Feng, Xiaodong_ Xie, Hong-Guang - Applying pharmacogenomics in therapeutics-CRC Press (2016)

120 Applying Pharmacogenomics in Therapeutics
allows phosphorylation of ALK without stimulation, which results in constitutively
activated ALK and signaling pathways that may abnormally increase cell proliferation
and cancer formation. EML4-ALK-positive lung cancers are found in patients
of all ages, although on average these patients may be somewhat younger. ALK lung
cancers are more common in light cigarette smokers or nonsmokers, but a significant
number of patients with this disease are current or former cigarette smokers. EML4-
ALK rearrangement in NSCLC is exclusive and not found in EGFR- or KRASmutated
tumors.
The gold standard test used to detect ALK rearrangements in tumor samples is
FISH by the US FDA–approved Vysis ALK Break Apart Rearrangement Probe kit
from Abbott Molecular. The FISH probe for the ALK gene region is labeled with dual
colors—Spectrum Orange and Spectrum Green (Figure 5.2c). Normal cells have two
signals with fusion color-yellow, whereas abnormal cells exhibit one fusion color (yellow)
and separated color of green and orange due to inversion of the chromosome
leading to break apart of the two-colored probe. A second method to detect ALK rearrangements
is IHC using an antibody specifically bound to the ALK protein. Roche
Ventana has got the approval of Chinese FDA and EMA to detect ALK protein by
IHC using anti-ALK (D5F3) rabbit monoclonal primary antibody in formalin-fixed,
paraffin-embedded neoplastic tissue. The result should be interpreted by a qualified
pathologist in conjunction with histological examination, relevant clinical information,
and appropriate controls. Molecular techniques, such as RT-PCR, can also be used to
detect ALK gene fusion in lung cancers, but it is not recommended.
ALK inhibitors are available for the treatment of EML4-ALK-positive NSCLC.
Crizotinib (Xalkori ® ), produced by Pfizer (www.pfizer.com), was approved by the
US FDA for the treatment of late-stage lung cancer patients positive for an ALK rearrangement
without regard to line of therapy. Compared to chemotherapy, patients
receiving crizotinib treatment experienced a higher ORR, longer PFS, and better
HRQOL (Kazandjian et al. 2014; Qian et al. 2014).
However, patients treated with ALK inhibitors may also experience acquired
resistance due to various mechanisms, such as secondary mutations within the ALK
tyrosine kinase domain, amplification of ALK fusion gene, amplification of KIT,
mutations in KRAS, increased autophosphorylation of the EGFR, and activation of
the EGFR signaling pathways. Another concern for crizotinib is a relatively low
penetration of the blood–brain barrier (BBB).
The second-generation ALK inhibitors have potential therapeutic advantages
compared with crizotinib. Recently, ceritinib (Zykadia ), produced by Novartis
(www.novartis.com), was approved by the US FDA to treat ALK-positive metastatic
NSCLC patients who experience acquired resistance or are intolerant to crizotinib.
Ceritinib is a more potent and selective ALK inhibitor than crizotinib. Another
second-generation ALK inhibitor, alectinib, has been recently approved by the
Japanese Ministry of Health, Labour and Welfare (MHLW) for the treatment of
ALK-positive NSCLC patients. Alectinib seems to show better penetration of the
BBB based on studies for treatment of patients with tumors metastasized to the
brain. This ALK inhibitor was granted Breakthrough Therapy Designation (BTD)
by the US FDA for ALK-positive patients who progressed while on crizotinib.
BTD is designed to expedite the development and review of medicines intended to