Antitumor effect of KT6124, a novel derivative of protein kinase inhibitor K-252a, and its mechanism of action

Targeting tropomyosin receptor kinase for cancer therapy

NTRKs and their expression product tropomyosin receptor kinases (Trks) are widely distributed in mammals. While neural growth factor (NGF)-induced normal Trk activation plays a key role in nerve growth, NTRK alternations occurring in tumor cells were highly correlated to tumor progression and invasion. Recent clinical data from several pan-Trk inhibitors have demonstrated potential and broad applications in various cancers. This intrigues us to summarize the development of inhibitors targeting Trks with different mechanisms of action and their applications in cancer therapy. We believe that this perspective would be of great help in investigating novel anticancer drugs with better therapeutic index.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

K252a induces anoikis-sensitization with suppression of cellular migration in Epstein-Barr virus (EBV)--associated nasopharyngeal carcinoma cells

Recent studies revealed an unexpected role of the neurotrophin receptor pathway, BDNF/TrkB signaling, in cancer metastasis and anoikis (i.e. detachment-induced cell death). Survival of cancer cells in detached state (known as anoikis-resistance) is known to be pre-requisite for metastasis. Nasopharyngeal carcinoma (NPC), an endemic head and neck cancer in Southeast Asia, is highly invasive, metastatic, and etiologically associated with Epstein-Barr virus (EBV, an oncovirus) infection. Mechanistic studies on the invasive/metastatic nature of NPC can facilitate the development of anti-metastatic therapy in NPC. Thus far, the role of BDNF/TrkB signaling in virus-associated human cancer is unclear. Here, using multiple cell line models of NPC with EBV-association (HONE-1-EBV, HK1-LMP1 and C666-1), we investigated the potential involvement of BDNF/TrkB signaling in cellular migration and anoikis-resistant characteristics of NPC. We found that all three EBV-associated NPC cell lines tested were intrinsically anoikis-resistant (i.e. survived in detached state) and expressed both BDNF and TrkB. BDNF stimulation induced cellular migration, but not proliferation of these cells. Further, we examined if pharmacologic targeting of anoikis-resistance of NPC cells can be achievable by a proof-of-concept Trk inhibitor, K252a, in these EBV-associated NPC models. Our results demonstrated that K252a, was able to attenuate BDNF-induced migration and proliferation of NPC cells. More importantly, we demonstrated for the first time that K252a harbored potent anoikis-sensitization activity (i.e. sensitizing cancer cells to detachment-induced cell death) against EBV-associated human cancer cells, namely NPC cells. This proof-of-concept study demonstrated that K252a, a Trk inhibitor, can potentially be used as an anoikis-sensitizing agent in NPC.

Striking the target in Wnt-y conditions: intervening in Wnt signaling during cancer progression

Wnt signaling can be divided into three pathways, namely the canonical Wnt/beta-catenin pathway, and the non-canonical (or heretical) Wnt/Ca(2+) and planar cell polarity (PCP) pathways. Although the canonical Wnt/beta-catenin pathway is the best described in cancer, increasing data points to the importance of the heretical Wnt pathways in several aspects of tumor progression. The recent advances in understanding the players and mechanisms by which these Wnt pathways contribute to cancer progression have led to the identification of numerous molecules that are already, or could be considered, targets for cancer therapy.

Phase I trial of orally administered CEP-701, a novel neurotrophin receptor-linked tyrosine kinase inhibitor

PURPOSE

A phase I clinical trial in patients with advanced carcinomas was conducted using the orally available neurotrophin receptor-linked tyrosine kinase receptor inhibitor, CEP-701. The objectives were to determine the maximum tolerated dose (MTD), dose-limiting toxicities, and pharmacokinetic profile of this orally administered agent.

PATIENTS AND METHODS

A total of 30 patients were accrued to receive escalating BID doses of CEP-701 in cycles lasting 28 days. Between 3 and 6 patients were enrolled at each dose level. Once the MTD was determined, nine de novo patients were recruited to receive that level of drug. Pharmacokinetic studies were performed after the first dose, with additional sampling to assess intraindividual variability.

RESULTS

The dosages ranged from 5 mg BID to 160 mg BID. While the criteria for MTD were not met at the dose levels administered, DLTs were observed at 80 and 120 mg BID. Treatment related adverse events, especially of the gastrointestinal system, made CEP-701 poorly tolerated at dosages above 40 mg BID. While CEP-701 did not produce an objective tumor response in any patient, 7 of the 30 patients received treatment for 3 months or more, including 3 who were on study with stable disease for more than 6 months. Orally administered CEP-701 was rapidly absorbed, with a mean t(max) between 1 and 3 hours. At higher dose levels, serum drug levels showed greater than dose-proportional increases by Day 28 versus Day 1.

CONCLUSION

CEP-701 40 mg BID was well tolerated by patients with advanced malignancy and is the recommended dose level for planned phase II trials. Further study is necessary to determine the clinical efficacy of this novel new chemotherapeutic agent.

K252a inhibits the oncogenic properties of Met, the HGF receptor

The ATP analog K252a is a potent inhibitor for receptor tyrosine kinases of the Trk family. Here we show that nanomolar concentrations of K252a prevent HGF-mediated scattering in MLP-29 cells (30 nM), reduce Met-driven proliferation in GTL-16 gastric carcinoma cells (100 nM), and cause reversion in NIH3T3 fibroblasts transformed by the oncogenic form of the receptor, Tpr-Met (75 nM). K252a inhibits Met autophosphorylation in cultured cells and in immunoprecipitates and prevents activation of its downstream effectors MAPKinase and Akt. Interestingly, K252a seems to be more effective at inhibiting the mutated form of Met (M1268T) found in papillary carcinoma of the kidney than the wild type receptor. Pretreatment of both Tpr-Met-transformed NIH3T3 fibroblasts and of GTL-16 gastric carcinoma cells with K252a results in loss of their ability to form lung metastases in nude mice upon injection into the caudal vein. These observations suggest that K252a derivatives, which are active in vivo as anti-cancer drugs in models of Trk-driven malignancies, should also be effective for treatment of Met-mediated tumors.

Syntheses and antiproliferative activities of new rebeccamycin derivatives with the sugar unit linked to both indole nitrogens

The synthesis of new rebeccamycin derivatives, in which the carbohydrate moiety is attached to both indole nitrogens, is described. The newly synthesized compounds were tested for their abilities to block the cell cycle of murine leukemia L1210 cells and their in vitro antiproliferative activities against four tumor cell lines (murine L1210 leukemia and human HT29 colon carcinoma, A549 non-small-cell lung carcinoma, K-562 leukemia). Their biological activities are compared with those of the parent compound rebeccamycin. Some of the new compounds exhibit potent antiproliferative activities, either against the four cell lines or mostly the two leukemias (L1210 and K-562 cell lines). The 3,9-diformyl analogue 9 was selective toward L1210 cells, whereas the 3,9-dibromo 16 was strongly cytotoxic toward the four cell lines tested. Nonselective compound 16 and 3,9-dinitro 13, which exhibited selectivity toward leukemia tumor cell lines, were selected for in-depth evaluation, including in vivo experiments.

CEP-751 inhibits TRK receptor tyrosine kinase activity in vitro exhibits anti-tumor activity

The present report describes the in vitro and in vivo profile of CEP-751, a novel receptor tyrosine kinase inhibitor. CEP-751 at 100 nM inhibits the receptor tyrosine kinase activity of the neurotrophin receptors trkA, trkB and trkC. CEP-751 has no effect on activity of receptors for EGF, IGF-I, insulin or on erbB2; inhibition of receptors for PDGF and bFGF was observed but occurred with lesser potency than inhibition of trk. CEP-751 exhibited anti-tumor efficacy against tumors derived from NIH3T3 cells transfected with trkA. Inhibition of trk phosphorylation could also be measured in these tumors, suggesting that anti-tumor efficacy of CEP-751 is related to inhibition of trk receptor tyrosine kinase activity. CEP-751 was found to be without effect when administered to nude mice bearing SK-OV-3 tumors, which overexpress erbB2 receptors, providing further evidence that inhibition of tumor growth may be related to inhibition of trk receptor tyrosine kinase activity. Our data indicate that CEP-751 is a potent trk inhibitor which possesses anti-tumor activity.

Structure-activity relationships in a series of substituted indolocarbazoles: topoisomerase I and protein kinase C inhibition and antitumoral and antimicrobial properties

A series of compounds structurally related to staurosporine, rebeccamycin, and corresponding aglycones was synthesized, and their activities toward protein kinase C and topoisomerases I and II were tested together with their in vitro antitumor efficiency against murine B16 melanoma and P388 leukemia cells. Their antimicrobial activities were also examined against a Gram-negative bacterium (Escherichia coli), a yeast (Candida albicans), and three Gram-positive bacteria (Bacillus cereus, Streptomyces chartreusis, and Streptomyces griseus). To avoid side effects expected with protein kinase C inhibitors, we introduced substitution on the maleimide nitrogen and/or a sugar moiety linked to one of the indole nitrogens to obtain specific inhibitors of topoisomerase I with minimal activities on protein kinase C. As expected, these structures were inefficient on topoisomerase II, and some of them exhibited a strong activity against topoisomerase I. Generally, dechlorinated compounds were found to be more active than chlorinated analogues against both purified topoisomerase I and protein kinase C. On the other hand, opposite results were obtained in the cell antiproliferative assays. These results suggest lack of cell membrane permeability in the absence of the chlorine residue or cleavage of carbon-chlorine bonds inside the cell.

Immobilized glucose-6-phosphate dehydrogenase as a substrate for solubilized epidermal growth factor receptor tyrosine kinase. A convenient microtiter plate assay system

Based on our previously reported solution assay protocol, a solid-phase assay for the tyrosine kinase activity of the epidermal growth factor receptor has been developed. Glucose-6-phosphate dehydrogenase, immobilized noncovalently on microtiter plates, was used as the substrate in the solid-phase assay. Phosphorylation of the immobilized substrate takes place in the presence of ATP and a solubilized epidermal growth factor receptor preparation. After washing off the soluble reaction mixture, the phosphotyrosine-containing dehydrogenase produced on the well surface is quantitated by an ELISA method using a polyclonal antiphosphotyrosine antibody, a second antibody conjugated with horseradish peroxidase, and finally the o-phenylenediamine reaction. The absorbance at 492 nm developed in the wells is a measure of the kinase activity of the solubilized receptor preparation. Putative inhibitors of receptor kinase can be conveniently incorporated in this assay system to test for potential inhibitory activity. This assay, being rapid and convenient, is useful in drug screening programs where a high through-put rate is required.

The potential of protein kinase C as a target for anticancer treatment

Many investigators have embarked upon the search for novel cellular targets for the treatment of cancer. A popular therapeutic strategy is to intervene with the components of cellular signalling systems that are altered during malignancy. The molecular heterogeneity of the protein kinase C (PKC) family and their functional divergence make them attractive targets for anticancer drug development. PKC can also influence the sensitivity of tumor tissue to conventional cytotoxic drugs. As discussed in this review, a complete understanding of the PKC signal transduction pathway is obligatory for the selective destruction of tumor tissue by exploiting PKC as either a target or a modulator of cancer chemotherapeutic agents.

Enhancement of antitumor activity of mitomycin C in vitro and in vivo by UCN-01, a selective inhibitor of protein kinase C

UCN-01 (7-hydroxy-staurosporine) is a potent and selective inhibitor of protein kinase C (PKC), one of several protein kinases examined. UCN-01 itself was shown to exhibit antitumor activity in vitro and in vivo in oncogene-activated human and murine tumor cell lines. Since the mechanism(s) of action of UCN-01 is thought to be different from those of alkylating agents, including mitomycin C (MMC), we tested the combined effect of UCN-01 with MMC on human epidermoid carcinoma A431 cells. UCN-01 potentiated the antiproliferative activity of MMC and yet it did not affect the growth of the cells in vitro. However, other nonselective protein kinase inhibitors, such as staurosporine, K-252a, KT6124 (a derivative of K-252a) and H7, did not enhance the activity of MMC. Isobologram analysis revealed that the interaction of UCN-01 with MMC was synergistic in its antiproliferative activity. A DNA histogram of A431 cells treated with both UCN-01 and MMC showed a block in the cell cycle at the G1/S phase. However, a histogram of cells treated with UCN-01 or MMC alone showed a G1 or a G2M block, respectively. The combined effect of UCN-01 with MMC was further examined in vivo in xenografted A431 cells in nude mice. The combination of both drugs in a single i.v. injection exhibited greater antitumor activity than MMC and UCN-01 alone (P < 0.01). This synergistic antitumor effect was also confirmed in two other solid tumor cell lines, i.e. human xenografted colon carcinoma Co-3 and murine sarcoma 180. The same was observed in the i.v.-inoculated P388 leukemia model, in which we saw an increased lifespan of mice when UCN-01 was combined with MMC. These results suggests the feasibility of using UCN-01 in clinical oncology, especially in combination with alkylating agents such as MMC. In addition, this combination therapy might be a novel chemotherapeutic approach to MMC-insensitive tumors in clinical trials.