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.