STereotactic Arrhythmia Radioablation in Europe: critical structure contouring benchmark results of the STOPSTORM Consortium

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU Horizon

Background/Introduction

In patients with refractory ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) showed promising results for otherwise untreatable patients [1]. The STOPSTORM.eu project coordinates European efforts to clinically validate STAR.

Purpose

The primary goal of the critical structures benchmark study was to harmonize contouring of organs at risk (OAR) for STAR within the STOPSTORM.eu consortium. The results enable to refine protocols and guidelines to ensure treatment harmonization.

Methods

Three well-selected STAR cases [2] were provided for this benchmark and sent to all radiation oncology centres within the consortium. Every case had a contrast-enhanced cardiac-CT which was already deformed to the primary planning-CT to contour the OAR in detail. Every centre was asked to contour 31 OAR’s according to literature-based guidelines. The resulting structure sets were evaluated within VelocityTM 4.1.

Results

Twenty centres participated in the critical structure contouring benchmark.

Contouring of the structures was performed with high accuracy according to the provided guidelines. The contours of common OAR’s in radiotherapy, such as the heart, lungs, stomach, oesophagus, bronchus, great vessels, and spinal canal were correctly contoured by all centres. In the substructures of the heart (chambers, valves, arteries, and nodes), deviations in the contours occurred more frequently, but no large systematic errors were found (see figure 1-2). The centres that already performed STAR treatments had markedly less difficulties with the contouring of the substructures. However, these structures do not have a consensus for treatment planning purposes and late toxicity but need to be contoured correctly for future analysis within the STOPSTORM project.

Conclusion

This large STOPSTORM.eu multi-centre critical structure benchmark study showed a high accuracy regarding standard critical structures. In the case of heart substructures some deviations occurred, which lead to new definitions for contouring these structures within the consortium. In addition, a close collaboration between radiation oncologist and cardiac electrophysiologist is recommended.

Efficacy and Toxicity of Alternative Radiation Treatment Schemes for Patients With Hematologic Malignancies: A Collaborative ILROG COVID Era Report

Purpose/Objective(s)

The COVID19 pandemic required radiation oncologists (ROs) to consider shorter treatment courses to minimize patient and staff exposure and conserve healthcare resources. Hematologic ROs adopted hypofractionated radiation therapy (hRT) regimens according to guidelines published by the International Lymphoma Radiation Oncology Group (ILROG). We report for the first time the preliminary efficacy and toxicity of these novel hypofractionated regimens in the treatment of hematologic malignancies.

Materials/Methods

We conducted a multicenter, multinational retrospective study under the direction of the ILROG. All patients receiving hRT according to ILROG guidelines from 1/1/2020 to 8/31/2020 were included. Patient and treatment details were abstracted from separate institutional databases. Toxicity was graded using CTCAE v5.0.

Results

Ninety-three patients from 4 institutions treated with 114 RT courses were included. Patient and treatment details are displayed in Table 1. Median follow up for the cohort was 179 days, and 77 patients (82%) were alive at last follow up. Maximal toxicity experienced by patients included Grade 1 (n = 16), Grade 2 (n = 1) and Grade 3 (n = 1) toxicities. Of 80 sites with response assessment within the RT field, 69% of patients achieved a complete response (n = 55), 20% partial response (n = 16), 9% stable disease (n = 7), and 2% progressive disease (n = 2). No COVID19 infections during or after RT have been documented in this patient cohort.

Conclusion

HRT according to ILROG guidelines resulted in low rates of acute toxicity and reasonable short-term treatment efficacy. Longer follow up and comparison with control groups is needed to draw more definitive conclusions and will be presented at the Annual Meeting.

Diagnosis and management of Cornelia de Lange syndrome: first international consensus statement

Cornelia de Lange syndrome (CdLS) is an archetypical genetic syndrome that is characterized by intellectual disability, well-defined facial features, upper limb anomalies and atypical growth, among numerous other signs and symptoms. It is caused by variants in any one of seven genes, all of which have a structural or regulatory function in the cohesin complex. Although recent advances in next-generation sequencing have improved molecular diagnostics, marked heterogeneity exists in clinical and molecular diagnostic approaches and care practices worldwide. Here, we outline a series of recommendations that document the consensus of a group of international experts on clinical diagnostic criteria, both for classic CdLS and non-classic CdLS phenotypes, molecular investigations, long-term management and care planning.

Mutations of FLT3/ITD confer resistance to multiple tyrosine kinase inhibitors

FMS-like tyrosine kinase 3 (FLT3) normally functions in the survival/proliferation of hematopoietic stem/progenitor cells, but its constitutive activation by internal tandem duplication (ITD) mutations correlates with a poor prognosis in AML. The development of FLT3 tyrosine kinase inhibitors (TKI) is a promising strategy, but resistance that arises during the course of treatment caused by secondary mutations within the mutated gene itself poses a significant challenge. In an effort to predict FLT3 resistance mutations that might develop in patients, we used saturation mutagenesis of FLT3/ITD followed by selection of transfected cells in FLT3 TKI. We identified F621L, A627P, F691L and Y842C mutations in FLT3/ITD that confer varying levels of resistance to FLT3 TKI. Western blotting confirmed that some FLT3 TKI were ineffective at inhibiting FLT3 autophosphorylation and signaling through MAP kinase, STAT5 and AKT in some mutants. Balb/c mice transplanted with the FLT3/ITD Y842C mutation confirmed resistance to sorafenib in vivo but not to lestaurtinib. These results indicate a growing number of FLT3 mutations that are likely to be encountered in patients. Such knowledge, combined with known remaining sensitivity to other FLT3 TKI, will be important to establish as secondary drug treatments that can be substituted when these mutants are encountered.

Phase I/II study of idarubicin (Ida), high-dose ara-C, and sorafenib (S) in patients (pts) younger than 65 years with acute myeloid leukemia (AML)

7018

Background: S is an oral multi-kinase inhibitor with activity against the Raf/ERK/MEK pathway and FLT3. It selectively induces apoptosis in FLT3-mutant human AML cell lines at nM concentrations. Methods: Objectives of this study are to determine the tolerability and efficacy of combination of S with chemotherapy. Ara-C 1.5 g/m2 over 24 hrs daily x 4 (x 3 for pts over 60) and Ida 12 mg/m2 daily x 3 are administered with S. In the phase I part, pts with relapsed AML were treated with escalating doses of S (400 mg qod, 400 mg daily, 400 mg bid) for 7 days during induction, and 400 mg bid was established as safe. Pts achieving CR receive up to 5 courses of consolidation with Ida 8 mg/m2 daily x 2 and Ara-C 0.75 g/m2 daily x 3 in addition to S 400 mg bid for up to 28 days per cycle repeated every 4 to 6 weeks. Maintenance is with S 400 mg bid for up to a year. Results: 10 pts (median age 34, range 21–58) with relapsed AML (median prior therapy 2, range 1–6) were treated in the phase I . 7 were FLT3-ITD positive. 4 achieved CR; 6 failed. In the phase II part, 45 pts (12 with FLT3-ITD and 2 with FLT3-TKD) were treated. Median age is 53 (range 18 - 65). Cytogenetics were diploid in 19, +8 in 5, -5/-7 in 5, 11q23 in 2, other in 14. Median presentation WBC was 4.9 x 109/L (range 0.6 - 122.7 x 109/L). 8 pts were FLT3-ITD+/NPM1-. 40 pts are evaluable for response and 85% achieved CR (n = 30) or CRp (n = 4) (13 of 14 FLT3 mutated pts); 5 pts are too early (1 FLT3 mutated). Most frequent grade 3 and higher related adverse events: hyperbilirubinemia (5), rash and hand-foot syndrome (3), raised transaminases (2), diarrhea (2), hypertension (2). With a median f/u of 5.4 mo (range, 0.5 - 11.3), the probability of survival at 6 mo is 81.6%. 5 pts have relapsed; median CR duration has not been reached, (range; 0.2+ - 10.6+ mo). Among pts with FLT3 mutation, 4 have relapsed and 9 remain in CR. Plasma inhibitory assay was performed using day 7 samples from 10 pts; mutant FLT3 was suppressed by all with 5-fold more potent suppression against mutant versus wild-type FLT3. Conclusions: S can be safely combined with IA; it has a high CR rate in frontline therapy of younger pts with AML, in particular those with FLT3 mutations. Correlative studies confirm potent activity of S against FLT3 signaling.

[Table: see text]

Phase I dose escalation trial of sorafenib as a single agent for adults with relapsed and refractory acute leukemias

7065

Background: Sorafenib is a multikinase inhibitor with activity against B-raf, VEGF, and FLT3. Based on preclinical activity in FLT3 mutant AML, sorafenib was studied in refractory acute leukemia. Methods: The primary objective was to determine the safety and tolerability of sorafenib in refractory acute leukemias. Secondary objectives included pharmacokinetics (PK) and pharmacodynamic (PD) effects of sorafenib on FLT3 phosphorylation. Dose escalation began at 400 mg BIDx14days per month, and proceeded through 600 mg BID x 21 days per month. Plasma concentration of sorafenib and its primary metabolite sorafenib N-oxide were measured by LC/MS//MS method. The plasma inhibitory assay was used to measure target inhibition of phosphorylated FLT3 and phosphorylated Erk. Results: Fifteen patients (13 = AML, 2 = ALL) were enrolled (ages 37–85) and treated on three dosing schedules (400 mg BID x 14 d, 400 mg BID x 21 days, 600 mg BID x 21days) of single agent sorafenib. The maximally tolerated dose was 400 mg BID x 21 days per month. Grade 3 or greater toxicities were experienced in 55% of cycles, most common grade 3 or greater toxicities being fatigue (16%) and hypokalemia (13%). No patients met criteria for complete or partial response, but 11 of 15 (73%) patients experienced stable disease as best response, with 6 showing a reduction in bone marrow blasts after only one cycle, half of who experienced a >50% reduction in bone marrow blasts. Interestingly, 2 pts with FLT3-ITD mutations both showed marrow blast response (1 pt >50%). Sorafenib resulted in sustained complete inhibition of FLT3 and Erk as demonstrated in all patients assessed (n = 11). Importantly, this inhibition was maintained throughout treatment cycle and 3/5 pts had FLT3 inhibitory activity 7 days post their last dose. Correlative studies suggest sorafenib N-oxide is an active metabolite. Conclusions: Sorafenib is a potent inhibitor of FLT3 with favorable PK and PD properties. Clinical activity as a single agent was limited to transient reductions in bone marrow blast counts and dose escalation was limited due to toxicities. Based on PK data in conjunction with standard curves for inhibition of FLT3 by sorafenib in plasma, the minimum FLT3 inhibitory dose of sorafenib is likely less than 400 mg BID.

No significant financial relationships to disclose.

Combinations of the FLT3 inhibitor CEP-701 and chemotherapy synergistically kill infant and childhood MLL-rearranged ALL cells in a sequence-dependent manner

Mixed lineage leukemia (MLL) rearrangements occur in 80% of infants and 5% of older children with acute lymphoblastic leukemia (ALL). These cases have a poor prognosis with current therapy. The FLT3 kinase is overexpressed and constitutively activated in MLL-rearranged ALL cells. The FLT3 inhibitor CEP-701 selectively kills these cells, but is unlikely to be curative if used as monotherapy. To identify potentially synergistic combination strategies, we studied CEP-701 and six standard chemotherapeutic agents in three sequences of exposure (S1: chemotherapy followed by CEP-701, S2: simultaneous exposure to both; and S3: CEP-701 followed by chemotherapy) using MLL-rearranged ALL cell lines and patient bone marrow samples. MTT cytotoxicity and annexin V binding apoptosis assays were used to assess antileukemic effects. Combination indices (CI) were calculated for each combination (CI<0.9 - synergistic; CI 0.9-1.1 - additive; CI>1.1 - antagonistic). A striking pattern of sequence-dependent synergy was observed: S1 was markedly synergistic (mean CI=0.59+/-0.10), S2 was additive (mean CI=0.99+/-0.09) and S3 was antagonistic (mean CI=1.23+/-0.10). The sequence dependence is attributable to the effect of CEP-701 on cell cycle kinetics, and is mediated specifically by FLT3 inhibition, as these effects are not seen in control cells without activated FLT3.

FLT3: ITDoes matter in leukemia

FMS-like tyrosine kinase-3 (FLT3), a receptor tyrosine kinase, is important for the development of the hematopoietic and immune systems. Activating mutations of FLT3 are now recognized as the most common molecular abnormality in acute myeloid leukemia, and FLT3 mutations may play a role in other hematologic malignancies as well. The poor prognosis of patients harboring these mutations renders FLT3 an obvious target of therapy. This review summarizes the data on the molecular biology and clinical impact of FLT3 mutations, as well as the therapeutic potential of several small-molecule FLT3 inhibitors currently in development.

Inhibition of the transforming activity of FLT3 internal tandem duplication mutants from AML patients by a tyrosine kinase inhibitor

FLT3 is a receptor tyrosine kinase that may play a role in a significant proportion of leukemias. In addition to being aberrantly expressed in acute leukemias, activating mutations of the FLT3 gene have been found in patients with AML, myelodysplastic syndrome (MDS) and more rarely, ALL. Internal tandem duplications (ITDs) of the FLT3 gene have been detected in 17-34% of patients with AML and portend a poor prognosis for these patients. FLT3 receptors containing ITD mutations (FLT3/ITDs) are constitutively activated in the absence of FLT3 ligand (FL) stimulation leading to the activation of downstream signaling proteins, including ERK and STAT 5. FLT3 activity, therefore, is a logical target for therapeutic intervention. AG1296 is a tyrosine kinase inhibitor of the tyrphostin class that shows inhibitory activity for wild-type FLT3, in addition to the PDGF and c-KIT receptors. We examined the inhibitory effects of AG1296 on FLT3/ITDs isolated from AML patients in the IL-3-dependent cell line, Ba/F3, as well as in primary leukemia samples from AML patients. Immunoprecipitation and immunoblotting analyses demonstrated that FLT3/ITDs were constitutively phosphorylated in the absence of FL. The auto-phosphorylation of FLT3/ITDs was inhibited by AG1296 with an IC(50) of approximately 1 microM. FLT3/ITDs were associated with constitutive phosphorylation of ERK, STAT 5A, STAT 5B, CBL, VAV and SHP2 in Ba/F3 cells. The phosphorylation of these downstream signaling molecules was suppressed in a dose-responsive fashion by AG1296. AG1296 inhibited IL-3 independent growth and induced apoptosis in Ba/F3 cells transformed by FLT3/ITDs. AG1296 also inhibited FLT3 auto-phosphorylation, and induced a cytotoxic effect, in primary AML cells. These findings suggest that inhibiting the activity of FLT3 may have a therapeutic value in some leukemias expressing FLT3/ITDs.

A FLT3 tyrosine kinase inhibitor is selectively cytotoxic to acute myeloid leukemia blasts harboring FLT3 internal tandem duplication mutations

Internal tandem duplication (ITD) mutations of the receptor tyrosine kinase FLT3 have been found in 20% to 30% of patients with acute myeloid leukemia (AML). These mutations constitutively activate the receptor and appear to be associated with a poor prognosis. Recent evidence that this constitutive activation is leukemogenic renders this receptor a potential target for specific therapy. In this study, dose-response cytotoxic assays were performed with AG1295, a tyrosine kinase inhibitor active against FLT3, on primary blasts from patients with AML. For each patient sample, the degree of cytotoxicity induced by AG1295 was compared to the response to cytosine arabinoside (Ara C) and correlated with the presence or absence of a FLT3/ITD mutation. AG1295 was specifically cytotoxic to AML blasts harboring FLT3/ITD mutations. The results suggest that these mutations contribute to the leukemic process and that the FLT3 receptor represents a therapeutic target in AML. (Blood. 2001;98:885-887)