Detection of ABL1 kinase domain mutations in therapy naïve BCR-ABL1 positive acute lymphoblastic leukemia

Not available.

Conformation and dynamics of the kinase domain drive subcellular location and activation of LRRK2

To explore how pathogenic mutations of the multidomain leucine-rich repeat kinase 2 (LRRK2) hijack its finely tuned activation process and drive Parkinson’s disease (PD), we used a multitiered approach. Most mutations mimic Rab-mediated activation by “unleashing” kinase activity, and many, like the kinase inhibitor MLi-2, trap LRRK2 onto microtubules. Here we mimic activation by simply deleting the inhibitory N-terminal domains and then characterize conformational changes induced by MLi-2 and PD mutations. After confirming that LRRK2RCKW retains full kinase activity, we used hydrogen-deuterium exchange mass spectrometry to capture breathing dynamics in the presence and absence of MLi-2. Solvent-accessible regions throughout the entire protein are reduced by MLi-2 binding. With molecular dynamics simulations, we created a dynamic portrait of LRRK2RCKW and demonstrate the consequences of kinase domain mutations. Although all domains contribute to regulating kinase activity, the kinase domain, driven by the DYGψ motif, is the allosteric hub that drives LRRK2 regulation.

Clinical activity of durvalumab and savolitinib in MET-driven, metastatic papillary renal cancer.

4511 Background: Savolitinib is a potent and selective MET inhibitor with activity in MET-driven papillary renal cancer (PRC). Durvalumab is a PD-L1 inhibitor which has been tested in combination with savolitinib in metastatic PRC with response rates of 29% (12/41). Here we describe the efficacy of this combination in MET-driven metastatic PRC. Methods: This single arm phase I/II trial explored durvalumab (1500mg Q4W) and savolitinib (600mg OD) together in metastatic PRC, with a 4wk savolitinib run in. Biomarker analysis results were compared with responses to treatment as planned in the protocol. The analysis presented here focuses on those patients with MET DNA alterations (central analysis:chromosome 7 gain/MET or HGF amplification/MET kinase domain mutations). Confirmed response rate (RR) (RECIST v1.1), progression-free survival (PFS), tolerability (CTCAE v4.03) and overall survival (OS) were analysed. Results: 42 patients were enrolled in the metastatic papillary cohort, of which 41 patients received treatment. The median follow up was 26.8 months. The confirmed RR was 29% (12/41) and median PFS was 4.9 months (95% CI 2.5-10.0). 14/41 (34%) of these patients had MET-driven disease. 71% (10/14) of MET-driven patients had not previously received systemic therapy and 7% (1/14) were PD-L1 positive. IMDC good, intermediate, and poor risk disease occurred in 36% (5/14), 57% (8/14), and 7% (1/14) of MET-driven patients respectively. Confirmed RR in MET-driven patients was 57% (8/14) with duration of response at 9.4 months (95% CI 3.9-Not reached [NR]). Median PFS and OS in MET-driven patients were 10.5 months (95% CI 2.9-15.7) and 27.4 months (95% CI 7.3-NR) respectively. No new safety signals were seen. Conclusions: The combination of savolitinib and durvalumab has clinical activity in MET-driven PRC. A randomised phase III study is planned based upon these data. Clinical trial information: NCT02819596.

NTRK kinase domain mutations in cancer variably impact sensitivity to type I and type II inhibitors

Tyrosine kinase domains dynamically fluctuate between two main structural forms that are referred to as type I (DFG-in) or type II (DFG-out) conformations. Comprehensive data comparing type I and type II inhibitors are currently lacking for NTRK fusion-driven cancers. Here we used a type II NTRK inhibitor, altiratinib, as a model compound to investigate its inhibitory potential for larotrectinib (type I inhibitor)-resistant mutations in NTRK. Our study shows that a subset of larotrectinib-resistant NTRK1 mutations (V573M, F589L and G667C) retains sensitivity to altiratinib, while the NTRK1V573M and xDFG motif NTRK1G667C mutations are highly sensitive to type II inhibitors, including altiratinib, cabozantinib and foretinib. Moreover, molecular modeling suggests that the introduction of a sulfur moiety in the binding pocket, via methionine or cysteine substitutions, specifically renders the mutant kinase hypersensitive to type II inhibitors. Future precision treatment strategies may benefit from selective targeting of these kinase mutants based on our findings.

Clinical Benefit and Tolerability of Crenolanib in Children with Relapsed Acute Myeloid Leukemia Harboring Treatment Resistant FLT3 ITD and Variant FLT3 TKD Mutations Treated on Compassionate Access

Background: FLT3-mutant pediatric AML represents a biological and clinically diverse disease and is associated with a poor outcome. Sorafenib has limited activity against tyrosine kinase domain mutations. Crenolanib is a pan-FLT3 inhibitor, which, at the time of this compassionate use program, had already been safely administered to over 55 children (age 2-18) with diffuse intrinsic pontine glioma as well as high grade gliomas. Crenolanib at a dose of 66mg/m2 TID has been well tolerated in pediatric patients. Methods: We here report our experience with five consecutive children (ages 4-12y) who received crenolanib for FLT3 mutant AML on a compassionate basis between April 2017 to October 2019. All patients treated had IRB/local ethics approval prior to treatment and all patients' guardians signed informed consent forms. Results: Patient Characteristics: Of the five patients, three were refractory to induction therapy and required salvage therapy to get into remission. All five patients were then able to undergo HSCT, but all subsequently relapsed. Two patients were successfully salvaged and underwent a second HSCT. Only two pts received sorafenib. By the time of the compassionate use request, all children had exhausted all standard and experimental therapies (3-9 prior therapies, Table 1). Two patients had FLT3-ITDs and three had FLT3 kinase domain mutations (A848P in one, D835H in another and both D835H and D835E in trans in third). Co-occurring events included KMT2A fusion/mutations in three pts as follows: i) one pt with KMT2A-rearranged infant AML, ii) one with treatment-related AML with KMT2A fusion and t(9;11) and iii) a third patient with KMT2A fusion along with p53 mutation. Another patient with biphenotypic AML had a co-occurring NOTCH1 mutation with 9;14 translocation. Three patients had complex karyotypes and a number of translocations were identified including t(9;11), t(3;5), t(1;16), and t(9;14) (Table 1). In addition to bone-marrow disease and circulating blasts, all patients had extramedullary AML. Three patients had CNS leukemia. Three patients had non-CNS extramedullary AML (submandibular, testicular, liver and spleen). Treatment: Crenolanib was given with curative intent to three patients, one in combination with Vyxeos (liposomal cytarabine/daunorubicin), one with high-dose cytarabine, and one as maintenance therapy after her second HSCT. Two patients received crenolanib as palliation for rapidly progressing AML. Tolerability: All children tolerated crenolanib well. Reasons for crenolanib discontinuation were bridge to HSCT in two patients and completion of 12 months of maintenance in another. One patient stopped crenolanib early as he developed fungal pneumonia and one patient stopped due to lack of benefit. Only one patient required dose reduction due to grade 2 transaminitis. There were no cardiac toxicities, pericardial effusion, fluid retention or weight gain. Response: Four of five patients reported clinical benefit with crenolanib. Interestingly, the child with KMT2A-rearranged infant AML achieved a molecular CR after salvage therapy with Vyxeos plus crenolanib. This child was successfully bridged to a second HSCT and remains in remission one year after the start of his compassionate use crenolanib. Another patient with KMT2A fusion, p53 mutation and CNS AML achieved a CR with crenolanib + sorafenib, was successfully bridged to 2nd HSCT and received one year of post-transplant crenolanib maintenance. She remains in remission 3.5 years after initiation of crenolanib. The third patient with KMT2A fusion was successfully bridged to allo HSCT but relapsed 4 months after HSCT (she did not receive maintenance). The patient with bi-phenotypic AML (and D835H mutation) had a quick reduction in circulating blasts (within 24 h) but died of fungal sepsis. The fifth patient received reduced doses of crenolanib due to transaminitis and did not have a clinical benefit. Conclusion: This series of five children with multiply relapsed FLT3-mutant AML shows that treatment with full doses of crenolanib can be safely combined with salvage chemotherapy. Rapid remissions could be obtained even in patients with co-occurring KMT2A, 3q, and p53 mutations. Crenolanib, which is novel type-I pan FLT3 inhibitor, was able to inhibit variant FLT3 mutations (D835H, D835E and D848P). Crenolanib can be safely combined with ITT (2 of these children remain alive 1-3.5 years). Figure Disclosures Rubnitz: AbbVie Inc.: Research Funding. Karol:AbbVie Inc.: Other: Unrelated to this study, St. Jude has received a charitable contribution from AbbVie, Inc. The charitable contribution is not being used for clinical or research activities, including any activities related to this study. . Pathan:Arog Pharmaceuticals: Current Employment. Messahel:AROG Pharmaceuticals: Current Employment.

EXTH-59. POTENT, SELECTIVE, AND BRAIN PENETRANT INHIBITORS OF EXTRACELLULAR DOMAIN EGFR ONCOGENIC MUTANTS EXPRESSED IN GBM DEMONSTRATE EFFICACY IN AN INTRACRANIAL PATIENT DERIVED XENOGRAFT MODEL

EGFR mutations identified in glioblastomas (GBM) occur nearly exclusively at the allosteric extracellular domain (ECD) and constitutively activate oncogenic signaling. Despite wide success in treating tumors expressing EGFR catalytic site mutants, no drug has demonstrated clinical utility against tumors expressing the extracellular domain EGFR mutants. We demonstrate that the family of ECD mutations are not only co-expressed in GBM, but that they all activate the oncogene through a similar disulfide bond-mediated receptor dimerization mechanism. This dimerization occurs independent of ligands and renders the Locked-dimer (LoDi)-EGFR insensitive to agents that target the EGFR kinase domain mutants in NSCLC. The kinase conformation induced by these ECD mutations seen in glioblastomas is both oncogenic and altered from kinase domain mutations, thus necessitating a new approach to targeting. By screening against cells expressing LoDi-EGFR mutants, we have identified the first inhibitors that potently and selectively target LoDi-EGFR mutants versus both canonical active site oncogenic mutants and wild type EGFR. Through an optimization effort, we have identified a novel family of potent and selective LoDi-EGFR mutant inhibitors that effectively penetrate the blood brain barrier (BBB) following oral dosing in preclinical studies. A leading exemplar, BDTX-GBM-001, inhibits the 5 major LoDi-EGFR mutants expressed in GBM with antiproliferative potency of ~10 nM while showing favorable selectivity versus the human kinome. When dosed orally in the intracranial GBM6 patient derived xenograft model at 50, 30, and 15 mg/kg, a dose responsive decrease in tumor growth, as well as a statistically significant increase in survival, were observed. These data support the continued evaluation of rationally designed BBB penetrant inhibitors selectively targeting the common LoDi-EGFR mutants and enable the first chance to fully test the clinical hypothesis of EGFR driver mutants in GBM.

ABL Kinase Domain Mutations in Iranian Chronic Myeloid Leukemia Patients with Resistance to Tyrosine Kinase Inhibitors

Objective Tyrosine kinase inhibitors (TKIs) are considered standard first-line treatment in patients with chronic myeloid leukemia. Because ABL kinase domain mutations are the most common causes of treatment resistance, their prevalence and assessment during treatment may predict subsequent response to therapy. Methods The molecular response in Bcr-Abl1IS was tested via quantitative real-time polymerase chain reaction. We used the direct sequencing technique to discover the mutations in the ABL kinase domain. The IRIS trial established a standard baseline for measurement – (100% BCR-ABL1 on the ‘international scale’) and a major molecular response (good response to therapy) was defined as a 3-log reduction in the amount of BCR-ABL1 – 0.1% BCR-ABL1 on the international scale. Results We observed 11 different mutations in 13 patients, including E255K, which had the highest mutation rate. A lack of hematologic response was found in 22 patients, who showed a significantly higher incidence of mutations. Conclusion Detection of kinase domain mutations is a reliable method for choosing the best treatment strategy based on patients’ conditions, avoiding ineffective treatments, and running high-cost protocols in patients with acquired resistance to TKIs.