Efficacy and pharmacodynamics of niraparib in BRCA-mutant and wild-type intracranial triple-negative breast cancer murine models.

Despite the poor prognosis of triple-negative breast cancer (TNBC) brain metastases, there are no approved systemic therapies. We explored the DNA-damaging poly(ADP-ribose) polymerase inhibitor (PARPi) niraparib in intracranial mouse models of breast cancer susceptibility protein (BRCA)-mutant TNBC. Mice bearing intracranial human-derived TNBC cell lines (SUM149, MDA-MB-231Br, or MDA-MB-436) were treated with niraparib and monitored for survival; intracranial tissues were analyzed for PAR levels and niraparib concentration by mass spectrometry. RNASeq data of primary breast cancers using The Cancer Genome Atlas were analyzed for DNA damage signatures. Combined RAD51 and PARP inhibition in TNBC cell lines was assessed in vitro by colony-forming assays. Daily niraparib increased median survival and decreased tumor burden in the BRCA-mutant MDA-MB-436 model, but not in the BRCA-mutant SUM149 or BRCA-wild-type MDA-MB-231Br models despite high concentrations in intracranial tumors. RAD51 inhibitor B02 was shown to sensitize all cell lines to PARP inhibition (PARPi). In the analysis of BRCA-mutant primary human TNBCs, gene expression predictors of PARPi sensitivity and DNA repair signatures demonstrate widespread heterogeneity, which may explain the differential response to PARPi. Interestingly, these signatures are significantly correlated to RAD51 expression including PARPi sensitivity (R 2 = 0.602, R 2= 0.758). Niraparib penetrates intracranial tumor tissues in mouse models of TNBC with impressive single-agent efficacy in BRCA-mutant MDA-MB-436. Clinical evaluation of niraparib to treat TNBC brain metastases, an unmet clinical need desperate for improved therapies, is warranted. Further compromising DNA repair through RAD51 inhibition may further augment TNBC's response to PARPi.

Sambade MJ ，Van Swearingen AED ，McClure MB ，Deal AM ，Santos C ，Sun K ，Wang J ，Mikule K ，Anders CK ... -  《-》

Efficacy of Carboplatin Alone and in Combination with ABT888 in Intracranial Murine Models of BRCA-Mutated and BRCA-Wild-Type Triple-Negative Breast Cancer.

Patients with breast cancer brain metastases have extremely limited survival and no approved systemic therapeutics. Triple-negative breast cancer (TNBC) commonly metastasizes to the brain and predicts poor prognosis. TNBC frequently harbors BRCA mutations translating to platinum sensitivity potentially augmented by additional suppression of DNA repair mechanisms through PARP inhibition. We evaluated brain penetrance and efficacy of carboplatin ± the PARP inhibitor ABT888, and investigated gene-expression changes in murine intracranial TNBC models stratified by BRCA and molecular subtype status. Athymic mice were inoculated intracerebrally with BRCA-mutant: SUM149 (basal), MDA-MB-436 (claudin-low); or BRCA-wild-type (wt): MDA-MB-468 (basal), MDA-MB-231BR (claudin-low). TNBC cells were treated with PBS control [intraperitoneal (IP), weekly], carboplatin (50 mg/kg/wk, IP), ABT888 (25 mg/kg/d, oral gavage), or their combination. DNA damage (γ-H2AX), apoptosis (cleaved caspase-3, cC3), and gene expression were measured in intracranial tumors. Carboplatin ± ABT888 significantly improved survival in BRCA-mutant intracranial models compared with control, but did not improve survival in BRCA-wt intracranial models. Carboplatin + ABT888 revealed a modest survival advantage versus carboplatin in BRCA-mutant models. ABT888 yielded a marginal survival benefit in the MDA-MB-436, but not in the SUM149 model. BRCA-mutant SUM149 expression of γ-H2AX and cC3 proteins was elevated in all treatment groups compared with control, whereas BRCA-wt MDA-MB-468 cC3 expression did not increase with treatment. Carboplatin treatment induced common gene-expression changes in BRCA-mutant models. Carboplatin ± ABT888 penetrates the brain and improves survival in BRCA-mutant intracranial TNBC models with corresponding DNA damage and gene-expression changes. Combination therapy represents a potential promising treatment strategy for patients with TNBC brain metastases warranting further clinical investigation.

Karginova O ，Siegel MB ，Van Swearingen AE ，Deal AM ，Adamo B ，Sambade MJ ，Bazyar S ，Nikolaishvili-Feinberg N ，Bash R ，O'Neal S ，Sandison K ，Parker JS ，Santos C ，Darr D ，Zamboni W ，Lee YZ ，Miller CR ，Anders CK ... -  《-》

Combining Carbon-Ion Irradiation and PARP Inhibitor, Olaparib Efficiently Kills BRCA1-Mutated Triple-Negative Breast Cancer Cells.

Triple-negative breast cancer (TNBC) exhibits poor prognosis due to the lack of targets for hormonal or antibody-based therapies, thereby leading to limited success in the treatment of this cancer subtype. Poly (ADP-ribose) polymerase 1 (PARP1) is a critical factor for DNA repair, and using PARP inhibitor (PARPi) is one of the promising treatments for BRCA-mutated (BRCA mut) tumors where homologous recombination repair is impaired due to BRCA1 mutation. Carbon ion (C-ion) radiotherapy effectively induces DNA damages in cancer cells. Thus, the combination of C-ion radiation with PARPi would be an attractive treatment for BRCA mut TNBC, wherein DNA repair systems can be severely impaired on account of the BRCA mutation. Till date, the effectiveness of C-ion radiation with PARPi in BRCA mut TNBC cell killing remains unknown. Triple-negative breast cancer cell lines carrying either wild type BRCA1, BRCA wt, (MDA-MB-231), or the BRCA1 mutation (HCC1937) were used, and the effectiveness of PARPi, olaparib, combined with C-ion beam or the conventional radiation, or X-ray, on TNBC cell killing were investigated. First, effective concentrations of olaparib for BRCA mut (HCC1937) cell killing were identified. Using these concentrations of olaparib, we then investigated their radio-sensitizing effects by examining the surviving fraction of MDA-MB-231 and HCC1937 upon X-ray or C-ion irradiation. In addition, the number of γH2AX (DSB marker) positive cells as well as their expression levels were determined by immunohistochemistry, and results were compared between X-ray irradiated or C-ion irradiated cells. Furthermore, PARP activities in these cells were also observed by performing immunohistochemistry staining for poly (ADP-ribose) polymer (marker for PARP activity), and their expression differences were determined. Treatment of cells with 25 nM olaparib enhanced radio-sensitivity of X-ray irradiated HCC1937, whereas lower dose (5 nM) olaparib showed drastic effects on increasing radio-sensitivity of C-ion irradiated HCC1937. Similar effect was not observed in MDA-MB-231, not possessing the BRCA1 mutation. Results of immunohistochemistry showed that X-ray or C-ion irradiation induced similar number of γH2AX-positive HCC1937 cells, but these induction levels were higher in C-ion irradiated HCC1937 with increased PARP activity compared to that of X-ray irradiated HCC1937. Elevated induction of DSB in C-ion irradiated HCC937 may fully activate DSB repair pathways leading to downstream activation of PARP, subsequently enhancing the effectiveness of PARPi, olaparib, with lower doses of olaparib exerting noticeable effects in cell killing of C-ion irradiated HCC1937. From this study, we demonstrate that C-ion irradiation can exert significant DSB in BRCA mut TNBC, HCC1937, with high PARP activation. Thus, PARPi, olaparib, would be a promising candidate as a radio-sensitizer for BRCA mut TNBC treatment, especially for C-ion radiotherapy.

Kawanishi M ，Fujita M ，Karasawa K 《-》

Synthetic Lethality of PARP Inhibitors in Combination with MYC Blockade Is Independent of BRCA Status in Triple-Negative Breast Cancer.

PARP inhibitors (PARPi) benefit only a fraction of breast cancer patients. Several of those patients exhibit intrinsic/acquired resistance mechanisms that limit efficacy of PARPi monotherapy. Here we show how the efficacy of PARPi in triple-negative breast cancers (TNBC) can be expanded by targeting MYC-induced oncogenic addiction. In BRCA-mutant/sporadic TNBC patients, amplification of the MYC gene is correlated with increased expression of the homologous DNA recombination enzyme RAD51 and tumors overexpressing both genes are associated with worse overall survival. Combining MYC blockade with PARPi yielded synthetic lethality in MYC-driven TNBC cells. Using the cyclin-dependent kinase inhibitor dinaciclib, which downregulates MYC expression, we found that combination with the PARPi niraparib increased DNA damage and downregulated homologous recombination, leading to subsequent downregulation of the epithelial-mesenchymal transition and cancer stem-like cell phenotypes. Notably, dinaciclib resensitized TBNC cells, which had acquired resistance to niraparib. We found that the synthetic lethal strategy employing dinaciclib and niraparib was also highly efficacious in ovarian, prostate, pancreatic, colon, and lung cancer cells. Taken together, our results show how blunting MYC oncogene addiction can leverage cancer cell sensitivity to PARPi, facilitating the clinical use of c-myc as a predictive biomarker for this treatment.Significance: Dual targeting of MYC-regulated homologous recombination and PARP-mediated DNA repair yields potent synthetic lethality in triple-negative breast tumors and other aggressive tumors characterized by MYC overexpression. Cancer Res; 78(3); 742-57. ©2017 AACR.

Carey JPW ，Karakas C ，Bui T ，Chen X ，Vijayaraghavan S ，Zhao Y ，Wang J ，Mikule K ，Litton JK ，Hunt KK ，Keyomarsi K ... -  《-》

Combined kinase inhibitors of MEK1/2 and either PI3K or PDGFR are efficacious in intracranial triple-negative breast cancer.

Triple-negative breast cancer (TNBC), lacking expression of hormone and human epidermal growth factor receptor 2 receptors, is an aggressive subtype that frequently metastasizes to the brain and has no FDA-approved systemic therapies. Previous literature demonstrates mitogen-activated protein kinase kinase (MEK) pathway activation in TNBC brain metastases. Thus, we aimed to discover rational combinatorial therapies with MEK inhibition, hypothesizing that co-inhibition using clinically available brain-penetrant inhibitors would improve survival in preclinical models of TNBC brain metastases. Using human-derived TNBC cell lines, synthetic lethal small interfering RNA kinase screens were evaluated with brain-penetrant inhibitors against MEK1/2 (selumetinib, AZD6244) or phosphatidylinositol-3 kinase (PI3K; buparlisib, BKM120). Mice bearing intracranial TNBC tumors (SUM149, MDA-MB-231Br, MDA-MB-468, or MDA-MB-436) were treated with MEK, PI3K, or platelet derived growth factor receptor (PDGFR; pazopanib) inhibitors alone or in combination. Tumors were analyzed by western blot and multiplexed kinase inhibitor beads/mass spectrometry to assess treatment effects. Screens identified MEK+PI3K and MEK+PDGFR inhibitors as tractable, rational combinations. Dual treatment of selumetinib with buparlisib or pazopanib was synergistic in TNBC cells in vitro. Both combinations improved survival in intracranial SUM149 and MDA-MB-231Br, but not MDA-MB-468 or MDA-MB-436. Treatments decreased mitogen-activated protein kinase (MAPK) and PI3K (Akt) signaling in sensitive (SUM149 and 231Br) but not resistant models (MDA-MB-468). Exploratory analysis of kinome reprogramming in SUM149 intracranial tumors after MEK ± PI3K inhibition demonstrates extensive kinome changes with treatment, especially in MAPK pathway members. Results demonstrate that rational combinations of the clinically available inhibitors selumetinib with buparlisib or pazopanib may prove to be promising therapeutic strategies for the treatment of some TNBC brain metastases. Additionally, effective combination treatments cause widespread alterations in kinase pathways, including targetable potential resistance drivers.

Van Swearingen AED ，Sambade MJ ，Siegel MB ，Sud S ，McNeill RS ，Bevill SM ，Chen X ，Bash RE ，Mounsey L ，Golitz BT ，Santos C ，Deal A ，Parker JS ，Rashid N ，Miller CR ，Johnson GL ，Anders CK ... -  《-》