Wang, Tao

Abstract Imatinib mesylate (IM) has revolutionized the treatment of gastrointestinal stromal tumor (GIST). However, most patients inevitably acquire IM resistance. Second- and third-line treatments exhibit modest clinical benefits with a median time to disease progression of 4 to 6 months, highlighting the urgency for novel therapeutic approaches. Here, we report that the expression of BCL6, a known oncogenic driver and transcriptional repressor, was significantly induced in GIST cells following IM treatment. Elevated BCL6 levels suppressed apoptosis and contributed to IM resistance. Mechanistically, BCL6 recruited SIRT1 to the TP53 promoter to modulate histone acetylation and transcriptionally repress TP53 expression. The reduction in p53 subsequently attenuated cell apoptosis and promoted tolerance of GIST cells to IM. Concordantly, treatment of GIST cells showing high BCL6 expression with a BCL6 inhibitor, BI-3802, conferred IM sensitivity. Furthermore, BI-3802 showed striking synergy with IM in IM-responsive and IM-resistant GIST cells in vitro and in vivo. Thus, these findings reveal a role for BCL6 in IM resistance and suggest that a combination of BCL6 inhibitors and IM could be a potentially effective treatment for GIST. Significance: BCL6 drives resistance to imatinib by inhibiting p53-mediated apoptosis and can be targeted in combination with imatinib to synergistically suppress tumor growth, providing a therapeutic strategy for treating gastrointestinal stromal tumor.

PURPOSE Sunitinib, a multitargeted tyrosine kinase inhibitor (TKI), is approved for advanced gastrointestinal stromal tumor (GIST) after imatinib failure. Ripretinib is a switch-control TKI approved for advanced GIST after prior treatment with three or more TKIs, including imatinib. We compared efficacy and safety of ripretinib versus sunitinib in patients with advanced GIST who were previously treated with imatinib (INTRIGUE, ClinicalTrials.gov identifier: NCT03673501 ). PATIENTS AND METHODS Random assignment was 1:1 to once-daily ripretinib 150 mg or once-daily sunitinib 50 mg (4 weeks on/2 weeks off) and stratified by KIT/ platelet-derived growth factor α mutation and imatinib intolerance. The primary end point was progression-free survival (PFS) by independent radiologic review using modified Response Evaluation Criteria in Solid Tumors version 1.1. Secondary end points included objective response rate by independent radiologic review, safety, and patient-reported outcome measures. RESULTS Overall, 453 patients were randomly assigned to ripretinib (intention-to-treat [ITT], n = 226; KIT exon 11 ITT, n = 163) or sunitinib (ITT, n = 227; KIT exon 11 ITT, n = 164). Median PFS for ripretinib and sunitinib ( KIT exon 11 ITT) was 8.3 and 7.0 months, respectively (hazard ratio, 0.88; 95% CI, 0.66 to 1.16; P = .36); median PFS (ITT) was 8.0 and 8.3 months, respectively (hazard ratio, 1.05; 95% CI, 0.82 to 1.33; nominal P = .72). Neither was statistically significant. Objective response rate was higher for ripretinib versus sunitinib in the KIT exon 11 ITT population (23.9% v 14.6%, nominal P = .03). Ripretinib was associated with a more favorable safety profile, fewer grade 3/4 treatment-emergent adverse events (41.3% v 65.6%, nominal P < .0001), and better scores on patient-reported outcome measures of tolerability. CONCLUSION Ripretinib was not superior to sunitinib in terms of PFS. However, meaningful clinical activity, fewer grade 3/4 treatment-emergent adverse events, and improved tolerability were observed with ripretinib.

11541 Background: Ripretinib (R) is a switch-control tyrosine kinase inhibitor (TKI) indicated for the treatment of patients (pts) with advanced gastrointestinal stromal tumor (GIST) after prior treatment with ≥3 TKIs. In the INTRIGUE study (NCT03673501) there was no significant difference in median PFS (primary endpoint) between R and sunitinib (S). We present exploratory analyses of tolerability data and selected pt reported outcomes (PROs). Methods: Pts were randomized 1:1 to R 150 mg QD or S 50 mg QD 4 weeks on/2 weeks off.Dose modification was allowed for toxicity management. The event of interest was severe or life-threatening (grade ≥3) treatment-related adverse event prior to progression (sTRAE). Days with at least one sTRAE were summed for all treated pts and for pts with ≥1 sTRAE event. PROs were assessed using questions from EORTC QLQ-C30 and Dermatology Life Quality Index (DLQI) at cycle 1 (C1) day 1 (D1), D15, and D29; D1 and D29 of all other cycles; as well as at end of treatment. Differences in PRO scores between baseline and later assessments were calculated across visits. Long-term data will be presented. Results: Pts receiving R (n = 223) versus (vs) S (n = 221) experienced fewer sTRAEs (24% vs 51%, respectively). For all treated pts, the mean time with sTRAEs was 11 days for R and 42 days for S (ratio 0.27, P<0.0001). For pts with ≥1 sTRAE, the mean number of days with a sTRAE was 48 days for R vs 81 days for S (ratio 0.59, p = 0.037). Completion of PRO assessments across the two treatment arms was similar (baseline: R [n = 199], S [n = 199]; C1 D29: R [n = 167], S [n = 177]). Significant differences in self-reported functioning and symptoms were observed by C1 D29. For PROs relating to commonly reported sTRAEs, except constipation, pts in the R arm reported better outcomes than pts in the S arm. Pts in the R arm reported significantly (p<0.05) less decline compared to baseline in pt-reported role function as well as less increase, or improvement, in symptoms of fatigue, appetite loss, diarrhea, nausea/vomiting, and pain vs pts in the S arm. Moderate or severe effect of skin toxicity on pt life, as measured by DLQI in the R arm (n = 165) and in the S arm (n = 175), was observed in 6.6% of pts in the R arm vs 14.8% of pts in the S arm (p = 0.015). Conclusions: In the INTRIGUE study the total number of days with sTRAEs was fewer for pts receiving R vs S. Pts in the R arm also reported significantly less decline in pt-reported role function and less increase in symptoms related to commonly reported sTRAEs, except constipation, vs pts in the S arm. Medical writing provided by Costello Medical. Clinical trial information: NCT03673501.

359881 Background: Sunitinib is approved for advanced gastrointestinal stromal tumor (GIST) after imatinib failure. Ripretinib, a broad-spectrum KIT and PDGFRA switch-control tyrosine kinase inhibitor (TKI), is indicated for the treatment of adult patients (pts) with GIST who received prior treatment with 3 or more TKIs, including imatinib. We compared the efficacy and safety of ripretinib vs sunitinib in pts with advanced GIST who progressed on or were intolerant to imatinib. Methods: This multicenter, global, randomized, open-label phase 3 study (NCT03673501) enrolled adult pts with GIST who progressed on or had intolerance to imatinib. Pts were randomized 1:1 to ripretinib 150 mg once daily (QD) or sunitinib 50 mg QD (4 wks on/2 wks off). Randomization was stratified by KIT mutational status and imatinib intolerance. The primary endpoint was progression-free survival (PFS) by independent radiologic review (IRR) using modified RECIST version 1.1. Key secondary endpoints were objective response rate (ORR) by IRR and overall survival (OS). Hierarchical testing was performed for primary and key secondary endpoints in a prespecified sequence; testing pts with a KIT exon 11 primary mutation (Ex11 intention-to-treat [ITT] population) preceded the all-patient (AP) ITT population. Data cutoff was 1 Sep 2021; final analyses of PFS and ORR and the first interim analysis of OS were conducted. Results: A total of 453 pts were randomized to ripretinib (n = 226; Ex11 ITT, n = 163) or sunitinib (n = 227; Ex11 ITT, n = 164). Median age was 60 yrs (range 18–88) and most pts were white (66.2%) males (62.0%). PFS was not statistically different between ripretinib and sunitinib in the Ex11 ITT (hazard ratio [HR] 0.88, 95% CI 0.66, 1.16; P = 0.36; median 8.3 vs 7.0 mos) or in the AP populations (HR 1.05, 95% CI 0.82, 1.33; P = 0.72; median 8.0 vs 8.3 mos). ORR was numerically higher for ripretinib vs sunitinib in the Ex11 ITT (23.9% vs 14.6%; difference 9.3%, 95% CI 0.7, 17.8; nominal P = 0.03) and AP ITT populations (21.7% vs 17.6%; difference 4.2%, 95% CI −3.2, 11.5; nominal P = 0.27). OS data was highly immature; median OS was not reached in either arm. Fewer pts in the ripretinib arm experienced Grade 3-4 (G3-4) treatment-emergent adverse events (TEAEs) vs sunitinib (41.3% vs 65.6%). Among G3-4 TEAEs with a difference ≥5% between arms, ripretinib had fewer events vs sunitinib (hypertension [8.5% vs 26.7%], palmar-plantar erythrodysesthesia [1.3% vs 10.0%], neutropenia [0% vs 6.3%], and neutrophil count decreased [0% vs 7.2%]). Conclusions: The PFS in both arms was longer than PFS achieved by sunitinib in its pivotal phase 3 trial. While the PFS for ripretinib did not meet the primary endpoint of superiority vs sunitinib, meaningful clinical activity and fewer G3-4 TEAEs were observed in pts with advanced GIST treated with ripretinib after imatinib failure. Clinical trial information: NCT03673501.