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e14526 Background: Uveal melanoma (UM) is the most common primary intraocular malignancy in adults. Cell free DNA (cfDNA) is a non-invasive mechanism for monitoring malignancy in UM patients. BET proteins activate transcription of oncogenic genes, and mivebresib (ABBV-075) is a potent pan-BET inhibitor. In the first-in-human phase 1 study, safety and pharmacokinetics of mivebresib were assessed in patients with advanced cancer (NCT02391480). We compared cfDNA mutational dynamics with the survival of UM patients treated with mivebresib. Methods: Adult patients with metastatic solid tumors and ≥1 line of prior treatment were treated with mivebresib on a schedule of daily; 3 days/week; or 4 days on, 3 days off. Two mL of plasma cfDNA (≥10ng) in 5 patients (3 progressive disease [PD], 2 stable disease [SD]) were sequenced with a targeted 63-gene panel (68 Kb) to ≥800X unique depth after barcode-based error-suppression and genomic alterations discovered in all patients. Results: As of May 2018, 10 UM patients received ≥1 dose of mivebresib with median 8.1 weeks (range, 3.6–39.6) of treatment. The median age was 55 years (range, 37–73). 9 patients experienced a treatment-emergent adverse event (TEAE), most commonly (≥40% patient incidence), dysgeusia (60%), thrombocytopenia and nausea (40%, each). 9 patients were evaluable, 4 achieved a best response of SD and 5 PD (RECIST v1.1). The mean pretreatment cfDNA concentration was 21.0 ng/mL (N = 5 with plasma available). cfDNA levels increased in two patients by 0.6% (SD) and 64.4% (PD). In PD patients, elevated cfDNA concentration (32.7 ng/mL [PD] vs 3.5 ng/mL [SD]) was associated with shorter progression-free survival and overall survival. At baseline, the cfDNA mutational load (median mutant molecules/mL plasma) of pathogenic (COSMIC) mutations with AF ≥1% was highest in PD (893.9; range, 78-4951.5) vs SD patients (53.1; range, 9.3-606.2) and negatively correlated with the patient’s survival (R2= 0.531). In 1 PD patient, multiple TP53 (C23G, V203M) and CDKN2A (A148T, L63P) mutations were acquired by the time of progression. Conclusions: These data suggest cfDNA as a potential marker for survival of UM patients. Further investigation of BET inhibition in this population is warranted. Clinical trial information: NCT02391480.

7030 Background: Bromodomain and extra-terminal (BET) proteins bind to acetyllysines and upregulate oncogenic target genes. Mivebresib (ABBV-075) is a pan-BET inhibitor with antitumor activity in vitro and xenograft models of AML. This 2-part phase 1 study evaluates the safety and pharmacokinetics of mivebresib at monotherapy or combination dosing schedules in patients with solid tumors (part 1) and acute myeloid leukemia (AML; part 2) (NCT02391480). Here, we report preliminary data from part 2 in patients with relapsed/refractory (RR) AML. Methods: Mivebresib monotherapy (MIV-mono), or combined with venetoclax (MIV-VEN), were administered daily to adult patients with AML. The dose-limiting toxicity (DLT) period was 28 d. Results: As of Dec 2018, 41 patients (median age: 69 y [range, 29–84]; 19 patients had > 2 prior therapies) were enrolled: 19 in MIV-mono (5 of whom switched to MIV-combo) and 22 who began treatment in MIV-VEN cohorts. 23 patients had high cytogenetic risk. Median time on treatment was 28 d (range, 8–562). There were no DLTs. All patients experienced a treatment-emergent adverse event (AE), most commonly (≥40% patient incidence), fatigue (56%), dysgeusia (46%), decreased appetite (44%), diarrhoea (42%), nausea (42%), vomiting (42%). 40 patients had grade ≥3 AEs (febrile neutropenia (37%), anemia (34%) and thrombocytopenia (32%). 33 patients had serious AEs, most commonly febrile neutropenia (19%). 25 deaths were reported; 15 patients died of causes unrelated to mivebresib and 10 patients due to AML progression. The median best % bone marrow blast change for 26 evaluable patients was -20% (range, -98% to +300%). Gene expression analysis in pre- and post-treatment peripheral blood samples showed that HEXIM1, DCXR and CD93 genes were reliable PD biomarkers of ABBV-075 which were consistently modulated in a dose-dependent manner. At the cutoff date, median overall survival for all patients was 2.6 m. Conclusions: Mivebresib was well tolerated and showed antileukemic effects in patients with RR AML. Clinical trial information: NCT02391480.

8510 Background: CRT is standard treatment (Tx) for pts with unresectable stage III NSCLC. Vel, a potent oral PARP1/2 inhibitor, interferes with repair of chemotherapy- or radiation-induced DNA damage. In a phase 2 study, Vel showed favorable efficacy vs placebo when added to C/P in stage IV NSCLC. The reported phase 1 trial assessed the safety and efficacy of Vel + C/P-based CRT in Tx of stage III NSCLC (NCT02412371). Methods: Eligible pts (≥18 yr, unresectable stage III NSCLC, no prior NSCLC therapy) received Vel + CRT of weekly C area under the curve (AUC) 2 + P 45 mg/m2 weekly + 60 Gy (2 Gy/day) RT over 6–9 weeks (wk). Vel was dose escalated from 60 mg twice daily (BID) to 240 mg BID followed by Vel 120 mg BID added to consolidation therapy (CON) once every 3 wk of C AUC 6 + P 200 mg/m2 for 2 cycles (cohort 1–5). Cohort 6 received Vel 240 mg BID + CRT followed by Vel 240 mg BID + CON. Samples for pharmacokinetic (PK) analysis were collected on wk 4 day –3. The primary endpoint was to establish the recommended phase 2 dose (RP2D) of Vel + CRT/Vel + CON. Results: As of Sep 2018, 48 pts enrolled into cohorts 1–6 at Vel 60 mg/120 mg (n = 7), 80 mg/120 mg (n = 9), 120 mg/120 mg (n = 7), 200 mg/120 mg (n = 8), 240 mg/120 mg (n = 12), and 240 mg/240 mg (n = 5) added to CRT/CON; median age 65 yr (range, 48–81). Vel PK was dose proportional; 39 (81.3%) pts completed therapy. Grade ≥3 Tx-emergent adverse events (AEs) were reported in 37 (77.1%) pts; anemia and febrile neutropenia (10.4% each) were the most common. Serious AEs were observed in 19 (39.6%) pts. Dose-limiting toxicities occurred at 200 mg/120 mg (n = 1; influenza and pneumonia), 240 mg/120 mg (n = 1; insomnia), and 240 mg/240 mg (n = 2; febrile neutropenia, neutropenia, thrombocytopenia, esophagitis, suprapubic pain, sepsis); Vel 240 mg BID + CRT/Vel 120 mg + CON was chosen as the maximum tolerated dose/RP2D. Of 41 pts evaluable for tumor assessment, 26 (63.4%) had a confirmed response. Interim median progression-free survival was 24.1 mo (range, 8.9 – not reached); updated results will be reported. Conclusions: Vel 240 + CRT/Vel 120 mg BID + CON was well tolerated with promising antitumor activity in stage III NSCLC and was determined as RP2D. Clinical trial information: NCT02412371.

2570Background: ABBV-075 is an oral small molecule inhibitor of the BET family of bromodomain-containing proteins that function as regulators controlling many transcriptional programs required for ...

2510Background: BDs are protein domains that bind to acetylated histone tails, leading to upregulation of target genes driving oncogenesis. Inhibition of the BET family prevents assembly of the macromolecular complex and its transcriptional response. ABBV-075 is a pan-BET inhibitor that induces death in cell lines and tumor growth inhibition in xenograft models. This first-in-human, phase 1, two-part study (NCT02391480) assessed the safety and pharmacokinetics of ABBV-075 in pts with advanced tumors. Results from the dose escalation part in pts with solid tumors are reported. Methods: The dose escalation part of this open-label study enrolled adult pts with R/R solid tumors in a 3+3 fashion. Endpoints included maximum tolerated dose, recommended phase 2 dose (RP2D) at different ABBV-075 dosing schedules (daily, Monday/Wednesday/Friday [MWF], or 4 days on/3 off [4/7]), safety and preliminary efficacy. Results: As of Dec 2017, 72 pts with solid tumors enrolled in the dose escalation cohort. Most common tumo...

8530 Background: The majority of SCLC cases are diagnosed as ED, for which there is a poor prognosis and no curative treatment (Tx). V, a potent PARP inhibitor, has been shown in preclinical studies to enhance the antitumor activity of platinum-based agents and E against SCLC. The presented phase 1 dose-escalation (NCT02289690) evaluated V combined with Cb/E. Methods: Pts (≥18 years) with ED SCLC or other advanced/metastatic solid tumors with ≤1 line of prior cytotoxic therapy and ECOG performance score 0/1 were included. This study followed a 3+3 design. V starting dose and schedule were 80 mg BID PO administered on days (D) –2 to 5 in combination with Cb AUC 5 mg/mL•min administered on D 1 and E 100 mg/m2 administered on D 1 to 3 via intravenous infusion in 21-D cycles. V schedules of D –2 to 12 and continuous dosing were also explored. Primary objectives were to establish the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) for V combined with Cb/E, and to evaluate the pharmacokinetic (PK) interaction between V and E. Results: Thirty-nine pts (n = 24 ED SCLC; n = 15 other solid tumors) with median age of 62 years (range 43–79) received study Tx. Most common adverse events (AEs; ≥40%) were nausea (54%), fatigue (51%), alopecia (46%), and anemia (44%); grade 3/4 AEs (≥30%) were decreased neutrophil count, neutropenia (31% each), and anemia (26%). Dose-limiting toxicity occurred in 1 pt (n = 1 grade 3 fatigue) at V 240 mg BID D –2 to 5. The MTD was not reached; RP2D for V was set at 240 mg BID on D –2 to 12 based on long-term tolerability. Continuous dosing of V 240 mg BID with Cb/E resulted in unacceptable Cb/E dose delays due to hematologic toxicity. Coadministration of V (80 to 240 mg BID) with Cb/E exhibited dose-proportional kinetics with no impact on the E PK. Confirmed responses: ED SCLC 63% (15/24 pts) across all dose levels and in 83% (5/6) at RP2D; other tumor types: 13% (2/15) across all dose levels. Conclusions: V + Cb/E had an acceptable safety profile in pts with ED SCLC, with an RP2D of 240 mg BID D –2 to 12. Coadministration of V with Cb/E had no effect on E PK. Responses were seen across all dose levels. A phase 2 study of V with Cb/E in ED SCLC is ongoing. Clinical trial information: NCT02289690.

8546 Background: CRT is a standard for patients with Stage III NSCLC. V is a potent, orally bioavailable PARP1/2 inhibitor that can delay DNA repair following chemotherapy or radiation induced damage. A Phase 2 study indicated favorable efficacy of V vs placebo when added to C/P in advanced NSCLC (Ramalingam et al. Clin Cancer Res. 2016). Based on these results, a Phase 1/2 trial was initiated to study the safety and efficacy of V/C/P-based CRT in the treatment of Stage III NSCLC. Methods: Subjects without prior NSCLC therapy suitable for definitive CRT received V plus C AUC 2 + P 45 mg/m2 weekly + 60 Gy over 6-9 weeks. V was escalated from 60 mg BID to a maximum planned dose based on prior studies of 240 mg BID via 3+3 design with allowed over-enrollment followed by consolidation therapy of V 120 mg BID + C AUC 6 + P 200 mg/m2 for up to two 21-day cycles. Results: Thirty-one subjects (median age 64; 10 male) have been enrolled to date into dosing cohorts at 60 mg (7), 80 mg (9), 120 mg (7) and 200 mg (8). PK of V was dose proportional. CRT or V required dose reduction for 0 or 1 subject, respectively. Four (13%) subjects discontinued study during CRT. No DLTs have been observed and an MTD has not yet been identified. The most common any grade AEs were fatigue (16), esophagitis (15), nausea (13), neutropenia (12), thrombocytopenia (12), constipation (10) and decreased appetite (10). 21 SAEs were observed including 8 with reasonable attribution to V but outside the DLT window including G3/4 febrile neutropenia (2), G3 dehydration (1), G3 vomiting (1), G3 radiation esophagitis (1), G3 esophageal stricture (1), G3 intractable N/V (1) and G5 sepsis during consolidation (1). Of 21 subjects evaluable for tumor assessment, best response was CR (1), PR (11), SD (6), and PD (3). Conclusions: V/C/P-based CRT followed by V/C/P consolidation therapy is a tractable regimen for the treatment of Stage III NSCLC. A randomized placebo-controlled Phase 2 extension of this study is planned. Clinical trial information: NCT02412371.

2510 Background: ABBV-221 is a 2nd-generation antibody-drug conjugate (ADC) targeting EGFR based on the 1st-generation ADC ABT-414. ABT-414 shows efficacy in glioblastoma (GBM) patients (pts) with EGFR amplification in ongoing studies. ABBV-221 is an affinity matured monoclonal antibody against EGFR linked to the toxin MMAE. ABBV-221 has higher affinity for overexpressed EGFR than ABT-414, potentially allowing it to target a broader range of tumor types. Methods: This is a Phase 1, multicenter study to determine maximum tolerated dose (MTD) and recommended Phase 2 dose (RPTD) of ABBV-221. Pts are required to have an EGFR-dependent cancer to be eligible. Starting dose of ABBV-221: 0.3 mg/kg IV infused over 3 hrs for each 21-day cycle, with alternate dosing schedules utilized (2 wks on, 1 wk off or weekly) to mitigate infusion reactions. Results: As of 11 January 2017, 42 pts were treated (13 colon, 5 head & neck (H&N) cancer, 5 non-small cell lung cancer, 5 GBM, 2 breast, 12 other). Ten dose escalation cohorts have been completed with the last cleared dose 4.5 mg/kg per cycle. Tumor tissue samples were evaluated for EGFR protein expression by IHC, EGFR and EGFR ligand mRNA expression by RNAseq, and the results compared to outcome. The most common adverse event (AE) was infusion reaction in 18/42 pts (43%); 3 pts experienced severe infusion reactions. Several mitigation strategies were used to permit continued dose escalation. The other most common AE was fatigue in 17/42 pts (41%). Only 1 pt had keratitis (Grade 4). Sixteen pts (38%) had stable disease (SD), including 4 pts who remained on study longer than 6 months. One H&N pt who has received 2 cycles of ABBV-221 had an unconfirmed partial response and continues to be treated. This pt had high levels of both EGFR and EGFR ligand. Preliminary pharmacokinetics (PK) analysis suggests ABBV-221 exposures are approximately dose-proportional. Conclusions: Safety, PK, pharmacodynamics, and preliminary efficacy data of ABBV-221 warrant further study in this population. Infusion reactions have been manageable and primarily a first dose phenomenon. The duration of SD in pts with refractory solid tumors is encouraging. Clinical trial information: NCT02365662.