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.

In an orthotopic mouse model of FLT3-mutant AML, tuspetinib exhibited greater antitumor activity than gilteritinib, entospletinib, venetoclax (VEN), and azacitidine (AZA) and combined favorably with VEN and AZA individually. Tuspetinib was well-tolerated and delivered single agent clinical responses across four dose levels among diverse AML genotypes; with a RP2D of 80 mg chosen for future single agent studies. Although early, the VEN/TUS combination has been well tolerated with preliminary objective responses noted.

The F691L mutation had relatively larger effect on gilteritinib than HM43239, which showed as the changed and fixed conformation, respectively. These observations rationalized that the binding affinity of gilteritinib decreased more than that of HM43239 in the F691L mutant.Communicated by Ramaswamy H. Sarma.

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

TUS-resistant cells (TUS/R) were 60-fold resistant to gilteritinib (FLT3 inhibitor) but not to quizartinib (FLT3 inhibitor). There was no observed resistance to azacitidine, luxeptinib (lymphoid & myeloid kinase inhibitor), brequinar (DHODH inhibitor), zelavespib (HSP90 inhibitor), or IMP-1088 (NMT1/2 inhibitor), and a small degree of hypersensitivity (<2-fold) of TUS/R cells to luxeptinib, brequinar, and IMP-1088... Resistance to TUS in MOLM-14 cells required prolonged high-level drug exposure. The fact that FLT3 remained fully inhibited in TUS/R cells growing in 75 nM TUS suggests that resistance is not due to a mutation of FLT3. Drug resistance in TUS/R cells in the absence of TUS over 60 days indicates a stable phenotype, distinct from "persister cell resistance" in which resistance fades during subsequent passages.

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.

In a preclinical xenograft and orthotopic model of AML, HM43239 exhibited greater antitumor potency than FLT3 inhibitor gilteritinib, SYK inhibitor entospletinib, BCL-2 inhibitor venetoclax, and demethylation agent azacitidine. As of July 14, 2022, HM43239 has delivered CRc at 80 mg, 120mg and 160 mg, and was well tolerated at these dose levels over multiple cycles with no DLTs or drug-related SAEs. Pharmacokinetic data illustrate increasing drug exposures through 120 mg and observed objective responses through 160 mg in both FLT3-WT and FLT3-mutated R/R AML patients even after gilteritinib and midostaurin treatment. An update of this study, including a planned single agent and venetoclax combination expansion, will be presented at the meeting.

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.

Seventy percent of enrolled patients had more than 3 prior anti-leukemic treatment attempts, and four patients had relapsed or refractory disease after treatment with other FLT3 inhibitors including gilteritinib, quizartinib, or HM43239. A dose-escalating phase 1a clinical data of PHI-101, which reflects up to cohort 4 of the study, indicates that PHI-101 generated potent FLT3 inhibition leading to encouraging anti-leukemic responses in R/R AML patients, including in those with prior FLT3 TKI therapeutic failure. PHI-101 showed good tolerance and favorable safety profile and reduced leukemic blasts significantly with 28-day dosing. PHI-101 sustained its activity to clear FLT3-ITD and/or FLT3-TKD mutations including D835Y or N676K identified in AML patients.

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).

HM43239 inhibited FcγR-induced SYK and JAK/STAT5 activation in KG-1a (FLT3-WT) cells that upregulate RAS signaling which is a mechanism of acquired resistance to gilteritinib. Its ability to also inhibit SYK and, by reducing the activity of these upstream kinases, to also impair the activity of EKR1/2 and JAK/STAT5 that participate in rescue pathways, makes this a particularly interesting molecule with the potential of offsetting the development of resistance that is common with other FLT3 inhibitors. A Phase 1/2 trial of HM43239 in patients with AML is open and accruing patients (NCT03850574).

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.