Temsirolimus combined with cyclophosphamide and etoposide for pediatric patients with relapsed/refractory acute lymphoblastic leukemia: a Therapeutic Advances in Childhood Leukemia Consortium trial (TACL 2014-001)

Abstract

Phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling is commonly dysregulated in acute lymphoblastic leukemia (ALL). The TACL2014-001 phase I trial of the mTOR inhibitor temsirolimus in combination with cyclophosphamide and etoposide was performed in children and adolescents with relapsed/refractory ALL. Temsirolimus was administered intravenously (IV) on days 1 and 8 with cyclophosphamide 440 mg/m2 and etoposide 100 mg/m2 IV daily on days 1-5. The starting dose of temsirolimus was 7.5 mg/m2 (DL1) with escalation to 10 mg/m2 (DL2), 15 mg/m2 (DL3), and 25 mg/m2 (DL4). PI3K/mTOR pathway inhibition was measured by phosphoflow cytometry analysis of peripheral blood specimens from treated patients. Sixteen heavily-pretreated patients were enrolled with 15 evaluable for toxicity. One dose-limiting toxicity of grade 4 pleural and pericardial effusions occurred in a patient treated at DL3. Additional dose-limiting toxicities were not seen in the DL3 expansion or DL4 cohort. Grade 3/4 non-hematologic toxicities occurring in three or more patients included febrile neutropenia, elevated alanine aminotransferase, hypokalemia, mucositis, and tumor lysis syndrome and occurred across all doses. Response and complete were observed at all dose levels with a 47% overall response rate and 27% complete response rate. Pharmacodynamic correlative studies demonstrated dose-dependent inhibition of PI3K/mTOR pathway phosphoproteins in all studied patients. Temsirolimus at doses up to 25 mg/m2 with cyclophosphamide and etoposide had an acceptable safety profile in children with relapsed/refractory ALL. Pharmacodynamic mTOR target inhibition was achieved and appeared to correlate with temsirolimus dose. Future testing of next-generation PI3K/mTOR pathway inhibitors with chemotherapy may be warranted to increase response rates in children with relapsed/refractory ALL.

Figure 1.

Constitutive activation of PI3K pathway signaling in children with relapsed/refractory acute lymphoblastic leukemia enrolled on TACL2014-001. Pre-treatment (basal, day 0) peripheral blood samples were obtained from study patients with acute lymphoblastic leukemia (ALL) for single-cell phosphoflow cytometry analysis of the PI3K pathway and other phosphoproteins as previously described. Pre-treatment blood specimens from most patients show basal activation of multiple PI3K/mTOR pathway phosphoproteins in gated human leukemia cells (CD45⁺/CD19⁺ B-ALL or CD45⁺/CD3⁺ for T-ALL) when compared to fluorescence-minus-one (FMO)-stained control cells. Solid symbols represent patients with partial response, stable disease, or progressive disease after cycle 1. Black-ringed symbols represent patients with complete response.

Figure 2.

Abrogation of constitutively-activated PI3K/mTOR pathway signaling with temsirolimus therapy. Pre-treatment (basal, day 0) and post-treatment (day 3-5) levels of PI3K/mTOR pathway phosphoproteins were measured as median fluorescence intensity (MFI) by single-cell phosphoflow cytometry in gated B-acute lymphoblastic leukemia (ALL) or T-ALL cells in peripheral blood specimens from TACL2014-001 patients. Phosphoprotein inhibition in peripheral blood ALL cells at day 3-5 of therapy after the first dose of temsirolimus in comparison to basal phosphoprotein levels is shown for each patient treated at the designated dose levels (DL1, DL2, DL3, DL4). MFI data were normalized intra-patient to pre-treatment levels of each phosphoprotein. Central horizontal solid lines depict mean phosphoprotein inhibition for inter-patient comparison. Dotted line set at y=0 indicates no change in phosphoprotein from baseline. Solid symbols represent patients with partial response, stable disease, or progressive disease after cycle 1. Black-ringed symbols represent patients with complete response. Summary pharmacodynamic data of all dose levels are shown in Online Supplementary Figure S2.