Rethink the Biology Fueling Resistance and Progression in GIST

DOES RESISTANCE IN GIST DEMAND A DIFFERENT APPROACH?

DNA

GIST is fueled by a myriad of mutations that play a key role in1-3:

  • Unregulated kinase activity
  • Mechanisms of resistance
Capsule and pill

A different approach may be needed to2-5:

  • Overcome resistance
  • Control disease progression
  • Provide patients, caregivers, and physicians with additional treatment options

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A MYRIAD OF MUTATIONS FUEL RESISTANCE AND PROGRESSION,
RESULTING IN UNREGULATED KINASE ACTIVITY2,3

GIST is most often fueled by activating mutations in kinase genes6:

KIT

70-80% OF CASES

PDGFRα

5-10% OF CASES

THESE KIT AND PDGFRα MUTATIONS KEEP THE KINASE IN THE ACTIVE STATE,
CAUSING UNCONTROLLED CELL PROLIFERATION AND/OR CELL SURVIVAL.7,8

The complexity of GIST is further complicated by2,9,10:

Multiple mutations in cells Multiple mutations in cells

Broad intra- and
inter-tumor heterogeneity

Multiple mutations in cells Multiple mutations in cells

Multiple evolving
resistance mutations

A single patient with GIST may have multiple mutations within or between tumors, contributing to resistance and disease progression.8

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SIGNIFICANT UNMET NEEDS REMAIN IN ADVANCED GIST3

TKI therapy is the standard of care for patients with recurrent or unresectable GIST. However, the vast majority of patients who respond to front-line treatment with imatinib will eventually develop resistance.6

CURRENT TKIs ARE UNABLE TO FULLY REGULATE KINASE ACTIVITY1,8

First-generation TKIs in GIST bind to the inactive state of the kinase via the ATP binding site.1,10

However, as resistance mutations develop, these inhibitors may lose their ability to prevent kinase activation, leading to cell proliferation.1,10

Research has uncovered two additional sites that are critical to kinase activation1,4:

  • Switch pocket
  • Activation loop

The activation loop acts as an “on-off switch” for kinase activation. When it binds to the switch pocket, the kinase activates or switches “on,” leading to uncontrolled cell growth and proliferation.1,4,7

TOLERABILITY ISSUES ADD TO THE BURDEN OF DISEASE5,11-13

As GIST progresses, patients may face not only an increased disease burden, but also tolerability challenges presented by second- and third-line TKIs. AEs associated with current treatments may lead to dose modifications, including reductions or interruptions. Effective management of AEs may help maintain adequate dosing and continuation of treatment.5,11-13

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SWITCH CONTROL IS A PROMISING APPROACH TO TARGETING THE
DRIVERS OF RESISTANCE AND PROGRESSION IN ADVANCED GIST4

Given the myriad of mutations that fuel drug resistance and progression in GIST, is there a need for a different therapeutic approach that broadly inhibit KIT and PDGRa mutations?4

Switch control involves targeting the kinase in two ways1,4:

  • Preventing the activation loop from binding to the switch pocket
  • Locking the kinase in the inactive (“off”) state

This unique approach has the potential to4:

  • Regulate kinase activity
  • Inhibit a broader spectrum of KIT and PDGFRα mutations driving GIST

Achieving switch control may prevent downstream signaling and cell proliferation, and potentially overcome the mechanisms of resistance associated with advanced GIST1,4

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References:

1. Hemming ML, Heinrich MC, Bauer S, George S. Translational insights into gastrointestinal stromal tumor and current clinical advances. Ann Oncol. 2018;29(10): 2037-2045. 2. Ordog T, Zörnig M, Hayashi Y. Targeting disease persistence in gastrointestinal stromal tumors. Stem Cells Transl Med. 2015;4(7):702-707. 3. Antonescu CR, DeMatteo RP. CCR 20th Anniversary commentary: A genetic mechanism of imatinib resistance in gastrointestinal stromal tumor—Where are we a decade later? Clin Cancer Res. 2015;21(15): 3363-3365. 4. Smith BD, Kaufman MD, Lu WP, et al. Ripretinib  (DCC-2618) is a switch control kinase inhibitor of a broad spectrum of oncogenic and drug-resistant KIT and PDGFRA variants. Cancer Cell. 2019;35(5):738-751. 5. Saponara M, Lolli C, Nannini M, et al. Alternative schedules or integration strategies to maximise treatment duration with sunitinib in patients with gastrointestinal stromal tumours. Oncol Lett. 2014;8(4): 1793-1799. 6. Lopes LF, Bacchi CE. Imatinib treatment for gastrointestinal stromal tumor (GIST). J Cell Mol Med. 2010;14(1-2):42-50. 7. Gramza AW, Corless CL, Heinrich MC. Resistance to tyrosine kinase inhibitors in gastrointestinal stromal tumors. Clin Cancer Res. 2009;15(24): 7510-7518. 8. Yan W, Zhang A, Powell MJ. Genetic alteration and mutation profiling of circulating cell-free tumor DNA (cfDNA) for diagnosis and targeted therapy of gastrointestinal stromal tumors. Chin J Cancer. 2016;35(1):68. 9. Liegl B, Kepten I, Le C, et al. Heterogeneity of kinase inhibitor resistance mechanisms in GIST. J Pathol. 2008;216(1):64-74. 10. Li K, Cheng H, Li Z, et al. Genetic progression in gastrointestinal stromal tumors: mechanisms and molecular interventions. Oncotarget. 2017;8(36): 60589-60604. 11. Reddy P, Boci K, Charbonneau C. The epidemiologic, health-related quality of life, and economic burden of gastrointestinal stromal tumours. J Clin Pharm Ther. 2007;32(6):557-565. 12. Poole CD, Connolly MP, Chang J, Currie CJ. Health utility of patients with advanced gastrointestinal stromal tumors (GIST) after failure of imatinib and sunitinib: findings from GRID, a randomized, double-blind, placebo-controlled phase III study of regorafenib versus placebo. Gastric Cancer. 2015;18(3):627-634. 13. Kim JJ, Ryu MH, Yoo C, Beck MY, Ma JE, Kang YK. Phase II trial of continuous regorafenib dosing in patients with gastrointestinal stromal tumors after failure of imatinib and sunitinib. The Oncologist. 2019;24:1-7.

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