Abstract 2587: Dasatinib-induced reduction of tumor growth is accompanied by the changes in the immune profile in melanoma B16.OVA mouse model
Authors: Hekim Can , Ilander Mette , Vähä-Koskela Markus , Savola Paula , Tähtinen Siri , Hemminki Akseli , Porkka Kimmo , Mustjoki Satu 
Published: May 2015

Dasatinib, a tyrosine kinase inhibitor used in the treatment of chronic myeloid leukemia and acute lymphoblastic leukemia, has been shown to exert immunomodulatory effects in addition to direct oncokinase inhibition. Recently, we observed that dasatinib induces a rapid (within one hour after oral administration) and marked mobilization of lymphocytes (up to 8-fold increase in lymphocyte count), which closely follows the drug plasma concentration. In addition, in a subgroup of patients a clonal expansion of large granular lymphocytes occurs, which is correlated with good therapy response.

As dasatinib-induced immunomodulatory effects are not leukemia specific, we aimed to exploit this activity to slow down or inhibit the growth of a syngeneic murine melanoma model and to characterize in detail the anti-tumor immune responses.

Ovalbumin expressing murine melanoma cell line B16.OVA was grown under the skin of immunocompetent mice. The mice (n=6/group) were treated daily i.g. either with 30 mg/kg dasatinib or vehicle only. Blood was collected before tumor transplantation, before treatment, and on treatment days 4, 7 and 10. Tumor volumes were measured manually and specific growth rate was calculated based on the first and the last day of the treatment. In addition to white blood cell differential counts, immunophenotyping of blood and tumor homogenate was done by flow cytometry using antibodies against CD45.1, CD3, CD4, CD8b and NK1.1, and SIINFEKL-pentamer to detect B16.OVA-specific cells. To assess the functional properties of lymphocytes, we used antibodies against immune checkpoint inhibitors CTLA-4 and PD-1, and a degranulation marker CD107.

On the 10th day of treatment, the tumor volumes were smaller in dasatinib group compared to control group, and there was a significant decrease in the tumor growth rate (0.06 vs. 0.18, p=0.01). Furthermore, dasatinib treated mice had increased proportion of CD8+ cells in the circulation (21% vs. 14%, p=0.04) and the CD4/CD8 ratio was significantly decreased (1.39 vs. 1.52, p= 0.04). During the tumor growth the mean CTLA-4 expression on CD8+ cells increased from 1.2% to 9% in the control group, whereas, in dasatinib group the increase was more modest (1.2% to 5.7%). Interestingly, 80% of tumor infiltrating CD8+ cells expressed PD1 antigen compared to &lt;5% of PD1 positive CD8+ cells in the peripheral blood suggesting lymphocyte anergy or exhaustion induced by tumor cells.

To conclude, dasatinib treatment slowed down the tumor growth in B16.OVA mouse model, which could be associated with the immunomodulatory effects of dasatinib. However, combinatorial treatment regimens may be needed as dasatinib is not able to fully break the immune cell anergy induced by tumor cells.

Citation Format: Can Hekim, Mette Ilander, Markus Vähä-Koskela, Paula Savola, Siri Tähtinen, Akseli Hemminki, Kimmo Porkka, Satu Mustjoki. Dasatinib-induced reduction of tumor growth is accompanied by the changes in the immune profile in melanoma B16.OVA mouse model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2587. doi:10.1158/1538-7445.AM2014-2587