Terzah M. Horton

A Phase 1 Study of the Proteasome Inhibitor Bortezomib in Pediatric Patients with Refractory Leukemia: a Children's Oncology Group Study

Purpose: A phase 1 study to determine the maximum-tolerated dose, dose-limiting toxicity, pharmacokinetics, and biological effects of bortezomib in children with recurrent/refractory leukemia. Experimental Design: Bortezomib was administered twice weekly for 2 consecutive weeks at either 1.3 or 1.7 mg/m2 dose followed by a 1-week rest. Bortezomib pharmacokinetics and nuclear factor κB (NF-κB) binding activity were evaluated during the first treatment cycle. Results: Twelve patients (nine with acute lymphoblastic leukemia, three with acute myelogenous leukemia), median age 11 years (range, 1-18 years), were enrolled between May 2004 and November 2005, of whom seven were not fully evaluable for toxicity due to rapidly progressive disease or uncontrolled infection. Dose-limiting toxicities occurred in two patients at the 1.7 mg/m2 dose level. One patient experienced grade 3 confusion and the other patient had grade 4 febrile neutropenia associated with grade 4 hypotension and grade 3 creatinine. Pharmacokinetic analysis at 1.3 mg/m2 revealed a clearance of 11 mL/h/m2, a central volume of distribution of 6.7 L/m2, and a terminal half-life of 12.6 h. NF-κB activity was examined in five patients and was noted to transiently increase and then decrease 4- to 6-fold by 24 h following bortezomib in two patients. There were no objective clinical responses. Conclusions: For children with leukemia, the recommended phase 2 dose of bortezomib, administered twice weekly for 2 weeks followed by a 1-week rest, is 1.3 mg/m2/dose. Although bortezomib treatment inhibited NF-κB activity, bortezomib had little activity as a single agent in this population.

Phase I Study of the Proteasome Inhibitor Bortezomib in Pediatric Patients With Refractory Solid Tumors: A Children's Oncology Group Study (ADVL0015)

PURPOSE To determine the maximum-tolerated dose, dose-limiting toxicity (DLT), and pharmacodynamics of the proteasome inhibitor bortezomib (formerly PS-341) in children with recurrent or refractory solid tumors. PATIENTS AND METHODS An intravenous bolus of bortezomib was administered twice weekly for 2 consecutive weeks at either 1.2 or 1.6 mg/m2/dose followed by a 1-week rest. The pharmacodynamics of bortezomib were evaluated by measurement of whole blood 20S proteasome activity. RESULTS Fifteen patients, 11 assessable, were enrolled between November 2001 and February 2003. Dose-limiting thrombocytopenia, which prevented administration of a complete course (four doses in 2 weeks) of therapy, occurred in two of five assessable children enrolled at the 1.6 mg/m2 dose level. There were no other DLTs. Inhibition of 20S proteasome activity seemed to be dose dependent. The average inhibition 1 hour after drug administration on day 1 was 67.2% +/- 7.6% at the 1.2 mg/m2/dose and 76.5% +/- 3.3% at the 1.6 mg/m2/dose. There were no objective antitumor responses. CONCLUSION Bortezomib is well tolerated in children with recurrent or refractory solid tumors. The recommended phase II dose of bortezomib for children with solid tumors is 1.2 mg/m2/dose, administered as an intravenous bolus twice weekly for 2 weeks followed by a 1-week break.

Poly(ADP-ribose) polymerase inhibitor ABT-888 potentiates the cytotoxic activity of temozolomide in leukemia cells: influence of mismatch repair status and O6-methylguanine-DNA methyltransferase activity

The poly(ADP-ribose) polymerase (PARP) inhibitor ABT-888 potentiates the antitumor activity of temozolomide (TMZ). TMZ resistance results from increased O6-methylguanine-DNA methyltransferase (MGMT) activity and from mismatch repair (MMR) system mutations. We evaluated the relative importance of MGMT activity, MMR deficiency, nonhomologous end joining (NHEJ), and PARP activity in ABT-888 potentiation of TMZ. MMR-proficient and MMR-deficient leukemia cells with varying MGMT activity, as well as primary leukemia samples, were used to determine TMZ IC50 alone and with ABT-888. ABT-888 effectively inhibited PARP activity and enhanced TMZ growth inhibition in most leukemia cells. ABT-888 potentiation was most effective in MMR-deficient cells with low MGMT activity [potentiation factor (PF) = 21]. ABT-888 also potentiated TMZ activity in MMR-deficient cells with elevated MGMT activity. Unexpectedly, ABT-888 also enhanced TMZ activity in MMR-proficient cells (PF = 3–7). ABT-888 potentiation was unrelated to NHEJ activity. ABT-888 potentiated TMZ (PF = 2–5) in two of four acute myeloid leukemia patient samples but showed little potentiation in primary acute lymphoblastic leukemia. In conclusion, although ABT-888 potentiation of TMZ was most pronounced in MMR-deficient cells with low MGMT activity, neither MMR proficiency nor MGMT overexpression completely abrogated ABT-888 potentiation of TMZ. [Mol Cancer Ther 2009;8(8):2232–42]

Improving T-cell Therapy for Relapsed EBV-Negative Hodgkin Lymphoma by Targeting Upregulated MAGE-A4

Purpose: Patients with Hodgkin lymphoma (HL) relapsing after hematopoietic stem cell transplant have limited options for long-term cure. We have shown that infused cytotoxic T cells (CTL) targeting Epstein Barr virus (EBV)–derived proteins induced complete remissions in EBV+ HL patients. A limitation of this approach is that up to 70% of relapsed HL tumors are EBV-negative. For these patients, an alternative is to target the cancer/testis antigen MAGE-A4 present in EBV antigen-negative HL tumors. Furthermore, epigenetic modification by clinically available demethylating agents can enhance MAGE-A4 expression in previously MAGE-negative tumors. Experimental Design: We explored the feasibility of combining adoptive T cell therapy with epigenetic modification of tumor antigen expression. We further characterized MAGE-A4–specific T-cell phenotype and function, and examined the effects of the epigenetic modifying drug decitabine on these T cells. Results: Cytotoxic T cells were generated specifically recognizing MAGE-A4 expressed by autologous HL targets and tumor cell lines. Decitabine—previously shown to increase tumor antigen expression in HL—did not compromise MAGE-A4–specific T-cell phenotype and function. In patients treated with decitabine, expanded MAGE-A4–specific T cells had a broader antitumor T cell repertoire, consistent with increased antigen stimulation in vivo. Conclusions: Adoptive transfer of MAGE-A4–specific T cells, combined with epigenetic modifying drugs to increase expression of the protein, may improve treatment of relapsed HL. Clin Cancer Res; 17(22); 7058–66. ©2011 AACR.

A phase I trial of vorinostat and bortezomib in children with refractory or recurrent solid tumors: A Children's Oncology Group phase I consortium study (ADVL0916)†

A pediatric Phase I trial was performed to determine the maximum‐tolerated dose, dose‐limiting toxicities (DLTs), and pharmacokinetics (PK) of vorinostat and bortezomib, in patients with solid tumors.

Endogenous knockdown of survivin improves chemotherapeutic response in ALL models

Although the cure rate of newly diagnosed acute lymphoblastic leukemia (ALL) has improved over the past four decades, the outcome for patients who relapse remains poor. New therapies are needed for these patients. Our previous global gene expression analysis in a series of paired diagnosis-relapse pediatric patient samples revealed that the antiapoptotic gene survivin was consistently upregulated upon disease relapse. In this study, we demonstrate a link between survivin expression and drug resistance and test the efficacy of a novel antisense agent in promoting apoptosis when combined with chemotherapy. Gene-silencing experiments targeting survivin mRNA using either short-hairpin RNA (shRNA) or a locked antisense oligonucleotide (LNA-ON) specifically reduced gene expression and induced apoptosis in leukemia cell lines. When used in combination with chemotherapy, the survivin shRNA and LNA-ON potentiated the chemotherapeutic antileukemia effect. Moreover, in a mouse primary xenograft model of relapse ALL, the survivin LNA-ON decreased survivin expression in a subset of animals, and produced a statistically significant decrease in tumor progression. Taken together, these findings suggest that targeting endogenous levels of survivin mRNA by LNA-ON methods may augment the response to standard chemotherapy by sensitizing otherwise resistant tumor cells to chemotherapy.

A pediatric phase 1 trial of vorinostat and temozolomide in relapsed or refractory primary brain or spinal cord tumors: A children's oncology group phase 1 consortium study

We conducted a pediatric phase I study to estimate the maximum tolerated dose (MTD), dose‐limiting toxicities (DLT), and pharmacokinetic properties of vorinostat, a histone deacetylase (HDAC) inhibitor, when given in combination with temozolomide in children with refractory or recurrent CNS malignancies.

Case series of thrombotic thrombocytopenic purpura in children and adolescents.

Thrombotic thrombocytopenic purpura (TTP) is a well-described entity in adults but is rarely observed in children. The authors describe a series of seven children with suspected acquired TTP. Clinical findings included petechiae, purpura, or jaundice (6), central nervous system events (5), fever (3), diarrhea (3), renal insufficiency (2), and hematuria (2). Significant central nervous system events included cerebral vascular accidents (2), altered mental status (2), seizures (1), and hemiparesis (1). Patients were treated with daily plasma infusions (1/7) or plasma exchange (5/7). Response was prompt, although relapses were frequent. Decreased vWF-protease activity was found in four of five cases and vWF-protease inhibitors were found in three of five cases. Although rare, TTP is a life-threatening illness that does occur in children and should be considered in the differential diagnosis of thrombocytopenia with hemolytic anemia.

Children's Oncology Group's 2013 blueprint for research: Hodgkin lymphoma

In childhood Hodgkin lymphoma, estimated 5 years survival rates exceed 90%. Long‐term survival continues to decline from delayed toxicities. Key findings from recent Childrens Oncology Group trials include: (1) Radiotherapy selection may be based on early chemotherapy response assessed by both FDG‐PET and CT imaging, (2) A new prognostic factor score stratifies patients into risk categories; and (3) novel retrieval regimens were identified. A phase I/II trial is investigating Brentuximab vedotin (Bv) with gemcitabine in relapsed patients. A phase 3 trial will modify conventional chemotherapy and radiotherapy approaches through the addition of Bv, while incorporating translational biology to identify molecular targets. Pediatr Blood Cancer 2013; 60: 972–978.

Higher ratio immune versus constitutive proteasome level as novel indicator of sensitivity of pediatric acute leukemia cells to proteasome inhibitors

The ex vivo sensitivity of pediatric leukemia cells to the proteasome inhibitor bortezomib was compared to 3 next generation proteasome inhibitors: the epoxyketone-based irreversible proteasome inhibitors carfilzomib, its orally bio-available analog ONX 0912, and the immunoproteasome inhibitor ONX 0914. LC50 values were determined by MTT cytotoxicity assays for 29 childhood acute lymphoblastic leukemia and 12 acute myeloid leukemia patient samples and correlated with protein expression levels of the constitutive proteasome subunits (β5, β1, β2) and their immunoproteasome counterparts (β5i, β1i, β2i). Acute lymphoblastic leukemia cells were up to 5.5-fold more sensitive to proteasome inhibitors than acute myeloid leukemia cells (P<0.001) and the combination of bortezomib and dexamethasone proved additive/synergistic in the majority of patient specimens. Although total proteasome levels in acute lymphoblastic leukemia and acute myeloid leukemia cells did not differ significantly, the ratio of immuno/constitutive proteasome was markedly higher in acute lymphoblastic leukemia cells over acute myeloid leukemia cells. In both acute lymphoblastic leukemia and acute myeloid leukemia, increased ratios of β5i/β5, β1i/β1 and β2i/β2 correlated with increased sensitivity to proteasome inhibitors. Together, differential expression levels of constitutive and immunoproteasomes in pediatric acute lymphoblastic leukemia and acute myeloid leukemia constitute an underlying mechanism of sensitivity to bortezomib and new generation proteasome inhibitors, which may further benefit from synergistic combination therapy with drugs including glucocorticoids.