2019 EHA: ASTX660, a non-peptidomimetic antagonist of cIAP1/2 and XIAP, induces apoptosis in T cell lymphoma by enhancing immune mediated and death receptor dependent killing

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ASTX660, a non-peptidomimetic antagonist of cIAP1/2 and XIAP, induces apoptosis in T cell lymphoma by enhancing immune mediated and death receptor dependent killing

 

Abstract:

Background: ASTX660 is a potent, non-peptidomimetic antagonist of the cellular and X-linked inhibitors of apoptosis proteins (cIAP1/2 and XIAP), which is currently being tested in a first in human phase I-II study in patients with advanced solid tumors and lymphomas (NCT02503423). IAP antagonists enhance tumor necrosis factor (TNF) receptor superfamily mediated apoptosis and are potent anti-tumor immune enhancers.

Aim: Herein, we describe the profile of ASTX660 in a range of T cell lymphoma (TCL) cell lines and evaluate ASTX660’s ability to enhance immune mediated killing of tumor cells.

Methods: A panel of human and mouse T-cell lymphoma cell lines were tested in proliferation (Alamar blue or CellTiterGlo) or apoptosis assays (activated caspase-3 substrate assays by IncuCyte or FACS) for sensitivity to ASTX660 alone or in combination with recombinant Death Receptor ligands (TNFa, FASL or TRAIL). Additionally, we used a novel co-culture system of tumor cell lines with anti-CD3 activated human peripheral blood mononuclear cells (PBMC) to assess ASTX660 effects on immune mediated cell killing. Target engagement and induction of apoptosis markers were analysed by Western blotting.

Results: ASTX660 antagonises IAPs in TCL cell lines, as indicated by a decrease in cIAP1 protein levels. This ASTX660-dependent decrease in cIAP was associated with an increase in TNFa-dependent apoptosis in the EL4 and L5178 TCL cell lines. Several T-cell lymphoma models, including HuT-78, HH and My-La expressed low levels of TNFR1 and therefore did not respond to ASTX660 in the presence of TNFa. However, in these cell lines, ASTX660 conferred a significant increase in FASL or TRAIL-dependent apoptosis, indicating that ASTX660 sensitises TCL cells to various death receptor ligands and response correlates with receptor expression levels. In addition to this direct effect on TCL cell lines, ASTX660 also enhances anti-CD3 stimulated PBMC-dependent killing of multiple tumour cell lines, including TCL lines, via induction of caspase activity. Additional preclinical experiments (both in vitro and in vivo) are underway to further characterise the mode of action of ASTX660 in TCL.

Conclusion: The combination of both direct and indirect effects of ASTX660 on TCL lines, described here, supports the ongoing clinical testing of ASTX660 in TCL (NCT02503423). Preliminary clinical efficacy and safety data of ASTX660 in relapsed/refractory (r/r) peripheral T cell lymphoma and cutaneous T cell lymphoma is the subject of a separate abstract.

 

2019 EHA: Preliminary Results of ASTX660, a Novel Non-Peptidomimetic cIAP1/2 and XIAP Antagonist, in Relapsed/Refractory Peripheral T-Cell Lymphoma and Cutaneous T-Cell Lymphoma

Background: ASTX660 is an oral, novel nonpeptidomimetic, small-molecule antagonist of cellular/X-linked inhibitors of apoptosis proteins (cIAP1/2 and XIAP). ASTX660 is currently being evaluated in a first-in-human phase 1‒2 study in patients (pts) with advanced solid tumors and lymphoma (ClinicalTrials.gov NCT02503423). In the phase 1 part of the study, the recommended phase 2 dose (RP2D) was identified with a favorable safety profile and initial evidence of clinical activity in a pt with mycoses fungoides (Mita et al, presented at the AACR-NCI-EORTC Conference 2017, abs #A091).

AIMS: Herein we report preliminary efficacy and safety data from the relapsed/refractory (r/r) peripheral T-cell lymphoma (PTCL) and cutaneous T-cell lymphoma (CTCL) Phase 2 cohorts.

Methods: Pts receive treatment with ASXT660 at the RP2D 180mg/day on Days 1 to 7, and 15 to 22 in a 28-day cycle. The primary endpoint is response rate as assessed by the investigator according to either the Lugano criteria (PTCL) or Global Assessment (CTCL). Adverse events (AEs) are assessed per CTCAE V4.03.

Results: As of 15 January 2019, 16 PTCL pts and 13 CTCL pts have received ASTX660. Pt characteristics: median (range) age: PTCL: 59 (39-81) years and CTCL: 57 (23-75) years; median prior therapies: PTCL: 3 (1-7) and CTCL: 3 (1-9). In the PTCL cohort the ORR is 28% (4/14); 2 pts have yet to reach their first assessment. Three responding pts remain on study drug for 7-10 months. Responses have been observed in pts with AITL and PTCL-NOS. In the CTCL cohort the global response is 25% (3/12); 1 pt has yet to reach their first assessment. Two responding pts remain on study drug for 4-6 months. Responses have been seen in pts with large cell transformation, sezary syndrome and visceral metastases. Among all pts, the most common related AEs of any grade (≥ 15%) were lipase elevation (38%), amylase elevation (34%), ALT elevation (28%), elevation (24%) and rash (24%). Related AEs ≥ Grade 3 occurring in ≥3 pts were rash (n=5) and lipase elevation (n=4). Accrual continues; updated efficacy and safety data will be presented at the meeting.

Conclusion: In ongoing Phase 2 cohorts ASTX660 has shown activity against PTCL and CTCL with manageable safety profile. These early data support continued development of ASXT660 for the treatment of r/r PTCL and CTCL. Correlative studies are aimed at identifying predictors of response.

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Preliminary Results of ASTX660, a Novel Non-Peptidomimetic cIAP1/2 and XIAP Antagonist, in Relapsed/Refractory Peripheral T-Cell Lymphoma and Cutaneous T-Cell Lymphoma