Folate Targeting Enables Durable and Specific Antitumor Responses from a Therapeutically Null Tubulysin B Analogue

Endocyte, Inc., West Lafayette, Indiana 47906, USA.
Cancer Research (Impact Factor: 9.33). 01/2009; 68(23):9839-44. DOI: 10.1158/0008-5472.CAN-08-2341
Source: PubMed


The membrane-bound high-affinity folate receptor (FR) is highly expressed on a wide range of primary and metastatic human cancers, such as those originating in ovary, lung, breast, endometrium, kidney, and brain. Because folate-linked conjugates bind to and become internalized within FR-expressing cells (similar to that of free folic acid), we explored the possibility of using the folate ligand to target a potent, semisynthetic analogue of the microtubule inhibitor tubulysin B to FR-enriched tumors. When tested in vitro, a novel folate conjugate, herein referred to as EC0305, was found to specifically inhibit the growth of a panel of FR-positive cell lines (IC50 range, 1-10 nmol/L) in a dose-dependent manner, whereas cells lacking FR expression were unaffected. The potency of EC0305 was also confirmed against a human KB xenograft-nu/nu mouse cancer model. Here, a brief three times per week, 2-week regimen yielded remarkable antitumor activity (100% tumor-free animals) without causing significant weight loss or major organ tissue degeneration. In contrast, antitumor activity was completely abolished in EC0305-treated animals that were co-dosed with an excess of a nontoxic folate-containing analogue, thereby confirming that the antitumor effect of this agent was mediated by FRs. The advantage provided by folate conjugation was further proved by the untargeted free drug, which was found to be completely inactive at both tolerable and highly toxic dose levels. Collectively, these results show that this potent antiproliferative tubulysin compound can be specifically delivered to FR-positive tumors to provide substantial therapeutic benefit using well-tolerable dosing regimens.

Download full-text


Available from: Nikki Parker,
47 Reads
  • Source
    • "It has been demonstrated that neoplastic tissues have significantly up-regulated levels of serine synthetic enzymes and SHMT, and the increased capacity for serine synthesis in cancer cells was coupled with its preferential utilization for the provision of nucleotide precursors for enhanced growth potential [32]. Based on their vital role in de novo biosynthesis of purines and thymidylate, folate-requiring enzymes have long been considered viable targets for anti-cancer therapy [33-37]. Methotrexate (MTX) is one of the most widely used anti-folate agents in chemotherapy, blocking de novo nucleotide synthesis by depleting reduced THFs, mainly through inhibition of dihydrofolate reductase (DHFR) and thymidylate synthase (TS). "
    [Show abstract] [Hide abstract]
    ABSTRACT: We have previously reported arginase expression in human breast cancer cells and demonstrated that the inhibition of arginase by N(ω) hydroxy L-arginine (NOHA) in MDA-MB-468 cells induces apoptosis. However, arginase expression and its possible molecular targets in human breast tumor samples and potential clinical implications have not been fully elucidated. Here, we demonstrate arginase expression in human breast tumor samples, and several established breast cancer cell lines, in which NOHA treatment selectively inhibits cell proliferation. The over-expression of Bcl2 in MDA-MB-468 cells abolished NOHA-induced apoptosis, suggesting that the mitochondria may be the main site of NOHA's action. We, therefore, undertook a proteomics approach to identify key mitochondrial targets of arginase in MDA-MB-468 cells. We identified 54 non-mitochondrial and 13 mitochondrial proteins that were differentially expressed in control and NOHA treated groups. Mitochondrial serine hydroxymethyltransferase (mSHMT) was identified as one of the most promising targets of arginase. Both arginase II (Arg II) and mSHMT expressions were higher in human breast tumor tissues compared to the matched normal and there was a strong correlation between Arg II and mSHMT protein expression. MDA-MB-468 xenografts had significant upregulation of Arg II expression that preceded the induction of mSHMT expression. Small inhibitory RNA (siRNA)-mediated inhibition of Arg II in MDA-MB-468 and HCC-1806 cells led to significant inhibition of both the mSHMT gene and protein expression. As mSHMT is a key player in folate metabolism, our data provides a novel link between arginine and folate metabolism in human breast cancer, both of which are critical for tumor cell proliferation.
    PLoS ONE 12/2013; 8(11):e79242. DOI:10.1371/journal.pone.0079242 · 3.23 Impact Factor
  • Source
    • "Although folate receptors are usually expressed in the normal cells and mediated the internalization of folic acid, two different types of these receptors have been actually isolated and characterized [13] [14]. The over-expression of high-affinity folate receptors on different human cancers and undifferentiated metastases [14] [15], compared to its low expression in normal tissues [16], provided advantages to treat tumor cells with respect to neighboring normal tissue. Moreover, folate receptor alpha (FR a), a membrane-bound transport protein, which targets selectively cancer immunotherapy, is largely shielded from the immune system in normal tissue but over-expressed on different cancer cells. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Supramolecular vesicular aggregates (SVAs), made up by self-assembling liposomes and polyasparthydrazide co-polymers conjugated to folic acid molecules were extensively investigated in this manuscript as potential active targeting formulation for anticancer drug delivery. Folate-targeted systems (FT-SVAs) were used to treat breast cancer and to further proof the potential in vivo administration of these systems for the therapeutic treatment for several aggressive solid tumors. The physicochemical and technological parameters of FT-SVAs are suitable for their potential in vivo administration. The chemotherapeutic activity of GEM-loaded FT-SVAs was increased during in vivo experiments. NOD-SCID mice bearing MCF-7 human xenograft is used as breast cancer model. The measurement of the volume and weight of tumor masses decreased when animal models are treated by using GEM-loaded FT-SVAs, compared to data obtained by using GEM-loaded mPEG-SUVs and the free form of GEM. An almost complete regression of the tumor (∼0.2cm(3)) was observed in NOD-SCID mice bearing MCF-7 human xenografts treated by GEM-loaded FT-SVAs due to the noticeable improvement of GEM pharmacokinetic parameters provided by FT-SVAs with respect to native anticancer drug. The obtained data showed that supramolecular systems could represent an innovative drug delivery system by self-assembling liposomes and biocompatible polymers to be potentially used for anticancer treatment.
    European journal of pharmaceutics and biopharmaceutics: official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 06/2012; 82(1):94-102. DOI:10.1016/j.ejpb.2012.06.001 · 3.38 Impact Factor
  • Source
    • "Thus, while native tubulysin B–H was unable to produce an antitumor effect due to its high nonspecific toxicity, EC0305 was able to induce tumor regression with no apparent dose-limiting toxicity.88 Furthermore, the IC50 values of EC0305 were three-fold lower than other similar folate-targeted chemotherapeutics, such as folate-mitomycin C and folate-camptothecin.32,61–64,89,91 Recent studies also demonstrated that EC0305 was more effective against M109 (murine lung) and 4T1-C12 (murine mammary) cancer cells compared to folate-desacetylvinblastine monohydrazide (EC145), a folate-targeted drug that has reached phase II clinical trials.88 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Overexpressed receptors, characteristic of many cancers, have been targeted by various researchers to achieve a more specific treatment for cancer. A common approach is to use the natural ligand for the overexpressed receptor as a cancer-targeting agent which can deliver a chemically or genetically conjugated toxic molecule. However, it has been found that the therapeutic efficacy of such ligand-drug molecular conjugates can be limited, since they naturally follow the intracellular trafficking pathways of the endogenous ligands. Therefore, a thorough understanding of the intracellular trafficking properties of these ligands can lead to novel design criteria for engineering ligands to be more effective drug carriers. This review presents a few commonly used ligand/receptor systems where intracellular trafficking considerations can potentially improve the therapeutic efficacy of the ligand-drug molecular conjugates.
    Annals of Biomedical Engineering 02/2011; 39(4):1235-51. DOI:10.1007/s10439-011-0280-y · 3.23 Impact Factor
Show more