Anaplastic lymphoma kinase: role in cancer pathogenesis and small-molecule inhibitor development for therapy

Abstract

Anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase in the insulin receptor superfamily, was initially identified in constitutively activated oncogenic fusion forms - the most common being nucleophosmin-ALK - in anaplastic large-cell lymphomas, and subsequent studies have identified ALK fusions in diffuse large B-cell lymphomas, systemic histiocytosis, inflammatory myofibroblastic tumors, esophageal squamous cell carcinomas and non-small-cell lung carcinomas. More recently, genomic DNA amplification and protein overexpression, as well as activating point mutations, of ALK have been described in neuroblastomas. In addition to those cancers for which a causative role for aberrant ALK activity is well validated, more circumstantial links implicate the full-length, normal ALK receptor in the genesis of other malignancies - including glioblastoma and breast cancer - via a mechanism of receptor activation involving autocrine and/or paracrine growth loops with the reported ALK ligands, pleiotrophin and midkine. This review summarizes normal ALK biology, the confirmed and putative roles of ALK in the development of human cancers and efforts to target ALK using small-molecule kinase inhibitors.

Figure 1

(A) ALK receptor tyrosine kinase and the NPM–ALK fusion protein created by t(2;5). Fusion of the chromosome 5 gene encoding NPM to the chromosome 2 gene encoding ALK generates the chimeric tyrosine kinase, NPM–ALK. NPM contains an OD (residues 1–117) a putative MB (residues 104–115), two ADs (Asp/Glu-rich acidic domain; residues 120–132 and 161–188) that function as acceptor regions for nucleolar targeting signals and two NLS (residues 152–157 and 191–197). ALK contains a single MAM domain, a region of approximately 170 aa homologous to the extracellular portions of a number of functionally diverse proteins that may have an adhesive function (residues 480–635). The LBS for pleiotrophin and midkine (ALK residues 391–401) is indicated. Note that the entire intracytoplasmic portion of ALK, exclusive of the TM, is incorporated into the NPM–ALK and all other ALK chimeric proteins. (B) Representative ALK fusion proteins, the chromosomalrearrangements that generate them, their occurrence in ALK-positivelymphomas and IMTs and their subcellular localizations. A partiallisting of the more common oncogenic ALK fusions is shown; a total of15 different ALK fusions have now been described (those not shown are ALO17–ALK, CARS–ALK, MYH9–ALK, SEC31L1– ALK and TFGXL–ALK). The exact frequency of the various ALK fusions expressed in IMT has not yet been determined. To date, six ALK fusions (CARS–ALK, CLTC–ALK, RANBP2–ALK, SEC31L1–ALK, TPM3–ALK and TPM4–ALK) have been identified in IMT. The TPM3–ALK, TPM4–ALK and CLTC–ALK fusions have been detected in both classical null or T-cell anaplastic large-cell lymphomas and IMT, whereas CARS-ALK, RANBP2–ALK and SEC31L1–ALK occur in IMT but have not yet been described in anaplastic large-cell lymphoma. CLTC–ALK and, to a lesser extent, NPM–ALK, also occur in rare B-cell plasmablastic/immunoblastic non-Hodgkin’s lymphomas. Two independent reports have also recently described the occurrence of the TPM4–ALK fusion in squamous cell carcinomas of the esophagus [177,178], and several studies have identified the presence of the novel ALK fusion, EML4–ALK, in a subset of non-small-cell lung cancers [180-187]. aa: Amino acid; AD: Acidic amino acid domain; ALK: Anaplastic lymphoma kinase; ATIC: 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase; C: Cytosolic; CLTC: Clathrin heavy chain; CM: Cell membrane; EML: Echinoderm microtubule-associated protein-like; LBS: Ligand-binding site; IMT: Inflammatory myofibroblastic tumor; MAM: Meprin/A5/protein tyrosine phosphatase Mu; MB: Metal-binding domain; MSN: Moesin; N: Nuclear; NLS: Nuclear localization signal; NPM: Nucleophosmin; NM: Nuclear membrane; OD: Oligomerization domain; RanBP2: Ran-binding protein 2; TFG: TRK-fused gene; TK: Tyrosine kinase catalytic domain; TM: Transmembrane domain; TPM3: Non-muscle tropomyosi.

Figure 2

Selected tyrosine kinase inhibitors approved for clinical anticancer indications.

Figure 3

Small molecules shown experimentally to inhibit a ‘gatekeeper residue-mutant’ form of anaplastic lymphoma kinase (ALK; L256T-NPM–ALK) but not wild-type ALK.

Figure 4

Naturally occurring inhibitors of anaplastic lymphoma kinase and selected derivative compounds.

Figure 5. Staurosporine-based anaplastic lymphoma kinase (ALK) inhibitors from Cephalon

In contrast to CEP-14083 and CEP-14513, both of which are potent ALK inhibitors (enzymatic IC₅₀ 2–4 nM; cellular IC₅₀ 10–30 nM for both), the structurally related CEP-11988 displays only weak ALK inhibition (enzymatic IC₅₀ > 20 μM; IC₅₀ for inhibition of cell-based ALK tyrosine phosphorylation > 30 μM). From [221].

Figure 6

ChemBridge–St Jude pyridone-based anaplastic lymphoma kinase inhibitor.

Figure 7

ChemBridge–St Jude IGF1 receptor-targeted inhibitor with anaplastic lymphoma kinase-inhibitory activity.

Figure 8

Amino-pyrimidine anaplastic lymphoma kinase inhibitors from Novartis.

Figure 9

PHA-665752, a MET (hepatocyte growth factor/scatter factor receptor)-selective inhibitor that has provided insight for anaplastic lymphoma kinase inhibitor design.

Figure 10

The Pfizer dual anaplastic lymphoma kinase/MET (hepatocyte growth factor/scatter factor receptor) inhibitor PF-2341066.

Figure 11. Dose-dependent anticancer activity of PF-2341066 in a Karpas-299 xenograft model

Immunocompromized mice bearing established (200-mm³) subcutaneous tumors of the human nucleolar protein nucleophosmin–anaplastic lymphoma kinase (ALK)-positive anaplastic large-cell lymphoma cell line Karpas-299 were treated with the Pfizer dual ALK/MET (hepatocyte growth factor/scatter factor receptor) inhibitor PF-2341066 at the indicated dosing regimens or with vehicle only. Treatments were administered from day 11 to day 23 except for the 100 mg/kg group, which received treatment through day 28. The mean tumor volumes at the time of the final measurements were significantly less in each of the three treatment groups compared with the control cohort (p < 0.001, one-way ANOVA). A subset of the mice treated at the 100 mg/kg/day dose of PF-2341066 (three mice total) experienced tumor regrowth after prolonged observation following the cessation of therapy; the tumors in these mice underwent complete regression again following a 13-day course of PF-2341066 100 mg/kg/day (not shown). p.o.: Orally; q.d.: Once daily. Modified with permission from [231].

Figure 12

Dual anaplastic lymphoma kinase/MET (hepatocyte growth factor/scatter factor receptor) inhibitor from Cephalon.