Kerstein, David

e23508 Background: Activating mutations in KIT are found in most pts with GIST. First-line imatinib provides initial clinical benefit in advanced disease, but prognosis is poor for pts whose tumors progress, despite 3 other approved tyrosine kinase inhibitors (TKIs). Resistance is typically driven by secondary KIT mutations in the ATP-binding pocket (exons 13/14) or activation loop (exons 17/18). No approved drug has potent activity against both classes of resistance mutations, and many pts have polyclonal resistance after multiple lines of therapy. THE-630 is an investigational pan-variant KIT inhibitor. Based on preclinical models, an average plasma concentration (Cav) of 100 nM is predicted to have potent activity against all major classes of KIT-activating and resistance mutations. Here, we report initial data from a first-in-human study in pts with advanced GIST (NCT05160168). Methods: This ph 1/2 study is assessing the safety (including dose-limiting toxicities [DLTs] and recommended ph 2 dose [RP2D]), pharmacokinetics (PK), and antitumor activity of THE-630. Pts enrolled in the ph 1 portion were ≥18 y, had unresectable or metastatic GIST previously treated with imatinib and ≥1 additional TKI, and had ECOG performance status ≤2. Pts received THE-630 (QD; 28-day cycles) in a 3+3 dose-escalation design. PK was assessed on days 1 and 15 in cycle 1, antitumor activity was assessed by modified RECIST 1.1, and circulating tumor DNA (ctDNA) was assessed using Guardant360. Results: As of 13 Jan 2023, 19 pts had been treated in the ph 1 portion at THE-630 daily doses of 3 mg (n = 3), 4 mg (n = 7), 6 mg (n = 3), 9 mg (n = 3), and 12 mg (n = 3). Median age was 57 y (range 39–72); 13 pts had ≥4 prior TKIs. Median treatment duration was 55 days (range 1–252). PK analysis shows approximately dose-proportional increase in systemic exposure across doses tested. Mean steady-state Cav at 12 mg was 47 nM. There was 1 DLT at 4 mg (grade 5 myocardial infarction in a pt with 8 prior TKIs and hyperlipidemia where relationship to THE-630 could not be incontrovertibly ruled out). No other DLTs or related serious adverse events have occurred; 13 pts had treatment-related AEs (TRAEs), 91% of which were grade 1–2. The most common TRAEs were fatigue (n = 4), dry mouth (n = 3), anemia, ALT increase, AST increase, diarrhea, dyspepsia, dyspnea, and hypertension (n = 2 each). Reductions in select KIT-mutant allele fractions in ctDNA were observed, consistent with THE-630 levels achieved thus far. Stable disease (SD) was the best response in 1/7 pts at 4 mg, 1/3 pts at 6 mg, and 3/3 pts at 9 mg. Post data cut, SD was seen in 3/3 pts at 12 mg. Dose escalation continues to determine the RP2D. Conclusions: THE-630 had an acceptable initial safety profile, and escalation continues, as target exposure for pan-variant KIT activity is not yet reached. Reduction in KIT-mutant allele fractions in ctDNA and initial evidence of disease control were observed. Clinical trial information: NCT05160168 .

e20502 Background: The CNS is often a site of first disease progression in CRZ-treated ALK+ NSCLC. The ALTA trial is assessing BRG, an investigational next-generation ALK inhibitor, in pts with CRZ-refractory advanced ALK+ NSCLC, including pts with baseline brain metastases. Methods: In ALTA (NCT02094573), pts were stratified by presence of baseline brain metastases and best response to prior CRZ and randomized 1:1 to receive BRG at 90 mg qd (arm A) or 180 mg qd with a 7-d lead-in at 90 mg (arm B). Here, we show data for pts with baseline brain metastases. An independent review committee (IRC) assessed intracranial efficacy. Results: Of 222 pts (112 in arm A; 110 in arm B), 80 (71%)/74 (67%) in A/B had baseline brain metastases per investigators, with median age 49/55 y; 74%/76% had received chemotherapy. As of May 31, 2016, 51%/59% of these pts continued to receive BRG in A/B; median follow-up was 9.6/11.4 mo. Intracranial efficacy is shown in the table. Among these pts, most common treatment-emergent adverse events were: nausea 35%/46% (A/B), headache 30%/31%, vomiting 29%/31%, diarrhea 21%/38%, cough 25%/32%; grade ≥3: increased blood CPK 1%/12%, hypertension 4%/7%, increased lipase 4%/3%. Conclusions: BRG yielded substantial intracranial responses with robust iPFS and acceptable safety in ALK+ NSCLC pts with baseline brain metastases in ALTA. 180 mg (with lead-in) showed consistently improved intracranial efficacy compared with 90 mg. Clinical trial information: NCT02094573. [Table: see text]

9065 Background: BRG is a potent and selective ALK inhibitor with preclinical and clinical activity against wild-type ALK and a broad range of mutants associated with clinical CRZ resistance, including G1202R. Herein we examine the association between BRG efficacy and ALK mutation status using plasma specimens from the initiation of BRG treatment (baseline [BL]) and the end of BRG treatment (EOT) in CRZ-resistant ALK+ NSCLC pts enrolled in the BRG Ph1/2 or pivotal Ph2 (ALTA) trials. Methods: Plasma samples were analyzed using the Resolution Bioscience ctDx Lung Panel v3.0. BRG activity was described using the confirmed objective response rate (cORR) (RECIST v1.1). Data are reported as of May 31, 2016 for the Ph1/2 (NCT01449461) and ALTA (NCT02094573) trials. Results: Of 291 CRZ-resistant ALK+ NSCLC pts enrolled in the Ph1/2 (N = 69) and ALTA (N = 222) trials, evaluable plasma samples were obtained from 67 pts at BL. cORR to BRG in these pts was 49% (33/67). An ALK fusion was detected in plasma in 45% (30/67) of these pts (cORR 57% [17/30]), of whom 33% (10/30) had secondary ALK mutations (cORR 50% [5/10]) and 67% (20/30) did not (cORR 60% [12/20]). Best responses in pts with secondary ALK mutations were: 2 CR (ALK amplification [Amp] copy number [CN] = 10; T1151M); 3 PR (L1196M; E1408V; Amp CN = 6); 4 SD (L1196M; E1419K; F1174C; C1156Y+S1206F+G1269A); 1 PD (T1151R+C1156Y+E1161D+F1174L). Of 67 pts with evaluable plasma at BL, 35 discontinued BRG therapy, of whom 20 had evaluable samples collected at EOT. No new mutations were detected at EOT in 75% (15/20) of pts. Complex mutation patterns were associated with resistance in the remaining 25% (5/20): High-level ALK-Amp (CN = 58); ALK-Amp (CN = 14)+MET-Amp (CN = 6); ALK-S1206F+S1206C+Amp (CN = 6); ALK-G1202R+L1196M+L1198Q; ALK-G1202R+BRAF-V600E+KRAS-G12D. Conclusions: ALK fusions were detected in plasma in < 50% of CRZ-resistant ALK+ NSCLC pts. BRG had substantial activity in ALK fusion–positive pts with a range of CRZ-resistance mutations. Neither primary nor secondary resistance to BRG was associated with any single plasma ALK mutation. The therapeutic implications of complex secondary resistance patterns associated with BRG require further exploration. Clinical trial information: NCT01449461, NCT02094573.