Are SRC family kinases responsible for imatinib- and dasatinib-resistant chronic myeloid leukemias?

Hematopoietic cell kinase (HCK) as a therapeutic target in immune and cancer cells

The hematopoietic cell kinase (HCK) is a member of the SRC family of cytoplasmic tyrosine kinases (SFKs), and is expressed in cells of the myeloid and B-lymphocyte cell lineages. Excessive HCK activation is associated with several types of leukemia and enhances cell proliferation and survival by physical association with oncogenic fusion proteins, and with functional interactions with receptor tyrosine kinases. Elevated HCK activity is also observed in many solid malignancies, including breast and colon cancer, and correlates with decreased patient survival rates. HCK enhances the secretion of growth factors and pro-inflammatory cytokines from myeloid cells, and promotes macrophage polarization towards a wound healing and tumor-promoting alternatively activated phenotype. Within tumor associated macrophages, HCK stimulates the formation of podosomes that facilitate extracellular matrix degradation, which enhance immune and epithelial cell invasion. By virtue of functional cooperation between HCK and bona fide oncogenic tyrosine kinases, excessive HCK activation can also reduce drug efficacy and contribute to chemo-resistance, while genetic ablation of HCK results in minimal physiological consequences in healthy mice. Given its known crystal structure, HCK therefore provides an attractive therapeutic target to both, directly inhibit the growth of cancer cells, and indirectly curb the source of tumor-promoting changes in the tumor microenvironment.

Src family kinases and their role in hematological malignancies

The Src family protein tyrosine kinases (SFKs) are non-receptor intracellular kinases that have important roles in both hematopoiesis and leukemogenesis. The derangement of their expression or activation has been demonstrated to contribute to hematological malignancies. This review first examines the mechanisms of SFK overexpression and hyperactivation, emphasizing the dysregulation of the upstream modulators. Subsequently, the role of SFK up-regulation in the initiation, progression and therapy resistance of many hematological malignancies is also analyzed. The presented evidence endeavors to highlight the influence of SFK up-regulation on an extensive number of hematological malignancies and the need to consider them as candidates in targeted anticancer therapy.

Src Family Kinase Inhibitor PP2 Has Different Effects on All-Trans-Retinoic Acid or Arsenic Trioxide-Induced Differentiation of an Acute Promyelocytic Leukemia Cell Line

Purpose

Leukemic promyelocytes have the unique ability to undergo differentiation after exposure to retinoic acid and both differentiation and apoptosis after exposure to arsenic trioxide (ATO). Recent studies have shown that inhibition of Src family kinases (SFKs) resulted in enhancement of retinoic acid-induced myeloid differentiation.

Materials and Methods

In this study, we investigated the question of whether the SFK inhibitor PP2 enhanced the differentiation of NB4 cells when combined with ATO as well as when combined with all-trans-retinoic acid (ATRA). In addition, we attempted to determine the difference in retinoic acid-induced gene expression between cells treated with PP2 in combination with ATRA and in combination with ATO.

Results

SFK inhibitor PP2 induced significant enhancement of ATRA- or ATO-induced differentiation of NB4 cells. A significantly stronger synergistic effect was observed when PP2 was combined with ATRA than when combined with ATO. Flow cytometric analysis demonstrated a significant increase in CD11b-positive granulocytes up to 60.73% and 31.58%, respectively. These results were confirmed by nitroblue tetrazolium staining. These effects were not related to apoptosis. Results of Annexin-V-fluorescein staining revealed that PP2 combined with ATRA or PP2 combined with ATO did not induce apoptosis in NB4 cells. Retinoic acid-induced gene expression was different in both groups. Intercellular adhesion molecule-1 expression showed a significant increase in cells treated with PP2 in combination with ATRA, whereas cathepsin D expression showed a significant increase in cells treated with PP2 in combination with ATO.

Conclusion

Our data showed that SFK inhibitor PP2 enhanced acute promyelocytic leukemia cell differentiation when combined with either ATRA or ATO with difference in activation of retinoic acid-induced genes.

Targeting Src family kinases in anti-cancer therapies: turning promise into triumph

Src is a non-receptor tyrosine kinase that is deregulated in many types of cancer. Decades of research have revealed the crucial role of Src in many aspects of tumor development, including proliferation, survival, adhesion, migration, invasion and, most importantly, metastasis, in multiple tumor types. Despite extensive preclinical evidence that warrants targeting Src as a promising therapeutic approach for cancer, Src inhibitor(s) showed only minimal therapeutic activity in various types of solid tumors when used as a single agent in recent early-phase clinical trials. In this review, we highlight the most recent advances from preclinical studies and clinical trials that shed light on potential clinical use of Src inhibitor-containing combinatorial regimens in overcoming resistance to current anticancer therapies and in preventing metastatic recurrence.

Targeting Src family kinases in anti-cancer therapies: turning promise into triumph

Src is a non-receptor tyrosine kinase that is deregulated in many types of cancer. Decades of research have revealed the crucial role of Src in many aspects of tumor development, including proliferation, survival, adhesion, migration, invasion and, most importantly, metastasis, in multiple tumor types. Despite extensive preclinical evidence that warrants targeting Src as a promising therapeutic approach for cancer, Src inhibitor(s) showed only minimal therapeutic activity in various types of solid tumors when used as a single agent in recent early-phase clinical trials. In this review, we highlight the most recent advances from preclinical studies and clinical trials that shed light on potential clinical use of Src inhibitor-containing combinatorial regimens in overcoming resistance to current anticancer therapies and in preventing metastatic recurrence.