Durable Responses With Mosunetuzumab in Relapsed/Refractory Indolent and Aggressive B-Cell Non-Hodgkin Lymphomas: Extended Follow-Up of a Phase I/II Study.

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.Mosunetuzumab is a CD20xCD3 T-cell-engaging bispecific antibody administered as an off-the-shelf, fixed-duration treatment in an outpatient setting. We report an updated analysis of the durability of response, by investigator assessment, after an overall median follow-up of 3.5 years in patients with relapsed/refractory indolent or aggressive B-cell non-Hodgkin lymphoma (iNHL/aNHL) from the dose-escalation stage of a phase I/II study of mosunetuzumab (ClinicalTrials.gov identifier: NCT02500407). Across dose levels, 65.7% of patients with iNHL and 36.4% with aNHL achieved a complete or partial response to mosunetuzumab. Median duration of response (DoR) in patients with iNHL for all responders was 23.2 months (95% CI, 13.8 to not estimable [NE]), but was not reached in complete responders (95% CI, 21.0 to NE). After a median time on study of 38.9 months, no relapses were observed beyond 26 months in complete responders. In patients with aNHL, median DoR for all responders was 7.8 months (95% CI, 4.6 to 22.8). Among 12 complete responders who progressed postmosunetuzumab treatment and were retreated with mosunetuzumab, 83.3% had an objective response and 58.3% achieved a second complete response. Our study reports the longest follow-up using bispecific antibodies in patients with B-cell non-Hodgkin lymphoma and demonstrates that mosunetuzumab can mediate durable remissions with time-limited treatment.

Mosunetuzumab with polatuzumab vedotin in relapsed or refractory aggressive large B cell lymphoma: a phase 1b/2 trial.

Relapsed/refractory aggressive large B cell lymphoma (LBCL) remains an area of unmet need. Here we report the primary analysis of a phase 1b/2 trial of outpatient mosunetuzumab (a CD20xCD3 T-cell-engaging bispecific antibody) plus polatuzumab vedotin (an anti-CD79B antibody-drug conjugate) in relapsed/refractory LBCL. The phase 2 component is a single arm of an ongoing multi-arm trial. The primary endpoint during dose expansion was independent review committee (IRC)-assessed best overall response rate. Secondary endpoints included investigator-assessed overall response rate, complete response, duration of response, progression-free survival and overall survival. At data cutoff, 120 patients were enrolled (22 dose escalation, 98 dose expansion). The primary endpoint was met during dose expansion, with IRC-assessed best overall response rate and complete response rates of 59.2% (58/98; 95% confidence interval (CI): 48.8-69.0) and 45.9% (45/98; 95% CI: 35.8-56.3), respectively (median follow-up, 23.9 months). Median duration of complete was not reached (95% CI: 20.5-not estimable (NE)). Median progression-free survival was 11.4 months (95% CI: 6.2-18.7). Median overall survival was 23.3 months (95% CI: 14.8-NE). Across dose escalation and expansion, the most common grade 3 or higher adverse events were neutropenia (25.0%, 30/120) and fatigue (6.7%, 8/120). Any-grade cytokine release syndrome occurred in 16.7% of patients. These data demonstrate that mosunetuzumab plus polatuzumab vedotin has a favorable safety profile with highly durable responses suitable as second-line therapy in transplant-ineligible relapsed/refractory LBCL. ClinicalTrials.gov identifier: NCT03671018 .

Loss of CD20 expression as a mechanism of resistance to mosunetuzumab in relapsed/refractory B-cell lymphomas.

ABSTRACT: CD20 is an established therapeutic target in B-cell malignancies. The CD20 × CD3 bispecific antibody mosunetuzumab has significant efficacy in B-cell non-Hodgkin lymphomas (NHLs). Because target antigen loss is a recognized mechanism of resistance, we evaluated CD20 expression relative to clinical response in patients with relapsed and/or refractory NHL in the phase 1/2 GO29781 trial investigating mosunetuzumab monotherapy. CD20 was studied using immunohistochemistry (IHC), RNA sequencing, and whole-exome sequencing performed centrally in biopsy specimens collected before treatment at predose, during treatment, or upon progression. Before treatment, most patients exhibited a high proportion of tumor cells expressing CD20; however, in 16 of 293 patients (5.5%) the proportion was <10%. Analyses of paired biopsy specimens from patients on treatment revealed that CD20 levels were maintained in 29 of 30 patients (97%) vs at progression, where CD20 loss was observed in 11 of 32 patients (34%). Reduced transcription or acquisition of truncating mutations explained most but not all cases of CD20 loss. In vitro modeling confirmed the effects of CD20 variants identified in clinical samples on reduction of CD20 expression and missense mutations in the extracellular domain that could block mosunetuzumab binding. This study expands the knowledge about the occurrence of target antigen loss after anti-CD20 therapeutics to include CD20-targeting bispecific antibodies and elucidates mechanisms of reduced CD20 expression at disease progression that may be generalizable to other anti-CD20 targeting agents. These results also confirm the utility of readily available IHC staining for CD20 as a tool to inform clinical decisions. This trial was registered at www.ClinicalTrials.gov as #NCT02500407.

Indirect Treatment Comparisons of Mosunetuzumab With Third- and Later-Line Treatments for Relapsed/Refractory Follicular Lymphoma.

BACKGROUND: No established standard of care exists for relapsed/refractory (RR) follicular lymphoma (FL) after ≥2 prior therapies. We conducted indirect treatment comparisons (ITCs) to compare the efficacy and tolerability of mosunetuzumab with those of available treatments used in this setting. METHODS: A systematic literature review (SLR) and subsequent feasibility assessments were conducted to identify the most suitable comparator studies in terms of design, available endpoints and populations. Imbalances in patient characteristics between NCT02500407 and studies featuring aggregate or patient-level data availability were accounted for using matching-adjusted indirect comparison (MAIC) and propensity score-based methodologies, respectively. RESULTS: ZUMA-5, ELARA, DELTA, DYNAMO, UNITY-NHL, AUGMENT and NCT01897571 passed the MAIC feasibility assessment. Patient-level data were available from GADOLIN, CONTRALTO and NCT02257567. MAIC results generally favored mosunetuzumab over tazemetostat in EHZ2wild-type patients for all outcomes and over PI3K inhibitors for complete response (CR), objective response rate (ORR), discontinuations due to adverse events and progression-free survival (PFS) with umbralisib. MAICs favored CART therapies for PFS and, to a lesser extent, ORR and CR. Comparisons with anti-CD20 antibody-based regimens yielded mixed results. CONCLUSIONS: ITCs suggest that mosunetuzumab may lead to superior outcomes over tazemetostat (in EHZ2wild-type patients) and PI3K inhibitors and may be a promising alternative to re-challenging with a different anti-CD20 regimen in patients who relapse after ≥2 prior anti-CD20 lines. Although preliminary results somewhat favored CART therapies, limitations and uncertainties remain because of intrinsic differences in study design. Mosunetuzumab could thus be a promising treatment option for patients with RR FL after ≥2 prior therapies.

Matching-adjusted indirect comparison from the Lymphoma Epidemiology of Outcomes Consortium for Real World Evidence (LEO CReWE) study to a clinical trial of mosunetuzumab in relapsed or refractory follicular lymphoma.

Mosunetuzumab is a novel bispecific antibody targeting epitopes on CD3 on T cells and CD20 on B cells with the goal of inducing T-cell mediated elimination of malignant B cells. A recent pivotal phase I/II clinical trial (GO29781) demonstrated that mosunetuzumab induced an overall response rate of 80%, complete response rate of 60%, and a median progression-free survival of 17.9 months in patients with relapsed/refractory (r/r) follicular lymphoma (FL) following at least two prior lines of systemic therapy, including alkylator and anti-CD20 antibody-based therapy. Historical data from cohorts receiving therapy for r/r FL can provide some context for interpretation of single-arm trials. We compared the results from the mosunetuzumab trial to outcomes from a cohort of patients with r/r FL from the LEO Consortium for Real World Evidence (LEO CReWE). We applied clinical trial eligibility criteria to the LEO CReWE cohort and utilized matching-adjusted indirect comparison weighting to balance the clinical characteristics of the LEO CReWE cohort with those from the mosunetuzumab trial. Overall response rates (73%, 95% CI:65-80%) and complete response rates (53%, 95% CI:45-61%) observed in the weighted LEO CReWE cohort were lower than those reported on the mosunetuzumab trial (ORR=80%, 95% CI:70-88%; CR=60%, 95% CI:49-70% respectively). Progression-free survival at 12 months was similar in the weighted LEO CReWE (60%, 95% CI:51-69%) and the mosunetuzumab trial (PFS 58%, 95% CI:47-68%). Sensitivity analyses examining the impact of matching variables, selection of line of therapy, and application of eligibility criteria, provide context for best practices in this setting.

Comparative effectiveness between mosunetuzumab monotherapy clinical trial and real-world data in relapsed/refractory follicular lymphoma in third or subsequent lines of systemic therapy.

A comparison of clinical outcomes in the third or subsequent line (3 L+) of systemic therapy between a real-world data (RWD) external control cohort and a mosunetuzumab single-arm clinical trial cohort is presented. Data for 3 L + patients with relapsed/refractory follicular lymphoma (FL) were obtained from the mosunetuzumab single-arm trial (n = 90) and a US electronic health records database (n = 158), with patients meeting key eligibility criteria from the trial, balanced on pre-specified prognostic factors. Overall response and complete response rates were 80% and 60% in the mosunetuzumab cohort and 75% and 33% in the RWD cohort, odds ratios of 1.23 (95% CI, 0.52-2.93) and 3.18 (95% CI, 1.41-7.17), respectively. Hazard ratios for progression-free survival and overall survival were 0.82 (95% CI, 0.53-1.27) and 0.43 (95% CI, 0.19-0.94). These findings support a clinically meaningful benefit of mosunetuzumab monotherapy as a chemotherapy-free option for the 3 L + FL population.

Mosunetuzumab in combination with CHOP in previously untreated DLBCL: safety and efficacy results from a phase 2 study.

Up to 40% of patients with diffuse large B-cell lymphoma (DLBCL) are refractory to or relapse after first-line therapy, highlighting the need for better treatments. Mosunetuzumab is a CD20 × CD3 bispecific antibody that engages and redirects T cells to eliminate malignant B cells. In this phase 2, open-label study (NCT03677141), 40 patients (52.5% with international prognostic index ≥3) with previously untreated DLBCL initiated 6 cycles of IV mosunetuzumab with CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy. Mosunetuzumab was administered in cycle 1 as step-up doses to mitigate cytokine release syndrome [CRS], and a dose of 30 mg was given on day 1 of cycles 2-6. Efficacy end points included objective and complete response rates, as determined by the investigator, via positron emission tomography-computed tomography, using Lugano 2014 criteria (87.5% and 85.0%, respectively). At a median follow-up of 32.0 months, the estimated 2-year progression-free survival and event-free survival rates were 65.4% (95% confidence interval [CI], 49.5-81.4) and 60.4% (95% CI, 44.7-76.1), respectively. CRS occurred in 60.0% of patients; all events were grade 1 (45.0%) or grade 2 (15.0%) and occurred primarily in cycle 1. Mosunetuzumab-related grade ≥3 neurologic adverse events (AEs) potentially consistent with immune effector cell-associated neurotoxicity syndrome occurred in 1 patient (2.5%). Grade 5 AEs were reported in 2 patients. Neutropenia occurred in 70.0% of patients, mostly during cycle 1 and was of short duration. These findings demonstrate promising activity and a manageable safety profile for mosunetuzumab-CHOP and warrant further investigation of mosunetuzumab in first-line combination regimens for DLBCL.

Mosunetuzumab monotherapy is active and tolerable in patients with relapsed/refractory diffuse large B-cell lymphoma.

As part of a phase 1 or 2 study, this single-arm expansion cohort established the efficacy and safety of mosunetuzumab monotherapy in patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) (received ≥2 previous lines of therapy). Intravenous mosunetuzumab was administered with cycle (C) 1 step-up dosing for cytokine release syndrome (CRS) mitigation: C1 day (D) 1: 1 mg; C1D8 2 mg; C1D15 and C2D1: 60 mg; C3 + D1: 30 mg. Hospitalization was not mandatory. Patients with complete response (CR) completed treatment after C8; those with partial response or stable disease continued treatment for a total of 17 cycles. The primary end point was CR rate (best response), assessed against a historical control CR rate (20%) by independent review facility. Eighty-eight patients (73.9% de novo DLBCL; 26.1% transformed follicular lymphoma) were enrolled; all had received previous anthracycline and anti-CD20 therapy. Overall response and CR rates were 42.0% (95% confidence interval [CI], 31.6-53.1) and 23.9% (95% CI, 15.4-34.1), respectively; CR rate did not reach statistical significance vs the historical control (P = .36). Median time to first response was 1.4 months. Median progression-free survival was 3.2 months (95% CI, 2.2-5.3). The CR rate in 26 patients who received previous chimeric antigen receptor T-cell (CAR-T) therapy was 12%. CRS was one of the most common adverse events (26.1% of patients); predominantly grade 1 to 2 and primarily in C1. Four patients (4.5%) discontinued mosunetuzumab owing to adverse events. Mosunetuzumab demonstrated notable efficacy and a manageable safety profile in patients with R/R DLBCL, including those previously treated with CAR-Ts. This trial was registered at www.clinicaltrials.gov as #NCT02500407.

Systems-based digital twins to help characterize clinical dose-response and propose predictive biomarkers in a Phase I study of bispecific antibody, mosunetuzumab, in NHL.

Phase I oncology clinical trials often comprise a limited number of patients representing different disease subtypes who are divided into cohorts receiving treatment(s) at different dosing levels and schedules. Here, we leverage a previously developed quantitative systems pharmacology model of the anti-CD20/CD3 T-cell engaging bispecific antibody, mosunetuzumab, to account for different dosing regimens and patient heterogeneity in the phase I study to inform clinical dose/exposure-response relationships and to identify biological determinants of clinical response. We developed a novel workflow to generate digital twins for each patient, which together form a virtual population (VPOP) that represented variability in biological, pharmacological, and tumor-related parameters from the phase I trial. Simulations based on the VPOP predict that an increase in mosunetuzumab exposure increases the proportion of digital twins with at least a 50% reduction in tumor size by day 42. Simulations also predict a left-shift of the exposure-response in patients diagnosed with indolent compared to aggressive non-Hodgkin's lymphoma (NHL) subtype; this increased sensitivity in indolent NHL was attributed to the lower inferred values of tumor proliferation rate and baseline T-cell infiltration in the corresponding digital twins. Notably, the inferred digital twin parameters from clinical responders and nonresponders show that the potential biological difference that can influence response include tumor parameters (tumor size, proliferation rate, and baseline T-cell infiltration) and parameters defining the effect of mosunetuzumab on T-cell activation and B-cell killing. Finally, the model simulations suggest intratumor expansion of pre-existing T-cells, rather than an influx of systemically expanded T-cells, underlies the antitumor activity of mosunetuzumab.

Safety and efficacy of mosunetuzumab, a bispecific antibody, in patients with relapsed or refractory follicular lymphoma: a single-arm, multicentre, phase 2 study.

BACKGROUND: Mosunetuzumab is a CD20 × CD3 T-cell-engaging bispecific monoclonal antibody that redirects T cells to eliminate malignant B cells. In a phase 1 study, mosunetuzumab was well tolerated and active in patients with relapsed or refractory B-cell lymphoma. We, therefore, aimed to evaluate the safety and anti-tumour activity of fixed-duration mosunetuzumab in patients with relapsed or refractory follicular lymphoma who had received two or more previous therapies. METHODS: We conducted a single-arm, multicentre, phase 2 study at 49 centres in seven countries (Australia, Canada, Germany, South Korea, Spain, UK, and USA). All patients were aged 18 years or older with histologically confirmed follicular lymphoma (grade 1-3a) and an Eastern Cooperative Oncology Group performance status of 0-1. Patients had disease that was relapsed or refractory to two or more previous lines of treatment, including an anti-CD20 therapy and an alkylating agent. Intravenous mosunetuzumab was administered in 21-day cycles with cycle 1 step-up dosing: 1 mg on cycle 1 day 1, 2 mg on cycle 1 day 8, 60 mg on cycle 1 day 15 and cycle 2 day 1, and 30 mg on day 1 of cycle 3 and onwards. Patients with a complete response by investigator assessment using the International Harmonisation Project criteria completed treatment after cycle 8, whereas patients with a partial response or stable disease continued treatment for up to 17 cycles. The primary endpoint was independent review committee-assessed complete response rate (as best response) in all enrolled patients; the primary efficacy analysis compared the observed IRC-assessed complete response rate with a 14% historical control complete response rate in a similar patient population receiving the pan class I PI3K inhibitor copanlisib. Safety was assessed in all enrolled patients. This study is registered with ClinicalTrials.gov, number NCT02500407, and is ongoing. FINDINGS: Between May 2, 2019, and Sept 25, 2020, we enrolled 90 patients. As of the data cutoff date (Aug 27, 2021), the median follow-up was 18·3 months (IQR 13·8-23·3). According to independent review committee assessment, a complete response was recorded in 54 patients (60·0% [95% CI 49·1-70·2]). The observed complete response rate was significantly higher than the historical control complete response rate with copanlisib of 14% (p<0·0001), thereby meeting the primary study endpoint. Cytokine release syndrome was the most common adverse event (40 [44%] of 90 patients) and was predominantly grade 1 (23 [26%] of 90) and grade 2 (15 [17%]), and primarily confined to cycle 1. The most common grade 3-4 adverse events were neutropenia or neutrophil count decreased (24 [27%] of 90 patients), hypophosphataemia (15 [17%]), hyperglycaemia (seven [8%]), and anaemia (seven [8%]). Serious adverse events occurred in 42 (47%) of 90 patients. No treatment-related grade 5 (ie, fatal) adverse event occurred. INTERPRETATION: Fixed-duration mosunetuzumab has a favourable safety profile and induces high rates of complete remissions, allowing potential administration as an outpatient regimen, in patients with relapsed or refractory follicular lymphoma and two or more previous therapies. FUNDING: F Hoffmann-La Roche and Genentech.

Treatment patterns and outcomes of patients with relapsed or refractory follicular lymphoma receiving three or more lines of systemic therapy (LEO CReWE): a multicentre cohort study.

BACKGROUND: Novel therapies for relapsed or refractory follicular lymphoma are commonly evaluated in single-arm studies without formal comparison with other treatments or historical controls. Consequently, rigorously defined treatment outcomes informing expectations for novel therapeutic strategies in this population are sparse. To inform outcome expectations, we aimed to describe treatment patterns, survival outcomes, and duration of response in patients with relapsed or refractory follicular lymphoma receiving three or more lines of systemic therapy. METHODS: In this multicentre cohort study, we developed a database of patients with relapsed or refractory follicular lymphoma from eight academic centres in the USA using data collected in the LEO Cohort study (NCT02736357) and the LEO Consortium. For this analysis, eligible patients were aged at least 18 years, had non-transformed grade 1-3a follicular lymphoma, and were receiving systemic therapy in the third line or later after previous therapy with an anti-CD20 antibody and an alkylating agent. Clinical data and patient outcomes were abstracted from medical records by use of a standard protocol. The index therapy for the primary analysis was defined as the first line of systemic therapy after the patient had received at least two previous systemic therapies that included an alkylating agent and an anti-CD20 therapy. The main endpoints of interest were overall response rate, progression-free survival, and overall survival. Outcomes were also evaluated in subsets of clinical interest (index therapy characteristics, patient and disease characteristics, treatment history, and best response assessment). FINDINGS: We screened 933 patients with follicular lymphoma, of whom 441 were included and diagnosed between March 6, 2002, and July 20, 2018. Index therapies included immunochemotherapy (n=133), anti-CD20 antibody monotherapy (n=53), lenalidomide with or without anti-CD20 (n=37), and phosphoinositide 3-kinase inhibitors with or without anti-CD20 (n=25). 57 (13%) of 441 patients received haematopoietic stem-cell transplantation and 98 (23%) of 421 patients with complete data received therapy on clinical trials. After a median follow-up of 71 months (IQR 64-79) from index therapy, 5-year overall survival was 75% (95% CI 70-79), median progression-free survival was 17 months (15-19), and the overall response rate was 70% (65-74; 280 of 400 patients evaluable for response). Patients who were refractory to therapy with an alkylating agent had a lower overall response rate (170 [68%] of 251 patients vs 107 [77%] of 139 patients) and a significantly lower 5-year overall survival (72%, 95% CI 66-78 vs 81%, 73-89; hazard ratio 1·60, 95% CI 1·04-2·46) than patients who were not refractory to therapy with an alkylating agent. INTERPRETATION: Patients with relapsed or refractory follicular lymphoma receive heterogeneous treatments in the third-line setting or later. We observed high response rates to contemporary therapies that were of short duration. These data identify unmet needs among patients with follicular lymphoma, especially those who are refractory to alkylating agents, and might provide evidence by which clinical trials evaluating novel treatments could be assessed. FUNDING: Genentech and the National Cancer Institute.

Single-Agent Mosunetuzumab Shows Durable Complete Responses in Patients With Relapsed or Refractory B-Cell Lymphomas: Phase I Dose-Escalation Study.

PURPOSE: Mosunetuzumab is a bispecific antibody targeting CD20 and CD3 that redirects T cells to engage and eliminate malignant B cells and is being developed for relapsed or refractory (R/R) B-cell non-Hodgkin lymphomas (B-NHLs). METHODS: This first-in-human trial (ClinicalTrials.gov identifier: NCT02500407) evaluated the safety and tolerability and efficacy of mosunetuzumab in patients with R/R B-NHL and established the recommended phase II dose. Data from dose escalation are presented. Single-agent mosunetuzumab was administered intravenously in 3-week cycles, at full dose in cycle 1 day 1 (group A) or with ascending (step-up) doses during cycle 1 on days 1, 8, and 15 (group B), for eight or 17 cycles on the basis of tumor response. RESULTS: Two hundred thirty patients were enrolled. Doses up to 2.8 mg and 60 mg were assessed in groups A and B, respectively; maximum tolerated dose was not exceeded. In group B (n = 197), common adverse events (≥ 20% of patients) were neutropenia (28.4%), cytokine release syndrome (27.4%), hypophosphatemia (23.4%), fatigue (22.8%), and diarrhea (21.8%). Cytokine release syndrome was mostly low-grade (grade ≥ 3: 1.0%) and mainly confined to cycle 1. Across the doses investigated (group B), best overall response rates were 34.9% and 66.2% in patients with aggressive and indolent B-NHL, respectively, and complete response rates were 19.4% and 48.5%. Among patients with a complete response, the median duration of response was 22.8 months (95% CI, 7.6 to not estimable) and 20.4 (95% CI, 16 to not estimable) in patients with aggressive and indolent B-NHL, respectively. CONCLUSION: Mosunetuzumab, administered with step-up dosing, has a manageable safety profile and induces durable complete responses in R/R B-NHL. The expansion stage of the study is ongoing at the dose level of 1/2/60/60/30 mg selected for further study.

Phase I Basket Study of Taselisib, an Isoform-Selective PI3K Inhibitor, in Patients with PIK3CA-Mutant Cancers.

PURPOSE: Somatic mutations in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), which encodes the p110α catalytic subunit of PI3K, are found in multiple human cancers. While recurrent mutations in PIK3CA helical, regulatory, and kinase domains lead to constitutive PI3K pathway activation, other mutations remain uncharacterized. To further evaluate their clinical actionability, we designed a basket study for patients with PIK3CA-mutant cancers with the isoform-specific PI3K inhibitor taselisib. PATIENTS AND METHODS: Patients were enrolled on the basis of local PIK3CA mutation testing into one of 11 histology-specific cohorts and treated with taselisib at 6 or 4 mg daily until progression. Tumor DNA from baseline and progression (when available) was sequenced using a next-generation sequencing panel. Exploratory analyses correlating genomic alterations with treatment outcomes were performed. RESULTS: A total of 166 patients with PIK3CA-mutant cancers were enrolled. The confirmed response rate was 9%. Activity varied by tumor type and mutant allele, with confirmed responses observed in head and neck squamous (15.4%), cervical (10%), and other cancers, plus in tumors containing helical domain mutations. Genomic analyses identified mutations potentially associated with resistance to PI3K inhibition upfront (TP53 and PTEN) and postprogression through reactivation of the PI3K pathway (PTEN, STK11, and PIK3R1). Higher rates of dose modification occurred at higher doses of taselisib, indicating a narrow therapeutic index. CONCLUSIONS: Taselisib had limited activity in the tumor types tested and is no longer in development. This genome-driven study improves understanding of the activity, limitations, and resistance mechanisms of using PI3K inhibitors as monotherapy to target PIK3CA-mutant tumors.

High-efficiency CRISPR induction of t(9;11) chromosomal translocations and acute leukemias in human blood stem cells.

Chromosomal rearrangements involving the mixed lineage leukemia (MLL) gene, also known as KMT2A, are often observed in human leukemias and are generally associated with a poor prognosis. To model these leukemias, we applied clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing to induce MLL chromosomal rearrangements in human hematopoietic stem and progenitor cells purified from umbilical cord blood. Electroporation of ribonucleoprotein complexes containing chemically modified synthetic single guide RNAs and purified Cas9 protein induced translocations between chromosomes 9 and 11 [t(9;11)] at an efficiency >1%. Transplantation of gene-edited cells into immune-compromised mice rapidly induced acute leukemias of different lineages and often with multiclonal origins dictated by the duration of in vitro culture prior to transplantation. Breakpoint junction sequences served as biomarkers to monitor clonal selection and progression in culture and in vivo. High-dimensional cell surface and intracellular protein analysis by mass cytometry (CyTOF) revealed that gene-edited leukemias recapitulated disease-specific protein expression observed in human patients and showed that MLL-rearranged (MLLr) mixed phenotype acute leukemias (MPALs) were more similar to acute myeloid leukemias (AMLs) than to acute lymphoblastic leukemias (ALLs). Therefore, highly efficient generation of MLL chromosomal translocations in primary human blood stem cells using CRISPR/Cas9 reliably models human acute MLLr leukemia and provides an experimental platform for basic and translational studies of leukemia biology and therapeutics.

A phase Ib, open-label, dose-escalation study of the safety and pharmacology of taselisib (GDC-0032) in combination with either docetaxel or paclitaxel in patients with HER2-negative, locally advanced, or metastatic breast cancer.

PURPOSE: This open-label, phase Ib, dose-escalation, and dose-expansion study (NCT01862081) evaluated taselisib with a taxane in locally advanced or metastatic breast cancer (BC) and/or non-small cell lung cancer (NSCLC). METHODS: Patients received taselisib (2-6 mg tablet or 3-6 mg capsule) plus docetaxel or paclitaxel. Primary endpoints were safety, dose-limiting toxicities, maximum tolerated dose, and identification of a recommended phase II dose. Secondary endpoints included pharmacokinetics and antitumor activity assessment. RESULTS: Eighty patients (BC: 72; NSCLC: 7; BC/NSCLC: 1) were enrolled (docetaxel-receiving arms: 21; paclitaxel-receiving arms: 59). Grade ≥ 3 adverse events (AEs), serious AEs, and AEs leading to death were reported in 90.5%, 42.9%, and 14.3% of patients, respectively (docetaxel-receiving arms), and 78.9%, 40.4%, and 3.5% of patients, respectively (paclitaxel-receiving arms). Eight patients experienced dose-limiting toxicities. The maximum tolerated dose was exceeded with 3 mg taselisib (capsule) for 21 consecutive days plus 75 mg/m2 docetaxel and not exceeded with 6 mg taselisib (tablet) for 5 days on/2 days off plus 80 mg/m2 paclitaxel. Objective response rates and clinical benefit rates were 35.0% and 45.0%, respectively (docetaxel-receiving arms), and 20.4% and 27.8%, respectively (paclitaxel-receiving arms). Exposure for paclitaxel or docetaxel plus taselisib was consistent with the single agents. CONCLUSIONS: Taselisib in combination with a taxane has a challenging safety profile. Despite evidence of antitumor activity, the benefit-risk profile was deemed not advantageous. Further development is not planned.

CBP Modulates Sensitivity to Dasatinib in Pre-BCR+ Acute Lymphoblastic Leukemia.

Dasatinib is a multi-tyrosine kinase inhibitor approved for treatment of Ph+ acute lymphoblastic leukemia (ALL), but its efficacy is limited by resistance. Recent preclinical studies suggest that dasatinib may be a candidate therapy in additional ALL subtypes including pre-BCR+ ALL. Here we utilized shRNA library screening and global transcriptomic analysis to identify several novel genes and pathways that may enhance dasatinib efficacy or mitigate potential resistance in human pre-BCR+ ALL. Depletion of the transcriptional coactivator CBP increased dasatinib sensitivity by downregulating transcription of the pre-BCR signaling pathway previously associated with dasatinib sensitivity. Acquired resistance was due, in part, to upregulation of alternative pathways including WNT through a mechanism, suggesting transcriptional plasticity. Small molecules that disrupt CBP interactions with the CREB KID domain or ß-catenin showed promising preclinical efficacy in combination with dasatinib. These findings highlight novel modulators of sensitivity to targeted therapies in human pre-BCR+ ALL, which can be reversed by small-molecule inhibitors. They also identify promising therapeutic approaches to ameliorate dasatinib sensitivity and prevent resistance in ALL.Significance: These findings reveal mechanisms that modulate sensitivity to dasatinib and suggest therapeutic strategies to improve the outcome of patients with acute lymphoblastic leukemia.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/22/6497/F1.large.jpg Cancer Res; 78(22); 6497-508. ©2018 AACR.

Phase II Study of Taselisib (GDC-0032) in Combination with Fulvestrant in Patients with HER2-Negative, Hormone Receptor-Positive Advanced Breast Cancer.

Purpose: This single-arm, open-label phase II study evaluated the safety and efficacy of taselisib (GDC-0032) plus fulvestrant in postmenopausal women with locally advanced or metastatic HER2-negative, hormone receptor (HR)-positive breast cancer.Patients and Methods: Patients received 6-mg oral taselisib capsules daily plus intramuscular fulvestrant (500 mg) until disease progression or unacceptable toxicity. Tumor tissue (if available) was centrally evaluated for PIK3CA mutations. Adverse events (AE) were recorded using NCI-CTCAE v4.0. Tumor response was investigator-determined using RECIST v1.1.Results: Median treatment duration was 4.6 (range: 0.9-40.5) months. All patients experienced ≥1 AE, 30 (50.0%) had grade ≥3 AEs, and 19 (31.7%) experienced 35 serious AEs. Forty-seven of 60 patients had evaluable tissue for central PIK3CA mutation testing [20 had mutations, 27 had no mutation detected (MND)]. In patients with baseline measurable disease, clinical activity was observed in tumors with PIK3CA mutations [best confirmed response rate: 38.5% (5/13; 95% CI, 13.9-68.4); clinical benefit rate (CBR): 38.5% (5/13; 95% CI, 13.9-68.4)], PIK3CA-MND [best confirmed response rate: 14.3% (3/21; 95% CI, 3.0-36.3); CBR: 23.8% (5/21; 95% CI, 8.2-47.2)], and unknown PIK3CA mutation status [best confirmed response rate: 20.0% (2/10; 95% CI, 2.5-55.6); CBR: 30.0% (3/10; 95% CI, 6.7-65.2)].Conclusions: Taselisib plus fulvestrant had clinical activity irrespective of PIK3CA mutation status, with numerically higher objective response rate and CBR in patients with PIK3CA-mutated (vs. -MND) locally advanced or metastatic HER2-negative, HR-positive breast cancer. No new safety signals were reported. A confirmatory phase III trial is ongoing. Clin Cancer Res; 24(18); 4380-7. ©2018 AACR.

SETDB2 Links E2A-PBX1 to Cell-Cycle Dysregulation in Acute Leukemia through CDKN2C Repression.

Acute lymphoblastic leukemia (ALL) is associated with significant morbidity and mortality, necessitating further improvements in diagnosis and therapy. Targeted therapies directed against chromatin regulators are emerging as promising approaches in preclinical studies and early clinical trials. Here, we demonstrate an oncogenic role for the protein lysine methyltransferase SETDB2 in leukemia pathogenesis. It is overexpressed in pre-BCR+ ALL and required for their maintenance in vitro and in vivo. SETDB2 expression is maintained as a direct target gene of the chimeric transcription factor E2A-PBX1 in a subset of ALL and suppresses expression of the cell-cycle inhibitor CDKN2C through histone H3K9 tri-methylation, thus establishing an oncogenic pathway subordinate to E2A-PBX1 that silences a major tumor suppressor in ALL. In contrast, SETDB2 was relatively dispensable for normal hematopoietic stem and progenitor cell proliferation. SETDB2 knockdown enhances sensitivity to kinase and chromatin inhibitors, providing a mechanistic rationale for targeting SETDB2 therapeutically in ALL.

CD47 is not Over-Expressed in Fibrolamellar Hepatocellular Carcinoma.

OBJECTIVES: CD47 is a transmembrane receptor that inhibits phagocytosis. Over-expression of CD47 is associated with an increased risk of tumor growth and metastasis. Clinical trials based on anti-CD47 therapy in adults are underway in a variety of malignancies. CD47 has been shown to be over-expressed in conventional hepatocellular carcinoma (HCC), a common liver tumor in adults. To our knowledge, there have been no studies to evaluate CD47 expression in the fibrolamellar subtype of HCC (FL-HCC), common in children and young adults. This study will evaluate CD47 expression in FL-HCC and shed light on its suitability for anti-CD47 therapy. METHODS: Using immunohistochemistry, 10 samples of FL-HCC from 8 patients were evaluated for CD47 (anti-phagocytic) and calreticulin (pro-phagocytic) expression. By direct comparison, CD47 and calreticulin expression were evaluated in 21 samples of conventional HCC. Additionally, transcriptome sequencing to detect CD47 mRNA expression was performed on fresh tissue from 1 FL-HCC institutional patient and previously published sequencing data from 20 additional samples was reviewed. RESULTS: Immunohistochemistry showed only weak CD47 expression in 20% of FL-HCC samples. In contrast, 57% of conventional HCC samples showed CD47 expression. All (100%) FL-HCC samples showed moderate or strong calreticulin expression. The difference between CD47 and calreticulin expression in FL-HCC is statistically significant (p=0.0007). Transcriptome sequencing revealed no difference in CD47 expression between FL-HCC and normal liver samples. CONCLUSIONS: CD47 is not over-expressed in FL-HCC. Our studies provide no support for expanding ongoing clinical trials in adults to include children and young adults with FL-HCC.

E2A-PBX1 Remodels Oncogenic Signaling Networks in B-cell Precursor Acute Lymphoid Leukemia.

There is limited understanding of how signaling pathways are altered by oncogenic fusion transcription factors that drive leukemogenesis. To address this, we interrogated activated signaling pathways in a comparative analysis of mouse and human leukemias expressing the fusion protein E2A-PBX1, which is present in 5%-7% of pediatric and 50% of pre-B-cell receptor (preBCR+) acute lymphocytic leukemia (ALL). In this study, we describe remodeling of signaling networks by E2A-PBX1 in pre-B-ALL, which results in hyperactivation of the key oncogenic effector enzyme PLCγ2. Depletion of PLCγ2 reduced proliferation of mouse and human ALLs, including E2A-PBX1 leukemias, and increased disease-free survival after secondary transplantation. Mechanistically, E2A-PBX1 bound promoter regulatory regions and activated the transcription of its key target genes ZAP70, SYK, and LCK, which encode kinases upstream of PLCγ2. Depletion of the respective upstream kinases decreased cell proliferation and phosphorylated levels of PLCγ2 (pPLCγ2). Pairwise silencing of ZAP70, SYK, or LCK showed additive effects on cell growth inhibition, providing a rationale for combination therapy with inhibitors of these kinases. Accordingly, inhibitors such as the SRC family kinase (SFK) inhibitor dasatinib reduced pPLCγ2 and inhibited proliferation of human and mouse preBCR+/E2A-PBX1+ leukemias in vitro and in vivo Furthermore, combining small-molecule inhibition of SYK, LCK, and SFK showed synergistic interactions and preclinical efficacy in the same setting. Our results show how the oncogenic fusion protein E2A-PBX1 perturbs signaling pathways upstream of PLCγ2 and renders leukemias amenable to targeted therapeutic inhibition. Cancer Res; 76(23); 6937-49. ©2016 AACR.