BTK C481Y

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.

Twenty-three (76.7%) of the patients were on ibrutinib, while 7 (23.3%) were on acalabrutinib...Six patients (20.0%) continued on the same BTKi with addition of venetoclax, 10 (33.3%) patients were switched to venetoclax and immunotherapy (either obinutuzumab or rituximab), and 3 (10.0%) patients were started on single agent venetoclax...Three (10.0%) patients were taken to chimeric T cell receptor (CAR-T) cell therapy of which one patient had no response and was started on salvage treatment with duvelisib... Our results reveal that durable responses can be achieved by switching to venetoclax based regimens in patients with BTKi. Though the early results of the use of noncovalent BTKi in this setting aree encouraging, the durability of response is limited as new BTK mutations are selected and future therapeutic alternatives are needed for these subset of patients.

main study Substudy patients treated with VenR (n = 194) patients treated with BR (n = 195) patients retreated with VenR (n = 25) Baseline characteristics mean age, years (SD) 63.9 (10.5) 64.4 (9.6) 65.8 (8.3) Number of prior cancer therapy, n (%) 1 111 (57.2) 117 (60.0) 0 (0.0) 2 58 (29.9) 43 (22.1) 20 (80.0) ≥3 25 (12.9) 35 (17.9) 5 (20.0) del(17p) and/or TP53 mutation (aCGh), n (%) mutated 53 (27.3) 55 (28.2) 14 (56.0) unmutated 104 (53.6) 98 (50.3) 9 (36.0) unknown 37 (19.1) 42 (21.5) 2 (8.0) Genomic complexity, n (%) n = 48 n = 46 n = 20 3–4 34 (70.8) 29 (63.0) 3 (15.0) ≥5 14 (29.2) 17 (37.0) 8 (40.0) iGhV, n (%) n = 180 n = 180 n = 23 mutated 53 (29.4) 51 (28.3) 2 (8.7) unmutated 123 (68.3) 123 (68.3) 21 (91.3) unknown 4 (2.2) 6 (3.3) 0 (0.0) efficacy results median follow-up, months 85.7 85.7 33.4 Best oRR, % 93.3 67.7 72.0 umRD at eoCT of main study, n (%) 121 (62.4) 26 (13.3) 16 (64.0) umRD at eoCT of substudy, n (%) N/a N/a 8 (32.0) umRD at eoT of main study, n (%) 83 (70.3)* N/a 14 (56.0) umRD at eoT of substudy, n (%) N/a N/a 0 (0.0) median pFS, months (95% Ci) 54.7 17.0 23.3 (52.3, 59.9) (15.5, 21.7) (15.6, 24.3) 3-year oS rate, % (95% Ci) 88.4 78.9 53.1 (83.8, 93.0) (72.8, 84.9) (25.1, 81.0) *patients who completed 2 years of Ven without pD (n = 118) aCGh: array comparative genomic hybridization; BR: bendamustine- rituximab; Ci: confidence interval; del(17p): deletion in chromosome 17p; eoCT: end of combination treatment; eoT: end of treatment; iGhV immu- noglobulin heavy chain gene; oRR: overall response rate; oS: overall sur- vival; pD: progressive disease; pFS: progression free survival; SD: standard deviation; TP53: tumor protein p53; umRD: undetectable minimal residual disease; Ven(R): venetoclax-(rituximab) cBTKi pre-treated CLL pts treated with pirtobrutinib monotherapy in the phase 1/2 BRUIN trial (NCT03740529) who subsequently developed disease progression (PD) were included in this analysis...Pts received one or more of the following cBTKi: ibrutinib (n = 44, 90%), acalabrutinib (n = 10, 20%), or zanubrutinib (n = 1, 2%)... Pts who progressed on pirtobrutinib showed clearance of BTK C481 clones and the emergence or outgrowth of non-C481 clones, particularly gatekeeper T474 and kinase-impaired L528W mutations, as well as other VUS. Many acquired BTK mutations were shown to pre-exist at baseline at low VAF, reflecting emergence on prior cBTKi. Importantly, these baseline kinase domain BTK mutations did not preclude pirtobrutinib efficacy.

73 patients had only one BTKi (ibrutinib (IBR), 64; acalabrutinib (ACA), 9). 12 pts had multiple BTKis, 8 with two drugs with IBR first followed by ACA (Nf3, 37.5%), vecabrutinib (Nf1, 12.5%), and PIR (Nf4, 50.0%); and 4 with three or more drugs... Our retrospective report summarizes mutations detected during BTKi treatment and shows that BTK L528W can occur during both covalent and non-covalent BTK inhibitor therapy. Four of six patients who progressed on PIR had T474 mutations. In addition, our results may suggest that activating mutations in RAS/RAF/MAPK pathway are related to BTKi resistance.

Novel, non-C481 BTK mutations have been described, including BTK L528W, which has been reported in patients treated with ibrutinib, zanubrutinib, and pirtobrutinib (Maddocks, JAMA Oncol. This is the largest dataset characterizing the incidence and patterns of BTK and PLCG2 mutations in patients with CLL treated with ibrutinib. BTK C481 mutations are the most frequently occurring mutations. PLCG2 mutations occur across the gene at a low incidence per locus (<5%).

Pts received one or more of the following cBTKi: ibrutinib (n=44, 90%), acalabrutinib (n=10, 20%), or zanubrutinib (n=1, 2%). Pts who progressed on pirtobrutinib showed clearance of BTK C481 clones and the emergence or outgrowth of non-C481 clones, particularly gatekeeper T474 and kinase-impaired L528W mutations, as well as other VUS. Many acquired BTK mutations were shown to pre-exist at baseline at low VAF, reflecting emergence on prior cBTKi. Importantly, these baseline kinase domain BTK mutations did not preclude pirtobrutinib efficacy.

Detection of acquired BTK and PLCG2 mutations in ctDNA while on therapy is feasible and may herald clinical disease progression. This trial was registered at https://anzctr.org.au/ as ACTRN12619000024145.

In summary, HZ-Q1070 is a potent and highly selective BTK degrader against both BTK-WT and multiple BTK inhibitors-resistant mutations. In vivo, HZ-Q1070 exhibits excellent pharmacokinetic properties, BTK degradation activity and robust tumor growth inhibition in TMD8 and Mino mouse xenograft tumor model. These findings support further clinical development of HZ-Q1070 for the treatment of B cell malignancies.

"Twenty-three pts were treated with standard of care brexucabtagene autoleucel (CART)... The clinical NGS-based assay for MCL pts at our institution has proven to have prognostic significance. Resistant MCL pts exhibit a preponderance of mutations involving TP53, epigenetic modifier and chromatin regulator genes. Comprehensive risk stratification of pts early on and during therapy is very useful and improves patient care, helps design next generation clinical trials and improves our understanding of the biology of resistant MCL in the BTKi and CART era."

By performing parallel genome-wide CRISPR-Cas9 screening in DLBCL cells with wild-type or kinase-inactive BTK, we discovered that DLBCL cells with kinase-inactive BTK displayed increased dependence on Toll-like receptor 9 (TLR9) for their growth and/or survival. Our study demonstrates that the kinase activity of BTK is not essential for oncogenic BCR signaling and suggests that BTK's non-catalytic function is sufficient to sustain the survival of diffuse large B-cell lymphoma.

Activated HCK subsequently phosphorylated PLCγ2, which propagated BCR signaling and promoted clonogenic cell proliferation. This kinase-independent mechanism could inform therapeutic approaches to CLL bearing either the C481F or C481Y BTK mutants.

Conclusion AS-PCR protocol effective for the analysis of the BTK gene muta tions leading to an amino acid substitution at position C481 has been developed and validated. Prospective studies of low burden BTK mutations in the pathogenesis of relapse in CLL patients treated with BTK inhibitors have been started using this approach.