Heterogeneous Profile of ROR1 Protein Expression across Tumor Types.

The Wnt receptor ROR1 has generated increased interest as a cancer therapeutic target. Research on several therapeutic approaches involving this receptor is ongoing; however, ROR1 tissue expression remains understudied. We performed an immunohistochemistry analysis of ROR1 protein expression in a large cohort of multiple tumor and histologic types. We analyzed 12 anonymized multi-tumor tissue microarrays (TMAs), including mesothelioma, esophageal and upper gastrointestinal carcinomas, and uterine endometrioid carcinoma, among other tumor types. Additionally, we studied 5 different sarcoma types of TMAs and 6 patient-derived xenografts (PDX) TMAs developed from 19 different anatomic sites and tumor histologic types. A total of 1142 patient cases from different histologic types and 140 PDXs placed in TMAs were evaluated. Pathologists assessed the percentage of tumor cells in each case that were positive for ROR1 and the intensity of staining. For determining the prevalence of staining for each tumor type, a case was considered positive if >1% of its tumor cells showed ROR1 staining. Our immunohistochemistry assays revealed a heterogeneous ROR1 expression profile. A high prevalence of ROR1 expression was found in mesothelioma (84.6%), liposarcoma (36.1%), gastrointestinal stromal tumors (33.3%), and uterine endometrioid carcinoma (28.9%). Other histologic types such as breast, lung, renal cell, hepatocellular, urothelial carcinoma, and colon carcinomas; glioblastoma; cholangiocarcinoma; and leiomyosarcoma showed less ROR1 overall expression, ranging between 0.9 and 13%. No ROR1 expression was seen in mesenchymal chondrosarcoma, rhabdomyosarcoma, or gastric adenocarcinoma cases. Overall, ROR1 expression was relatively infrequent and low in most tumor types investigated; however, ROR1 expression was infrequent but high in selected tumor types, such as gastroesophageal GIST, suggesting that ROR1 prescreening may be preferable for those indications. Further, mesothelioma exhibited frequent and high levels of ROR1 expression, which represents a previously unrecognized therapeutic opportunity. These findings can contribute to the development of ROR1-targeted therapies.

Co-clinical Trial of Novel Bispecific Anti-HER2 Antibody Zanidatamab in Patient-Derived Xenografts.

Zanidatamab is a bispecific human epidermal growth factor receptor 2 (HER2)-targeted antibody that has demonstrated antitumor activity in a broad range of HER2-amplified/expressing solid tumors. We determined the antitumor activity of zanidatamab in patient-derived xenograft (PDX) models developed from pretreatment or postprogression biopsies on the first-in-human zanidatamab phase I study (NCT02892123). Of 36 tumors implanted, 19 PDX models were established (52.7% take rate) from 17 patients. Established PDXs represented a broad range of HER2-expressing cancers, and in vivo testing demonstrated an association between antitumor activity in PDXs and matched patients in 7 of 8 co-clinical models tested. We also identified amplification of MET as a potential mechanism of acquired resistance to zanidatamab and demonstrated that MET inhibitors have single-agent activity and can enhance zanidatamab activity in vitro and in vivo. These findings provide evidence that PDXs can be developed from pretreatment biopsies in clinical trials and may provide insight into mechanisms of resistance. SIGNIFICANCE: We demonstrate that PDXs can be developed from pretreatment and postprogression biopsies in clinical trials and may represent a powerful preclinical tool. We identified amplification of MET as a potential mechanism of acquired resistance to the HER2 inhibitor zanidatamab and MET inhibitors alone and in combination as a therapeutic strategy. This article is featured in Selected Articles from This Issue, p. 695.

Efficacy of futibatinib, an irreversible fibroblast growth factor receptor inhibitor, in FGFR-altered breast cancer.

Several alterations in fibroblast growth factor receptor (FGFR) genes have been found in breast cancer; however, they have not been well characterized as therapeutic targets. Futibatinib (TAS-120; Taiho) is a novel, selective, pan-FGFR inhibitor that inhibits FGFR1-4 at nanomolar concentrations. We sought to determine futibatinib's efficacy in breast cancer models. Nine breast cancer patient-derived xenografts (PDXs) with various FGFR1-4 alterations and expression levels were treated with futibatinib. Antitumor efficacy was evaluated by change in tumor volume and time to tumor doubling. Alterations indicating sensitization to futibatinib in vivo were further characterized in vitro. FGFR gene expression between patient tumors and matching PDXs was significantly correlated; however, overall PDXs had higher FGFR3-4 expression. Futibatinib inhibited tumor growth in 3 of 9 PDXs, with tumor stabilization in an FGFR2-amplified model and prolonged regression (> 110 days) in an FGFR2 Y375C mutant/amplified model. FGFR2 overexpression and, to a greater extent, FGFR2 Y375C expression in MCF10A cells enhanced cell growth and sensitivity to futibatinib. Per institutional and public databases, FGFR2 mutations and amplifications had a population frequency of 1.1%-2.6% and 1.5%-2.5%, respectively, in breast cancer patients. FGFR2 alterations in breast cancer may represent infrequent but highly promising targets for futibatinib.

Epigenetically upregulating TROP2 and SLFN11 enhances therapeutic efficacy of TROP2 antibody drug conjugate sacitizumab govitecan.

TROP2 antibody drug conjugates (ADCs) are under active development. We seek to determine whether we can enhance activity of TROP2 ADCs by increasing TROP2 expression. In metaplastic breast cancers (MpBC), there is limited expression of TROP2, and downregulating transcription factor ZEB1 upregulates E-cad and TROP2, thus sensitizing cancers to TROP2 ADC sacituzumab govitecan (SG). Demethylating agent decitabine decreases DNA methyltransferase expression and TROP2 promoter methylation and subsequently increases TROP2 expression. Decitabine treatment as well as overexpression of TROP2 significantly enhance SG antitumor activity. Decitabine also increases SLFN11, a biomarker of topoisomerase 1 inhibitor (TOP1) sensitivity and is synergistic with SG which has a TOP1 payload, in TROP2-expressing SLFN11-low BC cells. In conclusion, TROP2 and SLFN11 expression can be epigenetically modulated and the combination of demethylating agent decitabine with TROP2 ADCs may represent a novel therapeutic approach for tumors with low TROP2 or SLFN11 expression.

Combined MEK/MDM2 inhibition demonstrates antitumor efficacy in TP53 wild-type thyroid and colorectal cancers with MAPK alterations.

Most tumors with activating MAPK (mitogen-activated protein kinase) pathway alterations respond poorly to MEK inhibitors alone. Here, we evaluated combination therapy with MEK inhibitor selumetinib and MDM2 inhibitor KRT-232 in TP53 wild-type and MAPK altered colon and thyroid cancer models. In vitro, we showed synergy between selumetinib and KRT-232 on cell proliferation and colony formation assays. Immunoblotting confirmed p53 upregulation and MEK pathway inhibition. The combination was tested in vivo in seven patient-derived xenograft (PDX) models (five colorectal carcinoma and two papillary thyroid carcinoma models) with different KRAS, BRAF, and NRAS mutations. Combination therapy significantly prolonged event-free survival compared with monotherapy in six of seven models tested. Reverse-phase protein arrays and immunohistochemistry, respectively, demonstrated upregulation of the p53 pathway and in two models cleaved caspase 3 with combination therapy. In summary, combined inhibition of MEK and MDM2 upregulated p53 expression, inhibited MAPK signaling and demonstrated greater antitumor efficacy than single drug therapy in both in vitro and in vivo settings. These findings support further clinical testing of the MEK/MDM2 inhibitor combination in tumors of epithelial origin with MAPK pathway alterations.

RAC1 Alterations Induce Acquired Dabrafenib Resistance in Association with Anaplastic Transformation in a Papillary Thyroid Cancer Patient.

BRAF-activating mutations are the most frequent driver mutations in papillary thyroid cancer (PTC). Targeted inhibitors such as dabrafenib have been used in advanced BRAF-mutated PTC; however, acquired resistance to the drug is common and little is known about other effectors that may play integral roles in this resistance. In addition, the induction of PTC dedifferentiation into highly aggressive KRAS-driven anaplastic thyroid cancer (ATC) has been reported. We detected a novel RAC1 (P34R) mutation acquired during dabrafenib treatment in a progressive metastatic lesion with ATC phenotype. To identify a potential functional link between this novel mutation and tumor dedifferentiation, we developed a cell line derived from the metastatic lesion and compared its behavior to isogenic cell lines and primary tumor samples. Our data demonstrated that RAC1 mutations induce changes in cell morphology, reorganization of F-actin almost exclusively at the cell cortex, and changes in cell adhesion properties. We also established that RAC1 amplification, with or without mutation, is sufficient to drive cell proliferation and resistance to BRAF inhibition. Further, we identified polyploidy of chromosome 7, which harbors RAC1, in both the metastatic lesion and its derived cell line. Copy number amplification and overexpression of other genes located on this chromosome, such as TWIST1, EGFR, and MET were also detected, which might also lead to dabrafenib resistance. Our study suggests that polyploidy leading to increased expression of specific genes, particularly those located on chromosome 7, should be considered when analyzing aggressive thyroid tumor samples and in further treatments.

Oxidative Phosphorylation Is a Metabolic Vulnerability in Chemotherapy-Resistant Triple-Negative Breast Cancer.

Oxidative phosphorylation (OXPHOS) is an active metabolic pathway in many cancers. RNA from pretreatment biopsies from patients with triple-negative breast cancer (TNBC) who received neoadjuvant chemotherapy demonstrated that the top canonical pathway associated with worse outcome was higher expression of OXPHOS signature. IACS-10759, a novel inhibitor of OXPHOS, stabilized growth in multiple TNBC patient-derived xenografts (PDX). On gene expression profiling, all of the sensitive models displayed a basal-like 1 TNBC subtype. Expression of mitochondrial genes was significantly higher in sensitive PDXs. An in vivo functional genomics screen to identify synthetic lethal targets in tumors treated with IACS-10759 found several potential targets, including CDK4. We validated the antitumor efficacy of the combination of palbociclib, a CDK4/6 inhibitor, and IACS-10759 in vitro and in vivo. In addition, the combination of IACS-10759 and multikinase inhibitor cabozantinib had improved antitumor efficacy. Taken together, our data suggest that OXPHOS is a metabolic vulnerability in TNBC that may be leveraged with novel therapeutics in combination regimens. SIGNIFICANCE: These findings suggest that triple-negative breast cancer is highly reliant on OXPHOS and that inhibiting OXPHOS may be a novel approach to enhance efficacy of several targeted therapies.

Genomic, Transcriptomic, and Proteomic Profiling of Metastatic Breast Cancer.

PURPOSE: Metastatic breast cancer (MBC) is not curable and there is a growing interest in personalized therapy options. Here we report molecular profiling of MBC focusing on molecular evolution in actionable alterations. EXPERIMENTAL DESIGN: Sixty-two patients with MBC were included. An analysis of DNA, RNA, and functional proteomics was done, and matched primary and metastatic tumors were compared when feasible. RESULTS: Targeted exome sequencing of 41 tumors identified common alterations in TP53 (21; 51%) and PIK3CA (20; 49%), as well as alterations in several emerging biomarkers such as NF1 mutations/deletions (6; 15%), PTEN mutations (4; 10%), and ARID1A mutations/deletions (6; 15%). Among 27 hormone receptor-positive patients, we identified MDM2 amplifications (3; 11%), FGFR1 amplifications (5; 19%), ATM mutations (2; 7%), and ESR1 mutations (4; 15%). In 10 patients with matched primary and metastatic tumors that underwent targeted exome sequencing, discordances in actionable alterations were common, including NF1 loss in 3 patients, loss of PIK3CA mutation in 1 patient, and acquired ESR1 mutations in 3 patients. RNA sequencing in matched samples confirmed loss of NF1 expression with genomic NF1 loss. Among 33 patients with matched primary and metastatic samples that underwent RNA profiling, 14 actionable genes were differentially expressed, including antibody-drug conjugate targets LIV-1 and B7-H3. CONCLUSIONS: Molecular profiling in MBC reveals multiple common as well as less frequent but potentially actionable alterations. Genomic and transcriptional profiling demonstrates intertumoral heterogeneity and potential evolution of actionable targets with tumor progression. Further work is needed to optimize testing and integrated analysis for treatment selection.

First in class dual MDM2/MDMX inhibitor ALRN-6924 enhances antitumor efficacy of chemotherapy in TP53 wild-type hormone receptor-positive breast cancer models.

BACKGROUND: MDM2/MDMX proteins are frequently elevated in hormone receptor-positive (ER+) breast cancer. We sought to determine the antitumor efficacy of the combination of ALRN-6924, a dual inhibitor of MDM2/MDMX, with chemotherapy in ER+ breast cancer models. METHODS: Three hundred two cell lines representing multiple tumor types were screened to confirm the role of TP53 status in ALRN-6924 efficacy. ER+ breast cancer cell lines (MCF-7 and ZR-75-1) were used to investigate the antitumor efficacy of ALRN-6924 combination. In vitro cell proliferation, cell cycle, and apoptosis assays were performed. Xenograft tumor volumes were measured, and reverse-phase protein array (RPPA), immunohistochemistry (IHC), and TUNEL assay of tumor tissues were performed to evaluate the in vivo pharmacodynamic effects of ALRN-6924 with paclitaxel. RESULTS: ALRN-6924 was active in wild-type TP53 (WT-TP53) cancer cell lines, but not mutant TP53. On ER+ breast cancer cell lines, it was synergistic in vitro and had enhanced in vivo antitumor activity with both paclitaxel and eribulin. Flow cytometry revealed signs of mitotic crisis in all treatment groups; however, S phase was only decreased in MCF-7 single agent and combinatorial ALRN-6924 arms. RPPA and IHC demonstrated an increase in p21 expression in both combinatorial and single agent ALRN-6924 in vivo treatment groups. Apoptotic assays revealed a significantly enhanced in vivo apoptotic rate in ALRN-6924 combined with paclitaxel treatment arm compared to either single agent. CONCLUSION: The significant synergy observed with ALRN-6924 in combination with chemotherapeutic agents supports further evaluation in patients with hormone receptor-positive breast cancer.

Targeting PI3Kß alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss.

Background: PTEN-deficient tumors are dependent on PI3Kß activity, making PI3Kß a compelling target. We evaluated the efficacy of PI3Kß inhibitor AZD8186 on tumors with PTEN loss. Results: In vitro cell viability assay and immunoblotting demonstrated that PTEN loss was significantly correlated with AZD8186 sensitivity in triple negative breast cancer (TNBC) cell lines. Colony formation assay confirmed sensitivity of PTEN-deficient cell lines to AZD8186. AZD8186 inhibited PI3K signaling in PTEN loss TNBC cells. AZD8186 in combination with paclitaxel, eribulin had synergistic effects on growth inhibition in PTEN loss cells. AZD8186 promoted apoptosis in PTEN loss cells which was synergized by paclitaxel. In vivo, AZD8186 had limited activity as a single agent, but enhanced antitumor activity when combined with paclitaxel in MDA-MB-436 and MDA-MB-468 cell-line xenografts. AZD8186 significantly enhanced antitumor efficacy of anti-PD1 antibodies in the PTEN-deficient BP murine melanoma xenograft model, but not in the PTEN-wild-type CT26 xenograft model. Methods: In vitro, cell proliferation and colony formation assays were performed to determine cell sensitivity to AZD8186. Immunoblotting was performed to assess PTEN expression and PI3K signaling activity. FACS was performed to evaluate apoptosis. In vivo, antitumor efficacy of AZD8186 and its combinations were evaluated. Conclusions: AZD8186 has single agent efficacy in PTEN-deficient TNBC cell lines in vitro, but has limited single agent efficacy in vivo. However, AZD8186 has enhanced efficacy when combined with paclitaxel and anti-PD1 in vivo. Further study is needed to determine optimal combination therapies for PTEN-deficient solid tumors.

TAK228 enhances antitumor activity of eribulin in triple negative breast cancer.

Background: Phosphatase and tensin homologue deleted from chromosome 10 (PTEN) negatively regulates the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway. Triple negative breast cancers (TNBC) are often PTEN-deficient, making mTOR a compelling target. We evaluated the efficacy of catalytic mTOR inhibitor TAK228 alone and in combination with eribulin in TNBC. Results: Five of eight triple negative breast cell lines were sensitive to TAK228, independent of PIK3CA/PTEN status. Western blotting demonstrated inhibition of mTORC1/2 signaling as demonstrated by decreased phospho-AKT, phospho-S6 and phospho-4EBP1. In vitro, TAK228 was synergistic with eribulin in all eight TNBC cell lines. The combination of TAK228 and eribulin did not enhance apoptosis but increased G2/M growth arrest. In vivo, TAK228 led to modest growth inhibition in TNBC patient-derived xenografts (PDXs) with no tumor regression observed. In two TNBC PDXs with PTEN loss, one with intrinsic eribulin sensitivity, another eribulin resistance, TAK228 in combination with eribulin did not enhance in vivo efficacy. In a third PTEN-negative TNBC model, eribulin alone achieved disease stabilization, but the combination of TAK228 and eribulin led to significantly smaller tumor volumes compared to eribulin alone (p < 0.001). Methods: We tested in vitro efficacy of TAK228 in a panel of TNBC cell lines with cell proliferation assays. In vivo antitumor efficacy of TAK228 was evaluated alone and in combination with eribulin. Conclusion: TAK228 enhances the antitumor efficacy of eribulin in TNBC models in vitro, and enhanced in vivo activity in selected models. Further study is needed to determine the potential of this combination, and optimal patient selection strategies.

Phase II trial of AKT inhibitor MK-2206 in patients with advanced breast cancer who have tumors with PIK3CA or AKT mutations, and/or PTEN loss/PTEN mutation.

BACKGROUND: The PI3K/AKT pathway is activated through PIK3CA or AKT1 mutations and PTEN loss in breast cancer. We conducted a phase II trial with an allosteric AKT inhibitor MK-2206 in patients with advanced breast cancer who had tumors with PIK3CA/AKT1 mutations and/or PTEN loss/mutation. METHODS: The primary endpoint was objective response rate (ORR). Secondary endpoints were 6-month progression-free survival (6 m PFS), predictive and pharmacodynamic markers, safety, and tolerability. Patients had pre-treatment and on-treatment biopsies as well as collection of peripheral blood mononuclear cells (PBMC) and platelet-rich plasma (PRP). Next-generation sequencing, immunohistochemistry, and reverse phase protein arrays (RPPA) were performed. RESULTS: Twenty-seven patients received MK-2206. Eighteen patients were enrolled into the PIK3CA/AKT1 mutation arm (cohort A): 13 had PIK3CA mutations, four had AKT1 mutations, and one had a PIK3CA mutation as well as PTEN loss. ORR and 6 m PFS were both 5.6% (1/18), with one patient with HR+ breast cancer and a PIK3CA E542K mutation experiencing a partial response (on treatment for 36 weeks). Nine patients were enrolled on the PTEN loss/mutation arm (cohort B). ORR was 0% and 6 m PFS was 11% (1/9), observed in a patient with triple-negative breast cancer and PTEN loss. The study was stopped early due to futility. The most common adverse events were fatigue (48%) and rash (44%). On pre-treatment biopsy, PIK3CA and AKT1 mutation status was concordant with archival tissue testing. However, two patients with PTEN loss based on archival testing had PTEN expression on the pre-treatment biopsy. MK-2206 treatment was associated with a significant decline in pAKT S473 and pAKT T308 and PI3K activation score in PBMC and PRPs, but not in tumor biopsies. By IHC, there was no significant decrease in median pAKT S473 or Ki-67 staining, but a drop was observed in both responders. CONCLUSIONS: MK-2206 monotherapy had limited clinical activity in advanced breast cancer patients selected for PIK3CA/AKT1 or PTEN mutations or PTEN loss. This may, in part, be due to inadequate target inhibition at tolerable doses in heavily pre-treated patients with pathway activation, as well as tumor heterogeneity and evolution in markers such as PTEN conferring challenges in patient selection. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01277757 . Registered 13 January 2011.

A Population of Heterogeneous Breast Cancer Patient-Derived Xenografts Demonstrate Broad Activity of PARP Inhibitor in BRCA1/2 Wild-Type Tumors.

Background: Breast cancer patients who do not respond to neoadjuvant therapy have a poor prognosis. There is a pressing need for novel targets and models for preclinical testing. Here we report characterization of breast cancer patient-derived xenografts (PDX) largely generated from residual tumors following neoadjuvant chemotherapy.Experimental Design: PDXs were derived from surgical samples of primary or locally recurrent tumors. Normal and tumor DNA sequencing, RNASeq, and reverse phase protein arrays (RPPA) were performed. Phenotypic profiling was performed by determining efficacy of a panel of standard and investigational agents.Results: Twenty-six PDXs were developed from 25 patients. Twenty-two were generated from residual disease following neoadjuvant chemotherapy, and 24 were from triple-negative breast cancer (TNBC). These PDXs harbored a heterogeneous set of genomic alterations and represented all TNBC molecular subtypes. On RPPA, PDXs varied in extent of PI3K and MAPK activation. PDXs also varied in their sensitivity to chemotherapeutic agents. PI3K, mTOR, and MEK inhibitors repressed growth but did not cause tumor regression. The PARP inhibitor talazoparib caused dramatic regression in five of 12 PDXs. Notably, four of five talazoparib-sensitive models did not harbor germline BRCA1/2 mutations, but several had somatic alterations in homologous repair pathways, including ATM deletion and BRCA2 alterations.Conclusions: PDXs capture the molecular and phenotypic heterogeneity of TNBC. Here we show that PARP inhibition can have activity beyond germline BRCA1/2 altered tumors, causing regression in a variety of molecular subtypes. These models represent an opportunity for the discovery of rational combinations with targeted therapies and predictive biomarkers. Clin Cancer Res; 23(21); 6468-77. ©2017 AACR.

Selinexor (KPT-330) demonstrates anti-tumor efficacy in preclinical models of triple-negative breast cancer.

BACKGROUND: Selinexor (KPT-330) is an oral agent that has been shown to inhibit the nuclear exporter XPO1. Given the pressing need for novel therapies for triple-negative breast cancer (TNBC), we sought to determine the antitumor effects of selinexor in vitro and in vivo. METHODS: Twenty-six breast cancer cell lines of different breast cancer subtypes were treated with selinexor in vitro. Cell proliferation assays were used to measure the half-maximal inhibitory concentration (IC50) and to test the effects in combination with chemotherapy. In vivo efficacy was tested both as a single agent and in combination therapy in TNBC patient-derived xenografts (PDXs). RESULTS: Selinexor demonstrated growth inhibition in all 14 TNBC cell lines tested; TNBC cell lines were more sensitive to selinexor (median IC50 44 nM, range 11 to 550 nM) than were estrogen receptor (ER)-positive breast cancer cell lines (median IC50 > 1000 nM, range 40 to >1000 nM; P = 0.017). In multiple TNBC cell lines, selinexor was synergistic with paclitaxel, carboplatin, eribulin, and doxorubicin in vitro. Selinexor as a single agent reduced tumor growth in vivo in four of five different TNBC PDX models, with a median tumor growth inhibition ratio (T/C: treatment/control) of 42% (range 31 to 73%) and demonstrated greater antitumor efficacy in combination with paclitaxel or eribulin (average T/C ratios of 27% and 12%, respectively). CONCLUSIONS: Collectively, these findings strongly suggest that selinexor is a promising therapeutic agent for TNBC as a single agent and in combination with standard chemotherapy.

Ability to Generate Patient-Derived Breast Cancer Xenografts Is Enhanced in Chemoresistant Disease and Predicts Poor Patient Outcomes.

BACKGROUND: Breast cancer patients who are resistant to neoadjuvant chemotherapy (NeoCT) have a poor prognosis. There is a pressing need to develop in vivo models of chemo resistant tumors to test novel therapeutics. We hypothesized that patient-derived breast cancer xenografts (BCXs) from chemo- naïve and chemotherapy-exposed tumors can provide high fidelity in vivo models for chemoresistant breast cancers. METHODS: Patient tumors and BCXs were characterized with short tandem repeat DNA fingerprinting, reverse phase protein arrays, molecular inversion probe arrays, and next generation sequencing. RESULTS: Forty-eight breast cancers (24 post-chemotherapy, 24 chemo-naïve) were implanted and 13 BCXs were established (27%). BCX engraftment was higher in TNBC compared to hormone-receptor positive cancer (53.8% vs. 15.6%, p = 0.02), in tumors from patients who received NeoCT (41.7% vs. 8.3%, p = 0.02), and in patients who had progressive disease on NeoCT (85.7% vs. 29.4%, p = 0.02). Twelve patients developed metastases after surgery; in five, BCXs developed before distant relapse. Patients whose tumors developed BCXs had a lower recurrence-free survival (p = 0.015) and overall survival (p<0.001). Genomic losses and gains could be detected in the BCX, and three models demonstrated a transformation to induce mouse tumors. However, overall, somatic mutation profiles including potential drivers were maintained upon implantation and serial passaging. One BCX model was cultured in vitro and re-implanted, maintaining its genomic profile. CONCLUSIONS: BCXs can be established from clinically aggressive breast cancers, especially in TNBC patients with poor response to NeoCT. Future studies will determine the potential of in vivo models for identification of genotype-phenotype correlations and individualization of treatment.

Epithelial to mesenchymal transition is associated with rapamycin resistance.

Rapamycin analogues have antitumor efficacy in several tumor types, however few patients demonstrate tumor regression. Thus, there is a pressing need for markers of intrinsic response/resistance and rational combination therapies. We hypothesized that epithelial-to-mesenchymal transition (EMT) confers rapamycin resistance. We found that the epithelial marker E-cadherin protein is higher in rapamycin sensitive (RS) cells and mesenchymal breast cancer cell lines selected by transcriptional EMT signatures are less sensitive to rapamycin. MCF7 cells, transfected with constitutively active mutant Snail, had increased rapamycin resistance (RR) compared to cells transfected with wild-type Snail. Conversely, we transfected two RR mesenchymal cell lines-ACHN and MDA-MB-231-with miR-200b/c or ZEB1 siRNA to promote mesenchymal-to-epithelial transition. This induced E-cadherin expression in both cell lines, and ACHN demonstrated a significant increase in RS. Treatment of ACHN and MDA-MB-231 with trametinib modulated EMT in ACHN cells in vitro. Treatment of MDA-MB-231 and ACHN xenografts with trametinib in combination with rapamycin resulted in significant growth inhibition in both but without an apparent effect on EMT. Future studies are needed to determine whether EMT status is predictive of sensitivity to rapalogs and to determine whether combination therapy with EMT modulating agents can enhance antitumor effects of PI3K/mTOR inhibitors.

SU2C phase Ib study of paclitaxel and MK-2206 in advanced solid tumors and metastatic breast cancer.

BACKGROUND: There is preclinical synergism between taxanes and MK-2206. We aim to determine the maximum tolerated dose, safety, and activity of combining MK-2206 and paclitaxel in metastatic cancer. METHODS: Patients received weekly doses of paclitaxel at 80mg/m2 on day 1, followed by MK-2206 orally on day 2 escalated at 90mg, 135mg, and 200mg. Treatment continued until progression, excessive toxicity, or patient request. Blood and tissue were collected for pharmacokinetic and pharmacodynamics markers. A cycle consisted of three weeks of therapy. Dose-limiting toxicity (DLT) was defined as unacceptable toxicity during the first cycle. All statistical tests were two-sided. RESULTS: Twenty-two patients were treated, nine in dose escalation and 13 in dose expansion. Median age was 55 years. Median number of cycles was four. Dose escalation was completed with no DLT. CTCAE Grade 3 or higher adverse events were fatigue (n = 2), rash (n = 2), hyperglycemia (n = 1), and neutropenia (n = 7). Four patients in the expansion phase required MK-2206 dose reduction. Phase II recommended dose was established as paclitaxel 80mg/m2 weekly on day 1, and MK-2206 135mg weekly on day 2. Paclitaxel systemic exposure was similar in the presence or absence of MK-2206. Plasma MK-2206 concentrations were similar to data from previous phase I monotherapy. There was a statistically significant decrease in expression of pAKT S473 (P = .01) and pAKT T308 (P = .002) after therapy. PI3K/AKT/mTOR downregulation in tumor tissues and circulating markers did not correlate with tumor response or clinical benefit. There were five objective responses, and nine patients had stable disease. CONCLUSION: MK-2206 was well tolerated with paclitaxel. Preliminary antitumor activity was documented.

Catalytic mTOR inhibitors can overcome intrinsic and acquired resistance to allosteric mTOR inhibitors.

We tested the antitumor efficacy of mTOR catalytic site inhibitor MLN0128 in models with intrinsic or acquired rapamycin-resistance. Cell lines that were intrinsically rapamycin-resistant as well as those that were intrinsically rapamycin-sensitive were sensitive to MLN0128 in vitro. MLN0128 inhibited both mTORC1 and mTORC2 signaling, with more robust inhibition of downstream 4E-BP1 phosphorylation and cap-dependent translation compared to rapamycin in vitro. Rapamycin-sensitive BT474 cell line acquired rapamycin resistance (BT474 RR) with prolonged rapamycin treatment in vitro. This cell line acquired an mTOR mutation (S2035F) in the FKBP12-rapamycin binding domain; mTORC1 signaling was not inhibited by rapalogs but was inhibited by MLN0128. In BT474 RR cells, MLN0128 had significantly higher growth inhibition compared to rapamycin in vitro and in vivo. Our results demonstrate that MLN0128 may be effective in tumors with intrinsic as well as acquired rapalog resistance. mTOR mutations are a mechanism of acquired resistance in vitro; the clinical relevance of this observation needs to be further evaluated.