An oligoclonal antibody durably overcomes resistance of lung cancer to third-generation EGFR inhibitors

Targeting metabolic adaptive responses induced by glucose starvation inhibits cell proliferation and enhances cell death in osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines

Osimertinib, a tyrosine kinase inhibitor targeting mutant EGFR, has received approval for initial treatment in patients with Non-Small Cell Lung Cancer (NSCLC). While effective in both first- and second-line treatments, patients eventually develop acquired resistance. Metabolic reprogramming represents a strategy through which cancer cells may resist and adapt to the selective pressure exerted by the drug. In the current study, we investigated the metabolic adaptations associated with osimertinib-resistance in NSCLC cells under low glucose culture conditions. We demonstrated that, unlike osimertinib-sensitive cells, osimertinib-resistant cells were able to survive under low glucose conditions by increasing the rate of glucose and glutamine uptake and by shifting towards mitochondrial metabolism. Inhibiting glucose/pyruvate contribution to mitochondrial respiration, glutamine deamination to glutamate, and oxidative phosphorylation decreased the proliferation and survival abilities of osimertinib-resistant cells to glucose starvation. Our findings underscore the remarkable adaptability of osimertinib-resistant NSCLC cells in a low glucose environment and highlight the pivotal role of mitochondrial metabolism in mediating this adaptation. Targeting the metabolic adaptive responses triggered by glucose shortage emerges as a promising strategy, effectively inhibiting cell proliferation and promoting cell death in osimertinib-resistant cells.

Targeting glucosylceramide synthase induces antiproliferative and proapoptotic effects in osimertinib-resistant NSCLC cell models

The EGFR tyrosine kinase inhibitor osimertinib has been approved for the first-line treatment of EGFR-mutated Non-Small Cell Lung Cancer (NSCLC) patients. Despite its efficacy, patients develop resistance. Mechanisms of resistance are heterogeneous and not fully understood, and their characterization is essential to find new strategies to overcome resistance. Ceramides are well-known regulators of apoptosis and are converted into glucosylceramides (GlcCer) by glucosylceramide synthase (GCS). A higher content of GlcCers was observed in lung pleural effusions from NSCLC patients and their role in osimertinib-resistance has not been documented. The aim of this study was to determine the therapeutic potential of inhibiting GCS in NSCLC EGFR-mutant models resistant to osimertinib in vitro and in vivo. Lipidomic analysis showed a significant increase in the intracellular levels of glycosylceramides, including GlcCers in osimertinib resistant clones compared to sensitive cells. In resistant cells, the GCS inhibitor PDMP caused cell cycle arrest, inhibition of 2D and 3D cell proliferation, colony formation and migration capability, and apoptosis induction. The intratumoral injection of PDMP completely suppressed the growth of OR xenograft models. This study demonstrated that dysregulation of ceramide metabolism is involved in osimertinib-resistance and targeting GCS may be a promising therapeutic strategy for patients progressed to osimertinib.

SOS2 modulates the threshold of EGFR signaling to regulate osimertinib efficacy and resistance in lung adenocarcinoma

Son of sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic receptor tyrosine kinase (RTK)-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR tyrosine kinase inhibitor (EGFR-TKI) osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion (SOS2KO ) sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation, oncogenic transformation, and survival. Bypassing RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2KO inhibited hepatocyte growth factor (HGF)-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long-term in situ resistance assay, most osimertinib-resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2KO cultures that became osimertinib resistant primarily underwent non-RTK-dependent epithelial-mesenchymal transition (EMT). Since bypassing RTK reactivation and/or tertiary EGFR mutations represent most osimertinib-resistant cancers, these data suggest that targeting proximal RTK signaling, here exemplified by SOS2 deletion, has the potential to delay the development osimertinib resistance and enhance overall clinical responses for patients with EGFR-mutated LUAD.

In situ modeling of acquired resistance to RTK/RAS-pathway-targeted therapies

Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Here, we describe an in situ resistance assay (ISRA) that reliably models acquired resistance to RTK/RAS-pathway-targeted therapies across cell lines. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show that acquired osimertinib resistance can be significantly delayed by inhibition of proximal RTK signaling using SHP2 inhibitors. Isolated osimertinib-resistant populations required SHP2 inhibition to resensitize cells to osimertinib and reduce MAPK signaling to block the effects of enhanced activation of multiple parallel RTKs. We additionally modeled resistance to targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.

Epidermal growth factor receptor dual-target inhibitors as a novel therapy for cancer: A review

Overexpression of the epidermal growth factor receptor (EGFR) has been linked to several human cancers, including esophageal cancer, pancreatic cancer, anal cancer, breast cancer, and lung cancer, particularly non-small cell lung cancer (NSCLC). Therefore, EGFR has emerged as a critical target for treating solid tumors. Many 1st-, 2nd-, 3rd-, and 4th-generation EGFR single-target inhibitors with clinical efficacy have been designed and synthesized in recent years. Drug resistance caused by EGFR mutations has posed a significant challenge to the large-scale clinical application of EGFR single-target inhibitors and the discovery of novel EGFR inhibitors. Therapeutic methods for overcoming multipoint EGFR mutations are still needed in medicine. EGFR dual-target inhibitors are more promising than single-target inhibitors as they have a lower risk of drug resistance, higher efficacy, lower dosage, and fewer adverse events. EGFR dual-target inhibitors have been developed sequentially to date, providing new options for remission in patients with previously untreatable malignancies and laying the groundwork for a future generation of compounds. This paper introduces the EGFR family proteins and their synergistic effects with other anticancer targets, and provides a comprehensive review of the development of EGFR dual-target inhibitors in cancer, as well as the opportunities and challenges associated with those fields.

SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status

KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.

20 years since the approval of first EGFR-TKI, gefitinib: Insight and foresight

Epidermal growth factor receptor (EGFR) actively involves in modulation of various cancer progression related mechanisms including angiogenesis, differentiation and migration. Therefore, targeting EGFR has surfaced as a prominent approach for the treatment of several types of cancers, including non-small cell lung cancer (NSCLC), pancreatic cancer, glioblastoma. Various first, second and third generation of EGFR tyrosine kinase inhibitors (EGFR-TKIs) have demonstrated effectiveness as an anti-cancer therapeutics. However, rapid development of drug resistance and mutations still remains a major challenge for the EGFR-TKIs therapy. Overcoming from intrinsic and acquired resistance caused by EGFR mutations warrants the further exploration of alternative strategies and discovery of novel inhibitors. In this review, we delve into the breakthrough discoveries have been made in previous 20 years, and discuss the currently ongoing efforts aimed to circumvent the chemo-resistance. We also highlight the new challenges, limitations and future directions for the development of improved therapeutic approaches such as fourth-generation EGFR-TKIs, peptides, nanobodies, PROTACs etc.

Resistance of Lung Cancer to EGFR-Specific Kinase Inhibitors: Activation of Bypass Pathways and Endogenous Mutators

Epidermal growth factor receptor (EGFR)-specific tyrosine kinase inhibitors (TKIs) have changed the landscape of lung cancer therapy. For patients who are treated with the new TKIs, the current median survival exceeds 3 years, substantially better than the average 20 month survival rate only a decade ago. Unfortunately, despite initial efficacy, nearly all treated patients evolve drug resistance due to the emergence of either new mutations or rewired signaling pathways that engage other receptor tyrosine kinases (RTKs), such as MET, HER3 and AXL. Apparently, the emergence of mutations is preceded by a phase of epigenetic alterations that finely regulate the cell cycle, bias a mesenchymal phenotype and activate antioxidants. Concomitantly, cells that evade TKI-induced apoptosis (i.e., drug-tolerant persister cells) activate an intrinsic mutagenic program reminiscent of the SOS system deployed when bacteria are exposed to antibiotics. This mammalian system imbalances the purine-to-pyrimidine ratio, inhibits DNA repair and boosts expression of mutation-prone DNA polymerases. Thus, the net outcome of the SOS response is a greater probability to evolve new mutations. Deeper understanding of the persister-to-resister transformation, along with the development of next-generation TKIs, EGFR-specific proteolysis targeting chimeras (PROTACs), as well as bispecific antibodies, will permit delaying the onset of relapses and prolonging survival of patients with EGFR+ lung cancer.

SOS2 regulates the threshold of mutant EGFR-dependent oncogenesis

Son of Sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic RTK-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR-TKI osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit PI3K/AKT pathway activation, oncogenic transformation, and survival. Bypass RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2 KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2 KO inhibited HGF-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long term in situ resistance assay, a majority of osimertinib resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2 KO cultures that became osimertinib resistant primarily underwent non-RTK dependent EMT. Since bypass RTK reactivation and/or tertiary EGFR mutations represent the majority of osimertinib-resistant cancers, these data suggest that targeting SOS2 has the potential to eliminate the majority of osimertinib resistance.

In situ modeling of acquired resistance to RTK/RAS pathway targeted therapies

Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Preclinical studies that identify synergistic combinations enhance therapeutic efficacy to target intrinsic resistance, however, methods to study acquired resistance in cell culture are lacking. Here, we describe a novel in situ resistance assay (ISRA), performed in a 96-well culture format, that models acquired resistance to RTK/RAS pathway targeted therapies. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show acquired resistance can be reliably modeled across cell lines using objectively defined osimertinib doses. Similar to patient populations, isolated osimertinib-resistant populations showed resistance via enhanced activation of multiple parallel RTKs so that individual RTK inhibitors did not re-sensitize cells to osimertinib. In contrast, inhibition of proximal RTK signaling using the SHP2 inhibitor RMC-4550 both re-sensitized resistant populations to osimertinib and prevented the development of osimertinib resistance as a primary therapy. Similar, objectively defined drug doses were used to model resistance to additional RTK/RAS pathway targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.

Design and selection of optimal ErbB-targeting bispecific antibodies in pancreatic cancer

The ErbB family of receptor tyrosine kinases is a primary target for small molecules and antibodies for pancreatic cancer treatment. Nonetheless, the current treatments for this tumor are not optimal due to lack of efficacy, resistance, or toxicity. Here, using the novel BiXAb™ tetravalent format platform, we generated bispecific antibodies against EGFR, HER2, or HER3 by considering rational epitope combinations. We then screened these bispecific antibodies and compared them with the parental single antibodies and antibody pair combinations. The screen readouts included measuring binding to the cognate receptors (mono and bispecificity), intracellular phosphorylation signaling, cell proliferation, apoptosis and receptor expression, and also immune system engagement assays (antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity). Among the 30 BiXAbs™ tested, we selected 3Patri-1Cetu-Fc, 3Patri-1Matu-Fc and 3Patri-2Trastu-Fc as lead candidates. The in vivo testing of these three highly efficient bispecific antibodies against EGFR and HER2 or HER3 in pre-clinical mouse models of pancreatic cancer showed deep antibody penetration in these dense tumors and robust tumor growth reduction. Application of such semi-rational/semi-empirical approach, which includes various immunological assays to compare pre-selected antibodies and their combinations with bispecific antibodies, represents the first attempt to identify potent bispecific antibodies against ErbB family members in pancreatic cancer.

Covalent Binding Mechanism of Furmonertinib and Osimertinib With Human Serum Albumin

As third-generation tyrosine kinase inhibitors, furmonertinib and osimertinib exhibit better efficacy than first- and second-generation tyrosine kinase inhibitors in patients with advanced non-small cell lung cancer. However, radioactive pharmacokinetics studies showed that parent-related components remain in human plasma for at least 21 days after oral administration. Similar pharmacokinetic profiles were found in pyrotinib and neratinib, which have been identified to covalently bind with human serum albumin at Lys-190, leading to low extraction recovery in protein precipitation. However, the binding mechanism of furmonertinib and osimertinib in human plasma has not been confirmed. Comprehensive techniques were used to investigate the mechanism of this binding, including ultra high-performance liquid chromatography coupled with high-resolution mass spectrometry and online/offline radioactivity profiling. SDS-PAGE and further autoradiography were also used to detect drug-protein adducts. We found that most furmonertinib exists in the human plasma following ex vivo incubation in the form of protein-drug adducts. Only lysine-furmonertinb adducts were found in pronase digests. A standard reference of lysine-furmonertinib was synthesized and confirmed by NMR. Through peptide mapping analysis, we confirmed that furmonertinib almost exclusively binds with human serum albumin (HSA) in plasma following ex vivo incubation, via Michael addition at Lys-195 and Lys-199, instead of Lys-190. Two peptides found to bond with furmonertinib were ASSAKQR and LKCASLQK. Osimertinib was also found to bond with Lys-195 and Lys-199 of HSA via peptide mapping analysis. SIGNIFICANCE STATEMENT: Here we report that furmonertinib and osimertinib can covalently bind with human serum albumin at the site of Lys-195 and Lys-199 instead of Lys-190, potentially leading to the long duration of drug-protein adducts in the human body.

Polyclonal antibody-induced downregulation of HER1/EGFR and HER2 surpasses the effect of combinations of specific registered antibodies

Background

Antitumor therapies targeting HER1/EGFR and HER2, such as monoclonal antibodies (MAbs) and tyrosine-kinase inhibitors (TKIs), have demonstrated a significant clinical benefit, but the emergence of resistance limits long-term efficacy. While secondary HER1 mutations confer tolerance to TKI, compensatory upregulation of HER2 drives resistance to anti-HER1 MAbs, which identifies MAb combinations targeting both receptors as an attractive therapeutic strategy. Nevertheless, toxicity hampers the clinical validation of this approach. Alternatively, cancer vaccines may induce antibodies directed against several antigens with less concern about induced toxicity.

Methods

Polyclonal antibodies (PAbs) targeting HER1 and HER2 were induced in mice or rabbits through immunization. Recognition of different epitopes on targets by PAbs was validated by phage-display technology. Receptor downregulation was evaluated by flow cytometry, immunofluorescence, and Western blot. MTT assays assessed cytotoxicity, while the antitumor effect of PAbs was assayed in nude mice.

Results

PAbs promoted degradation of HER1 and HER2 regarding clinical MAbs or their combinations. As a result, inhibition of cytotoxicity on tumor cell lines was improved, even in the presence of oncogenic mutations in HER1, as well as in cetuximab-insensitive cells. Accordingly, the antitumor effect of vaccination-induced PAbs was observed in lung tumor lines representative of sensitivity or resistance to HER1 targeting therapies.

Conclusions

Immunization against HER1 and HER2 receptors offers an alternative to passive administration of combinations of MAbs, since vaccination-induced PAbs promote the downregulation of both receptors and they have a higher impact on the survival of tumor cells.

AXL and Error-Prone DNA Replication Confer Drug Resistance and Offer Strategies to Treat EGFR-Mutant Lung Cancer

Anticancer therapies have been limited by the emergence of mutations and other adaptations. In bacteria, antibiotics activate the SOS response, which mobilizes error-prone factors that allow for continuous replication at the cost of mutagenesis. We investigated whether the treatment of lung cancer with EGFR inhibitors (EGFRi) similarly engages hypermutators. In cycling drug-tolerant persister (DTP) cells and in EGFRi-treated patients presenting residual disease, we observed upregulation of GAS6, whereas ablation of GAS6's receptor, AXL, eradicated resistance. Reciprocally, AXL overexpression enhanced DTP survival and accelerated the emergence of T790M, an EGFR mutation typical to resistant cells. Mechanistically, AXL induces low-fidelity DNA polymerases and activates their organizer, RAD18, by promoting neddylation. Metabolomics uncovered another hypermutator, AXL-driven activation of MYC, and increased purine synthesis that is unbalanced by pyrimidines. Aligning anti-AXL combination treatments with the transition from DTPs to resistant cells cured patient-derived xenografts. Hence, similar to bacteria, tumors tolerate therapy by engaging pharmacologically targetable endogenous mutators.

SIGNIFICANCE

EGFR-mutant lung cancers treated with kinase inhibitors often evolve resistance due to secondary mutations. We report that in similarity to the bacterial SOS response stimulated by antibiotics, endogenous mutators are activated in drug-treated cells, and this heralds tolerance. Blocking the process prevented resistance in xenograft models, which offers new treatment strategies. This article is highlighted in the In This Issue feature, p. 2483.

HER3 in cancer: from the bench to the bedside

The HER3 protein, that belongs to the ErbB/HER receptor tyrosine kinase (RTK) family, is expressed in several types of tumors. That fact, together with the role of HER3 in promoting cell proliferation, implicate that targeting HER3 may have therapeutic relevance. Furthermore, expression and activation of HER3 has been linked to resistance to drugs that target other HER receptors such as agents that act on EGFR or HER2. In addition, HER3 has been associated to resistance to some chemotherapeutic drugs. Because of those circumstances, efforts to develop and test agents targeting HER3 have been carried out. Two types of agents targeting HER3 have been developed. The most abundant are antibodies or engineered antibody derivatives that specifically recognize the extracellular region of HER3. In addition, the use of aptamers specifically interacting with HER3, vaccines or HER3-targeting siRNAs have also been developed. Here we discuss the state of the art of the preclinical and clinical development of drugs aimed at targeting HER3 with therapeutic purposes.

Triple Targeting of HER Receptors Overcomes Heregulin-mediated Resistance to EGFR Blockade in Colorectal Cancer

Current treatment options for patients with advanced colorectal cancers include anti-EGFR/HER1 therapy with the blocking antibody cetuximab. Although a subset of patients with KRAS WT disease initially respond to the treatment, resistance develops in almost all cases. Relapse has been associated with the production of the ligand heregulin (HRG) and/or compensatory signaling involving the receptor tyrosine kinases HER2 and HER3. Here, we provide evidence that triple-HER receptor blockade based on a newly developed bispecific EGFR×HER3-targeting antibody (scDb-Fc) together with the HER2-blocking antibody trastuzumab effectively inhibited HRG-induced HER receptor phosphorylation, downstream signaling, proliferation, and stem cell expansion of DiFi and LIM1215 colorectal cancer cells. Comparative analyses revealed that the biological activity of scDb-Fc plus trastuzumab was sometimes even superior to that of the combination of the parental antibodies, with PI3K/Akt pathway inhibition correlating with improved therapeutic response and apoptosis induction as seen by single-cell analysis. Importantly, growth suppression by triple-HER targeting was recapitulated in primary KRAS WT patient-derived organoid cultures exposed to HRG. Collectively, our results provide strong support for a pan-HER receptor blocking approach to combat anti-EGFR therapy resistance of KRAS WT colorectal cancer tumors mediated by the upregulation of HRG and/or HER2/HER3 signaling.

An allosteric inhibitor against the therapy-resistant mutant forms of EGFR in non-small cell lung cancer

Epidermal growth factor receptor (EGFR) therapy using small-molecule tyrosine kinase inhibitors (TKIs) is initially efficacious in patients with EGFR-mutant lung cancer, although drug resistance eventually develops. Allosteric EGFR inhibitors, which bind to a different EGFR site than existing ATP-competitive EGFR TKIs, have been developed as a strategy to overcome therapy-resistant EGFR mutations. Here we identify and characterize JBJ-09-063, a mutant-selective allosteric EGFR inhibitor that is effective across EGFR TKI-sensitive and resistant models, including those with EGFR T790M and C797S mutations. We further uncover that EGFR homo- or heterodimerization with other ERBB family members, as well as the EGFR L747S mutation, confers resistance to JBJ-09-063, but not to ATP-competitive EGFR TKIs. Overall, our studies highlight the potential clinical utility of JBJ-09-063 as a single agent or in combination with EGFR TKIs to define more effective strategies to treat EGFR-mutant lung cancer.

Osimertinib and anti-HER3 combination therapy engages immune dependent tumor toxicity via STING activation in trans

Over the past decade, immunotherapy delivered novel treatments for many cancer types. However, lung cancer still leads cancer mortality, and non-small-cell lung carcinoma patients with mutant EGFR cannot benefit from checkpoint inhibitors due to toxicity, relying only on palliative chemotherapy and the third-generation tyrosine kinase inhibitor (TKI) osimertinib. This new drug extends lifespan by 9-months vs. second-generation TKIs, but unfortunately, cancers relapse due to resistance mechanisms and the lack of antitumor immune responses. Here we explored the combination of osimertinib with anti-HER3 monoclonal antibodies and observed that the immune system contributed to eliminate tumor cells in mice and co-culture experiments using bone marrow-derived macrophages and human PBMCs. Osimertinib led to apoptosis of tumors but simultaneously, it triggered inositol-requiring-enzyme (IRE1α)-dependent HER3 upregulation, increased macrophage infiltration, and activated cGAS in cancer cells to produce cGAMP (detected by a lentivirally transduced STING activity biosensor), transactivating STING in macrophages. We sought to target osimertinib-induced HER3 upregulation with monoclonal antibodies, which engaged Fc receptor-dependent tumor elimination by macrophages, and STING agonists enhanced macrophage-mediated tumor elimination further. Thus, by engaging a tumor non-autonomous mechanism involving cGAS-STING and innate immunity, the combination of osimertinib and anti-HER3 antibodies could improve the limited therapeutic and stratification options for advanced stage lung cancer patients with mutant EGFR.

Development of Dual Inhibitors Targeting Epidermal Growth Factor Receptor in Cancer Therapy

Epidermal growth factor receptor (EGFR) is of great significance in mediating cell signaling transduction and tumor behaviors. Currently, third-generation inhibitors of EGFR, especially osimertinib, are at the clinical frontier for the treatment of EGFR-mutant non-small-cell lung cancer (NSCLC). Regrettably, the rapidly developing drug resistance caused by EGFR mutations and the compensatory mechanism have largely limited their clinical efficacy. Given the synergistic effect between EGFR and other compensatory targets during tumorigenesis and tumor development, EGFR dual-target inhibitors are promising for their reduced risk of drug resistance, higher efficacy, lower dosage, and fewer adverse events than those of single-target inhibitors. Hence, we present the synergistic mechanism underlying the role of EGFR dual-target inhibitors against drug resistance, their structure-activity relationships, and their therapeutic potential. Most importantly, we emphasize the optimal target combinations and design strategies for EGFR dual-target inhibitors and provide some perspectives on new challenges and future directions in this field.

Improving Biologics' Effectiveness in Clinical Oncology: From the Combination of Two Monoclonal Antibodies to Oligoclonal Antibody Mixtures

Simple Summary

The approval of the two antibody combinations trastuzumab/pertuzumab and ipilimumab/nivolumab in oncology has paved the way for novel antibody combinations or oligoclonal antibody mixtures to improve their efficacy in cancer. The underlying biological mechanisms and challenges of these strategies will be discussed using data from clinical trials listed in databases. These therapeutic combinations also lead to questions on how to optimize their formulation and delivery to induce a therapeutic polyclonal response in patients with cancer.

Abstract

Monoclonal antibodies have revolutionized the treatment of many diseases, but their clinical efficacy remains limited in some other cases. Pre-clinical and clinical trials have shown that combinations of antibodies that bind to the same target (homo-combinations) or to different targets (hetero-combinations) to mimic the polyclonal humoral immune response improve their therapeutic effects in cancer. The approval of the trastuzumab/pertuzumab combination for breast cancer and then of the ipilimumab/nivolumab combination for melanoma opened the way to novel antibody combinations or oligoclonal antibody mixtures as more effective biologics for cancer management. We found more than 300 phase II/III clinical trials on antibody combinations, with/without chemotherapy, radiotherapy, small molecules or vaccines, in the ClinicalTrials.gov database. Such combinations enhance the biological responses and bypass the resistance mechanisms observed with antibody monotherapy. Usually, such antibody combinations are administered sequentially as separate formulations. Combined formulations have also been developed in which separately produced antibodies are mixed before administration or are produced simultaneously in a single cell line or a single batch of different cell lines as a polyclonal master cell bank. The regulation, toxicity and injection sequence of these oligoclonal antibody mixtures still need to be addressed in order to optimize their delivery and their therapeutic effects.

Acquired resistance to third-generation EGFR-TKIs and emerging next-generation EGFR inhibitors

The discovery that mutations in the EGFR gene are detected in up to 50% of lung adenocarcinoma patients, along with the development of highly efficacious epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), has revolutionized the treatment of this frequently occurring lung malignancy. Indeed, the clinical success of these TKIs constitutes a critical milestone in targeted cancer therapy. Three generations of EGFR-TKIs are currently approved for the treatment of EGFR mutation-positive non-small cell lung cancer (NSCLC). The first-generation TKIs include erlotinib, gefitinib, lapatinib, and icotinib; the second-generation ErbB family blockers include afatinib, neratinib, and dacomitinib; whereas osimertinib, approved by the FDA on 2015, is a third-generation TKI targeting EGFR harboring specific mutations. Compared with the first- and second-generation TKIs, third-generation EGFR inhibitors display a significant advantage in terms of patient survival. For example, the median overall survival in NSCLC patients receiving osimertinib reached 38.6 months. Unfortunately, however, like other targeted therapies, new EGFR mutations, as well as additional drug-resistance mechanisms emerge rapidly after treatment, posing formidable obstacles to cancer therapeutics aimed at surmounting this chemoresistance. In this review, we summarize the molecular mechanisms underlying resistance to third-generation EGFR inhibitors and the ongoing efforts to address and overcome this chemoresistance. We also discuss the current status of fourth-generation EGFR inhibitors, which are of great value in overcoming resistance to EGFR inhibitors that appear to have greater therapeutic benefits in the clinic.

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EGFR gene mutations are detected in about 50% of non-small cell lung cancer (NSCLC) patients worldwide

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The three generations of EGFR tyrosine kinase inhibitors (TKIs) are critical milestones for NSCLC patients

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Like other targeted therapies, new EGFR mutations and coupled drug resistances emerge rapidly after TKI treatment, posing formidable obstacles to cancer management

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The investigational fourth-generation EGFR inhibitors are of great promise, through a number of novel mechanisms, in overcoming these resistances after third-generation TKI treatment, and will bring more benefits to NSCLC patients

Upfront admixing antibodies and EGFR inhibitors preempts sequential treatments in lung cancer models

Some antibacterial therapies entail sequential treatments with different antibiotics, but whether this approach is optimal for anti-cancer tyrosine kinase inhibitors (TKIs) remains open. EGFR mutations identify lung cancer patients who can derive benefit from TKIs, but most patients develop resistance to the first-, second-, and third-generation drugs. To explore alternatives to such whack-a-mole strategies, we simulated in patient-derived xenograft models the situation of patients receiving first-line TKIs. Monotherapies comprising approved first-line TKIs were compared to combinations with antibodies specific to EGFR and HER2. We observed uniform and strong superiority of all drug combinations over the respective monotherapies. Prolonged treatments, high TKI dose, and specificity were essential for drug-drug cooperation. Blocking pathways essential for mitosis (e.g., FOXM1), along with downregulation of resistance-conferring receptors (e.g., AXL), might underlie drug cooperation. Thus, upfront treatments using combinations of TKIs and antibodies can prevent emergence of resistance and hence might replace the widely applied sequential treatments utilizing next-generation TKIs.

Tackling Drug Resistance in EGFR Exon 20 Insertion Mutant Lung Cancer

Insertion mutations in exon 20 (Ex20ins) of the epidermal growth factor receptor (EGFR) gene are the largest class of EGFR mutations in non-small cell lung cancer (NSCLC) for which there are currently no approved targeted therapies. NSCLC patients with these mutations do not respond to clinically approved EGFR tyrosine kinase inhibitors (TKIs) and have poor outcomes. A number of early phase clinical trials are currently underway to evaluate the efficacy of a new generation of TKIs that are capable of binding to and blocking Ex20ins. Although these agents have shown some clinical activity, patient responses have been restricted by dose-limiting toxicity or rapid acquisition of resistance after a short response. Here we review the current understanding of the mechanisms of resistance to these compounds, which include on-target EGFR secondary mutations, compensatory bypass pathway activation and acquisition of an EMT phenotype. Taking lessons from conventional EGFR inhibitor therapy in NSCLC, we also consider other potential sources of resistance including the presence of drug-tolerant persister cells. We will discuss therapeutic strategies which have the potential to overcome different forms of drug resistance. We conclude by evaluating recent technological developments in drug discovery such as PROTACs as a means to better tackle TKI resistance in NSCLC harbouring Ex20ins mutations.

Thirty Years of HER3: From Basic Biology to Therapeutic Interventions

HER3 is a pseudokinase member of the EGFR family having a role in both tumor progression and drug resistance. Although HER3 was discovered more than 30 years ago, no therapeutic interventions have reached clinical approval to date. Because the evidence of the importance of HER3 is accumulating, increased amounts of preclinical and clinical trials with HER3-targeting agents are emerging. In this review article, we discuss the most recent HER3 biology in tumorigenic events and drug resistance and provide an overview of the current and emerging strategies to target HER3.

Anti-tumoral activity of the Pan-HER (Sym013) antibody mixture in gemcitabine-resistant pancreatic cancer models

Chemoresistance, particularly to gemcitabine, is a major challenge in pancreatic cancer. The epidermal growth factor receptor (EGFR) and human epidermal growth factor receptors 2 and 3 (HER2, HER3) are expressed in many tumors, and they are relevant therapeutic targets due to their synergistic interaction to promote tumor aggressiveness and therapeutic resistance. Cocktails of antibodies directed against different targets are a promising strategy to overcome these processes. Here, we found by immunohistochemistry that these three receptors were co-expressed in 11% of patients with pancreatic adenocarcinoma. We then developed gemcitabine-resistant pancreatic cancer cell models (SW-1990-GR and BxPC3-GR) and one patient-derived xenograft (PDX2846-GR) by successive exposure to increasing doses of gemcitabine. We showed that expression of EGFR, HER2 and HER3 was increased in these gemcitabine-resistant pancreatic cancer models, and that an antibody mixture against all three receptors inhibited tumor growth in mice and downregulated HER receptors. Finally, we demonstrated that the Pan-HER and gemcitabine combination has an additive effect in vitro and in mice xenografted with the gemcitabine-sensitive or resistant pancreatic models. The mixture of anti-EGFR, HER2 and HER3 antibodies is a good candidate therapeutic approach for gemcitabine-sensitive and -resistant pancreatic cancer.

Efficacy of the CDK4/6 Dual Inhibitor Abemaciclib in EGFR-Mutated NSCLC Cell Lines with Different Resistance Mechanisms to Osimertinib

Simple Summary

Osimertinib, a third-generation irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI), has shown marked clinical benefit for non-small cell lung cancer (NSCLC) patients with EGFR activating mutations. However, resistance to osimertinib inevitably develops and heterogeneous mechanisms of acquired resistance have been documented. Therefore, new strategies to bypass resistance are urgently needed. In this study, we investigated the potential activity of abemaciclib as second-line therapeutic approach after osimertinib progression and the effect of combining abemaciclib with osimertinib on the appearance of resistance in osimertinib-sensitive models.

Abstract

Abemaciclib is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6 that inhibits the transition from the G1 to the S phase of the cell cycle by blocking downstream CDK4/6-mediated phosphorylation of Rb. The effects of abemaciclib alone or combined with the third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) osimertinib were examined in a panel of PC9 and HCC827 osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines carrying EGFR-dependent or -independent mechanisms of intrinsic or acquired resistance. Differently from sensitive cells, all the resistant cell lines analyzed maintained p-Rb, which may be considered as a biomarker of osimertinib resistance and a potential target for therapeutic intervention. In these models, abemaciclib inhibited cell growth, spheroid formation, colony formation, and induced senescence, and its efficacy was not enhanced in the presence of osimertinib. Interestingly, in osimertinib sensitive PC9, PC9T790M, and H1975 cells the combination of abemaciclib with osimertinib significantly inhibited the onset of resistance in long-term experiments. Our findings provide a preclinical support for using abemaciclib to treat resistance in EGFR mutated NSCLC patients progressed to osimertinib either as single treatment or combined with osimertinib, and suggest the combination of osimertinib with abemaciclib as a potential approach to prevent or delay osimertinib resistance in first-line treatment.

Randomized Trial of Afatinib Plus Cetuximab Versus Afatinib Alone for First-Line Treatment of EGFR-Mutant Non-Small-Cell Lung Cancer: Final Results From SWOG S1403

PURPOSE

The irreversible ErbB family tyrosine kinase inhibitor (TKI) afatinib plus the EGFR monoclonal antibody cetuximab was previously shown to overcome resistance to EGFR TKIs. We studied whether the combination of afatinib plus cetuximab compared with afatinib alone would improve progression-free survival (PFS) in patients with treatment-naive EGFR-mutant non-small-cell lung cancer (NSCLC) by preventing or delaying resistance.

METHODS

Patients with EGFR-mutant NSCLC without prior treatment of advanced disease were enrolled in this phase II, multicenter trial and randomly assigned to receive afatinib 40 mg orally daily plus cetuximab 500 mg/m² intravenously every 2 weeks or afatinib alone. The primary end point was PFS.

RESULTS

Between March 25, 2015 and April 23, 2018, 174 patients were randomly assigned, and 168 (83 on afatinib + cetuximab and 85 on afatinib) were eligible. There was no improvement in PFS in patients receiving afatinib plus cetuximab compared with afatinib alone (hazard ratio [HR], 1.01; 95% CI, 0.72 to 1.43; P = .94; median, 11.9 months v 13.4 months). Similarly, there was no difference in response rate (67% v 74%; P = .38) or overall survival (HR, 0.82; 95% CI, 0.50 to 1.36; P = .44). Toxicity was greater with the combination: grade ≥ 3 adverse events related to treatment occurred in 72% of patients receiving afatinib plus cetuximab compared with 40% of those receiving afatinib alone, most commonly rash and diarrhea. Dose reductions were more common in patients receiving the combination, and 30% of patients in this arm discontinued cetuximab due to toxicity. At interim analysis, there was insufficient evidence to support continued accrual, and the trial was closed.

CONCLUSIONS

The addition of cetuximab to afatinib did not improve outcomes in previously untreated EGFR-mutant NSCLC, despite recognized activity in the acquired resistance setting.

Applied electric fields suppress osimertinib-induced cytotoxicity via inhibiting FOXO3a nuclear translocation through AKT activation

Osimertinib is a third-generation epidermal growth factor receptor tyrosine kinase inhibitor against T790M-mutant non-small cell lung cancer (NSCLC). Acquired resistance to osimertinib is a growing clinical challenge that is not fully understood. Endogenous electric fields (EFs), components of the tumor microenvironment, are associated with cancer cell migration and proliferation. However, the impact of EFs on drug efficiency has not been studied. In this study, we observed that EFs counteracted the effects of osimertinib. EFs of 100 mV/mm suppressed osimertinib-induced cell death and promoted cell proliferation. Transcriptional analysis revealed that the expression pattern induced by osimertinib was altered by EFs stimulation. KEGG analysis showed that differential expression genes were mostly enriched in PI3K-AKT pathway. Then, we found that osimertinib inhibited AKT phosphorylation, while EFs stimulation resulted in significant activation of AKT, which could override the effects generated by osimertinib. Importantly, pharmacological inhibition of PI3K/AKT by LY294002 diminished EF-induced activation of AKT and restored the cytotoxicity of osimertinib suppressed by EFs, which proved that AKT activation was essential for EFs to attenuate the efficacy of osimertinib. Furthermore, activation of AKT by EFs led to phosphorylation of forkhead box O3a (FOXO3a), and reduction in nuclear translocation of FOXO3a induced by osimertinib, resulting in decreased expression of Bim and attenuated cytotoxicity of osimertinib. Taken together, we demonstrated that EFs suppressed the antitumor activity of osimertinib through AKT/FOXO3a/Bim pathway, and combination of PI3K/AKT inhibitor with osimertinib counteracted the effects of EFs. Our findings provided preliminary data for therapeutic strategies to enhance osimertinib efficacy in NSCLC patients.

Notch inhibition overcomes resistance to tyrosine kinase inhibitors in EGFR-driven lung adenocarcinoma

EGFR-mutated lung adenocarcinoma patients treated with gefitinib and osimertinib show a therapeutic benefit limited by the appearance of secondary mutations, such as EGFRT790M and EGFRC797S. It is generally assumed that these secondary mutations render EGFR completely unresponsive to the inhibitors, but contrary to this, we uncovered here that gefitinib and osimertinib increased STAT3 phosphorylation (p-STAT3) in EGFRT790M and EGFRC797S tumoral cells. Interestingly, we also found that concomitant Notch inhibition with gefitinib or osimertinib treatment induced a p-STAT3-dependent strong reduction in the levels of the transcriptional repressor HES1. Importantly, we showed that tyrosine kinase inhibitor-resistant tumors, with EGFRT790M and EGFRC797S mutations, were highly responsive to the combined treatment of Notch inhibitors with gefitinib or osimertinib, respectively. Finally, in patients with EGFR mutations treated with tyrosine kinase inhibitors, HES1 protein levels increased during relapse and correlated with shorter progression-free survival. Therefore, our results offer a proof of concept for an alternative treatment to chemotherapy in lung adenocarcinoma osimertinib-treated patients after disease progression.

Marked synergy by vertical inhibition of EGFR signaling in NSCLC spheroids shows SOS1 is a therapeutic target in EGFR-mutated cancer

Drug treatment of 3D cancer spheroids more accurately reflects in vivo therapeutic responses compared to adherent culture studies. In EGFR-mutated lung adenocarcinoma, EGFR-TKIs show enhanced efficacy in spheroid cultures. Simultaneous inhibition of multiple parallel RTKs further enhances EGFR-TKI effectiveness. We show that the common RTK signaling intermediate SOS1 was required for 3D spheroid growth of EGFR-mutated NSCLC cells. Using two distinct measures of pharmacologic synergy, we demonstrated that SOS1 inhibition strongly synergized with EGFR-TKI treatment only in 3D spheroid cultures. Combined EGFR- and SOS1-inhibition markedly inhibited Raf/MEK/ERK and PI3K/AKT signaling. Finally, broad assessment of the pharmacologic landscape of drug-drug interactions downstream of mutated EGFR revealed synergy when combining an EGFR-TKI with inhibitors of proximal signaling intermediates SOS1 and SHP2, but not inhibitors of downstream RAS effector pathways. These data indicate that vertical inhibition of proximal EGFR signaling should be pursued as a potential therapy to treat EGFR-mutated tumors.

Lung cancer is the leading cause of cancer-related deaths worldwide. In non-smokers, this disease is usually caused by a mutation in a protein found on the surface of a cell, called EGFR. In healthy lung cells, these proteins trigger a chain of chemical signals that tell the cells to multiply. However, faulty forms of EFGR make the cells grow uncontrollably, leading to the formation of tumors.

Current treatments use EGFR inhibitors that block the activity of these proteins. But cancer cells often become resistant to these treatments by activating other types of growth proteins. One way to overcome this resistance has been by targeting the signaling pathways within individual tumors. But since those pathways differ between tumors, it has been challenging to find a single therapy that can treat all drug-resistant cancer cells.

Now, Theard et al. assessed the therapeutic effects of blocking a specific protein inside lung cells, called SOS1, which is involved in growth signaling in all tumor cells. Six different types of human lung cancer cells were used, all of which had faulty forms of EGFR, with three of the cell types showing drug resistance to current therapies. The cancer cells were either exposed to EGFR inhibitors only or to a combination of EGFR and SOS1 inhibitors. The most effective treatment was found to be through combinational therapy, with enhanced killing of drug-resistant cells.

Theard et al. further assessed the effect of combinational therapy using cells kept in two different ways. Cancer cells were either grown in a two-dimensional format, with cells forming a single cell layer, or in a three-dimensional format, where cells were multi-layered and grew on top of each other as self-aggregating spheroids. Combinational therapy treatment was only successful when the cells where grown in a three-dimensional format.

These findings highlight that future drug development studies should give consideration to the way cells are grown, as it can impact the results. They also provide a steppingstone towards tackling drug resistance in lung cancers that arise from EGFR mutations.

Targeting HER3, a Catalytically Defective Receptor Tyrosine Kinase, Prevents Resistance of Lung Cancer to a Third-Generation EGFR Kinase Inhibitor

Although two growth factor receptors, EGFR and HER2, are amongst the best targets for cancer treatment, no agents targeting HER3, their kinase-defective family member, have so far been approved. Because emergence of resistance of lung tumors to EGFR kinase inhibitors (EGFRi) associates with compensatory up-regulation of HER3 and several secreted forms, we anticipated that blocking HER3 would prevent resistance. As demonstrated herein, a neutralizing anti-HER3 antibody we generated can clear HER3 from the cell surface, as well as reduce HER3 cleavage by ADAM10, a surface metalloproteinase. When combined with a kinase inhibitor and an anti-EGFR antibody, the antibody completely blocked patient-derived xenograft models that acquired resistance to EGFRi. We found that the underlying mechanism involves posttranslational downregulation of HER3, suppression of MET and AXL upregulation, as well as concomitant inhibition of AKT signaling and upregulation of BIM, which mediates apoptosis. Thus, although HER3 is nearly devoid of kinase activity, it can still serve as an effective drug target in the context of acquired resistance. Because this study simulated in animals the situation of patients who develop resistance to EGFRi and remain with no obvious treatment options, the observations presented herein may warrant clinical testing.

[Mimicking polyclonal immune response in therapy: from combination of two monoclonal antibodies to oligoclonal antibody-based mixtures]

Monoclonal antibodies have revolutionized the treatment of many diseases, but their clinical effectiveness remains limited in some cases. Associations of antibodies binding to the same target (homo-combination) or to several different targets (hetero-combination), thereby mimicking a polyclonal humoral immune response, have demonstrated a therapeutic improvement in pre-clinical and clinical trials, mainly in the field of oncology and infectious diseases. The combinations increase the efficacy of the biological responses and override resistance mechanisms observed with antibody monotherapy. The most common method of formulating and administering antibody combinations is a separate formulation, with sequential injection of each antibody as individual drug substance. Alternatively, combined formulations are developed where the separately-produced antibodies are mixed before administration or produced simultaneously by a single cell line, or a mixture of cell lines as a polyclonal master cell bank. The regulation, the toxicity and the injection sequence of these oligoclonal antibody-based mixtures remain points to be clarified and optimized for a better therapeutic effect.

Next generation sequencing identifies novel potential actionable mutations for grade I meningioma treatment

Meningiomas are common brain tumors that arise from the meningeal membranes that envelope the brain and spinal cord. The World Health Organization classifies these tumors into three histopathological grades. Because of tumor recurrence, treating meningiomas may be challenging even in well-differentiated grade I (GI) neoplasms. Indeed, around 5% of completely resected GI meningiomas relapse within 5 years. Therefore, identifying driver mutations in GI meningiomas through next generation sequencing (NGS) assays is paramount. The aim of this study was to validate the use of the 50-gene AmpliSeq Hotspot Cancer Panel v2 to identify the mutational status of 23 GI meningioma, namely, 12 non recurrent and 11 recurrent. In 18 out of the 23 GI meningiomas analyzed, we identified at least one gene mutation (78.2%). The most frequently mutated genes were c-kit (39.1%), ATM (26.1%), TP53 (26.1%), EGFR (26.1%), STK11 (21.7%), NRAS (17.4%), SMAD4 (13%), FGFR3 (13%), and PTPN11 (13%); less frequent mutations were SMARCB1 (8.7%), FLT3 (8.7%), KRAS (8.7%), FBWX7 (8.7%), ABL1 (8.7%), ERBB2 (8.7%), IDH1 (8.7%), BRAF (8.7%), MET (8.7%), HRAS (4.3%), RB1 (4.3%), CTNNB1 (4.3%), PIK3CA (4.3%), VHL (4.3%), KDR (4.3%), APC (4.3%), NOTCH1 (4.3%), JAK3 (4.3%), and SRC (4.3%). To our knowledge, mutations in all of these genes, except for TP53, STK11, SMARCB1, PIK3CA, VHL, and BRAF, have never been described before in meningiomas. Hence, these findings demonstrate the viability of NGS to detect new genetic alterations in GI meningiomas. Equally important, this technology enabled us to detect possible novel actionable mutations not previously associated with GI and for which selective inhibitors already exist.

Overcoming malignant cell-based mechanisms of resistance to immune checkpoint blockade antibodies

Traditional cancer treatment approaches have focused on surgery, radiation therapy, and cytotoxic chemotherapy. However, with rare exceptions, metastatic cancers were considered to be incurable by traditional therapy. Over the past 20 years a fourth modality - immunotherapy - has emerged as a potentially curative approach for patients with advanced metastatic cancer. However, in many patients cancer "finds a way" to evade the anti-tumor effects of immunotherapy. Immunotherapy resistance mechanisms can be employed by both cancer cells and the non-cancer elements of tumor microenvironment. This review focuses on the resistance mechanisms that are specifically mediated by cancer cells. In order to extend the impact of immunotherapy to more patients and across all cancer types, and to inhibit the development of acquired resistance, the underlying biology driving immune escape needs to be better understood. Elucidating mechanisms of immune escape may shed light on new therapeutic targets, and lead to successful combination therapeutic strategies.

Targeting amphiregulin (AREG) derived from senescent stromal cells diminishes cancer resistance and averts programmed cell death 1 ligand (PD-L1)-mediated immunosuppression

Aging is characterized by a progressive loss of physiological integrity, while cancer represents one of the primary pathological factors that severely threaten human lifespan and healthspan. In clinical oncology, drug resistance limits the efficacy of most anticancer treatments, and identification of major mechanisms remains a key to solve this challenging issue. Here, we highlight the multifaceted senescence-associated secretory phenotype (SASP), which comprises numerous soluble factors including amphiregulin (AREG). Production of AREG is triggered by DNA damage to stromal cells, which passively enter senescence in the tumor microenvironment (TME), a process that remarkably enhances cancer malignancy including acquired resistance mediated by EGFR. Furthermore, paracrine AREG induces programmed cell death 1 ligand (PD-L1) expression in recipient cancer cells and creates an immunosuppressive TME via immune checkpoint activation against cytotoxic lymphocytes. Targeting AREG not only minimized chemoresistance of cancer cells, but also restored immunocompetency when combined with classical chemotherapy in humanized animals. Our study underscores the potential of in vivo SASP in driving the TME-mediated drug resistance and shaping an immunosuppressive niche, and provides the proof of principle of targeting major SASP factors to improve therapeutic outcome in cancer medicine, the success of which can substantially reduce aging-related morbidity and mortality.

Third generation EGFR inhibitor osimertinib combined with pemetrexed or cisplatin exerts long-lasting anti-tumor effect in EGFR-mutated pre-clinical models of NSCLC

Background

The third generation Epidermal Growth Factor Receptor (EGFR) Tyrosine Kinase Inhibitor (TKI) osimertinib has been initially approved for T790M positive Non-Small Cell Lung Cancer (NSCLC) and more recently for first-line treatment of EGFR-mutant T790M negative NSCLC patients. Similarly to previous generation TKIs, despite the high response rate, disease progression eventually occurs and current clinical research is focused on novel strategies to delay the emergence of osimertinib resistance. In this study we investigated the combination of osimertinib with pemetrexed or cisplatin in EGFR-mutated NSCLC cell lines and xenografts.

Methods

Tumor growth was evaluated in a PC9T790M xenograft model and tissue composition was morphometrically determined. PC9, PC9T790M and HCC827 cell lines were employed to test the efficacy of osimertinib and chemotherapy combination in vitro. Cell viability and cell death were evaluated by MTT assay and fluorescence microscopy. Protein expression and gene status were analysed by Western blotting, fluorescence in situ hybridization analysis, next-generation sequencing and digital droplet PCR.

Results

In xenograft models, osimertinib significantly inhibited tumor growth, however, as expected, in 50% of mice drug-resistance developed. A combination of osimertinib with pemetrexed or cisplatin prevented or at least delayed the onset of resistance. Interestingly, such combinations increased the fraction of fibrotic tissue and exerted a long-lasting activity after stopping therapy. In vitro studies demonstrated the stronger efficacy of the combination over the single treatments in inhibiting cell proliferation and inducing cell death in PC9T790M cells as well as in T790M negative PC9 and HCC827 cell lines, suggesting the potential role of this strategy also as first-line treatment. Finally, we demonstrated that osimertinib resistant clones, either derived from resistant tumors or generated in vitro, were less sensitive to pemetrexed prompting to use a chemotherapy regimen non-containing pemetrexed in patients after progression to osimertinib treatment.

Conclusions

Our results identify a combination between osimertinib and pemetrexed or cisplatin potentially useful in the treatment of EGFR-mutated NSCLC patients, which might delay the appearance of osimertinib resistance with long-lasting effects.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1240-x) contains supplementary material, which is available to authorized users.

Cancer Immunotherapy: The Dawn of Antibody Cocktails

Since the approval of the first monoclonal antibody (mAb), rituximab, for hematological malignancies, almost 30 additional mAbs have been approved in oncology. Despite remarkable advances, relatively weak responses and resistance to antibody monotherapy remain major open issue. Overcoming resistance might require combinations of drugs blocking both the major target and the emerging secondary target. We review clinically approved combinations of antibodies and either cytotoxic regimens (chemotherapy and irradiation) or kinase inhibitors. Thereafter, we focus on the most promising and currently very active arena that combines mAbs inhibiting immune checkpoints or growth factor receptors. Clinically approved and experimental oligoclonal mixtures of mAbs targeting different antigens (hetero-combinations) or different epitopes of the same antigen (homo-combinations) are described. Effective oligoclonal mixtures of antibodies that mimic the polyclonal immune response will likely become a mainstay of cancer therapy.

ERBBal Remedies: Combination Therapy for EGFR-mutant Lung Cancers

Multiple members of the ERBB/HER family of the receptor tyrosine kinases have been implicated in mediating acquired resistance to EGFR inhibitors that are used to treat EGFR-mutant lung cancers. New single agents and combination therapies targeting the ERBB/HER family members are being investigated to either prevent or overcome the emergence of acquired resistance. Clin Cancer Res; 24(22); 5499-501. ©2018 AACR See related article by Romaniello et al., p. 5610.

Targeting SPINK1 in the damaged tumour microenvironment alleviates therapeutic resistance

Chemotherapy and radiation not only trigger cancer cell apoptosis but also damage stromal cells in the tumour microenvironment (TME), inducing a senescence-associated secretory phenotype (SASP) characterized by chronic secretion of diverse soluble factors. Here we report serine protease inhibitor Kazal type I (SPINK1), a SASP factor produced in human stromal cells after genotoxic treatment. DNA damage causes SPINK1 expression by engaging NF-κB and C/EBP, while paracrine SPINK1 promotes cancer cell aggressiveness particularly chemoresistance. Strikingly, SPINK1 reprograms the expression profile of cancer cells, causing prominent epithelial-endothelial transition (EET), a phenotypic switch mediated by EGFR signaling but hitherto rarely reported for a SASP factor. In vivo, SPINK1 is expressed in the stroma of solid tumours and is routinely detectable in peripheral blood of cancer patients after chemotherapy. Our study substantiates SPINK1 as both a targetable SASP factor and a novel noninvasive biomarker of therapeutically damaged TME for disease control and clinical surveillance.

A Combination of Approved Antibodies Overcomes Resistance of Lung Cancer to Osimertinib by Blocking Bypass Pathways

Purpose: Because of emergence of resistance to osimertinib, a third-generation EGFR tyrosine kinase inhibitor (TKI), no targeted treatments are available for patients with lung cancer who lose sensitivity due to new mutations or bypass mechanisms. We examined in animals and in vitro an alternative therapeutic approach making use of antibodies.Experimental Design: An osimertinib-sensitive animal model of lung cancer, which rapidly develops drug resistance, has been employed. To overcome compensatory hyperactivation of ERK, which we previously reported, an anti-EGFR antibody (cetuximab) was combined with other antibodies, as well as with a subtherapeutic dose of osimertinib, and cancer cell apoptosis was assayed.Results: Our animal studies identified a combination of three clinically approved drugs, cetuximab, trastuzumab (an anti-HER2 mAb), and osimertinib (low dose), as an effective and long-lasting treatment that is able to prevent onset of resistance to osimertinib. A continuous schedule of concurrent treatment was sufficient for effective tumor inhibition and for prevention of relapses. Studies employing cultured cells and analyses of tumor extracts indicated that the combination of two mAbs and a subtherapeutic TKI dose sorted EGFR and HER2 for degradation; cooperatively enhanced apoptosis; inhibited activation of ERK; and reduced abundance of several bypass proteins, namely MET, AXL, and HER3.Conclusions: Our in vitro assays and animal studies identified an effective combination of clinically approved drugs that might overcome resistance to irreversible TKIs in clinical settings. The results we present attribute the long-lasting effect of the drug combination to simultaneous blockade of several well-characterized mechanisms of drug resistance. Clin Cancer Res; 24(22); 5610-21. ©2018 AACR See related commentary by Fan and Yu, p. 5499.