1 2719 114 EXOME SEQUENCING REVEALS DNMT3A AND ASXL1 VARIANTS ASSOCIATE WITH PROGRESSION OF CHRONIC MYELOID LEUKEMIA AFTER TYROSINE KINASE INHIBITOR THERAPY. OBJECTIVE: THE DEVELOPMENT OF TYROSINE KINASE INHIBITORS (TKIS) HAS SIGNIFICANTLY IMPROVED THE TREATMENT OF CHRONIC MYELOID LEUKEMIA (CML). HOWEVER, APPROXIMATELY ONE THIRD OF PATIENTS ARE RESISTANT TO TKI AND/OR PROGRESS TO ADVANCED DISEASE STAGES. TKI THERAPY FAILURE HAS A WELL-KNOWN ASSOCIATION WITH ABL1 KINASE DOMAIN (KD) MUTATIONS, BUT ONLY AROUND HALF OF TKI NON-RESPONDERS HAVE DETECTABLE ABL1 KD MUTATIONS. METHOD: WE ATTEMPT TO IDENTIFY GENETIC MARKERS ASSOCIATED WITH TKI THERAPY FAILURE IN 13 PATIENTS (5 RESISTANT, 8 PROGRESSED) WITHOUT ABL1 KD MUTATIONS USING WHOLE-EXOME SEQUENCING. RESULTS: IN 6 PATIENTS, WE DETECTED MUTATIONS IN 6 GENES COMMONLY MUTATED IN OTHER MYELOID NEOPLASMS: ABL1, ASXL1, DNMT3A, IDH1, SETBP1, AND TP63. WE THEN USED TARGETED DEEP SEQUENCING TO VALIDATE OUR FINDING IN AN INDEPENDENT COHORT CONSISTING OF 100 CML PATIENTS WITH VARYING DRUG RESPONSES (74 RESPONSIVE, 18 RESISTANT, AND 8 PROGRESSED PATIENTS). MUTATIONS IN GENES ASSOCIATED WITH EPIGENETIC REGULATIONS SUCH AS DNMT3A AND ASXL1 SEEM TO PLAY AN IMPORTANT ROLE IN THE PATHOGENESIS OF CML PROGRESSION AND TKI-RESISTANCE INDEPENDENT OF ABL1 KD MUTATIONS. CONCLUSION: THIS STUDY SUGGESTS THE INVOLVEMENT OF OTHER SOMATIC MUTATIONS IN THE DEVELOPMENT OF TKI RESISTANT PROGRESSION TO ADVANCED DISEASE STAGES IN CML, PARTICULARLY IN PATIENTS LACKING ABL1 KD MUTATIONS. 2017 2 536 40 ASXL1 MUTATIONS PREDICT INFERIOR MOLECULAR RESPONSE TO NILOTINIB TREATMENT IN CHRONIC MYELOID LEUKEMIA. GENE MUTATIONS INDEPENDENT OF BCR::ABL1 HAVE BEEN IDENTIFIED IN NEWLY DIAGNOSED PATIENTS WITH CHRONIC MYELOID LEUKEMIA (CML) IN CHRONIC PHASE, WHEREBY MUTATIONS IN EPIGENETIC MODIFIER GENES WERE MOST COMMON. THESE FINDINGS PROMPTED THE SYSTEMATIC ANALYSIS OF PREVALENCE, DYNAMICS, AND PROGNOSTIC SIGNIFICANCE OF SUCH MUTATIONS, IN A CLINICALLY WELL-CHARACTERIZED PATIENT POPULATION OF 222 CML PATIENTS FROM THE TIGER STUDY (CML-V) BY TARGETED NEXT-GENERATION SEQUENCING COVERING 54 MYELOID LEUKEMIA-ASSOCIATED GENES. IN TOTAL, 53/222 CML PATIENTS (24%) CARRIED 60 MUTATIONS AT DIAGNOSIS WITH ASXL1 BEING MOST COMMONLY AFFECTED (N = 20). TO STUDY MUTATION DYNAMICS, LONGITUDINAL DEEP SEQUENCING ANALYSIS OF SERIAL SAMPLES WAS PERFORMED IN 100 PATIENTS AFTER 12, 24, AND 36 MONTHS OF THERAPY. TYPICAL PATTERNS OF CLONAL EVOLUTION INCLUDED ERADICATION, PERSISTENCE, AND EMERGENCE OF MUTATED CLONES. PATIENTS CARRYING AN ASXL1 MUTATION AT DIAGNOSIS SHOWED A LESS FAVORABLE MOLECULAR RESPONSE TO NILOTINIB TREATMENT, AS A MAJOR MOLECULAR RESPONSE (MMR) WAS ACHIEVED LESS FREQUENTLY AT MONTH 12, 18, AND 24 COMPARED TO ALL OTHER PATIENTS. PATIENTS WITH ASXL1 MUTATIONS WERE ALSO YOUNGER AND MORE FREQUENTLY FOUND IN THE HIGH RISK CATEGORY, SUGGESTING A CENTRAL ROLE OF CLONAL EVOLUTION ASSOCIATED WITH ASXL1 MUTATIONS IN CML PATHOGENESIS. 2022 3 32 41 A CASE OF TYROSINE KINASE INHIBITOR-RESISTANT CHRONIC MYELOID LEUKEMIA, CHRONIC PHASE WITH ASXL1 MUTATION. HEMATOLOGICAL MALIGNANCIES, INCLUDING CHRONIC MYELOID LEUKEMIA (CML), EXHIBIT ASXL1 MUTATIONS; HOWEVER, THE FUNCTION AND MOLECULAR MECHANISM OF THESE MUTATIONS REMAIN UNCLEAR. ASXL1 WAS ORIGINALLY IDENTIFIED AS TUMOR SUPPRESSOR GENE, IN WHICH LOSS OF FUNCTION CAUSES MYELODYSPLASTIC SYNDROME (MDS). ASXL1 MUTATIONS ARE COMMON AND ASSOCIATED WITH DISEASE PROGRESSION IN MYELOID MALIGNANCIES INCLUDING MDS, ACUTE MYELOID LEUKEMIA, AND SIMILARLY IN CML. IN MDS, ASXL1 MUTATIONS HAVE BEEN ASSOCIATED WITH POOR PROGNOSIS; HOWEVER, THE IMPACT OF ASXL1 MUTATIONS IN CML HAS NOT BEEN WELL DESCRIBED. A 31-YEAR-OLD MALE WAS DIAGNOSED AS CML-CHRONIC PHASE (CP). LABORATORY FINDINGS SHOWED A WHITE BLOOD CELL COUNT OF 187,200/MICROL, WITH ASYMPTOMATIC SPLENOMEGALY. BLAST COUNT WAS 5.0% IN PERIPHERAL BLOOD AND 7.3% IN BONE MARROW. THERE WAS NO ADDITIONAL CHROMOSOMAL ABNORMALITY EXCEPT FOR T(9;22)(Q34;Q11.2) BY CHROMOSOMAL ANALYSIS. AT ONSET, THE SOKAL SCORE WAS 1.4, INDICATING HIGH RISK. THE PATIENT RECEIVED TYROSINE KINASE INHIBITOR (TKI) THERAPY, COMPRISING NILOTINIB APPROXIMATELY 600 MG/DAY, BOSUTINIB APPROXIMATELY 600 MG/DAY, PONATINIB APPROXIMATELY 45 MG/DAY, AND DASATINIB APPROXIMATELY 100 MG/DAY. NEVERTHELESS, AFTER 1.5 YEARS OF CONTINUOUS TKI THERAPY, THE BEST OUTCOME WAS A HEMATOLOGICAL RESPONSE. ALTHOUGH ADDITIONAL CHROMOSOMAL ABERRATIONS AND ABL1 KINASE MUTATIONS WERE ANALYZED REPEATEDLY BEFORE AND DURING TKI THERAPY, KNOWN GENETIC ABNORMALITIES WERE NOT DETECTED. THEREAFTER, THE PATIENT UNDERWENT BONE MARROW TRANSPLANTATION FROM AN HLA 7/8 MATCHED UNRELATED DONOR (HLA-CW 1 LOCUS MISMATCH, GRAFT-VERSUS-HOST DIRECTION). THE PATIENT ACHIEVED NEUTROPHIL ENGRAFTMENT, 18 DAYS AFTER TRANSPLANTATION, LEADING TO COMPLETE REMISSION WITH AN UNDETECTABLE LEVEL OF BCR-ABL1 MRNA. THE PATIENT, HOWEVER, DIED FROM GRAFT-VERSUS-HOST DISEASE AND THROMBOTIC MICROANGIOPATHY AFTER 121 DAYS. GENE SEQUENCE ANALYSIS OF HIS CML CELL BEFORE STEM CELL TRANSPLANTATION REVEALED ASXL1 MUTATIONS. PHYSIOLOGICALLY, ASXL1 CONTRIBUTES TO EPIGENETIC REGULATION. IN THE CML-CP PATIENT IN THIS CASE REPORT, ASXL1 MUTATION CONFERRED RESISTANCE TO TKI THROUGH OBSCURE RESISTANCE MECHANISMS. EVEN THOUGH A MOLECULAR MECHANISM FOR TKI RESISTANCE IN ASXL1 MUTATION IN CML HAS REMAINED OBSCURE, EPIGENETIC MODULATION IS A PLAUSIBLE MODE OF CML DISEASE PROGRESSION. THE CLINICAL IMPACT INCLUDING PROGNOSIS OF ASXL1 FOR CML IS UNDERSCORED. AND THE TREATMENT STRATEGY OF CML WITH ASXL1 MUTATION HAS NOT BEEN ESTABLISHED. A DISCUSSION OF THIS CASE WAS EXPECTED TO FACILITATE TREATMENT OPTIONS. 2020 4 1082 41 CML - NOT ONLY BCR-ABL1 MATTERS. BCR-ABL1 IS IN THE CENTER OF CHRONIC MYELOID LEUKEMIA (CML) PATHOLOGY, DIAGNOSIS AND TREATMENT, AS CONFIRMED BY THE SUCCESS OF TYROSINE KINASE INHIBITOR (TKI) THERAPY. HOWEVER, ADDITIONAL MECHANISMS AND EVENTS, MANY OF WHICH FUNCTION INDEPENDENTLY OF BCR-ABL1, PLAY IMPORTANT ROLES, PARTICULARLY IN TERMS OF LEUKEMIC STEM CELL (LSC) PERSISTENCE, PRIMARY AND SECONDARY RESISTANCE, AND DISEASE PROGRESSION. PROMISING THERAPEUTIC APPROACHES AIM TO DISRUPT PATHWAYS WHICH MEDIATE LSC SURVIVAL DURING SUCCESSFUL TKI TREATMENT, IN THE HOPE OF IMPROVING LONG-TERM TREATMENT-FREE-REMISSION AND PERHAPS PROVIDE A FUNCTIONAL CURE FOR SOME PATIENTS. OVER THE YEARS THROUGH ADVANCES IN SEQUENCING TECHNOLOGY FREQUENT MOLECULAR ABERRATIONS IN ADDITION TO BCR-ABL1 HAVE BEEN IDENTIFIED NOT ONLY IN ADVANCED DISEASE BUT ALSO IN CHRONIC PHASE CML, OFTEN AFFECTING EPIGENETIC REGULATORS SUCH AS ASXL1, DNMT3A AND TET2. ANALYSES OF SERIAL SAMPLES HAVE REVEALED VARIOUS PATTERNS OF CLONAL EVOLUTION WITH SOME MUTATIONS PRECEDING THE BCR-ABL1 ACQUISITION. SUCH MUTATIONS CAN BE CONSIDERED TO BE IMPORTANT CO-FACTORS IN THE PATHOGENESIS OF CML AND COULD POTENTIALLY INFLUENCE THERAPEUTIC STRATEGIES IN THE FUTURE. 2020 5 149 38 ABERRANT HYDROXYMETHYLATION IN PROMOTER CPG REGIONS OF GENES RELATED TO THE CELL CYCLE AND APOPTOSIS CHARACTERIZES ADVANCED CHRONIC MYELOID LEUKEMIA DISEASE, POOR IMATINIB RESPONDENTS AND POOR SURVIVAL. BACKGROUND: THERE IS STRONG EVIDENCE THAT DISEASE PROGRESSION, DRUG RESPONSE AND OVERALL CLINICAL OUTCOMES OF CML DISEASE ARE NOT ONLY DECIDED BY BCR/ABL1 ONCOPROTEIN BUT DEPEND ON ACCUMULATION OF ADDITIONAL GENETIC AND EPIGENETIC ABERRATIONS. DNA HYDROXYMETHYLATION IS IMPLICATED IN THE DEVELOPMENT OF VARIETY OF DISEASES. DNA HYDROXYMETHYLATION IN GENE PROMOTERS PLAYS IMPORTANT ROLES IN DISEASE PROGRESSION, DRUG RESPONSE AND CLINICAL OUTCOME OF VARIOUS DISEASES. THEREFORE IN THIS STUDY, WE AIMED TO EXPLORE THE ROLE OF ABERRANT HYDROXYMETHYLATION IN PROMOTER REGIONS OF DIFFERENT TUMOR SUPPRESSOR GENES IN RELATION TO CML DISEASE PROGRESSION, RESPONSE TO IMATINIB THERAPY AND CLINICAL OUTCOME. METHODS: WE RECRUITED 150 CML PATIENTS AT DIFFERENT CLINICAL STAGES OF THE DISEASE. PATIENTS WERE FOLLOWED UP FOR 48 MONTHS AND HAEMATOLOGICAL/MOLECULAR RESPONSES WERE ANALYSED. HAEMATOLOGICAL RESPONSE WAS ANALYSED BY PERIPHERAL BLOOD SMEAR. BCR/ABL1 SPECIFIC TAQMAN PROBE BASED QRT-PCR WAS USED FOR ASSESSING THE MOLECULAR RESPONSE OF CML PATIENTS ON IMATINIB THERAPY. PROMOTER HYDROXYMETHYLATION OF THE GENES WAS CHARACTERIZED USING MS-PCR. RESULTS: WE OBSERVED THAT PROMOTER HYDROXYMETHYLATION OF DAPK1, RIZ1, P16INK4A, RASSF1A AND P14ARF(ARF) GENES CHARACTERIZE ADVANCED CML DISEASE AND POOR IMATINIB RESPONDENTS. ALTHOUGH, CYTOKINE SIGNALLING (SOCS1) GENE WAS HYPERMETHYLATED IN ADVANCED STAGES OF CML AND ACCUMULATED IN PATIENTS WITH POOR IMATINIB RESPONSE, BUT THE DIFFERENCES WERE NOT STATISTICALLY SIGNIFICANT. MOREOVER, WE FOUND HYPERMETHYLATION OF P14(ARF), RASSF1 AND P16(INK4A) GENES AND CYTOKINE SIGNALLING GENE (SOCS1) SIGNIFICANTLY ASSOCIATED WITH POOR OVERALL SURVIVAL OF CML PATIENTS ON IMATINIB THERAPY. THE RESULTS OF THIS STUDY ARE IN AGREEMENT OF THE ROLE OF ABERRANT DNA METHYLATION OF DIFFERENT TUMOR SUPPRESSOR GENES AS POTENTIAL BIOMARKERS OF CML DISEASE PROGRESSION, POOR IMATINIB RESPONSE AND OVERALL CLINICAL OUTCOME. CONCLUSION: IN THIS STUDY, WE REPORT THAT PROMOTER HYDROXYMETHYLATION OF DAPK1, RIZ1, P16INK4A, RASSF1A AND P14ARF(ARF) GENES IS A CHARACTERISTIC FEATURE OF CML DISEASE PROGRESSIONS, DEFINES POOR IMATINIB RESPONDENTS AND POOR OVERALL SURVIVAL OF CML PATIENTS TO IMATINIB THERAPY. 2022 6 535 28 ASXL1 MUTATION CORRECTION BY CRISPR/CAS9 RESTORES GENE FUNCTION IN LEUKEMIA CELLS AND INCREASES SURVIVAL IN MOUSE XENOGRAFTS. RECURRENT SOMATIC MUTATIONS OF THE EPIGENETIC MODIFIER AND TUMOR SUPPRESSOR ASXL1 ARE COMMON IN MYELOID MALIGNANCIES, INCLUDING CHRONIC MYELOID LEUKEMIA (CML), AND ARE ASSOCIATED WITH POOR CLINICAL OUTCOME. CRISPR/CAS9 HAS RECENTLY EMERGED AS A POWERFUL AND VERSATILE GENOME EDITING TOOL FOR GENOME ENGINEERING IN VARIOUS SPECIES. WE HAVE USED THE CRISPR/CAS9 SYSTEM TO CORRECT THE ASXL1 HOMOZYGOUS NONSENSE MUTATION PRESENT IN THE CML CELL LINE KBM5, WHICH LACKS ASXL1 PROTEIN EXPRESSION. CRISPR/CAS9-MEDIATED ASXL1 HOMOZYGOUS CORRECTION RESULTED IN PROTEIN RE-EXPRESSION WITH RESTORED NORMAL FUNCTION, INCLUDING DOWN-REGULATION OF POLYCOMB REPRESSIVE COMPLEX 2 TARGET GENES. SIGNIFICANTLY REDUCED CELL GROWTH AND INCREASED MYELOID DIFFERENTIATION WERE OBSERVED IN ASXL1 MUTATION-CORRECTED CELLS, PROVIDING NEW INSIGHTS INTO THE ROLE OF ASXL1 IN HUMAN MYELOID CELL DIFFERENTIATION. MICE XENOGRAFTED WITH MUTATION-CORRECTED KBM5 CELLS SHOWED SIGNIFICANTLY LONGER SURVIVAL THAN UNCORRECTED XENOGRAFTS. THESE RESULTS SHOW THAT THE SOLE CORRECTION OF A DRIVER MUTATION IN LEUKEMIA CELLS INCREASES SURVIVAL IN VIVO IN MICE. THIS STUDY PROVIDES PROOF-OF-CONCEPT FOR DRIVER GENE MUTATION CORRECTION VIA CRISPR/CAS9 TECHNOLOGY IN HUMAN LEUKEMIA CELLS AND PRESENTS A STRATEGY TO ILLUMINATE THE IMPACT OF ONCOGENIC MUTATIONS ON CELLULAR FUNCTION AND SURVIVAL. 2015 7 5762 41 SOMATIC VARIANTS IN EPIGENETIC MODIFIERS CAN PREDICT FAILURE OF RESPONSE TO IMATINIB BUT NOT TO SECOND-GENERATION TYROSINE KINASE INHIBITORS. THERE ARE NO VALIDATED MOLECULAR BIOMARKERS TO IDENTIFY NEWLY-DIAGNOSED INDIVIDUALS WITH CHRONIC-PHASE CHRONIC MYELOID LEUKEMIA LIKELY TO RESPOND POORLY TO IMATINIB AND WHO MIGHT BENEFIT FROM FIRST-LINE TREATMENT WITH A MORE POTENT SECOND-GENERATION TYROSINE KINASE INHIBITOR. OUR INABILITY TO PREDICT THESE 'HIGH-RISK' INDIVIDUALS REFLECTS THE POORLY UNDERSTOOD HETEROGENEITY OF THE DISEASE. TO INVESTIGATE THE POTENTIAL OF GENETIC VARIANTS IN EPIGENETIC MODIFIERS AS BIOMARKERS AT DIAGNOSIS, WE USED ION TORRENT NEXT-GENERATION SEQUENCING OF 71 CANDIDATE GENES FOR PREDICTING RESPONSE TO TYROSINE KINASE INHIBITORS AND PROBABILITY OF DISEASE PROGRESSION. A TOTAL OF 124 SUBJECTS WITH NEWLY-DIAGNOSED CHRONIC-PHASE CHRONIC MYELOID LEUKEMIA BEGAN WITH IMATINIB (N=62) OR SECOND-GENERATION TYROSINE KINASE INHIBITORS (N=62) AND WERE CLASSIFIED AS RESPONDERS OR NON-RESPONDERS BASED ON THE BCRABL1 TRANSCRIPT LEVELS WITHIN THE FIRST YEAR AND THE EUROPEAN LEUKEMIANET CRITERIA FOR FAILURE. SOMATIC VARIANTS AFFECTING 21 GENES (E.G. ASXL1, IKZF1, DNMT3A, CREBBP) WERE DETECTED IN 30% OF SUBJECTS, MOST OF WHOM WERE NON-RESPONDERS (41% NON-RESPONDERS, 18% RESPONDERS TO IMATINIB, 38% NON-RESPONDERS, 25% RESPONDERS TO SECOND-GENERATION TYROSINE KINASE INHIBITORS). THE PRESENCE OF VARIANTS PREDICTED THE RATE OF ACHIEVING A MAJOR MOLECULAR RESPONSE, EVENT-FREE SURVIVAL, PROGRESSION-FREE SURVIVAL AND CHRONIC MYELOID LEUKEMIA-RELATED SURVIVAL IN THE IMATINIB BUT NOT THE SECOND-GENERATION TYROSINE KINASE INHIBITORS COHORT. RARE GERMLINE VARIANTS HAD NO PROGNOSTIC SIGNIFICANCE IRRESPECTIVE OF TREATMENT WHILE SOME PRE-LEUKEMIA VARIANTS SUGGEST A MULTI-STEP DEVELOPMENT OF CHRONIC MYELOID LEUKEMIA. OUR DATA SUGGEST THAT IDENTIFICATION OF SOMATIC VARIANTS AT DIAGNOSIS FACILITATES STRATIFICATION INTO IMATINIB RESPONDERS/NON-RESPONDERS, THEREBY ALLOWING EARLIER USE OF SECOND-GENERATION TYROSINE KINASE INHIBITORS, WHICH, IN TURN, MAY OVERCOME THE NEGATIVE IMPACT OF SUCH VARIANTS ON DISEASE PROGRESSION. 2019 8 572 32 BCR-ABL1 KINASE-DEPENDENT ALTERATION OF MRNA METABOLISM: POTENTIAL ALTERNATIVES FOR THERAPEUTIC INTERVENTION. THE USE OF FIRST- AND SECOND-GENERATION TYROSINE KINASE INHIBITORS (TKIS) SIGNIFICANTLY IMPROVES PROGNOSIS FOR PATIENTS WITH EARLY CHRONIC PHASE CHRONIC MYELOID LEUKEMIA (CML) AND EFFICIENTLY COUNTERACTS LEUKEMIA IN MOST PATIENTS WITH CML BEARING A DISEASE CHARACTERIZED BY THE EXPRESSION OF BCR-ABL1 MUTANTS. HOWEVER, THE SO-CALLED 'TINIB' TKIS (E.G. IMATINIB, NILOTINIB, DASATINIB, AND BOSUTINIB) ARE BOTH INEFFECTIVE IN PATIENTS WHO UNDERGO BLASTIC TRANSFORMATION AND UNABLE TO ERADICATE CML AT THE STEM CELL LEVEL. THIS RAISES A FEW IMPORTANT QUESTIONS. IS BCR-ABL1 EXPRESSION AND/OR ACTIVITY ESSENTIAL FOR BLASTIC TRANSFORMATION? IS BLASTIC TRANSFORMATION THE RESULT OF GENETIC OR EPIGENETIC EVENTS THAT OCCUR AT THE STEM CELL LEVEL WHICH ONLY BECOME APPARENT IN THE GRANULOCYTE-MACROPHAGE PROGENITOR (GMP) CELL POOL, OR DOES IT ARISE DIRECTLY AT THE GMP LEVEL? AS ALTERED MRNA METABOLISM CONTRIBUTES TO THE PHENOTYPE OF BLAST CRISIS CML PROGENITORS (DECREASED TRANSLATION OF TUMOR SUPPRESSOR GENES AND TRANSCRIPTION FACTORS ESSENTIAL FOR TERMINAL DIFFERENTIATION AND INCREASED TRANSLATION OF ANTI-APOPTOTIC GENES), ONE ATTRACTIVE CONCEPT IS TO RESTORE LEVELS OF THESE ESSENTIAL MOLECULES TO THEIR NORMAL LEVELS. IN THIS REVIEW, WE DISCUSS THE MECHANISMS BY WHICH MRNA PROCESSING, TRANSLATION, AND DEGRADATION ARE DEREGULATED IN BCR-ABL1 MYELOID BLAST CRISIS CML PROGENITORS, AND PRESENT ENCOURAGING RESULTS FROM STUDIES WITH PHARMACOLOGIC INHIBITORS WHICH SUPPORT THEIR INCLUSION IN THE CLINIC. 2011 9 4552 37 MUTATIONAL LANDSCAPE OF CHRONIC MYELOID LEUKEMIA: MORE THAN A SINGLE ONCOGENE LEUKEMIA. THE BCR-ABL1 FUSION GENE, WHICH CAUSES ABERRANT KINASE ACTIVITY AND UNCONTROLLED CELL PROLIFERATION, IS THE HALLMARK OF CHRONIC MYELOID LEUKEMIA (CML). THE DEVELOPMENT OF TYROSINE KINASE INHIBITORS (TKI) THAT TARGET THE BCR-ABL ONCOPROTEIN HAS LED TO DRAMATIC IMPROVEMENT IN CML MANAGEMENT. HOWEVER, SOME CHALLENGES REMAIN TO BE ADDRESSED IN THE TKI ERA, INCLUDING PATIENT STRATIFICATION AND THE SELECTION OF FRONTLINE TKIS AND CML PROGRESSION. ADDITIONALLY, WITH THE EMERGING GOAL OF TREATMENT-FREE REMISSION (TFR) IN CML MANAGEMENT, BIOMARKERS THAT PREDICT THE OUTCOMES OF STOPPING TKI REMAIN TO BE IDENTIFIED. NOTABLY, RECENT REPORTS HAVE REVEALED THE POWER OF GENOME SCREENING IN UNDERSTANDING THE ROLE OF GENOME ABERRATIONS OTHER THAN BCR-ABL1 IN CML PATHOGENESIS. THESE STUDIES HAVE DISCOVERED THE PRESENCE OF DISEASE-PHASE SPECIFIC MUTATIONS AND LINKED CERTAIN MUTATIONS TO INFERIOR RESPONSES TO TKI TREATMENT AND CML PROGRESSION. A PERSONALIZED APPROACH THAT INCORPORATES GENETIC DATA IN TAILORING TREATMENT STRATEGIES HAS BEEN SUCCESSFULLY IMPLEMENTED IN ACUTE LEUKEMIA, AND IT REPRESENTS A PROMISING APPROACH FOR THE MANAGEMENT OF HIGH-RISK CML PATIENTS. IN THIS ARTICLE, WE WILL REVIEW CURRENT KNOWLEDGE ABOUT THE MUTATIONAL PROFILE IN DIFFERENT PHASES OF CML AS WELL AS PATTERNS OF MUTATIONAL DYNAMICS IN PATIENTS HAVING DIFFERENT OUTCOMES. WE HIGHLIGHT THE EFFECTS OF SOMATIC MUTATIONS INVOLVING CERTAIN GENES (E.G. EPIGENETIC MODIFIERS) ON THE OUTCOMES OF TKI TREATMENT. WE ALSO DISCUSS THE POTENTIAL VALUE OF INCORPORATING GENETIC DATA IN TREATMENT DECISIONS AND THE ROUTINE CARE OF CML PATIENTS AS A FUTURE DIRECTION FOR OPTIMIZING CML MANAGEMENT. 2021 10 1507 28 DNA METHYLATION AND INTRA-CLONAL HETEROGENEITY: THE CHRONIC MYELOID LEUKEMIA MODEL. CHRONIC MYELOID LEUKEMIA (CML) IS A MODEL TO INVESTIGATE THE IMPACT OF TUMOR INTRA-CLONAL HETEROGENEITY IN PERSONALIZED MEDICINE. INDEED, TYROSINE KINASE INHIBITORS (TKIS) TARGET THE BCR-ABL FUSION PROTEIN, WHICH IS CONSIDERED THE MAJOR CML DRIVER. TKI USE HAS HIGHLIGHTED THE EXISTENCE OF INTRA-CLONAL HETEROGENEITY, AS INDICATED BY THE PERSISTENCE OF A MINORITY SUBCLONE FOR SEVERAL YEARS DESPITE THE PRESENCE OF THE TARGET FUSION PROTEIN IN ALL CELLS. EPIGENETIC MODIFICATIONS COULD PARTLY EXPLAIN THIS HETEROGENEITY. THIS REVIEW SUMMARIZES THE RESULTS OF DNA METHYLATION STUDIES IN CML. NEXT-GENERATION SEQUENCING TECHNOLOGIES ALLOWED FOR MOVING FROM SINGLE-GENE TO GENOME-WIDE ANALYSES SHOWING THAT METHYLATION ABNORMALITIES ARE MUCH MORE WIDESPREAD IN CML CELLS. THESE DATA SHOWED THAT GLOBAL HYPOMETHYLATION IS ASSOCIATED WITH HYPERMETHYLATION OF SPECIFIC SITES ALREADY AT DIAGNOSIS IN THE EARLY PHASE OF CML. THE BCR-ABL-INDEPENDENCE OF SOME METHYLATION PROFILE ALTERATIONS AND THE RECENT DEMONSTRATION OF THE INITIAL INTRA-CLONAL DNA METHYLATION HETEROGENEITY SUGGESTS THAT SOME DNA METHYLATION ALTERATIONS MAY BE BIOMARKERS OF TKI SENSITIVITY/RESISTANCE AND OF DISEASE PROGRESSION RISK. THESE RESULTS ALSO OPEN PERSPECTIVES FOR UNDERSTANDING THE EPIGENETIC/GENETIC BACKGROUND OF CML PREDISPOSITION AND FOR DEVELOPING NEW THERAPEUTIC STRATEGIES. 2021 11 2971 16 GENETIC AND EPIGENETIC SILENCING OF MICRORNA-203 ENHANCES ABL1 AND BCR-ABL1 ONCOGENE EXPRESSION. THE MAMMALIAN GENOME CONTAINS SEVERAL HUNDRED MICRORNAS THAT REGULATE GENE EXPRESSION THROUGH MODULATION OF TARGET MRNAS. HERE, WE REPORT A FRAGILE CHROMOSOMAL REGION LOST IN SPECIFIC HEMATOPOIETIC MALIGNANCIES. THIS 7 MB REGION ENCODES ABOUT 12% OF ALL GENOMIC MICRORNAS, INCLUDING MIR-203. THIS MICRORNA IS ADDITIONALLY HYPERMETHYLATED IN SEVERAL HEMATOPOIETIC TUMORS, INCLUDING CHRONIC MYELOGENOUS LEUKEMIAS AND SOME ACUTE LYMPHOBLASTIC LEUKEMIAS. A PUTATIVE MIR-203 TARGET, ABL1, IS SPECIFICALLY ACTIVATED IN THESE HEMATOPOIETIC MALIGNANCIES IN SOME CASES AS A BCR-ABL1 FUSION PROTEIN (PHILADELPHIA CHROMOSOME). RE-EXPRESSION OF MIR-203 REDUCES ABL1 AND BCR-ABL1 FUSION PROTEIN LEVELS AND INHIBITS TUMOR CELL PROLIFERATION IN AN ABL1-DEPENDENT MANNER. THUS, MIR-203 FUNCTIONS AS A TUMOR SUPPRESSOR, AND RE-EXPRESSION OF THIS MICRORNA MIGHT HAVE THERAPEUTIC BENEFITS IN SPECIFIC HEMATOPOIETIC MALIGNANCIES. 2008 12 2781 35 EZH2 IN MYELOID MALIGNANCIES. OUR UNDERSTANDING OF THE SIGNIFICANCE OF EPIGENETIC DYSREGULATION IN THE PATHOGENESIS OF MYELOID MALIGNANCIES HAS GREATLY ADVANCED IN THE PAST DECADE. ENHANCER OF ZESTE HOMOLOG 2 (EZH2) IS THE CATALYTIC CORE COMPONENT OF THE POLYCOMB REPRESSIVE COMPLEX 2 (PRC2), WHICH IS RESPONSIBLE FOR GENE SILENCING THROUGH TRIMETHYLATION OF H3K27. EZH2 DYSREGULATION IS HIGHLY TUMORIGENIC AND HAS BEEN OBSERVED IN VARIOUS CANCERS, WITH EZH2 ACTING AS AN ONCOGENE OR A TUMOR-SUPPRESSOR DEPENDING ON CELLULAR CONTEXT. WHILE LOSS-OF-FUNCTION MUTATIONS OF EZH2 FREQUENTLY AFFECT PATIENTS WITH MYELODYSPLASTIC/MYELOPROLIFERATIVE NEOPLASMS, MYELODYSPLASTIC SYNDROME AND MYELOFIBROSIS, CASES OF CHRONIC MYELOID LEUKEMIA (CML) SEEM TO BE LARGELY CHARACTERIZED BY EZH2 OVEREXPRESSION. A VARIETY OF OTHER FACTORS FREQUENTLY ABERRANT IN MYELOID LEUKEMIA CAN AFFECT PRC2 FUNCTION AND DISEASE PATHOGENESIS, INCLUDING ADDITIONAL SEX COMBS LIKE 1 (ASXL1) AND SPLICING GENE MUTATIONS. AS THE GENETIC BACKGROUND OF MYELOID MALIGNANCIES IS LARGELY HETEROGENEOUS, IT IS NOT SURPRISING THAT EZH2 MUTATIONS ACT IN CONJUNCTION WITH OTHER ABERRATIONS. SINCE EZH2 MUTATIONS ARE CONSIDERED TO BE EARLY EVENTS IN DISEASE PATHOGENESIS, THEY ARE OF THERAPEUTIC INTEREST TO RESEARCHERS, THOUGH TARGETING OF EZH2 LOSS-OF-FUNCTION DOES PRESENT UNIQUE CHALLENGES. PRELIMINARY RESEARCH INDICATES THAT COMBINED TYROSINE KINASE INHIBITOR (TKI) AND EZH2 INHIBITOR THERAPY MAY PROVIDE A STRATEGY TO ELIMINATE THE RESIDUAL DISEASE BURDEN IN CML TO ALLOW PATIENTS TO REMAIN IN TREATMENT-FREE REMISSION. 2020 13 2848 40 FREQUENT SOMATIC MUTATIONS IN EPIGENETIC REGULATORS IN NEWLY DIAGNOSED CHRONIC MYELOID LEUKEMIA. ALTHOUGH TYROSINE KINASE INHIBITORS (TKIS) HAVE SIGNIFICANTLY IMPROVED THE PROGNOSIS OF CHRONIC MYELOID LEUKEMIA (CML), THE ABILITY OF TKIS TO ERADICATE CML REMAINS UNCERTAIN AND PATIENTS MUST CONTINUE TKI THERAPY FOR INDEFINITE PERIODS. IN THIS STUDY, WE PERFORMED WHOLE-EXOME SEQUENCING TO IDENTIFY SOMATIC MUTATIONS IN 24 PATIENTS WITH NEWLY DIAGNOSED CHRONIC PHASE CML WHO WERE REGISTERED IN THE JALSG CML212 STUDY. WE IDENTIFIED 191 SOMATIC MUTATIONS OTHER THAN THE BCR-ABL1 FUSION GENE (MEDIAN 8, RANGE 1-17). AGE, HEMOGLOBIN CONCENTRATION AND WHITE BLOOD CELL COUNTS WERE CORRELATED WITH THE NUMBER OF MUTATIONS. PATIENTS WITH MUTATIONS ?6 SHOWED HIGHER RATE OF ACHIEVING MAJOR MOLECULAR RESPONSE THAN THOSE<6 (P=0.0381). MUTATIONS IN EPIGENETIC REGULATOR, ASXL1, TET2, TET3, KDM1A AND MSH6 WERE FOUND IN 25% OF PATIENTS. TET2 OR TET3, AKT1 AND RUNX1 WERE MUTATED IN ONE PATIENT EACH. ASXL1 WAS MUTATED WITHIN EXON 12 IN THREE CASES. MUTATED GENES WERE SIGNIFICANTLY ENRICHED WITH CELL SIGNALING AND CELL DIVISION PATHWAYS. FURTHERMORE, DNA COPY NUMBER ANALYSIS SHOWED THAT 2 OF 24 PATIENTS HAD UNIPARENTAL DISOMY OF CHROMOSOME 1P OR 3Q, WHICH DISAPPEARED MAJOR MOLECULAR RESPONSE WAS ACHIEVED. THESE MUTATIONS MAY PLAY SIGNIFICANT ROLES IN CML PATHOGENESIS IN ADDITION TO THE STRONG DRIVER MUTATION BCR-ABL1. 2017 14 5687 34 SIGNIFICANCE OF INACTIVATED GENES IN LEUKEMIA: PATHOGENESIS AND PROGNOSIS. EPIGENETIC AND GENETIC ALTERATIONS ARE TWO MECHANISMS PARTICIPATING IN LEUKEMIA, WHICH CAN INACTIVATE GENES INVOLVED IN LEUKEMIA PATHOGENESIS OR PROGRESSION. THE PURPOSE OF THIS REVIEW WAS TO INTRODUCE VARIOUS INACTIVATED GENES AND EVALUATE THEIR POSSIBLE ROLE IN LEUKEMIA PATHOGENESIS AND PROGNOSIS. BY SEARCHING THE MESH WORDS "GENE, SILENCING AND LEUKEMIA" IN PUBMED WEBSITE, RELEVANT ENGLISH ARTICLES DEALT WITH HUMAN SUBJECTS AS OF 2000 WERE INCLUDED IN THIS STUDY. GENE INACTIVATION IN LEUKEMIA IS LARGELY MEDIATED BY PROMOTER'S HYPERMETHYLATION OF GENE INVOLVING IN CELLULAR FUNCTIONS SUCH AS CELL CYCLE, APOPTOSIS, AND GENE TRANSCRIPTION. INACTIVATED GENES, SUCH AS ASPP1, TP53, IKZF1 AND P15, MAY CORRELATE WITH POOR PROGNOSIS IN ACUTE LYMPHOID LEUKEMIA (ALL), CHRONIC LYMPHOID LEUKEMIA (CLL), CHRONIC MYELOGENOUS LEUKEMIA (CML) AND ACUTE MYELOID LEUKEMIA (AML), RESPECTIVELY. GENE INACTIVATION MAY PLAY A CONSIDERABLE ROLE IN LEUKEMIA PATHOGENESIS AND PROGNOSIS, WHICH CAN BE CONSIDERED AS COMPLEMENTARY DIAGNOSTIC TESTS TO DIFFERENTIATE DIFFERENT LEUKEMIA TYPES, DETERMINE LEUKEMIA PROGNOSIS, AND ALSO DETECT RESPONSE TO THERAPY. IN GENERAL, THIS REVIEW SHOWED SOME GENES INACTIVATED ONLY IN LEUKEMIA (WITH DIFFERENCES BETWEEN B-ALL, T-ALL, CLL, AML AND CML). THESE DIFFERENCES COULD BE OF INTEREST AS AN ADDITIONAL TOOL TO BETTER CATEGORIZE LEUKEMIA TYPES. FURTHERMORE; BASED ON INACTIVATED GENES, A DIVERSE CLASSIFICATION OF LEUKEMIAS COULD REPRESENT A POWERFUL METHOD TO ADDRESS A TARGETED THERAPY OF THE PATIENTS, IN ORDER TO MINIMIZE SIDE EFFECTS OF CONVENTIONAL THERAPIES AND TO ENHANCE NEW DRUG STRATEGIES. 2017 15 3087 33 GENOME?WIDE EXPRESSION AND METHYLATION ANALYSES REVEAL ABERRANT CELL ADHESION SIGNALING IN TYROSINE KINASE INHIBITOR?RESISTANT CML CELLS. ALTHOUGH CHRONIC MYELOID LEUKEMIA (CML) CAN BE EFFECTIVELY TREATED USING BCR?ABL1 KINASE INHIBITORS, RESISTANCE DUE TO KINASE ALTERATIONS OR TO BCR?ABL1 INDEPENDENT MECHANISMS REMAIN A THERAPEUTIC CHALLENGE. FOR THE LATTER, THE UNDERLYING MECHANISMS ARE WIDELY DISCUSSED; FOR INSTANCE, GENE EXPRESSION CHANGES, EPIGENETIC FACTORS AND ALTERNATIVE SIGNALING PATHWAY ACTIVATION. IN THE PRESENT STUDY, IN VITRO?CML CELL MODELS OF RESISTANCE AGAINST THE TYROSINE KINASE INHIBITORS (TKIS) IMATINIB (0.5 AND 2 MICROM) AND NILOTINIB (0.1 MICROM) WITH BIOLOGICAL REPLICATES WERE GENERATED TO IDENTIFY NOVEL MECHANISMS OF RESISTANCE. SUBSEQUENTLY, GENOME?WIDE MRNA EXPRESSION AND DNA METHYLATION WERE ANALYZED. WHILE MRNA EXPRESSION PATTERNS DIFFERED LARGELY BETWEEN BIOLOGICAL REPLICATES, THERE WAS AN OVERLAP OF 71 GENES DIFFERENTIALLY EXPRESSED BETWEEN CELLS RESISTANT AGAINST IMATINIB OR NILOTINIB. MOREOVER, ALL TKI RESISTANT CELL LINES DEMONSTRATED A SLIGHT HYPERMETHYLATION COMPARED WITH NATIVE CELLS. IN A COMBINED ANALYSIS OF 151 GENES DIFFERENTIALLY EXPRESSED IN THE BIOLOGICAL REPLICATES OF IMATINIB RESISTANCE, CELL ADHESION SIGNALING, IN PARTICULAR THE CELLULAR MATRIX PROTEIN FIBRONECTIN 1 (FN1), WAS SIGNIFICANTLY DYSREGULATED. THIS GENE WAS ALSO DOWNREGULATED IN NILOTINIB RESISTANCE. FURTHER ANALYSES SHOWED SIGNIFICANT FN1?DOWNREGULATION IN IMATINIB RESISTANCE ON MRNA (P<0.001) AND PROTEIN LEVEL (P<0.001). SIRNA?MEDIATED FN1?KNOCKDOWN IN NATIVE CELLS REDUCED CELL ADHESION (P=0.02), DECREASED IMATINIB SUSCEPTIBILITY VISIBLE BY HIGHER KI?67 EXPRESSION (1.5?FOLD, P=0.04) AND INCREASED CELL NUMBER (1.5?FOLD, P=0.03). VICE VERSA, RECOVERY OF FN1?EXPRESSION IN IMATINIB RESISTANT CELLS WAS SUFFICIENT TO PARTIALLY RESTORE THE RESPONSE TO IMATINIB. OVERALL, THESE RESULTS SUGGESTED A ROLE OF CELL ADHESION SIGNALING AND FIBRONECTIN 1 IN TKI RESISTANT CML AND A POTENTIAL TARGET FOR NOVEL STRATEGIES IN TREATMENT OF RESISTANT CML. 2022 16 109 41 A REVIEW ON THE THERAPEUTIC ROLE OF TKIS IN CASE OF CML IN COMBINATION WITH EPIGENETIC DRUGS. CHRONIC MYELOID LEUKEMIA IS A MALIGNANCY OF BONE MARROW THAT AFFECTS WHITE BLOOD CELLS. THERE IS STRONG EVIDENCE THAT DISEASE PROGRESSION, TREATMENT RESPONSES, AND OVERALL CLINICAL OUTCOMES OF CML PATIENTS ARE INFLUENCED BY THE ACCUMULATION OF OTHER GENETIC AND EPIGENETIC ABNORMALITIES, RATHER THAN ONLY THE BCR/ABL1 ONCOPROTEIN. BOTH GENETIC AND EPIGENETIC FACTORS INFLUENCE THE EFFICACY OF CML TREATMENT STRATEGIES. TARGETED MEDICINES KNOWN AS TYROSINE-KINASE INHIBITORS HAVE DRAMATICALLY IMPROVED LONG-TERM SURVIVAL RATES IN CML PATIENTS DURING THE PREVIOUS 2 DECADES. WHEN COMPARED TO EARLIER CHEMOTHERAPY TREATMENTS, THESE DRUGS HAVE REVOLUTIONIZED CML TREATMENT AND ALLOWED MOST PEOPLE TO LIVE LONGER LIVES. ALTHOUGH EPIGENETIC INHIBITORS' ACTIVITY IS DISRUPTED IN MANY CANCERS, INCLUDING CML, BUT WHEN COMBINED WITH TKI, THEY MAY OFFER POTENTIAL THERAPEUTIC STRATEGIES FOR THE TREATMENT OF CML CELLS. THE EPIGENETICS OF TYROSINE KINASE INHIBITORS AND RESISTANCE TO THEM IS BEING STUDIED, WITH A PARTICULAR FOCUS ON IMATINIB, WHICH IS USED TO TREAT CML. IN ADDITION, THE USE OF EPIGENETIC DRUGS IN CONJUNCTION WITH TKIS HAS BEEN DISCUSSED. RESISTANCE TO TKIS IS STILL A PROBLEM IN CURING THE DISEASE, NECESSITATING THE DEVELOPMENT OF NEW THERAPIES. THIS STUDY FOCUSED ON EPIGENETIC PATHWAYS INVOLVED IN CML PATHOGENESIS AND TUMOR CELL RESISTANCE TO TKIS, BOTH OF WHICH CONTRIBUTE TO LEUKEMIC CLONE BREAKOUT AND PROLIFERATION. 2021 17 954 24 CHRONIC MYELOID LEUKEMIA: CURRENT PERSPECTIVES. CHRONIC MYELOID LEUKEMIA (CML), CHARACTERIZED BY THE T(9;22) AND BCR/ABL1 FUSION, IS A DISEASE MODEL FOR STUDYING THE MECHANISMS OF GENETIC ABNORMALITIES IN LEUKEMOGENESIS. THE DETECTION OF THE T(9;22), CHARACTERIZATION OF THE BCR/ABL FUSION, AND THE DISCOVERY OF IMATINIB HAVE ELEGANTLY REFLECTED THE SUCCESS OF OUR RESEARCH EFFORTS IN CML. HOWEVER, GENOMIC INSTABILITIES THAT LEAD TO THE FORMATION OF THE BCR/ ABL1 FUSION ARE NOT FULLY UNDERSTOOD. IT IS IMPORTANT TO UNDERSTAND HOW VARIOUS GENES THAT ARE INVOLVED IN REGULATING THE SIGNALING PATHWAY AND EPIGENETIC DEREGULATION COOPERATE WITH THE BCR/ABL1 FUSION IN THE INITIATION AND PROGRESSION OF CML. 2011 18 955 29 CHRONIC MYELOID LEUKEMIA: MECHANISMS OF BLASTIC TRANSFORMATION. THE BCR-ABL1 ONCOPROTEIN TRANSFORMS PLURIPOTENT HSCS AND INITIATES CHRONIC MYELOID LEUKEMIA (CML). PATIENTS WITH EARLY PHASE (ALSO KNOWN AS CHRONIC PHASE [CP]) DISEASE USUALLY RESPOND TO TREATMENT WITH ABL TYROSINE KINASE INHIBITORS (TKIS), ALTHOUGH SOME PATIENTS WHO RESPOND INITIALLY LATER BECOME RESISTANT. IN MOST PATIENTS, TKIS REDUCE THE LEUKEMIA CELL LOAD SUBSTANTIALLY, BUT THE CELLS FROM WHICH THE LEUKEMIA CELLS ARE DERIVED DURING CP (SO-CALLED LEUKEMIA STEM CELLS [LSCS]) ARE INTRINSICALLY INSENSITIVE TO TKIS AND SURVIVE LONG TERM. LSCS OR THEIR PROGENY CAN ACQUIRE ADDITIONAL GENETIC AND/OR EPIGENETIC CHANGES THAT CAUSE THE LEUKEMIA TO TRANSFORM FROM CP TO A MORE ADVANCED PHASE, WHICH HAS BEEN SUBCLASSIFIED AS EITHER ACCELERATED PHASE OR BLASTIC PHASE DISEASE. THE LATTER RESPONDS POORLY TO TREATMENT AND IS USUALLY FATAL. HERE, WE DISCUSS WHAT IS KNOWN ABOUT THE MOLECULAR MECHANISMS LEADING TO BLASTIC TRANSFORMATION OF CML AND PROPOSE SOME NOVEL THERAPEUTIC APPROACHES. 2010 19 1465 25 DISSECTING THE ROLE OF ABERRANT DNA METHYLATION IN HUMAN LEUKAEMIA. CHRONIC MYELOID LEUKAEMIA (CML) IS A MYELOPROLIFERATIVE DISORDER CHARACTERIZED BY THE GENETIC TRANSLOCATION T(9;22)(Q34;Q11.2) ENCODING FOR THE BCR-ABL FUSION ONCOGENE. HOWEVER, MANY MOLECULAR MECHANISMS OF THE DISEASE PROGRESSION STILL REMAIN POORLY UNDERSTOOD. A GROWING BODY OF EVIDENCE SUGGESTS THAT THE EPIGENETIC ABNORMALITIES ARE INVOLVED IN TYROSINE KINASE RESISTANCE IN CML, LEADING TO LEUKAEMIC CLONE ESCAPE AND DISEASE PROPAGATION. HERE WE SHOW THAT, BY APPLYING CELLULAR REPROGRAMMING TO PRIMARY CML CELLS, ABERRANT DNA METHYLATION CONTRIBUTES TO THE DISEASE EVOLUTION. IMPORTANTLY, USING A BCR-ABL INDUCIBLE MURINE MODEL, WE DEMONSTRATE THAT A SINGLE ONCOGENIC LESION TRIGGERS DNA METHYLATION CHANGES, WHICH IN TURN ACT AS A PRECIPITATING EVENT IN LEUKAEMIA PROGRESSION. 2015 20 5259 33 PROGRESSIVE DE NOVO DNA METHYLATION AT THE BCR-ABL LOCUS IN THE COURSE OF CHRONIC MYELOGENOUS LEUKEMIA. DE NOVO METHYLATION OF CPG ISLANDS IS A RARE EVENT IN MAMMALIAN CELLS. IT HAS BEEN OBSERVED IN THE COURSE OF DEVELOPMENTAL PROCESSES, SUCH AS X CHROMOSOME INACTIVATION AND GENOMIC IMPRINTING. THE METHYLATION OF DNA, AN IMPORTANT FACTOR IN THE EPIGENETIC CONTROL OF GENE EXPRESSION, MAY ALSO BE INVOLVED IN TUMORIGENESIS. AFTER THE T(9;22) CHROMOSOMAL TRANSLOCATION AND GENERATION OF THE PHILADELPHIA CHROMOSOME, THE INITIATING EVENT IN CHRONIC MYELOGENOUS LEUKEMIA (CML), MOST OF THE ABL CODING SEQUENCE IS FUSED TO THE 5' REGION OF THE BCR GENE. EXPRESSION OF THE HYBRID BCR-ABL GENE IS, THEREFORE, REGULATED BY THE BCR PROMOTER. IN MOST CASES OF CML, ONE OF THE TWO ABL PROMOTERS (PA) IS NESTED WITHIN THE BCR-ABL TRANSCRIPTIONAL UNIT AND SHOULD BE ABLE TO TRANSCRIBE THE TYPE IA 6-KB NORMAL ABL MRNA FROM THE PHILADELPHIA CHROMOSOME. HOWEVER, WE HAVE FOUND THAT THE 6-KB TRANSCRIPT IS PRESENT ONLY IN CML CELL LINES CONTAINING A NORMAL ABL ALLELE AND THAT THE APPARENT INACTIVATION OF THE NESTED PA PROMOTER IS ASSOCIATED WITH ALLELE-SPECIFIC METHYLATION. FURTHERMORE, WE HAVE NOTICED THAT THE PA PROMOTER IS CONTAINED WITHIN A CPG ISLAND AND UNDERGOES PROGRESSIVE DE NOVO METHYLATION IN THE COURSE OF THE DISEASE. THIS IS ATTESTED TO BY THE FACT THAT DNA SAMPLES FROM CML PATIENTS THAT ARE METHYLATION-FREE AT THE TIME OF DIAGNOSIS INVARIABLY BECOME METHYLATED IN ADVANCED CML. SINCE TUMOR PROGRESSION IN CML CANNOT ALWAYS BE INFERRED FROM THE CLINICAL PRESENTATION, ASSESSMENT OF DE NOVO CPG METHYLATION MAY PROVE TO BE OF CRITICAL VALUE IN MANAGEMENT OF THE DISEASE. IT COULD HERALD BLASTIC TRANSFORMATION AT A STAGE WHEN BONE MARROW TRANSPLANTATION, THE ONLY POTENTIALLY CURATIVE THERAPEUTIC PROCEDURE IN CML, IS STILL EFFECTIVE. 1994