BTK C481

The first-in-class covalent BTK inhibitor, Ibrutinib, binds to the C481 amino acid residue to block the BTK enzyme and prevent the downstream signaling...To bypass the C481S mutation, non-covalent BTKi, such as Pirtobrutinib, were developed and are active against both wild-type and the C481S mutation...In addition, we discuss the new emerging class of BTK degraders, which utilize the evolution of proteolysis-targeting chimeras (PROTACs) to degrade the BTK protein and constitute an important avenue of overcoming resistance. The moving landscape of resistance to BTKi and the development of new therapeutic strategies highlight the ongoing advances being made towards the pursuit of a cure for B-cell lymphoid malignancies.

One acalabrutinib-treated patient and 4 ibrutinib-treated patients had emergent BTK/PLCG2 co-mutations. While common BTK C481 mutations were observed with both treatments, patterns of mutation and co-mutation frequency, mutation VAF, and uncommon BTK variants varied with acalabrutinib (T474I and E41V) and ibrutinib (L528W, A428D) in this patient population.

The findings of the RAINBOW trial (NCT046152), comparing the dexamethasone, rituximab, and cyclophosphamide (DRC) regimen to the first-generation, ibrutinib are awaited, but more studies are needed to draw definitive conclusions on the comparative efficacy of chemoimmunotherapy and BTKi. Complete response is elusive with BTKi, and combination regimens to improve upon the efficacy and limit the treatment duration are also under evaluation in WM.

P1/2, N=190, Active, not recruiting, ArQule, Inc., a subsidiary of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc. (Rahway, NJ USA) | Trial completion date: Sep 2024 --> Sep 2025 | Trial primary completion date: Sep 2024 --> Sep 2025

This is the first study to describe the genomic landscape of patients with B-cell malignancies who were intolerant to ibrutinib and/or acalabrutinib. Here we show that the gene mutational profile of these patients at baseline or at/after disease progression is comparable with patients with relapse/refractory disease who tolerate ibrutinib and, consistent with other studies, patients with mutations in TP53, SF3B1 or ATM genes had less favorable prognosis on BTKi. Further, intolerant patients who progressed on zanubrutinib acquired new BTK mutations and/or had an increase in the frequency of BTK mutations.

Pirtobrutinib continues to demonstrate durable efficacy in pre-treated R/R CLL/SLL pts treated with a prior covalent BTKi, regardless of prior therapy, reason for prior BTKi discontinuation, age, high-risk TP53 mutations, C481 mutational status, and/or del(17p). It was well tolerated with low rates of discontinuation due to drug-related toxicity.

Pts received 1 or more cBTKi: ibrutinib (n=44, 90%), acalabrutinib (n=10, 20%) or zanubrutinib (n=1, 2%). Whether similar resistance patterns would manifest if pirtobrutinib was utilized prior to cBTKi treatment remains uncertain. Figure 1.

P1, N=160, Active, not recruiting, Nurix Therapeutics, Inc. | Recruiting --> Active, not recruiting

We performed whole exome sequencing on matched tumor and normal samples from 19 CLL patients treated with BTK inhibitors (Ibrutinib, Ibr, 42% (8/19); Acalabrutinib, Acala, 21% (4/19) and Pirtobrutinib, Pirto, 37% (7/19))...The ibr cohort had no prior BTKi therapy whereas 1 patient in the acala cohort had received spebrutinib, another cBTKi...The approach of combining WES data with growth pattern modeling can help unravel the complexities of tumor evolution and drug resistance for the different classes of BTKi. Data on comparative clone growth rates will be presented at the meeting.

Ibrutinib, Zanubrutinib, Orelabrutinib were administered in 55.3%,18.3% and 17.9% of patients respectively, in addition to 6 patients with Acalabrutinib and one with Loxo-305, among them 47.7% (125/262) received BTKi as first line treatment...Venetoclax-based regimen might be an effective salvage therapy which could showed a benefit trend in PFS as compared to other post BTKi therapy (10.1 months vs 3.1 months, p= 0.1818)...Acquired BTK/PLCG2 mutations remained to be key drivers of BTKis resistance and BTKC481S mutation was the dominant mutation, while BTKT474 mutation was only detected in Orelabrutinib-resistant patients. The prognosis was rather poor for relapsed patients especially for RTs, treatment strategy after disease progression remains to be optimized.

In this real-world cross-sectional study, BTK C481 mutations were observed in 21% of BTKi-experienced pts with CLL/SLL, all of whom had a cumulative exposure to BTKis of >36 mo. Because two-thirds of BTKi-experienced pts had <36 mo of BTKi exposure, the prevalence of BTK C481 mutations may be higher in populations with longer BTKi exposure. Further analyses of the natural history of BTK C481 mutations will help identify patients who are at risk of covalent BTKi resistance.

Secondary end points for part 2 include undetectable minimal residual disease in bone marrow at month 14 as assessed by central laboratory, ORR, and DOR per iwCLL 2018 criteria by BICR, OS, and safety. Exploratory end points include ORR including partial response with lymphocytosis, pharmacokinetics, and health-related quality of life.