence of GPR109109 agonists. We found that GPR109A expression is significantly reduced in CC cell lines, especially in p53 mutant cell lines, when compared to normal immortalized colonic epithelial cell lines. Treatment of CC cell lines with GPR109A agonists-induced apoptosis in wild-type p53 expressing CC by activating p53 and its targets. However, some lesser extent in p53 mutant or p53 null cell lines. Lentiviral-mediated GPR109A expression in CC cell lines itself induced apoptosis in both wild-type and mutant p53 expressing CC cell lines and GPR109A agonists treatment induced further. Interestingly, GPR109A agonists BTR and BHB significantly increased apoptosis in p53 mutant and p53 null CC cell lines in a p53-independent manner. Overall, our results provide evidence that GPR109A activation can be used as an effective therapeutic strategy for the treatment of CC. Citation Format: Muthusamy Thangaraju, Nanditi N. Thangaraju, Lauren Gilstrap, Madison Chimenti, Tulshi Patel, Sathish Sivaprakasam, Nikhil Patel, Santhakumar Manicassamy, Puttur D. Prasad, Vadivel Ganapathy. GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells [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 3022.

Abstract 1925: Wild-type RAS signaling is an essential therapeutic target in RAS-mutated cancers

Abstract Single-agent targeting of RAS-mutated cancers using RAF/MEK/ERK or PI3K/AKT pathway inhibitors is ineffective; blocking one pathway relieves negative feedback control of RTK signaling and hyperactivates parallel effector pathways. While combined MEK and PI3K inhibition is effective in preclinical models, toxicity of this combination prevents its clinical use. Alternative strategies for treating RAS-mutated cancers are essential. Therapeutics directly targeting mutated RAS proteins have the potential to spare normal cellular function thereby lessening overall toxicity. Unfortunately, direct RAS inhibition as a monotherapy does not fully block RAS effector signaling. RAS proteins show differential activation of RAF and PI3K pathways: KRAS potently activates RAF but poorly activates PI3K, whereas HRAS effectively activates PI3K but poorly activates RAF. Further, mutant RAS inhibition relieves negative feedback controls leading to rapid hyperactivation of RTK−WT RAS signaling. A more comprehensive understanding of the interplay between mutant RAS and RTK−WT RAS signaling is essential to developing rational therapeutic approaches to treat RAS-mutated cancers. We found that WT RAS enhanced mutant RAS-driven transformation by activating RAS effectors poorly engaged by mutated RAS. Further, inhibition of RAS effectors activated poorly by mutant RAS synergized with and limited resistance to mutant HRAS and KRAS inhibitors. The mutant HRAS inhibitor tipifarnib blocked PI3K signaling and synergized with MEK inhibitors in HRAS-mutated cancer cell lines; covalent KRASG12C inhibitors blocked MEK signaling and synergized with PI3K inhibitors in KRASG12C- mutated cell lines. Synergy between inhibitors of mutant RAS and RAS effectors was dependent on intact RTK/WT RAS signaling and was lost in both RASless or SOSless MEFs. Dual knock-out of WT RAS isoforms in KRAS- and HRAS-mutated cancer cell lines reduced PI3K signaling in KRAS-mutant cell lines and MAPK signaling in HRAS-mutant cell lines and reduced proliferation, confirming our findings in MEF cells. Overall, our data highlight the critical role of WT RAS isoforms in supporting mutant RAS signaling and should be considered when designing combination therapies in RAS-mutated cancers. Citation Format: Nancy E. Sealover, Bridget Finniff, Jacob Hughes, Hyun Lee, Robert L. Kortum. Wild-type RAS signaling is an essential therapeutic target in RAS-mutated cancers [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 1925.

Abstract 6512: BPI-501836: A highly potent small molecule inhibitor targeting KRASG12D mutation

Abstract As one of the most notorious un-druggable oncogenes, mutant KRAS impairs the transition of RAS from its active GTP-binding form to the inactive GDP-binding form, leading to sustained activation of downstream MAPK pathway and ultimately tumorigenesis. The recent approved KRASG12C inhibitors have demonstrated clinical benefits in KARSG12C mutant patients. However, the other prevalent KRAS mutations, such as KRASG12D, remain a huge unmet medical challenge. There’s no approved KRASG12D specific inhibitors yet. Here we present BPI-501836, a highly potent and selective small molecular inhibitor for KRASG12D. In vitro, BPI-501836 exhibited very high potency by disrupting the KRASG12D and cRAF interaction in a cell-free assay. In cell-based assays, BPI-501836 inhibited proliferation of KRASG12D mutant cell lines with sub-nanomolar IC50 values, without affecting wide type or non-G12D KRAS mutant cell lines. Moreover, it also attenuated ERK phosphorylation in KRASG12D mutant cells. In vivo, tumor regression was observed following the administration of 6 mg/kg (iv, QW) BPI-501836 in KRASG12D human pancreatic Panc04.03 xenograft mouse models, or in the KRASG12D human pancreatic PK-59 xenograft mouse models with an intraperitoneal injection of 20 mg/kg per week. Noteworthy was the prolonged half-life of BPI-501836 observed across various species, coupled with its high distribution in tumor tissues. Moreover, sustained suppression of ERK phosphorylation in tumor tissues persisted for up to 144 hours after the last dose of BPI-501836 in both xenograft mouse models. This extended pharmacodynamic effect supports the feasibility of a once-weekly dosing schedule in clinical applications. Safety assessments conducted through a 4-week repeated infusion (intravenous, twice weekly) of BPI-501836 in beagle dog demonstrated favorable safety profiles. In conclusion, BPI-501836 emerges as a highly potent and selective KRASG12D inhibitor, exhibiting promising pharmacokinetics, pharmacodynamics, and safety profiles in pre-clinicalstudies. BPI-501836 is currently in IND-enabling stage and holds potential for further development as a therapeutic agent. Citation Format: Xiang Yang, Yuan Lu, Renqi Xu, Xiaoqiang Kong, Yongqing Sun, Xingjie Zhu, Xiaoyun Liu, Zhengyao Zou, Haibo Chen, Yanju Liu, Jialing Sun, Han Han, Cheng Yang, Jing Guo, Hong Lan, Quan Zhou, Lieming Ding, Hao Wu, Jiabing Wang. BPI-501836: A highly potent small molecule inhibitor targeting KRASG12D mutation [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 6512.

Abstract 3136: Towards development of a novel biparatopic trop2-ADC

Abstract Background: Trophoblast cell surface antigen 2 (TROP-2) is a member of Tumor-associated Calcium Signal Transducer family (TACSTD2), which is a 35kDa transmembrane protein with 4 N-linked glycosylation sites. The overexpression of TROP2 in various cancers is associated with poor prognosis and increased risk of metastasis. Anti-TROP2 antibody drug conjugates (ADCs) are emerging as an innovative therapeutic intervention for cancer treatment. While these efforts were rewarded by the FDA approval of Trodelvy (Sacituzumab govitecan), a Trop2 targeted ADC, in 2020 for the TNBC patients, tumor heterogeneity could present one of the limitations for the Trop2-targeting therapy, leading to drug resistance. Here, we report our effort in developing a novel biparatopic TROP2 ADC which demonstrate superior cell killing activity compared with the monospecific TROP2 ADC, including certain resistant cell lines for the approved therapy. Methods: Various biparatopic Abs were engineered using two different mAbs targeting the two non-overlapping epitopes of Trop2. The physical stability and biological activities were characterized. Binding competition assay was utilized for epitope binning using SPR. Cell binding affinity was determined using flow cytometry. Cellular internalization activity was measured using Incucyte system, and tumor cell killing efficacy was evaluated in multiple cancer cell lines. CDX mouse models were utilized to investigate the TROP2-ADC in vivo efficacy. Results: We identified a biparatopic TROP2 mAb using two monospecific TROP2 mAbs with A recognizing the same epitope as Trodelvy, and B binding to a non-overlapping epitope vs Sacituzumab’s. mAb-B demonstrates superior ability to recognize a few resistance cell lines to mAb-A. The biparatopic TROP2 mAb-A/B displays a KD of 0.81 nM protein binding compared with 6.42 nM and 0.26 nM, respectively for mAb-A and mAb-B. Importantly, the biparatopic mAb-A/B demonstrates significantly faster cellular internalization activity compared to those of the individual mAbs, signifying the biparatopic scaffold could drive receptor clustering and subsequently enhance the internalization, trafficking to the lysosome and degradation of the target. As expected, the ADC of the biparatopic mAb-A/B conjugated with a TOPi payload shows cancer cell killing efficacy in both in vitro and in vivo experiments. Furthermore, we tested mAb-A, -B and biparatopic mAb-A/B for their binding affinity to 14 missense mutations in TROP2 ECD expressed in HEK293 cells. Interestingly, mAb-A showed decreased binding in 5 mutant cell lines, while mAb-B and biparatopic mAb-A/B maintains activity. Conclusion: We have engineered a novel TROP2 biparatopic antibody with unique biological features as well as superior in vitro and in vivo activities. Such a biparatopic ADC presents its potential to be a best-in-class ADC therapy by overcoming the limitation of the monospecific ADC therapy such as drug resistance. Citation Format: Yinan Wu, Brittany Jiang, Julliet Rivera, Fang Wang, Jing Zhou, Lin Liu, Silvia Hudson, Will Draper, Jennifer Li, Xiaoshan Min, Hang Chen, Zhulun Wang. Towards development of a novel biparatopic trop2-ADC [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 3136.

Abstract 1932: Overcoming acquired resistance to KRAS(G12D) inhibition using a KRAS-HSP90 hetero-bifunctional small molecule therapeutic agent

Abstract KRAS mutations are highly prevalent across many different cancer types. Recent advancements in KRAS-targeted drugs, such as the FDA-approved KRAS(G12C) inhibitors sotorasib and adagrasib for NSCLC patients, have shown great promise in the clinic. Nonetheless, these new agents fail to address other mutations, such as KRAS(G12D), which overall is the most common KRAS mutation in cancers, being found in 37% of pancreatic ductal adenocarcinomas, 12.5% of colorectal cancers and 4.9% of lung adenocarcinomas. Recently, MRTX1133 has been described as a selective, non-covalent inhibitor of KRAS(G12D) that shows promising preclinical efficacy and is undergoing clinical testing. However, based on prior clinical experience with sotorasib and adagrasib, acquired resistance to MRTX1133 may reasonably be anticipated. In fact, we find that KRAS(G12D)-mutated cell lines and a patient-derived organoid model exhibit varying degrees of inherent resistance to MRTX1133. To examine the consequences of blocking KRAS signaling, we employed a KRAS(G12D)-specific PROTAC, which simulated the effects of KRAS deletion. This demonstrated that receptor tyrosine kinase (RTK) activation could compensate for loss of KRAS signaling and was a key de novo resistance mechanism. This suggests that combination therapies may need to be individually tailored to treat patients resistant to KRAS(G12D)-targeted therapies. Additionally, we developed MRTX1133 resistant cells by culturing sensitive AsPC-1 pancreatic cancer cells in gradually increasing concentrations of the inhibitor. The resulting resistant cells displayed a complex RTK activation profile compared to parental cells. To counteract this, we employed KRAS(G12D)-CHAMP RNK08179, a hetero-bifunctional small molecule agent that simultaneously targets both KRAS(G12D) and HSP90, an RTK-regulating chaperone protein. RNK08179 effectively suppressed both KRAS signaling and RTK activation in MRTX1133-resistant cancer models, overcoming the compensatory resistance mechanisms observed with MRTX1133 alone. These findings highlight the potential of KRAS-CHAMPs as a novel, effective treatment strategy for KRAS-driven cancers, particularly those resistant to KRAS(G12D) inhibitors. Citation Format: Ines Pulido Endrino, Laura gunder, Qiyue Luan, Chenghao Ying, Zimo Yang, Jinhua Li, Yaya Wang, Yuetong Sun, Chuhe Liu, Yan Dai, Haoxin Zhou, Malek Massad, Ian Papautsky, Thomas L. Prince, Guoqiang Wang, Kevin P. Foley, Weiwen Ying. Overcoming acquired resistance to KRAS(G12D) inhibition using a KRAS-HSP90 hetero-bifunctional small molecule therapeutic agent [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 1932.

Abstract 3290: FTO mediates tumor growth and resistance to erlotinib in NSCLC

Abstract Lung cancer, among the most common cancer types, ranks first in cancer associated deaths. Nearly 85% of the lung cancer cases are non-small cell lung cancer (NSCLC). Epidermal growth factor receptor (EGFR), an established marker for NSCLC, is frequently overexpressed on the cell surface. Amplifying mutations often render these receptors activated in a ligand independent manner, therefore, therapies such as erlotinib, an EGFR tyrosine kinase inhibitor (EGFR-TKI), target these activating mutations and inhibit tumor growth. Nevertheless, patients acquire resistance to EGFR TKI within 9-14 months of treatment. Recent studies show that fat mass and obesity- associated (FTO) gene, initially identified to increase the body mass index, plays a major role in cancer development and acquired therapy resistance in several cancer types. FTO demethylates m6A mRNA and modulates tumorigenesis, and drug resistance. In this study, we explored the functions of FTO in EGFR TKI resistance in NSCLC. To study the expression of FTO in erlotinib resistant cells, we used wildtype-EGFR NSCLC cell lines (H2170, H358) and mutant EGFR NSCLC cell lines (H1975, PC9) that were rendered resistant to erlotinib. Our RT-qPCR results demonstrated that FTO was upregulated by 1.7-3.0 fold in erlotinib resistant H2170, H358, PC9 and H1975 cells. FTO protein was upregulated by 1.3-1.6 fold as seen by western blotting, and by 1.7 to 2.6 fold in the nucleus of erlotinib resistant H1975, H2170 and PC9 cell lines by immunofluorescence. Furthermore, we investigated FTO inhibition with Dac51 (FTOi) on cell viability and cell migration properties. MTT cell viability assay showed a 9-17% decrease in cell viability when treated with a combination of Dac51 and erlotinib compared to Dac51 alone in erlotinib resistant H2170 and PC9 cells, respectively. The combinatory treatment showed an additive effect compared to the Dac51 and erlotinib treatments alone. Wound healing assay revealed an 18% open wound area after 48-hour treatment with both Dac51 and erlotinib compared to 0.1% after treatment with erlotinib alone in erlotinib resistant H2170 cells. To evaluate the effect of siRNA mediated FTO (siFTO) knockdown on cell viability and energy metabolism, MTT and luciferase assays were performed. MTT assay showed a 21-28% decrease in viability in erlotinib resistant H1975, H2170, PC9 cells, demonstrating increase in the erlotinib efficacy, as compared to the mock siRNA treatment. Luciferase assay showed an inverse relationship between the FTO and ATP, where the latter was upregulated by 1.3 to 3.4 folds in erlotinib resistant H1975, H2170 and PC9 cells, when treated with siFTO, suggesting its involvement in the energy requirements of the NSCLC cells. In conclusion, our study suggests FTO was upregulated in erlotinib resistant NSCLC cells on both the gene and protein levels. FTO could mediate resistance to EGFR TKI possibly through cell proliferation and migration and help with prognosis of NSCLC patients. Citation Format: Aayush Rastogi, Rong Qiu, Neelu Puri. FTO mediates tumor growth and resistance to erlotinib in NSCLC [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 3290.

Abstract 3142: NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models

Abstract c-Kit (CD117) is a type III receptor tyrosine kinase (RTK), which is known to be activated upon binding to its cognate ligand stem cell factor (SCF) to induce critical signaling pathways involved in cell proliferation, survival, and differentiation. Indicative of poor prognosis, overexpression and activating mutations of c-Kit have been implicated in a variety of human cancers including small cell lung cancer (SCLC), gastrointestinal stromal tumors (GIST), and acute myelogenous leukemia (AML). While imatinib, a small molecule c-Kit inhibitor, has been a beneficial treatment for GIST, resistance eventually develops to the drug, moreover, shows limited efficacy in c-Kit overexpressing tumors such as SCLC. Herein, we developed NN3201, a novel c-Kit targeting antibody-drug conjugate (ADC), comprised of fully human 2G4 antibody with a picomolar binding affinity to c-Kit and cytotoxic monomethyl auristatin E (MMAE) as the payload. NN3201 displayed potent in vitro cytotoxicity in various wild-type and mutant c-Kit positive SCLC and GIST cell lines with IC50 in the nanomolar range. In addition, NN3201 was rapidly internalized and inhibited c-Kit-mediated signaling., NN3201 treatment resulted in the increased proportions of the sub G1 and G2/M in the c-Kit positive cancer cell lines, indicating that release of MMAE induced cell cycle arrest. Moreover, bystander effect was confirmed by co-culturing c-Kit high and negative cell lines. Most importantly, in mouse xenograft models, NN3201 showed a remarkable tumor growth inhibition of several wild type, mutant c-Kit positive, and imatinib resistant SCLC and GIST cell lines. Enhanced anti-tumor activity and delayed tumor growth were observed in an SOC-treated (etoposide and carboplatin) SCLC xenograft model, by NN3201 in comparison to second line SOC (topotecan or irinotecan). In the GLP study, repeated intravenous administration of NN3201 was well tolerated at all doses (0.5, 1, 2 mg/kg Q3Wx3) without unscheduled death. Dose-dependent, yet transient, cytotoxicity of NN3201 was observed in the bone marrow. We confirmed HNSTD (Highest Non-Severely Toxic Dose) of NN3201 to be 2 mg/kg through exploratory and GLP repeat dose toxicity studies as no serious irreversible toxicity was observed. Accumulating data suggest that NN3201 is a promising therapeutic alternative for the treatment of SCLC and GIST regardless of wild-type or activating mutations in c-Kit. Citation Format: Chansik Kim, Jin Gu Cho, TaeMin Wi, Jiwoo Moon, Han-Jik Ko, Jina Lee, Jin Woo Park, Yeonjy Lee, Sanghee Kim, Jin-Ock Kim, Jaeyoung Song, Sun-Hwa Lee, Sang Gyu Park. NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models [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 3142.

Abstract 1972: Preclinical activity of the type II RAF inhibitor tovorafenib in tumor models harboring either a BRAF fusion or a NF1-LOF mutation

Abstract Genomic alterations and dysregulation of the MAPK pathway have been described in many different types of cancers. BRAF V600 point mutations and BRAF fusions, which are found in both pediatric and adult cancers, are oncogenic drivers that drive constitutive activation of the RAF pathway (Jones 2009, Yaeger 2019). Neurofibromatosis 1 (NF1) loss-of-function (LOF) mutations, which occur in many cancer types, result in decreased neurofibromin GAP function, thus activating RAS (Basu 1992). Tovorafenib is an investigational, selective, CNS-penetrant, small molecule type II RAF inhibitor which inhibits both RAF monomers and dimers and has been shown preclinically to impact the KIAA1549::BRAF fusion (Sun 2017). In this study, the impact of tovorafenib alone or in combination with MEK inhibitor, pimasertib, was explored in adult or pediatric tumor models harboring BRAF fusions or NF1-LOF mutations. At clinically relevant doses, tovorafenib treatment resulted in tumor regression in an AGK::BRAF fusion melanoma patient-derived xenograft (PDX) model in vivo. In contrast, little anti-tumor activity was observed in response to tovorafenib in vivo in two tumor models harboring NF1-LOF mutations. Ongoing PK-PD studies in both the AGK::BRAF fusion model and the NF1-LOF models will assess the extent and duration of target inhibition. In vitro, anti-proliferative activity of tovorafenib was also evaluated in NF1-LOF mutant tumor cell lines or PDX models of different tumor types, including melanoma, lung and malignant peripheral nerve sheath tumor (MPNST). While tovorafenib was potent in the BRAF V600E tumor cell line, little activity was observed in the NF1-LOF tumor cell lines. Modulation of phosphorylated-ERK (pERK) was also assessed. At very low concentrations, modest induction of pERK was observed in the NF1-LOF tumor cell lines, with inhibition at higher concentrations. In vitro combination studies were conducted using pimasertib and tovorafenib, or a tool compound. Synergy was observed in a NF1-LOF embryonal rhabdomyosarcoma PDX model ex vivo and a NF1-LOF MPNST cell line in vitro, suggesting that vertical pathway inhibition is impactful in the NF1-LOF mutant setting. Tovorafenib is currently being evaluated as a monotherapy in relapsed or progressive pediatric low-grade glioma (pLGG) harboring RAF alterations (NCT04775485) and in combination with pimasertib in patients ≥12 years of age with recurrent, progressive, or refractory solid tumors harboring MAPK pathway alterations (NCT04985604). Ongoing preclinical translational work will continue to explore potential biomarker-defined tumor indications for these agents. Citation Format: Shubhra Rastogi, Sam Perino, Madhu Lal-Nag, Yujin Wang, Samuel C. Blackman, Eleni Venetsanakos. Preclinical activity of the type II RAF inhibitor tovorafenib in tumor models harboring either a BRAF fusion or a NF1-LOF mutation [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 1972.

Abstract 4663: Establishing the role of PRMT5 in lung cancer tumorigenicity and modulation of expression in smokers

Abstract Studies show that PRMT5 (protein arginine methyl transferase 5) is responsible for increased tumorigenicity by activation of the PI3K/Akt signaling pathway promoting increased cancer cell proliferation. However, the role of PRMT5 in modulating EGFR TKI resistance is minimally studied. We hypothesize that over-expression of PRMT5 could promote tumorigenesis and TKI resistance by activating PI3K-Akt-mTOR signaling pathways. Hence, modulating this key biomarker may help reduce tumorigenicity and overcome TKI resistance. We performed qPCR to study the expression of PRMT5 in normal lung cells and NSCLC cell lines. We also compared the expression of these biomarkers in erlotinib resistant (ER) and Osimertinib resistant (OR) cells using Western blotting. PRMT5 was inhibited using GSK591 (PRMT5i) to evaluate its sensitivity to EGFR TKIs (ER and OR). PRMT5 expression in normal lung cells and NSCLC cells treated with Cigarette smoke extract (CSE) were also studied and correlated with immunostaining results from smoker and non-smoker lung tumor tissue samples. Changes in PRMT5 expression were analyzed in WT-EGFR lung cancer cell lines (H358, H2170), mutant EGFR lung cancer cell lines (H3255, H1975, PC9) and normal lung fibroblast cells (HLF). PRMT5 expression was upregulated by 1.6-2.1 fold in HLF, H2170 and H358 cells after 1 week of treatment with CSE. CSE treatment also upregulated expression of inflammatory cytokines (IL-1β, IL-8 and TNF-α) in H358 cells by 1.6-7 fold as analyzed by qPCR. PRMT5 expression was upregulated in EGFR-TKI resistant cell lines, by 1.5-1.9 fold in PC9ER, PC9OR and H2170ER cells, compared to parental cells. Similar results were found using qPCR, with 1.6-2.3 fold increase in PRMT5 mRNA expression in H2170OR, PC9ER/OR and H3255OR cells compared to parental cells. An MTT assay was done to assess percentage viability of cells after treatment of PRMT5i. While 2μM PRMT5i treatment of PC9OR cells decreased cell viability by 42%, an inhibitory effect that was more than additive was seen with a combination of 2μM of PRMT5i and 21nM of OR. Similar results were also observed in H2170ER cells. Migratory properties of OR resistant cells, were studied by wound healing assays. Percentage wound area in PRMT5i treated PC9OR cells was 29.3% as compared to 6.1% and 10.5% in diluent and OR treated cells respectively after 48 hrs. Combination treatment of PRMT5i and OR further inhibited cell migration with higher wound area of 41.7%. Immunostaining of lung tumor sections from smokers and non-smokers showed high expression of PRMT5 localized in the cytoplasm and nucleus. Microscopic analysis of 20 tumor sections from smokers showed higher expression of PRMT5 (p<0.05) compared to non-smokers. We can conclude that PRMT5 is upregulated in TKI resistant cells causing tumorigenesis. Modulation of PRMT5 can prove to be groundbreaking and revolutionary, as it may increase the efficacy of EGFR TKIs. Citation Format: Syed N. Ali, Meet Patel, Bamby Dieng, Cody Lund, Neelu Puri. Establishing the role of PRMT5 in lung cancer tumorigenicity and modulation of expression in smokers [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 4663.

Abstract 7153: PHI-101 synergizes with chemotherapy and venetoclax in preclinical models of acute myeloid leukemia

Abstract FLT3 mutations are one of the most frequent genetic alterations in AML, resulting in poor prognosis. Although the development of FLT3 tyrosine kinase inhibitors (TKIs) provided new treatment options, patients with FLT3-mutant AML still suffer from high relapse rates when treated with FLT3 TKI alone. Accumulating evidence supports a combination treatment strategy to lower the recurrence rate. We have previously shown that PHI-101 demonstrated potent activity in various FLT3 mutant AML cell lines when used alone. Here we explore the use of PHI-101 in combination with other therapeutics in preclinical models of AML. We investigated the preclinical efficacy of the combination of PHI-101 with FDA-approved AML therapeutic agents in FLT3 mutant (MV4-11, Molm13, Molm14) and wild-type (THP-1) AML cell lines. Cell growth inhibition was assessed by CCK-8 and/or CellTiter-Glo assays. The Chou-Talalay method was used to calculate the combination index (CI) to test for synergy. Western blotting analysis was performed to explore the potential mechanisms underlying the combination effects. AML xenograft mouse models were used to assess the in vivo efficacy of PHI-101 combination therapy. Statistical comparisons included unpaired t-tests or one-way ANOVA. Combination treatment of PHI-101 with venetoclax or azacytidine showed strong synergistic effects on growth inhibition against both FLT3-ITD mutant (CI<0.3) and wild-type AML cells (CI <0.6). It is noteworthy that the FLT3-ITD homozygous cell line (MV4-11) showed especially strong synergism (CI <0.1). In the xenograft mouse model experiments, 14-day treatment with either PHI-101 alone or in combination with venetoclax or azacytidine showed significant suppression of tumor growth compared to venetoclax or azacytidine alone (in average tumor growth inhibition (TGI) 88.3% vs 8.6%)(p<0.05). In particular, PHI-101 3 mg/kg/day (mpk) with venetoclax 80mpk resulted in a stronger anti-tumor effect (TGI 94.2%) compared to PHI-101 (TGI 87.4%) or venetoclax alone (-9.6% of TGI) (p<0.05) even 21 days after stopping the treatment. In addition, PHI-101 treatment showed a survival advantage in AML animal models, and the combination with venetoclax led to significantly longer survival compared to the control groups. Our preclinical data showed that the combination of PHI-101 with venetoclax or azacytidine resulted in a highly effective anti-leukemic response against AML cells by inducing DNA damage, BCL-2 inhibition, and MCL-1 degradation. Additionally, treatment of mice with low-dose PHI-101 inhibited tumor regrowth and further potentiated venetoclax or azacytidine response in vivo. Our results suggest that the combination of PHI-101 and venetoclax or azacitidine may have the advantage of improving clinical responses in FLT3-ITD AML patients and offers a potential therapeutic option to treat patients with newly diagnosed or relapsed/refractory FLT3-mutant AML. Citation Format: Hee-sun Hwang, Gi-Jun Sung, Kyung-Ah Kim, Ky-Youb Nam, Kyu-Tae Kim, June H. Han, Jeong-Hyeok Yoon, Bao Nguyen, Li Li, Tessa Seale, Donald Small. PHI-101 synergizes with chemotherapy and venetoclax in preclinical models of acute myeloid leukemia [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 7153.

Abstract 2093: Co-treatment with KRAS G12D inhibitor MRTX1133 plus TTFields against human pancreatic and Colorectal cancer cell lines results in synergistic up-regulation of cleaved PARP in KRAS G12D & unexpectedly in KRAS G12V as well

Abstract Background: Both colorectal and pancreatic cancers are major global health issues and among deadliest cancers with great disease burden. The most commonly mutated oncogenic alteration in human cancers is KRAS, which is prevalent in pancreatic malignancies. The KRAS G12D mutation subtype is present in more than 40% of pancreatic ductal adenocarcinoma (PDAC). To this date there is no available targeted therapy options for patients with KRAS subtype mutations. MRTX1133 has been identified as a non-covalent, potent, and selective inhibitor of KRASG12D. This small molecule inhibitor has been shown to suppress KRASG12D signaling in cells and in vivo. Tumor Treating Fields (TTFields) therapy is a novel approach to treating cancer, the electric fields alter the behavior of cancer cells and prevent them from growing and dividing. We hypothesize that the co-application of MRTX1133 with TTFields will enhance the effects of MRTX1133 in PDAC and colorectal cancer (CRC). Martials and Methods: PDAC cell line CFPAC1 with KRAS G12 V mutation and LS513 CRC cell line with KRAS G12D Mutation were treated with same dose of MRTX1133 (500 nM) and were co-treated with 150kHz TTFields. After 48 hours western blot was used to probe for cleaved PARP, cleaved C3, phosphor-ERK and DUSP6. Results: In both KRAS G12D & KRAS G12V cell lines, synergistic upregulation of cPARP was observed following 48-hour co-treatment. Synergistic inhibition of pERK happened in KRAS G12D cell line but no change in pERK level following TTFields or MRTX1133 treatment was seen. Upregulation of cC3 in KRAS G12D happened in only co-treatment conditions. DUSP6 levels increased following MRTX1133 treatment in KRAS G12V cell line. Conclusions: The surprising synergistic upregulation of cPARP in both KRAS G12V and G12D cells following co-treatment of KRAS G12D inhibitor MRTX1133 and TTFields can bring hope for other KRAS mutation subtypes as well as G12D. the increase in cPARP in KRAS G12V with no effect on pERK is particularly interesting and demonstrates the need of more studies to investigate the mechanisms of this synergy. Citation Format: Vida Tajiknia, Praveen Srinivasan, Maximilian PInho-Schwermann, William MacDonald, Connor Purcell, Wafik El-Deiry. Co-treatment with KRAS G12D inhibitor MRTX1133 plus TTFields against human pancreatic and Colorectal cancer cell lines results in synergistic up-regulation of cleaved PARP in KRAS G12D & unexpectedly in KRAS G12V as well [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 2093.