Activation Of Alternative Signaling Pathways Research Articles

Abstract 1926: MRAS the forgotten member of the GTPase superfamily plays a role in KRASG12Ci resistance

Abstract KRASG12C inhibitors have achieved impressive results in the clinic. However, intrinsic or acquired resistance to therapy invariably develops leading to disease progression in most treated patients. Emerging pre-clinical and clinical evidence points to multiple mechanisms being responsible for resistance to KRASG12C inhibitors, including receptor tyrosine kinase (RTK) activation, KRASG12C amplification, activation of alternative signaling pathways including PI3K, mTOR, YAP/TAZ, acquisition of KRAS mutations that would preclude compound binding (e.g. R68S, Y96C/D, H95D/Q/R), conversion of the G12C codon mutation, and additional activating KRAS mutations (G13D, Q61H). In the clinic, many of the described mutations were detected at low frequency, some patients displayed multiple mutations and in 40% of patients no potential driving mutations were identified. It is therefore likely that other non-genetic alterations are also involved in resistance to KRASG12Ci monotherapy. Here, we used preclinical models of KRASG12C non-small cell lung cancer (NSCLC) and colorectal cancer (CRC) to study intrinsic and acquired resistance to KRASG12C inhibitors. Increased expression of the RAS superfamily gene MRAS was observed in most KRASG12C-naïve tumor cells upon treatment with a KRASG12C inhibitors. In line with this, we observed an increase of MRAS-GTP levels in cells treated with KRASG12Ci in vitro. Interestingly, the increase in active MRAS did not lead to concomitant upregulation of MAPK signaling. Long term treatment with adagrasib was used for generating in vitro and in vivo KRASG12C models with acquired resistance to KRASG12Ci. A strong increase in MRAS expression was observed under these conditions, that surpassed the levels seen with short term treatment in naïve models. This data suggests that activation of MRAS-SHOC2-PP1C complex may play a role in compensating for the KRASG12C-driven signaling in both the intrinsic and acquired resistance setting. Knockdown of SHOC2 to baseline levels resulted in re-sensitization to KRASG12Ci monotherapy and to the effects of combinations in adagrasib-resistant NCI-H358 NSCLC cells. Pathway suppression was deepened by combining adagrasib with either a SOS1i (e.g. BI-3406) or SHP2i (e.g. TNO155) resulting in enhanced anti-tumor effects observed in the KRASG12Ci-resistant models. Our findings underscore the role of MRAS in acquired resistance in KRASG12Ci and the potential to overcome this with vertical pathway combinations, such as SOS1i or SHP2i. Citation Format: Venu Thatikonda, Kaja Kostyrko, Sabine Jurado, Simone Lieb, Melanie Hinkel, Donat Alpar, Oliver Bergner, Astrid Jeschko, Mark Pearson, Marco H. Hofmann. MRAS the forgotten member of the GTPase superfamily plays a role in KRASG12Ci resistance [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 1926.

Structure-Based In Silico Approaches Reveal IRESSA as a Multitargeted Breast Cancer Regulatory, Signalling, and Receptor Protein Inhibitor.

Breast cancer begins in the breast cells, mainly impacting women. It starts in the cells that line the milk ducts or lobules responsible for producing milk and can spread to nearby tissues and other body parts. In 2020, around 2.3 million women across the globe received a diagnosis, with an estimated 685,000 deaths. Additionally, 7.8 million women were living with breast cancer, making it the fifth leading cause of cancer-related deaths among women. The mutational changes, overexpression of drug efflux pumps, activation of alternative signalling pathways, tumour microenvironment, and cancer stem cells are causing higher levels of drug resistance, and one of the major solutions is to identify multitargeted drugs. In our research, we conducted a comprehensive screening using HTVS, SP, and XP, followed by an MM/GBSA computation of human-approved drugs targeting HER2/neu, BRCA1, PIK3CA, and ESR1. Our analysis pinpointed IRESSA (Gefitinib-DB00317) as a multitargeted inhibitor for these proteins, revealing docking scores ranging from -4.527 to -8.809 Kcal/mol and MM/GBSA scores between -49.09 and -61.74 Kcal/mol. We selected interacting residues as fingerprints, pinpointing 8LEU, 6VAL, 6LYS, 6ASN, 5ILE, and 5GLU as the most prevalent in interactions. Subsequently, we analysed the ADMET properties and compared them with the standard values of QikProp. We extended our study for DFT computations with Jaguar and plotted the electrostatic potential, HOMO and LUMO regions, and electron density, followed by a molecular dynamics simulation for 100 ns in water, showing an utterly stable performance, making it a suitable drug candidate. IRESSA is FDA-approved for lung cancer, which shares some pathways with breast cancers, clearing the hurdles of multitargeted drugs against breast and lung cancer. This has the potential to be groundbreaking; however, more studies are needed to concreate IRESSA's role.

Management of patients with advanced-stage HER2-positive breast cancer: current evidence and future perspectives.

Amplification and/or overexpression of ERBB2, the gene encoding HER2, can be found in 15-20% of invasive breast cancers and is associated with an aggressive phenotype and poor clinical outcomes. Relentless research efforts in molecular biology and drug development have led to the implementation of several HER2-targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors and antibody-drug conjugates, constituting one of the best examples of bench-to-bedside translation in oncology. Each individual drug class has improved patient outcomes and, importantly, the combinatorial and sequential use of different HER2-targeted therapies has increased cure rates in the early stage disease setting and substantially prolonged survival for patients with advanced-stage disease. In this Review, we describe key steps in the development of the modern paradigm for the treatment of HER2-positive advanced-stage breast cancer, including selecting and sequencing new-generation HER2-targeted therapies, and summarize efficacy and safety outcomes from pivotal studies. We then outline the factors that are currently known to be related to resistance to HER2-targeted therapies, such as HER2 intratumoural heterogeneity, activation of alternative signalling pathways and immune escape mechanisms, as well as potential strategies that might be used in the future to overcome this resistance and further improve patient outcomes.

Virtual Screening for Identification of Dual Inhibitors against CDK4/6 and Aromatase Enzyme.

CDK4/6 and aromatase are prominent targets for breast cancer drug discovery and are involved in abnormal cell proliferation and growth. Although aromatase inhibitors have proven to be effective (for example exemestane, anastrozole, letrozole), resistance to treatment eventually occurs through the activation of alternative signaling pathways, thus evading the antiproliferative effects of aromatase inhibitors. One of the evasion pathways is Cylin D-CDK4/6-Rb signaling that promotes tumor proliferation and resistance to aromatase inhibitors. There is significant evidence that the sequential inhibition of both proteins provides therapeutic benefits over the inhibition of one target. The basis of this study objective is the identification of molecules that are likely to inhibit both CDK4/6 and aromatase by computational chemistry techniques, which need further biochemical studies to confirm. Initially, a structure-based pharmacophore model was constructed for each target to screen the sc-PDB database. Consequently, pharmacophore screening and molecular docking were performed to evaluate the potential lead candidates that effectively mapped both of the target pharmacophore models. Considering abemaciclib (CDK4/6 inhibitor) and exemestane (aromatase inhibitor) as reference drugs, four potential virtual hit candidates (1, 2, 3, and 4) were selected based on their fit values and binding interaction after screening a sc-PDB database. Further, molecular dynamics simulation studies solidify the stability of the lead candidate complexes. In addition, ADMET and DFT calculations bolster the lead candidates. Hence, these combined computational approaches will provide a better therapeutic potential for developing CDK4/6-aromatase dual inhibitors for HR+ breast cancer therapy.

Gut Molecules in Cardiometabolic Diseases: The Mechanisms behind the Story

Atherosclerotic cardiovascular disease is the most common cause of morbidity and mortality worldwide. Diabetes mellitus increases cardiovascular risk. Heart failure and atrial fibrillation are associated comorbidities that share the main cardiovascular risk factors. The use of incretin-based therapies promoted the idea that activation of alternative signaling pathways is effective in reducing the risk of atherosclerosis and heart failure. Gut-derived molecules, gut hormones, and gut microbiota metabolites showed both positive and detrimental effects in cardiometabolic disorders. Although inflammation plays a key role in cardiometabolic disorders, additional intracellular signaling pathways are involved and could explain the observed effects. Revealing the involved molecular mechanisms could provide novel therapeutic strategies and a better understanding of the relationship between the gut, metabolic syndrome, and cardiovascular diseases.

From targeted therapy to a novel way: Immunogenic cell death in lung cancer.

Lung cancer (LC) is one of the most incident malignancies and a leading cause of cancer mortality worldwide. Common tumorigenic drivers of LC mainly include genetic alterations of EGFR, ALK, KRAS, BRAF, ROS1, and MET. Small inhibitory molecules and antibodies selectively targeting these alterations or/and their downstream signaling pathways have been approved for treatment of LC. Unfortunately, following initial positive responses to these targeted therapies, a large number of patients show dismal prognosis due to the occurrence of resistance mechanisms, such as novel mutations of these genes and activation of alternative signaling pathways. Over the past decade, it has become clear that there is no possible cure for LC unless potent antitumor immune responses are induced by therapeutic intervention. Immunogenic cell death (ICD) is a newly emerged concept, a form of regulated cell death that is sufficient to activate adaptive immune responses against tumor cells. It transforms dying cancer cells into a therapeutic vaccine and stimulates long-lasting protective antitumor immunity. In this review, we discuss the key targetable genetic aberrations and the underlying mechanism of ICD in LC. Various agents inducing ICD are summarized and the possibility of harnessing ICD in LC immunotherapy is further explored.

Preclinical Models for Acquired Resistance to Third-Generation EGFR Inhibitors in NSCLC: Functional Studies and Drug Combinations Used to Overcome Resistance.

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) are currently recommended as first-line treatment for advanced non-small-cell lung cancer (NSCLC) with EGFR-activating mutations. Third-generation (3rd G) EGFR-TKIs, including osimertinib, offer an effective treatment option for patients with NSCLC resistant 1st and 2nd EGFR-TKIs. However, the efficacy of 3rd G EGFR-TKIs is limited by acquired resistance that has become a growing clinical challenge. Several clinical and preclinical studies are being carried out to better understand the mechanisms of resistance to 3rd G EGFR-TKIs and have revealed various genetic aberrations associated with molecular heterogeneity of cancer cells. Studies focusing on epigenetic events are limited despite several indications of their involvement in the development of resistance. Preclinical models, established in most cases in a similar manner, have shown different prevalence of resistance mechanisms from clinical samples. Clinically identified mechanisms include EGFR mutations that were not identified in preclinical models. Thus, NRAS genetic alterations were not observed in patients but have been described in cell lines resistant to 3rd G EGFR-TKI. Mainly, resistance to 3rd G EGFR-TKI in preclinical models is related to the activation of alternative signaling pathways through tyrosine kinase receptor (TKR) activation or to histological and phenotypic transformations. Yet, preclinical models have provided some insight into the complex network between dominant drivers and associated events that lead to the emergence of resistance and consequently have identified new therapeutic targets. This review provides an overview of preclinical studies developed to investigate the mechanisms of acquired resistance to 3rd G EGFR-TKIs, including osimertinib and rociletinib, across all lines of therapy. In fact, some of the models described were first generated to be resistant to first- and second-generation EGFR-TKIs and often carried the T790M mutation, while others had never been exposed to TKIs. The review further describes the therapeutic opportunities to overcome resistance, based on preclinical studies.

Nintedanib overcomes drug resistance from upregulation of FGFR signalling and imatinib-induced KIT mutations in gastrointestinal stromal tumours.

Drug resistance remains a major challenge in the clinical treatment of gastrointestinal stromal tumours (GISTs). While acquired on‐target mutations of mast/stem cell growth factor receptor (KIT) kinase is the major resistance mechanism, activation of alternative signalling pathways may also play a role. Although several second‐ and third‐generation KIT kinase inhibitors have been developed that could overcome some of the KIT mutations conferring resistance, the low clinical responses and narrow safety window have limited their broad application. The present study revealed that nintedanib not only overcame resistance induced by a panel of KIT primary and secondary mutations, but also overcame ERK‐reactivation‐mediated resistance caused by the upregulation of fibroblast growth factor (FGF) activity. In preclinical models of GISTs, nintedanib significantly inhibited the proliferation of imatinib‐resistant cells, including GIST‐5R, GIST‐T1/T670I and GIST patient‐derived primary cells. In addition, it also exhibited dose‐dependent inhibition of ERK phosphorylation upon FGF ligand stimulation. In vivo antitumour activity was also observed in several xenograft GIST models. Considering the well‐documented safety and pharmacokinetic profiles of nintedanib, this finding provides evidence for the repurposing of nintedanib as a new therapy for the treatment of GIST patients with de novo or acquired resistance to imatinib.

When the MET receptor kicks in to resist targeted therapies.

Although targeted therapies have increased the life expectancy of patients with druggable molecular alterations directly involved in tumor development, the efficacy of these therapies is limited by acquired resistances leading to treatment failure. Most targeted therapies, including ones exploiting therapeutic antibodies and kinase inhibitors, are directed against receptor tyrosine kinases (RTKs) or major signaling hubs. Resistances to these therapies arise when inhibition of these targets is bypassed through activation of alternative signaling pathways. In recent years, activation of the receptor tyrosine kinase MET has been shown to promote resistance to various targeted therapies. This casts MET as important actor in resistance. In this review, we describe how the MET receptor triggers resistance to targeted therapies against RTKs such as EGFR, VEGFR, and HER2 and against signaling hubs such as BRAF. We also describe how MET can be its own resistance factor, as illustrated by on-target resistance of lung tumors harboring activating mutations causing MET exon 14 skipping. Interestingly, investigation of all these situations reveals functional physiological relationships between MET and the target of the therapy to which the cancer becomes resistant, suggesting that resistance stems from preexisting mechanisms. Identification of MET as a resistance factor opens the way to co-treatment strategies that are being tested in current clinical trials.

CRISPR-Cas deployment in non-small cell lung cancer for target screening, validations, and discoveries.

Continued advancements in CRISPR-Cas systems have accelerated genome research. Use of CRISPR-Cas in cancer research has been of great interest that is resulting in development of orthogonal methods for drug target validations and discovery of new therapeutic targets through genome-wide screens of cancer cells. CRISPR-based screens have also revealed several new cancer drivers through alterations in tumor suppressor genes (TSGs) and oncogenes inducing resistance to targeted therapies via activation of alternate signaling pathways. Given such dynamic status of cancer, we review the application of CRISPR-Cas in non-small cell lung cancer (NSCLC) for development of mutant models, drug screening, target validation, novel target discoveries, and other emerging potential applications. In addition, CRISPR-based approach for development of novel anticancer combination therapies is also discussed in this review.

Abstract CT116: A phase I study of ribociclib plus everolimus in patients with metastatic pancreatic adenocarcinoma refractory to chemotherapy

Abstract Background: Metastatic pancreatic adenocarcinoma (mPC) has a poor prognosis, with a 5-year survival rate of 2.9%. CDK4/6 is often deregulated in mPC due to loss of CDKN2A via homozygous deletion or epigenetic silencing, resulting in the loss of the p16INK4a protein that naturally inhibits CDK4/6. CDK4/6 inactivates the retinoblastoma protein (RB), allowing E2F family transcription factors to promote cell cycle progression. Inhibitors of CDK4/6 have been ineffective as single agents in part due to Ras-mediated activation of alternate signaling pathways including the PI3K-mTOR pathway. We have shown that co-inhibition of the CDK4/6 and mTOR pathways suppresses growth in mPC patient-derived xenografts. Methods: The combination of ribociclib (RIBO; a CDK4/6 inhibitor) and everolimus (EVE; an mTOR inhibitor) was investigated in a phase I, third-line study in patients (pts) with mPC and disease progression on 5-fluorouracil- and gemcitabine-based chemotherapy regimens. A 3+3 design was used to test the safety of RIBO (250 or 300 mg daily on days 1-21) and fixed-dose EVE (2.5 mg daily on days 1-28) every 28 days. Secondary endpoints were median progression-free survival (mPFS), median overall survival (mOS), overall response rate by RECIST 1.1, and safety. Correlative studies included assessing the pharmacodynamic effects on the RB pathway using pre- and on-treatment tumor biopsies. Results: Twelve pts were enrolled between 2017 and 2019. One dose-limiting toxicity (DLT) of grade 3 rash was seen in a pt at the 250 mg dose level, so the 250 mg level was expanded. Six pts were treated at each dose level, and no other DLTs were seen. The recommended phase 2 dose was RIBO 300 mg. mPFS was 1.8 months (95% CI (0.6, 2.1)), and mOS was 3.7 months (95% CI (2.3, 5.6)). No clinical responses were seen. Three pts (25%) had stable disease at 8 weeks. There was a significant (> 50% on average) decrease in expression of CDK4/6 regulated genes (e.g. BIRC5, CCNA2, STMN1, TOP2A) in pre- vs. post-treatment tumor samples (N = 6, p < 0.001), indicating that there was on-target activity as observed in preclinical models. The baseline tumor sample from 1 patient with long term survival (17.1 months) had significantly less baseline expression of CDK4/6 regulated genes than other baseline patient samples (N = 5, p = 2.8 x 10^-18 using Student's paired t-test). Conclusions: The combination of RIBO 300 mg daily on days 1-21 and EVE 2.5 mg daily on days 1-28 every 28 days was safe and well tolerated in this heavily pre-treated patient population. Pharmacodynamic studies demonstrated a decrease in expression of CDK4/6 regulated genes. However, minimal efficacy was noted, and this combination should not be studied further in this treatment setting. NCT02985125. Citation Format: Benjamin Adam Weinberg, Hongkun Wang, Agnieszka K. Witkiewicz, John L. Marshall, Aiwu R. He, Erik S. Knudsen, Michael J. Pishvaian. A phase I study of ribociclib plus everolimus in patients with metastatic pancreatic adenocarcinoma refractory to chemotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT116.

AKT drives sustained motility following MEK inhibition via promoting SNAIL and AXL in MDA-MB-231 LM2

The adaptive activation of alternative signaling pathways contributes to acquired resistance against targeted cancer therapies. Our previous research has shown that blocking Ras/ERK signaling promotes PI3K/AKT signaling in the lung metastatic derivative of MDA-MB-231 (LM2). Because AKT activation was required to drive sustained cell motility following MEK suppression, we extend our research to elucidate how activation of the PI3K/AKT signaling drives sustained motility following MEK inhibition. Reverse phase protein array (RPPA) revealed that SNAIL (SNAI1) was upregulated in U0126 (MEK inhibitor)-treated LM2 cells. Importantly, LM2 cells simultaneously treated with U0126 and PI3K inhibitor LY294002 exhibited reduced expression of SNAIL. Furthermore, depletion of SNAIL led to reduced cell motility in U0126-treated LM2 cells. In addition, we identified AXL as another downstream effector of AKT. These results suggest that SNAIL and AXL are key factors mediating sustained motility of LM2 cells following MEK suppression. Because AKT mediates motile behavior under MEK suppression, our results suggest that AKT and AXL may be targeted to overcome resistance against drugs targeting the Ras/ERK pathway.

Combinatorial Therapies in Thyroid Cancer: An Overview of Preclinical and Clinical Progresses.

Accounting for about 2% of cancers diagnosed worldwide, thyroid cancer has caused about 41,000 deaths in 2018. Despite significant progresses made in recent decades in the treatment of thyroid cancer, many resistances to current monotherapies are observed. In our complete review, we report all treatments that were tested in combination against thyroid cancer. Many preclinical studies investigating the effects of inhibitors of the MAPK and PI3K pathways highlighted the importance of mutations in such signaling pathways and their impacts on the subsequent efficacy of targeted therapies, thus reinforcing the need of more personalized therapeutic strategies. Our review also points out the multiple possibilities of combinatory strategies, particularly using therapies targeting proliferation, survival, angiogenesis, and in combination with conventional treatments such as chemotherapies. In any case, resistances to anticancer therapies always develop through the activation of alternative signaling pathways. Combinatory treatments aim to blockade such mechanisms, which are gradually decrypted, thus offering new perspectives for the future. The preclinical and clinical aspects of our review allow us to have a global opinion of the different therapeutic options currently evaluated in combination and to be aware about new perspectives of treatment of thyroid cancer.

Determining Resistance Mechanisms in BRAF-mutated Multiple Myeloma

Introduction: Constant clonal evolution and outgrowth of clones that harbor resistance mutations are likely explanations for the emergence of drug-resistant disease in multiple myeloma (MM). Activating mutations in BRAF, KRAS and NRAS have been suggested as potential therapeutic targets. In this study, we investigate resistance to BRAF inhibition in the context of BRAF-mutated MM which accounts for about 5-12% of all patients with relapsed/ refractory MM. Methods: Resistance to dabrafenib was modeled in vitro in the BRAF-mutated MM cell lines (MMCL) U266 (K601Nmut) and DP6 (BRAFV600Emut). Low-pass whole genome sequencing (LPWGS), RNA sequencing, ChIP sequencing and immunoblotting were performed for genomic, transcriptomic, epigenomic and molecular characterization. Functional validation was performed by genome editing using CRISPR/Cas9 technology. Results: Modeling of dabrafenib resistance in vitro revealed an initial decline of cell numbers, followed by a plateau phase and a gradual outgrowth of resistant cells after ~80 days of treatment. As expected, exposure of BRAFmut MMCL to dabrafenib led to initial downregulation of pERK and pMEK. At later timepoints, upregulation of pERK and pMEK was observed, suggesting that re-activation of the ERK/MEK pathway ultimately overcomes BRAF inhibition. This outgrowth was associated with highly distinct copy number profiles in each resistant clone, implying clonal selection with outgrowth of genetically resistant clones as one mechanism of drug resistance in MM. Additionally, we found that BRAF inhibition of BRAFmut MMCL promotes changes of the transcriptional circuitry that appears independent of clonal outgrowth of genetically resistant clones. These transcriptional changes were highly homogenous, occurred as early as 7-14 days after starting treatment and were associated with de-differentiation of MMCL into a more immature B lymphocytic phenotype. This phenotype was associated with greater mRNA expression of CD19 and CD81, as well as upregulation of the B-lymphocyte activation antigen B7-2 (CD86) and PI3K pathway genes. We next investigated if targeting the PI3K pathway and B7.2 can be exploited for effective killing of dabrafenib-resistant BRAFmut MM cells. Studies for the PI3Kδ inhibitor idelalisib in dabrafenib-persistent MMCL revealed higher sensitivity as compared to dabrafenib-naïve controls. Genome editing suggests a survival advantage for CD86WT as compared to CD86KO MMCL. Conclusions: Our data suggest that resistance to BRAF inhibition in vitro is mediated by two distinct mechanisms: 1) clonal outgrowth of genetically distinct resistant clones, and 2) transcriptional rewiring that leads to activation of alternative signaling pathways. The latter is characterized by changes in cellular differentiation and upregulation of PI3K and CD28/CD86 signaling. These concepts may provide a framework for revealing therapeutic vulnerabilities and to overcome drug resistance mediated by genetic heterogeneity in MM. Disclosures Munshi: Oncopep: Consultancy; Takeda: Consultancy; Janssen: Consultancy; Celgene: Consultancy; Oncopep: Consultancy; Abbvie: Consultancy; Adaptive: Consultancy; Amgen: Consultancy. Anderson:Sanofi-Aventis: Other: Advisory Board; Bristol-Myers Squibb: Other: Scientific Founder; Oncopep: Other: Scientific Founder; Amgen: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau. Yee:Karyopharm: Consultancy; Bristol-Myers Squibb: Consultancy, Research Funding; Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy; Adaptive: Consultancy. Raje:Amgen Inc.: Consultancy; Bristol-Myers Squibb: Consultancy; Celgene Corporation: Consultancy; Takeda: Consultancy; Janssen: Consultancy; Merck: Consultancy. Lohr:Celgene: Research Funding; T2 Biosystems: Honoraria. OffLabel Disclosure: Dabrafenib is a potent inhibitor of BRAF mutated at codon 600 (BRAFV600). Here we explored the efficacy of dabrafenib a preclinical model of multiple myeloma cell lines with BRAFV600E and BRAFK601N mutations.

Abstract 2114: Co-delivery nanoparticle to overcome therapeutic resistance in human head and neck cancer promoted by insufficient Src-targeted treatment

Abstract Head and neck cancer (HNC) exhibiting resistance to molecular-targeted therapeutics poses a challenge to their effective clinical management and alternative treatment strategies are actively sought to improve results. Src is commonly hyperactivated in HNC cells and has been implicated as an oncogenic driver in the development and progression of HNC. Unfortunately, the clinical benefit is dampened significantly in HNC patients because only a small fraction of patients respond positively to Src-targeted treatment, and many develop drug resistance. Here, we demonstrate that the addition of AKT blockade in Src-targeted treatment may prevent activation of alternative signaling pathways to bypass the Src inhibition in HNC cells. The combination of Src and AKT inhibitors significantly suppressed HNC growth more efficiently than either drug alone. However, the properties and pharmacokinetics of two inhibitors required a novel approach to optimal delivery into the same tumor cells. To address this, we developed novel tumor-targeting nanoparticles to selectively co-deliver Src and AKT inhibitors to the tumor site in an orthotopic mouse model of HNC. This nanotherapeutic modality significantly improved the efficacy of tumor repression, which was mainly attributed to the highly specific tumor-targeted drug delivery system and synergistic anticancer effect by co-inactivation of AKT and Src. The results of this study will enable us to take a major step toward addressing the urgent need for single drug resistance and failure, and strongly impact on the development of clinically acceptable therapeutics to combat HNC. Citation Format: Liwei Lang, Chloe Shay, Xuli Wang, Yong Teng. Co-delivery nanoparticle to overcome therapeutic resistance in human head and neck cancer promoted by insufficient Src-targeted treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2114.

Treatment of advanced renal cell carcinoma patients with cabozantinib, an oral multityrosine kinase inhibitor of MET, AXL and VEGF receptors.

Von Hippel-Lindau (VHL), a tumor suppressor gene, is frequently inactivated in renal cell carcinoma (RCC). It drives tumorigenesis by activating downstream hypoxia responsive genes and proangiogenic factors like VEGFR, and is responsible for the activity of tyrosine kinase inhibitors in RCC. Resistance to VEGFR therapy eventually occurs, in part due to activation of alternative signaling pathways like AXL and MET. Cabozantinib is a potent inhibitor of VEGF, AXL and MET receptors providing rationale for its use in RCC. Cabozantinib has been approved for use in the first- and second-line setting in patients with advanced RCC. This manuscript reviews the preclinical data, pharmacology, clinical efficacy and safety of the use of cabozantinib in RCC.

Targeting the androgen receptor and overcoming resistance in prostate cancer.

Prostate cancer (PCa) is diagnosed in one out of every nine men and is the second leading cause of cancer death among men. Although therapies targeting the androgen receptor (AR) are highly effective, development of resistance is universal and remains a major therapeutic challenge. Nonetheless, signaling via AR is frequently maintained despite standard androgen-signaling inhibition. We review the current understanding of mechanisms of resistance as well as therapeutic approaches to improving treatment of PCa via targeting of the AR. Resistance to AR-targeting therapies may be mediated by several mechanisms, including amplification, mutation, and alternative splicing of AR; intratumoral androgen synthesis; activation of alternative signaling pathways; and in a minority of cases, emergence of AR-independent phenotypes. Recent trials demonstrate that intensification of androgen blockade in metastatic castration-sensitive PCa can significantly improve survival. Similar strategies are being explored in earlier disease states. In addition, several other cellular signaling pathways have been identified as mechanisms of resistance, offering opportunities for cotargeted therapy. Finally, immune-based approaches are in development to complement AR-targeted therapies. Targeting the AR remains a critical focus in the treatment of PCa.

Mechanisms of acquired resistance to fibroblast growth factor receptor targeted therapy.

Oncogenic activation of the fibroblast growth factor receptor (FGFR) through mutations and fusions of the FGFR gene occur in a variety of different malignancies such as urothelial carcinoma and cholangiocarcinoma. Inhibition of the kinase domain of the FGFR with targeted oral FGFR inhibitors has been shown in both preclinical and early phase clinical trials to lead to meaningful reductions in tumour size and larger confirmatory randomized trials are underway. Acquired resistance to FGFR inhibition using a variety of mechanisms that includes, activation of alternate signaling pathways and expansion of tumour clones with gatekeeper mutations in the FGFR gene. This review summarizes the acquired resistance mechanisms to FGFR therapy and therapeutic approaches to circumventing resistance.

IL6/STAT3 axis mediates resistance to BRAF inhibitors in thyroid carcinoma cells

Thyroid carcinomas (TCs) bearing BRAF mutations represent approximately 26–53% of human thyroid malignancies and, differently from melanomas, are poorly sensitive to BRAF inhibitors (BRAFi), and develop acquired resistance through activation of alternative signaling pathways. A whole-genome gene expression analysis of TC BRAF V600E cells exposed to PLX4032 identified JAK/STAT among the most significantly modulated signaling pathways. Interestingly, both transient exposure and chronic adaptation to PLX4032 resulted in upregulation of IL6/STAT3 axis and this impaired the cytostatic activity of PLX4032. Mechanistically, exposure to PLX4032 enhanced IL6 secretion and this, in turn, was responsible for STAT3 upregulation, activation of ERK signaling and poor sensitivity to BRAF inhibition. Consistently, the dual blockade of STAT3 (by siRNA or pharmacological inhibition) or IL6 signaling (by the humanized anti-human IL6 receptor antibody, tocilizumab) and BRAF (by PLX4032) improved the inhibition of cell cycle progression compared to PLX4032 single agent. These data support the role of IL6/STAT3 signaling pathway in modulating TC cell response to PLX4032 and candidate IL6 targeting as a strategy to improve the activity of PLX4032 in BRAF V600E TC cells.

Abstract 836: ISU104, a fully human anti-ErbB3 antibody, overcomes acquired cetuximab resistance

Abstract ErbB3 is noted as one of major causes of acquired cetuximab resistance in colorectal and head and neck cancers. ErbB3 causes activation of alternative signaling pathways that bypass the original target and sustained PI3K/AKT activation, and these are associated with cetuximab resistance. We confirmed the induced ErbB3 activation by the cetuximab treatment in FaDu head and neck squamous-cell carcinoma (HNSCC) xenograft model. Immunoblot analysis was shown that twice weekly 10 mg/kg of cetuximab treatment upregulated ErbB3 expression and phosphorylation even though tumor growth was well controlled. To investigate whether ErbB3 activation by ligand, heregulin (HRG,) might induce cetuximab resistance, two cetuximab-sensitive colorectal cancer cell lines, DiFi and LIM1215, were treated 0-25 ng/mL of HRG. HRG induced dose-dependent cetuximab resistance in cell proliferation assay, and this was reversed via ISU104 treatment. To evaluate if ISU104 could overcome resistance to cetuximab in vivo, acquired cetuximab-resistant FaDu xenograft model was established. Tumors that had acquired resistance to 5 mg/kg of cetuximab treatment were significantly regressed by replaced treatment of ISU104 alone (10 mg/kg) or combination treatment of ISU104 and cetuximab, while mice continued on cetuximab only showed uncontrolled tumor growth like vehicle-treated group. Our results suggest that ISU104 effectively overcomes cetuximab resistance and may provide clinical benefit to cetuximab-resistant patients. Citation Format: Miyoung Kim, Youngmi Hur, Mirim Hong, Youngsoo Sohn, Kum-Joo Shin, Kyungyong Kim, Seung-Beom Hong, Kum-Joo Shin, Donggoo Bae. ISU104, a fully human anti-ErbB3 antibody, overcomes acquired cetuximab resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 836.