Defects in apoptotic pathways can promote cancer cell survival and also confer resistance to antineoplastic drugs. One pathway being targeted for antineoplastic therapy is the anti-apoptotic B-cell lymphoma-2 (Bcl-2) family of proteins (Bcl-2, Bcl-X L , Bcl-w, Mcl-1, Bfl1/A-1, and Bcl-B) that bind to and inactivate BH3-domain pro-apoptotic proteins. Signals transmitted by cellular damage (including antineoplastic drugs) or cytokine deprivation can initiate apoptosis via the intrinsic apoptotic pathway. It is controversial whether some BH3-domain proteins (Bim or tBid) directly activate multidomain pro-apoptotic proteins (e.g., Bax and Bak) or act via inhibition of those anti-apoptotic Bcl-2 proteins (Bcl-2, Bcl-X L , Bcl-w, Mcl-1, Bfl1/A-1, and Bcl-B) that stabilize pro-apoptotic proteins. Overexpression of anti-apoptotic Bcl-2 family members has been associated with chemotherapy resistance in various human cancers, and preclinical studies have shown that agents targeting anti-apoptotic Bcl-2 family members have preclinical activity as single agents and in combination with other antineoplastic agents. Clinical trials of several investigational drugs targeting the Bcl-2 family (oblimersen sodium, AT-101, ABT-263, GX15-070) are ongoing. Here, we review the role of the Bcl-2 family in apoptotic pathways and those agents that are known and/or designed to inhibit the anti-apoptotic Bcl-2 family of proteins.

Background-MLN8237 is a small molecule inhibitor of Aurora Kinase A (AURKA) that is currently in early phase clinical testing. AURKA plays a pivotal role in centrosome maturation and spindle formation during mitosis.

Depsipeptide (FR901228) is a bicyclic peptide isolated from Chromobacterium violaceum that has demonstrated potent in vitro cytotoxic activity against human tumor cell lines and in vivo efficacy against human tumor xenografts. The primary mechanism of action is through inhibition of histone deacetylase. Initial development was halted due to significant cardiac toxicity. Subsequent studies performed at the National Cancer Institute demonstrated administration without cardiotoxicity was possible by varying the schedule of administration. A phase I trial was designed to determine the maximum tolerated dose and toxicity profile when administered as a 4-hour infusion weekly x 3 with one week rest. 33 Patients with advanced, incurable cancers were enrolled into this trial and treated with doses of Depsipeptide ranging from 1 mg/m2 to 17.7 mg/m2. At doses above 5 mg/m2, we observed common symptoms of nausea, vomiting, fatigue, and anorexia. Subtle changes in ECGs were seen in several patients. However, no cardiac enzyme abnormalities or reduction in ejection fraction were observed. The MTD was defined as 13.3 mg/m2 with dose limiting toxicities being grade 3 thrombocytopenia and fatigue. Depsipeptide can be safely administered when given as a 4-hour infusion and further clinical trials are warranted.

Background Inhibitors of poly-ADP ribose polymerase (PARP), an enzyme involved in base excision repair (BER) 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. Procedures 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). Results 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 maximum tolerated doses 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. Conclusions The high level of activity observed for talazoparib plus temozolomide in Ewing sarcoma xenografts makes this an interesting combination to consider for pediatric evaluation.

The DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. As a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, DNA-PK is best known as a mediator of the cellular response to DNA damage. In this context, DNA-PK has emerged as an intriguing therapeutic target in the treatment of a variety of cancers, especially when used in conjunction with genotoxic chemotherapy or ionizing radiation. Beyond the DNA damage response, DNA-PK activity is necessary for multiple cellular functions, including the regulation of transcription, progression of the cell cycle, and in the maintenance of telomeres. Here, we review what is currently known about DNA-PK regarding its structure and established roles in DNA repair. We also discuss its lesser-known functions, the pharmacotherapies inhibiting its function in DNA repair, and its potential as a therapeutic target in a broader context.

Background The National Cancer Institute (NCI) has established the Pediatric Preclinical Testing Program (PPTP) for testing drugs against in vitro and in vivo childhood cancer models to aid in the prioritization of drugs considered for early phase pediatric clinical trials. Procedures In vitro cytotoxicity testing employs a semi-automated fluorescence-based digital imaging cytotoxicity assay (DIMSCAN) that has a 4-log dynamic range of detection. Curve fitting of the fractional survival data of the cell lines in response to various concentrations of the agents was used to calculate relative IC50, absolute IC50, and Ymin values The panel of 23 pediatric cancer cell lines included leukemia (n=6), lymphoma (n=2), rhabdomyosarcoma (n=4), brain tumors (n=3), Ewing family of tumors (EFT, n=4), and neuroblastoma (n=4). The doubling times obtained using DIMSCAN were incorporated into data analyses to estimate the relationship between input cell numbers and final cell number. Results We report in vitro activity data for three drugs (vincristine, melphalan, and etoposide) that are commonly used for pediatric cancer and for the mTOR inhibitor rapamycin, an agent that is currently under preclinical investigation for cancer. To date, the PPTP has completed in vitro testing of 39 investigational and approved agents for single drug activity and two investigational agents in combination with various “standard” chemotherapy drugs. Conclusions This robust in vitro cytotoxicity testing system for pediatric cancers will enable comparisons to response data for novel agents obtained from xenograft studies and from clinical trials.

Background Antimitotic agents are essential components for curative therapy of pediatric acute leukemias and many solid tumors. Eribulin is a novel agent that differs from both Vinca alkaloids and taxanes in its mode of binding to tubulin polymers. Procedures Eribulin was tested against the PPTP in vitro cell line panel at concentrations from 0.1 nM to 1.0 μM and against the PPTP in vivo xenograft panels at a dose of 1 mg/kg (solid tumors) or 1.5 mg/kg (ALL models) using a q4dx3 schedule repeated at Day 21. Results In vitro eribulin demonstrated cytotoxic activity, with a median relative IC50 value of 0.27 nM, (range <0.1–14.8 nM). Eribulin was well tolerated in vivo, and all 43 xenograft models were considered evaluable for efficacy. Eribulin induced significant differences in event-free survival (EFS) distribution compared to control in 29 of 35 (83%) of the solid tumors and in 8 of 8 (100%) of the ALL xenografts. Objective responses were observed in 18 of 35 (51%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in panels of Wilms tumor, Ewing sarcoma, rhabdomyosarcoma, glioblastoma, and osteosarcoma xenografts. All eight ALL xenografts achieved CR or MCR. Conclusions The high level of activity observed for eribulin against the PPTP preclinical models makes this an interesting agent to consider for pediatric evaluation. The activity pattern observed for eribulin in the solid tumor panels is equal or superior to that observed previously for vincristine.

Rapamycin demonstrated broad-spectrum tumor growth inhibition activity against the in vivo panels of childhood tumors used in the Pediatric Preclinical Testing Program (PPTP). Here we have evaluated rapamycin combined with agents used frequently in the treatment of childhood malignancies. Rapamycin was tested in vitro against 23 cell lines alone or in combination with melphalan, cisplatin, vincristine, or dexamethasone (leukemic models only). In vivo, the impact of combining rapamycin with a cytotoxic agent was evaluated using two measures: 1) the therapeutic enhancement measure, and 2) a linear regression model for time-to-event to formally evaluate for sub-and supraadditivity for the combination compared to the agents used alone. Combining rapamycin with cytotoxic agents in vitro gave predominantly subadditive or additive effects, except for dexamethasone in leukemia models for which supra-additive activity was observed. In vivo testing demonstrated that therapeutic enhancement was common for rapamycin in combination with cyclophosphamide and occurred for 4 of 11 evaluable xenografts for the rapamycin and vincristine combination. The combinations of rapamycin with either cyclophosphamide or vincristine were significantly more effective than the respective standard agents used alone at their maximum tolerated doses (MTD) for most evaluable xenografts. The combination of rapamycin and cisplatin produced excessive toxicity requiring cisplatin dose reductions, and therapeutic enhancement was not observed for this combination. Addition of rapamycin to either cyclophosphamide or vincristine at their respective MTDs appears promising, as these combinations are relatively well tolerated and as many of the pediatric preclinical models evaluated demonstrated therapeutic enhancement for these combinations. Mol Cancer Ther; 9(1); 101-12. ©2010 AACR.