Bruton’s Tyrosine Kinase Degradation as a Therapeutic Strategy for Cancer
The covalent Bruton’s Tyrosine Kinase (BTK) inhibitor ibrutinib is highly efficacious against multiple B-cell malignancies. However, it also has off-target effects and multiple mechanisms of resistance, including the C481S mutation. We hypothesized that small molecule-induced BTK degradation might be able to overcome some of the limitations of traditional enzymatic inhibitors. Here, we demonstrate that BTK degradation results in more durable suppression of signaling and proliferation in cancer cells than BTK inhibition and that BTK degraders are able to efficiently degrade BTK C481S. Moreover, we generated DD-03-171, an optimized lead compound that exhibits enhanced anti-proliferative effects on mantle cell lymphoma (MCL) cells in vitro as well as efficacy in a patient-derived xenograft model of MCL. These data suggest that targeted BTK degradation is an effective therapeutic approach in treating MCL and overcoming ibrutinib resistance, thereby addressing a major unmet need in the treatment of MCL and other B-cell lymphomas.
Sample Processing Protocol
Mino cells were treated with DMSO or 200 nM of compounds DD-03-171, and DD-04-118 in biological triplicates for 4 hours and cells harvested by centrifugation. Lysis buffer (8 M Urea, 50 mM NaCl, 50 mM 4-(2hydroxyethyl)-1-piperazineethanesulfonic acid (EPPS) pH 8.5, Protease and Phosphatase inhibitors from Roche) was added to the cell pellets and homogenized by 20 passes through a 21 gauge (1.25 in. long) needle to achieve a cell lysate with a protein concentration between 1 – 4 mg mL-1. A micro-BCA assay (Pierce) was used to determine the final protein concentration in the cell lysate. 200 µg of protein for each sample were reduced and alkylated as previously described. Proteins were precipitated using methanol/chloroform. In brief, four volumes of methanol were added to the cell lysate, followed by one volume of chloroform, and finally three volumes of water. The mixture was vortexed and centrifuged to separate the chloroform phase from the aqueous phase. The precipitated protein was washed with three volumes of methanol, centrifuged and the resulting washed precipitated protein was allowed to air dry. Precipitated protein was resuspended in 4 M Urea, 50 mM HEPES pH 7.4, followed by dilution to 1 M urea with the addition of 200 mM EPPS, pH 8. Proteins were first digested with LysC (1:50; enzyme:protein) for 12 hours at room temperature. The LysC digestion was diluted to 0.5 M Urea with 200 mM EPPS pH 8l followed by digestion with trypsin (1:50; enzyme:protein) for 6 hours at 37 °C. Tandem mass tag (TMT) reagents (Thermo Fisher Scientific) were dissolved in anhydrous acetonitrile (ACN) according to manufacturer’s instructions. Anhydrous ACN was added to each peptide sample to a final concentration of 30% v/v, and labeling was induced with the addition of TMT reagent to each sample at a ratio of 1:4 peptide:TMT label. The 10-plex labeling reactions were performed for 1.5 hours at room temperature and the reaction quenched by the addition of hydroxylamine to a final concentration of 0.3% for 15 minutes at room temperature. The sample channels were combined at a 1:1:1:1:1:1:1:1:1:1 ratio, desalted using C18 solid phase extraction cartridges (Waters) and analyzed by LC-MS for channel ratio comparison. Samples were then combined using the adjusted volumes determined in the channel ratio analysis and dried down in a speed vacuum. The combined sample was then resuspended in 1% formic acid, and acidified (pH 2−3) before being subjected to desalting with C18 SPE (Sep-Pak, Waters). Samples were then offline fractionated into 96 fractions by high pH reverse-phase HPLC (Agilent LC1260) through an aeris peptide xb-c18 column (phenomenex) with mobile phase A containing 5% acetonitrile and 10 mM NH4HCO3 in LC-MS grade H2O, and mobile phase B containing 90% acetonitrile and 10 mM NH4HCO3 in LC-MS grade H2O (both pH 8.0). The 96 resulting fractions were then pooled in a non-continuous manner into 24 fractions and these fractions were used for subsequent mass spectrometry analysis. Data were collected using an Orbitrap Fusion Lumos mass spectrometer (Thermo Fisher Scientific, San Jose, CA, USA) coupled with a Proxeon EASY-nLC 1200 LC pump (Thermo Fisher Scientific). Peptides were separated on an EasySpray ES803 75 μm inner diameter microcapillary column (ThermoFisher Scientific). Peptides were separated using a 3 hr gradient of 6–27% acetonitrile in 1.0% formic acid with a flow rate of 400 nL/min. Each analysis used an MS3-based TMT method as described previously. The data were acquired using a mass range of m/z 350 – 1350, resolution 120,000, AGC target 1 x 106, maximum injection time 100 ms, dynamic exclusion of 90 seconds for the peptide measurements in the Orbitrap. Data dependent MS2 spectra were acquired in the ion trap with a normalized collision energy (NCE) set at 35%, AGC target set to 1.8 x 104 and a maximum injection time of 120 ms. MS3 scans were acquired in the Orbitrap with a HCD collision energy set to 55%, AGC target set to 1.5 x 105, maximum injection time of 150 ms, resolution at 50,000 and with a maximum synchronous precursor selection (SPS) precursors set to 10.
Data Processing Protocol
Proteome Discoverer 2.2 (Thermo Fisher) was used to for .RAW file processing and controlling peptide and protein level false discovery rates, assembling proteins from peptides, and protein quantification from peptides. MS/MS spectra were searched against a Uniprot human database (September 2016) with both the forward and reverse sequences. Database search criteria are as follows: tryptic with two missed cleavages, a precursor mass tolerance of 20 ppm, fragment ion mass tolerance of 0.6 Da, static alkylation of cysteine (57.02146 Da), static TMT labelling of lysine residues and N-termini of peptides (229.16293 Da), and variable oxidation of methionine (15.99491 Da). TMT reporter ion intensities were measured using a 0.003 Da window around the theoretical m/z for each reporter ion in the MS3 scan. Peptide spectral matches with poor quality MS3 spectra were excluded from quantitation (summed signal-to-noise across 10 channels < 200 and precursor isolation specificity < 0.5), and resulting data was filtered to only include proteins that had a minimum of 3 unique peptides identified. Reporter ion intensities were normalised and scaled using in-house scripts in the R framework. Statistical analysis was carried out using the limma package within the R framework.
Eric Fischer, Dana-Farber Cancer Institute
Eric S. Fischer, Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA., Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA ( lab head )
Dobrovolsky D, Wang ES, Morrow S, Leahy C, Faust T, Nowak RP, Donovan KA, Yang G, Li Z, Fischer ES, Treon SP, Weinstock DM, Gray NS. Bruton's Tyrosine Kinase degradation as a therapeutic strategy for cancer. Blood. 2018 PubMed: 30545835