bmn-673 and Sarcoma--Ewing

A synthetic lethality-based strategy has been developed to identify therapeutic targets in cancer harboring tumor-suppressor gene mutations, as exemplified by the effectiveness of poly ADP-ribose polymerase (PARP) inhibitors in BRCA1/2-mutated tumors. However, many synthetic lethal interactors are less reliable due to the fact that such genes usually do not perform fundamental or indispensable functions in the cell. Here, we developed an approach to identifying the "essential lethality" arising from these mutated/deleted essential genes, which are largely tolerated in cancer cells due to genetic redundancy. We uncovered the cohesion subunit SA1 as a putative synthetic-essential target in cancers carrying inactivating mutations of its paralog, SA2. In SA2-deficient Ewing sarcoma and bladder cancer, further depletion of SA1 profoundly and specifically suppressed cancer cell proliferation, survival, and tumorigenic potential. Mechanistically, inhibition of SA1 in the SA2-mutated cells led to premature chromatid separation, dramatic extension of mitotic duration, and consequently, lethal failure of cell division. More importantly, depletion of SA1 rendered those SA2-mutated cells more susceptible to DNA damage, especially double-strand breaks (DSBs), due to reduced functionality of DNA repair. Furthermore, inhibition of SA1 sensitized the SA2-deficient cancer cells to PARP inhibitors in vitro and in vivo, providing a potential therapeutic strategy for patients with SA2-deficient tumors.

Topics: Animals; Antigens, Nuclear; Cell Cycle Proteins; Cell Line, Tumor; Chromosomal Proteins, Non-Histone; Cohesins; DNA Breaks, Double-Stranded; Female; Gene Knockdown Techniques; Genes, Essential; Humans; Mice; Mice, Nude; Mutation; Neoplasms; Nuclear Proteins; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Protein Subunits; Sarcoma, Ewing; Urinary Bladder Neoplasms; Xenograft Model Antitumor Assays

BMN 673 is a potent inhibitor of poly-ADP ribose polymerase (PARP) that is in clinical testing with a primary focus on BRCA-mutated cancers. BMN 673 is active both through inhibiting PARP catalytic activity and by tightly trapping PARP to DNA at sites of single strand breaks.. BMN 673 was tested in vitro at concentrations ranging from 0.1 nM to 1 μM and in vivo at a daily dose of 0.33 mg/kg administered orally twice daily (Mon-Fri) and once daily on weekends (solid tumors) for 28 days.. The median relative IC50 (rIC50 ) concentration against the PPTP cell lines was 25.8 nM. The median rIC50 for the Ewing cell lines was lower than for the remaining cell lines (6.4 vs. 31.1 nM, respectively). In vivo BMN 673 induced statistically significant differences in EFS distribution in 17/43 (39.5%) xenograft models. Three objective regressions were observed: a complete response (CR) in a medulloblastoma line (BT-45), a maintained CR in a Wilms tumor line (KT-10), and a maintained CR in an ependymoma line (BT-41). BMN 673 maintained its high level of activity against KT-10 with a threefold reduction in dose. KT-10 possesses a truncating mutation in PALB2 analogous to PALB2 mutations associated with hereditary breast and ovarian cancer that abrogate homologous recombination (HR) repair.. The PPTP results suggest that single agent BMN 673 may have limited clinical activity against pediatric cancers. Single agent activity is more likely for patients whose tumors have defects in HR repair.

Topics: Animals; Bone Neoplasms; Drug Evaluation, Preclinical; Enzyme Inhibitors; Fanconi Anemia Complementation Group N Protein; Female; Glioblastoma; Humans; Mice; Mutation; Neuroblastoma; Nuclear Proteins; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Rhabdomyosarcoma; Sarcoma, Ewing; Tumor Suppressor Proteins

Inhibitors of PARP, an enzyme involved in base excision repair, have demonstrated single-agent activity against tumors deficient in homologous repair processes. Ewing sarcoma cells are also sensitive to PARP inhibitors, although the mechanism is not understood. Here, we evaluated the stereo-selective PARP inhibitor, talazoparib (BMN 673), combined with temozolomide or topotecan.. Talazoparib was tested in vitro in combination with temozolomide (0.3-1,000 μmol/L) or topotecan (0.03-100 nmol/L) and in vivo at a dose of 0.1 mg/kg administered twice daily for 5 days combined with temozolomide (30 mg/kg/daily x 5; combination A) or 0.25 mg/kg administered twice daily for 5 days combined with temozolomide (12 mg/kg/daily x 5; combination B). Pharmacodynamic studies were undertaken after 1 or 5 days of treatment.. In vitro talazoparib potentiated the toxicity of temozolomide up to 85-fold, with marked potentiation in Ewing sarcoma and leukemia lines (30-50-fold). There was less potentiation for topotecan. In vivo, talazoparib potentiated the toxicity of temozolomide, and combination A and combination B represent the MTDs when combined with low-dose or high-dose talazoparib, respectively. Both combinations demonstrated significant synergism against 5 of 10 Ewing sarcoma xenografts. The combination demonstrated modest activity against most other xenograft models. Pharmacodynamic studies showed a treatment-induced complete loss of PARP only in tumor models sensitive to either talazoparib alone or talazoparib plus temozolomide.. The high level of activity observed for talazoparib plus temozolomide in Ewing sarcoma xenografts makes this an interesting combination to consider for pediatric evaluation.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Bone Neoplasms; Cell Line, Tumor; Dacarbazine; Drug Synergism; Female; Humans; Immunoblotting; Mice; Mice, SCID; Phthalazines; Poly(ADP-ribose) Polymerase Inhibitors; Reverse Transcriptase Polymerase Chain Reaction; Sarcoma, Ewing; Temozolomide; Xenograft Model Antitumor Assays

Ewing sarcoma (EWS) is a tumor of the bone and soft tissue that primarily affects adolescents and young adults. With current therapies, 70% of patients with localized disease survive, but patients with metastatic or recurrent disease have a poor outcome. We found that EWS cell lines are defective in DNA break repair and are sensitive to PARP inhibitors (PARPis). PARPi-induced cytotoxicity in EWS cells was 10- to 1,000-fold higher after administration of the DNA-damaging agents irinotecan or temozolomide. We developed an orthotopic EWS mouse model and performed pharmacokinetic and pharmacodynamic studies using three different PARPis that are in clinical development for pediatric cancer. Irinotecan administered on a low-dose, protracted schedule previously optimized for pediatric patients was an effective DNA-damaging agent when combined with PARPis; it was also better tolerated than combinations with temozolomide. Combining PARPis with irinotecan and temozolomide gave complete and durable responses in more than 80% of the mice.

Topics: Animals; Benzimidazoles; Camptothecin; Cell Death; Cell Line, Tumor; Dacarbazine; DNA Breaks, Double-Stranded; DNA Repair; Drug Synergism; Enzyme Inhibitors; Irinotecan; Mice, Nude; Molecular Targeted Therapy; Phthalazines; Piperazines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Sarcoma, Ewing; Temozolomide; Xenograft Model Antitumor Assays