bmn-673 and Leukemia--Myeloid--Acute

Patients with acute myeloid leukemia (AML) unfit for, or resistant to, intensive chemotherapy are often treated with DNA methyltransferase inhibitors (DNMTi). Novel combinations may increase efficacy. In addition to demethylating CpG island gene promoter regions, DNMTis enhance PARP1 recruitment and tight binding to chromatin, preventing PARP-mediated DNA repair, downregulating homologous recombination (HR) DNA repair, and sensitizing cells to PARP inhibitor (PARPi). We previously demonstrated DNMTi and PARPi combination efficacy in AML in vitro and in vivo. Here, we report a phase I clinical trial combining the DNMTi decitabine and the PARPi talazoparib in relapsed/refractory AML.. Decitabine and talazoparib doses were escalated using a 3 + 3 design. Pharmacodynamic studies were performed on cycle 1 days 1 (pretreatment), 5 and 8 blood blasts.. Doses were escalated in seven cohorts [25 patients, including 22 previously treated with DNMTi(s)] to a recommended phase II dose combination of decitabine 20 mg/m2 intravenously daily for 5 or 10 days and talazoparib 1 mg orally daily for 28 days, in 28-day cycles. Grade 3-5 events included fever in 19 patients and lung infections in 15, attributed to AML. Responses included complete remission with incomplete count recovery in two patients (8%) and hematologic improvement in three. Pharmacodynamic studies showed the expected DNA demethylation, increased PARP trapping in chromatin, increased γH2AX foci, and decreased HR activity in responders. γH2AX foci increased significantly with increasing talazoparib doses combined with 20 mg/m2 decitabine.. Decitabine/talazoparib combination was well tolerated. Expected pharmacodynamic effects occurred, especially in responders.

Topics: Antineoplastic Combined Chemotherapy Protocols; Azacitidine; Decitabine; DNA; Humans; Leukemia, Myeloid, Acute; Methyltransferases; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors

The cohesin complex plays an essential role in chromosome maintenance and transcriptional regulation. Recurrent somatic mutations in the cohesin complex are frequent genetic drivers in cancer, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Here, using genetic dependency screens of stromal antigen 2-mutant (STAG2-mutant) AML, we identified DNA damage repair and replication as genetic dependencies in cohesin-mutant cells. We demonstrated increased levels of DNA damage and sensitivity of cohesin-mutant cells to poly(ADP-ribose) polymerase (PARP) inhibition. We developed a mouse model of MDS in which Stag2 mutations arose as clonal secondary lesions in the background of clonal hematopoiesis driven by tet methylcytosine dioxygenase 2 (Tet2) mutations and demonstrated selective depletion of cohesin-mutant cells with PARP inhibition in vivo. Finally, we demonstrated a shift from STAG2- to STAG1-containing cohesin complexes in cohesin-mutant cells, which was associated with longer DNA loop extrusion, more intermixing of chromatin compartments, and increased interaction with PARP and replication protein A complex. Our findings inform the biology and therapeutic opportunities for cohesin-mutant malignancies.

Topics: Animals; Cell Cycle Proteins; Cell Line, Tumor; Chromatin; Chromosomal Proteins, Non-Histone; Cohesins; Disease Models, Animal; DNA Damage; DNA Repair; Female; Humans; K562 Cells; Leukemia, Myeloid, Acute; Male; Mice; Mice, Inbred C57BL; Mice, Inbred NOD; Mice, Mutant Strains; Mice, SCID; Mice, Transgenic; Mutation; Myelodysplastic Syndromes; Nuclear Proteins; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; U937 Cells; Xenograft Model Antitumor Assays

Mutations in FMS-like tyrosine kinase 3 (FLT3), such as internal tandem duplications (ITDs), can be found in up to 23% of patients with acute myeloid leukemia (AML) and confer a poor prognosis. Current treatment options for FLT3(ITD)-positive AMLs include genotoxic therapy and FLT3 inhibitors (FLT3i's), which are rarely curative. PARP1 inhibitors (PARP1i's) have been successfully applied to induce synthetic lethality in tumors harboring BRCA1/2 mutations and displaying homologous recombination (HR) deficiency. We show here that inhibition of FLT3(ITD) activity by the FLT3i AC220 caused downregulation of DNA repair proteins BRCA1, BRCA2, PALB2, RAD51, and LIG4, resulting in inhibition of 2 major DNA double-strand break (DSB) repair pathways, HR, and nonhomologous end-joining. PARP1i, olaparib, and BMN673 caused accumulation of lethal DSBs and cell death in AC220-treated FLT3(ITD)-positive leukemia cells, thus mimicking synthetic lethality. Moreover, the combination of FLT3i and PARP1i eliminated FLT3(ITD)-positive quiescent and proliferating leukemia stem cells, as well as leukemic progenitors, from human and mouse leukemia samples. Notably, the combination of AC220 and BMN673 significantly delayed disease onset and effectively reduced leukemia-initiating cells in an FLT3(ITD)-positive primary AML xenograft mouse model. In conclusion, we postulate that FLT3i-induced deficiencies in DSB repair pathways sensitize FLT3(ITD)-positive AML cells to synthetic lethality triggered by PARP1i's. Therefore, FLT3(ITD) could be used as a precision medicine marker for identifying AML patients that may benefit from a therapeutic regimen combining FLT3 and PARP1i's.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Benzothiazoles; BRCA1 Protein; BRCA2 Protein; Cell Line, Tumor; DNA Ligase ATP; DNA Repair; Fanconi Anemia Complementation Group N Protein; fms-Like Tyrosine Kinase 3; Humans; Leukemia, Myeloid, Acute; Mice; Mutation; Phenylurea Compounds; Phthalazines; Piperazines; Poly (ADP-Ribose) Polymerase-1; Protein Kinase Inhibitors; Rad51 Recombinase; Tumor Suppressor Proteins; Xenograft Model Antitumor Assays

Poly (ADP-ribose) polymerase inhibitors (PARPis) are clinically effective predominantly for BRCA-mutant tumors. We introduce a mechanism-based strategy to enhance PARPi efficacy based on DNA damage-related binding between DNA methyltransferases (DNMTs) and PARP1. In acute myeloid leukemia (AML) and breast cancer cells, DNMT inhibitors (DNMTis) alone covalently bind DNMTs into DNA and increase PARP1 tightly bound into chromatin. Low doses of DNMTis plus PARPis, versus each drug alone, increase PARPi efficacy, increasing amplitude and retention of PARP1 directly at laser-induced DNA damage sites. This correlates with increased DNA damage, synergistic tumor cytotoxicity, blunting of self-renewal, and strong anti-tumor responses, in vivo in unfavorable AML subtypes and BRCA wild-type breast cancer cells. Our combinatorial approach introduces a strategy to enhance efficacy of PARPis in treating cancer.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Chromatin; DNA Breaks, Double-Stranded; DNA Methylation; Drug Synergism; Female; Humans; Leukemia, Myeloid, Acute; Male; Mice; Mice, Inbred NOD; Mice, Nude; Phthalazines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Triple Negative Breast Neoplasms; Xenograft Model Antitumor Assays