Bcr-Abl mutations, resistance to imatinib, and imatinib plasma levels

Nanoformulations of small molecule protein tyrosine kinases inhibitors potentiate targeted cancer therapy

Protein tyrosine kinases (PTKs) are closely related to tumor development and usually participate in apoptosis, DNA repair, and cell proliferation by activating signaling pathways. Therefore, PTKs have become the most promising targets for cancer therapy. In recent years, a large number of studies on the mechanism of tyrosine kinase activation have indicated that tyrosine kinase inhibitors (TKIs) have important clinical significance and application prospects as targeted anticancer drugs because they can effectively block certain cellular signaling pathways, inhibit tumor metastases and reduce tumor proliferation. Although the increasing emergence of anticancer drug resistance limits the clinical application of TKIs, emerging nanotechnology has made it possible to solve this problem. In this work, the state-of-art of small molecule protein tyrosine kinase inhibitors and the applications of drug delivery systems for TKIs are reviewed, and the potentials and challenges for future research of small molecule TKIs are addressed.

Expanding the portfolio of anti-ALK weapons

The anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase involved in the onset of several malignancies. In particular, ALK is the driving oncogenic lesion in a small but significant fraction of non-small cell lung cancer (NSCLC) patients. ALK+ NSCLCs can be treated with the dual ALK/MET inhibitor crizotinib, with better outcome compared to standard chemotherapy. However, relapses frequently occur, due to various mechanisms, limiting overall efficacy of the treatment. Point mutations within the ALK catalytic domain or ALK gene amplification account for approximately 30-40% of crizotinib-resistant cases, suggesting that the diseases still relies on ALK activity and that more potent inhibitors could be useful in this setting. Ceritinib is a novel selective ALK inhibitor with preclinical activity against crizotinib-resistant ALK mutants. A recent article in the New England Journal of Medicine reports on clinical evaluation of ceritinib. Response rate and progression-free survival (PFS) were comparable to crizotinib, but most importantly, crizotinib-resistant patients were successfully treated, with efficacy similar to crizotinib-naïve patients. The study extends the array of available anti-ALK drugs. Based on these data, ceritinib was approved by FDA in April 2014.

Nilotinib based pharmacophore models for BCRABL

Tyrosine kinase inhibitors have revolutionized the treatment of several malignancies, converting lethal diseases in a manageable aspect. Imitanib, a small molecule ABL kinase inhibitor is a highly effective therapy for early phase chronic myeloid leukemia (CML), which has constitutively active ABL kinase activity owing to the over expression of the BCR-ABL fusion protein. But some patients develop imatinib resistance, particularly in the advanced phases of CML.The discovery of resistance mechanisms of imitanib; urge forward the development of second generation drugs. Nilotinib, a second generation drug is more potent inhibitor of BCR-ABL than imatinib. But nilotinib also develops dermatologic events and headache in patients. Large information about BCR-ABL structure and its inhibitors are now available. Based on the pharmacophore modeling approaches, it is possible to decipher the molecular determinants to inhibit BCR-ABL. We conducted a structure based and ligand based study to identify potent natural compounds as BCR-ABL inhibitor. First kinase inhibitors were docked with the receptor (BCR-ABL) and nilotinib was selected as a pharmacophore due its high binding efficiency. Eleven compounds were selected out of 1457 substances which have mutual pharmacopohre features with nilotinib. These eleven compounds were validated and used for docking study to find the drug like molecules. The best molecules from the final set of screening candidates can be evaluated in cell lines and may represent a novel class of BCR-ABL inhibitors.

ABBREVIATIONS

CML - Chronic myeloid leukemia, PDGFR - Platelet derived growth factor receptor, TKI - Tyrosine kinase inhibitors.

Imatinib assay by HPLC with photodiode-array UV detection in plasma from patients with chronic myeloid leukemia: Comparison with LC-MS/MS

BACKGROUND

Imatinib, a competitive inhibitor of BCR-ABL tyrosine kinase, is now the first-line treatment for chronic myelogenous leukemia (CML). Therapeutic drug monitoring targeting trough plasma levels of about 1000ng/mL may help to optimize the therapeutic effect.

METHODS

We developed a high-performance liquid chromatography (HPLC) method with UV/Diode Array Detection (DAD) for trough imatinib concentration determination in human plasma. Imatinib trough levels were measured in plasma from 65 CML patients using our method and LC-MS/MS as the reference method. Results with these two methods were compared using Deming regression, chi-square test, and sign test.

RESULTS

The calibration curve was prepared in blank human plasma. HPLC-UV/DAD calibration curves were linear from 80 to 4000ng/mL, and the limit of quantification was set at 80ng/mL. The between-day variation was 6.1% with greater than 96% recovery after direct plasma deproteinization and greater than 98% recovery from the column. No significant differences in imatinib plasma levels were found between HPLC-UV/DAD and LC-MS/MS.

CONCLUSIONS

This HPLC-UV/DAD method was sufficiently specific and sensitive for imatinib TDM, with no evidence of interference. Our rapid inexpensive HPLC-UV/DAD method that requires only widely available equipment performs well for plasma imatinib assays.

Two different point mutations in ABL gene ATP-binding domain conferring Primary Imatinib resistance in a Chronic Myeloid Leukemia (CML) patient: A case report

Imatinib (Gleevec) is the effective therapy for BCR-ABL positive CML patients. Point mutations have been detected in ATP-binding domain of ABL gene which disturbs the binding of Gleevec to this target leading to resistance. Detection of mutations is helpful in clinical management of imatinib resistance. We established a very sensitive (ASO) PCR to detect mutations in an imatinib-resistant CML patient. Mutations C944T and T1052C were detected which cause complete partial imatinib resistance, respectively. This is the first report of multiple point mutations conferring primary imatinib resistance in same patient at the same time. Understanding the biological reasons of primary imatinib resistance is one of the emerging issues of pharmacogenomics and will be helpful in understanding primary resistance of molecularly-targeted cancer therapies. It will also be of great utilization in clinical management of imatinib resistance. Moreover, this ASO-PCR assay is very effective in detecting mutations related to imatinib resistance.