luxeptinib (CG-806)

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

1, 2 Treatment of CLL cells with entospletinib, but not other BCR-signaling inhibitors, led to a disruption of BAFF-BCR cross-talk and downmodulation of MCL1 mRNA and protein, thus implicating SYK in transduction of multiple pro-survival signals emanating from the tumor microenvironment.1 Entospletinib has shown promising clinical activity in CLL, alone or in combination with obinutuzumab, including in patients with high-risk disease such as TP53 aberrant.3, 4 The drug is very well tolerated, however its development in CLL has been halted. Meanwhile, we have shown that luxeptinib, a dual SYK/BTK kinase inhibitor, has activity in BTK inhibitor-resistant lymphoid models in vitro.5 Luxeptinib is now being investigated in lcinical trials in hematologic malignancies...The early results of MS-553, a selective PKC-β inhibitor, indicates that this agent is tolerable and effective both as single agent and in combination with venetoclax.8 Proteolysis-targeting chimeras (PROTACs) are a new class of small molecules with two covalently-linked ligands recruiting target protein and E3 ubiquitin ligase together to trigger and enable proteasomal degradation of the target protein.9 “BTK degraders”, such as NRX- 2127 (Nurix Therapeutics) and BGB-16673 (Beigene), have entered clinical trials in patients with lymphoid malignancies...Additionally, NX-2127 has shown preclinical activity similar to immunomodulatory drugs (IMiDs) by catalyzing the ubiquitination of Ikaros (IKZF1) and Aiolos (IKZF3), resulting in increased T-cell activation.10 Early results of an ongoing clinical trial of NX-2127 demonstrate an ORR of 33% in heavily pre-treated patients with CLL, and overall good tolerability 11...The preclinical activity of AZD5991 has shown that selective targeting of MCL1 induced metabolic dysfunction and abrogated survival of diffuse large B cell lymphoma and ibrutinib-resistant mantle cell lymphoma cell lines in vivo and in vitro.13 Other BH3-mimetics targeting MCL1 include AMG176 and S63845.14-16 In an experimental design testing the effects of AMG-176 on CLL and normal hematopoietic cell death it was demonstrated that AMG-176 is an active agent in inducing CLL cell death while sparing normal blood cells...Anti-CD20 monoclonal antibodies – rituximab, obinutuzumab and ofatumumab – have significantly improved the survival outcomes. The B cell activating factor receptor (BAFF-R) is one of the main pro-survival receptors in B cells.18 In a preclinical study, ianalumab (VAY-736), a humanized defucosylated engineered antibody directed against BAFF-R, antagonized pro-survival effects of BAFF in CLL cells and showed promising activity both as a single agent and in combination with ibrutinib.19 A phase 1 study of dose escalation and dose expansion investigated the combination of ianalumab with ibrutinib in 32 patients with CLL with median one prior line of therapy (range, 0-4)...This study showed promising results not expected with ibrutinib alone.20 Tafasitamab – a Fc-enhanced, humanized, monoclonal antibody to CD19 – in combination with idelalisib or venetoclax in 24 patients has been associated with an ORR of 77% and 91%, respectively...In a phase 1 study involving 26 patients with R/R CLL, cirmtuzumab administered at four biweekly infusions was shown to have a long plasma half-life and did not have dose-limiting toxicity, potentially providing another treatment opportunity for patients with CLL.22 Immune Cell Enabling Therapies...A recent report of a phase 1/2 study of lisocabtagene maraleucel, an autologous CD19-directed CAR T-cell therapy (TRANSCEND CLL 004), confirmed efficacy in patients with R/R CLL.23 In this study, 23 patients with median 4 prior lines of therapy (range 2-11) were enrolled, 10 of whom were considered double exposed/refractory...In total, 65% of patients required administration of tocilizumab and/or corticosteroids.23 In addition to the ongoing phase 2 portion of this study, efforts now focus on innovative CAR T-cell designs as well as combination strategies...A phase 1b/2 ongoing trial is currently examining the safety and tolerability of the product in patients with R/R CLL. The early results suggest that epcoritamab administered subcutaneously is well tolerated in a heavily pretreated patient population with multiple high-risk features and shows clinical activity.25 Furthermore, an ongoing study is demonstrating preliminary efficacy of epcoritamab in patients with Richters transformation, a notoriously difficult-to-treat complication of CLL.26

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.

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.

It also inhibits the kinases p38MAPK, ERK1/2, SAPK/JNK and activation of transcription factor NF-κBp65 with a concentration profile similar to its inhibition of cytokine release. Implications: The ability of luxeptinib to inhibit the NLRP3-mediated release of IL-1β and pathways involved in the release of IL-6 and TNFα at concentrations which are well-tolerated in patients makes it a candidate for the treatment of inflammatory diseases and inflammation-associated resistance in cancer.

Luxeptinib simultaneously 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...One heavily pretreated AML patient (8 prior regimens including alloSCT and FLT3 inhibitors gilteritinib and crenolanib) had 99% reduction of blasts in peripheral blood (from 6.38x10 3 /µL at C1D1 to 0.09x10 3 /µL at C1D15), though the decrease in blasts reversed during Cycle 2...MRD-negative complete remission (CR) was confirmed in one FLT3-ITD AML patient (6 prior regimens including 2 alloSCT and FLT3 inhibitor sorafenib) at Cycle 5 of treatment evidenced by reduction of FLT3-ITD VAF and blasts in bone marrow to below limit of detection (LOD) of PCR-based FLT3-ITD assay and high-sensitivity flow cytometry (LOD < 0.1%), respectively... As of June 7, 2021, luxeptinib is well tolerated at dose levels of 450 and 600 mg BID over multiple cycles and escalated to 750 mg BID (Cohort 3). Pharmacodynamic studies documented inhibition of FLT3 signaling, and anti-leukemic activity has been observed in heavily pretreated relapsed FLT3-ITD AML patients as evidenced by significant reduction of FLT3-ITD VAF and blasts in bone marrow and / or peripheral blood. One FLT3-ITD AML patient has had confirmed MRD negative CR and continues treatment.

It suppresses BCR signaling pathways (LYN, SYK, BTK, AKT, ERK) and other oncogenic pathways in cell lines and primary CLL cells, kills malignant B-cells insensitive to ibrutinib or venetoclax at low nM concentrations, and shows enhanced activity in combination with venetoclax. Luxeptinib has a favorable safety profile in patients treated with 150 mg to 600 mg BID over multiple cycles. A single apparent DLT (grade 4 hypertension in one patient with pre-existing hypertension) led to expansion of the 750 mg dose level to 6 patients. Pharmacodynamic studies documented inhibition of SYK, BTK and ERK in the BCR signaling pathway.

AZD5991 is a highly selective BH3-mimetic that demonstrates high in vitro potency in MCL1-dependent cell lines with an IC50 <1 nM.7 We have demonstrated that direct MCL1 inhibition with AZD5991 disrupts survival of neoplastic B-cells in lymph-node mimicking conditions, induces mitochondrial dysfunction and cooperates with BCL2/X inhibitors in vitro and in vivo.8 A phase 1 clinical trial of AZD5991 alone or in combination with venetoclax in hematologic malignancies is ongoing (NCT03218683)...AMG-176 demonstrated synergy with venetoclax in AML models; however, it also caused cytopenias.9 AMG-176 was shown to induce apoptosis of CLL cells independent of prognostic markers and overcame the protective effect of stromal microenvironment.10 However, suppressive effects on hematopoiesis will likely become the dose- limiting factor in clinical trials of MCL1-targeting agents. The effect of MCL1 inhibition on cord blood-derived CD34+ cells was studied using a small-molecule inhibitor, S63845,11 resulting in almost complete depletion of human hematopoietic stem and progenitor cells, while mature blood cells survived normally...We have shown that SYK inhibition with entospletinib leads to downmodulation of MCL1 protein in CLL both in vitro and in the clinic.12,13 Treatment of CLL cells with entospletinib, but not other BCR-signaling inhibitors, led to a disruption of BAFF-BCR cross-talk and downmodulation of MCL1 mRNA and protein, thus implicating SYK in transduction of multiple pro-survival signals emanating from the tumor microenvironment.13 Entospletinib has shown promising clinical activity in CLL.12,14 It is currently being developed in myeloid malignancies.15 A novel dual SYK/BTK inhibitor luxeptinib also was shown to downregulate MCL1 and other pro-survival BCL2 proteins in CLL.16 Transcriptional cyclin-dependent kinases (CDK7/9) regulate activity of RNA polymerase, thereby controlling production of mRNA. Downmodulation of MCL1 has been considered a key mechanistic event accounting for the pro-apoptotic activity of CDK inhibitors in neoplastic B-cells.17,18 Pan-CDK inhibitors (flavopiridol, dinaciclib) demonstrate clinical efficacy in lymphoid malignancies. We and others reported that preclinical efficacy of AZ5576, a selective inhibitor of CDK9, and its clinical congener AZD4573 in lymphoid tumors depended on rapid downmodulation of MCL1, BFL1, and MYC.19–21 CDK9 inhibition can increase efficacy of BH3-mimetics, but safety of this combination will need to be explored.22,23 CDK9 inhibitors in development, in addition to AZD4573, include VIP152, CYC065, and voruciclib...Navitoclax is a small-molecule inhibitor of BCL2, BCLX, and BCL2L2; however, its use in CLL has been plagued by thrombocytopenia.24 AZD4320 is an alternative agent that co-targets BCL2/X...ABBV-155, an antibody-drug conjugate targeting BCLX, where BCLX is being used as a payload to avoid “off-tumor” effects, demonstrated promise in solid tumor models.26 Finally, as many microenvironment-driven pro-survival pathways converge on NFB, leading to induction of chemokines, cell cycle regulators, and BCL2 family proteins themselves, this transcription factor continues to be an attractive target in CLL...When combined with ibrutinib in murine CLL models, VAY-736 produced prolonged survival compared with either therapy alone.28 Alternative targets for therapeutic antibodies include ROR1 (cirmtuzumab), CD19 (tafasitamab), and others.29 As resistance to novel agents is becoming an unmet need in CLL, exploration of novel targets is of paramount importance...Multiple CDK inhibitors are currently being explored and have anti-tumor effects not restricted to MCL1 inhibition. CAR T cells and bi-specific antibodies have exceptional efficacy in lymphoid malignancies and thus are of high relevance in CLL.

It suppresses BCR signaling pathways (through inhibition of LYN, SYK, BTK, AKT, ERK) in cell lines and primary CLL cells, kills malignant B-cells insensitive to ibrutinib or venetoclax at low nM concentrations, and shows enhanced activity in combination with venetoclax. Pharmacodynamic studies documented inhibition of SYK, BTK and ERK in the BCR signaling pathway. Enrollment of patients with R/R CLL/SLL and NHL at dose level 5 (750 mg) is ongoing and updated clinical data will be presented at the meeting.

Luxeptinib simultaneously 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...One heavily pretreated patient with relapsed AML with mutated NPM1, DNMT3A, and FLT3-ITD who had previously progressed after chemotherapy, alloSCT, and two FLT3 inhibitors (gilteritinib, crenolanib) demonstrated clinical anti-leukemic activity with a decrease in peripheral blood blasts from 93% to 10% during Cycle 1...Pharmacodynamic studies documented inhibition of FLT3 signaling pathway, and anti-leukemic activity has been observed in the setting of AML relapsed following therapy with multiple prior FLT3 inhibitors. Enrollment of patients with R/R AML continues and updated clinical data from this dose escalation study will be presented at the meeting.

In cell lines and primary samples from chronic lymphocytic leukemia (CLL) patients, CG-806 suppressed BCR signaling (LYN, SYK, BTK, AKT, ERK) and pathways operative in AML (FLT3, AKT, CSF1R, MAPK, PDGFRα, others), killed malignant B-cell cells insensitive to ibrutinib or venetoclax at low nM concentrations, and showed enhanced activity in combination with venetoclax. CG-806 demonstrated a favorable safety profile in patients treated to date with 150, 300, 450 or 600 mg BID over multiple cycles. Oral absorption in patients produced plasma concentrations known to be effective in murine leukemia models. Pharmacodynamic studies using patient whole blood and plasma documented inhibition of SYK, BTK and ERK in the BCR signaling pathway.

While targeting BTK (ibrutinib, acalabrutinib) and PI3K (idelalisib, duvelisib) has shown efficacy in CLL, clinical responses fall short in aggressive NHL, necessitating the development of novel approaches to suppress BCR signaling...Consistent with the above observations, synergy was observed between CG-806 and inhibitors of metabolic enzymes (teleglenastat, perhexiline maleate) and BH3-mimetics targeting BCL2/X proteins (venetoclax, AZD4320)...BCL2 family proteins may be implicated in resistance to CG-806. These results provide rationale for further investigation of CG-806 in aggressive NHL.

our study showed that CG-806 inhibited expression of the anti-apoptotic protein MCL1, overcame the effect of venetoclax-induced MCL1 and increased the level of proapoptotic BIM. While venetoclax produced no effect on MAPK signaling, CG-806 alone and in combination with venetoclax reduced p-MEK1/2, p-JNK and MYC in a cell line dependent manner.In conclusion, CG-806 inhibits driver and rescue pathways to directly and potently kill the aggressive B-cell lymphomas including DHL/THL/DEL and enhances the proapoptotic effect of venetoclax, thereby highlighting CG-806 as a promising candidate for the treatment of patients harboring unfavorable BCL2/MYC/BCL6 translocations and/or overexpression and supporting clinical development of CG-806 in patients with B-cell malignancies intolerant, resistant, or refractory to venetoclax.

The first patient at 150 mg BID, who has CLL with TP53 mutation and had previously failed chemotherapy, ibrutinib, venetoclax, rituximab, and idelalisib, remains on treatment after 8 cycles. Pharmacodynamic studies using patient whole blood and plasma documented engagement of the BTK target. Enrollment of patients with R/R CLL/SLL and NHL is continuing and updated safety, PK, and available biomarker data will be presented at the meeting.

The first patient, who has CLL with TP53 mutation and had previously failed chemotherapy, ibrutinib, venetoclax, rituximab, and idelalisib, remains on treatment after 8 cycles at 150 mg BID. CG-806 was well-tolerated in the patients treated at 150 and 300 mg BID over multiple cycles. There have been no TEAE. Oral absorption was sufficient to produce plasma concentrations in humans approaching exposures known to be effective in murine leukemia models.