Outcome of chimeric antigen receptor T-cell therapy following treatment with inotuzumab ozogamicin in children with relapsed or refractory acute lymphoblastic leukemia.

Chimeric antigen receptor T cells targeting CD19 (CART-19) have shown remarkable efficacy for relapsed/refractory (R/R) B-cell precursor acute lymphoblastic leukemia (BCP-ALL). We investigated whether prior use of inotuzumab ozogamicin (InO), an anti-CD22 antibody conjugated to calicheamicin, may impact CAR T-cell manufacturing or efficacy via pre-CART-19 depletion of the B-cell compartment. In this international, retrospective analysis, 39 children and young adults receiving InO before (n = 12) and/or after (n = 27) T-cell apheresis as bridging therapy to CART-19 treatment were analyzed. Median age at infusion was 13 years (range 1.4-23 years). Thirty-four out of 39 patients (87.2%) obtained complete remission. With a median follow-up of 18.2 months after CART-19 infusion, 12-month event-free survival (EFS) was 53.3% (95% confidence interval (CI): 38.7-73.4) and overall survival (OS) was 77.8% (95% CI: 64.5-93.9). Seventeen patients (44%) relapsed with a median of 159 days (range 28-655) after CART-19 infusion. No difference in day 28 minimal residual disease negative complete response rate, 12-month OS/EFS, or incidence of CD19-positive or -negative relapses was observed among patients receiving InO before or after apheresis. Compared to published data for patients treated with CART-19 therapy without prior InO exposure, response and OS/EFS for patients treated with InO prior to CART-19 are similar.

CD19 CAR T-cells for pediatric relapsed acute lymphoblastic leukemia with active CNS involvement: a retrospective international study.

Relapse of B-cell precursor acute lymphoblastic leukemia (BCP-ALL) may occur in the central nervous system (CNS). Most clinical trials of CAR T-cell therapy excluded patients with active CNS leukemia, partially for concerns of neurotoxicity. Here, we report an international study of fifty-five children and adolescents who received CAR T-cell therapy for relapsed BCP-ALL with CNS involvement at the time of referral. All patients received bridging therapy, 16 still having active CNS disease at the time of lymphodepletion. Twelve patients received CD28-based CAR T-cells, 9 being subsequently treated with allogeneic hematopoietic stem-cell transplantation (allo-HSCT). Forty-three patients received 4-1BB-based CAR T-cells. Cytokine-release syndrome (CRS) and neurotoxicity occurred in 65% and 38% of patients, respectively, more frequently following treatment with CD28-based CARs. Fifty-one of 54 evaluable patients (94%) achieved complete response following this therapy. Relapse occurred in 22 patients: 19/43 following 4-1BB-based CARs (12 CNS relapses), and 3/12 after CD28-based CARs with subsequent HSCT (no CNS relapse). Patients treated with tisagenlecleucel for an isolated CNS relapse had a high incidence of a subsequent CNS relapse (6 of 8). CAR T-cells were found to be effective in this cohort, though the risk of CNS relapse was not completely mitigated by this approach.

Selumetinib in combination with dexamethasone for the treatment of relapsed/refractory RAS-pathway mutated paediatric and adult acute lymphoblastic leukaemia (SeluDex): study protocol for an international, parallel-group, dose-finding with expansion phase I/II trial.

INTRODUCTION: Event-free survival rates at 15 years for paediatric patients with relapsed/refractory acute lymphoblastic leukaemia (ALL) are 30%-50%, with 5-year survival for adult patients only 20%. Many patients with newly diagnosed and relapsed ALL harbour somatic RAS-signalling activation mutations. Induction therapy for ALL involves steroids, with preclinical data suggesting the combination of dexamethasone with the MEK1/2 inhibitor, selumetinib (ARRY-142886) has a synergistic anticancer effect. METHODS AND ANALYSIS: The SeluDex trial is an international, parallel-group, dose-finding with expansion, phase I/II trial to assess the selumetinib/dexamethasone combination in adult and paediatric patients with relapsed/refractory, RAS pathway mutant ALL. The Cancer Research UK Clinical Trials Unit at University of Birmingham is the UK Coordinating Centre, with national hubs in Copenhagen, Denmark; Monza, Italy; Münster, Germany; Paris, France; and Utrecht, Netherlands. Patients with morphologically proven relapsed/refractory or progressive B-cell precursor or T-cell ALL, with demonstrated RAS pathway activating mutations are eligible. Adult patients are >18 years old, ECOG <2 and paediatric <18 years old, Lansky play scale ≥60% or Karnofsky score ≥60%. Phase I primary objective is the recommended phase II dose of selumetinib as defined by occurrence/non-occurrence of dose limiting toxicities using the continual reassessment method; phase II will evaluate preliminary antileukaemic activity of the combination, as defined by morphological response 28 days post-treatment using a Bayesian approach. Target recruitment is between 26 and 42 patients (minimum 13 and maximum 21 per group), depending the number of phase I patients included in phase II. ETHICS AND DISSEMINATION: Medical ethical committees of all the participating countries have approved the study protocol; initial (UK) ethics approval (17/YH/0123) was granted by Yorkshire & The Humber-Leeds West Research Ethics Committee. Participants are required to provide written informed consent/assent. Results will be disseminated through national and international presentations and peer-reviewed publications. TRIAL REGISTRATION NUMBER: ISRCTN92323261.

Fludarabine exposure predicts outcome after CD19 CAR T-cell therapy in children and young adults with acute leukemia.

The addition of fludarabine to cyclophosphamide as a lymphodepleting regimen prior to CD19 chimeric antigen receptor (CAR) T-cell therapy significantly improved outcomes in patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL). Fludarabine exposure, previously shown to be highly variable when dosing is based on body surface area (BSA), is a predictor for survival in allogeneic hematopoietic cell transplantation (allo-HCT). Hence, we hypothesized that an optimal exposure of fludarabine might be of clinical importance in CD19 CAR T-cell treatment. We examined the effect of cumulative fludarabine exposure during lymphodepletion, defined as concentration-time curve (AUC), on clinical outcome and lymphocyte kinetics. A retrospective analysis was conducted with data from 26 patients receiving tisagenlecleucel for r/r B-ALL. Exposure of fludarabine was shown to be a predictor for leukemia-free survival (LFS), B-cell aplasia, and CD19-positive relapse following CAR T-cell infusion. Minimal event probability was observed at a cumulative fludarabine AUCT0-∞ ≥14 mg*h/L, and underexposure was defined as an AUCT0-∞ <14 mg*h/L. In the underexposed group, the median LFS was 1.8 months, and the occurrence of CD19-positive relapse within 1 year was 100%, which was higher compared with the group with an AUCT0-∞ ≥14 mg*h/L (12.9 months; P < .001; and 27.4%; P = .0001, respectively). Furthermore, the duration of B-cell aplasia within 6 months was shorter in the underexposed group (77.3% vs 37.3%; P = .009). These results suggest that optimizing fludarabine exposure may have a relevant impact on LFS following CAR T-cell therapy, which needs to be validated in a prospective clinical trial.

MAPK-ERK is a central pathway in T-cell acute lymphoblastic leukemia that drives steroid resistance.

(Patho-)physiological activation of the IL7-receptor (IL7R) signaling contributes to steroid resistance in pediatric T-cell acute lymphoblastic leukemia (T-ALL). Here, we show that activating IL7R pathway mutations and physiological IL7R signaling activate MAPK-ERK signaling, which provokes steroid resistance by phosphorylation of BIM. By mass spectrometry, we demonstrate that phosphorylated BIM is impaired in binding to BCL2, BCLXL and MCL1, shifting the apoptotic balance toward survival. Treatment with MEK inhibitors abolishes this inactivating phosphorylation of BIM and restores its interaction with anti-apoptotic BCL2-protein family members. Importantly, the MEK inhibitor selumetinib synergizes with steroids in both IL7-dependent and IL7-independent steroid resistant pediatric T-ALL PDX samples. Despite the anti-MAPK-ERK activity of ruxolitinib in IL7-induced signaling and JAK1 mutant cells, ruxolitinib only synergizes with steroid treatment in IL7-dependent steroid resistant PDX samples but not in IL7-independent steroid resistant PDX samples. Our study highlights the central role for MAPK-ERK signaling in steroid resistance in T-ALL patients, and demonstrates the broader application of MEK inhibitors over ruxolitinib to resensitize steroid-resistant T-ALL cells. These findings strongly support the enrollment of T-ALL patients in the current phase I/II SeluDex trial (NCT03705507) and contributes to the optimization and stratification of newly designed T-ALL treatment regimens.

Sensitizing Ewing sarcoma to chemo- and radiotherapy by inhibition of the DNA-repair enzymes DNA protein kinase (DNA-PK) and poly-ADP-ribose polymerase (PARP) 1/2.

BACKGROUND: DNA-PK and PARP inhibitors sensitize cancer cells to chemo- and radiotherapy. ETS transcription factors (EWS-FLI1) have been described as biomarkers for PARP-inhibitor sensitivity. Sensitivity to single agent PARP inhibitors has so far been limited to homologous recombination repair (HRR) deficient tumors, exploiting synthetic lethality. RESULTS: In clonogenic assays, single agent rucaparib LD50 values for continuously exposed cells were similar to those observed in HRR-defective cells (CAPAN-1 cell line, BRCA2 defective); however, both ES cell lines (TC-71, CADO-ES1) had functional HRR. In vivo rucaparib administration (10 mg/kg daily) showed no responses. In clonogenic assays, rucaparib enhanced temozolomide, camptothecin and radiation cytotoxicity, which was most profound for temozolomide (15-29 fold enhancement). NU7441 increased the cytotoxicity of etoposide, doxorubicin and radiation. MATERIALS AND METHODS: We assessed PARP1/2 (rucaparib) and DNA-PK (NU7441) inhibitors in Ewing sarcoma (ES) cell lines by performing growth inhibition and clonogenic assays. HRR was measured by RAD51 focus formation. Single agent rucaparib was assessed in an in vivo orthotopic model. CONCLUSIONS: Single agent rucaparib ES sensitivity in vitro was not replicated in vivo. DNA-PK and PARP inhibitors are good chemo-/radiosensitizers in ES. The future of these inhibitors lies in their combination with chemo-/radiotherapy, which needs to be evaluated in clinical trials.

Poly(ADP-ribose) polymerase inhibitors in Ewing sarcoma.

PURPOSE OF REVIEW: In 2012, two publications revealed a particular sensitivity of Ewing sarcoma cells to the inhibition of poly(ADP-ribose) polymerase (PARP). This review updates the reader on PARP function, the development of PARP inhibitors (PARPi) and the evidence for targeting PARP in Ewing sarcoma. It concludes with a description of ongoing/emerging PARPi clinical trials in patients with Ewing sarcoma. RECENT FINDINGS: PARP has a major role in DNA repair, and is a transcription regulator. The oncoprotein in Ewing sarcoma, EWS-FLI1, is proposed to interact with PARP-1, driving PARP-1 expression, which further promotes transcriptional activation by EWS-FLI1. Thus, there are two rationales for PARPi in the treatment of Ewing sarcoma: to disrupt the interaction between EWS-FLI1 and PARP, and for chemo-potentiation or radio-potentiation. The first clinical trial with a single agent PARPi failed to show significant responses, but preclinical evidence for combinations of PARPi with chemotherapy or radiotherapy is very promising. SUMMARY: Despite initial excitement for the potential of PARPi as single agent therapy in Ewing sarcoma, the emerging preclinical data now strongly support testing PARPi in combination with chemo/radiotherapy clinically.

Development of a preclinical orthotopic xenograft model of ewing sarcoma and other human malignant bone disease using advanced in vivo imaging.

Ewing sarcoma and osteosarcoma represent the two most common primary bone tumours in childhood and adolescence, with bone metastases being the most adverse prognostic factor. In prostate cancer, osseous metastasis poses a major clinical challenge. We developed a preclinical orthotopic model of Ewing sarcoma, reflecting the biology of the tumour-bone interactions in human disease and allowing in vivo monitoring of disease progression, and compared this with models of osteosarcoma and prostate carcinoma. Human tumour cell lines were transplanted into non-obese diabetic/severe combined immunodeficient (NSG) and Rag2(-/-/)γc(-/-) mice by intrafemoral injection. For Ewing sarcoma, minimal cell numbers (1000-5000) injected in small volumes were able to induce orthotopic tumour growth. Tumour progression was studied using positron emission tomography, computed tomography, magnetic resonance imaging and bioluminescent imaging. Tumours and their interactions with bones were examined by histology. Each tumour induced bone destruction and outgrowth of extramedullary tumour masses, together with characteristic changes in bone that were well visualised by computed tomography, which correlated with post-mortem histology. Ewing sarcoma and, to a lesser extent, osteosarcoma cells induced prominent reactive new bone formation. Osteosarcoma cells produced osteoid and mineralised "malignant" bone within the tumour mass itself. Injection of prostate carcinoma cells led to osteoclast-driven osteolytic lesions. Bioluminescent imaging of Ewing sarcoma xenografts allowed easy and rapid monitoring of tumour growth and detection of tumour dissemination to lungs, liver and bone. Magnetic resonance imaging proved useful for monitoring soft tissue tumour growth and volume. Positron emission tomography proved to be of limited use in this model. Overall, we have developed an orthotopic in vivo model for Ewing sarcoma and other primary and secondary human bone malignancies, which resemble the human disease. We have shown the utility of small animal bioimaging for tracking disease progression, making this model a useful assay for preclinical drug testing.