Abstract 536: Excessive HCK kinase activity in the tumor stroma promotes colorectal cancer progression

Excessive activation of the myeloid-specific Src-family kinase Hematopoietic Cell Kinase (HCK) acts as a tumor intrinsic oncogene by promoting proliferation and survival of immune cells, and confers a poor prognosis for leukemia. However, the role of HCK in the tumor stroma of solid malignancies remains unexplored. We analyzed the expression level of HCK in matched biopsies from sporadic colorectal cancer patients and observed elevated HCK phosphorylation in tumors compared to unaffected colons. Analysis of corresponding RNAseq data revealed a striking correlation between tumors with high HCK gene expression and a gene signature indicative of a tumor-promoting alternatively-activated macrophage (AAM) endotype. To functionally assess this observation, we exploited HckCA mice [Ernst et al., J Exp Med 2002] that express a constitutively active form of Hck as a knockin mutation, and subjected these mice to a chemically-induced model of sporadic colorectal cancer. HckCA mice developed more and larger tumors compared to wild-type (WT) animals, and this was associated with a significant bias towards CD206+ AAMs in tumors of HckCA mice without affecting the total number of tumor-associated leukocyte and lymphocytes. Likewise, adoptive bone-marrow transfer experiments revealed enhanced tumor formation and AAM differentiation in WT mice reconstituted with HckCA bone marrow, with a reciprocal decrease of these parameters in HckCA mice reconstituted with WT marrow. Finally, pharmacologic targeting of the catalytic activity of Hck with a small molecule inhibitor significantly reduced tumor progression and impaired AAM polarisation. Collectively, our findings suggest that excessive Hck activity in the tumor stroma promotes the progression of solid cancers by modulating the endotype of tumor-associated myeloid cells. Therefore, Hck represents a rational therapeutic target for macrophage re-education in solid cancers by limiting polarization of tumor-promoting AAM. Citation Format: Matthias Ernst, Ashleigh Poh, Frederic Masson, Tracy Putoczki, Robert O’Donoghue. Excessive HCK kinase activity in the tumor stroma promotes colorectal cancer progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 536.