Early Immune Remodeling Steers Clinical Response to First-Line Chemoimmunotherapy in Advanced Gastric Cancer

Adding anti-programmed cell death protein 1 (anti-PD-1) to 5-fluorouracil (5-FU)/platinum improves survival in some advanced gastroesophageal adenocarcinomas (GEA). To understand the effects of chemotherapy and immunotherapy, we conducted a phase II first-line trial (n = 47) sequentially adding pembrolizumab to 5-FU/platinum in advanced GEA. Using serial biopsy of the primary tumor at baseline, after one cycle of 5-FU/platinum, and after the addition of pembrolizumab, we transcriptionally profiled 358,067 single cells to identify evolving multicellular tumor microenvironment (TME) networks. Chemotherapy induced early on-treatment multicellular hubs with tumor-reactive T-cell and M1-like macrophage interactions in slow progressors. Faster progression featured increased MUC5A and MSLN containing treatment resistance programs in tumor cells and M2-like macrophages with immunosuppressive stromal interactions. After pembrolizumab, we observed increased CD8 T-cell infiltration and development of an immunity hub involving tumor-reactive CXCL13 T-cell program and epithelial interferon-stimulated gene programs. Strategies to drive increases in antitumor immune hub formation could expand the portion of patients benefiting from anti-PD-1 approaches.

SIGNIFICANCE

The benefit of 5-FU/platinum with anti-PD-1 in first-line advanced gastric cancer is limited to patient subgroups. Using a trial with sequential anti-PD-1, we show coordinated induction of multicellular TME hubs informs the ability of anti-PD-1 to potentiate T cell-driven responses. Differential TME hub development highlights features that underlie clinical outcomes. This article is featured in Selected Articles from This Issue, p. 695.

Gastroesophageal Adenocarcinomas With Defective Mismatch Repair: Current Knowledge and Clinical Management

Esophageal, gastroesophageal junction, and gastric adenocarcinomas, referred to collectively as gastroesophageal adenocarcinomas (GEAs), are a major cause of global cancer-related mortality. Our increasing molecular understanding has led to the addition of biomarker-directed approaches to defined subgroups and has improved survival in selected patients, such as those with HER2 and Claudin18.2 overexpression. Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of cancer, including GEA, but biomarkers beyond PD-L1 expression are lacking. Mismatch repair deficiency and/or high microsatellite instability (dMMR/MSI-H) is observed in 8% to 22% of nonmetastatic GEA, and 3% to 5% of patients with metastatic disease. dMMR/MSI-H tumors are associated with more favorable prognosis and significant benefit from ICIs, although some heterogeneity exists. The activity of ICIs in advanced dMMR/MSI-H cancer is seen across lines of therapy and should be recommended in the frontline setting. In patients with nonmetastatic dMMR/MSI-H cancer, increasing evidence suggests that perioperative and adjuvant chemotherapy may not provide benefit to the dMMR/MSI-H subgroup. The activity of perioperative chemotherapy-free immune checkpoint regimens in patients with nonmetastatic dMMR/MSI-H cancer is highly promising and underscores the need to identify this unique subgroup. We recommend MMR/MSI testing for all patients with GEA at diagnosis, and review the key rationale and clinical management implications for patient with dMMR/MSI-H tumors across disease stages.

Development and validation of a nomogram to predict pathological complete response in patients with locally advanced gastric adenocarcinoma treated with neoadjuvant chemotherapy in combination with PD-1 antibodies

Background

Currently, the survival benefits of combining neoadjuvant chemotherapy with programmed death 1 (PD-1) antibody immunotherapy in advanced gastric adenocarcinoma remain controversial. Emerging evidence suggests that the survival benefits of neoadjuvant therapy in advanced gastric adenocarcinoma hinge upon the attainment of pathological complete response (pCR). Therefore, the prediction of pCR in patients undergoing neoadjuvant chemotherapy combined with PD-1 antibody immunotherapy holds significant importance and is beneficial for the individualized treatment of gastric cancer (GC) patients.

Methods

Clinical and pathological characteristics of patients with GC who received neoadjuvant chemotherapy combined with PD-1 inhibitor (camrelizumab) therapy and radical gastrectomy between January 2019 and December 2020 at the Affiliated Cancer Hospital of Zhengzhou University & Henan Cancer Hospital were retrospectively analyzed. A total of 52 patients were enrolled in the study, with all subjects assigned to the training set. The neoadjuvant regimen consisted of a combination of PD-1 inhibitor and fluorouracil analogues plus oxaliplatin, comprising two drugs. The patients were divided into a pCR group and a non-pCR group according to pCR occurrence. Multifactor logistic regression analysis was applied to determine the correlation between each factor and pCR. A prediction model was developed based on the results of the logistic regression analysis. The predictive performance of the model was evaluated using the receiver operating characteristic curves. Internal verification was completed via the bootstrapping method.

Results

The pCR was observed in 10 out of 52 patients (19.2%). The results of binary logistic regression multivariate analysis showed that cN stage [odds ratio (OR): 0.215; P=0.03], combined positive score (CPS) (OR: 6.364; P=0.026), and tumor diameter (OR: 0.112; P=0.026) were independent predictors of pCR. The nomogram prediction model for the pCR was plotted with a concordance index of 0.923 [95% confidence interval (CI): 0.8441-1].

Conclusions

Neoadjuvant chemotherapy combined with PD-1 antibodies may be the preferred option for patients with advanced gastric adenocarcinoma who have a small tumor diameter, no or few lymph node metastases, and high CPS. The presented nomogram model exhibits the potential to predict pCR in advanced gastric adenocarcinoma patients, showcasing satisfactory predictive performance and potentially facilitating the implementation of personalized treatment strategies.

DNA Damage by Radiopharmaceuticals and Mechanisms of Cellular Repair

DNA is an organic molecule that is highly vulnerable to chemical alterations and breaks caused by both internal and external factors. Cells possess complex and advanced mechanisms, including DNA repair, damage tolerance, cell cycle checkpoints, and cell death pathways, which together minimize the potentially harmful effects of DNA damage. However, in cancer cells, the normal DNA damage tolerance and response processes are disrupted or deregulated. This results in increased mutagenesis and genomic instability within the cancer cells, a known driver of cancer progression and therapeutic resistance. On the other hand, the inherent instability of the genome in rapidly dividing cancer cells can be exploited as a tool to kill by imposing DNA damage with radiopharmaceuticals. As the field of targeted radiopharmaceutical therapy (RPT) is rapidly growing in oncology, it is crucial to have a deep understanding of the impact of systemic radiation delivery by radiopharmaceuticals on the DNA of tumors and healthy tissues. The distribution and activation of DNA damage and repair pathways caused by RPT can be different based on the characteristics of the radioisotope and molecular target. Here we provide a comprehensive discussion of the biological effects of RPTs, with the main focus on the role of varying radioisotopes in inducing direct and indirect DNA damage and activating DNA repair pathways.

Ultrasensitive Detection of Circulating LINE-1 ORF1p as a Specific Multicancer Biomarker

Improved biomarkers are needed for early cancer detection, risk stratification, treatment selection, and monitoring treatment response. Although proteins can be useful blood-based biomarkers, many have limited sensitivity or specificity for these applications. Long INterspersed Element-1 (LINE-1) open reading frame 1 protein (ORF1p) is a transposable element protein overexpressed in carcinomas and high-risk precursors during carcinogenesis with negligible expression in normal tissues, suggesting ORF1p could be a highly specific cancer biomarker. To explore ORF1p as a blood-based biomarker, we engineered ultrasensitive digital immunoassays that detect mid-attomolar (10-17 mol/L) ORF1p concentrations in plasma across multiple cancers with high specificity. Plasma ORF1p shows promise for early detection of ovarian cancer, improves diagnostic performance in a multianalyte panel, provides early therapeutic response monitoring in gastroesophageal cancers, and is prognostic for overall survival in gastroesophageal and colorectal cancers. Together, these observations nominate ORF1p as a multicancer biomarker with potential utility for disease detection and monitoring.

SIGNIFICANCE

The LINE-1 ORF1p transposon protein is pervasively expressed in many cancers and is a highly specific biomarker of multiple common, lethal carcinomas and their high-risk precursors in tissue and blood. Ultrasensitive ORF1p assays from as little as 25 μL plasma are novel, rapid, cost-effective tools in cancer detection and monitoring. See related commentary by Doucet and Cristofari, p. 2502. This article is featured in Selected Articles from This Issue, p. 2489.

Microenvironmental Landscape of Human Melanoma Brain Metastases in Response to Immune Checkpoint Inhibition

Melanoma-derived brain metastases (MBM) represent an unmet clinical need because central nervous system progression is frequently an end stage of the disease. Immune checkpoint inhibitors (ICI) provide a clinical opportunity against MBM; however, the MBM tumor microenvironment (TME) has not been fully elucidated in the context of ICI. To dissect unique elements of the MBM TME and correlates of MBM response to ICI, we collected 32 fresh MBM and performed single-cell RNA sequencing of the MBM TME and T-cell receptor clonotyping on T cells from MBM and matched blood and extracranial lesions. We observed myeloid phenotypic heterogeneity in the MBM TME, most notably multiple distinct neutrophil states, including an IL8-expressing population that correlated with malignant cell epithelial-to-mesenchymal transition. In addition, we observed significant relationships between intracranial T-cell phenotypes and the distribution of T-cell clonotypes intracranially and peripherally. We found that the phenotype, clonotype, and overall number of MBM-infiltrating T cells were associated with response to ICI, suggesting that ICI-responsive MBMs interact with peripheral blood in a manner similar to extracranial lesions. These data identify unique features of the MBM TME that may represent potential targets to improve clinical outcomes for patients with MBM.

Activity of Adagrasib (MRTX849) in Brain Metastases: Preclinical Models and Clinical Data from Patients with KRASG12C-Mutant Non-Small Cell Lung Cancer

PURPOSE

Patients with KRAS-mutant non-small cell lung cancer (NSCLC) with brain metastases (BM) have a poor prognosis. Adagrasib (MRTX849), a potent oral small-molecule KRASG12C inhibitor, irreversibly and selectively binds KRASG12C, locking it in its inactive state. Adagrasib has been optimized for favorable pharmacokinetic properties, including long half-life (∼24 hours), extensive tissue distribution, dose-dependent pharmacokinetics, and central nervous system penetration; however, BM-specific antitumor activity of KRASG12C inhibitors remains to be fully characterized.

EXPERIMENTAL DESIGN

A retrospective database query identified patients with KRAS-mutant NSCLC to understand their propensity to develop BM. Preclinical studies assessed physiochemical and pharmacokinetic properties of adagrasib. Mice bearing intracranial KRASG12C-mutant NSCLC xenografts (LU99-Luc/H23-Luc/LU65-Luc) were treated with clinically relevant adagrasib doses, and levels of adagrasib in plasma, cerebrospinal fluid (CSF), and brain were determined along with antitumor activity. Preliminary clinical data were collected from 2 patients with NSCLC with untreated BM who had received adagrasib 600 mg twice daily in the phase Ib cohort of the KRYSTAL-1 trial; CSF was collected, adagrasib concentrations measured, and antitumor activity in BM evaluated.

RESULTS

Patients with KRAS-mutant NSCLC demonstrated high propensity to develop BM (≥40%). Adagrasib penetrated into CSF and demonstrated tumor regression and extended survival in multiple preclinical BM models. In 2 patients with NSCLC and untreated BM, CSF concentrations of adagrasib measured above the target cellular IC50. Both patients demonstrated corresponding BM regression, supporting potential clinical activity of adagrasib in the brain.

CONCLUSIONS

These data support further development of adagrasib in patients with KRASG12C-mutant NSCLC with untreated BM. See related commentary by Kommalapati and Mansfield, p. 3179.

Abstract 1841: MRTX849 inhibits P-gp and demonstrates CNS exposure in mouse models and cancer patients and demonstrates antitumor activity in intracranial mouse models of lung cancer brain metastasis

MRTX849 is a covalent, mutant selective, KRAS G12C inhibitor in development for cancer patients harboring this mutation. KRAS G12C is mutated in ~14% of lung adenocarcinoma and KRAS G12C inhibitors adagrasib and sotorasib have demonstrated clinical activity. While early data are encouraging, approximately one-third of KRAS-mutant non-small cell lung cancer (NSCLC) patients develop brain metastases and this remains a significant unmet medical need. P-glycoprotein 1 (P-gp)-mediated efflux is a major mechanism for the active transport of small molecules out of the CNS. MRTX849 is a P-gp inhibitor and inhibits its own efflux at plasma exposure levels achieved in humans at the 600 mg BID dose level resulting in achieving appreciable drug levels in cerebrospinal fluid (CSF). Total and free-fraction adjusted plasma concentrations of MRTX849 were 8.6 μM and 43 nM; respectively, 8 hours post administration of a clinically relevant oral dose of 200 mg/kg to mice. In addition, the CSF concentration, a measure of the free brain concentration, was 52 nM, which is above the cellular pERK1/2 IC50 value measured at 24 hours in cancer cell lines (~5 nM). Administration of 100 mg/kg MRTX849 to mice also resulted in CSF exposure above the cellular IC50 and a CSF/plasma (free-fraction adjusted) partition coefficient (Kp,uu) value of 0.4. To evaluate the tumor growth inhibition following oral administration of MRTX849 in an orthotopic model of lung cancer brain metastasis, immunocompromised mice were intracranially implanted with luciferase-labeled human NSCLC LU99 cells. Lower bioluminescence imaging (BLI)-based tumor flux was observed for the 100 mg/kg BID MRTX849-treated mice compared to vehicle and an 88% reduction in bioluminescence signal compared to baseline was observed suggesting strong tumor regression and consistent with significantly longer survival in treated mice. In addition, MRTX849 treated brain tumors demonstrated 85% reduced ERK phosphorylation. Similarly, treatment with MRTX849 resulted in potent tumor regression and significant survival extension in another intracranial KRAS G12C model of NSCLC using LU65 cells. CSF levels were determined at steady-state in two patients in the MRTX849-001 Phase1/2 clinical trial. The CSF/plasma (free fraction adjusted) Kp,uu value was 0.47 with patient CSF levels achieved consistent with CSF levels observed in responding mouse models (24-35 nM). These data demonstrate MRTX849 crosses the blood brain barrier in preclinical models and cancer patients. In addition, antitumor activity observed in mouse models of brain metastases provides rationale for exploring the utility of MRTX849 for the treatment of patients harboring KRAS G12C mutant lung cancer with brain metastases.

Citation Format: Kazuhide Shimizu, Jill Hallin, Mohini Singh, Naema Nayyar, Matthew R. Strickland, Aaron C. Burns, Cornelius Cilliers, Lauren Hargis, Peter A. Olson, Matthew A. Marx, Priscilla K. Brastianos, Hiroaki Wakimoto, James G. Christensen. MRTX849 inhibits P-gp and demonstrates CNS exposure in mouse models and cancer patients and demonstrates antitumor activity in intracranial mouse models of lung cancer brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1841.

Tumor Immune Microenvironment of Brain Metastases: Toward Unlocking Antitumor Immunity

Brain metastasis (BrM) is a devastating complication of solid tumors associated with poor outcomes. Immune-checkpoint inhibitors (ICI) have revolutionized the treatment of cancer, but determinants of response are incompletely understood. Given the rising incidence of BrM, improved understanding of immunobiologic principles unique to the central nervous system (CNS) and dissection of those that govern the activity of ICIs are paramount toward unlocking BrM-specific antitumor immunity. In this review, we seek to discuss the current clinical landscape of ICI activity in the CNS and CNS immunobiology, and we focus, in particular, on the role of glial cells in the CNS immune response to BrM.

SIGNIFICANCE

There is an urgent need to improve patient selection for and clinical activity of ICIs in patients with cancer with concomitant BrM. Increased understanding of the unique immunobiologic principles that govern response to ICIs in the CNS is critical toward identifying targets in the tumor microenvironment that may potentiate antitumor immunity.

Phase II study of ipilimumab and nivolumab in leptomeningeal carcinomatosis

Leptomeningeal disease (LMD) is a common complication from solid tumor malignancies with a poor prognosis and limited treatment options. We present a single arm Phase II study of 18 patients with LMD receiving combined ipilimumab and nivolumab until progression or unacceptable toxicity (NCT02939300). The primary end point is overall survival at 3 months (OS3). Secondary end points include toxicity, cumulative time-to-progression at 3 months, and progression-free survival. A Simon two-stage design is used to compare a null hypothesis OS3 of 18% against an alternative of 44%. Median follow up based on patients still alive is 8.0 months (range: 0.5 to 15.9 months). The study has met its primary endpoint as 8 of 18 (OS3 0.44; 90% CI: 0.24 to 0.66) patients are alive at three months. One third of patients have experienced one (or more) grade-3 or higher adverse events. Two patients have discontinued protocol treatment due to unacceptable toxicity (hepatitis and colitis, respectively). The most frequent adverse events include fatigue (N = 7), nausea (N = 6), fever (N = 6), anorexia (N = 6) and rash (N = 6). Combined ipilimumab and nivolumab has an acceptable safety profile and demonstrates promising activity in LMD patients. Larger, multicenter clinical trials are needed to validate these results.

Clinical and Imaging Features of Non-Small Cell Lung Cancer with G12C KRAS Mutation

Simple Summary

KRAS G12C mutations are important oncogenic mutations in lung cancer that can now be targeted by allosteric small molecule inhibitors. We assessed the imaging features and patterns of metastases in these lung cancers compared to other mutated lung cancers. We found that KRAS G12C NSCLC has distinct primary tumor imaging features and patterns of metastasis when compared to those of NSCLC driven by other genetic alterations. These distinct imaging features may offer clues to its presence and potentially guide management in the future.

Abstract

KRAS G12C mutations are important oncogenic mutations that confer sensitivity to direct G12C inhibitors. We retrospectively identified patients with KRAS+ NSCLC from 2015 to 2019 and assessed the imaging features of the primary tumor and the distribution of metastases of G12C NSCLC compared to those of non-G12C KRAS NSCLC and NSCLC driven by oncogenic fusion events (RET, ALK, ROS1) and EGFR mutations at the time of initial diagnosis. Two hundred fifteen patients with KRAS+ NSCLC (G12C: 83; non-G12C: 132) were included. On single variate analysis, the G12C group was more likely than the non-G12C KRAS group to have cavitation (13% vs. 5%, p = 0.04) and lung metastasis (38% vs. 21%; p = 0.043). Compared to the fusion rearrangement group, the G12C group had a lower frequency of pleural metastasis (21% vs. 41%, p = 0.01) and lymphangitic carcinomatosis (4% vs. 39%, p = 0.0001) and a higher frequency of brain metastasis (42% vs. 22%, p = 0.005). Compared to the EGFR+ group, the G12C group had a lower frequency of lung metastasis (38% vs. 67%, p = 0.0008) and a higher frequency of distant nodal metastasis (10% vs. 2%, p = 0.02). KRAS G12C NSCLC may have distinct primary tumor imaging features and patterns of metastasis when compared to those of NSCLC driven by other genetic alterations.

Abstract 4729: Identifying genomic drivers of lung adenocarcinoma brain metastases

Although lung adenocarcinomas frequently metastasize to the brain, treatment options for lung adenocarcinoma brain metastases (BM-LUAD) are limited. We discovered novel candidate drivers of progression by using case-control analyses to compare whole-exome sequencing data from a cohort of 73 BM-LUAD to a control cohort of 503 primary lung adenocarcinomas. We identified MYC, YAP1 and MMP13 as genomic regions with significantly more frequent amplifications in BM-LUAD compared to control cohort. We validated that MYC, YAP1 and MMP13 can drive brain metastases in a patient-derived xenograft mouse model, where incidence of brain metastases was higher in mice injected with tumor cells expressing the candidate drivers compared to tumor cells expressing LacZ. These results indicate that somatic alterations can drive lung adenocarcinomas to metastasize to the brain. These candidate drivers may serve as therapeutic targets in patients with brain metastatic lung adenocarcinomas.

Citation Format: Naema Nayyar, David J. Shih, Ivanna Bihun, Ibiayi Dagogo-Jack, Corey M. Gill, Elisa Aquilanti, Mia Bertalan, Alexander Kaplan, Megan R. D'Andrea, Ugonma Chukwueke, Christopher Alvarez-Breckenridge, Matthew Lastrapes, Ben Kuter, Matthew R. Strickland, Juan Carlos Martinez-Gutierrez, Deepika Nagabhushan, Magali De Sauvage, Michael D. White, Brandyn A. Castro, Kaitlin Hoang, Sun Ha Paek, Sun Hye Park, Maria Martinez-Lage, Anna S. Berghoff, Parker Merrill, Elizabeth R. Gerstner, Tracy T. Batchelor, Matthew P. Frosch, Ryan P. Frazier, Darrell R. Borger, A John Iafrate, Sandro Santagata, Matthias Preusser, Daniel P. Cahill, Scott L. Carter, Priscilla K. Brastianos. Identifying genomic drivers of lung adenocarcinoma brain metastases [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4729.

Genomic characterization of human brain metastases identifies drivers of metastatic lung adenocarcinoma

Brain metastases from lung adenocarcinoma (BM-LUAD) frequently cause patient mortality. To identify genomic alterations that promote brain metastases, we performed whole-exome sequencing of 73 BM-LUAD cases. Using case-control analyses, we discovered candidate drivers of brain metastasis by identifying genes with more frequent copy-number aberrations in BM-LUAD compared to 503 primary LUADs. We identified three regions with significantly higher amplification frequencies in BM-LUAD, including MYC (12 versus 6%), YAP1 (7 versus 0.8%) and MMP13 (10 versus 0.6%), and significantly more frequent deletions in CDKN2A/B (27 versus 13%). We confirmed that the amplification frequencies of MYC, YAP1 and MMP13 were elevated in an independent cohort of 105 patients with BM-LUAD. Functional assessment in patient-derived xenograft mouse models validated the notion that MYC, YAP1 or MMP13 overexpression increased the incidence of brain metastasis. These results demonstrate that somatic alterations contribute to brain metastases and that genomic sequencing of a sufficient number of metastatic tumors can reveal previously unknown metastatic drivers.

Genomic Analysis of Posterior Fossa Meningioma Demonstrates Frequent AKT1 E17K Mutations in Foramen Magnum Meningiomas

Objective  Posterior fossa meningiomas are surgically challenging tumors that are associated with high morbidity and mortality. We sought to investigate the anatomical distribution of clinically actionable mutations in posterior fossa meningioma to facilitate identifying patients amenable for systemic targeted therapy trials. Methods  Targeted sequencing of clinically targetable AKT1 , SMO , and PIK3CA mutations was performed in 61 posterior fossa meningioma using Illumina NextSeq 500 to a target depth of >500 × . Samples were further interrogated for 53 cancer-relevant RNA fusions by the Archer FusionPlex panel to detect gene rearrangements. Results   AKT 1 ( E17K ) mutations were detected in five cases (8.2%), four in the foramen magnum and one in the cerebellopontine angle. In contrast, none of the posterior fossa tumors harbored an SMO ( L412F ) or a PIK3CA ( E545K ) mutation. Notably, the majority of foramen magnum meningiomas (4/7, 57%) harbored an AKT1 mutation. In addition, common clinically targetable gene fusions were not detected in any of the cases. Conclusion  A large subset of foramen magnum meningiomas harbor AKT1 E17K mutations and are therefore potentially amenable to targeted medical therapy. Genotyping of foramen magnum meningiomas may enable more therapeutic alternatives and guide their treatment decision process.

Enrichment of HER2 Amplification in Brain Metastases from Primary Gastrointestinal Malignancies

BACKGROUND

In nongastric gastrointestinal (GI) cancers, HER2-positive (HER2+) disease is not common. In breast cancer, HER2 status is associated with increased risk of brain metastases and response to HER2-targeted therapy. The purpose of this project was to compare HER2 status in GI cancer brain metastases versus matched prior sites of disease in order to determine if HER2+ disease is more common intracranially.

MATERIALS AND METHODS

We identified 28 patients with GI cancer who had craniotomy for brain metastases between 1999 and 2017 with intracranial metastatic tissue available at Massachusetts General Hospital. Twenty-four patients also had tissue from a prior site of disease. Fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) for HER2 were performed on all samples. A tumor was defined as HER2+ if it had 3+ staining by IHC or amplification by FISH.

RESULTS

A prior site of disease (including intracranial metastases) was HER2+ for 13% of evaluable patients: 3 of 11 patients with colorectal cancer and no patients with esophageal or pancreatic cancer. The most recent brain metastases were HER2+ for 32% of patients: 2 of 3 esophageal squamous cell carcinomas, 3 of 10 esophageal adenocarcinomas (ACs), 3 of 14 colorectal ACs, and 1 of 1 pancreatic AC. Only 37.5% of patients with HER2+ brain metastasis had concordant HER2+ prior tissue (κ = 0.38, p = .017).

CONCLUSION

In this cohort of patients with GI cancer with brain metastases, HER2+ status was more common intracranially compared with prior sites of disease. These findings suggest that testing HER2 in patients with GI cancer with brain metastases may lead to additional therapeutic options, regardless of HER2 status in previously examined tissue.

IMPLICATIONS FOR PRACTICE

HER2 amplification is a well-known driver of oncogenesis in breast cancer, with associated increased risk of brain metastases and response to HER2-directed therapy. In nongastric gastrointestinal (GI) cancers, HER2 amplification is not common and consequently is infrequently tested. The current study shows that brain metastases in patients with GI primary malignancies have a relatively high likelihood of being HER2 positive despite HER2 amplification or overexpression being less commonly found in matched tissue from prior sites of disease. This suggests that regardless of prior molecular testing, patients with GI cancer with brain metastases who have tissue available are likely to benefit from HER2 assessment to identify potential novel therapeutic options.

Targeted sequencing of SMO and AKT1 in anterior skull base meningiomas

OBJECTIVE Meningiomas located in the skull base are surgically challenging. Recent genomic research has identified oncogenic SMO and AKT1 mutations in a small subset of meningiomas. METHODS The authors performed targeted sequencing in a large cohort of patients with anterior skull base meningiomas (n = 62) to better define the frequency of SMO and AKT1 mutations in these tumors. RESULTS The authors found SMO mutations in 7 of 62 (11%) and AKT1 mutations in 12 of 62 (19%) of their cohort. Of the 7 meningiomas with SMO mutations, 6 (86%) occurred in the olfactory groove. Meningiomas with an SMO mutation presented with significantly larger tumor volume (70.6 ± 36.3 cm³) compared with AKT1-mutated (18.2 ± 26.8 cm³) and wild-type (22.7 ± 23.9 cm³) meningiomas, respectively. CONCLUSIONS Combined, these data demonstrate clinically actionable mutations in 30% of anterior skull base meningiomas and suggest an association between SMO mutation status and tumor volume. Genotyping of SMO and AKT1 is likely to be high yield in anterior skull base meningiomas with available surgical tissue.

PRKACA mediates resistance to HER2-targeted therapy in breast cancer cells and restores anti-apoptotic signaling

Targeting HER2 with antibodies or small molecule inhibitors in HER2-positive breast cancer leads to improved survival, but resistance is a common clinical problem. To uncover novel mechanisms of resistance to anti-HER2 therapy in breast cancer, we performed a kinase open reading frame screen to identify genes that rescue HER2-amplified breast cancer cells from HER2 inhibition or suppression. In addition to multiple members of the MAPK (mitogen-activated protein kinase) and PI3K (phosphoinositide 3-kinase) signaling pathways, we discovered that expression of the survival kinases PRKACA and PIM1 rescued cells from anti-HER2 therapy. Furthermore, we observed elevated PRKACA expression in trastuzumab-resistant breast cancer samples, indicating that this pathway is activated in breast cancers that are clinically resistant to trastuzumab-containing therapy. We found that neither PRKACA nor PIM1 restored MAPK or PI3K activation after lapatinib or trastuzumab treatment, but rather inactivated the pro-apoptotic protein BAD, the BCl-2-associated death promoter, thereby permitting survival signaling through BCL-XL. Pharmacological blockade of BCL-XL/BCL-2 partially abrogated the rescue effects conferred by PRKACA and PIM1, and sensitized cells to lapatinib treatment. These observations suggest that combined targeting of HER2 and the BCL-XL/BCL-2 anti-apoptotic pathway may increase responses to anti-HER2 therapy in breast cancer and decrease the emergence of resistant disease.

Abstract P5-08-01: Systematic interrogation of resistance to HER2-directed therapy identifies a survival pathway activated by PRKACA and PIM1

Amplification and/or overexpression of the receptor tyrosine kinase HER2 occurs in 20-25% of breast cancers, and is associated with poor prognosis. Targeting of HER2 with drugs such as trastuzumab, lapatinib, or pertuzumab has led to clinical benefit in patients with both metastatic and early-stage HER2-amplified breast cancer. However, resistance and disease progression always occurs in patients with metastatic disease, and many patients with early-stage breast cancer experience recurrences despite adjuvant anti-HER2 therapy. As such, understanding the mechanisms of resistance to anti-HER2 therapy has important clinical implications.

Recent studies have identified mutations in PIK3CA, the gene encoding the catalytic subunit of Phosphatidylinositol 3 kinase (PI3K), as one mechanism of resistance to trastuzumab. However, such mutations are present in only a fraction of trastuzumab-resistant breast cancers. We therefore sought to uncover novel mechanisms of resistance to anti-HER2 therapy through an unbiased screen for kinases and kinase-related molecules that are able to rescue HER2-amplified breast cancer cells from HER2 inhibition.

We utilized a library of nearly 600 lentivirally-delivered open reading frames (ORFs) to constitutively express the coding sequence of each molecule individually in HER2-amplified BT474 breast cancer cells in arrayed high-throughput format. We conducted two parallel screens for the ability of each of these molecules to rescue cells from anti-HER2 therapy: one in which we treated the cells with a lapatinib-like drug that inhibits the kinase activity of HER2 and EGFR, and one in which we lentivirally delivered a short hairpin RNA that suppresses expression of HER2.

We identified those ORFs that restored viability of BT474 cells to greater than two standard deviations above the median of all ORFs in each screen. Multiple members of the MAPK and PI3K signaling pathways scored in both screens, serving to validate the approach. In addition, the survival kinases PIM1 and PRKACA scored robustly. Mechanistic studies suggest that these kinases may confer resistance by restoring the phosphorylation of, and thereby inactivating, the pro-apoptotic protein BAD. Consistent with this finding, overexpression of Bcl-xl, which is inhibited by BAD, also conferred resistance to lapatinib in HER2-amplified breast cancer cells. Furthermore, pharmacological blockade of Bcl-xl and Bcl-2 with ABT-263 enhanced lapatinib-induced killing of HER2-amplified breast cancer cells in vitro, and partially abrogated the rescue conferred by both PRKACA and PIM1. These findings suggest that combined inhibition of HER2 and the anti-apoptotic molecules Bcl-xl and Bcl-2 could enhance tumor cell eradication and prevent or delay the emergence of resistant disease.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-08-01.

Cancer vulnerabilities unveiled by genomic loss

Due to genome instability, most cancers exhibit loss of regions containing tumor suppressor genes and collateral loss of other genes. To identify cancer-specific vulnerabilities that are the result of copy number losses, we performed integrated analyses of genome-wide copy number and RNAi profiles and identified 56 genes for which gene suppression specifically inhibited the proliferation of cells harboring partial copy number loss of that gene. These CYCLOPS (copy number alterations yielding cancer liabilities owing to partial loss) genes are enriched for spliceosome, proteasome, and ribosome components. One CYCLOPS gene, PSMC2, encodes an essential member of the 19S proteasome. Normal cells express excess PSMC2, which resides in a complex with PSMC1, PSMD2, and PSMD5 and acts as a reservoir protecting cells from PSMC2 suppression. Cells harboring partial PSMC2 copy number loss lack this complex and die after PSMC2 suppression. These observations define a distinct class of cancer-specific liabilities resulting from genome instability.