P1, N=160, Active, not recruiting, Aptose Biosciences Inc. | Trial completion date: Dec 2024 --> May 2025 | Trial primary completion date: Feb 2024 --> Dec 2024

P1, N=80, Active, not recruiting, Aptose Biosciences Inc. | Trial completion date: Dec 2024 --> May 2025 | Trial primary completion date: Feb 2024 --> Dec 2024

The results of this study suggest that CG-806 is a promising multi-kinase inhibitor with anti-leukemic efficacy regardless of FLT3 mutational status. A phase 1 clinical trial of CG-806 for the treatment of AML has been initiated (NCT04477291).Key pointsThe multi-kinase inhibitor CG-806 exerts superior anti-leukemic activity in AML, regardless of its FLT3 status.CG-806 triggered G1 arrest in FLT3 mutated cells and G2/M arrest in FLT3 WT cells through the suppression of FLT3/BTK and aurora kinases.Concomitantly targeting FLT3 and Bcl-2 and/or Mcl-1 exerted synergistic pro-apoptotic effects on both FLT3 WT and mutated AML cells.

P1, N=160, Active, not recruiting, Aptose Biosciences Inc. | Trial completion date: Mar 2024 --> Dec 2024 | Trial primary completion date: Oct 2023 --> Feb 2024

P1, N=80, Active, not recruiting, Aptose Biosciences Inc. | Recruiting --> Active, not recruiting | Trial completion date: Mar 2024 --> Dec 2024 | Trial primary completion date: Oct 2023 --> Feb 2024

Introduction: Luxeptinib (CG-806; LUX) is an orally active noncovalent kinase inhibitor of Bruton's tyrosine kinase (BTK), wild type and mutant forms of Fms-like tyrosine kinase 3 (FLT3) (including the internal tandem duplicates (ITD), tyrosine kinase domain (TKD), and F691L mutant forms), and growth receptors like KIT, CSF1R, PDGFRα, and TRKs. LUX has a favorable safety profile in patients at all tested dose levels, for multiple cycles, for both studies. Antitumor activity was observed in a heavily pretreated relapsed AML patient and in multiple B-NHL subtypes and CLL/SLL patients including several with prior ibrutinib exposure. Continuous dosing of patients with R/R AML and Higher-Risk MDS with the G3 formulation is ongoing; with updated clinical data (200 mg dose level) to be presented at the meeting.

P1, N=80, Recruiting, Aptose Biosciences Inc. | Trial completion date: Jun 2024 --> Mar 2024

P1, N=160, Active, not recruiting, Aptose Biosciences Inc. | Recruiting --> Active, not recruiting

This study sought to refine understanding of how LUX modulates the earliest steps downstream of the BCR following its activation by anti-IgM in lymphoma cells in comparison to ibrutinib (IB). These results indicate that LUX is targeting autophosphorylation of LYN or a step further upstream of LYN in the cascade of signal generated by BCR and that it does so more effectively than IB. The fact that LUX has activity at or upstream of LYN is important because LYN is an essential signaling intermediate in multiple cellular signaling processes that regulate growth, differentiation, apoptosis, immunoregulation, migration and EMT in normal and cancer cells.

Luxeptinib suppresses additional signaling pathways in AML cells (CSF1R, PDGFRα, TRK, SYK, BTK, LYN, AKT, ERK, MAPK), kills primary AML cells insensitive to other FLT3 inhibitors at pM and low nM concentrations, and shows enhanced activity in combination with venetoclax...At 450 mg BID, one heavily pretreated AML patient (received 8 prior regimens including alloSCT and FLT3 inhibitors gilteritinib and crenolanib) had a 99% reduction in peripheral blasts (6.4x103/µL at C1D1 to 0.1x103/µL at C1D15), though the blast proportion increased during Cycle 2... As of July 8, 2022, luxeptinib is well tolerated at dose levels of 450, 600, 750, and 900 mg BID over multiple cycles without evidence of having reached the MTD. Luxeptinib in heavily pretreated relapsed FLT3-ITD AML patients has shown anti-tumor activity including a durable, MRD negative CR. Enrollment of patients with R/R AML is ongoing and updated clinical data with the G3 formulation will be presented at the meeting.

Luxeptinib kills malignant B-cells insensitive to ibrutinib or venetoclax with concentrations in the nanomolar range and shows enhanced activity in combination with venetoclax. Luxeptinib has a favorable safety profile in patients treated with 150 mg to 900 mg BID over multiple cycles. Antitumor activity was observed in multiple B-NHL subtypes and CLL/SLL patients post ibrutinib relapse. Enrollment of additional patients at dose level 6 (900 mg) is ongoing while the more bioavailable G3 formulation is being explored.

CG-806 further significantly reduced AML burden and extended survival in an in vivo PDX leukemia murine model of FLT3 inhibitorresistant FLT3-ITD/TKD double mutant primary AML. Taken together, CG-806 exerts a unique mechanistic action and pre-clinical activity, suggesting further development in FLT3 wild-type and mutant AML.

It has also been studied in combination with idelalisib or entospletinib in CLL and other B-cell lymphomas though without clear benefi t for the combinations over monotherapy16,17. Tirabrutinib is approved in Japan for WM, lymphoplasmacytic lymphoma (LPL), and RRPCNSL, and in South Korea for RR-PCNSL18. TG-1701 is a selective covalent BTKi that has been studied as a monotherapy and in combination with ublituximab and umbralisib with preliminary results suggesting both effi cacy and manageable safety19. Orelabrutinib, another selective covalent BTKi, has been studied as a monotherapy in CLL in addition to other B-cell malignancies, also with favorable safety and effi cacy20,21 and it is approved in China for rel/ref CLL and MCL22. Finally, DTRMWXHS-12 is a covalent BTKi that uniquely is being studied in combination with everolimus and pomalidomide (triplet referred to as DTRM-555), given that this combination was determined to lead to synthetic lethality in both in vivo and in vitro screening studies, with safety and activity seen in early studies23,24...This resistance mechanism appears shared among available irreversible BTK inhibitors including ibrutinib, acalabrutinib and zanubrutinib26...Three such inhibitors have completed phase 1 studies in CLL: vecabrutinib, nemtabrutinib, and pirtobrutinib with another currently in phase 1, luxeptinib...Subsequently, pirtobrutinib is being further studied as both a monotherapy and in combination with venetoclax-rituximab in phase 3 trials in both the frontline and relapsed/refractory settings in CLL in addition to MCL...These non-C481 BTK mutations conferred resistance across multiple non-covalent BTKi’s (in addition to pirtobrutinib, vecabrutinib, nemtabrutinib and fenebrutinib were tested) in addition to variable levels of resistance to covalent BTKi’s36...This is being accomplished by improved tolerability, allowing for patients to stay on drug for longer, and potentially improved effi cacy, including activity despite acquisition of C481 resistance mutations, in the case of the non-covalent inhibitors. The non-covalent inhibitors would help fi ll a major area of unmet need for CLL patients progressing on covalent BTK inhibitors who are not candidates for or progress following venetoclax therapy.

Luxeptinib administered continuously PO every 12 h at a dose that yielded a mean Cmin plasma concentration of 1.0 {plus minus} 0.3 µM (SEM) demonstrated strong antitumor activity but no myelosuppression or evidence of tissue damage in mice or dogs in acute toxicology studies. On the basis of these studies, luxeptinib was advanced into a phase 1 trial for patients with AML and myelodysplastic/myeloproliferative neoplasms (MDS/MPN).

Contrary to ibrutinib, CG-806 downmodulated the anti-apoptotic proteins Mcl-1 and Bcl-xL, abrogated survival of ibrutinib-resistant MCL cell lines, and partially reversed the pro-survival effects of stromal microenvironment-mimicking conditions in primary MCL cells. In sum, dual BTK/SYK inhibitor CG-806 disrupts BCR signaling and induces metabolic reprogramming and apoptosis in MCL. The Bcl-2 network is a key mediator of sensitivity to CG-806 and combined targeting of Bcl-2 demonstrates synergy with CG-806 warranting continued exploration in lymphoid malignancies.