We have established 51 solid tumor and 10 ALL in vivo models. The models identify vincristine and cyclophosphamide as having broad-spectrum activity. The PPTP tumor panels appear to generally recapitulate the activity of these agents against specific childhood cancers and to have the potential for identifying novel agents having significant clinical activity.

Purpose:Vinca alkaloids, agents that cause depolymerization of microtubules, are highly active in treatment of many pediatric cancers. In contrast, taxanes, agents that stabilize microtubules, are far less effective against the same cancer types.The purpose of the current study was to evaluate the antitumor activity of ixabepilone, an epothilone B derivative representing a new class of microtubule-stabilizing antimitotic agent in a wide variety of pediatric solid tumor models. Experimental Design: Ixabepilone was administered i.v. every 4 days for three doses to scid mice bearing s.c. human rhabdomyosarcoma (three lines), neuroblastoma (four), Wilms' tumors (six), osteosarcoma (four), or brain tumors (seven). Tumor diameters were measured weekly, and tumor growth or regressions were determined. Pharmacokinetic studies were done following a single administration of drug at the maximum tolerated dose (MTD) level (10 mg/kg). Results: At the MTD (10 mg/kg), ixabepilone induced objective responses (all tumors in a group achieved z50% volume regression) in three of three rhabdomyosarcoma lines, three of five neuroblastomas, six of seven Wilms' tumor models, two of six osteosarcoma, and four of eight brain tumor models. However, the dose-response curve was steep with only 2 of 19 tumors models regressing (z50%) at 4.4 mg/kg. In comparison, paclitaxel administered at the MTD on the same schedule failed to induce objective regressions of three tumor lines that were highly sensitive to treatment with ixabepilone. Pharmacokinetics following single i.v. administration of ixabepilone at its MTD (10 mg/kg) were biexponential with C max of 12.5 Amol/L, elimination half-life of 19.2 hours, and total area under the curve of 5.8 Amol/L-h.The achieved drug exposure of ixabepilone at this efficacious MTD dose level in mice is similar to those achieved in patients given the recommended phase II dose of 40 mg/m 2 by either1-or 3-hour infusion every 3 weeks, a regimen that has shown significant anticancer activity in phase II clinical trials in adult patients. Conclusions: Administered at doses ranging from 66% to100% of its MTDinmice, the epothilone B derivativeixabepilone shows broad spectrum activity against apanelof pediatric tumor xenograft models.Pharmacokineticanalysisindicates that the systemicixabepiloneexposureachievedinmice at its MTD is similar to that achieved in patients at the recommended phase II dose of 40 mg/m 2 administered every 3 weeks. Importantly, the present results showed a clear distinction in sensitivity of pediatric solid tumors to this epothilone derivative compared with paclitaxel.

Background Tazemetostat (EPZ-6438) is a selective inhibitor of the histone methyltransferase EZH2, currently in clinical development for non-Hodgkin lymphoma and genetically defined tumors. Procedures Tazemetostat was tested against the PPTP solid tumor xenografts using a dose of 400 mg/kg administered twice-daily by oral gavage for 28 days. H3K27me3:H3 ratios were determined in control and treated tumors. Results Tazemetostat induced significant differences in event free survival (EFS) distribution compared to control in 9 of 30 (30%) of the xenografts studied. Significant differences in EFS distribution were observed in 5 of 7 (71%) rhabdoid tumor xenograft lines compared to 4 of 23 (17%) non-rhabdoid xenograft lines [chi square (χ2) test p=0.006]. Tazemetostat induced tumor growth inhibition meeting criteria for intermediate and high EFS treated to control (T/C) activity in 2 of 25 (8%) and 1 of 25 (4%) xenografts, respectively. Intermediate and high activity for the EFS T/C metric was observed exclusively among rhabdoid tumor xenografts (3 of 5 rhabdoid tumor versus 0 of 22 non-rhabdoid tumors (χ2 test p<0.001). One rhabdoid tumor xenograft (G401) showed stable disease. For one rhabdoid tumor (G401), delayed tumor regression to tazemetostat was noted following 1 week of tumor growth. Tazemetostat induced significant reduction of H3K27me3 levels in the majority of tumors compared to controls. Conclusions Tazemetostat demonstrated significant antitumor activity in rhabdoid tumor models, but showed no consistent activity against any other histology. Tazemetostat reduced H3K27me3 levels irrespective of tumor response. Further preclinical testing to evaluate tazemetostat in combination with other anticancer agents is warranted.