Oncogenic RAS simultaneously protects against anti-EGFR antibody-dependent cellular cytotoxicity and EGFR signaling blockade

BCL-XL PROTAC degrader DT2216 synergizes with sotorasib in preclinical models of KRASG12C-mutated cancers

KRAS mutations are the most common oncogenic drivers. Sotorasib (AMG510), a covalent inhibitor of KRAS^G12C, was recently approved for the treatment of KRAS^G12C-mutated non-small cell lung cancer (NSCLC). However, the efficacy of sotorasib and other KRAS^G12C inhibitors is limited by intrinsic resistance in colorectal cancer (CRC) and by the rapid emergence of acquired resistance in all treated tumors. Therefore, there is an urgent need to develop novel combination therapies to overcome sotorasib resistance and to maximize its efficacy. We assessed the effect of sotorasib alone or in combination with DT2216 (a clinical-stage BCL-X_L proteolysis targeting chimera [PROTAC]) on KRAS^G12C-mutated NSCLC, CRC and pancreatic cancer (PC) cell lines using MTS cell viability, colony formation and Annexin-V/PI apoptosis assays. Furthermore, the therapeutic efficacy of sotorasib alone and in combination with DT2216 was evaluated in vivo using different tumor xenograft models. We observed heterogeneous responses to sotorasib alone, whereas its combination with DT2216 strongly inhibited viability of KRAS^G12C tumor cell lines that partially responded to sotorasib treatment. Mechanistically, sotorasib treatment led to stabilization of BIM and co-treatment with DT2216 inhibited sotorasib-induced BCL-X_L/BIM interaction leading to enhanced apoptosis in KRAS^G12C tumor cell lines. Furthermore, DT2216 co-treatment significantly improved the antitumor efficacy of sotorasib in vivo. Collectively, our findings suggest that due to cytostatic activity, the efficacy of sotorasib is limited, and therefore, its combination with a pro-apoptotic agent, i.e., DT2216, shows synergistic responses and can potentially overcome resistance.

APC and TP53 Mutations Predict Cetuximab Sensitivity across Consensus Molecular Subtypes

Simple Summary

Colorectal cancer (CRC) is a major cause of cancer deaths. Cetuximab is an FDA-approved, underutilized therapeutic targeting the epidermal growth factor receptor (EGFR) in metastatic CRC. To date, despite selection of patients with wild-type RAS, it is still difficult to identify patients who may benefit from EGFR inhibitor (e.g., cetuximab) therapy. Our aim is to molecularly classify CRC patients to better identify subpopulations sensitive to EGFR targeted therapy. APC and TP53 are two major tumor suppressor genes in CRC whose mutations contribute to tumor initiation and progression and may identify cetuximab-sensitive tumors. Recently, it has been suggested that the consensus molecular subtype (CMS) classification may be used to help identify cetuximab-sensitive patients. Here, we report an analysis of multiple CRC tumor/PDX/cell line datasets using combined APC and TP53 mutations to refine the CMS classification to better predict responses to cetuximab to improve patient outcomes.

Abstract

Recently, it was suggested that consensus molecular subtyping (CMS) may aide in predicting response to EGFR inhibitor (cetuximab) therapies. We recently identified that APC and TP53 as two tumor suppressor genes, when mutated, may enhance cetuximab sensitivity and may represent easily measured biomarkers in tumors or blood. Our study aimed to use APC and TP53 mutations (AP) to refine the CMS classification to better predict responses to cetuximab. In total, 433 CRC tumors were classified into CMS1-4 subtypes. The cetuximab sensitivity (CTX-S) signature scores of AP vs. non-AP tumors were determined across each of the CMS classes. Tumors harboring combined AP mutations were predominantly enriched in the CMS2 class, and to a lesser degree, in the CMS4 class. On the other hand, AP mutated CRCs had significantly higher CTX-S scores compared to non-AP CRCs across all CMS classes. Similar results were also obtained in independent TCGA tumor collections (n = 531) and in PDMR PDX/PDO/PDC models (n = 477). In addition, the in vitro cetuximab growth inhibition was preferentially associated with the CMS2 cell lines harboring A/P genotypes. In conclusion, the AP mutation signature represents a convenient biomarker that refines the CMS classification to identify CRC subpopulations predicted to be sensitive to EGFR targeted therapies.

Systematic review of the immunological landscape of Wilms tumors

Results of immunotherapy in childhood solid cancer have been so far, with the exception of neuroblastoma, quite disappointing. Lack of knowledge of the immune contexture of these tumors may have contributed to the failure of immunotherapies so far. Here, we systematically reviewed the literature regarding the immunology of Wilms tumor (WT), one of the most frequent pediatric solid tumors of the abdomen. In Wilms tumor patients the high cure rate of >90%, achieved by the combination of surgery and radio-chemotherapy, is at the expense of a high early and late toxicity. Moreover, treatment-resistant entities, such as diffuse anaplastic tumors or recurrent disease, still pose unsolved clinical problems. Successful immunotherapy could represent a novel and possibly less-toxic treatment option. Employing the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) method of literature search, we analyzed the current knowledge of the immunological landscape of Wilms tumors in terms of tumor microenvironment, prognostic implications of single biomarkers, and immunotherapy response.

Identification of a Prognostic Clinical Score for Patients With Recurrent or Metastatic Squamous Cell Carcinoma of the Head and Neck Treated With Systemic Therapy Including Cetuximab

Cetuximab-based chemoimmunotherapy has been the standard of care for recurrent or metastatic squamous cell carcinoma of the head and neck (r/m SCCHN) for more than a decade. To date, no predictive or prognostic biomarkers have been established to further guide the systemic treatment with cetuximab-based chemoimmunotherapy in r/m SCCHN. Against this background, we retrospectively analyzed clinical and blood-based parameters from 218 r/m SCCHN patients treated with chemoimmunotherapy including cetuximab. Multivariate Cox-regression models were used to assess their prognostic or predictive value. Eastern Co-operative Oncology Group (ECOG) performance status (≥2), older age (≥61.8 years), anemia (hemoglobin <11.80), and increased neutrophil-to-lymphocyte ratio (NLR ≥5.73) were independently and strongly associated with inferior overall survival (OS). To group patients according to risk profiles we established a prognostic clinical score (PCS) that can easily be used in clinical practice. The PCS stratified the cohort into low, intermediate, poor or very poor risk subgroups with median OS times of 23.4, 12.1, 7.5, and 4.0 months, respectively. Patients with low risk PCS had a prolonged progression-free survival (PFS) and increased overall response rate (ORR) under first-line cetuximab-based therapy. Interestingly, only patients with low and intermediate risk benefitted from the more intensive first-line cisplatin/cetuximab combination compared to carboplatin/cetuximab therapy, whereas the intensity of first-line treatment had no impact in the poor and very poor risk subgroups. Following external validation, particularly in the context of newly established first-line options, the PCS may guide clinical decision making and serve for stratification of patients with r/m SCCHN in future clinical trials.

Augmented antibody-based anticancer therapeutics boost neutrophil cytotoxicity

Most clinically used anticancer mAbs are of the IgG isotype, which can eliminate tumor cells through NK cell-mediated antibody-dependent cellular cytotoxicity and macrophage-mediated antibody-dependent phagocytosis. IgG, however, ineffectively recruits neutrophils as effector cells. IgA mAbs induce migration and activation of neutrophils through the IgA Fc receptor (FcαRI) but are unable to activate NK cells and have poorer half-life. Here, we combined the agonistic activity of IgG mAbs and FcαRI targeting in a therapeutic bispecific antibody format. The resulting TrisomAb molecules recruited NK cells, macrophages, and neutrophils as effector cells for eradication of tumor cells in vitro and in vivo. Moreover, TrisomAb had long in vivo half-life and strongly decreased B16F10gp75 tumor outgrowth in mice. Importantly, neutrophils of colorectal cancer patients effectively eliminated tumor cells in the presence of anti-EGFR TrisomAb but were less efficient in mediating killing in the presence of IgG anti-EGFR mAb (cetuximab). The clinical application of TrisomAb may provide potential alternatives for cancer patients who do not benefit from current IgG mAb therapy.

Signaling pathways in intestinal homeostasis and colorectal cancer: KRAS at centre stage

The intestinal epithelium acts as a physical barrier that separates the intestinal microbiota from the host and is critical for preserving intestinal homeostasis. The barrier is formed by tightly linked intestinal epithelial cells (IECs) (i.e. enterocytes, goblet cells, neuroendocrine cells, tuft cells, Paneth cells, and M cells), which constantly self-renew and shed. IECs also communicate with microbiota, coordinate innate and adaptive effector cell functions. In this review, we summarize the signaling pathways contributing to intestinal cell fates and homeostasis functions. We focus especially on intestinal stem cell proliferation, cell junction formation, remodelling, hypoxia, the impact of intestinal microbiota, the immune system, inflammation, and metabolism. Recognizing the critical role of KRAS mutants in colorectal cancer, we highlight the connections of KRAS signaling pathways in coordinating these functions. Furthermore, we review the impact of KRAS colorectal cancer mutants on pathway rewiring associated with disruption and dysfunction of the normal intestinal homeostasis. Given that KRAS is still considered undruggable and the development of treatments that directly target KRAS are unlikely, we discuss the suitability of targeting pathways downstream of KRAS as well as alterations of cell extrinsic/microenvironmental factors as possible targets for modulating signaling pathways in colorectal cancer.

Polymorphisms within Immune Regulatory Pathways Predict Cetuximab Efficacy and Survival in Metastatic Colorectal Cancer Patients

Simple Summary

Cetuximab is an antibody that blocks EGFR signaling and stimulates an immune response against cancer cells. For patients with advanced colorectal cancer, tumor sidedness and RAS mutation status are the primary factors used to select systemic therapy. Additional biomarkers are needed to better predict which patients will benefit from cetuximab-based regimens. The aim of our retrospective study was to assess the predictive and prognostic value of 12 germline single nucleotide polymorphisms in five immune related genes in 924 patients with advanced colorectal cancer undergoing therapy with cetuximab. We identified a CD24 germline genetic variant which independently predicted survival in a discovery cohort and confirmed these findings in a validation cohort. If confirmed in prospective studies, CD24 and other immune related polymorphisms may guide the use of cetuximab in patients with advanced colorectal cancer.

Abstract

Cetuximab, an IgG1 EGFR-directed antibody, promotes antibody-dependent cell-mediated cytotoxicity. We hypothesized that single-nucleotide polymorphisms (SNPs) in immune regulatory pathways may predict outcomes in patients with metastatic colorectal cancer treated with cetuximab-based regimens. A total of 924 patients were included: 105 received cetuximab in IMCL-0144 and cetuximab/irinotecan in GONO-ASL608LIOM01 (training cohort), 225 FOLFIRI/cetuximab in FIRE-3 (validation cohort 1), 74 oxaliplatin/cetuximab regimens in JACCRO CC-05/06 (validation cohort 2), and 520 FOLFIRI/bevacizumab in FIRE-3 and TRIBE (control cohorts). Twelve SNPs in five genes (IDO1; PD-L1; PD-1; CTLA-4; CD24) were evaluated by PCR-based direct sequencing. We analyzed associations between genotype and clinical outcomes. In the training cohort; patients with the CD24 rs52812045 A/A genotype had a significantly shorter median PFS and OS than those with the G/G genotype (PFS 1.3 vs. 3.6 months; OS 2.3 vs. 7.8 months) in univariate (PFS HR 3.62; p = 0.001; OS HR 3.27; p = 0.0004) and multivariate (PFS HR 3.18; p = 0.009; OS HR 4.93; p = 0.001) analyses. Similarly; any A allele carriers in the JACCRO validation cohort had a significantly shorter PFS than G/G carriers (9.2 vs. 11.8 months; univariate HR 1.90; p = 0.011; multivariate HR 2.12; p = 0.018). These associations were not demonstrated in the control cohorts. CD24 genetic variants may help select patients with metastatic colorectal cancer most likely to benefit from cetuximab-based therapy.

Histone deacetylase inhibitors valproic acid and vorinostat enhance trastuzumab-mediated antibody-dependent cell-mediated phagocytosis

Background

The monoclonal antibody (mAb) trastuzumab is part of the standard of care for patients with human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer. Antibody-dependent cell-mediated phagocytosis (ADCP) and cytotoxicity (ADCC) are major mechanisms of action of the mAb trastuzumab. Histone deacetylase inhibitors (HDACi), such as valproic acid (VPA) or vorinostat (SAHA), exert several immunostimulatory properties, which contribute at least in part to their anticancer effect. However, the impact of HDACi-induced immunostimulatory effects on trastuzumab-mediated anti-tumor immune response is not well characterized.

Methods

We analyzed the ADCP and ADCC activity of peripheral blood mononuclear cells (PBMCs) from age and gender-matched healthy volunteers (n=5) against HDACi-treated HER2-overexpressing breast cancer cells (SKBR3), using a well-established in vitro three-color imaging flow cytometry and flow cytometry approach.

Results

VPA and SAHA enhanced trastuzumab-mediated ADCP and trastuzumab-independent cytotoxicity. Mechanistically, VPA upregulated the activating antibody-binding receptor Fc-gamma receptor (FcγR) IIA (CD32A) on monocytes (CD14+). Moreover, VPA and SAHA downregulated the anti-apoptotic protein myeloid leukemia cell differentiation 1 (MCL1) in breast cancer cells. Additionally, VPA and SAHA induced an immunogenic cell death, characterized by the exposure of calreticulin (CALR), as well as decreased the “do not eat me” signal CD47 on tumor cells.

Conclusions

HDACi VPA and SAHA increase trastuzumab-mediated phagocytosis and trastuzumab-independent cytotoxicity. The immunomodulatory activities of those HDACi support a rationale combined treatment approach with mAb for cancer treatment.

Flow cytometry-based assessment of direct-targeting anti-cancer antibody immune effector functions

Monoclonal antibody-based therapies are increasingly being used to treat cancer. Some mediate their therapeutic effects through modifying the function of immune cells globally, while others bind directly to tumor cells and can recruit immune effector cells through their Fc regions. As new direct-binding agents are developed, having the ability to test their Fc-mediated functions in a high-throughput manner is important for selecting antibodies with immune effector properties. Here, using monoclonal anti-CD20 antibody (rituximab) as an example and the CD20⁺ Raji cell line as tumor target, we describe flow cytometry-based assays for determining an antibody's capacity for mediating antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC). These assays are sensitive, reliable, affordable and avoid the use of radioactivity.

GC1118, a novel anti-EGFR antibody, has potent KRAS mutation-independent antitumor activity compared with cetuximab in gastric cancer

BACKGROUND

EGFR overexpression in gastric cancer (GC) has been reported in about 30% of patients. However, the anti-EGFR antibodies cetuximab and panitumumab have failed to improve overall survival of GC patients in combination with cytotoxic chemotherapy compared with chemotherapy alone. GC1118, a novel anti-EGFR antibody with a distinct binding epitope compared with cetuximab or panitumumab, has not been tested in GC.

METHODS

GC cell lines, SNU-1, SNU-5, SNU-16, SNU-216, SNU-484, SNU-601, SNU-620, SNU-638, SNU-668, SNU-719, AGS, MKN-45, NCI-N87, and KATO-III, were employed to test the effect of cetuximab or GC1118 alone, and combined with the cytotoxic agent cisplatin or 5-fluorouracil (5-FU). Cells were also treat with or without high-affinity ligands EGF 20 ng/ml or HB-EGF 100 ng/ml.

RESULTS

GC1118 exhibited a more potent growth inhibition effect in the majority of cell lines than cetuximab in MTT assay, regardless of the KRAS mutation status of cell lines. Co-treatment of GC1118 and cisplatin or 5-FU inhibited colony formation and migration to a greater extent, even following EGFR ligand stimulation. Ligand-induced p-AKT and p-ERK upregulation were more potently inhibited by combination treatment with GC1118 and chemotherapeutic agents compared with cetuximab plus chemotherapeutic agents. GC1118 also showed more potent anti-tumor effects compared with cetuximab in a mouse xenograft model.

CONCLUSION

Taken together, GC1118 alone or in combination with cytotoxic chemotherapeutic agents exerted more potent anti-tumor effects than cetuximab in GC cells, regardless of KRAS status. These findings support the further clinical development of GC1118 for the treatment of GC.

NK-mediated antibody-dependent cell-mediated cytotoxicity in solid tumors: biological evidence and clinical perspectives

The process of antibody-dependent cell-mediated cytotoxicity (ADCC) makes use of the innate immune cells providing antitumor cytotoxicity activated by antibodies linked to target cells. Natural killer (NK) cells are a small set of lymphocytes, but are considered the most important cells among those able to induce ADCC. They provoke innate immune responses and harmonise spontaneous cytotoxicity towards tumor and virus-infected cells. They are able to swiftly produce biochemical signals and cytokines so as to stimulate subsequent adaptive immune responses. Immunotherapeutics that target NK cells, augmenting their immune response, can cause the antitumor dynamics of the antibodies to be improved. The recent developments in the field of NK cell immunotherapy and genotypic factors which might affect patient responses to antibody-dependent immunotherapies are the main subject of this review, with a particular focus on the manipulations and strategies used to augment ADCC. In the next years combined treatment with monoclonal antibodies (mAbs) and immunomodulatory drugs will be an important part in antitumor therapy. The main challenge remains the difficulty in distinguishing in the clinical setting, between the target effect that many mAbs exert against specific cell membrane receptors and the ADCC effect that they too also can induce. Drugs able to activate NK cells, that are major actors in mAb-mediated ADCC, will improve the ADCC effect against tumors.

Restoring PUMA induction overcomes KRAS-mediated resistance to anti-EGFR antibodies in colorectal cancer

Intrinsic and acquired resistance to anti-EGFR antibody therapy, frequently mediated by a mutant or amplified KRAS oncogene, is a significant challenge in the treatment of colorectal cancer (CRC). However, the mechanism of KRAS-mediated therapeutic resistance is not well understood. In this study, we demonstrate that clinically used anti-EGFR antibodies, including cetuximab and panitumumab, induce killing of sensitive CRC cells through p73-dependent transcriptional activation of the pro-apoptotic Bcl-2 family protein PUMA. PUMA induction and p73 activation are abrogated in CRC cells with acquired resistance to anti-EGFR antibodies due to KRAS alterations. Inhibition of aurora kinases preferentially kills mutant KRAS CRC cells and overcomes KRAS-mediated resistance to anti-EGFR antibodies in vitro and in vivo by restoring PUMA induction. Our results suggest that PUMA plays a critical role in meditating the sensitivity of CRC cells to anti-EGFR antibodies, and that restoration of PUMA-mediated apoptosis is a promising approach to improve the efficacy of EGFR-targeted therapy.

Molecular dissection of effector mechanisms of RAS-mediated resistance to anti-EGFR antibody therapy

Monoclonal antibodies targeting the epidermal growth factor receptor (EGFR), cetuximab and panitumumab, are a mainstay of metastatic colorectal cancer (mCRC) treatment. However, a significant number of patients suffer from primary or acquired resistance. RAS mutations are negative predictors of clinical efficacy of anti-EGFR antibodies in patients with mCRC. Oncogenic RAS activates the MAPK and PI3K/AKT pathways, which are considered the main effectors of resistance. However, the relative impact of these pathways in RAS-mutant CRC is less defined. A better mechanistic understanding of RAS-mediated resistance may guide development of rational intervention strategies. To this end we developed cancer models for functional dissection of resistance to anti-EGFR therapy in vitro and in vivo. To selectively activate MAPK- or AKT-signaling we expressed conditionally activatable RAF-1 and AKT in cancer cells. We found that either pathway independently protected sensitive cancer models against anti-EGFR antibody treatment in vitro and in vivo. RAF-1- and AKT-mediated resistance was associated with increased expression of anti-apoptotic BCL-2 proteins. Biomarkers of MAPK and PI3K/AKT pathway activation correlated with inferior outcome in a cohort of mCRC patients receiving cetuximab-based therapy. Dual pharmacologic inhibition of PI3K and MEK successfully sensitized primary resistant CRC models to anti-EGFR therapy. In conclusion, combined targeting of MAPK and PI3K/AKT signaling, but not single pathways, may be required to enhance the efficacy of anti-EGFR antibody therapy in patients with RAS-mutated CRC as well as in RAS wild type tumors with clinical resistance.

Rationale for combination of therapeutic antibodies targeting tumor cells and immune checkpoint receptors: Harnessing innate and adaptive immunity through IgG1 isotype immune effector stimulation

Immunoglobulin (Ig) G1 antibodies stimulate antibody-dependent cell-mediated cytotoxicity (ADCC). Cetuximab, an IgG1 isotype monoclonal antibody, is a standard-of-care treatment for locally advanced and recurrent and/or metastatic squamous cell carcinoma of the head and neck (SCCHN) and metastatic colorectal cancer (CRC). Here we review evidence regarding the clinical relevance of cetuximab-mediated ADCC and other immune functions and provide a biological rationale concerning why this property positions cetuximab as an ideal partner for immune checkpoint inhibitors (ICIs) and other emerging immunotherapies. We performed a nonsystematic review of available preclinical and clinical data involving cetuximab-mediated immune activity and combination approaches of cetuximab with other immunotherapies, including ICIs, in SCCHN and CRC. Indeed, cetuximab mediates ADCC activity in the intratumoral space and primes adaptive and innate cellular immunity. However, counterregulatory mechanisms may lead to immunosuppressive feedback loops. Accordingly, there is a strong rationale for combining ICIs with cetuximab for the treatment of advanced tumors, as targeting CTLA-4, PD-1, and PD-L1 can ostensibly overcome these immunosuppressive counter-mechanisms in the tumor microenvironment. Moreover, combining ICIs (or other immunotherapies) with cetuximab is a promising strategy for boosting immune response and enhancing response rates and durability of response. Cetuximab immune activity–including, but not limited to, ADCC–provides a strong rationale for its combination with ICIs or other immunotherapies to synergistically and fully mobilize the adaptive and innate immunity against tumor cells. Ongoing prospective studies will evaluate the clinical effect of these combination regimens and their immune effect in CRC and SCCHN and in other indications.

Control of cell death and mitochondrial fission by ERK1/2 MAP kinase signalling

The ERK1/2 signalling pathway is best known for its role in connecting activated growth factor receptors to changes in gene expression due to activated ERK1/2 entering the nucleus and phosphorylating transcription factors. However, active ERK1/2 also translocate to a variety of other organelles including the endoplasmic reticulum, endosomes, golgi and mitochondria to access specific substrates and influence cell physiology. In this article, we review two aspects of ERK1/2 signalling at the mitochondria that are involved in regulating cell fate decisions. First, we describe the prominent role of ERK1/2 in controlling the BCL2-regulated, cell-intrinsic apoptotic pathway. In most cases ERK1/2 signalling promotes cell survival by activating prosurvival BCL2 proteins (BCL2, BCL-xL and MCL1) and repressing prodeath proteins (BAD, BIM, BMF and PUMA). This prosurvival signalling is co-opted by oncogenes to confer cancer cell-specific survival advantages and we describe how this information has been used to develop new drug combinations. However, ERK1/2 can also drive the expression of the prodeath protein NOXA to control 'autophagy or apoptosis' decisions during nutrient starvation. We also describe recent studies demonstrating a link between ERK1/2 signalling, DRP1 and the mitochondrial fission machinery and how this may influence metabolic reprogramming during tumorigenesis and stem cell reprogramming. With advances in subcellular proteomics it is likely that new roles for ERK1/2, and new substrates, remain to be discovered at the mitochondria and other organelles.

Contribution of KRAS mutations and c.2369C > T (p.T790M) EGFR to acquired resistance to EGFR-TKIs in EGFR mutant NSCLC: a study on circulating tumor DNA

INTRODUCTION

KRAS oncogene mutations (MUTKRAS) drive resistance to EGFR inhibition by providing alternative signaling as demonstrated in colo-rectal cancer. In non-small cell lung cancer (NSCLC), the efficacy of treatment with EGFR tyrosine kinase inhibitors (EGFR-TKIs) depends on activating EGFR mutations (MUTEGFR). However, inhibition of EGFR may select resistant cells displaying alternative signaling, i.e., KRAS, or restoration of EGFR activity due to additional MUTEGFR, i.e., the c.2369C > T (p.T790MEGFR).

AIM

The aim of this study was to investigate the appearance of MUTKRAS during EGFR-TKI treatment and their contribution to drug resistance.

METHODS

This study used cell-free circulating tumor DNA (cftDNA) to evaluate the appearance of codon 12 MUTKRAS and p.T790MEGFR mutations in 33 advanced NSCLC patients progressing after an EGFR-TKI.

RESULTS

p.T790MEGFR was detected in 11 (33.3%) patients, MUTKRAS at codon 12 in 3 (9.1%) while both p.T790MEGFR and MUTKRAS codon 12 were found in 13 (39.4%) patients. Six patients (18.2%) were KRAS wild-type (WTKRAS) and negative for p.T790MEGFR. In 8 subjects paired tumor re-biopsy/plasma samples were available; the percent concordance of tissue/plasma was 62.5% for p.T790MEGFR and 37.5% for MUTKRAS. The analysis of time to progression (TTP) and overall survival (OS) in WTKRAS vs. MUTKRAS were not statistically different, even if there was a better survival with WTKRAS vs. MUTKRAS, i.e., TTP 14.4 vs. 11.4 months (p = 0.97) and OS 40.2 vs. 35.0 months (p = 0.56), respectively.

CONCLUSIONS

MUTKRAS could be an additional mechanism of escape from EGFR-TKI inhibition and cftDNA is a feasible approach to monitor the molecular development of drug resistance.

Surveilling the Potential for Precision Medicine-driven PD-1/PD-L1-targeted Therapy in HNSCC

Immunotherapy is becoming an accepted treatment modality for many patients with cancer and is now approved for use in platinum-refractory recurrent or metastatic head and neck squamous cell carcinoma (HNSCC). Despite these successes, a minority of patients with HNSCC receiving immunotherapy respond to treatment, and few undergo a complete response. Thus, there is a critical need to identify mechanisms regulating immune checkpoints in HNSCC such that one can predict who will benefit, and so novel combination strategies can be developed for non-responders. Here, we review the immunotherapy and molecular genetics literature to describe what is known about immune checkpoints in common genetic subsets of HNSCC. We highlight several highly recurrent genetic lesions that may serve as biomarkers or targets for combination immunotherapy in HNSCC.

Generation and characterization of a target-selectively activated antibody against epidermal growth factor receptor with enhanced anti-tumor potency

Panitumumab, as a commercially available antibody, is an effective anticancer therapeutic against epidermal growth factor receptor (EGFR), although it exerts weak antibody-dependent cell-mediated cytotoxicity (ADCC) activity owing to its IgG2 nature. Here, we firstly engineered panitumumab by grafting its variable region into an IgG1 backbone. The engineered panitumumab (denoted as Pan) retained binding activity identical to the parental antibody while exhibiting stronger ADCC activity in vitro and more potent antitumor effect in vivo. To further enhance the target selectivity of Pan, we generated Pan-P by tethering an epitope-blocking peptide to Pan via a tumor-specific protease selective linker. Pan-P showed almost 40-fold weaker affinity compared with Pan, but functional activity was restored to a similar extent as Pan when Pan-P was selectively activated by urokinase-type plasminogen activator (uPA). More importantly, targeted localization of Pan-P was observed in tumor samples from colorectal cancer (CRC) patients and tumor-bearing nude mice, strongly indicating that specific activation also existed ex vivo and in vivo. Furthermore, Pan-P also exhibited effective in vivo antitumor potency similar to Pan. Taken together, our data evidence the enhanced antitumor potency and excellent target selectivity of Pan-P, suggesting its potential use for minimizing on-target toxicity in anti-EGFR therapy.

The Mutant KRAS Gene Up-regulates BCL-XL Protein via STAT3 to Confer Apoptosis Resistance That Is Reversed by BIM Protein Induction and BCL-XL Antagonism

In colorectal cancers with oncogenic GTPase Kras (KRAS) mutations, inhibition of downstream MEK/ERK signaling has shown limited efficacy, in part because of failure to induce a robust apoptotic response. We studied the mechanism of apoptosis resistance in mutant KRAS cells and sought to enhance the efficacy of a KRAS-specific MEK/ERK inhibitor, GDC-0623. GDC-0623 was shown to potently up-regulate BIM expression to a greater extent versus other MEK inhibitors in isogenic KRAS HCT116 and mutant KRAS SW620 colon cancer cells. ERK silencing enhanced BIM up-regulation by GDC-0623 that was due to its loss of phosphorylation at Ser(69), confirmed by a BIM-EL phosphorylation-defective mutant (S69G) that increased protein stability and blocked BIM induction. Despite BIM and BIK induction, the isogenic KRAS mutant versus wild-type cells remained resistant to GDC-0623-induced apoptosis, in part because of up-regulation of BCL-XL. KRAS knockdown by a doxycycline-inducible shRNA attenuated BCL-XL expression. BCL-XL knockdown sensitized KRAS mutant cells to GDC-0623-mediated apoptosis, as did the BH3 mimetic ABT-263. GDC-0623 plus ABT-263 induced a synergistic apoptosis by a mechanism that includes release of BIM from its sequestration by BCL-XL. Furthermore, mutant KRAS activated p-STAT3 (Tyr(705)) in the absence of IL-6 secretion, and STAT3 knockdown reduced BCL-XL mRNA and protein expression. These data suggest that BCL-XL up-regulation by STAT3 contributes to mutant KRAS-mediated apoptosis resistance. Such resistance can be overcome by potent BIM induction and concurrent BCL-XL antagonism to enable a synergistic apoptotic response.

Mutant KRAS as a critical determinant of the therapeutic response of colorectal cancer

Mutations in the KRAS oncogene represent one of the most prevalent genetic alterations in colorectal cancer (CRC), the third leading cause of cancer-related death in the US. In addition to their well-characterized function in driving tumor progression, KRAS mutations have been recognized as a critical determinant of the therapeutic response of CRC. Recent studies demonstrate that KRAS-mutant tumors are intrinsically insensitive to clinically-used epidermal growth factor receptor (EGFR) targeting antibodies, including cetuximab and panitumumab. Acquired resistance to the anti-EGFR therapy was found to be associated with enrichment of KRAS-mutant tumor cells. However, the underlying molecular mechanism of mutant-KRAS-mediated therapeutic resistance has remained unclear. Despite intensive efforts, directly targeting mutant KRAS has been largely unsuccessful. This review summarizes the recent advances in understanding the biological function of KRAS mutations in determining the therapeutic response of CRC, highlighting several recently developed agents and strategies for targeting mutant KRAS, such as synthetic lethal interactions.

Beyond KRAS status and response to anti-EGFR therapy in metastatic colorectal cancer

In patients with metastatic colorectal cancer, overall survival has improved over the last decade mainly due to the use of effective targeted therapies such as anti-EGFR. However, survival improvement is linked to proper selection of patients expected to benefit from these treatments. KRAS codons 12 and 13 mutation status was the first validated molecular biomarker for anti-EGFR antibodies. Today, rare KRAS alterations and NRAS mutations were implemented, defining the 'RAS' status as the new validated marker of response to anti-EGFR antibodies. Moreover, other biomarkers are under investigation to screen for other targets and help with patients selection. Here, we reviewed these promising biomarkers: mutations in the RAS-MAPK and PI3K-AKT pathways genes, MET activation, HER/ErbB receptors activation (EGFR, HER2 and HER3), EGFR ligands, antibody-dependent cell-mediated cytotoxicity) and miRNAs. Further data are needed to define their impact for the treatment of patients with metastatic colorectal cancer.

Functional expression cloning identifies COX-2 as a suppressor of antigen-specific cancer immunity

The efficacy of immune surveillance and antigen-specific cancer immunotherapy equally depends on the activation of a sustained immune response targeting cancer antigens and the susceptibility of cancer cells to immune effector mechanisms. Using functional expression cloning and T-cell receptor (TCR) transgenic mice, we have identified cyclooxygenase 2/prostaglandin-endoperoxide synthase 2 (COX-2) as resistance factor against the cytotoxicity induced by activated, antigen-specific T cells. Expressing COX-2, but not a catalytically inactive COX-2 mutant, increased the clonogenic survival of E1A-transformed murine cancer cells when cocultured with lymphocytes from St42Rag2^−/− mice harboring a transgenic TCR directed against an E1A epitope. COX-2 expressing tumors established in immune-deficient mice were less susceptible to adoptive immunotherapy with TCR transgenic lymphocytes in vivo. Also, immune surveillance of COX-2-positive tumor cells in TCR transgenic mice was less efficient. The growth of murine MC-GP tumors, which show high endogenous COX-2 expression, in immunocompetent mice was effectively suppressed by treatment with a selective COX-2 inhibitor, celecoxib. Mechanistically, COX-2 expression blunted the interferon-gamma release of antigen-specific T cells exposed to their respective cellular targets, and increased the expression of interleukin-4 and indoleamine 2,3-dioxygenase by tumor cells. Addition of interferon-gamma sensitized COX-2 expressing cancer cells to tumor suppression by antigen-specific T cells. In conclusion, COX-2, which is frequently induced in colorectal cancer, contributes to immune evasion and resistance to antigen-specific cancer immunotherapy by local suppression of T-cell effector functions.

Heterogeneous EGFR gene copy number increase is common in colorectal cancer and defines response to anti-EGFR therapy

Anti-EGFR therapy is commonly used to treat colorectal cancer (CRC), although only a subset of patients benefit from the treatment. While KRAS mutation predicts non-responsiveness, positive predictive markers are not in clinical practice. We previously showed that immunohistochemistry (IHC)-guided EGFR gene copy number (GCN) analysis may identify CRC patients benefiting from anti-EGFR treatment. Here we tested the predictive value of such analysis in chemorefractory metastatic CRC, elucidated EGFR GCN heterogeneity within the tumors, and evaluated the association between EGFR GCN, KRAS status, and anti-EGFR antibody response in CRC cell lines. The chemorefractory patient cohort consisted of 54 KRAS wild-type (WT) metastatic CRC patients. EGFR GCN status was analyzed by silver in situ hybridization using a cut-off value of 4.0 EGFR gene copies/cell. KRAS-WT and KRAS mutant CRC cell lines with different EGFR GCN were used in in vitro studies. The chemorefractory CRC tumors with EGFR GCN increase (≥4.0) responded better to anti-EGFR therapy than EGFR GCN (<4.0) tumors (clinical benefit, P = 0.0004; PFS, HR = 0.23, 95% CI 0.12–0.46). EGFR GCN counted using EGFR IHC guidance was significantly higher than the value from randomly selected areas verifying intratumoral EGFR GCN heterogeneity. In CRC cell lines, EGFR GCN correlated with EGFR expression. Best anti-EGFR response was seen with KRAS-WT, EGFR GCN = 4 cells and poorest response with KRAS-WT, EGFR GCN = 2 cells. Anti-EGFR response was associated with AKT and ERK1/2 phosphorylation, which was effectively inhibited only in cells with KRAS-WT and increased EGFR GCN. In conclusion, IHC-guided EGFR GCN is a promising predictor of anti-EGFR treatment efficacy in chemorefractory CRC.

Targeted drugs in combination with radiotherapy for the treatment of solid tumors: current state and future developments

The continuously rising use of novel drugs, especially of molecules belonging to the group of targeted drugs is now shaping the therapeutic landscape. However, treatment combinations of targeted drugs with radiotherapy are still rare. Only the monoclonal antibody cetuximab (Erbitux®) has been approved for the treatment of locally advanced squamous cell cancer of the head and neck in combination with radiotherapy. Several targeted compounds are in advanced stages of clinical development for combination treatments with radiotherapy, of which substances with either anti-EGFR or anti-angiogenic mechanisms, such as trastuzumab, panitumumab, erlotinib, cilengitide and bevacizumab are the most promising. Aim of this article is to provide, mainly from a radio-oncological point of view, an overview about the current state as well as to give an outlook on the near future of the most advanced targeted combined treatment concepts for solid tumors.

Impact of human papilloma virus infection on the response of head and neck cancers to anti-epidermal growth factor receptor antibody therapy

Infection with human papillomaviruses (HPVs) characterizes a distinct subset of head and neck squamous cell cancers (HNSCCs). HPV-positive HNSCC preferentially affect the oropharynx and tonsils. Localized HPV-positive HNSCCs have a favorable prognosis and treatment outcome. However, the impact of HPV in advanced or metastatic HNSCC remains to be defined. In particular, it is unclear whether HPV modulates the response to cetuximab, an antibody targeting the epidermal growth factor receptor (EGFR), which is a mainstay of treatment of advanced HNSCC. To this end, we have examined the sensitivity of HPV-positive and -negative HNSCC models to cetuximab and cytotoxic drugs in vitro and in vivo. In addition, we have stably expressed the HPV oncogenes E6 and E7 in cetuximab-sensitive cancer cell lines to specifically investigate their role in the antibody response. The endogenous HPV status or the expression of HPV oncogenes had no significant impact on cetuximab-mediated suppression of EGFR signaling and proliferation in vitro. Cetuximab effectively inhibited the growth of E6- and E7-expressing tumors grafted in NOD/SCID mice. In support, formalin-fixed, paraffin-embedded tumor samples from cetuximab-treated patients with recurrent or metastatic HNSCC were probed for p16^INK4a expression, an established biomarker of HPV infection. Response rates (45.5% versus 45.5%) and median progression-free survival (97 versus 92 days) following cetuximab-based therapy were similar in patients with p16^INK4A-positive and p16^INK4A-negative tumors. In conclusion, HPV oncogenes do not modulate the anti-EGFR antibody response in HSNCC. Cetuximab treatment should be administered independently of HPV status.

Increase in antibody-dependent cellular cytotoxicity (ADCC) in a patient with advanced colorectal carcinoma carrying a KRAS mutation under lenalidomide therapy

The failure of EGFR inhibitors in colorectal tumors with KRAS mutations requires the development of alternative treatment strategies for this patient subgroup. Among the hallmarks of cancer the disturbed immunosurveillance and cancer immune evasion have become emerging targets for cancer therapy. Due to their pleiotropic functions immunomodulatory drugs (IMiDs) are interesting agents for combination therapies in solid tumors. However, their possible contribution and a way of monitoring their biological effects have yet to be revealed. In a heavily pretreated patient with advanced colorectal cancer carrying mutations in APC and KRAS genes, we show an early metabolic response and enhanced NK cell activity to monotherapy with lenalidomide. After subsequent lenalidomide/cetuximab combination treatment, the patient had progressive disease. At the same time a reduced performance status, complicated by febrile neutropenia, occurred, as well as a slight increase in metabolic activity. Concordantly NK cell activity dropped back to baseline. Thus, laboratory measurements and metabolic response assessment correlated with clinical conditions. This case report describes the feasibility and potential of a functional assessment of patient derived immune competent cells in combination with functional imaging for the detection of a biological response.

Open-label, multicentre expansion cohort to evaluate imgatuzumab in pre-treated patients with KRAS-mutant advanced colorectal carcinoma

AIM

Imgatuzumab (GA201) is a novel anti-epidermal growth factor receptor (anti-EGFR) antibody glycoengineered for enhanced antibody-dependent cell-mediated cytotoxicity (ADCC). We investigated the efficacy of imgatuzumab in patients with EGFR-positive, KRAS-mutant advanced colorectal cancer.

METHODS

Patients received single-agent imgatuzumab (1400mg on day 1 and 8 followed by q2W) as third line therapy in an open-label, multicentre, non-randomised, expansion study. The primary end-point was tumour response. Pre- and on-treatment biopsies and blood samples were investigated for biomarkers related to imgatuzumab's believed mechanism of action (MoA).

RESULTS

25 patients were treated and the best overall response was stable disease occurring in 40% of patients at 8weeks, 24% at 16weeks and 8% (two patients) at 32weeks. Median overall survival was 9.3months (95% confidence interval (CI): 5.1-12.3). Treatment-related rash, hypomagnesaemia and infusion-related reactions were the most common adverse events. Comparison of pre- and post-treatment biopsies revealed that the number of tumour-infiltrating immune cells increased notably after one cycle of therapy (median compound immune reactive score of 1491 versus 898 cells/mm(3) at baseline), whereas the number of peripheral natural killer cells decreased. A potential association between baseline tumour immune infiltration and clinical efficacy was seen.

CONCLUSIONS

These data may suggest that the MoA of imgatuzumab involves ADCC-related immune effects in the tumour and is not limited to simple receptor blockade.

Stabilization of physical RAF/14-3-3 interaction by cotylenin A as treatment strategy for RAS mutant cancers

One-third of all human cancers harbor somatic RAS mutations. This leads to aberrant activation of downstream signaling pathways involving the RAF kinases. Current ATP-competitive RAF inhibitors are active in cancers with somatic RAF mutations, such as BRAF(V600) mutant melanomas. However, they paradoxically promote the growth of RAS mutant tumors, partly due to the complex interplay between different homo- and heterodimers of A-RAF, B-RAF, and C-RAF. Based on pathway analysis and structure-guided compound identification, we describe the natural product cotylenin-A (CN-A) as stabilizer of the physical interaction of C-RAF with 14-3-3 proteins. CN-A binds to inhibitory 14-3-3 interaction sites of C-RAF, pSer233, and pSer259, but not to the activating interaction site, pSer621. While CN-A alone is inactive in RAS mutant cancer models, combined treatment with CN-A and an anti-EGFR antibody synergistically suppresses tumor growth in vitro and in vivo. This defines a novel pharmacologic strategy for treatment of RAS mutant cancers.