Chemotherapy resistance and relapse are two of the main causes of death in patients with acute myeloid leukemia (AML). Thus, the development of novel chemotherapy-free approaches is crucial for these patients. Such targeted antibody-based or cell-based therapies including; chimeric antigen receptor T cells (CAR-T), antibody-drug conjugates (ADCs), bispecific T-cell engagers (BiTEs) and dual affinity retargeting (DART) antibodies.
During the 2019 Society of Hematologic Oncology (SOHO) annual meeting, in Houston, TX, US, two presentations showcased chemotherapy-free approaches for the treatment of AML. Elizabeth Budde from City of Hope National Medical Center, Duarte, CA, US, presented the current landscape of CAR-T trials for AML1, while, John DiPersio from Washington University School of Medicine in St. Louis, St. Louis, MO, US, spoke about the use of ADCs, DARTs and BiTEs in the clinical setting of AML.2 We hereby provide a summary of these talks regarding the latest updates on these chemotherapy-free approaches for the treatment of AML.
CAR-T trial landscape in AML1
One of the major challenges of CAR-T therapy for AML is the identification of a good CAR-T target, which should only or primarily be expressed by leukemic stem cells, so as to avoid CAR-T cell resistance and off-target toxicities. Such a target is yet to be identified with multiple options being evaluated pre-clinically (i.e. CD7, CD25, CD32, CD38, CD47 etc.). At the moment, the CAR-T constructs that have made it to the clinic target CD33, CD123, NKG2DL or LewisY.1 Some of the ongoing clinical trials using the CAR-Ts mentioned above are shown in Table 1.
Table 1. Ongoing CAR-T trials in AML1
|CAR-T target||Clinical trial ID||CAR||T cell source||Patient age (years)||Lymphodepletion||CAR-T dose||Efficacy & safety|
|CD33||NCT01864902 China||Lentivirus 4-1BB||Auto or allo||5-90||None in one patient||4.25x108 in one patient||One patient with transient blast reduction>50% at week 2
Fevers and hyperbilirubinemia
|NCT03126864||Lentivirus 4-1BB||Auto||1-80||Fludarabine (Flu) Cytarabine (Cy)||N/A||N/A|
|NCT02799680China||Lentivirus||Allo||≥ 50||Idarubicin Cy||N/A||N/A|
|LewisY||NCT01716364||RetrovirusCD28||Auto||≥ 18||Fludarabine (Flu)Cytarabine (Cy)||1.48-9.2x108||One patient achieved cytogenic complete response (CR)|
||RetrovirusDAP10||Auto||≥ 18||None||3x108-3x109||3/8 patients responded41% CRS3/10 grade 3-4 CRS|
|CD123||Lentivirus CD28||Auto or allo||≥ 12||Flu/Cy||50-500x106||N/A|
|mRNA electroporation 4-1BB||Auto||≥ 18||None or Cy||4x106/kg x 4 4x106/kg x 6||No anti-AML activityGrade1-4 CRS but no neurotoxicity or hematological toxicity|
|NCT03190278||Lentivirus 4-1BB||Universal donor||18-75||Flu/Cy||6.25x104/kg 6.25x106/kg||One patient death; trial reopened 11.2017|
|NCT03766126||Lentivirus 4-1BB||Auto||≥ 18||Flu/Cy||2x106/kg||N/A (opened 02.2019)|
The speaker highlighted that CAR-T therapy for AML is still at early stages with multiple ongoing and planned trials worldwide on different molecular targets (Table 1). CD123 and NKG2D targeted CAR-T treatment has led to encouraging early data with regards to feasibility, tolerability and patient responses. As Elizabeth Budde pinpointed, the ways to improve the effectiveness of CAR-T therapies for AML involve the optimization not only of the manufacturing but also the CAR-T design and dosing. Moreover, combination treatments with immunomodulatory drugs and dual-targeting therapies carry great potential for AML patients and should be further investigated.1
ADCs, DARTs & BiTEs for AML2
To date, there are eight clinical trials investigating the efficacy and safety of bispecific antibodies for the treatment of AML. These are shown in Table 2.2
Table 2. Bispecific DART antibodies in clinical trials for AML2
|Dual targets||Clinical trial ID||Drug name||Sponsor||Status|
|CD123 & CD3||NCT02715011||JNJ-63709178||Janssen||Suspended|
|CD33 & CD3||NCT02520427||AMG 330||Amgen||Recruiting|
|CLL1 & CD3||NCT03038230||MCLA-117||Merus||Recruiting|
* Preliminary data are described below
The speaker presented preliminary data from the phase I trial of flotetuzumab (FLZ), the humanized DART that targets CD3 and CD123 as explained below.
- FLZ was administered intravenously to n= 50 patients with relapsed/refractory AML at the stepwise dosing schedule from 30ng/kg at Day one to 500 ng/kg and at Day seven (week one)
- During weeks 2-4, patients received 500ng/kg of FLZ per day of cycle one and a four days on/ three days off schedule for cycle two onwards
- The recommended phase II dose of FLZ was 500ng/kg per day administered as a seven day/week continuous intravenous infusion
- Among the patients with primary refractory AML (62%), 32% achieved a complete response (CR)
- FLZ was well tolerated especially due to the stepwise escalation with mild tp moderate CRS events of short duration with a median of one day (grade one: 82%; grade two: 76%; grade three: 8%; grade four: 0%)
Last but not least, the investigators showed that PD-L1 expression was linked to decreased FLZ activity, as patients who progressed early (< 15 days) had significantly higher PD-L1 expression. Further results are expected the expansion cohort and an additionally planned FLZ plus MGA012 (anti-PD1) cohort.
- n= 40 enrolled patients with R/R AML, aged ³ 18 with high-risk disease
- Study design 3+3
- AMV564 was administered on a 14-day continuous stepwise dose escalation from 0.5-15mg on Day one to 450mg on Day 14
- Thirty-three patients have been dosed to date
- Treatment was well-tolerated with no donor lymphocyte infusions and grade 1-2 CRS events
- One long duration (7 months) CRi was observed and one stable disease at seven months
- AMV564 led to quick and selective depletion of leukemic blasts and myeloid-derived suppressor cells (MDSCs) was observed by flow cytometry
- Further results are expected from this ongoing trial in the near future
This is an exciting time for the clinical setting of R/R AML as numerous CAR-Ts, ADCs, BiTEs/DARTs are under pre-clinical and early clinical investigation. With many of these chemotherapy-free therapies showing promising activity and tolerability, it is certain that the future of patients with R/R AML seems more hopeful than ever.