Acquired Cross-Resistance in Small Cell Lung Cancer due to Extrachromosomal DNA Amplification of MYC Paralogs

Small cell lung cancer (SCLC) presents as a highly chemosensitive malignancy but acquires cross-resistance after relapse. This transformation is nearly inevitable in patients but has been difficult to capture in laboratory models. Here, we present a preclinical system that recapitulates acquired cross-resistance, developed from 51 patient-derived xenograft (PDX) models. Each model was tested in vivo against three clinical regimens: cisplatin plus etoposide, olaparib plus temozolomide, and topotecan. These drug-response profiles captured hallmark clinical features of SCLC, such as the emergence of treatment-refractory disease after early relapse. For one patient, serial PDX models revealed that cross-resistance was acquired through MYC amplification on extrachromosomal DNA (ecDNA). Genomic and transcriptional profiles of the full PDX panel revealed that MYC paralog amplifications on ecDNAs were recurrent in relapsed cross-resistant SCLC, and this was corroborated in tumor biopsies from relapsed patients. We conclude that ecDNAs with MYC paralogs are recurrent drivers of cross-resistance in SCLC.

SIGNIFICANCE

SCLC is initially chemosensitive, but acquired cross-resistance renders this disease refractory to further treatment and ultimately fatal. The genomic drivers of this transformation are unknown. We use a population of PDX models to discover that amplifications of MYC paralogs on ecDNA are recurrent drivers of acquired cross-resistance in SCLC. This article is featured in Selected Articles from This Issue, p. 695.

Acquired Cross-resistance in Small Cell Lung Cancer due to Extrachromosomal DNA Amplification of MYC paralogs

Small cell lung cancer (SCLC) presents as a highly chemosensitive malignancy but acquires cross-resistance after relapse. This transformation is nearly inevitable in patients but has been difficult to capture in laboratory models. Here we present a pre-clinical system that recapitulates acquired cross-resistance in SCLC, developed from 51 patient-derived xenografts (PDXs). Each model was tested for in vivo sensitivity to three clinical regimens: cisplatin plus etoposide, olaparib plus temozolomide, and topotecan. These functional profiles captured hallmark clinical features, such as the emergence of treatment-refractory disease after early relapse. Serially derived PDX models from the same patient revealed that cross-resistance was acquired through a MYC amplification on extrachromosomal DNA (ecDNA). Genomic and transcriptional profiles of the full PDX panel revealed that this was not unique to one patient, as MYC paralog amplifications on ecDNAs were recurrent among cross-resistant models derived from patients after relapse. We conclude that ecDNAs with MYC paralogs are recurrent drivers of cross-resistance in SCLC.

SIGNIFICANCE

SCLC is initially chemosensitive, but acquired cross-resistance renders this disease refractory to further treatment and ultimately fatal. The genomic drivers of this transformation are unknown. We use a population of PDX models to discover that amplifications of MYC paralogs on ecDNA are recurrent drivers of acquired cross-resistance in SCLC.

Translesion DNA synthesis mediates acquired resistance to olaparib plus temozolomide in small cell lung cancer

In small cell lung cancer (SCLC), acquired resistance to DNA-damaging therapy is challenging to study because rebiopsy is rarely performed. We used patient-derived xenograft models, established before therapy and after progression, to dissect acquired resistance to olaparib plus temozolomide (OT), a promising experimental therapy for relapsed SCLC. These pairs of serial models reveal alterations in both cell cycle kinetics and DNA replication and demonstrate both inter- and intratumoral heterogeneity in mechanisms of resistance. In one model pair, up-regulation of translesion DNA synthesis (TLS) enabled tolerance of OT-induced damage during DNA replication. TLS inhibitors restored sensitivity to OT both in vitro and in vivo, and similar synergistic effects were seen in additional SCLC cell lines. This represents the first described mechanism of acquired resistance to DNA damage in a patient with SCLC and highlights the potential of the serial model approach to investigate and overcome resistance to therapy in SCLC.

Abstract B50: ERK MAPK inhibition enhances the immunogenicity of KRAS-mutant colorectal cancer

The three RAS genes are the most commonly mutated oncogenes in cancer and are refractory to conventional therapies. Oncogenic mutation of KRAS in 44% of colorectal cancers (CRC) leads to aberrant activation of downstream effector pathways, including the ERK MAPK signaling cascade, which can lead to an immunosuppressive tumor microenvironment. Single-agent therapies targeting the ERK MAPK cascade or immune checkpoint (PD-1/PD-L1) have been mostly unsuccessful in KRAS-mutant CRC, and efforts are under way to identify effective combination strategies. We employed an unbiased RNA-seq approach to identify gene signatures significantly upregulated upon ERK MAPK pathway inhibition in a panel of KRAS-mutant CRC cell lines. We found that treatment with either the MEK inhibitor trametinib or ERK inhibitor Vx-11e induced upregulation of interferon gene signatures and JAK/STAT pathway signaling components. Inhibition of MEK or ERK also transcriptionally increased levels of MHC Class I and antigen presentation machinery. Upregulation of MHC Class I was reversed with either pharmacologic inhibition of JAK/STAT signaling or genetic knockdown of the transcription factor IRF1. We propose that combining MAPK inhibition with checkpoint immunotherapy may provide an effective treatment in KRAS-mutant CRC tumors in vivo and that potential synergy may be due to enhancing the immunogenicity of tumors through priming of interferon response pathways and antigen presentation machinery.

Citation Format: Meagan B. Ryan, Ferran Fece de la Cruz, Leanne G. Ahronian, Sarah Phat, David T. Myers, Heather A. Shahzade, Catriona Hong, Ryan B. Corcoran. ERK MAPK inhibition enhances the immunogenicity of KRAS-mutant colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr B50.

Vertical Pathway Inhibition Overcomes Adaptive Feedback Resistance to KRASG12C Inhibition

PURPOSE

Although KRAS represents the most commonly mutated oncogene, it has long been considered an "undruggable" target. Novel covalent inhibitors selective for the KRASG12C mutation offer the unprecedented opportunity to target KRAS directly. However, prior efforts to target the RAS-MAPK pathway have been hampered by adaptive feedback, which drives pathway reactivation and resistance.

EXPERIMENTAL DESIGN

A panel of KRASG12C cell lines were treated with the KRASG12C inhibitors ARS-1620 and AMG 510 to assess effects on signaling and viability. Isoform-specific pulldown of activated GTP-bound RAS was performed to evaluate effects on the activity of specific RAS isoforms over time following treatment. RTK inhibitors, SHP2 inhibitors, and MEK/ERK inhibitors were assessed in combination with KRASG12C inhibitors in vitro and in vivo as potential strategies to overcome resistance and enhance efficacy.

RESULTS

We observed rapid adaptive RAS pathway feedback reactivation following KRASG12C inhibition in the majority of KRASG12C models, driven by RTK-mediated activation of wild-type RAS, which cannot be inhibited by G12C-specific inhibitors. Importantly, multiple RTKs can mediate feedback, with no single RTK appearing critical across all KRASG12C models. However, coinhibition of SHP2, which mediates signaling from multiple RTKs to RAS, abrogated feedback reactivation more universally, and combined KRASG12C/SHP2 inhibition drove sustained RAS pathway suppression and improved efficacy in vitro and in vivo.

CONCLUSIONS

These data identify feedback reactivation of wild-type RAS as a key mechanism of adaptive resistance to KRASG12C inhibitors and highlight the potential importance of vertical inhibition strategies to enhance the clinical efficacy of KRASG12C inhibitors.See related commentary by Yaeger and Solit, p. 1538.

A post-transcriptional program of chemoresistance by AU-rich elements and TTP in quiescent leukemic cells

BACKGROUND

Quiescence (G0) is a transient, cell cycle-arrested state. By entering G0, cancer cells survive unfavorable conditions such as chemotherapy and cause relapse. While G0 cells have been studied at the transcriptome level, how post-transcriptional regulation contributes to their chemoresistance remains unknown.

RESULTS

We induce chemoresistant and G0 leukemic cells by serum starvation or chemotherapy treatment. To study post-transcriptional regulation in G0 leukemic cells, we systematically analyzed their transcriptome, translatome, and proteome. We find that our resistant G0 cells recapitulate gene expression profiles of in vivo chemoresistant leukemic and G0 models. In G0 cells, canonical translation initiation is inhibited; yet we find that inflammatory genes are highly translated, indicating alternative post-transcriptional regulation. Importantly, AU-rich elements (AREs) are significantly enriched in the upregulated G0 translatome and transcriptome. Mechanistically, we find the stress-responsive p38 MAPK-MK2 signaling pathway stabilizes ARE mRNAs by phosphorylation and inactivation of mRNA decay factor, Tristetraprolin (TTP) in G0. This permits expression of ARE mRNAs that promote chemoresistance. Conversely, inhibition of TTP phosphorylation by p38 MAPK inhibitors and non-phosphorylatable TTP mutant decreases ARE-bearing TNFα and DUSP1 mRNAs and sensitizes leukemic cells to chemotherapy. Furthermore, co-inhibiting p38 MAPK and TNFα prior to or along with chemotherapy substantially reduces chemoresistance in primary leukemic cells ex vivo and in vivo.

CONCLUSIONS

These studies uncover post-transcriptional regulation underlying chemoresistance in leukemia. Our data reveal the p38 MAPK-MK2-TTP axis as a key regulator of expression of ARE-bearing mRNAs that promote chemoresistance. By disrupting this pathway, we develop an effective combination therapy against chemosurvival.

Identification of DHODH as a therapeutic target in small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive lung cancer subtype with extremely poor prognosis. No targetable genetic driver events have been identified, and the treatment landscape for this disease has remained nearly unchanged for over 30 years. Here, we have taken a CRISPR-based screening approach to identify genetic vulnerabilities in SCLC that may serve as potential therapeutic targets. We used a single-guide RNA (sgRNA) library targeting ~5000 genes deemed to encode "druggable" proteins to perform loss-of-function genetic screens in a panel of cell lines derived from autochthonous genetically engineered mouse models (GEMMs) of SCLC, lung adenocarcinoma (LUAD), and pancreatic ductal adenocarcinoma (PDAC). Cross-cancer analyses allowed us to identify SCLC-selective vulnerabilities. In particular, we observed enhanced sensitivity of SCLC cells toward disruption of the pyrimidine biosynthesis pathway. Pharmacological inhibition of dihydroorotate dehydrogenase (DHODH), a key enzyme in this pathway, reduced the viability of SCLC cells in vitro and strongly suppressed SCLC tumor growth in human patient-derived xenograft (PDX) models and in an autochthonous mouse model. These results indicate that DHODH inhibition may be an approach to treat SCLC.

Combination Olaparib and Temozolomide in Relapsed Small-Cell Lung Cancer

Small-cell lung cancer (SCLC) is an aggressive malignancy in which inhibitors of PARP have modest single-agent activity. We performed a phase I/II trial of combination olaparib tablets and temozolomide (OT) in patients with previously treated SCLC. We established a recommended phase II dose of olaparib 200 mg orally twice daily with temozolomide 75 mg/m² daily, both on days 1 to 7 of a 21-day cycle, and expanded to a total of 50 patients. The confirmed overall response rate was 41.7% (20/48 evaluable); median progression-free survival was 4.2 months [95% confidence interval (CI), 2.8-5.7]; and median overall survival was 8.5 months (95% CI, 5.1-11.3). Patient-derived xenografts (PDX) from trial patients recapitulated clinical OT responses, enabling a 32-PDX coclinical trial. This revealed a correlation between low basal expression of inflammatory-response genes and cross-resistance to both OT and standard first-line chemotherapy (etoposide/platinum). These results demonstrate a promising new therapeutic strategy in SCLC and uncover a molecular signature of those tumors most likely to respond. SIGNIFICANCE: We demonstrate substantial clinical activity of combination olaparib/temozolomide in relapsed SCLC, revealing a promising new therapeutic strategy for this highly recalcitrant malignancy. Through an integrated coclinical trial in PDXs, we then identify a molecular signature predictive of response to OT, and describe the common molecular features of cross-resistant SCLC.See related commentary by Pacheco and Byers, p. 1340.This article is highlighted in the In This Issue feature, p. 1325.

Abstract 4736: Dose optimization of olaparib plus temozolomide in small cell lung cancer (SCLC) patient-derived xenograft (PDX) models for clinical translation

Introduction: SCLC is an aggressive high-grade neuroendocrine malignancy in which targeting DNA-damage repair pathways has shown efficacy in pre-clinical and clinical contexts. We previously conducted a phase I/II trial combining the PARP inhibitor olaparib (O) tablets with the alkylating agent temozolomide (T) in patients with relapsed SCLC, in which O and T were both given days (d) 1-7 of each 21 d cycle. The recommended phase 2 dose (RP2D) was O 200 mg PO BID and T 75 mg/m2 PO daily, and the response rate among the first 29 evaluable patients was 41.4%, with the primary toxicities being hematologic (Farago et al., ASCO 2018). Continuous PARP inhibition with O may improve efficacy, though it is unknown how best to incorporate T onto this backbone. Simultaneous clinical testing of multiple dosing schedules for concurrent OT would be impractical. Here we present an optimization of the OT regimen using PDX models generated from patients treated with OT. Methods: SCLC PDX models derived from two patients prior to their durable responses to OT, MGH1518-1B and MGH1528-1, were used for dose optimization. Based on a human-murine comparison of serum Cmax for OT, the estimated murine-equivalents for the RP2D doses were O 25 mg/kg BID and T 6.25 mg/kg/d. The RP2D regimen was then modulated in both dose intensity and duration in a 9-arm PDX trial. The arms included 3 schedule categories, with doses varied within each category: discontinuous regimens (OT d 1-7); continuous O regimens (O d1-21 + T d 1-7); and rapid- or slow-alternating regimens administering O and T on non-overlapping days. Tumor bearing mice were treated when subcutaneous tumors reached a volume of 400-800 cc, enabling measurement of tumor regression (PDX response) and time to volume doubling (PDX TTP). Findings: The RP2D regimen resulted in near-complete response in both models. This degree of regression was recapitulated with nearly all dosing schedules, and was not improved by increasing T to 2x-RP2D. However, the PDX TTP varied. In both models, the longest TTP was seen with continuous O at full- or half-RP2D and d 1-7 T at half-RP2D. This regimen prolonged TTP by 12% in MGH1518-1B and 20% in MGH1528-1, versus discontinuous OT at RP2D. Based on these results, we initiated clinical treatment in a new cohort of patients on OT, with a phase 1 dose escalation starting with O 50 mg BID d 1-21 and T 50 mg/m2 d 1-7 of each 21 d cycle (NCT02446704). At this first dose level, a partial response by RECIST 1.1 criteria was observed in a heavily pre-treated patient, indicating clinical activity of this combination with this new dosing strategy. Conclusions: In PDX models sensitive to OT at our previously determined RP2D, we find that continuous O with intermittent T permits dose reduction of both O and T without loss of efficacy. A clinical trial is ongoing to determine whether this strategy may enable longer-term dosing and improve efficacy in patients.

Citation Format: Benjamin J. Drapkin, Sarah Phat, David T. Myers, Jun Zhong, Beow Y. Yeap, Elisabetta Leo, Anna Stansiszewska, Aaron Smith, Elaine Cadogan, Maria C. Pietanza, Nicholas J. Dyson, Anna Farago. Dose optimization of olaparib plus temozolomide in small cell lung cancer (SCLC) patient-derived xenograft (PDX) models for clinical translation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4736.

Abstract 381: Combined inhibition of Bcl-2 and MCL-1 in small cell lung cancer (SCLC) is most effective in tumors with low Bcl-xL expression

Introduction: SCLC is an aggressive high-grade neuroendocrine malignancy in which targeting anti-apoptotic regulators such as Bcl-2 and Bcl-xL has shown efficacy in pre-clinical models but has not resulted in successful clinical trials (Rudin et al., Clin Cancer Res. 2012). Although SCLC cell-lines do not reflect the clinical impact of these inhibitors, patient-derived xenograft (PDX) models may more accurately recapitulate Bcl-2 family expression profiles and BH3 mimetic efficacy. One promising hypothesis is that the fellow anti-apoptotic protein MCL-1 rescues viability in the presence of Bcl-2/Bcl-xL antagonists. Here we evaluate the efficacy of the MCL-1 inhibitor S63845 in combination with a novel specific inhibitor of Bcl-2, BCL201/S55746, in SCLC patient-derived xenografts. Methods: BH3 mimetic compounds were tested for synergy in vitro in SCLC cell lines. A set of ten cell lines was chosen based on relative expression of BCL2, MCL1, and BCL2L1 (Bcl-xL) mRNA. Single agent and and pair-wise combinations of Bcl2 family inhibitors were compared in three-day growth inhibition assays. Loewe synergy scores were plotted versus Bcl2 family mRNA expression to identify the determinants of drug sensitivity. Based on the cell line synergy assays, a combination of BCL201/S55746 and S63845 was selected to test in PDX models of SCLC. Bcl-2 family expression was profiled across a panel of 37 SCLC PDX models generated at MGH by quantitative western blot, and standardized to the most sensitive SCLC cell line, NCI-H211. Ten models were selected based on absolute expression of Bcl-2, Bcl-xL and MCL-1. Mice were treated when subcutaneous tumors reached a volume of 400-800 cc, enabling precise measurement of tumor regression and time to tumor regrowth. Findings: Bcl-2 family dependency in SCLC cell lines was profiled with selective inhibitors as single agents or combinations. Maximum synergy was found between BCL201/S55746 and S63845 in cell lines with the highest Bcl-2:Bcl-xL expression ratio. Bcl-2 family expression was profiled across a panel of 37 PDX models of SCLC, and a representative set of 10 models was selected for in vivo testing. Consistent with cell line results, the two most sensitive models to BCL201/S55746+S63845 demonstrated the highest Bcl-2:Bcl-xL ratios, with moderate to high expression of MCL-1. In these models BCL201/S55746+S63845 resulted in a 44-70% tumor regression that was stable throughout 4 weeks of treatment. Efficacy was not dependent on MCL-1 expression, and was not strongly correlated with PDX sensitivity to platinum-etoposide. Conclusions: Combined inhibition of Bcl-2 with BCL201 and MCL-1 with S63845 is effective in SCLC tumors with relatively low Bcl-xL expression. This combination overcomes MCL-1 mediated resistance to Bcl-2 inhibitors, and represents a promising strategy to target anti-apoptotic dependency in SCLC.

Citation Format: Benjamin J. Drapkin, Sneha Sanghavi, David T. Myers, Jun Zhong, Sarah Phat, Youzhen Wang, Ensar Halilovic, Javad Golji, Anna Farago, Erick Morris, Nicholas J. Dyson. Combined inhibition of Bcl-2 and MCL-1 in small cell lung cancer (SCLC) is most effective in tumors with low Bcl-xL expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 381.

Visualizing Engrafted Human Cancer and Therapy Responses in Immunodeficient Zebrafish

Xenograft cell transplantation into immunodeficient mice has become the gold standard for assessing pre-clinical efficacy of cancer drugs, yet direct visualization of single-cell phenotypes is difficult. Here, we report an optically-clear prkdc-/-, il2rga-/- zebrafish that lacks adaptive and natural killer immune cells, can engraft a wide array of human cancers at 37°C, and permits the dynamic visualization of single engrafted cells. For example, photoconversion cell-lineage tracing identified migratory and proliferative cell states in human rhabdomyosarcoma, a pediatric cancer of muscle. Additional experiments identified the preclinical efficacy of combination olaparib PARP inhibitor and temozolomide DNA-damaging agent as an effective therapy for rhabdomyosarcoma and visualized therapeutic responses using a four-color FUCCI cell-cycle fluorescent reporter. These experiments identified that combination treatment arrested rhabdomyosarcoma cells in the G2 cell cycle prior to induction of apoptosis. Finally, patient-derived xenografts could be engrafted into our model, opening new avenues for developing personalized therapeutic approaches in the future.

KRAS G12C NSCLC Models Are Sensitive to Direct Targeting of KRAS in Combination with PI3K Inhibition

PURPOSE

KRAS-mutant lung cancers have been recalcitrant to treatments including those targeting the MAPK pathway. Covalent inhibitors of KRAS p.G12C allele allow for direct and specific inhibition of mutant KRAS in cancer cells. However, as for other targeted therapies, the therapeutic potential of these inhibitors can be impaired by intrinsic resistance mechanisms. Therefore, combination strategies are likely needed to improve efficacy.Experimental Design: To identify strategies to maximally leverage direct KRAS inhibition we defined the response of a panel of NSCLC models bearing the KRAS G12C-activating mutation in vitro and in vivo. We used a second-generation KRAS G12C inhibitor, ARS1620 with improved bioavailability over the first generation. We analyzed KRAS downstream effectors signaling to identify mechanisms underlying differential response. To identify candidate combination strategies, we performed a high-throughput drug screening across 112 drugs in combination with ARS1620. We validated the top hits in vitro and in vivo including patient-derived xenograft models.

RESULTS

Response to direct KRAS G12C inhibition was heterogeneous across models. Adaptive resistance mechanisms involving reactivation of MAPK pathway and failure to induce PI3K-AKT pathway inactivation were identified as likely resistance events. We identified several model-specific effective combinations as well as a broad-sensitizing effect of PI3K-AKT-mTOR pathway inhibitors. The G12Ci+PI3Ki combination was effective in vitro and in vivo on models resistant to single-agent ARS1620 including patient-derived xenografts models.

CONCLUSIONS

Our findings suggest that signaling adaptation can in some instances limit the efficacy of ARS1620 but combination with PI3K inhibitors can overcome this resistance.

Abstract 2972: Co-clinical trial of olaparib and temozolomide in SCLC PDX models uncovers new biomarkers of sensitivity

Introduction: Small cell lung cancer (SCLC) is a common and rapidly fatal malignancy for which no biomarker-targeted therapies have been developed. Despite a critical need, progress suffers from (1) scarcity of cutting-edge laboratory models and (2) absence of promising targets. Patient-derived xenografts (PDX) may faithfully model the clinical disease, but because SCLC is rarely biopsied or resected, specimens for PDX generation are scarce. PARP inhibition has recently emerged as a compelling strategy for SCLC, and an ongoing phase 1/2 trial of combination olaparib tablets and temozolomide (O/T) has shown promising activity in patients. However, biomarkers for patient selection remain elusive.

Methods: We generated SCLC PDX models from circulating tumor cells (CTCs), biopsies and malignant effusions. CTCs were enriched with an automated microfluidic device, the CTC-iChip. To assess the genomic fidelity of the models, we performed comparative whole exome sequencing (WES) and RNA-seq on 6 sets of corresponding patient biopsies, founder (P0) PDX tumors, and early-passage PDXs. We then assessed the activity of combination O/T in a panel of PDX models, and compared PDX responses with molecular profiles to identify candidate biomarkers.

Results: 44 PDXs were generated from 32 patients, including 6 sets of serial models and 4 synchronous CTC- and biopsy-derived models. PDXs were derived with high efficiency from both CTCs (35% per blood draw) and biopsies/effusions (82% per implant). WES demonstrated that somatic alterations in tumor biopsies were stably maintained in both CTC and biopsy-derived models, without significant accumulation of new mutations, and transcriptional profiles remained consistent through early passages. Six models were derived from O/T trial patients, including two sets of serial models before and after durable responses. The serial models faithfully recapitulated patient responses to O/T: pre-trial models were highly sensitive and post-relapse were highly resistant. The co-clinical trial was expanded to 30 models, using the models derived from trial patients to delineate the margins of clinical sensitivity (6 models), intermediate sensitivity (6 models) and resistance (18 models). Among the molecular features evaluated, basal protein PARylation best distinguished the O/T-sensitive category from both intermediate (p < 0.001) and resistant models (p < 0.0001). In addition, PARylation decreased after relapse in serial models from O/T trial patients.

Conclusions: Both biopsy- and CTC-derived SCLC PDX models faithfully recapitulate the genomic and functional features of the donor patient tumor. O/T sensitivity in this panel correlated with basal PARylation. The value of the co-clinical trial is the potential to refine the clinical application of O/T in real time, to optimize follow-on clinical trials and to develop biomarker-directed therapy for SCLC.

Citation Format: Benjamin J. Drapkin, Julie George, Marcello Stanzione, Beow Y. Yeap, Mari Mino-Kenudson, Camilla L. Christensen, Ruben Dries, Sarah Phat, Jun Zhong, David T. Myers, Joseph A. Licausi, Tilak Sundaresan, Marina Kem, Nima Abedpour, Leica V. Sequist, Alice T. Shaw, Aaron N. Hata, Mehmet Toner, Shyamala Maheswaran, Daniel A. Haber, Martin Peifer, Roman K. Thomas, Anna F. Farago, Nicholas J. Dyson. Co-clinical trial of olaparib and temozolomide in SCLC PDX models uncovers new biomarkers of sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2972.

Genomic and Functional Fidelity of Small Cell Lung Cancer Patient-Derived Xenografts

Small cell lung cancer (SCLC) patient-derived xenografts (PDX) can be generated from biopsies or circulating tumor cells (CTC), though scarcity of tissue and low efficiency of tumor growth have previously limited these approaches. Applying an established clinical-translational pipeline for tissue collection and an automated microfluidic platform for CTC enrichment, we generated 17 biopsy-derived PDXs and 17 CTC-derived PDXs in a 2-year timeframe, at 89% and 38% efficiency, respectively. Whole-exome sequencing showed that somatic alterations are stably maintained between patient tumors and PDXs. Early-passage PDXs maintain the genomic and transcriptional profiles of the founder PDX. In vivo treatment with etoposide and platinum (EP) in 30 PDX models demonstrated greater sensitivity in PDXs from EP-naïve patients, and resistance to EP corresponded to increased expression of a MYC gene signature. Finally, serial CTC-derived PDXs generated from an individual patient at multiple time points accurately recapitulated the evolving drug sensitivities of that patient's disease. Collectively, this work highlights the translational potential of this strategy.Significance: Effective translational research utilizing SCLC PDX models requires both efficient generation of models from patients and fidelity of those models in representing patient tumor characteristics. We present approaches for efficient generation of PDXs from both biopsies and CTCs, and demonstrate that these models capture the mutational landscape and functional features of the donor tumors. Cancer Discov; 8(5); 600-15. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 517.

Abstract 1007: SHP2 inhibition restores sensitivity to ALK inhibition in resistant ALK-rearranged non-small cell lung cancer (NSCLC)

Despite development of highly potent and selective inhibitors (e.g., ceritinib, alectinib, lorlatinib) targeting anaplastic lymphoma kinase (ALK), resistance invariably develops and limits the efficacy of these inhibitors in the clinic. The major classes of resistance are on-target genetic alterations (e.g., secondary ALK kinase domain mutations) and activation of alternative or bypass signaling pathways. While most patients are responsive to sequential treatment with two or more ALK inhibitors, ALK-independent resistance eventually emerges and leads to failure of further ALK-directed monotherapy. We used a synthetic lethal pooled shRNA screen to discover loss-of-function events that could sensitize resistant patient-derived cell lines to ALK inhibition. In addition to identifying known bypass targets such as FGFR, EGFR and SRC, we also identified PTPN11 (which encodes SHP2, a non-receptor protein tyrosine phosphatase that modulates signaling downstream of growth factor receptors) as a common hit shared by cell lines exhibiting different mechanisms of bypass activation. In parallel with the shRNA screen, we also performed a high throughput combination compound screen in the same patient-derived models, and identified activation of the same bypass signaling pathways. We showed that the highly potent and selective small-molecule SHP2 inhibitor SHP099 could sensitize resistant cell lines to ALK inhibition. In biochemical studies, co-targeting of ALK and SHP2 overcame resistance mediated by ALK-independent bypass mechanisms by decreasing RAS-GTP loading potential of cells and inhibiting phospho-ERK rebound. These results suggest that dual ALK and SHP2 inhibition may represent a new therapeutic strategy for ALK-positive patients, whose lung cancers have evolved ALK-independent mechanisms of resistance, including activation of bypass signaling pathways.

Citation Format: Leila Dardaei, Hui Qin Wang, Paul Fordjour, Manrose Singh, Grainne Kerr, Satoshi Yoda, Jinsheng Liang, Yichen Cao, Yan Chen, Justin F. Gainor, Luc Friboulet, Ibiayi Dagogo-Jack, David T. Myers, Emma Labrot, David Ruddy, Melissa Parks, Dana Lee, Richard H. DiCecca, Susan Moody, Huaixiang Hao, Morvarid Mohseni, Matthew LaMarche, Juliet Williams, Keith Hoffmaster, Giordano Caponigro, Cyril H. Benes, Alice T. Shaw, Aaron N. Hata, Fang Li, Jeffrey A. Engelman. SHP2 inhibition restores sensitivity to ALK inhibition in resistant ALK-rearranged non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1007. doi:10.1158/1538-7445.AM2017-1007

Solid pseudopapillary tumours of the pancreas: spectrum of imaging findings with histopathological correlation

Solid pseudopapillary tumour (SPT) is an uncommon cystic exocrine pancreatic neoplasm. The typical patient is a female in the third decade of life presenting with pain and/or palpable mass. Classic imaging characteristics include large size, mixed solid and cystic nature, encapsulation and haemorrhage. A pancreatic mass with these features in a young adult female should raise suspicion for an SPT. Although typically a non-aggressive neoplasm with surgery curative in most cases, SPT may exhibit more aggressive features such as local invasion, metastases or recurrence in up to 20% of cases.