The PTPN2/PTPN1 Inhibitor Abbv-CLS-484 Augments Immune Responses Against Leukemic Blasts and Impedes Leukemia Cell Proliferation in AML Alone and in Combination with Venetoclax

Background: The introduction of immune checkpoint inhibitors has changed tumor therapy in the last years. But reactivation of exhausted T-cells is still incompletely understood. Recently it has been revealed that the protein tyrosine phosphatases PTPN2 and PTPN1 reduce JAK, STAT1/3/5 signaling thereby abrogating T-cell receptor and cytokine responses. The novel inhibitor of PTPN1/2 phosphatases ABBV-CLS-484 has been shown to augment anti-tumor T-cell function in many solid tumor models (Baumgartner CK et al., Nature 2023). In the current study, we examined the effect of ABBV-CLS-484 in acute myeloid leukemia alone and in combination with venetoclax.

Methods: To analyze the activity of ABBV-CLS-484 alone or in combination with venetoclax in the AML setting, we examined the T-cell mediated killing of leukemic cells. In this regards, either AML cell lines were incubated with PBMC from healthy donors or primary AML blasts with their corresponding T-cells isolated from peripheral blood of AML patients. Killing was determined by FACS analysis after staining with 7-AAD. Furthermore, expression of immune checkpoints such as TIGIT, PD-1 or LAG-3 were analyzed by FACS before and after the 48h incubation of T-cells and AML cells. In addition, colony formation assays of the leukemic blasts of AML patients as well as proliferation assays of several AML cell lines in the presence of ABBV-CLS-484 and IFN were performed.

Results: T-cell mediated killing was performed in an autologous and allogeneic setting. Immune destruction of AML cells was significantly augmented by ABBV-CLS-484 in a dose dependent manner from 0.2 to 10µM. Killing of AML cell lines MV4-11, Molm13, OCI AML5 and IMS-M2 by healthy donor T-cells was significantly augmented by addition of ABBV-CLS-484 and especially in combination with venetoclax. AML blasts from 6 individual AML patients were incubated with autologous T-cells from the same patient. After 24h significantly increased destruction of AML blast by T- cells was noted with ABBV-CLS-484 compared to solvent control. This effect was more pronounced in combination with venetoclax.

As previously described, AML patient´s T-cells have an exhausted phenotype with expression of PD-1, TIGIT, LAG-3 and Tim-3. After 48h of incubation of AML blasts from 5 individual AML patients with their corresponding T-cells in the presence of ABBV-CLS-484 and venetoclax a significant reduction of these markers was noted implying a reduction of T-cell exhaustion.

Proliferation assays were performed with the AML cell lines Molm-13, MV4-11, HL60, IMS-M2, OCI AML3, OCI AML 5. After 7days a 90% reduction of cell numbers compared to solvent control was noted in the presence of 10µM ABBV-CLS-484 and 100ng/ml IFN. Colony formation assays were performed with AML cells from 11 individual AML patients. A highly significant reduction in colony number was found in the presence of ABBV-CLS-484, IFN and venetoclax implying a direct inhibitory effect on AML growth and colony forming cells.

Conclusions: Our data show that the PTPN1/2 phosphatase inhibitor ABBV-CLS-484 mediates strong anti-leukemic effects either by directly targeting AML cells or by immune cell-mediated effects. Therefore, therapy with ABBV-CLS-484 alone or in combination with venetoclax may represent a new effective therapeutic option in AML. Further investigations are warranted.