Efficacy of dual-specific Bcr-Abl and Src-family kinase inhibitors in cells sensitive and resistant to imatinib mesylate

Abstract

Monotherapy of chronic myeloid leukemia (CML) with imatinib mesylate has been cast into shadow by the evolution of clinical resistance during therapy. Resistance to imatinib can arise by multiple mechanisms including amplification or mutation of Bcr-Abl, and continuity of imatinib therapy is probably a poor option for either of these patient groups. Recently, however, a structurally distinct new class of drugs, the pyrido[2,3-d]pyrimidines, has been described, and these compounds are predicted to make different molecular contacts in the Abl kinase domain. These drugs potently target both the Bcr-Abl and Src-family kinase activities, both of which are thought to be relevant to survival of the leukemic cell. We asked whether these drugs could selectively induce cell death in murine cell line models of CML cells sensitive and resistant to imatinib by different mechanisms. We show that whereas the pyrido [2,3-d] pyrimidines are indeed highly potent in suppressing proliferation of Bcr-Abl-overexpressing imatinib-resistant cells, they are almost completely ineffective against cells expressing the T315I mutant. This implies that despite structural differences from imatinib, these drugs are unlikely to be useful in patients expressing this mutant Bcr-Abl protein, but may be effective in cases where selection of cells overexpressing the oncoprotein leads to refractoriness to imatinib.

Dual targeting of Src and ER prevents acquired antihormone resistance in breast cancer cells

“…We and others have recently identified a role for Src kinase in acquired endocrine resistance in vitro [11,19], where it may regulate both proliferative and invasive responses in such cells. Data is emerging which reveals Src kinase as a novel tumour target, where its inhibition is effective at suppressing proliferation and/or metastatic events in a wide range of tumour types including CML [30,31], colon tumours [32,33] and pancreatic cancer [34,35]. Further studies [36,37] also provide compelling evidence that targeting Src may be of value in combination with existing chemotherapy to provide an augmented antitumour response.…”

Sustained regression of tumors upon MYC inactivation requires p53 or thrombospondin-1 to reverse the angiogenic switch

“…Understanding the molecular mechanisms of tumor escape from oncogene dependence may lead to the development of more effective targeted therapeutics for cancer treatment (15,17,18).…”

Assaying Bcr-Abl kinase activity and inhibition in whole cell extracts by phosphorylation of substrates immobilized on agarose beads

“…AG 957, Genestein, PD 1666326, and PD 173955 were compared with IM. AG 957 and Genestein are considered to be nonspecific PTK inhibitors, whereas PD 1666326 and PD 173955 are Src/Abl dual-specificity inhibitors that have been evaluated as alternatives to IM [34,35]. As shown in Fig.…”

“…Indeed, conventional assays typically require kinases to be immunopurified from cell extract or affinity-purified from recombinant expression systems and then combined with a peptide or recombinant protein substrate. Classically, kinase activity has been assayed via incorporation of radionuclides from ATP-γ- 32 P or ATP-γ- 35 S and then detected by filter binding or electrophoresis and autoradiography [13][14][15]. Recently, detection with phosphospecific antibodies has provided a viable alternative to radioactive nucleotides.…”