ALBERT

Description: Background CD33is expressed in approximately 90% of AML, representing a promising target despite age, prior therapies, or mutational heterogeneity. SGN-CD33A (or 33A) is a CD33-directed antibody conjugated to 2 molecules of a pyrrolobenzodiazepine (PBD) dimer. Upon binding, 33A is internalized and transported to the lysosomes where PBD dimer is released via proteolytic cleavage of the linker, crosslinking DNA, and leading to cell death. Methods The dose-escalation portion of this phase 1 study (NCT01902329) is designed to evaluate the safety, tolerability, pharmacokinetics (PK), and antileukemic activity of 33A as monotherapy. Eligible patients (ECOG 0-1) must have CD33-positive AML, and have either relapsed disease following initial remission (CR) of 〉3 months, or have declined conventional induction/consolidation. 33A monotherapy is administered outpatient via IV every 3 weeks for up to 2 cycles, followed by optional low-dose maintenance treatment for patients who achieve a CR/CRi. Investigator assessment of response is per IWG criteria; CRi requires either platelet count of ≥100,000/µL or neutrophils of ≥1,000/µL (Cheson 2003). Results To date, 87 patients (62% male) with a median age of 74 years (range, 27-89) have been treated. 34 patients had relapsed AML after 1st CR with intensive therapy; 52 had declined conventional intensive therapy (40 of these patients had received 1-2 prior low intensity therapies, primarily hypomethylating agents). Most patients had intermediate I-II (51%) or adverse (31%) risk by ELN classification and 54% of patients had AML with underlying myelodysplasia-related changes. 9% of patients displayed NPM1 mutations without FLT3 mutation (NPM1+/FLT3-). Dose levels ranged from 5-60 mcg/kg (n=75) and also included fractionated dosing of 20 mcg/kg on Day 1 and Day 4 (n=12). Five patients remain on treatment. Six dose-limiting toxicities were reported in the monotherapy escalation cohorts: 2 Grade 4 bone marrow failures (40 and 60 mcg/kg), 2 mucositis (Grade 3 at 50 mcg/kg; Grade 3 at fractionated 20+20 mcg/kg), Grade 3 pulmonary embolism (20 mcg/kg), and Grade 5 sepsis (50 mcg/kg). The most common Grade 3 or higher adverse events (AE) reported were febrile neutropenia (69%), thrombocytopenia (29%), and anemia (23%). Increased myelosuppression was observed at doses higher than 40 mcg/kg and the fractionated dosing cohort, including febrile neutropenia observed in 68% of patients and sepsis observed in 26% of patients. Other common treatment-emergent AEs regardless of relationship to study treatment were fatigue (48%), decreased appetite (28%), constipation, diarrhea, dyspnea, nausea (26% each), and peripheral edema (25%). The 30-day mortality was 6%. Across all dose levels, the CR+CRi rate was 86% in the patients with NPM1+/FLT3- disease (n=7). Of the 21 efficacy evaluable patients treated at 40 mcg/kg, 3 patients achieved a best clinical response of CR, 4 achieved CRi, and 5 had morphologic leukemia-free state (mLFS). Three of 5 treatment-naïve patients within the 40 mcg/kg dose level achieved a CR or CRi. In patients across dose levels who achieved at least mLFS, the mean time to full count recovery was 5 weeks for neutrophils (≥1,000/µL) and 6 weeks for platelets (≥100,000/µL). Median OS in patients treated at 40 mcg/kg is 10 months with 17 patients alive at the time of this data cut. Across all dose levels, 8 patients went on to receive an allogeneic SCT. PK data demonstrated generally dose-dependent increase in plasma ADC exposures and target-mediated rapid clearance. Conclusions Dose escalation is complete and a recommended monotherapy 33A dose of 40 mcg/kg was identified. AEs observed were generally manageable, often associated with underlying myelosuppression. 33A has demonstrated favorable antileukemic activity with 33% achieving a CR+CRi at the 40 mcg/kg dose level (60% CR+CRi in treatment naïve patients). The rapid clearance of marrow blasts in patients with poor risk factors and low 30-day mortality (6%) are encouraging. Enrollment is ongoing in multiple expansion cohorts, including previously untreated AML patients who declined intensive therapy, relapsed NPM1 mutant disease, and relapsed APL. In addition, a study evaluating 33A with intensive therapy in newly diagnosed patients with AML is ongoing. Disclosures Stein: Amgen: Speakers Bureau. Off Label Use: SGN-CD33A is an investigational agent being studied in patients with CD33-positive AML. SGN-CD33A is not approved for use. Walter:Pfizer, Inc.: Consultancy; Covagen AG: Consultancy; AstraZeneca, Inc.: Consultancy; CSL Behring: Research Funding; AbbVie, Inc.: Research Funding; Amgen: Research Funding; Amphivena Therapeutics, Inc.: Consultancy, Research Funding; Seattle Genetics, Inc.: Consultancy, Research Funding. Erba:GlycoMimetics; Janssen: Other: Data Safety & Monitoring Committees; Sunesis; Pfizer; Daiichi Sankyo; Ariad: Consultancy; Millennium/Takeda; Celator; Astellas: Research Funding; Seattle Genetics; Amgen: Consultancy, Research Funding; Novartis; Incyte; Celgene: Consultancy, Patents & Royalties. Fathi:Agios Pharmaceuticals: Other: Advisory Board participation; Seattle Genetics: Other: Advisory Board participation, Research Funding; Merck: Other: Advisory Board participation. Lancet:Seattle Genetics: Consultancy; Pfizer: Research Funding; Boehringer-Ingelheim: Consultancy; Kalo-Bios: Consultancy; Amgen: Consultancy; Celgene: Consultancy, Research Funding. Kovacsovics:Seattle Genetics, Inc.: Research Funding. DeAngelo:Pfizer: Consultancy; Amgen: Consultancy; Ariad: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Consultancy; Incyte: Consultancy; Agios: Consultancy; Celgene: Consultancy. Bixby:Seattle Genetics, Inc.: Research Funding. Faderl:Onyx: Speakers Bureau; BMS: Research Funding; Seattle Genetics, Inc.: Research Funding; JW Pharma: Consultancy; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy, Research Funding, Speakers Bureau; Pfizer: Research Funding; Astellas: Research Funding; Celator: Research Funding; Ambit: Research Funding. Jillella:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Stein:Seattle Genetics, Inc.: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees.

Description: Background CD33 is expressed on the surface of myeloblasts in 85 to 90% of patients with AML and represents a promising target regardless of age, risk factors, or underlying mutational heterogeneity. SGN-CD33A is an anti-CD33 engineered cysteine antibody conjugated to an average of 2 molecules of a pyrrolobenzodiazepine (PBD) dimer, a highly potent DNA crosslinking agent. Upon binding to the cell surface, SGN-CD33A is internalized and transported to the lysosomes where PBD dimer is released within the cell through proteolytic cleavage of the linker, crosslinking DNA and leading to cell death. Methods This phase 1, open-label, 3+3 dose-escalation study (NCT01902329) is designed to evaluate the safety, tolerability, pharmacokinetics (PK), and anti-leukemic activity of SGN-CD33A. Eligible patients (ECOG 0-1) must have CD33-positive AML, and have either relapsed disease following initial remission (CR) of 〉 3 months, or have declined conventional induction/consolidation. SGN-CD33A is administered outpatient IV every 3 weeks for up to 4 cycles (Part A), followed by optional maintenance treatment for patients achieving a CR/CRi (Part B). Investigator assessment of response is per IWG criteria (Cheson 2003). Results To date, 40 patients (48% female) with a median age of 75 years (range, 27-86) have been treated. Twenty patients had relapsed AML after 1st CR with intensive therapy (3 of these had intensive frontline therapy plus 1 additional line of low intensity therapy); 20 had declined conventional intensive therapy (13 of these patients had received 1-2 prior low intensity therapies, primarily hypomethylating agents). Of the patients enrolled, 45% had underlying myelodysplasia and most had disease with intermediate (70%) or adverse (18%) cytogenetic risk, 8% with mutated NPM1 (without FLT3 mutation) and 13% with mutated FLT3. Dose levels tested were 5 mcg/kg (n=3), 10 mcg/kg (n=3), 20 mcg/kg (n=13), 40 mcg/kg (n=18), and 60 mcg/kg (n=3). To date, a maximum of 4 cycles was received in Part A and 10 cycles in Part B (total median of 2 cycles on treatment; range, 1-13 cycles). Thirteen patients remain on treatment and enrollment is ongoing. Two dose-limiting toxicities have been reported, a Grade 3 pulmonary embolism (20 mcg/kg) and a Grade 4 hypocellular marrow (〉28 days; 40 mcg/kg). The only Grade 3 or higher adverse event (AE) reported in 〉10% of patients was febrile neutropenia (55%). Other treatment-emergent AEs regardless of relationship to study treatment reported in ˃10% of patients were fatigue (48%), diarrhea (20%), constipation (18%), cough (18%), dyspnea (18%), epistaxis (18%), peripheral edema (18%), malaise (15%), hypokalemia (13%), and pleural effusion (13%). The 30-day mortality was 2.5%, with no treatment-related deaths occurring during that time; 1 elderly patient died from a traumatic fall unrelated to SGN-CD33A. Blast clearance in marrow was obtained in 16 of 38 efficacy evaluable patients (42%) across all dose levels. A dose-response relationship is evolving with rapid and marked decreases in bone marrow blasts at 40 and 60 mcg/kg in 19 of 21 patients (Figure 1). Of 17 efficacy evaluable patients treated at 40 mcg/kg, 8 experienced clearance of marrow blasts; these patients achieved a best clinical response of CR (2), CRi (3), and morphologic leukemia-free state (mLFS; 3) thus far. In addition, complete remissions were observed at 5 mcg/kg (1 CR), 10 mcg/kg (1 CRi), and 20 mcg/kg (2 CRis). Preliminary PK data demonstrated rapid clearance of ADC, suggesting target-mediated disposition. Plasma ADC exposure generally increased with increasing dose levels. Conclusions A MTD for SGN-CD33A is not yet identified and enrollment continues. AEs observed were generally manageable, often associated with underlying myelosuppression. To date, SGN-CD33A has demonstrated antileukemic activity with 47% achieving blast clearance at the 40 mcg/kg dose level. The observed low 30-day mortality (2.5%) and rapid clearance of marrow blasts in patients with poor risk factors (median age 75, predominantly intermediate and adverse cytogenetic risk, and 45% underlying myelodysplasia) with outpatient administration are encouraging. Enrollment is ongoing to further define optimal dose and schedule. In addition, combinations of SGN-CD33A with standard AML and MDS agents will be evaluated. Figure 1: Bone Marrow Blasts Over Time Figure 1:. Bone Marrow Blasts Over Time Disclosures Stein: Seattle Genetics, Inc.: Research Funding; Janssen Pharmaceuticals: Consultancy. Off Label Use: SGN-CD33A is an investigational agent being studied in patients with AML. SGN-CD33A is not approved for use. Stein:Seattle Genetics, Inc.: Research Funding. Walter:Seattle Genetics, Inc.: Consultancy, Research Funding; Amphivena Therapeutics, Inc.: Consultancy; Amgen: Research Funding; Amphivena Therapeutics, Inc.: Consultancy; Amgen: Research Funding. Fathi:Exelixis: Research Funding; Takeda Pharmaceuticals International Co.: Research Funding; Ariad: Consultancy; Seattle Genetics, Inc.: Consultancy, Research Funding. Lancet:Seattle Genetics, Inc.: Consultancy, Research Funding. Kovacsovics:Seattle Genetics, Inc.: Research Funding. Advani:Seattle Genetics, Inc.: Research Funding. DeAngelo:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc.: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Kennedy:Seattle Genetics, Inc.: Employment, Equity Ownership. Erba:Incyte: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Seattle Genetics, Inc.: Consultancy, Research Funding.

Description: Key Points Vadastuximab talirine, a novel antibody-drug conjugate, consists of an anti-CD33 monoclonal antibody conjugated to pyrrolobenzodiazepine dimers. In a phase 1 trial, vadastuximab talirine demonstrated single-agent activity and minimal nonhematologic toxicity in patients with AML.

Description: Background CD19, a B-cell specific marker, is expressed in the majority of patients with B-cell non-Hodgkin lymphoma (NHL). SGN-CD19A is a novel antibody-drug conjugate (ADC) composed of a humanized anti-CD19 monoclonal antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a maleimidocaproyl linker. Methods This ongoing phase 1, open-label, dose-escalation study investigates the safety, tolerability, pharmacokinetics, and antitumor activity of SGN-CD19A in patients with relapsed or refractory B-cell NHL (NCT 01786135). Eligible patients are ≥12 years of age and must have a confirmed diagnosis of diffuse large B-cell lymphoma (DLBCL), including transformed follicular histology; mantle cell lymphoma (MCL); follicular lymphoma grade 3 (FL3); Burkitt lymphoma; or B-cell lymphoblastic lymphoma. Patients must be relapsed or refractory to at least 1 prior systemic regimen. Patients with DLBCL or FL3 must have also received intensive salvage therapy with or without autologous stem cell transplant (SCT), unless they refused or were deemed ineligible. A modified continual reassessment method is used for dose allocation and maximum tolerated dose (MTD) estimation. SGN-CD19A is administered IV on Day 1 of 21-day cycles (0.5–6 mg/kg). Response is assessed with CT and PET scans according to the Revised Response Criteria for Malignant Lymphoma (Cheson 2007). Results To date, 44 patients have been treated: 39 patients (89%) with DLBCL (including 10 with transformed DLBCL), 4 (9%) with MCL, and 1 (2%) with FL3. Median age was 65 years (range, 33–81). Patients had a median of 2 prior systemic therapies (range, 1–7), and 10 patients (23%) had autologous SCT. Twenty-six patients (59%) were refractory to their most recent prior therapy, and 18 (41%) were relapsed. Patients received a median of 3 cycles of treatment (range, 1–12) at doses from 0.5–6 mg/kg. Eleven patients (25%) remain on treatment, and 33 have discontinued treatment (18 due to progressive disease [PD], 5 for investigator decision, 5 for adverse events [AE], 4 because of patient decision/non-AE, and 1 for SCT). No dose-limiting toxicity (DLT) in Cycle 1 has been reported. Treatment-emergent AEs reported in ≥20% of patients were blurred vision (59%), dry eye (39%), fatigue (39%), constipation (32%), keratopathy (23%), and pyrexia (20%). Corneal exam findings consistent with superficial microcystic keratopathy were observed in 25 patients (57%) and were mostly Grade 1/2. Grade 3/4 corneal AEs were observed in 4 patients at the higher doses; the majority resolved or improved to Grade 1/2 at last follow-up. Corneal AEs were treated with ophthalmic steroids, and during the trial steroid eye drop prophylaxis was instituted with each dose of study drug. SGN-CD19A ADC plasma exposures were approximately dose-proportional. Accumulation was observed following multiple dose administrations, consistent with a mean terminal half-life of about 2 weeks, suggesting less frequent dosing might be possible. In the 43 efficacy-evaluable patients, the objective response rate (ORR) is 30% (95% CI [17, 46]), including 7 complete responses (CRs; 16%) and 6 partial responses (PRs; 14%). Of the 13 patients with an objective response, 8 are still on study with follow-up times of 0.1–31 weeks; 2 are no longer on study; and 3 had subsequent PD or death with response durations of 14, 19, and 31 weeks. Table Best Clinical Response by Disease Status Relative to Most Recent Therapy, n (%) Relapsed N=17 Refractory N=26 Total N=43 CR 5 (29) 2 (8) 7 (16) PR 4 (24) 2 (8) 6(14) SD 4 (24) 9 (35) 13 (30) PD 4 (24) 13 (50) 17 (40) ORR (CR + PR), (95% CI) 53 (28, 77) 15 (4, 35) 30 (17, 46) Conclusions To date, SGN-CD19A has shown evidence of clinical activity with an ORR of 30% and CR rate of 16%. Enrollment in the trial is ongoing to further refine optimal dose and schedule. SGN-CD19A is generally well-tolerated. No DLTs have been observed in tested dose levels. Observed ocular AEs are manageable with steroid eye drops and dose modifications. The high response rate (53%) in relapsed patients and low rate of bone marrow suppression or neuropathy suggest that SGN-CD19A could be incorporated into novel combination regimens in earlier lines of therapy. Disclosures Moskowitz: Merck: Research Funding; Genentech: Research Funding; Seattle Genetics, Inc.: Consultancy, Research Funding. Off Label Use: SGN-CD19A is an investigational agent being studied in patients with B-cell malignancies. SGN-CD19A is not approved for use. . Forero-Torres:Seattle Genetics, Inc.: Research Funding, Speakers Bureau. Shah:Pharmacyclics: Speakers Bureau; SWOG: Consultancy; Celgene: Consultancy, Speakers Bureau; NCCN: Consultancy; Seattle Genetics, Inc.: Research Funding; Janssen: Speakers Bureau. Advani:Janssen Pharmaceuticals: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Celgene: Research Funding; Takeda International Pharmaceuticals Co.: Research Funding; Seattle Genetics, Inc.: Research Funding, Travel expenses Other. Hamlin:Seattle Genetics, Inc.: Consultancy, Research Funding. Kim:Bayer: Consultancy; Eli Lily: Consultancy; Seattle Genetics, Inc.: Consultancy, Research Funding. Kostic:Seattle Genetics, Inc.: Employment, Equity Ownership. Sandalic:Seattle Genetics, Inc.: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Fanale:Seattle Genetics, Inc.: Consultancy, Honoraria, Research Funding, Travel expenses Other.

Description: Background CD19, a B cell-specific marker, is expressed in the majority of patients with B-lineage leukemia and non-Hodgkin lymphoma. SGN-CD19A is a novel antibody-drug conjugate (ADC) composed of a humanized anti-CD19 monoclonal antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a maleimidocaproyl linker. Methods This first-in-human, phase 1, open-label, dose-escalation study is investigating the safety, tolerability, pharmacokinetics, and antitumor activity of SGN-CD19A in adult and pediatric patients with relapsed or refractory B-cell leukemia or highly aggressive lymphoma (NCT 01786096). Eligible patients must have B-cell acute lymphoblastic leukemia (B-ALL) or lymphoma (B-LBL), Burkitt leukemia or lymphoma, and be relapsed or refractory to at least 1 prior systemic regimen. A modified continual reassessment method is used for dose allocation and maximum tolerated dose (MTD) estimation for both pediatric and adult patients. The study is evaluating 2 schedules of IV SGN-CD19A administration: weekly (Days 1 and 8 of 21-day cycles; 0.3-4.5 mg/kg) or every 3weeks (q3week; 0.5-6 mg/kg). Results To date, 49 patients with relapsed or refractory leukemia (n=40) or lymphoma (n=9) have been treated. Median age of adult (n=38) and pediatric patients (n=11) was 37 and 11 years (range, 18-74 and 1-16), respectively. Patients received a median of 2 prior therapies (range 1-9); 14 patients (29%) previously received an allogeneic stem cell transplant. On the weekly schedule, 39 patients (28 adult, 11 pediatric) have been treated, and the median number of cycles is 2.5 (adults; range, 1-12) or 1 (pediatric; range, 1-4). On the q3week schedule, 10 adult patients have been treated, and the median number of cycles is 2.5 (range, 1-4) to date. Six patients remain on study treatment (3 on each schedule), and enrollment is ongoing. The toxicity profiles were similar across both dosing schedules (0.3-2.3 mg/kg weekly and 4-5 mg/kg q3week) and across adult and pediatric patients. The most frequently reported drug-related AEs included pyrexia, nausea, chills, vomiting, blurred vision, and dry eye. Frequent infusion-related reactions were observed early in the study, and recommendation for premedication was instituted. Ocular events were also observed and treated with ophthalmic steroids; steroid eye drop prophylaxis was instituted with each dose. Corneal findings consistent with superficial microcystic keratopathy were observed in 13 adult patients (34%) and in 1 pediatric patient (9%). Grade 3/4 corneal AEs have been observed in 4 adult patients; the majority of these events have resolved or improved to Grade 1 or 2. Steroid eye drop prophylaxis has reduced the incidence of Grade 3/4 events at this interim analysis. Three DLTs were observed: acidosis in a pediatric patient at 1 mg/kg weekly, cytokine release syndrome in an adult patient at 2 mg/kg weekly, and asymptomatic Grade 4 AST elevation in an adult patient at 5 mg/kg q3week. MTD has not yet been determined. SGN-CD19A ADC pharmacokinetic profiles indicate target-mediated drug disposition in patients with leukemia. Plasma ADC exposures generally increased with doses and were lower than those in patients with lymphoma. To date, no objective responses were observed in 9 efficacy-evaluable pediatric patients or in 3 adult patients with Burkitt lymphoma/leukemia. However, in efficacy-evaluable adult patients with B-ALL/B-LBL, objective responses were observed in 6 of 25 patients treated on the weekly schedule (3 CR, 2 CRp, 1 PR), and in 4 of 8 patients treated on the q3week schedule (2 CR, 2 CRp). Of 8 B-ALL patients with CR/CRp, 6 were MRD negative. Conclusions MTDs have not yet been identified, and dose escalation continues on weekly and q3week schedules. SGN-CD19A has been generally well tolerated. At this interim analysis, objective responses were observed in 30% (10 of 33) of heavily pretreated adult B-ALL/B-LBL patients dosed weekly or q3week. Evidence of activity in relapsed/refractory patients and lack of overlapping toxicities suggest opportunities for combination with conventional anti-leukemic therapies in lymphoblastic malignancies. Disclosures Fathi: Ariad: Consultancy; Exelixis: Research Funding; Takeda pharmaceuticals International Co.: Research Funding; Seattle Genetics, Inc.: Consultancy, Research Funding. Off Label Use: SGN-CD19A is an investigational agent being studied in patients with B-cell malignancies. SGN-CD19A is not approved for use. . Chen:Seattle Genetics, Inc.: Consultancy, Research Funding, Speakers Bureau, Travel expenses Other. Trippett:OSI Pharmaceuticals: Research Funding; Seattle Genetics, Inc.: Research Funding. O'Brien:Seattle Genetics, Inc.: Research Funding. DeAngelo:Seattle Genetics, Inc.: Research Funding. Shah:Pharmacyclics: Consultancy; SWOG: Consultancy; Celgene: Consultancy, Speakers Bureau; NCCN: Consultancy; Seattle Genetics, Inc.: Research Funding; Janssen: Consultancy. Cooper:Seattle Genetics, Inc.: Research Funding. Foran:Seattle Genetics, Inc.: Research Funding. Hale:Seattle Genetics, Inc.: Research Funding. Pressey:Seattle Genetics, Inc.: Research Funding. Silverman:Seattle Genetics, Inc.: Research Funding. Tibes:Seattle Genetics, Inc.: Research Funding. Kim:Bayer: Consultancy; Eli Lily: Consultancy; Seattle Genetics, Inc.: Consultancy, Research Funding. Albertson:Seattle Genetics, Inc.: Employment, Equity Ownership. Sandalic:Seattle Genetics, Inc.: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Borate:Genoptix: Consultancy; Seattle Genetics, Inc.: Research Funding.