Edward K. Han

ABT-888, an Orally Active Poly(ADP-Ribose) Polymerase Inhibitor that Potentiates DNA-Damaging Agents in Preclinical Tumor Models

Purpose: To evaluate the preclinical pharmacokinetics and antitumor efficacy of a novel orally bioavailable poly(ADP-ribose) polymerase (PARP) inhibitor, ABT-888. Experimental Design:In vitro potency was determined in a PARP-1 and PARP-2 enzyme assay. In vivo efficacy was evaluated in syngeneic and xenograft models in combination with temozolomide, platinums, cyclophosphamide, and ionizing radiation. Results: ABT-888 is a potent inhibitor of both PARP-1 and PARP-2 with Kis of 5.2 and 2.9 nmol/L, respectively. The compound has good oral bioavailability and crosses the blood-brain barrier. ABT-888 strongly potentiated temozolomide in the B16F10 s.c. murine melanoma model. PARP inhibition dramatically increased the efficacy of temozolomide at ABT-888 doses as low as 3.1 mg/kg/d and a maximal efficacy achieved at 25 mg/kg/d. In the 9L orthotopic rat glioma model, temozolomide alone exhibited minimal efficacy, whereas ABT-888, when combined with temozolomide, significantly slowed tumor progression. In the MX-1 breast xenograft model (BRCA1 deletion and BRCA2 mutation), ABT-888 potentiated cisplatin, carboplatin, and cyclophosphamide, causing regression of established tumors, whereas with comparable doses of cytotoxic agents alone, only modest tumor inhibition was exhibited. Finally, ABT-888 potentiated radiation (2 Gy/d × 10) in an HCT-116 colon carcinoma model. In each model, ABT-888 did not display single-agent activity. Conclusions: ABT-888 is a potent inhibitor of PARP, has good oral bioavailability, can cross the blood-brain barrier, and potentiates temozolomide, platinums, cyclophosphamide, and radiation in syngeneic and xenograft tumor models. This broad spectrum of chemopotentiation and radiopotentiation makes this compound an attractive candidate for clinical evaluation.

Acquired Resistance to Combination Treatment with Temozolomide and ABT-888 Is Mediated by Both Base Excision Repair and Homologous Recombination DNA Repair Pathways

Many established cancer therapies involve DNA-damaging chemotherapy or radiotherapy. Gain of DNA repair capacity of the tumor represents a common mechanism used by cancer cells to survive DNA-damaging therapy. Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that is activated by DNA damage and plays a critical role in base excision repair. Inhibition of PARP represents an attractive approach for the treatment of cancer. Previously, we have described the discovery and characterization of a potent PARP inhibitor, ABT-888. ABT-888 potentiates the activity of DNA-damaging agents such as temozolomide (TMZ) in a variety of preclinical models. We report here the generation of HCT116 cells resistant to treatment with TMZ and ABT-888 (HCT116R cells). HCT116R cells exhibit decreased H2AX phosphorylation in response to treatment with TMZ and ABT-888 relative to parental HCT116 cells. Microarray and Western blot studies indicate that HCT116R cells have decreased PARP-1 and elevated Rad51 expression levels. HCT116R cells are dependent on Rad51 for proliferation and survival, as shown by inhibition of proliferation and induction of apoptosis upon treatment with Rad51 small interfering RNA. In addition, HCT116R cells are more resistant to radiation than the parental HCT116 cells. Our study suggests that cancer cells upregulate the homologous recombination DNA repair pathway to compensate for the loss of base excision repair, which may account for the observed resistance to treatment with TMZ and ABT-888. (Mol Cancer Res 2009;7(10):1686–92)

The α isoform of protein kinase C mediates phorbol ester-induced growth inhibition and p21cip1 induction in HC11 mammary epithelial cells

To clarify the roles of specific isoforms of PKC in regulating growth and cell cycle progression of the HC11 mammary epithelial cell line, we investigated the effects of activating endogenous PKC isoforms with the phorbol ester tumor promoter TPA, and also the effects of TPA on genetically engineered cells containing increased levels of individual PKC isoforms. We found that TPA treatment of HC11 cells induced a transient cell cycle arrest in G0/G1. Western blot analyses of the TPA treated cells provided evidence that the endogenous PKCα present in these cells mediated these effects. Indeed, derivatives of the HC11 cell line that inducibly overexpress an exogenous PKCα or ectopic PKCβ1 exhibited more marked growth inhibition by TPA than control cells. Immunohistochemical staining of cells following treatment with TPA revealed selective translocation of PKCα into the nucleus, whereas PKCβ1 remained in the cytoplasm. The transient arrest of HC11 cells following treatment with TPA was associated with marked induction of both p21cip1 mRNA and protein. This induction was exaggerated in the derivatives that overexpressed either PKCα or PKCβ1. Therefore, in mouse mammary epithelial cells activation of the endogenous PKCα can transiently arrest cells in G0/G1 which may be due, at least in part, to induction of the transcription of p21cip1.

Role of focal adhesion kinase in human cancer: a potential target for drug discovery.

The focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that localizes to the points of cell contact with the extracellular matrix, called focal adhesions. FAK is involved in several cellular processes including invasion, motility, proliferation and apoptosis. In in vivo animal studies, FAK has been shown to contribute to tumor development and malignancy. Furthermore, FAK expression was shown to be elevated in a number of human cancers. Increased FAK expression and activity are correlated with malignant phenotype and poor prognosis in patients. Taken together, these studies suggest that FAK is a potentially good target for drug discovery. In this review, FAK and its relationship to cancer, as well as approaches to therapeutic intervention of FAK will be discussed.

Aminopyrimidinone Cdc7 Kinase Inhibitors

We have investigated the SAR of a series of pyrimidinone-containing Cdc7 kinase inhibitors. A wide range of amine substitutions give potent compounds with activities (K(i)) less than 1nM. Kinase selectivity is reasonable and cytotoxicity corresponds to inhibition of MCM2 phosphorylation.

ABBV-399, a c-Met Antibody Drug Conjugate that Targets Both MET Amplified and c-Met Overexpressing Tumors, Irrespective of MET Pathway Dependence.

Purpose: Despite the importance of the MET oncogene in many malignancies, clinical strategies targeting c-Met have benefitted only small subsets of patients with tumors driven by signaling through the c-Met pathway, thereby necessitating selection of patients with MET amplification and/or c-Met activation most likely to respond. An ADC targeting c-Met could overcome these limitations with potential as a broad-acting therapeutic. Experimental Design: ADC ABBV-399 was generated with the c-Met–targeting antibody, ABT-700. Antitumor activity was evaluated in cancer cells with overexpressed c-Met or amplified MET and in xenografts including patient-derived xenograft (PDX) models and those refractory to other c-Met inhibitors. The correlation between c-Met expression and sensitivity to ABBV-399 in tumor and normal cell lines was assessed to evaluate the risk of on-target toxicity. Results: A threshold level of c-Met expressed by sensitive tumor but not normal cells is required for significant ABBV-399–mediated killing of tumor cells. Activity extends to c-Met or amplified MET cell line and PDX models where significant tumor growth inhibition and regressions are observed. ABBV-399 inhibits growth of xenograft tumors refractory to other c-Met inhibitors and provides significant therapeutic benefit in combination with standard-of-care chemotherapy. Conclusions: ABBV-399 represents a novel therapeutic strategy to deliver a potent cytotoxin to c-Met–overexpressing tumor cells enabling cell killing regardless of reliance on MET signaling. ABBV-399 has progressed to a phase I study where it has been well tolerated and has produced objective responses in c-Met–expressing non–small cell lung cancer (NSCLC) patients. Clin Cancer Res; 23(4); 992–1000. ©2016 AACR.

Abstract A161: Acquired resistance to combination treatment with TMZ and ABT‐888 is mediated by both BER and HR DNA repair pathways

Many established cancer therapies involve DNA‐damaging chemotherapy or radiotherapy. Gain of DNA repair capacity of the tumor represents a common mechanism employed by cancer cells to survive DNA‐damaging therapy. Poly (ADP‐ribose) polymerase‐1 (PARP‐1) is a nuclear enzyme that is activated by DNA‐damage and plays a critical role in base excision repair (BER). Inhibition of PARP represents an attractive approach for the treatment of cancer. Previously, we have described the discovery and characterization of a potent PARP inhibitor, ABT‐888. ABT‐888 potentiates the activity of DNA‐damaging agents such as temozolomide (TMZ) in a variety of preclinical models. Previously, we demonstrated that ABT‐888 potentiated the cytotoxic effect of TMZ by converting TMZ‐induced single strand DNA breaks (SSB) to double strand breaks (DSB). We report here the generation of HCT116 cells resistant to treatment with TMZ and ABT‐888 (HCT116R cells). HCT116R cells exhibit decreased H2AX phosphorylation in response to the treatment with TMZ and ABT‐888 relative to parental HCT116 cells. Microarray and western blot studies indicate that HCT116R cells have decreased PARP‐1 and elevated Rad51 expression levels. HCT116R cells are dependent on Rad51 for proliferation and survival, as demonstrated by inhibition of proliferation and induction of apoptosis upon treatment with Rad51 siRNA. In addition, HCT116R cells are more resistant to radiation than the parental HCT116 cells. Our study suggests that cancer cells up‐regulate the homologous recombination DNA repair pathway to compensate for the loss of BER, which may account for the observed resistance to the treatment with TMZ and ABT‐888. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A161.