S55746

Our previous studies have shown that pegcrisantaspase (PegC), a long-acting pegylated crisantaspase, synergizes with the BCL2 inhibitor, Venetoclax (Ven), to kill several AML cell lines and patient-derived primary AML cells with complex karyotype in vitro and in vivo in a xenograft mouse model... Using a panel of 4 human AML cell lines (MOLM14, MV411, MonoMac6, HL60) as well as primary AML patient samples, weestablished the anti-leukemic activity of the BCL2 inhibitor S55746 and the MCL1 inhibitor S63845 alone and in combination with the long-acting E. coli asparaginase, calaspargase pegol-mknl (CalPegA)... We report that the E. coli asparaginase, CalPegA, enhances the anti-leukemic effect of the BCL2 inhibitor, S55746, but does not impact the activity of the MCL1 inhibitor, S63845, in AML cell lines, patient derived primary AML samples, and in an AML xenograft mouse model. Ongoing studies are further investigating the anti-leukemic mechanism of S55476/S63845 + CalPegA and examining the efficacy and pharmacodynamic/pharmacokinetic effects of these agents in a patient derived xenograft model of AML.

To further validate this finding, the combination of roginolisib with venetoclax or with another bcl-2 inhibitor S55746 was tested in a broad range of lymphoma cell lines including GRANTA519, JVM2, SP49 (MCL); FARAGE, TMD8 (diffuse large B cell lymphoma); MEC1 (chronic lymphocytic leukemia); MJ (cutaneous T cell lymphoma); and YT (NK lymphoma)...Other BCRi such as idelalisib, duvelisib and acalabrutinib were used at 5 μM concentrations as positive controls...In addition, roginolisib synergized with venetoclax in lymphoma cell lines and CLL patient samples. Our data support extending this combination strategy to clinical trials in hematological malignancies.

Among 52 patients with hematological malignancies the maximum tolerated dose (MTD) was not reached and no clinical TLS was observed.20 In this study of 22 evaluable patients with RR CLL there was an overall response rate (ORR) of 63.6% (14/22).20 A larger study of 114 patients with RR CLL evaluated lisaftoclax in combination with either the Bruton's tyrosine kinase inhibitor (BTKi) acalabrutinib or the anti CD20 monoclonal antibody rituximab (NCT04215809)...In CLL an overall response rate (ORR) to BGB-1147 of 100% as monotherapy was observed among 8 patients with RR disease.25 In 12 patients with RR MM, the ORR to BGB-1147 in combination with dexamethasone varied from 0–68% depending on the dose cohort.26 In combination with azacytidine in AML the ORR to BGB-11417 was 74% among those with treatment naïve (TN) disease (n=20/27) and 65% (n=13/20) in the cohort with RR disease.27 BGB-11417 monotherapy in 23 patients with RR NHL demonstrated responses in 2 patients with diffuse large B cell lymphoma (DLBCL) and one patient with marginal zone lymphoma (MZL).28 In 11 patients with RR MCL treated with BGB-11417 in combination with zanubrutinib there was a 55% (6/11) ORR.28 S55746 is a potent BAX/BAK dependent BCL2 inhibitor administered orally.18,29 Developed by Servier, it has been tested in phase I studies in CLL, NHL and AML. In a study of S55746 among 37 patients with RR NHL, no dose limiting toxicities (DLT) or TLS was observed after a medium duration of treatment of 42 days.30 FCN-338 is another orally available selective BCL2 inhibitor developed by Fochon currently undergoing phase I testing in RR CLL.18,31 Clinical outcomes with this drug are yet to be publicly reported...More recently navitoclax has been tested in RR myelofibrosis (MF) in combination with ruxolinitib with evidence of clinical response to the combination.35 AZD0466 by Astrazeneca is a nanomedicine potent dual BCL2/ BCLxL inhibitor that mediates BAX/BAK induced apoptosis36,37 and is administered intravenously...Among 9 patients reported undergoing testing for RR hematological malignancy the DLT had not yet been reached.38 Pelcitoclax or APG1252 by Ascentage is a more recent BAX/BAK dependent dual BCL2 and BCLxL inhibitor18,39,40 currently in phase I trials in RR NHL (NCT05186012)...There are multiple emerging BCL2 inhibitors currently undergoing clinical trial testing in hematological malignancies, and it remains too early to appreciate the differential efficacy and toxicity profiles that these agents may carry compared with venetoclax. It is hoped that the results seen with venetoclax can be improved upon across a raft of disease groups over the coming years.

In chronic lymphocytic leukaemia, the pro-survival protein BCL2 is highly expressed and inhibiting BCL2 with a selective small molecule inhibitor venetoclax has proven to be highly effective...Unlike S63845 and its chemical analogs, the action of AMG-176, a distinct MCL1i, was not affected by overexpressing MDR1. Amongst the other BH3-mimetics we tested, the action of the BCL2 inhibitor S55746 was also compromised by MDR1 overexpression.Taken together, our findings suggest that MDR1 overactivity could potentially pose a barrier to the clinical efficacy of distinct classes of BH3-mimetics that target MCL1 (S63845 and its relatives) and BCL2 (S55746 and compounds of the same class). We conclude that other inhibitors of MCL1 or BCL2 should be considered in cancers with MDR1 overexpression.

Background: Recent randomized trials have demonstrated improvements in overall survival (OS) for the BCL-2 inhibitor venetoclax (VEN) in combination with azacitidine and low dose cytarabine in older unfit patients with AML...S63845 and S55746 were obtained from Servier/Novartis, A1155463 from G. Lessene (WEHI), venetoclax and cytarabine from Selleckchem... We identified the presence of BAX mutations in AML samples from patients progressing on VEN-containing regimens. We show that BAX, but not BAK loss in an AML cell line is associated with resistance to BH3-mimetic drug combinations resulting in reduced survival in AML xenograft models. In contrast, BAX deficiency does not impede the cytotoxic actions of conventional chemotherapy.

Relapsed disease has a poor prognosis despite the use of tyrosine kinase inhibitors (TKIs) for Philadelphia chromosome positive (Ph+ ALL) cases and immunotherapeutic approaches, including blinatumomab and chimeric antigen receptor T cells. Targeting aberrant cell survival pathways with selective small molecule BH3-mimetic inhibitors of BCL-2 (venetoclax, S55746), BCL-XL (A1331852), or MCL1 (S63845) is an emerging therapeutic option...Moreover, combined BCL-2 or MCL1 inhibition with dasatinib showed potent killing in primary Ph+ B-ALL cases, but the BH3-mimetic combination appeared superior in vitro in a variety of Ph-like ALL samples. In PDX models, combined BCL-2 and MCL1 targeting eradicated ALL from Ph- and Ph+ B-ALL cases, although fatal tumor lysis was observed in some instances of high tumor burden. We conclude that a dual BH3-mimetic approach is highly effective in diverse models of high-risk human B-ALL and warrants assessment in clinical trials that incorporate tumor lysis precautions.

It recently received accelerated US FDA approval for use in combination with hypomethylating agents or with low-dose cytarabine in elderly or unfit acute myeloid leukemia (AML) patients...The MV4-11 ABT-199R clones also demonstrated co-resistance to ABT-737 (BCL-2 and BCL-XL inhibitor), S63845 (MCL-1 inhibitor), and S55746 (BCL-2 inhibitor)...As a result of BAX gene deletion, the inhibitors of BCL-2, BCL-XL, and MCL-1 are rendered ineffective in inducing apoptosis. Alternative mechanisms of apoptosis induction need to be explored to overcome BAX deletion-induced resistance.