Overall survival in patients with hormone receptor-positive, HER2-negative, advanced or metastatic breast cancer treated with a cyclin-dependent kinase 4/6 inhibitor plus fulvestrant: a US Food and Drug Administration pooled analysis.

BACKGROUND: Cyclin-dependent kinase 4/6 inhibitors (CDKIs) are oral targeted agents approved for use in combination with endocrine therapy as first-line or second-line treatment of patients with hormone receptor-positive, HER2-negative, advanced or metastatic breast cancer. We previously reported the pooled analyses of progression-free survival in patients in specific clinicopathological subgroups, all of whom received consistent benefit from the addition of a CDKI to hormonal therapy. Here, we report the pooled overall survival results in patients treated with a CDKI and fulvestrant. METHODS: In this exploratory analysis, we pooled individual patient data from three phase 3 randomised trials of CDKI or placebo in combination with fulvestrant in patients with breast cancer submitted to the US Food and Drug Administration and approved before Aug 1, 2020, in support of marketing applications. All analysed patients were aged at least 18 years, had an Eastern Cooperative Oncology Group performance status of 0-1, had hormone receptor-positive, HER2-negative advanced or metastatic breast cancer, and received at least one dose of CDKI or placebo in combination with fulvestrant. The median overall survival was estimated using Kaplan-Meier methods, and hazard ratios (HRs) with corresponding 95% CIs were estimated using Cox regression models. Patients were analysed collectively, by number of previous lines of systemic endocrine therapy in any disease setting (first-line or endocrine naive vs second-line and later), and in various clinicopathological subgroups of interest. The estimated median overall survival was not reported by group when the pooled population included patients treated across lines of therapy because of potential patient heterogeneity. All results presented are considered exploratory and hypothesis generating. FINDINGS: Across the three pooled trials, 1960 patients were randomly assigned between Oct 7, 2013, and June 10, 2016 (12 patients were not treated and 1296 [66%] patients were randomly assigned to CDKI and 652 [33%] to placebo). In all treated patients (n=1948), the estimated HR for overall survival was 0·77 (95% CI 0·68-0·88), with a median follow-up of 43·7 months (IQR 37·8-47·7) and deaths in 935 (48%) of the 1948 patients. The difference in estimated median overall survival was 7·1 months, favouring CDKIs. In patients who received CDKIs or placebo in combination with fulvestrant as first-line systemic endocrine therapy (two trials; n=396), the estimated HR for overall survival was 0·74 (95% CI 0·52-1·07), with a median follow-up of 39·4 months (IQR 37·0-42·2). 123 (31%) of these patients died. The difference in estimated median overall survival could not be calculated because median overall survival was not estimable (95% CI 50·9-not estimable) in the CDKI group and was 45·7 months (95% CI 41·7-not estimable) in the placebo group. In patients who received CDKIs or placebo in combination with fulvestrant as second-line or later systemic endocrine therapy (three trials; n=1552), the estimated HR for overall survival was 0·77 (95% CI 0·67-0·89), with a median follow-up of 45·1 months (95% CI 39·2-48·5). 812 (52%) of these patients died. The difference in estimated median overall survival was 7·0 months, favouring CDKIs. INTERPRETATION: The addition of CDKIs to fulvestrant resulted in a consistent overall survival benefit in all pooled patients and within most clinicopathological subgroups of interest. These findings support the existing standard of care of CDKIs plus fulvestrant for the treatment of patients with hormone receptor-positive, HER2-negative, advanced breast cancer. FUNDING: None.

Clostridium difficile infection in the pediatric transplant patient.

CDIs are on the rise in both hospital and community settings in adults and children. Children with cancer or a history of HSCT or SOT appear to be at higher risk for primary disease, recurrent disease, and severe outcomes when compared to children with other comorbidities. The reasons for this are not clear and no studies to date have analyzed risk factors for CDI in pediatric transplant patients. Colonization rates in children with cancer and a transplant history are also high. Determining which children are colonized with Clostridium difficile and symptomatic from another source vs. symptomatic from CDI is difficult and a clinical conundrum for the transplant physician. The use of fecal transplantation for severe or rCDI is likely safe and effective in the immunosuppressed pediatric cancer or transplant patient, but this will need to be more thoroughly studied in this patient population.

FDA Approval Summary: Capecitabine Labeling Update under Project Renewal.

On December 14, 2022, the U.S. Food and Drug Administration (FDA) approved revisions to the United States Prescribing Information (USPI) for capecitabine that revised existing indications and dosage regimens, added new indications and their recommended dosage regimens, revised safety information, updated the description of the risk of capecitabine in patients with dihydropyrimidine dehydrogenase (DPD) deficiency, and edited other sections of the USPI to conform with FDA's current labeling guidance. These supplements were reviewed and approved under Project Renewal, a public health initiative established by the FDA's Oncology Center of Excellence that aims to update the prescribing information of certain older oncology drugs to ensure information is clinically meaningful and scientifically up to date. This article summarizes the FDA approach that supported revisions to the capecitabine USPI within the context of Project Renewal.

US Food and Drug Administration Approval Summary: Capivasertib With Fulvestrant for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Locally Advanced or Metastatic Breast Cancer With PIK3CA/AKT1/PTEN Alterations.

PURPOSE: The US Food and Drug Administration (FDA) approved capivasertib in combination with fulvestrant for adult patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative, locally advanced, or metastatic breast cancer (MBC) who have received at least one previous endocrine therapy and whose tumors harbor one or more phosphatidylinositol 3-kinase (PIK3CA)/AKT Serine/Threonine Kinase 1 (AKT1)/phosphatase and tensin homolog (PTEN) alterations, as detected by an FDA-approved test. PATIENTS AND METHODS: Approval was based on CAPItello-291, a randomized, double-blind, multicenter trial of 708 patients with hormone receptor-positive, HER2-negative advanced or MBC, including 289 patients with PIK3CA/AKT1/PTEN tumor alterations. Patients were randomly assigned 1:1 to receive capivasertib 400 mg twice daily for 4 days per week with fulvestrant versus placebo with fulvestrant. Random assignment was stratified by presence of liver metastases, previous treatment with CDK4/6i, cyclin-dependent kinase four and six (CDK4/6) inhibitors, and geographical region. RESULTS: A statistically significant progression-free survival (PFS) benefit was demonstrated in the overall population (hazard ratio [HR], 0.6 [95% CI, 0.51 to 0.71]); this result was driven by 289 patients in the biomarker-positive population (HR, 0.5 [95% CI, 0.37 to 0.68]). An exploratory analysis of investigator-assessed PFS in the 313 (44%) patients in the biomarker-negative population showed uncertain benefit (HR, 0.78 [95% CI, 0.60 to 1.01]). With capivasertib, more patients had Grade ≥3 toxicities. Key concerns included hyperglycemia (18% all-grade, 2.8% Grade ≥3), cutaneous toxicity (58% all-grade, 17% Grade ≥3), and diarrhea (72% all-grade, 9% Grade ≥3). CONCLUSION: Capivasertib with fulvestrant was approved for patients whose tumors harbored PIK3CA/AKT1/PTEN alterations. Benefit-risk assessment in this subgroup was favorable based on a statistically significant and clinically meaningful improvement in PFS in the context of an acceptable safety profile including no evidence of a potential detriment in overall survival. By contrast, the benefit-risk was unfavorable in the biomarker-negative population.

US Food and Drug Administration Approval Summary: Fam-Trastuzumab Deruxtecan-nxki for Human Epidermal Growth Factor Receptor 2-Low Unresectable or Metastatic Breast Cancer.

PURPOSE: The US Food and Drug Administration approved fam-trastuzumab deruxtecan-nxki (DS-8201a, T-DXd) for the treatment of adult patients with unresectable or metastatic human epidermal growth factor receptor 2 (HER2)-low (immunohistochemistry 1 + or immunohistochemistry 2+/in situ hybridization-) breast cancer who have received a prior chemotherapy in the metastatic setting or developed disease recurrence during or within 6 months of completing adjuvant chemotherapy. PATIENTS AND METHODS: Approval was based on DESTINY-Breast04, a phase III, randomized, open-label, multicenter trial in patients with unresectable or metastatic HER2-low breast cancer, determined at a central laboratory. A total of 557 patients were randomly assigned (2:1) to receive either T-DXd 5.4 mg/kg intravenously once every 3 weeks (n = 373) or physicians' choice of chemotherapy (n = 184). RESULTS: The study met its primary efficacy end point of progression-free survival (PFS) by blinded independent central review assessment in the hormone receptor-positive (HR+) cohort (N = 494) with an estimated hazard ratio (HR) of 0.51(95% CI, 0.40 to 0.64; P < .0001). Key secondary end points were also met, including PFS in the intent-to-treat population with an HR of 0.50 (95% CI, 0.40 to 0.63; P < .0001), overall survival (OS) in the HR+ cohort with an HR of 0.64 (95% CI, 0.48 to 0.86; P = .0028) and OS in the intent-to-treat with an HR of 0.64 (95% CI, 0.49 to 0.84; P = .0010). The safety profile of T-DXd was consistent with previously approved indications, and no new safety signals were observed in this study population. CONCLUSION: The approval of T-DXd in HER2-low metastatic breast cancer was based on statistically significant and clinically meaningful PFS and OS improvements observed in the DESTINY-Breast04 trial and represents the first approved therapy specifically for the treatment of HER2-low metastatic breast cancer.

FDA Approval Summary: Ribociclib Indicated for Male Patients with Hormone Receptor-Positive, HER2-Negative Advanced or Metastatic Breast Cancer.

On December 10, 2021, the FDA expanded the indications for ribociclib to include male patients for the treatment of hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. Ribociclib is now indicated in combination with an aromatase inhibitor (AI) as initial endocrine-based therapy in adult patients, or with fulvestrant as initial endocrine-based therapy or following disease progression on endocrine therapy (ET), in postmenopausal women or in men. The efficacy of ribociclib + AI for male patients was primarily based on previous favorable benefit-risk assessments of ribociclib from MONALEESA-2 and MONALEESA-7 trials, and supported by COMPLEEMENT-1, an open-label, single-arm, multicenter clinical trial, in which 39 male patients (n = 3,246 total patients) received ribociclib + letrozole + goserelin/leuprolide. The overall response rate (ORR) based on confirmed responses in male patients with measurable disease at baseline was 46.9% [95% confidence interval (CI), 29.1-65.3], consistent with an ORR of 43.6% (95% CI, 41.5-45.8) in the overall population. Overall, adverse reactions occurring in male patients were similar to those occurring in female patients treated with ribociclib + ET. The efficacy of ribociclib + fulvestrant for male patients was primarily based on the previous findings of a favorable benefit-risk assessment from the MONALEESA-3 trial, supported by FDA review of clinical data of a limited number of male patients treated in clinical practice receiving ribociclib + fulvestrant. The known mechanism of action, biologic rationale, and clinical information available adequately demonstrate that the efficacy and safety of ribociclib + AI/fulvestrant are similar in male and female patients. This article summarizes the FDA's decision-making and data supporting the approval of ribociclib in male patients with breast cancer, and discusses regulatory insights.

FDA Approval Summary: Abemaciclib With Endocrine Therapy for High-Risk Early Breast Cancer.

PURPOSE: The US Food and Drug Administration approved abemaciclib in combination with endocrine therapy (ET) for the adjuvant treatment of adult patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, early breast cancer (EBC) at high risk of recurrence and a Ki-67 score ≥ 20%. PATIENTS AND METHODS: The approval was based on monarchE, a phase III, open-label, 2-cohort, multicenter trial of patients with EBC randomly assigned to receive abemaciclib plus ET (n = 2,808) or ET alone (n = 2,829). Abemaciclib was given at 150 mg orally twice daily for 2 years. RESULTS: Invasive disease-free survival (IDFS) in the intent-to-treat population was statistically significant at the second IDFS interim analysis (IA; March 2020; hazard ratio [HR; 95% CI], 0.747 [0.598 to 0.932]; P = .0096); however, only 12.5% of patients had completed adjuvant therapy, and the HR for overall survival (OS) was > 1. A prespecified, controlled analysis of IDFS in patients with Ki-67 ≥ 20% in cohort 1 was statistically significant at the final IDFS analysis (July 2020; HR [95% CI], 0.643 [0.475 to 0.872]; P = .0042). At the first OS IA (April 2021), the majority of patients had completed adjuvant therapy, IDFS remained consistent, and potential detriment in OS was not observed for this subgroup (HR [95% CI], 0.767 [0.511 to 1.152]). The HR for OS in the intent-to-treat population at OS IA remained > 1 (HR [95% CI], 1.091 [0.818 to 1.455]). More patients in the abemaciclib plus ET arm experienced treatment emergent adverse events (all grades 98.4% v 88.8%, grade 3 ≥ 49.7% v 16.3%). CONCLUSION: The approval of abemaciclib in adjuvant EBC was limited to patients with high risk of recurrence and Ki-67 ≥ 20%, given their favorable benefit:risk with a statistically significant IDFS advantage and no observed detriment on survival.

FDA Approval Summary: Pembrolizumab for Neoadjuvant and Adjuvant Treatment of Patients with High-Risk Early-Stage Triple-Negative Breast Cancer.

On July 26, 2021, the FDA granted approval to pembrolizumab in combination with chemotherapy for neoadjuvant treatment and then continued as a single agent for adjuvant treatment following surgery for patients with high-risk, early-stage triple-negative breast cancer. Approval was based on results from KEYNOTE-522, an ongoing randomized (2:1) trial evaluating pembrolizumab or placebo in combination with chemotherapy for neoadjuvant treatment and then as a single agent for adjuvant treatment. The co-primary endpoints were pathological complete response (pCR) rate and event-free survival (EFS). The trial demonstrated an improvement in pCR and EFS in the pembrolizumab arm compared with the control arm. The number of patients who experienced an EFS event was 123 (16%) and 93 (24%), respectively [HR: 0.63, 95% confidence interval (CI), 0.48-0.82, P = 0.00031]. Patients on the pembrolizumab arm experienced EFS benefit regardless of tumor PD-L1 status. The absolute pCR rate improvement with the addition of pembrolizumab was 7.5% (95% CI, 1.6-13.4). Among patients receiving pembrolizumab, 44% experienced an immune-related adverse reaction. This article summarizes FDA's review of pembrolizumab and the data supporting the favorable benefit-risk assessment.

U.S. FDA Drug Approvals for Gynecological Malignancies: A Decade in Review.

Over the last decade, there has been tremendous progress in the treatment of patients with gynecologic cancers with a changing therapy landscape. This summary provides an overview of U.S. Food and Drug Administration (FDA) approvals for gynecologic cancers from 2010 to 2020, totaling 17 new indications. For each of the approved indications, endpoints, trial design, results, and regulatory considerations are outlined. Among these 17 indications, six received accelerated approval (AA) and 11 received regular approval (RA). As of September 2021, of the six AA, three have subsequently demonstrated clinical benefit resulting in conversion to RA and the remaining three have ongoing clinical trials that have not yet reported results. Approval decisions for these 17 indications were supported by primary efficacy endpoints of progression-free survival (n = 10), objective response rate (n = 6), and overall survival (n = 1) and showed a favorable benefit-risk profile. Among the 17 indications, 15 received priority review and three applications participated in one or more novel Oncology Center of Excellence initiatives, including Real Time Oncology Review, Assessment Aid, and Project Orbis. Current FDA thinking on drug development opportunities and regulatory initiatives currently under way will be discussed.

U.S. FDA Drug Approvals for Breast Cancer: A Decade in Review.

Over the last decade, the treatment of patients with breast cancer has been greatly impacted by the approval of multiple drugs and indications. This summary describes 30 FDA approvals of treatments for breast cancer from 2010 to 2020. The trial design endpoints, results, and regulatory considerations are described for each approved indication. Of the 30 indications, 23 (76.6%) received regular and 7 (23.3%) received accelerated approval. Twenty-six approvals were granted in metastatic breast cancer (MBC) and four in early breast cancer. Approval decisions for the 26 MBC indications were initially supported by progression-free survival (PFS) in 21 (80.8%), overall survival (OS) or a combination of OS and PFS in two (7.7%), and objective response rate (ORR) in three (11.5%). The four approvals in early breast cancer utilized pathologic complete response (pCR) in one (25%) and invasive disease-free survival (iDFS) in three (75%) trials. Among the 30 indications, 22 received priority review, seven were granted Breakthrough Therapy Designation, and 10 applications participated in one or more pilot Oncology Center of Excellence regulatory review initiatives, including Real Time Oncology Review, Assessment Aid, and Project Orbis. FDA initiatives to advance breast cancer drug development are also described.

FDA Approval Summary: Margetuximab plus Chemotherapy for Advanced or Metastatic HER2-Positive Breast Cancer.

On December 16, 2020, the FDA granted regular approval to margetuximab-cmkb (MARGENZA), in combination with chemotherapy, for the treatment of adult patients with HER2-positive (HER2+) metastatic breast cancer who have received two or more prior anti-HER2 regimens, at least one of which was for metastatic disease. Approval was based on data from SOPHIA, a multicenter, randomized, open-label, active controlled study comparing margetuximab with trastuzumab, in combination with chemotherapy. The primary efficacy endpoint was progression-free survival (PFS) by blinded independent central review. SOPHIA demonstrated a 0.9-month difference in median PFS between the two treatment arms [5.8 vs. 4.9 months, respectively; stratified HR, 0.76 (95% confidence interval: 0.59-0.98; P = 0.0334)]. Overall survival (OS) was immature at the data cut-off date of September 10, 2019. Infusion-related reactions (IRR) are an important safety signal associated with margetuximab plus chemotherapy. In SOPHIA, 13% of patients treated with margetuximab plus chemotherapy reported IRRs, of which 1.5% were grade 3. The most commonly reported adverse drug reactions (>10%) with margetuximab in combination with chemotherapy were fatigue/asthenia, nausea, diarrhea, vomiting, constipation, headache, pyrexia, alopecia, abdominal pain, peripheral neuropathy, arthralgia/myalgia, cough, decreased appetite, dyspnea, IRR, palmar-plantar erythrodysesthesia, and extremity pain. Overall, the favorable risk-benefit profile for margetuximab when added to chemotherapy supported its approval for the intended indication.

FDA Approval Summary: Fam-Trastuzumab Deruxtecan-Nxki for the Treatment of Unresectable or Metastatic HER2-Positive Breast Cancer.

On December 20, 2019, the FDA granted accelerated approval to fam-trastuzumab deruxtecan-nxki [DS-8201a; T-DXd; tradename ENHERTU (Daiichi Sankyo)] for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received two or more prior anti-HER2-based regimens in the metastatic setting. Approval was based on data from study DS8201-A-U201 (DESTINY-Breast01) with supportive safety data from study DS8201-A-J101. The primary efficacy endpoint in DESTINY-Breast01 was overall response rate (ORR) based on confirmed responses by blinded independent central review (ICR) using RECIST v1.1 in all participants who were assigned to receive the recommended dose of 5.4 mg/kg while secondary endpoints included duration of response (DoR). The confirmed ORR based on ICR in these 184 patients was 60.3% [95% confidence interval (CI): 52.9-67.4] and the median DoR was 14.8 months (95% CI: 13.8-16.9). Interstitial lung disease, including pneumonitis, was experienced in patients treated with T-DXd and can be severe, life threatening, or fatal. In addition, neutropenia and left ventricular dysfunction were included as Warnings and Precautions in labeling. Other important common adverse reactions were nausea, fatigue, vomiting, alopecia, constipation, decreased appetite, anemia, diarrhea, and thrombocytopenia. Overall, the totality of efficacy and safety data supported the accelerated approval of T-DXd for the intended indication.

FDA Approval Summary: Accelerated Approval of Sacituzumab Govitecan-hziy for Third-line Treatment of Metastatic Triple-negative Breast Cancer.

On April 22, 2020, the FDA granted accelerated approval to sacituzumab govitecan-hziy (TRODELVY; Immunomedics, Inc.) for the treatment of patients with metastatic triple-negative breast cancer (mTNBC) who have received at least two prior therapies for metastatic disease. Approval was based on data from the IMMU-132-01 trial, a single-arm, multicohort, multicenter, phase I/II trial of sacituzumab govitecan. The assessment of efficacy was based on 108 patients with mTNBC who had previously received at least two prior lines of therapy in the metastatic setting and who received sacituzumab govitecan 10 mg/kg i.v. The assessment of safety was based on 408 patients with advanced solid tumors who had received sacituzumab govitecan at doses up to 10 mg/kg i.v. The primary efficacy endpoint was investigator-assessed objective response rate (ORR) and duration of response (DoR) was a key secondary endpoint. The ORR was 33.3% [36/108; 95% confidence interval (CI), 24.6-43.1], and median DoR among responders was 7.7 months (95% CI, 4.9-10.8). The most common adverse reactions occurring in ≥25% of patients were nausea, neutropenia, diarrhea, fatigue, anemia, vomiting, alopecia, constipation, rash, decreased appetite, and abdominal pain. This article summarizes the FDA review process and data supporting the approval of sacituzumab govitecan.

FDA Approval Summary: Pertuzumab, Trastuzumab, and Hyaluronidase-zzxf Injection for Subcutaneous Use in Patients with HER2-positive Breast Cancer.

On June 29, 2020, the FDA approved pertuzumab, trastuzumab, and hyaluronidase-zzxf subcutaneous injection (Phesgo) for the treatment of patients with HER2-positive early-stage and metastatic breast cancer. Patients should be selected for therapy based on an FDA-approved companion diagnostic test. Approval was primarily based on the FeDeriCa trial, a randomized, open-label, multicenter comparability study of pertuzumab, trastuzumab, and hyaluronidase-zzxf subcutaneous injection compared with intravenous pertuzumab and intravenous trastuzumab administered in the neoadjuvant and adjuvant settings with chemotherapy for the treatment of patients with early breast cancer. The pharmacokinetic endpoints were, first, to demonstrate that the exposure of subcutaneous pertuzumab was not inferior to that of intravenous pertuzumab, and then to demonstrate that the exposure of subcutaneous trastuzumab was not inferior to that of intravenous trastuzumab. The primary endpoints were met with the observed lower limit of the two-sided 90% confidence intervals above the prespecified noninferiority margins. The most common adverse reactions were alopecia, nausea, diarrhea, anemia, and asthenia. The totality of the evidence demonstrated comparability of the subcutaneous product to intravenous, allowing for extrapolation and approval of all breast cancer indications for which intravenous trastuzumab and pertuzumab are approved.

FDA Approval Summary: Eribulin for Patients with Unresectable or Metastatic Liposarcoma Who Have Received a Prior Anthracycline-Containing Regimen.

On January 28, 2016, the FDA approved eribulin (Halaven; Eisai Inc.) for the treatment of patients with unresectable or metastatic liposarcoma who have received a prior anthracycline-containing regimen. The approval was based on results from a single, randomized, open-label, active-controlled trial (Trial E7389-G000-309) enrolling 452 patients with advanced, locally recurrent or metastatic liposarcoma or leiomyosarcoma. Patients were randomized to eribulin 1.4 mg/m2 intravenously (i.v.) on days 1 and 8 or dacarbazine 850, 1,000, or 1,200 mg/m2 i.v. on day 1 of a 21-day cycle. There was a significant improvement in overall survival [OS; HR, 0.75; 95% confidence interval (CI), 0.61-0.94; P = 0.0119, stratified log-rank] for the overall population. Estimated median OS was 13.5 months (95% CI, 11.1-16.5) in the eribulin arm and 11.3 months (95% CI, 9.5-12.6) in the dacarbazine arm (HR, 0.75; 95% CI, 0.61-0.94; P = 0.011).There were no differences in PFS for the overall population. The effects of eribulin were limited to patients with liposarcoma (n = 143) based on preplanned, exploratory subgroup analyses of OS (HR, 0.51; 95% CI, 0.35-0.75) and progression-free survival (PFS; 0.52; 95% CI, 0.35-0.78). Response rates in both treatment arms were less than 5% in the overall population and in the liposarcoma subgroup. The safety profile was similar to that previously reported for eribulin. The FDA determined that, based on the data reviewed, the benefit-risk assessment for eribulin is positive for patients with advanced, pretreated liposarcoma. Clin Cancer Res; 23(21); 6384-9. ©2017 AACR.

Postmarketing Colitis Cases Associated With Alpelisib Use Reported to the US Food and Drug Administration.

This case series investigates reports of 20 patients with colitis temporally associated with alpelisib use.

18F-FLT Positron Emission Tomography (PET) is a Pharmacodynamic Marker for EWS-FLI1 Activity and Ewing Sarcoma.

Ewing sarcoma is a bone and soft-tissue tumor that depends on the activity of the EWS-FLI1 transcription factor for cell survival. Although a number of compounds have been shown to inhibit EWS-FLI1 in vitro, a clinical EWS-FLI1-directed therapy has not been achieved. One problem plaguing drug development efforts is the lack of a suitable, non-invasive, pharmacodynamic marker of EWS-FLI1 activity. Here we show that 18F-FLT PET (18F- 3'-deoxy-3'-fluorothymidine positron emission tomography) reflects EWS-FLI1 activity in Ewing sarcoma cells both in vitro and in vivo. 18F-FLT is transported into the cell by ENT1 and ENT2, where it is phosphorylated by TK1 and trapped intracellularly. In this report, we show that silencing of EWS-FLI1 with either siRNA or small-molecule EWS-FLI1 inhibitors suppressed the expression of ENT1, ENT2, and TK1 and thus decreased 18F-FLT PET activity. This effect was not through a generalized loss in viability or metabolic suppression, as there was no suppression of 18F-FDG PET activity and no suppression with chemotherapy. These results provide the basis for the clinical translation of 18F-FLT as a companion biomarker of EWS-FLI1 activity and a novel diagnostic imaging approach for Ewing sarcoma.

Identification of Mithramycin Analogues with Improved Targeting of the EWS-FLI1 Transcription Factor.

PURPOSE: The goal of this study was to identify second-generation mithramycin analogues that better target the EWS-FLI1 transcription factor for Ewing sarcoma. We previously established mithramycin as an EWS-FLI1 inhibitor, but the compound's toxicity prevented its use at effective concentrations in patients. EXPERIMENTAL DESIGN: We screened a panel of mithralogs to establish their ability to inhibit EWS-FLI1 in Ewing sarcoma. We compared the IC50 with the MTD established in mice to determine the relationship between efficacy and toxicity. We confirmed the suppression of EWS-FLI1 at the promoter, mRNA, gene signature, and protein levels. We established an improved therapeutic window by using time-lapse microscopy to model the effects on cellular proliferation in Ewing sarcoma cells relative to HepG2 control cells. Finally, we established an improved therapeutic window using a xenograft model of Ewing sarcoma. RESULTS: EC-8105 was found to be the most potent analogue and was able to suppress EWS-FLI1 activity at concentrations nontoxic to other cell types. EC-8042 was substantially less toxic than mithramycin in multiple species but maintained suppression of EWS-FLI1 at similar concentrations. Both compounds markedly suppressed Ewing sarcoma xenograft growth and inhibited EWS-FLI1 in vivo CONCLUSIONS: These results provide a basis for the continued development of EC-8042 and EC-8105 as EWS-FLI1 inhibitors for the clinic. Clin Cancer Res; 22(16); 4105-18. ©2016 AACR.