Rau, Rachel E.

AbstractPurposeWe conducted a phase 1/2 trial of the poly(ADP‐ribose) polymerase 1/2 inhibitor talazoparib in combination with low‐dose temozolomide (TMZ) to determine the dose‐limiting toxicities (DLTs), recommended phase 2 dose (RP2D), and pharmacokinetics of this combination in children with recurrent/refractory solid tumors; and to explore clinical activity in Ewing sarcoma (EWS) (NCT02116777).MethodsTalazoparib (400‐600 µg/m2/dose, maximum daily dose 800‐1000 µg) was administered q.d. or b.i.d. orally on day 1 followed by q.d. dosing concomitant with q.d. dosing of oral TMZ (20‐55 mg/m2/day) on days 2 to 6, every 28 days.ResultsForty patients, aged 4 to 25 years, were enrolled. Talazoparib was increased to 600 µg/m2/dose b.i.d. on day 1, and q.d. thereafter, with 20 mg/m2/day of TMZ, without DLTs. TMZ was subsequently increased, during which dose‐limiting neutropenia and thrombocytopenia occurred in two of three subjects at 55 mg/m2/day, two of six subjects at 40 mg/m2/day, and one of six subjects at 30 mg/m2/day. During dose‐finding, two of five EWS and four of 25 non‐EWS subjects experienced prolonged stable disease (SD), and one subject with malignant glioma experienced a partial response. In phase 2, 0 of 10 EWS subjects experienced an objective response; two experienced prolonged SD.ConclusionsTalazoparib and low‐dose TMZ are tolerated in children with recurrent/refractory solid tumors. Reversible neutropenia and thrombocytopenia were dose limiting. The RP2D is talazoparib 600 µg/m2 b.i.d. on day 1 followed by 600 µg/m2 q.d. on days 2 to 6 (daily maximum 1000 µg) in combination with temozolomide 30 mg/m2/day on days 2 to 6. Antitumor activity was not observed in EWS, and limited antitumor activity was observed in central nervous system tumors.

Abstract Abstract 2742 Poster Board II-718 Background: The BCR-ABL inhibitor imatinib has revolutionized the treatment of CML, and improves the efficacy of chemotherapy in Ph+ ALL. Acquired imatinib resistance (IR) is an emerging problem. Patients who develop IR have a dismal prognosis and novel therapeutic strategies are needed. Mechanisms of resistance include mutations and overexpression of BCR/ABL. In addition, BCR/ABL-independent pathways may contribute to resistance. Mounting evidence suggests that aberrant histone deacetylase (HDAC) expression plays a key role in acquired IR. HDAC inhibition has been shown to downregulate BCR/ABL expression via multiple mechanisms. The functional effects of HDAC inhibition include cell cycle arrest and induction of mitochondrial damage and caspase-dependent apoptosis, both in cells that are imatinib sensitive (IS) and IR. We hypothesized that HDAC inhibition will demonstrate synergistic activity in combination with imatinib in IR cells. To test this hypothesis, we employed entinostat (SNDX-275), a novel, class I HDAC isoform selective inhibitor currently being tested in multiple phase 2 clinical trials. We explored the use of SNDX-275 alone and in combination with imatinib and dasatinib in IR and IS p210BCR/ABL expressing cell lines. Methods: K562 (p210BCR/ABL expressing CML cell line), IR K562 cells (Weisberg E, et al. Blood. 2000;95:3498), Ba/F3 cells, Ba/F3 cells transfected with p210BCR/ABL and Ba/F3 cells transfected with the T315I mutant form of BCR/ABL were treated with increasing concentrations of SNDX-275 (0.2 to 1.6μM), imatinib (0.1 to 1.6 μM), and dasatinib (0.3 to 250 nM) for 72 hours. The cells were also treated with combinations of SNDX-275 plus imatinib and SNDX-275 plus dasatinib at the same range of concentrations for 72 hours. All experiments were done in triplicate. Drug-related effects on cell viability were determined by MTT cytotoxicity assays. CalcuSyn software was used to calculate the IC50 for each drug in each cell line and to calculate the combination index (CI) for cell lines treated with combinations of imatinib or dasatinib plus SNDX-275. A CI from 0.9 to 1.1 indicates that the two drugs have an additive effect, below 0.9 indicates synergy between the two drugs and above 1.1 indicates antagonism. Results: In the Ba/F3 p210BCR/ABL and Ba/F3 T315I cells, SNDX-275 alone had minimal activity up to 1 μM. In K562 and IR K562 cells SNDX-275 alone led to significant cytotoxicity with an IC50 of 0.662 μM and 0.495 μM respectively. In the IR cell lines, cotreatment with SNDX-275 enhanced the activity of both imatinib and dasatinib. For the IR K562 cells, imatinib plus SNDX275 was potently synergistic with a CI of 0.6234. Dasatinib plus SNDX275 treatment of IR K562 cells was additive with a CI of 1.1015 (figure 1). Similarly, in the Ba/F3 T315I cells imatinib plus SNDX275 resulted in synergistic activity (CI = 0.87) and additive activity when treated with dasatinib plus SNDX275 (CI = 0.97). On the contrary, cotreatment of non-IR cell lines with dasatinib or imatinib plus SNDX-275 did not result in synergistic activity and revealed evidence of antagonism. In the K562 cells, the combination of imatinib plus SNDX-275 was antagonistic with a CI of 1.308 (figure 1A). In the Ba/F3 p210BCR/ABL cells, the combination of dasatinib plus SNDX-275 was strikingly antagonistic with a CI of 2.9. Conclusions: BCR/ABL-independent mechanisms of resistance, including aberrant acetylation of histone and non-histone proteins secondary to the deregulation of HDACs, contribute to IR in patients with CML and Ph+ ALL. Our data support this hypothesis, as the HDAC inhibitor SNDX-275 enhances the activity of imatinib and, to a lesser extent, dasatinib in IR p210BCR/ABL expressing cell lines. Therefore, SNDX-275 may represent a novel therapeutic approach to patients with IR CML and Ph+ ALL, and a phase I clinical study is planned. In contrast, SNDX-275 may antagonize the activity of the tyrosine kinase inhibitors in nonresistant CML and Ph+ ALL. To our knowledge, this is the first report of antagonism between a HDAC inhibitor and tyrosine kinase inhibitors in CML. Further investigation is necessary to define the mechanism and clinical significance of this antagonism. Disclosures: No relevant conflicts of interest to declare.

Abstract Background Eribulin mesylate is a novel anticancer agent that inhibits microtubule growth, without effects on shortening, and promotes nonproductive tubulin aggregate formation. We performed a phase 1 trial to determine the dose‐limiting toxicities (DLTs), maximum tolerated or recommended phase 2 dose (MTD/RP2D), and pharmacokinetics (PK) of eribulin in children with refractory or recurrent solid (excluding central nervous system) tumors. Methods Eribulin was administered intravenously on days 1 and 8 in 21‐day cycles. Three dose levels (1.1, 1.4, and 1.8 mg/m 2 /dose) were evaluated using the rolling six design with additional patients enrolled into a PK expansion cohort at the MTD. PK samples were obtained following the day 1, cycle 1 dose. Results Twenty‐three patients, ages 3–17 (median 14) years were enrolled; 20 were evaluable for toxicity. DLTs occurred in 0/6 and 1/6 subjects at the 1.1 and 1.4 mg/m 2 /dose, respectively. One subject at the 1.4 mg/m 2 /dose had grade 4 neutropenia and grade 3 fatigue. At the 1.8 mg/m 2 /dose, 2/5 subjects experienced dose‐limiting (grade 4) neutropenia. Grade 3/4 non‐DLTs included lymphopenia and hypokalemia, while low‐grade toxicities included anorexia and nausea. No episodes of grade > 2 corrected QT interval prolongation or peripheral neuropathy were reported. Eribulin pharmacokinetic parameters were highly variable; the median elimination half‐life was 39.6 (range 24.2–96.4) hr. A partial response was observed in one patient (Ewing sarcoma). Conclusions Eribulin was well tolerated in children with refractory or recurrent solid tumors with neutropenia identified as the primary DLT. The RP2D of eribulin is 1.4 mg/m 2 /dose on days 1 and 8 of a 21‐day cycle.