Donghaecyclinones A-C: New Cytotoxic Rearranged Angucyclinones from a Volcanic Island-Derived Marine Streptomyces sp

Chemical profiling of the Streptomyces sp. strain SUD119, which was isolated from a marine sediment sample collected from a volcanic island in Korea, led to the discovery of three new metabolites: donghaecyclinones A–C (1–3). The structures of 1–3 were found to be rearranged, multicyclic, angucyclinone-class compounds according to nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. The configurations of their stereogenic centers were successfully assigned using a combination of quantum mechanics–based computational methods for calculating the NMR shielding tensor (DP4 and CP3) as well as electronic circular dichroism (ECD) along with a modified version of Mosher’s method. Donghaecyclinones A–C (1–3) displayed cytotoxicity against diverse human cancer cell lines (IC₅₀: 6.7–9.6 μM for 3).

Z-Ajoene Inhibits Growth of Colon Cancer by Promotion of CK1α Dependent β-Catenin Phosphorylation

Aberrant activation of a Wnt/β-catenin pathway results in nuclear accumulation of β-catenin in colon cancer. Inhibiting β-catenin is one strategy for treating colon cancer. Here, we identified Z-ajoene, a sulfur containing compound isolated from crushed garlic, as an inhibitor of colon cancer cell growth. Z-Ajoene repressed β-catenin response transcriptional activity, intracellular β-catenin levels, and its representative target protein levels (c-Myc and cyclin D1) in SW480 colon cancer cells. To clarify the regulatory mechanism of decreased β-catenin levels, we examined the effect of Z-ajoene on β-catenin phosphorylation, which is involved in β-catenin degradation. Z-Ajoene promoted the phosphorylation of β-catenin at Ser45 in a casein kinase 1α (CK1α)-dependent manner, which is an essential step in β-catenin degradation in the cytosol. These findings indicate that Z-ajoene from garlic may be a potential chemotherapeutic agent by modulating CK1α activity and the Wnt/β-catenin signaling pathway.

Prior acquired resistance to paclitaxel relays diverse EGFR-targeted therapy persistence mechanisms

Secondary drug resistance stems from dynamic clonal evolution during the development of a prior primary resistance. This collateral type of resistance is often a characteristic of cancer recurrence. Yet, mechanisms that drive this collateral resistance and their drug-specific trajectories are still poorly understood. Using resistance selection and small-scale pharmacological screens, we find that cancer cells with primary acquired resistance to the microtubule-stabilizing drug paclitaxel often develop tolerance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), leading to formation of more stable resistant cell populations. We show that paclitaxel-resistant cancer cells follow distinct selection paths under EGFR-TKIs by enriching the stemness program, developing a highly glycolytic adaptive stress response, and rewiring an apoptosis control pathway. Collectively, our work demonstrates the alterations in cellular state stemming from paclitaxel failure that result in collateral resistance to EGFR-TKIs and points to new exploitable vulnerabilities during resistance evolution in the second-line treatment setting.

An Ultrasonically Powered Implantable Microprobe for Electrolytic Ablation

Electrolytic ablation (EA) is a promising nonthermal tumor ablation technique that destroys malignant cells through induction of a locoregional pH change. EA is typically performed by inserting needle electrodes inside the tumor followed by application of direct current (DC), thus inducing electrolysis and creating localized pH changes around the electrodes. In this paper, we report an ultrasonically powered implantable EA microprobe that may increase the clinical relevance of EA by allowing wireless control over device operation (capability to remotely turn the device on and off) and providing flexibility in treatment options (easier to administer fractionated doses over a longer period). The wireless EA microprobe consists of a millimeter-sized piezoelectric ultrasonic receiver, a rectifier circuit, and a pair of platinum electrodes (overall size is 9 × 3 × 2 mm³). Once implanted through a minimally invasive procedure, the microprobe can stay within a solid tumor and be repeatedly used as needed. Ultrasonic power allows for efficient power delivery to mm-scale devices implanted deep within soft tissues of the body. The microprobe is capable of producing a direct current of 90 µA at a voltage of 5 V across the electrodes under low-intensity ultrasound (~200 mW/cm²). The DC power creates acidic (pH < 2) and alkaline (pH > 12.9) regions around the anode and the cathode, respectively. The pH change, measured using tissue-mimicking agarose gel, extends to 0.8 cm³ in volume within an hour at an expansion rate of 0.5 mm³/min. The microprobe-mediated EA ablative capability is demonstrated in vitro in cancer cells and ex vivo in mouse liver.

Photoprotective Activity of Topsentin, A Bis(Indole) Alkaloid from the Marine Sponge Spongosorites genitrix, by Regulation of COX-2 and Mir-4485 Expression in UVB-Irradiated Human Keratinocyte Cells

Skin is an important barrier to protect the body from environmental stress. However, exposure to ultraviolet radiation (UV) and various environmental oxidative stresses can cause skin inflammation. Cyclooxygenase-2 (COX-2) is an inducible enzyme that mediates the formation of prostaglandin E2 (PGE2) against internal and external inflammatory stimulations. Therefore, the inhibition of COX-2 is an important approach to maintain skin health and prevent skin inflammation and carcinogenesis. Topsentin, a bis(indolyl)imidazole alkaloid isolated from the marine sponge Spongosorites genitrix, has been reported to exhibit anti-tumor and anti-microbial activities. However, the effect of topsentin on skin inflammation and its underlying molecular mechanism has not been elucidated. In the present study, we identified the photoprotective effects of topsentin on UVB irradiated human epidermal keratinocyte HaCaT cells. Topsentin suppresses COX-2 expression and its upstream signaling pathways, AP-1 and MAPK. Furthermore, topsentin inhibits miR-4485, a new biomarker selected from a microarray, and its target gene tumor necrosis factor alpha induced protein 2 (TNF-α IP2). The photoprotective effect of topsentin was also confirmed in a reconstructed human skin model. These findings suggest that topsentin may serve as a potential candidate for cosmetic formulations with skin inflammatory-mediated disorder.

Antitumor Activity of Ohmyungsamycin A through the Regulation of the Skp2-p27 Axis and MCM4 in Human Colorectal Cancer Cells

Ohmyungsamycin A (1), a novel cyclic peptide discovered from a marine Streptomyces sp., was previously reported with antibacterial and anticancer activities. However, the antitumor activities and the underlying molecular mechanisms of 1 remain to be elucidated. Compound 1 inhibited the proliferation and tumor growth of HCT116 human colorectal cancer cells based on both in vitro cell cultures and an in vivo animal model. A cDNA microarray analysis revealed that 1 downregulated genes involved in cell cycle checkpoint control. Compound 1 also induced G₀/G₁ cell cycle arrest that was mediated by the regulation of S-phase kinase-associated protein 2 (Skp2)-p27 axis and minichromosome maintenance protein 4 (MCM4). Furthermore, a longer exposure of 1 exhibited an accumulation of a sub-G₁ phase cell population, which is characteristic of apoptotic cells. The induction of apoptosis by 1 was also associated with the modulation of caspase family proteins. Compound 1 effectively suppressed tumor growth in a xenograft mouse model subcutaneously implanted with HCT116 cells. In addition, analysis of tumors revealed that 1 upregulated the expression of the CDK inhibitor p27 but downregulated the expression of Skp2 and MCM4. These findings demonstrate the involvement of 1 in cell cycle regulation and the induction of apoptosis in human colorectal cancer cells.

The Antiproliferative Activity of Oxypeucedanin via Induction of G2/M Phase Cell Cycle Arrest and p53-Dependent MDM2/p21 Expression in Human Hepatoma Cells

Oxypeucedanin (OPD), a furocoumarin compound from Angelica dahurica (Umbelliferae), exhibits potential antiproliferative activities in human cancer cells. However, the underlying molecular mechanisms of OPD as an anticancer agent in human hepatocellular cancer cells have not been fully elucidated. Therefore, the present study investigated the antiproliferative effect of OPD in SK-Hep-1 human hepatoma cells. OPD effectively inhibited the growth of SK-Hep-1 cells. Flow cytometric analysis revealed that OPD was able to induce G₂/M phase cell cycle arrest in cells. The G₂/M phase cell cycle arrest by OPD was associated with the downregulation of the checkpoint proteins cyclin B1, cyclin E, cdc2, and cdc25c, and the up-regulation of p-chk1 (Ser345) expression. The growth-inhibitory activity of OPD against hepatoma cells was found to be p53-dependent. The p53-expressing cells (SK-Hep-1 and HepG2) were sensitive, but p53-null cells (Hep3B) were insensitive to the antiproliferative activity of OPD. OPD also activated the expression of p53, and thus leading to the induction of MDM2 and p21, which indicates that the antiproliferative activity of OPD is in part correlated with the modulation of p53 in cancer cells. In addition, the combination of OPD with gemcitabine showed synergistic growth-inhibitory activity in SK-Hep-1 cells. These findings suggest that the anti-proliferative activity of OPD may be highly associated with the induction of G₂/M phase cell cycle arrest and upregulation of the p53/MDM2/p21 axis in SK-HEP-1 hepatoma cells.

Overcoming the Intrinsic Gefitinib-resistance via Downregulation of AXL in Non-small Cell Lung Cancer

Background

Resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib, is a limited factor in the treatment of non-small-cell lung cancer (NSCLC) patients. Therefore, ongoing studies are trying to identify EGFR-TKIs-resistant mechanisms and to discover novel therapeutic strategies and targets for NSCLC treatment.

Methods

In the present study, the possibility of overcoming intrinsic gefitinib-resistance was examined by regulating the expression of AXL. A natural product-derived antitumor agent, yuanhuadine (YD) was employed to modulate the expression of AXL in the cells.

Results

Treatment with YD effectively downregulated AXL expression in AXL-overexpressed gefitinib-resistant H1299 cells. The combination of gefitinib and YD exhibited a synergistic grwoth-inhibitory activity in H1299 cells by downregulation of AXL expression.

Conclusions

Based on these findings, AXL was found to be a promising therapeutic target to overcome the intrinsic resistance to gefitinib in NSCLC. Furthermore, YD is able to effectively regulate the expression of AXL and thus it may be applicable as a potential lead compound for the treatment of gefitinib-resistant NSCLC.

Targeting Histone Methyltransferase DOT1L by a Novel Psammaplin A Analog Inhibits Growth and Metastasis of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most intractable cancer in women with a high risk of metastasis. While hyper-methylation of histone H3 catalyzed by disruptor of telomeric silencing 1-like (DOT1L), a specific methyltransferase for histone H3 at lysine residue 79 (H3K79), is reported as a potential target for TNBCs, early developed nucleoside-type DOT1L inhibitors are not sufficient for effective inhibition of growth and metastasis of TNBC cells. We found that TNBC cells had a high expression level of DOT1L and a low expression level of E-cadherin compared to normal breast epithelial cells and non-TNBC cells. Here, a novel psammaplin A analog (PsA-3091) exhibited a potent inhibitory effect of DOT1L-mediated H3K79 methylation. Consistently, PsA-3091 also significantly inhibited the proliferation, migration, and invasion of TNBC cells along with the augmented expression of E-cadherin and the suppression of N-cadherin, ZEB1, and vimentin expression. In an orthotopic mouse model, PsA-3091 effectively inhibited lung metastasis and tumor growth by the regulation of DOT1L activity and EMT biomarkers. Together, we report here a new template of DOT1L inhibitor and suggest that targeting DOT1L-mediated H3K79 methylation by a novel PsA analog may be a promising strategy for the treatment of metastatic breast cancer patients.

Glechomanamides A-C, Germacrane Sesquiterpenoids with an Unusual Δ8-7,12-Lactam Moiety from Salvia scapiformis and Their Antiangiogenic Activity

Three new germacrane sesquiterpenoid-type alkaloids with an unusual Δ⁸-7,12-lactam moiety, glechomanamides A-C (1-3), and two pairs of 7,12-hemiketal sesquiterpenoid epimers (4a/b, 5a/b) were isolated from Salvia scapiformis. Their structures were elucidated by spectroscopic methods including HRESIMS, IR, UV, and 1D and 2D NMR and also confirmed by single-crystal X-ray diffraction analysis. The chemical transformation of compounds 1-5 in a solution environment was analyzed by 2D NMR spectroscopy. The aza acetallactams (1-3) were stable in organic solvent, while single crystals of the hemiacetal esters (4a/b, 5a/b) underwent a tautomeric equilibrium after being dissolved. Single crystals of 4a, 4b, and 5a were obtained for the first time as their naturally occurring forms. Glechomanamide B (2) exhibited antiangiogenic activity by suppression of vascular endothelial growth factor (VEGF)-induced tube formation through modulation of VEGF receptor 2 (VEGFR2)-mediated signaling pathways in human umbilical vascular endothelial cells (HUVECs). In addition, compound 2 also showed the significant suppression of mRNA expression associated with glycolysis and angiogenesis biomarkers in high glucose (30 mM)-induced HUVECs. These findings suggest that compound 2 might be a potential lead compound candidate for the management of diabetic retinopathy.

Antitumor Activity of Vanicoside B Isolated from Persicaria dissitiflora by Targeting CDK8 in Triple-Negative Breast Cancer Cells

A flavonoid glycoside, quercitrin (1), and two phenylpropanoyl sucrose derivatives, vanicoside B (2) and lapathoside C (3), were isolated for the first time from the herb Persicaria dissitiflora. Vanicoside B (2) exhibited antiproliferative activity against a panel of cancer cell lines in triple-negative breast cancer (TNBC) MDA-MB-231 cells. The underlying mechanisms of the antitumor activity of 2 were investigated in TNBC cells. Upregulation of cyclin-dependent kinase 8 (CDK8) was observed in a claudin-low molecular subtype of TNBC cells. A molecular modeling study indicated that 2 showed a high affinity for CDK8. Further investigations revealed that 2 suppressed CDK8-mediated signaling pathways and the expression of epithelial-mesenchymal transition proteins and induced cell cycle arrest and apoptosis in MDA-MB-231 and HCC38 TNBC cells. Moreover, 2 inhibited tumor growth without overt toxicity in a nude mouse xenograft model implanted with MDA-MB-231 cells. Taken together, these findings demonstrate the significance of CDK8 activity in TNBC and suggest a potential use of 2 as a therapeutic candidate for the treatment of aggressive human triple-negative breast cancer.

The Potential Impacts of Tylophora Alkaloids and their Derivatives in Modulating Inflammation, Viral Infections, and Cancer

Cancer chemotherapies or antitumor agents mainly remain the backbone of current treatment based on killing the rapidly dividing cancer cell such as tylophora alkaloids and their analogues which have also demonstrated anticancer potential through diverse biological pathways including regulation of the immune system. The introduction of durable clinically effective monoclonal antibodies, however, unmasked a new era of cancer immunotherapies. Therefore, the understanding of cancer pathogenesis will provide new possible treatment options, including cancer immunotherapy and targeted agents. Combining cytotoxic agents and immunotherapies may offer several unique advantages that are complementary to and potentially synergistic with biologic modalities. Herein, we highlight the dynamic mechanism of action of immune modulation in cancer and the immunological aspects of the orally active antitumor agents tylophora alkaloids and their analogues. We also suggest that future cancer treatments will rely on the development of combining tumor-targeted agents and biologic immunotherapies.

Abstract 4304: Anti-proliferative activity of nodosin is associated with the regulation of wnt signaling pathway in colon cancer cell

Wnt signaling is a critical mechanism of biological processes, including cell proliferation, tissue homeostasis and development. The aberrant activity of Wnt signaling pathway is highly correlated with the colorectal carcinogenesis. Therefore, the effective compounds targeting Wnt signaling pathway could be applicable for colorectal cancer treatment. The bioactivity of nodosin, a component of Isodon serra, was evaluated in HCT116 colorectal cancer cells. Nodosin exhibited a potential growth inhibition of colon cancer cells. Nodosin also showed an effective inhibition upon wnt/β-catenin reporter gene assay in HEK293 and HCT116 cells. In addition, Wnt target genes such as β-catenin, Axin2, cyclin D1 and survivin were suppressed by nodosin in HCT116 cells. The inhibition of cell proliferation by nodosin was in part associated with the G2/M phase cell cycle arrest in colon cancer cell. These findings suggest that the anti-proliferative activity of nodosin against colorectal cancer cell should be associated with the regulation of Wnt/β-catenin signaling pathway.

This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MEST) (NRF-2016M3A9B6903499).

Citation Format: Eunseo Bae, Donghwa Kim, Woong sub Byun, Sang Kook Lee, Young-Won Chin. Anti-proliferative activity of nodosin is associated with the regulation of wnt signaling pathway in colon cancer cell [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 4304.

Abstract 75: Anti-tumor activity of a novel selenonucleoside via targeting Skp2 degradation in paclitaxel-resistant prostate cancer

Prostate cancer (PC) is the most common disease in men over age 50, and its prevalence rate has been gradually increasing since 1980. Taxane-derived anticancer agents are the primary agents used to treat metastatic prostate cancer patients; however, the side effects and acquired drug resistance limit the success of these therapies. Because there is no specific treatment for paclitaxel-resistant prostate cancer, it is necessary to develop new targets and therapeutic strategies to overcome the acquired resistance. In this study, the antitumor activity of a novel selenonucleoside (4′-selenofuranosyl-2,6-dichloropurine, LJ-2618), a third-generation nucleoside, and its plausible mechanisms of action in paclitaxel-resistant prostate cancer (PC-3-Pa) cells were investigated. The established PC-3-Pa cells exhibited over 100-fold resistance against paclitaxel compared to the paclitaxel-sensitive PC-3 cells. LJ-2618, however, effectively inhibited the proliferation of both cell lines with similar IC50values in vitro. In PC-3-Pa cells, the activated PI3K/Akt signaling pathway was suppressed by LJ-2618 treatment. In addition, Skp2 was found to be over-expressed in paclitaxel-resistant cells, and the transfection of Skp2 siRNA recovered the sensitivity of paclitaxel in PC-3-Pa cells. Furthermore, LJ-2618 significantly down-regulated Skp2 expression in PC-3-Pa cells by promoting degradation and inducing destabilization of Skp2, which triggers G2/M cell cycle arrest. In a xenograft mouse model implanted with PC-3-Pa cells, LJ-2618 (3 or 10 mg/kg) effectively inhibited tumor growth with the enhancement of Skp2 degradation and induction of p27 expression in tumor tissues. These findings suggest that LJ-2618 may have a potential for overcoming paclitaxel resistance via promoting Skp2 degradation and stabilizing p27 expression in PC-3-Pa cells. Therefore, the novel selenonucleoside LJ-2618 may lead to the development of a new treatment strategy for patients with paclitaxel-resistant, castration-resistant prostate cancer. This study was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (NRF-2016M3A9B6903499).

Citation Format: Woong Sub Byun, Minkyung Jin, Jinha Yu, Won Kyung Kim, Lak Shin Jeong, Sang Kook Lee. Anti-tumor activity of a novel selenonucleoside via targeting Skp2 degradation in paclitaxel-resistant prostate cancer [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 75.

Abstract 3584: Role of long noncoding RNA LINC00461 in EGFR-TKIs resistant non-small cell lung cancer

Chemo-resistance is one of the major factors limiting the therapeutic efficacy and prognosis of non-small cell lung cancer (NSCLC) patients, especially with patients who harbor epidermal growth factor receptor (EGFR)-activating mutations. Accumulating evidence suggests that aberrant expression of long noncoding RNAs (lncRNAs) is in part associated with carcinogenesis. Therefore, we tried to identify lncRNAs and their potential target genes in drug-resistant NSCLC. We evaluated lncRNAs with drug-resistant NSCLC using microarray data and in vitro assays. W found that lots of lncRNAs were differentially expressed between the drug-resistant NSCLC cells (HCC827-gef) and its parental (HCC827) cells. Among them, LINC00461 was found to be up-regulated lncRNAs, and highly correlated with the drug resistance. Taken together, the present study provides the expression profiles of chemo-resistant lncRNAs and identifies LINC00461 as a potential biomarker associated with EGFR-TKI resistance in non-small cell lung cancer cells.

This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MEST) (NRF-2016M3A9B6903499).

Citation Format: Ji Yun Lee, Thi-Thu-Trang Luu, Duc-Hiep Bach, Ruoci Hu, Donghwa Kim, Sang Kook Lee. Role of long noncoding RNA LINC00461 in EGFR-TKIs resistant non-small cell lung cancer [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 3584.

Circular RNAs in Cancer

Circular RNAs (circRNAs) are a class of single-stranded closed RNA molecules that are formed by precursor mRNA back-splicing or skipping events of thousands of genes in eukaryotes as covalently closed continuous loops. High-throughput sequencing and bioinformatics approaches have uncovered the broad expression of circRNAs across species. Their high stability, abundance, and evolutionary conservation among species points to their distinct properties and diverse cellular functions as efficient microRNAs and protein sponges; they also play important roles in modulating transcription and splicing. Additionally, most circRNAs are aberrantly expressed in pathological conditions and in a tissue-specific manner such as development and progression of cancer. Herein, we highlight the characteristics, functions, and mechanisms of action of circRNAs in cancer; we also provide an overview of recent progress in the circRNA field and future application of circRNAs as cancer biomarkers and novel therapeutic targets.

Clinical characteristics of pediatric cutaneous lupus erythematosus: experience from a tertiary referral center in Korea

The clinical characteristics of cutaneous lupus erythematosus (CLE) are well delineated in adults, but pediatric data, particularly in Asian populations, are limited. Therefore, we evaluated the characteristics of pediatric cases by retrospectively reviewing the medical records of children with CLE during a 15-year period in a tertiary care dermatology clinic in South Korea. The study included 21 children (8 males and 13 females), 4 of whom had neonatal lupus erythematosus (NLE). Among 17 patients with CLE, discoid lupus erythematosus (DLE) was most common (47.1%), followed by acute CLE (ACLE, 35.3%). All ACLE cases had systemic lupus erythematosus (SLE). Female predominance was conspicuous in ACLE/SLE (6/11 females versus 0/6 males), as was older age, whereas DLE and NLE showed near-equal sex distributions. The median age at the diagnosis of CLE was significantly higher in females than in males (15 years versus 4.5 years, p = 0.02). All patients with ACLE/SLE simultaneously showed skin and systemic symptoms from onset. The kidney was the most commonly involved organ. This study revealed unique characteristics of pediatric CLE, further warranting a comprehensive review among various ethnicities to understand the wide spectrum of CLE in the pediatric population.

Camporidines A and B: Antimetastatic and Anti-inflammatory Polyketide Alkaloids from a Gut Bacterium of Camponotus kiusiuensis

Chemical studies of gut bacteria of the carpenter ant Camponotus kiusiuensis led to the discovery of two new alkaloids, camporidines A and B (1 and 2), from Streptomyces sp. STA1. The structures of 1 and 2 were established as new polyketide alkaloids bearing a piperidine-cyclopentene-epoxide 6/5/3 tricyclic system based on NMR spectroscopic and mass spectrometric analysis. The relative configurations of the camporidines were determined by their ¹H-¹H NOESY/ROESY and 1D NOE NMR correlations. The experimental ECD spectra of 1 and 2 were compared with their calculated ECD spectra to assign their absolute configurations. Camporidine A (1) displayed antimetastatic activity by suppression of cell invasion against the metastatic breast cancer cell line MDA-MB-231 and showed an anti-inflammatory effect by suppressing nitric oxide production induced by lipopolysaccharide. In addition, the putative biosynthetic gene cluster of the camporidines was identified, and the biosynthetic pathway of the camporidines was proposed based on bioinformatic analysis of the full genome of Streptomyces sp. STA1. Camporidines A and B (1 and 2) could be biosynthesized by a modular type I PKS containing an acyl transferase domain that accepts an unusual extender unit, which becomes the (C1'-C6') hexyl side chain. The post-PKS modification enzymes were predicted to perform an amination and an oxidation along with spontaneous Schiff base formation and generate the unique piperidine-cyclopentene-epoxide 6/5/3 tricyclic framework.

Abstract P3-08-12: PIK3CA mutations in breast cancer: Mutational landscape and clinical implications in ER+/HER2- subtype

Introduction: PIK3CA mutation is one of the most frequent genomic alterations in breast cancer. We evaluated PIK3CA mutational status including spatial and temporal heterogeneity, clinical characteristics and prognostic impact focused on ER+/HER2- subtype.

Methods: We performed targeted ultra-deep sequencing (CancerSCAN™) of breast cancer tissue in a prospective cohort. Burden of disease was assessed by metabolic tumor volume(MTV) in 18F-FDG-PET scan. Association with clinical characteristics or survival were tested in ER+/HER2- subtype, using Chi square test or Kaplan-Meier method.

Results: PIK3CA analyses were performed in 1274 breast cancer specimens from 1091 patients. 957 patients had early breast cancer. PIK3CA alterations were found in 397 patients(36.3%), and frequency of PIK3CA mutation was significantly lower in triple negative breast cancer(19.0%), compared with 40.4% in ER+/HER2-, 40.9% in ER+/HER2+, and 45.2% in ER-/HER2+ subtype(p&lt;0.0001). 158 patients had more than two biopsies. Among 92 patients with second biopsy within one month, 11%(10/92) had spatial heterogeneity of PIK3CA mutation. After neoadjuvant chemotherapy, 10%(3/30) of patients had change of PIK3CA mutational status. Serial biopsy at time of recurrence revealed loss or gain of PIK3CA mutation in 10 out of 59 patients (17%). In ER+/HER2- subtype, PIK3CA had a trend toward longer distant disease free survival without statistical significance. In patients with stage IV ER+/HER2- disease, PIK3CA hotspot mutations were associated with significant longer overall survival(OS) (71.0 vs. 37.8 months, p=0.048) and better progression free survival(PFS) at 1st line palliative treatment (37.7 vs. 9.4 months, p = 0.0004). Frequency of symptomatic recurrence, recurrence as oligometastases, and specific metastatic sites were not associated with PIK3CA mutational status, except that bone metastases at first distant metastases was less prevalent in patients with PIK3CA hotspot mutations(35.6% vs. 53.8% in PIK3CA wt, p=0.048). Metabolic tumor volume(MTV) at time of first distant metastases was not associated with presence of PIK3CA mutation.

Conclusion: We observed variations in PIK3CA mutational status in more than 10% of patients with &gt;1 repeated biopsy. In stage IV ER+/HER2- disease, PIK3CA hotspot mutation seemed to be associated with longer PFS and OS, however metabolic tumor burden was not associated with PIK3CA alterations.

Citation Format: Ahn HK, Park S, Hyun SH, Park K, Lee E, Kim J-Y, Nam SJ, Kim SW, Lee JE, Lee SK, Yu JH, Ahn JS, Im Y-H, Park YH. PIK3CA mutations in breast cancer: Mutational landscape and clinical implications in ER+/HER2- subtype [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-08-12.

Abstract P1-09-11: Prognostication of genetic alterations of ESR 1 in estrogen receptor positive metastatic breast cancers using targeted ultra-deep sequencing data analysis

Introduction: Genetic alteration of Estrogen Receptor 1(ESR1) gene have been associated with acquired endocrine resistance and occurred in about 20% of endocrine resistant estrogen receptor(ER)-positive metastatic breast cancer(MBC). Mutations in ligand binding domain of ESR1 lead to constitutive activity of the ER without ligand estrogen and stimulated down stream cell growth signal. Therefore, ESR1 ligand binding domain alteration is known resistant mechanism of aromatase inhibitor. Among these ESR1 mutations, Y537S, one of the ligand binding domain mutations, caused ER antagonist, fulvestrant resistance. Therefore, assessment of ESR1 mutation in ER-positive MBC had significant benefit to further precision medicine for MBCs. In this study, we explored to identify the frequency and type of ESR1 genetic alterations of ER-positive MBC.

Methods: We performed targeted ultra-deep sequencing (CancerSCAN™) using BC tissue specimens. This sequencing was covered entire coding area of ESR1 gene and also detected copy number alteration and translocation of ESR1.

Results: Targeted ultra-deep sequencing of ESR1 was performed using 990 BC tissues. Of 990 tissue samples, 341(34.5%) were MBCs. Of MBCs, 112(11.3%) were ER-positive and human epidermal growth factor receptor 2(HER2)-negative BCs. In ER-positive HER2-negative MBCs (N=112), 21 ESR1 genetic alterations were identified in 19 BCs (17.0%). Nineteen were single nucleotide variats (SNVs) and three were copy number (CN) amplification. Most commonly detected single nucleotide variant (SNV) was D538G (6 of 19, 31.6%) followed by Y537N, Y537S, V382I (4, 2 and 2 cases, respectively). Three mutations occurred in non-ligand binding domain (G415V, V392I and P79A). Two BC samples harbored two ESR1 mutations, respectively (Y537S and D538G, L536P and Y537N). In terms of treatment, 11 of 12 patients with ER-positive MBC harboring ESR1 mutation received palliative endocrine therapies. Eight patients received aromatase inhibitor and two patients received tamoxifen. One patient received letrozole plus palbociclib. In 2 MBCs with Y537S mutation, progression free survival (PFS) of endocrine therapy was 1.4 and 5.3 months. MBCs with D538G had 12.3months of PFS (range, 5.3-23.7(months)) and BCs harboring another ligand binding domain mutations (Y537N, L536H and L536P) had 15.7months of PFS of endocrine therapy (range, 8.4-17.3(months)). BC with mutation observed in non-lignand binding domain had short PFS (1.8 (V392I) and 2.7 (P79A) months, respectively). In terms of ESR1 CN amplification, patients could not receive endocrine therapy because their BCs rapidly progressed and extensive distant metastases were occurred within 3 months after curative surgery.

Conclusion: In this exploratory study, ESR1 genetic alterations were detected in about 20% of ER-positive MBC. The type of genetic alterations varied including SNVs, CNAs. Each locus of ESR1 mutation predicted endocrine resistance. In addition, we might suggest that ESR1 CN amplification is prognostic marker of ER-positive BCs.

Citation Format: Kim J-Y, Park KH, Park W-Y, Nam SJ, Kim SW, Lee JE, Lee SK, Yu JH, Ahn JS, Im Y-H, Park YH. Prognostication of genetic alterations of ESR 1 in estrogen receptor positive metastatic breast cancers using targeted ultra-deep sequencing data analysis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-09-11.