Complete Inhibition Of Tumor Growth Research Articles

Abstract PO5-27-09: Pharmacological eIF4E inhibition suppresses anti-tumor activity in ER+ breast cancer

Abstract Elevated levels of eukaryotic initiation factor 4E (eIF4E) are found in a broad range of cancers, including breast, and have been associated with aggressive, drug resistant tumors. Furthermore, elevated eIF4E activity is sufficient to cause transformation in various cancers, while inhibition suppresses tumor growth. eIF4E, the main regulator and rate limiting factor of protein synthesis, is the downstream integrator of several important oncogenic signaling pathways (PI3K/AKT/mTOR, Ras/Raf/MEK, and Myc). Activation of eIF4E results in increased protein levels of key proliferation and metabolism proteins such as Cyclin D1 (CCND1) and Ornithine Decarboxylase 1 (ODC1), as well as an overall increase in cellular synthesis machinery, causing cellular growth and proliferation. Here, we describe the development and characterization of novel, potent, and selective eIF4E inhibitors. Compounds from this chemical series have nanomolar activity in multiple biochemical and biophysical m7G cap-competition assays as well as potent inhibition of translation in cellular and biochemical assays. In cells, these compounds rapidly and reversibly decrease protein levels of several oncogenes, including CCND1, leading to a G1 cell cycle arrest. We demonstrate that eIF4E inhibitors cause growth inhibition in a variety of breast cancer cell lines, including ER+ breast cancer. These inhibitors also inhibit growth of breast cancer lines with acquired resistance to Palbociclib with the same potency as the parental cell lines. Additionally, eIF4E inhibition shows an increased sensitivity in resistant cell lines when combined with standard of care (SOC), including Palbociclib. Select analogs from the series demonstrate favorable ADMET/PK properties with good oral bioavailability and low safety risk. Lastly, these compounds have demonstrated near complete tumor growth inhibition in non-breast cancer in vivo models. Ongoing experiments will address in vivo efficacy in ER+ breast cancer in both monotherapy and in combination with SOC. Citation Format: Matthew Friedersdorf, Devon Blake, Sarah Thompson, Krista Marran, Jessica Sorrentino. Pharmacological eIF4E inhibition suppresses anti-tumor activity in ER+ breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-27-09.

Abstract 5082: Novel TSHR CAR T therapy for targeting oncocytic carcinoma

Abstract Oncocytic carcinoma (Hurthle cell carcinoma) has the highest incidence of metastasis among the differentiated thyroid cancers. Metastatic disease is reported at the initial diagnosis in 10-20% of patients and 34% overall. Thyroid-stimulating hormone receptor (TSHR) expression is limited to the thyroid gland. It is abundantly expressed on thyroid tumor cells, making TSHR a compelling target for advanced thyroid cancer diagnostics and therapeutics. We developed a potent anticancer strategy for treating oncocytic carcinoma using a novel thyroid hormone stimulating receptor (TSHR)- targeted (chimeric antigen receptor) CAR T cell therapy. TSHR CAR T was generated by transducing T cells derived from healthy donors. In vitro effector functions (cytotoxicity, proliferation, degranulation) were tested in TSHR+ tumor models, and subsequent in vivo studies using NSG mice were performed to assess anti-tumor activity efficacy. We observed strong anti-tumor activity against metastatic oncocytic carcinoma cell line XCT.UC1 using the TSHR CAR T therapy in vivo. Re-challenging treated mice with XCT.UC1 cells reactivated TSHR CART cells with enhanced proliferation and complete suppression of tumor growth of the newly injected tumor cells. Our work represents a promising strategy to improve treatment outcomes of patients with metastatic oncocytic carcinoma that may provide a durable response. Citation Format: Justyna J. Gleba, Aylin Alasonyalilar-Demirer, Matthew Pawlush, Claudia Manriquez-Roman, Elizabeth L. Siegler, Robert C. Smallridge, Abba Zubair, Han W. Tun, Saad S. Kenderian, John A. Copland. Novel TSHR CAR T therapy for targeting oncocytic carcinoma [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 5082.

Abstract 3306: RGT-M001, a first-in-class small molecule mRNA degrader of the oncogenic transcription factor c-Myb, demonstrated remarkable single agent anti-tumor efficacy in cancer patient-derived xenograft model

Abstract Dysregulated transcription factors (TFs) represent a unique class of drug targets that drive aberrant gene expression programs involved in the major hallmarks of cancers. However, developing drug-like small molecules targeting TF proteins for clinical purposes has proven to be extremely challenging. Here, we present a novel and innovative approach to degrade the RNA transcript of the master oncogenic transcription factor C-MYB, thereby preventing its undesirable expression, using potent and orally available small molecules. C-MYB is a transcription factor that regulates differentiation and proliferation programs in normal cells, including hematopoietic, stem and epithelial cells. In numerous cancer types, such as adenoid cystic carcinoma (ACC), leukemia, colorectal cancer, and breast cancer, C-MYB is a well-established oncogenic transcription factor, overactivated via different mechanisms, including chromosomal translocations and gene amplification. Here, we leveraged our integrative RNA-targeting platform to identify and validate actionable cryptic exon target sites in the human C-MYB gene. We identified RGT-M001, a potent small molecule that can selectively induce the inclusion of the cryptic exon into the final C-MYB transcripts, resulting in a robust decrease of C-MYB canonical transcripts and C-MYB protein in cells. In a functional assay, we demonstrated that RGT-M001 has potent cell-killing activity against a large panel of cancer cell lines overexpressing C-MYB (EC50 ~ 20 - 300nM), while sparing normal cells. To confirm RGT-M001's on-target effect, we demonstrated a robust correlation between RGT-M001 cell-killing activity and the knockdown of C-MYB RNA and protein. We further investigated the anti-tumor activity of RGT-M001 in an ACC patient-derived xenograft (PDx) mouse model harboring C-MYB-NFBI fusion. Recurrent or metastatic ACC is a malignant neoplasm of predominantly salivary gland origin for which effective approved therapies are lacking; the best reported ORR being 15.6% for lenvatinib. As a single agent, RGT-M001 reduced in vivo C-MYB transcript levels by >80% at peak drug exposure and induced a remarkable tumor growth inhibition response (~70% TGI) in the ACCX11 PDx mouse model, surpassing the therapeutic benchmark Lenvatinib (40% TGI). Importantly, the RGT-M001 regimen was well tolerated. Finally, we showed that the combination of RGT-M001 with the Notch Inhibitor AL-101 resulted in complete inhibition of tumor growth. In conclusion, these data demonstrate that small molecules targeting RNA are a safe and effective approach to address previously undruggable protein targets. Down-regulation of C-MYB by our RNA-targeting small molecules is an attractive therapeutic strategy to treat ACC and other cancers driven by C-MYB dysregulations. Citation Format: Norman Lu, Patricia Soulard, Kay Li, Heather Sadlish, Chris Yates, Xiubin Gu, Ibrahim Kays, Jae Lee, Sam Hasson, Zhiping Weng, Simon Xi, Travis Wager. RGT-M001, a first-in-class small molecule mRNA degrader of the oncogenic transcription factor c-Myb, demonstrated remarkable single agent anti-tumor efficacy in cancer patient-derived xenograft model [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 3306.

Abstract 661: An oral Cbl-b inhibitor with sustained T cell activation demonstrated robust anti-tumor efficacy along with enhanced infiltration and activation of functional T cells

Abstract The E3 ubiquitin ligase Casitas B-lineage lymphoma b (Cbl-b) is a member of the highly conserved family of Cbl (casitas b-lineage lymphoma) proteins, which associates with multi-immune response regulations including Teff and NK activation, Treg differentiation. Cbl-b KO mice showed enhanced immune responses and resistance to tumor transplantation. Previously, we reported a novel Cbl-b inhibitor, ZM-8026, which robustly activated T cells and efficiently inhibited tumor growth as monotherapy or in combination with anti-PD-1. Here, we further demonstrated that Cbl-b inhibition restores the Teff cells' function in immune suppression conditions, such as in the presence of PGE2, A2AR agonist, and TGF-β. CD8+T proliferation and cytokines induction were maintained in the presence of MDSC. Furthermore, CD8+T function was reversed from an exhausting status induced by a continuous anti-CD3/CD28 activation for a long period. To investigate whether continuous target occupancy was necessary for sustained TCR activation, the dynamic impacts of Cbl-b inhibition on CD8+T cell activation were explored using a washout assay. The results showed that the high-level activated T cells lasted for 48 h after more than 4hs preincubation with 1 µM Cbl-b inhibitor followed by a washout, however, short and weak activation states were found with less than 4hs preincubation or low inhibitor concentration treatment (< 0.1 uM). This finding revealed sufficient inhibitor concentration and treatment time ensure high T-cell activation. Further, in vivo efficacy studies demonstrated less anti-tumor growth efficacy for intermittent dosing (Q2D, Q3D) compared with QD dosing. In vitro and in vivo pharmacokinetics studies exhibited favorable ADME profiles and bioavailability of our Cbl-b inhibitor for oral administration in mice, rats, and dogs. At least in two syngeneic models, our Cbl-b inhibitor exhibited efficient anti-tumor growth with more than 70% TGI (tumor growth inhibition). In a CT26 syngeneic model, complete tumor growth inhibition in 6 of 8 mice was found in the Cbl-b inhibitor combined with an anti-PD1 antibody. The complete regression mice were re-challenged with the same tumor cells, and no measurable tumors were found for up to 30 days, suggesting the treatment-induced immune memory. Tumor samples in mice were collected, RNAseq showed that activated functions of tumor-infiltrated T, NK, DC, and macrophage were dramatically increased in the Cbl-b inhibitor treatment group, and the T and NK activation signature genes such as Gzmb, Ifng were significantly upregulated by RT-PCR. In conclusion, our Cbl-b inhibitor exhibited a favorable PK profile in multi-preclinical animals. The sustained T cell activation in vitro was identified and robust anti-tumor growth in vivo was demonstrated with optimized dosing frequency. Citation Format: Feng Zhou, Guimei Yang, Yajing Liu, Liting Xue, Weijie Chen, Zhengtao Li, Xiaowu Liu, Jian Li, Renhong Tang. An oral Cbl-b inhibitor with sustained T cell activation demonstrated robust anti-tumor efficacy along with enhanced infiltration and activation of functional T 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 661.

Abstract 4573: Pre-clinical evaluation of small molecule CHK2 inhibitor, ART446, pre-IND candidate that enhances the olaparib and irinotecan

Abstract Background: Poly (ADP-ribose) polymerase (PARP) plays a pivotal role in DNA damage repair. Tumors with DNA Damage Response (DDR) defects exhibit increased susceptibility to drugs targeting PARP. The drugs induce DNA damage like Irinotecan (a Topoisomerase I inhibitor) are widely used in clinic as well. However, intrinsic resistance remains a significant obstacle, leading to frequent treatment failures. Chk2 is activated in response to these DNA damage inducing agents and hold the cell cycle. We developed pre-IND candidate ART446, with the aim of exploring its therapeutic potential in sensitizing DNA damage-targeting reagents. Results: In the radiometric HopSpot Kinase Assay, ART446 demonstrated significant inhibition of Chk2 (IC50, 9 nM). In HT-29 colon adenocarcinomas, co-treatment with SN38 and ART446 exhibited a synergistic therapeutic effect in vitro, with a subsequent in vivo tumor growth assay demonstrating a remarkable combined effect (TGI; Irinotecan, 46%; ART446, 16%; combined, 83.4%). Further extending our investigation to triple-negative breast adenocarcinoma MDA-MB-436, characterized by a BRCA1 mutation, we explored the sensitization potential of ART446 to PARP inhibitors. Strikingly, the combination therapy with a PARP inhibitor, Olaparib surpassed monotherapy outcomes, resulting in complete tumor growth inhibition (TGI: Olaparib, 73%; ART446, 20%; combined, 102%). Mechanistic insights revealed an increase in gamma H2AX levels by ART446 and a decrease in active forms of Chk2 which were activated by Olaparib affirming that Olaparib-induced Chk2 inhibition contributed to the sensitization effect. Conclusions: The pre-IND candidate ART446 exhibits promising potential in enhancing the therapeutic effects of Olaparib and Irinotecan. These findings provide a robust foundation for further clinical development, offering a strategic approach to overcome resistance in cancer treatment. Citation Format: Taegon Baik, Young Woo Kang, Ha Young Lee, Jin Whan Kim, A Hyeon Jeong, Jong Oh Kim, Woo-Young Kim. Pre-clinical evaluation of small molecule CHK2 inhibitor, ART446, pre-IND candidate that enhances the olaparib and irinotecan [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 4573.

Abstract 676: The integrated stress activator BTM-3566 overcomes therapeutic resistance in mantle cell lymphoma

Abstract Successive generations of BTK inhibitors and CAR T-cell therapy have transformed the treatment of mantle cell lymphoma (MCL). However, treatment resistance has inevitably emerged, creating significant medical need. Recently a novel, clinical stage small molecule, BTM-3566, has been described that targets a mitochondrial process essential for Diffuse Large B-cell lymphoma (DLBCL) survival. BTM-3566 activates the mitochondrial protease OMA1, triggering the ATF4 integrated stress response (ISR). BTM-3566 has robust in vitro efficacy in DLBCL cell lines irrespective of genomic background and elicits complete tumor regression in multiple CDX and PDX mouse models of DLBCL. Based on the activity observed in DLBCL, we further explored the effectiveness of BTM-3566 in MCL models in vitro and in xenograft mouse models in vivo. BTM-3566 inhibited cell proliferation across a panel of MCL cell lines, irrespective of resistance status to ibrutinib and venetoclax (IC50s of 142.5-687.6 nM). Following a 24-hour treatment with BTM-3566, a dose-dependent increase in apoptosis was observed in four tested MCL cell lines—JeKo-1, JeKo-IBN-R, Mino, and Mino-VEN-R, as determined by increased caspase-3 activation and PARP cleavage. Similarly, western blot analysis revealed dose-dependent reductions in MCL-1 and c-MYC, accompanied by an increase in the transcription factor ATF4, indicative of activation of the stress response. We evaluated the in vivo efficacy of BTM-3566 in the JeKo-CDX mouse model. Daily oral administration of BTM-3566 at 10, 20 and 30 mg/kg (n = 5 for each group) in a 5-day on and 2-day off schedule resulted in tumor regression at all three doses (Treatment vs. Vehicle, p < 0.01). We expanded our investigation to PDX mouse models, including those derived from patients resistant to multiple therapies. Four PDX models encompassing naive, rituximab-resistant, BTKi-CAR T dual-resistant and BTKi-VEN-CAR T triple-resistant models were evaluated. BTM-3566 treatment results in nearly complete tumor growth inhibition associated with robust reductions in tumor burden in treated mice across all four PDX models (reduction in tumor weight at the study endpoint, p < 0.001). Notably, no toxicity was observed during the treatment period. In summary, BTM-3566 is effective in treating MCL in vitro and in vivo in preclinical studies. Citation Format: Yang Liu, Heng-Huan Lee, Joseph McIntosh, Yijing Li, Tianci Zhang, Wei Wang, Matthew J. Kostura, Michael Wang. The integrated stress activator BTM-3566 overcomes therapeutic resistance in mantle cell lymphoma [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 676.

Probiotic-derived ferrichrome induces DDIT3-mediated antitumor effects in esophageal cancer cells

Esophageal cancer, which is common among the elderly, has the poorest prognosis among gastrointestinal cancers. Previously, we demonstrated that ferrichrome, produced by the probiotic Lactobacillus casei, exhibited anti-tumor effects in various gastrointestinal cancers, including colorectal and gastric cancers, with minimal effects on non-cancerous intestinal cells. However, it remains unclear whether ferrichrome exerts anti-tumor effects in esophageal cancer. A sulforhodamine B assay revealed that ferrichrome suppressed esophageal adenocarcinoma (OE33, OE19) and squamous cell carcinoma (KYSE70) cells. Ki-67 staining indicated that ferrichrome inhibited the proliferation of esophageal cancer cells. Cell cycle analysis showed that ferrichrome inhibited the DNA synthesis. TUNEL staining revealed that ferrichrome-induced DNA fragmentation. We also confirmed the cleavage of caspase-9 and PARP in ferrichrome-treated cells. Reverse transcription polymerase chain reaction demonstrated an increase in the mRNA of DNA damage-inducible transcript 3 (DDIT-3), a key regulator of programmed cell death, in ferrichrome-treated OE33 cells. In an in vivo OE33 xenograft model, intraperitoneal administration of 5-mg/kg ferrichrome for 14 days resulted in an almost complete inhibition of tumor growth. However, 14 days of intraperitoneal administration of 20-mg/kg 5-fluorouracil (5-FU), but not 20-mg/kg ferrichrome, induced weight loss and myelosuppression in both young and aged mice. Our findings indicate that ferrichrome induces DNA damage-inducible transcript-3, thereby producing anti-tumor effects, including cell cycle arrest and apoptosis, with minimal adverse effects in esophageal cancer cells. This illustrates the high potential of ferrichrome as an anti-tumor drug against esophageal carcinoma.

Abstract LB_C03: Protein translation inhibition enforces histone deacetylase inhibitor activity resulting in synergistic pancreatic cancer cell death

Abstract Management of pancreatic cancer presents significant challenges due to late-stage diagnosis, aggressive tumor biology, and limited efficacy of existing treatment options. Gemcitabine and FOLFIRINOX (folinic acid, 5-FU, irinotecan hydrochloride, oxaliplatin) are standard treatments for advanced pancreatic cancer. Despite these therapies the overall 5-year survival rate for pancreatic cancer patients is at 12%, largely due to drug resistance. Thus, there is a critical need to explore new therapeutic strategies. Our study explores a small molecule combination that induces epigenetic reprogramming as a potential novel therapeutic strategy for pancreatic cancer. We have identified marked sensitivity of pancreatic cancer cells to the combination of a novel inhibitor of RNA helicase eIF4A, DMPatA (MZ735), and a histone deacetylase (HDAC) inhibitor, romidepsin. A short-term, low dose romidepsin treatment, when combined with MZ735, triggers persistent global histone acetylation, transcriptional upregulation, replication inhibition, and augmented DNA damage. This combined effect induces a synergistic anti-proliferative response in pancreatic cancer cells. We have identified a tolerable protocol for this combination regimen in animals, demonstrating its efficacy against tumor growth in a MIA PaCa-2 xenograft mouse model of pancreatic cancer. Treatment with the combination resulted in inhibition and then complete suppression of tumor growth in animals for 39 days. Our in vitro studies aimed at understanding the mechanism of this combination treatment showed that at low doses of romidepsin monotherapy, histone acetylation rapidly faded, while robust acetylation persisted to 18 and 24 hours with the combination. Additionally, R-loop accumulation was observed using confocal microscopy and DRIP-qPCR, along with a reduction in replication fork speed, which might account for the identified DNA damage and genome instability. The combination treatment significantly reduces acetyl-CoA and c-MYC protein levels and disrupts glycolysis and oxidative phosphorylation. We show that a structurally different HDAC inhibitor exhibits the same synergistic effects when co-administered with MZ735, confirming a unique method of eliciting synthetic lethality in PDAC cells. In conclusion, this combination shows significant antitumor activity in both in vitro and in vivo models of pancreatic cancer and warrant translation to the clinic. Citation Format: Maryam Safari, Luigi Scotto, Agnes Basseville, Thomas Litman, Haoran Xue, Luba Petrukhin, Ping Zhou, Christopher Damoci, Minhzhao Zhu, Kenneth Hull, Kenneth P Olive, Antonio T Fojo, Daniel Romo, Susan E Bates. Protein translation inhibition enforces histone deacetylase inhibitor activity resulting in synergistic pancreatic cancer cell death [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr LB_C03.

Enhanced synergy of pacritinib with temsirolimus and sunitinib in preclinical renal cell carcinoma model by targeting JAK2/STAT pathway

Pacritinib is an oral medication that inhibits several kinases including JAK2, FLT3, IRAK and STAT3. It has been recently approved to treat patients with thrombocytopenia and myelofibrosis. Studies are currently exploring the potential use of pacritinib in treating other types of cancer such as leukaemia, breast cancer and prostate cancer. Our study aimed to investigate the effects of pacritinib alone and its combination with standard of care in renal cell carcinoma (RCC). We showed that pacritinib dose-dependently decreased viability of RCC cells, with IC50 at nanomolar or low micromolar concentration rage. Pacritinib inhibited cell proliferation, decreased colony formation, and increased apoptosis. Interestingly, pacritinib exhibited synergistic effects when combined with temsirolimus and sunitinib, but antagonistic effects when combined with doxorubicin, in a panel of RCC cell lines. We also confirmed that the combination of pacritinib with temsirolimus and sunitinib resulted in synergistic effects in RCC mouse models, with complete inhibition of tumour growth throughout the treatment period. Mechanistic studies indicated that the inhibition of JAK2, but not IRAK, was the main contributor to the anti-RCC activity of pacritinib. Our study is the first to demonstrate that pacritinib shows promise as a treatment option for RCC and underscores the therapeutic potential of targeting the JAK2/STAT signalling pathway in RCC.

Combination of BET Inhibition with Radiation Induces Anti-Tumor Immune Response in Pre-Clinical Models of ER-Positive Breast Cancer

Despite advances in multidisciplinary care, the risk of late recurrence in Estrogen Receptor-positive (ER+) breast cancer (BC) patients following standard-of-care treatment ranges from 20-52% at 20 years. While immune checkpoint inhibitors (CPI), have shown enormous potential in inducing long term remission in some cases, patients with ER+ BC show poor response to these agents. The objective of this study is to develop effective radiation therapy (RT)-based combination regimens that induce anti-tumor immunity against immunologically cold ER+ breast tumors. We have previously shown that pharmacological inhibition of bromodomain and extraterminal domain (BET) family of epigenetic regulator proteins overcomes both endocrine therapy resistance and radiation resistance in pre-clinical models of ER+ BC by reversing pathological reprogramming of transcriptional and DNA repair pathways, respectively. In this study, we explore the potential of RT+BET inhibition combination to elicit anti-tumor immunity against ER+ BC. A unique ER+ BC model, MXT+, was used to generate tumors in female, BDF1 mice. PD-L1 expression following RT or RT+OTX015 (a BET inhibitor) was assessed by Western blot analysis. Comet assay was used to assess the degree of unrepaired DNA damage following treatment with RT alone, OTX015 alone and RT+OTX015. Multiplex IHC was used to assess changes in tumor microenvironment after various treatments. Tumor growth characteristics were established following treatment with vehicle, RT alone (8 Gy x 3), OTX015 alone (100 mg/kg x 3 days) and RT+OTX015. Using murine ER+ BC model, MXT+, we show that RT is a potent inducer of PD-L1 expression. Combination of RT+OTX015 completely ablated RT-mediated PD-L1 induction at the transcription level. OTX015 also accentuated RT-induced DNA damage through inhibition of NHEJ pathway, resulting in increased micronuclei formation (which activate cGAS/STING pathway, a critical bridge between innate and adaptive immunity). Combination of OTX015 with RT also caused a statistically significant (on unpaired t test) increase tumor infiltrating lymphocytes. In in vivo therapeutic studies, combination of OTX015 with RT (8 Gy x 3) resulted in extraordinary synergy and caused complete inhibition of long-term tumor growth. Treatment with RT alone (8 Gy x 3) or OTX015 alone (on 3 consecutive days) only caused modest inhibition of tumor growth. ANOVA with Dunnett's test was used to adjust for multiple comparisons and showed statistically significant difference in tumor growth between OTX015+RT arm and OTX alone as well as OTX015+RT arm and RT alone. Patients with ER+ BC face high risk of late recurrence after definitive treatment and show poor response to immune CPIs. We show that combination of BET inhibition with RT induces anti-tumor immunity and completely prevents tumor growth. Clinical validation of this regimen is warranted to prevent late recurrences in ER+ BC patients.

Discovery of ERD-3111 as a Potent and Orally Efficacious Estrogen Receptor PROTAC Degrader with Strong Antitumor Activity.

Estrogen receptor α (ERα) is a prime target for the treatment of ER-positive (ER+) breast cancer. Despite the development of several effective therapies targeting ERα signaling, clinical resistance remains a major challenge. In this study, we report the discovery of a new class of potent and orally bioavailable ERα degraders using the PROTAC technology, with ERD-3111 being the most promising compound. ERD-3111 exhibits potent in vitro degradation activity against ERα and demonstrates high oral bioavailability in mice, rats, and dogs. Oral administration of ERD-3111 effectively reduces the levels of wild-type and mutated ERα proteins in tumor tissues. ERD-3111 achieves tumor regression or complete tumor growth inhibition in the parental MCF-7 xenograft model with wild-type ER and two clinically relevant ESR1 mutated models in mice. ERD-3111 is a promising ERα degrader for further extensive evaluations for the treatment of ER+ breast cancer.

Effectiveness of irinotecan plus trabectedin on a desmoplastic small round cell tumor patient-derived xenograft.

This study exploited a novel patient-derived xenograft (PDX) of desmoplastic small round cell tumor (DSRCT), which reproduces histomorphological and molecular characteristics of the clinical tumor, to assess the activity of cytotoxic and targeted anticancer agents. Antitumor effect was moderate for doxorubicin, pazopanib and larotrectenib [maximum tumor volume inhibition (max TVI), 55-66%], while trabectedin had higher activity (max TVI, 82%). Vinorelbine, irinotecan and eribulin achieved nearly complete tumor growth inhibition (max TVI, 96-98%), although tumors regrew after the end of treatment. The combination of irinotecan with either eribulin or trabectedin resulted in complete responses, which were maintained until the end of the experiment for irinotecan plus trabectedin. Irinotecan-based combinations nearly abrogated the expression of proteins of the G2/M checkpoint, preventing cell entrance in mitosis, and induced apoptotic and necroptotic cell death. Consistently, irinotecan plus trabectedin resulted in reprogramming of DSCRT transcriptome, with downregulation of E2F targets, G2/M checkpoint and mitotic spindle gene sets. This study emphasizes the importance of patient-derived preclinical models to explore new treatments for DSRCT and fosters clinical investigation into the activity of irinotecan plus trabectedin.

Abstract 2937: Preclinical characterization of CBA-1535, a novel bi-specific tribody, with two binding sites to 5T4 and one site to CD3ε

Abstract 5T4 oncofetal tumor-associated antigen (also known as TPGB or WAIF1) is over-expressed in a wide range of solid tumors but shows very limited expression in normal adult tissues thus suggesting 5T4 as an attractive target for antibody therapy. CBA-1535, originally developed by Biotecnol (UK), is a novel trivalent biological construct named a Tribody™ with two binding sites to the tumor associated antigen 5T4 and one to the T cell expressed antigen CD3ε. CD-3 based T cell engagers (TCE) is one of the attractive strategy to treat cancer patients resistant to conventional therapies, however, the effects of TCE on solid tumors are limited due to the immunosuppressive tumor microenvironment. To overcome this limitation, CBA-1535 is designed to have stronger binding activity to 5T4 with two binding sites, and to have the lower affinity to CD3 than to 5T4 to prevent non-specific T cell activation.CBA-1535 does not have a Fc region with a molecular weight of ~100 kDa and it has a low nM Kd for bivalent binding to 5T4, a 20 to 30 nM Kd for monovalent binding to CD3ε. CBA-1535 efficiently induced T cell activation in human PBMCs as exemplified as CD25 and CD69 expressions and showed cytokine release, i.e., IL-2, IL-6, TNFα, and IFN-ɤ, at the concentration between 0.01 and 10 nM only when co-cultured with target cancer cells, however, those T cell activation and cytokine release were not observed under the conditions without target cancer cells, even at the concentration of 1 µM. In the presence of activated human PBMCs as effector cells, CB-1535 elicited 5T4 expressing target cell cytotoxicity with an EC50 of approximately 1-30 pM in a variety of cancer cells. The anti-tumor efficacy of CB-1535 has examined in immunocompromised mice bearing human lung mesothelioma (MSTO-211H) and alveolar epithelial adenocarcinoma (A549) xenografts (such as the 5T4 expressing target cell) and human PBMCs (as effector cells). Anti-tumor efficacy was observed with complete suppression of tumor growth at doses as low as 1 mg/kg in both xenograft models. No abnormalities related to CBA-1535 administration were observed regarding to body weight and clinical signs. Importantly, CBA-1535 showed a synergistic cytotoxicity against 5T4 expressing target cancer cells in vitro when combined with PD-1 antibody Pembrolizumab in a co-culture experiment. In conclusion, we demonstrated encouraging preclinical profile of CBA-1535 as a novel CD-3 based T-cell engager antibody. These results provide the strong rationale for further clinical evaluation of CBA-1535 in 5T4 positive tumors. CBA-1535 is now under the phase 1 trial in Japan (jRCT2031210708), with 2 parts, the monotherapy and the combination with Pembrolizumab. Citation Format: Fumitake Takizawa, Kotaro Yamamoto, Koji Nakamura, Ana R. Richard, Philip J. Cunnah, Nico Mertens, Pedro D. Pissarra, Yukihito Tsukumo. Preclinical characterization of CBA-1535, a novel bi-specific tribody, with two binding sites to 5T4 and one site to CD3ε [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2937.

Abstract 5501: Vertical inhibition of the MAPK pathway with D3S-002, a potent and selective ERK1/2 inhibitor, to improve anti-tumor activity of and overcome resistance to KRAS G12C inhibitors

Abstract While covalent KRAS G12C inhibitors have demonstrated encouraging clinical efficacy in patients with KRAS G12C mutation, the overall response rate and progression-free survival appear to be suboptimal. Achieving deeper and more durable responses in these patients remain as major challenges. Preclinical and clinical translation research highlights adaptive feedback reactivation of the RAS-RAF-MEK-ERK signaling cascade as key molecular mechanisms driving primary and acquired resistance to KRAS G12C inhibitors. Concurrent inhibition of KRAS G12C and downstream MAPK pathway is thus an attractive combination strategy to improve clinical outcomes for KRAS G12C-mutant population. D3S-002 is a potent and selective kinase inhibitor targeting ERK1/2, the final node of the RAS-MAPK pathway and the central mediator of the feedback activation loop. To investigate the combination effect of D3S-002 with KRAS G12C inhibitor D3S-001, this study utilized multiple preclinical in vivo models including cancer cell line-derived xenograft (CDX) tumors that are sensitive to, or primarily resistant to KRAS G12C inhibitors, and patient-derived xenograft (PDX) tumors that have progressed on KRAS G12C inhibitor treatment in the clinic. In NCI-H358 NSCLC and SW837 CRC models that are sensitive to KRAS G12C inhibitor monotherapy, adding D3S-002 to D3S-001 or to D3S-001 and cetuximab doublet regimen led to faster, deeper, and more durable anti-tumor responses at dose levels that are well tolerated in mice with no body weight loss observed. In NCI-H2122 NSCLC model that is primarily resistant to KRAS G12C inhibitor alone, the addition of D3S-002 resulted in near complete tumor growth inhibition. Furthermore, CR9537 PDX model was established from tumor biopsy of a CRC patient who had progressed on combination treatment of KRAS G12C inhibitor MRTX849 and a SHP2 inhibitor in a clinical trial. Next generation sequencing (NGS) analysis identified secondary KRAS Q61H mutation as an acquired resistance mechanism. In this PDX model, KRAS G12C inhibitor, D3S-001 or MRTX849, monotherapy only achieved approximately 50% tumor growth inhibition, highlighting the acquired resistant phenotype. Adding D3S-002 to D3S-001 or MRTX849 resulted in over 80% tumor growth inhibition and significantly prolonged survival, suggesting the combination treatment can be beneficial for KRAS G12C inhibitor pre-treated patient population. Collectively, vertical inhibition by concurrently targeting KRAS G12C and ERK1/2 with respective inhibitor D3S-001 and D3S-002 demonstrated enhanced anti-tumor activity in NSCLC and CRC models with different sensitivity to KRAS G12C inhibitor monotherapy. These results provide a strong rationale for further investigation of the combination strategy of D3S-001 and D3S-002 in KRAS G12C-mutant solid tumors in the clinic. Citation Format: Jing Zhang, Jingtao Lu, Zhiqiang Zheng, Jiang Lu, Allison Wang, Jia Wang, Janet Chen, Haopeng Rui, Cheng Chen, Zhi Jian Chen. Vertical inhibition of the MAPK pathway with D3S-002, a potent and selective ERK1/2 inhibitor, to improve anti-tumor activity of and overcome resistance to KRAS G12C inhibitors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5501.

Abstract 4865: Mechanisms of EGFR inhibitor sensitivity and resistance in chordoma

Abstract Target discovery studies have identified EGFR inhibition as a promising therapeutic strategy in chordoma, motivating ongoing clinical trials. Yet EGFR is not mutated in chordoma, leaving the mechanisms associated with EGFR inhibitor (EGFRi) sensitivity and resistance unclear. In this study, we profiled a panel of over 10 chordoma cell lines to categorize their sensitivity to afatinib, a second-generation EGFRi with potency against the wild-type receptor. Several cell lines, including U-CHCF365, UM-Chor1, MUG-Chor1, and U-CH1, were highly sensitive to afatinib in cell viability assays, with absolute IC50 values below 50 nanomolar. In contrast, other chordoma cell lines, including UM-Chor5C and U-CHCF359B, exhibited limited response to EGFRi at concentrations exceeding 1 micromolar. Among sensitive cell lines, we found that afatinib promoted cell death in some cases (e.g., U-CH1) whereas in others it induced a profound cell cycle arrest. Moreover, in U-CH1 cells, acute afatinib treatment enriched a population of drug-tolerant persister cells with a fusiform morphology, potentially indicative of an epithelial-mesenchymal transition. Ongoing studies are focused on understanding the mechanisms of afatinib-induced cell death, drug tolerance, and acquired resistance, with a view to designing rational combination strategies capable of enhancing the magnitude and duration of therapeutic response. In cell lines with matched xenograft models, in vitro responses to afatinib were consistent in vivo. In a panel of 12 chordoma patient-derived xenograft (PDX) models treated with afatinib or cetuximab, differential sensitivity to EGFRi was recapitulated - with EGFRi promoting complete or negligent tumor growth inhibition in sensitive or resistant models, respectively. Finally, we combined drug sensitivity profiling of chordoma cell lines and PDXs with whole-exome and whole-transcriptome sequencing to identify genomic and transcriptomic features associated with sensitivity and resistance to EGFRi in chordoma. Collectively, our data identify a striking degree of differential sensitivity to EGFRi in chordoma, and begin to shed light on factors associated with primary and acquired resistance. These results provide a framework for guiding patient selection and identifying potential combination therapy regimens to improve EGFRi efficacy and address resistance. Citation Format: Nindo Punturi, Lee Dolat, Joan Levy, Josh Sommer, Daniel M. Freed. Mechanisms of EGFR inhibitor sensitivity and resistance in chordoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4865.

Abstract 6313: IND-enabling studies for GrB-Fc-IT4: in vivo efficacy, pharmacokinetics, schedule optimization and maximum tolerated dose

Abstract Fn14 (fibroblast growth factor-inducible 14) is the only known receptor of TWEAK (tumor necrosis factor-related weak inducer of apoptosis). The binding of TWEAK to Fn14 activates several intracellular signal transduction cascades that lead to cell death, proliferation, migration, or survival depending on the cellular contexts. Several studies have shown that Fn14 is upregulated in many solid tumors when compared with healthy tissues. The activation of TWEAK/Fn14 signaling increases the proliferation, invasion, and migration of tumor cells. Moreover, angiogenesis, pro-inflammatory cytokine expression, and epithelial-mesenchymal transitions are promoted upon TWEAK/Fn14 activation. Therefore, Fn14 is considered a potential therapeutic target, and attempts to generate targeted therapeutics have achieved limited success in pre-clinical and clinical trials. We generated a completely human fusion protein, GrB-Fc-IT4, consisting of the IT4 scFv antibody targeting the Fn14 receptor and the serine protease granzyme B (GrB) as the cytotoxic payload. Comprehensive mechanism of action studies showed that GrB-Fc-IT4 effectively induced cell death in vitro against a broad selection of tumor types with high specificity. The intracellular pathway included rapid, irreversible activation of the caspase cascade and independent mitochondrial depolarization leading to intense apoptotic cellular damage. Pharmacokinetic studies in mice showed that GrB-Fc-IT4 cleared bi-exponentially from plasma with a rapid initial clearance (t ½α = 0.36 hours) followed by a prolonged terminal-phase plasma half-life (t 1/2β = 35 hours), similar to that of IgGs. Based on our PK study, we compared the in vivo antitumor efficacy of GrB-Fc-IT4 against A549 (NSCLC) tumors, using two different dosing schedules (QODx5 vs QWx5). Tumor efficacy showed a clear dose and schedule dependence. Mice bearing A549 tumors treated with 32 mg/kg/dose (QOWx5) exhibited complete tumor growth inhibition (7/10 tumors regressed) with 3/10 tumors showing no growth up to 50 days after the last dose. Thus, GrB-Fc-IT4 displays impressive in vitro and in vivo cytotoxic effects. Even though GrB-Fc-IT4 cross-reacts with the murine Fn14 antigen, maximum tolerated dose studies in mice have confirmed that GrB-Fc-IT4 is a safe product, as mice treated with the drug up to 500 mg/kg showed no evidence of toxicity (changes in respiration, rough hair coat, unusual behavior or hunched posture). Taking in consideration these results we estimate that the therapeutic index for this class of drug is higher than four. Our data suggest that GrB-Fc-IT4 is a novel antitumor agent with a unique mechanism of action compared to all other therapeutic agents. The exceptionally safe and effective profile of this drug makes it an ideal candidate for advancing to clinical trials. Research conducted, in part, by the Clayton Foundation for Research. Citation Format: Ana Alvarez-Cienfuegos, Lawrence H. Cheung, Khalid A. Mohamedali, Mihai Gagea, Michael G. Rosenblum. IND-enabling studies for GrB-Fc-IT4: in vivo efficacy, pharmacokinetics, schedule optimization and maximum tolerated dose [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6313.

Interactions between driver genes shape the signaling pathway landscape and direct hepatocellular carcinoma therapy.

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies, whose initiation and development are driven by alterations in driver genes. In this study, we identified four driver genes (TP53, PTEN, CTNNB1, and KRAS) that exhibit a high frequency of somatic mutations or copy number variations (CNVs) in patients with HCC. Four different spontaneous HCC mouse models were constructed to screen for changes in various kinase signaling pathways. The sgTrp53+sgPten tumor upregulated mTOR and noncanonical NF-κB signaling, which was shown to be strongly inhibited by rapamycin (an mTOR inhibitor) in vitro and in vivo. JAK-STAT signaling was activated in the Ctnnb1mut +sgPten tumor, the proliferation of which was strongly inhibited by napabucasin (a STAT3 inhibitor). MTOR, cytoskeleton, and AMPK signaling were upregulated while rapamycin and ezrin inhibitors exerted potent anti-proliferative effects in the sgPten+KrasG12D tumor. JAK-STAT, MAPK, and cytoskeleton signaling were activated in the sgTrp53+KrasG12D tumor and the combination of sorafenib and napabucasin led to the complete inhibition of tumor growth in vivo. In patients with HCC, who had the same molecular classification as our mouse models, the downstream signaling pathway landscapes associated with genomic alterations were identical. Our research provides novel targeted therapeutic options for the clinical treatment of HCC, based on the presence of specific genetic alterations within the tumor.

Photothermal induced chemo-immunological synergistic therapy for anaplastic thyroid carcinoma treatment

It is still of great challenge for anaplastic thyroid carcinoma (ATC) treatment since ATC is an extremely destructive and lethal thyroid malignancy. Herein, a kind of multifunctional nanoplatform (denoted as PDA-dsCpG-DOX NP) has been prepared and applied for tri-modal ATC therapy including photothermal therapy (PTT), chemotherapy, and immunotherapy. Polydopamine nanoparticle (PDA NP) serves as a photothermal agent to generate PTT, as well as a carrier of doxorubicin (DOX) and immunotherapeutic DNA (i.e., oligonucleotide comprising unmethylated cytosine-phosphate-guanine dinucleotide (CpG ODN)). The high temperature induced by PTT results in the release of CpG ODNs for immunotherapy and the liberation of DOX for chemotherapy. PDA-dsCpG-DOX NPs exhibit a phenomenal collaborative therapy effect contrasted with a corresponding single therapy or dual-modal treatment. By use of mice bearing C643 thyroid tumors as a model, PDA-dsCpG-DOX NPs have been demonstrated to realize nearly complete tumor growth suppression with good biocompatibility. Hence, PDA-dsCpG-DOX NPs introduce a synergistic scheme for ATC treatment and foreground the congregate effects of tri-modal therapy.

Polymer theranostics with multiple stimuli-based activation of photodynamic therapy and tumor imaging.

Background: Efficient theranostic strategies concurrently bring and use both the therapeutic and diagnostic features, serving as a cutting-edge tool to combat advanced cancers. Goals of the Investigation: Here, we develop stimuli-sensitive theranostics consisting of tailored copolymers forming micellar conjugates carrying pyropheophorbide-a (PyF) attached by pH-sensitive hydrazone bonds, thus enabling the tumor microenvironment-sensitive activation of the photodynamic therapy (PDT) effect, fluorescence or phosphorescence. Results: The nanomedicines show superior anti-tumor PDT efficacy and huge tumor-imaging potential, while reducing their accumulation, and potentially side effects, in the liver and spleen. The developed theranostics exhibit clear selective tumor accumulation at high levels in the mouse sarcoma S180 tumor model with almost no PyF found in the healthy tissues after 48 h. Once in the tumor, illumination at λexc = 420 nm reaches the therapeutic effect due to the 1O2 generation. Indeed, an almost complete inhibition of tumor growth is observed up to 18 days after the treatment. Conclusion: The clear benefit of the specific PyF release and activation in the acidic tumor environment for the targeted delivery and tissue distribution dynamics was proved. Conjugates carrying pyropheophorbide-a (PyF) attached by pH-sensitive hydrazone bonds showed their excellent antitumor PDT effect and its applicability as advanced theranostics at very low dose of PyF.

Disease-driven engineering of peptide-targeted DM1 loaded liposomal nanoparticles for enhanced efficacy in treating multiple myeloma by exploring DM1 prodrug chemistry

Here, we report a CD138 receptor targeting liposomal formulation (TNP[Prodrug-4]) that achieved efficacious tumor growth inhibition in treating multiple myeloma by overcoming the dose limiting severe toxicity issues of a highly potent drug, Mertansine (DM1). Despite the promising potential to treat various cancers, due to poor solubility and pharmacokinetic profile, DM1's translation to the clinic has been unsatisfactory. We hypothesized that the optimal prodrug chemistry would promote efficient loading of the prodrug into targeted nanoparticles and achieve controlled release following endocytosis by the cancer cells, consequently, accomplish the most potent tumor growth inhibition. We evaluated four functional linker chemistries for synthesizing DM1-Prodrug molecules and evaluated their stability and cancer cell toxicity in vitro. It was determined that the phosphodiester moiety, as part of nanoparticle formulations, demonstrated most favorable characteristics with an IC50 of ∼16 nM. Nanoparticle formulations of Prodrug-4 enabled its administration at 8-fold higher dosage of equivalent free drug while remaining below maximum tolerated dose. Importantly, TNP[Prodrug-4] achieved near complete inhibition of tumor growth (∼99% by day 10) compared to control, without displaying noticeable systemic toxicity. TNP[Prodrug-4] promises a formulation that could potentially make DM1 treatment available for wider clinical applications with a long-term goal for better patient outcomes.