Simvastatin enhances the efficacy of nilotinib in chronic myeloid leukaemia by post-translational modification and drug transporter modulation.

The resistance of chronic myeloid leukaemia (CML) to tyrosine kinase inhibitors (TKIs) remains a significant clinical problem. Targeting alternative pathways, such as protein prenylation, is known to be effective in overcoming resistance. Simvastatin inhibits 3-hydroxy-3-methylglutaryl-CoA reductase (a key enzyme in isoprenoid-regulation), thereby inhibiting prenylation. We demonstrate that simvastatin alone effectively inhibits proliferation in a panel of TKI-resistant CML cell lines, regardless of mechanism of resistance. We further show that the combination of nilotinib and simvastatin synergistically kills CML cells via an increase in apoptosis and decrease in prosurvival proteins and cellular proliferation. Mechanistically, simvastatin inhibits protein prenylation as shown by increased levels of unprenylated Ras and rescue experiments with mevalonate resulted in abrogation of synergism. The combination also leads to an increase in the intracellular uptake and retention of radio-labelled nilotinib, which further enhances the inhibition of Bcr-Abl kinase activity. In primary CML samples, this combination inhibits clonogenicity in both imatinib-naive and resistant cells. Such combinatorial effects provide the basis for utilising these Food and Drug Administration-approved drugs as a potential clinical approach in overcoming resistance and improving CML treatment.

In-vitro modeling of TKI resistance in the high-risk B-cell acute lymphoblastic leukemia fusion gene RANBP2-ABL1 - implications for targeted therapy.

Acute lymphoblastic leukemia remains a leading cause of cancer-related death in children. Furthermore, subtypes such as Ph-like ALL remain at high-risk of relapse, and treatment resistance remains a significant clinical issue. The patient-derived Ph-like ALL RANBP2-ABL1 fusion gene was transduced into Ba/F3 cells and allowed to become resistant to the tyrosine kinase inhibitors (TKIs) imatinib or dasatinib, followed by secondary resistance to ponatinib. RANBP2-ABL1 Ba/F3 cells developed the clinically relevant ABL1 p.T315I mutation and upon secondary resistance to ponatinib, developed compound mutations, including a novel ABL1 p.L302H mutation. Significantly, compound mutations were targetable with a combination of asciminib and ponatinib. In-vitro modeling of Ph-like ALL RANBP2-ABL1 has identified kinase domain mutations in response to TKI treatment, that may have important clinical ramifications. Early detection of mutations is paramount to guide treatment strategies and improve survival in this high-risk group of patients.

Inhibition of isoprenylcysteine carboxylmethyltransferase augments BCR-ABL1 tyrosine kinase inhibition-induced apoptosis in chronic myeloid leukemia.

Despite the success of BCR-ABL1 tyrosine kinase inhibitors in patients with chronic myeloid leukemia (CML), resistance to tyrosine kinase inhibitors remains a therapeutic challenge. One strategy used to overcome resistance is combination of existing BCR-ABL1 tyrosine kinase inhibitors with agents that target alternative pathways. We report that inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt), a key enzyme in the protein prenylation pathway, with the selective inhibitor cysmethynil enhances the effect of BCR-ABL1 tyrosine kinase inhibitors in killing CML cells. Cysmethynil augments tyrosine kinase inhibitor-induced apoptosis in both BCR-ABL1 wild type and BCR-ABL1 kinase domain mutant-expressing cell lines. Importantly, the enhanced apoptosis observed with the combination of cysmethynil and imatinib is significant only in primary CML CD34+ progenitor cells, not normal cord blood progenitor cells. The combination was also selective in inhibiting colony formation in CML CD34+ cells. The enhanced apoptosis appears to be due to combination of immediate and persistent inhibition of MAPK signaling. Consistent with in vitro studies, cysmethynil and imatinib, in combination, enhance the in vivo effects of either drug used alone. We found that simultaneous inhibition of BCR-ABL1 and Icmt may represent a potential therapeutic strategy for CML.

Pyrvinium selectively targets blast phase-chronic myeloid leukemia through inhibition of mitochondrial respiration.

The use of BCR-ABL1 tyrosine kinase inhibitors (TKI) has led to excellent clinical responses in patients with chronic phase chronic myeloid leukemia (CML). However these inhibitors have been less effective as single agents in the terminal blast phase (BP). We show that pyrvinium, a FDA-approved anthelminthic drug, selectively targets BP-CML CD34+ progenitor cells. Pyrvinium is effective in inducing apoptosis, inhibiting colony formation and self-renewal capacity of CD34+ cells from TKI-resistant BP-CML patients, while cord blood CD34+ are largely unaffected. The effects of pyrvinium are further enhanced upon combination with dasatinib, a second generation BCR-ABL1 TKI. In a CML xenograft model pyrvinium significantly inhibits tumor growth as a single agent, with complete inhibition in combination with dasatinib. While pyrvinium has been shown to inhibit the Wnt/ß-catenin signalling pathway via activation of casein kinase 1α , we find its activity in CML is not dependent on this pathway. Instead, we show that pyrvinium localizes to mitochondria and induces apoptosis by inhibiting mitochondrial respiration. Our study suggests that pyrvinium is a useful addition to the treatment armamentarium for BP-CML and that targeting mitochondrial respiration may be a potential therapeutic strategy in aggressive leukemia.