Christopher P Leamon

Paul Scherrer Institut, Villigen, AG, Switzerland

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Publications (73)369.77 Total impact

  • Yehuda G. Assaraf, Christopher P. Leamon, Joseph A Reddy
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    ABSTRACT: Conventional cancer treatment modalities have several limitations including lack of sufficient efficacy, serious untoward toxicity, as well as innate and acquired drug resistance. In contrast, targeted imaging agents can identify patients with receptors overexpressed on the surface of cancer cells, thus allowing appropriate selection of patients for personalized treatment with a desirable targeted therapeutic. The folate receptor (FR) has been identified as a new molecularly targeted entity, which is highly overexpressed on the surface of a spectrum of solid tumor cells, including ovarian, kidney, lung, brain, endometrial, colorectal, pancreatic, gastric, prostate, testicular, bladder, head and neck, breast, and non–small cell lung cancer. Folic acid conjugation is a novel approach for targeting FR-expressing tissues for personalized treatment. With the development of FRα-targeted therapies comes a concomitant prerequisite for reliable methods for the quantification of FRα tissue expression. Therefore, attaching a radioactive probe to folic acid to target diseased tissue has become a novel and powerful imaging technique. Currently available diagnostic tools frequently require invasive surgical biopsy. In contrast, the noninvasive single-photon emission computed tomography-based companion imaging agent, 99mTc-etarfolatide (99mTc-EC20), is in development for use as a companion diagnostic with the FRα-targeted folate conjugate, vintafolide (EC145), to identify patients whose tumors express FRα. Vintafolide is a folic acid conjugate of Vinca alkaloid (desacetylvinblastine hydrazide) that targets FRα-expressing tumors, thereby disrupting microtubule polymerization. 99mTc-etarfolatide is taken up by FR-positive tumors and allows for noninvasive, whole-body monitoring of FRα expression status throughout treatment. The combination of vintafolide plus etarfolatide has been evaluated in three Phase 2 studies for the treatment of various solid tumors, including ovarian, endometrial, peritoneal, and platinum-resistant ovarian cancer, as well as lung cancer. Patients with FR-positive tumors, as identified by etarfolatide uptake, have had better clinical outcomes than patients with FR-negative tumors, indicating the potential of etarfolatide as a companion biomarker for predicting vintafolide response. Targeted therapies combined with a reliable companion diagnostic test represent a novel approach towards efficient personalized medicine for malignant and nonmalignant disorders. Furthermore, the recent availability of the crystal structures of FRα and FRβ in complex with folates and antifolates forms a realistic basis for the rational design and implementation of novel FR-targeted drugs for the treatment of cancer and inflammatory disorders.
    Drug Resistance Updates 10/2014; · 8.82 Impact Factor
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    ABSTRACT: Background. Vintafolide is a potent folate-targeted vinca alkaloid SMDC that has shown promising results in multiple clinical oncology studies. Structurally, vintafolide is a small molecule drug conjugate (SMDC) consisting of 4 essential modules: 1) folic acid, 2) a hydrophilic peptide spacer, 3) a disulfide-containing, self-immolative linker, and 4) the cytotoxic drug, desacetylvinblastine hydrazide (DAVLBH). Here we report a structure-activity study evaluating the biological impact of i) substituting DAVLBH within the vintafolide molecule with other vinca alkaloid analogues such as vincristine, vindesine, vinflunine or vinorelbine, ii) substituting the naturally (S)-configured Asp-Arg-Asp-Asp-Cys peptide with alternative hydrophilic spacers of varied composition, and iii) varying the composition of the linker module. Methods. A series of vinca alkaloid-containing SMDCs were synthesized and purified by HPLC and LCMS. The SMDCs were screened in vitro against folate receptor (FR)-positive cells, and anti-tumor activity was tested against well-established subcutaneous FR-positive tumor xenografts. The cytotoxic and anti-tumor activities were directly compared to that produced by vintafolide. Results. Among all the folate vinca alkaloid SMDCs tested, DAVLBH-containing SMDCs were active while those constructed with vincristine, vindesine or vinorelbine analogues failed to produce meaningful biological activity. Within the DAVLBH series, having a bio-releasable, self-immolative linker system was found to be critical for activity since multiple analogues constructed with thioether-based linkers all failed to produce meaningful activity both in vitro and in vivo. Substitutions of some or all of the natural amino acids within vintafolide's hydrophilic spacer module did not significantly change the in vitro or in vivo potency of the SMDCs. Conclusion. Vintafolide remains one of the most potent folate-vinca alkaloid SMDCs produced to date, and continued clinical development is warranted.
    Bioconjugate Chemistry 02/2014; · 4.82 Impact Factor
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    ABSTRACT: Objective-To determine expression of folate receptors (FRs) and folate uptake in multicentric lymphomas in dogs. Sample-10 dogs with histopathologically confirmed multicentric lymphoma and 20 archival lymph node biopsy specimens from dogs with multicentric lymphoma. Procedures-Multicentric lymphomas in 10 dogs were prospectively evaluated for FR expression by use of immunohistochemical analysis and for in vivo folate uptake by use of nuclear scintigraphy. Dogs with FR-expressing tumors were eligible for FR-targeted chemotherapy. Twenty archival lymphoma biopsy specimens were also evaluated with immunohistochemical analysis. Results-FRs were not detected with immunohistochemical analysis in lymph node samples obtained from the 10 dogs or in archival biopsy specimens. However, nuclear scintigraphy revealed uptake of radioactive tracer in 6 of 10 dogs. Five of these 6 dogs were treated with an FR-targeted chemotherapeutic agent; results of treatment were complete remission in 1 dog, stable disease in 2 dogs, and progressive disease in 2 dogs. Treatment-related toxicoses generally were mild. Conclusions and Clinical Relevance-This study provided strong evidence for folate uptake in a substantial portion of multicentric lymphomas of dogs and indicated the antitumor activity of FR-targeted chemotherapeutics for these cancers. Use of FR-targeted chemotherapeutics may be promising for the treatment of FR-expressing multicentric lymphomas in dogs. Further studies are needed to determine reasons for lack of immunoreactivity to currently identified anti-FR antibodies and to develop improved methods for detecting FRs in lymphomas of dogs.
    American Journal of Veterinary Research 02/2014; 75(2):187-94. · 1.21 Impact Factor
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    ABSTRACT: When evaluated in ovarian and other cancer patients, vintafolide (EC145), a potent folate-targeted vinca alkaloid conjugate, displayed a toxicity profile that appeared to be non-overlapping with many standard of care cancer therapeutics. It was therefore hypothesized that combining vintafolide with certain approved anticancer drugs may afford greater therapeutic efficacy compared to single-agent therapy. To explore this concept, vintafolide was evaluated in combination with pegylated liposomal doxorubicin (PLD; DOXIL®), cisplatin, carboplatin, paclitaxel, docetaxel, topotecan, and irinotecan against folate-receptor (FR)-positive models. FR-expressing KB, M109, IGROV, and L1210 cells were first exposed to graded concentrations of vintafolide, either alone or in combination with doxorubicin (active ingredient in PLD), and isobologram plots and combination index values generated. The vintafolide combinations were also studied in mice bearing various FR-expressing tumors. Vintafolide displayed strong synergistic activity against KB cells when combined with doxorubicin, and no less-than-additive effects resulted when tested against M109, IGROV, and L1210 cells. In contrast, when either desacetylvinblastine hydrazide (DAVLBH; the vinca alkaloid moiety in vintafolide) or vindesine (the vinca alkaloid most structurally similar to DAVLBH) were tested in combination with doxorubicin, less-than-additive antitumor effects were observed. In vivo, all vintafolide drug combinations produced far greater antitumor effect (complete responses and cures) compared to the single agents alone, without significant increase in overall toxicity. Importantly, these benefits were not observed with combinations of PLD and DAVLBH or vindesine. Based on these encouraging preclinical results, clinical studies to evaluate vintafolide drug combination therapies are now underway.
    Clinical Cancer Research 01/2014; · 8.19 Impact Factor
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    ABSTRACT: EC0746 is a rationally designed anti-inflammatory drug conjugate consisting of a modified folic acid-based ligand linked to a γ-hydrazide analog of aminopterin. In this report, EC0746's effectiveness was evaluated against experimental retinal S-antigen (PDSAg) induced autoimmune uveitis (EAU) and myelin-basic-protein induced autoimmune encephalomyelitis (EAE). In both models, functional FR-β was detected on activated macrophages in local (retinal or central-nervous-system, respectively) and systemic (peritoneal cavity) sites of inflammation. In myelin-rich regions of EAE rats, an increased uptake of (99m)Tc-EC20 (etarfolatide; a FR-specific radioimaging agent) was also observed. EC0746 treatment at disease onset suppressed the clinical severity of both EAU and EAE, and it strongly attenuated progressive histopathological changes in the affected organs. In all parameters assessed, EC0746 activity was completely blocked by a benign folate competitor, suggesting that these therapeutic outcomes were specifically FR-β mediated. EC0746 may emerge as a useful macrophage-modulating agent for treating inflammatory episodes of organ-specific autoimmunity.
    Clinical Immunology 10/2013; 150(1):64-77. · 3.77 Impact Factor
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    ABSTRACT: Human pituitary adenomas express folate receptors (FR); therefore, we hypothesized that parathyroid (PT) tumors also might express FR, whereas normal human thyroids might not. The purpose of our study was to characterize the functionality of FRs on human PT tumors, with the goal of developing an imaging tool that would concentrate in PT more than in the thyroid. Human PTs and thyroids were evaluated for FR expression by immunohistochemistry. Expression of genes for FRα and FRβ was measured with the Illumina Human HT-12 Expression Bead Chips and verified by quantitative reverse-transcription polymerase chain reaction. Folate incorporation by PT cells versus normal thyroid cells was determined by incubation with (99m)Technetium ((99m)Tc)(CO)3-folate and (99m)Tc-Etarfolatide, and uptake was determined by gamma counting. Specific targeting of FRs was demonstrated by blocking with cold folate. A549 cells and Jurkat cells served as FR-negative controls, and KB cells and HeLa cells were FR-positive controls. On immunohistochemistry and Western blotting, human PT cells expressed FRs, whereas human thyroid cells did not. The FRα gene was expressed in all PTs analyzed, and the FRβ gene was expressed by most. Uptake of (99m)Tc(CO)3-folate was increased in PT cells versus thyroid cells. There was dose-dependent uptake of (99m)Tc-etarfolatide, and uptake was inhibited by preincubation with cold folate, confirming FR-mediated binding. This is the first report of the expression and functionality of FRs on human PT cells. These findings suggest that (99m)Tc-folate holds potential for localization of PT tumors preoperatively and their treatment.
    Surgery 10/2013; · 3.37 Impact Factor
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    ABSTRACT: Vintafolide (EC145) is a folic acid-desacetylvinblastine conjugate that binds to the folate receptor (FR), which is expressed on the majority of epithelial ovarian cancers. This randomized phase II trial evaluated vintafolide combined with pegylated liposomal doxorubicin (PLD) compared with PLD alone. The utility of an FR-targeted imaging agent, (99m)Tc-etarfolatide (EC20), in selecting patients likely to benefit from vintafolide was also examined. Women with recurrent platinum-resistant ovarian cancer who had undergone ≤ two prior cytotoxic regimens were randomly assigned at a 2:1 ratio to PLD (50 mg/m(2) intravenously [IV] once every 28 days) with or without vintafolide (2.5 mg IV three times per week during weeks 1 and 3). Etarfolatide scanning was optional. The primary objective was to compare progression-free survival (PFS) between the groups. The intent-to-treat population comprised 149 patients. Median PFS was 5.0 and 2.7 months for the vintafolide plus PLD and PLD-alone arms, respectively (hazard ratio [HR], 0.63; 95% CI, 0.41 to 0.96; P = .031). The greatest benefit was observed in patients with 100% of lesions positive for FR, with median PFS of 5.5 compared with 1.5 months for PLD alone (HR, 0.38; 95% CI, 0.17 to 0.85; P = .013). The group of patients with FR-positive disease (10% to 90%) experienced some PFS improvement (HR, 0.873), whereas patients with disease that did not express FR experienced no PFS benefit (HR, 1.806). Vintafolide plus PLD is the first combination to demonstrate an improvement over standard therapy in a randomized trial of patients with platinum-resistant ovarian cancer. Etarfolatide can identify patients likely to benefit from vintafolide.
    Journal of Clinical Oncology 10/2013; · 17.88 Impact Factor
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    ABSTRACT: Targeted radionuclide therapy has shown impressive results for the palliative treatment of several types of cancer diseases. The folate receptor (FR) has been identified specifically associated with a variety of frequent tumor types. Therefore, it is an attractive target for the development of new radionuclide therapies using folate-based radioconjugates. Previously, we found that pemetrexed (PMX) has a favorable effect to reduce undesired renal uptake of radiofolates. Moreover, PMX also acts as a chemotherapeutic and radiosensitizing agent on tumors. Thus, the aim of our study was to investigate the combined application of PMX and the therapeutic radiofolate, 177Lu-EC0800. Determination of the combination index (CI) revealed a synergistic inhibitory effect of 177Lu-EC0800 and PMX on the viability of FR positive cervical (KB) and ovarian (IGROV-1) cancer cells in vitro (CI < 0.8). In an in vivo study, tumor bearing mice were treated with 177Lu-EC0800 (20 MBq) and a subtherapeutic (0.4 mg) or therapeutic amount (1.6 mg) of PMX. Application of 177Lu-EC0800 with PMXther resulted in a 2-4-fold enhanced tumor growth delay and a prolonged survival of KB and IGROV-1 tumor-bearing mice, as compared to the combination with PMXsubther or untreated control mice. PMXsubther protected the kidneys from undesired side effects of 177Lu-EC0800 (20 MBq) by reducing the absorbed radiation dose. Intact kidney function was demonstrated by determination of plasma parameters and quantitative SPECT using 99mTc-DMSA. Our results confirmed the anticipated dual role of PMX. Its unique features resulted in an improved antitumor effect of folate-based radionuclide therapy, and prevented undesired radio-nephrotoxicity.
    Molecular Cancer Therapeutics 09/2013; · 5.60 Impact Factor
  • Cancer Research 08/2013; 73(8 Supplement):2145-2145. · 9.28 Impact Factor
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    ABSTRACT: Folate receptor (FR) targeting is an attractive strategy for nuclear imaging of cancer and activated macrophages through application of folic acid radioconjugates. However, significant renal accumulation of folate radioconjugates and hence exceedingly high emission of radiation from the kidneys may mask uptake of radioactivity at sites of interest such as small metastases in the abdominal region of animal models of ovarian cancer. Recently it was observed that the antifolate pemetrexed (PMX) reduces undesired renal uptake of radiofolates. A disadvantage of this strategy is the fact that pemetrexed is a chemotherapeutic agent which may have toxic side effects. The aims of this study were therefore to investigate whether the desired effect of PMX to reduce renal accumulation of folate radioconjugates would be maintained if it was applied as a cocktail together with its antidote, thymidine, and to explore whether thymidine was an effective rescue agent against PMX's related toxicity in vitro and in vivo. In vitro internalization of (67)Ga-EC0800 was investigated using FR-positive KB tumor cells and embryonic monkey MA104 kidney cells in the absence and presence of PMX alone and in combination with thymidine. Uptake of (67)Ga-EC0800 into KB cells was increased by coincubation of the cells with PMX. In contrast uptake of (67)Ga-EC0800 into MA104 cells was reduced under the same conditions. In both cell lines coincubation of thymidine did not change the results obtained with PMX. Biodistribution and SPECT/CT imaging studies of (67)Ga-EC0800 were performed with KB tumor bearing mice injected with PMX alone or with a cocktail of PMX and thymidine. The radiofolate's kidney uptake reducing effect of PMX in mice was maintained also if PMX was employed together with its antidote thymidine. The tumor uptake of (67)Ga-EC0800 remained unchanged independent of the administration of PMX or a combination of PMX and thymidine. The effect of thymidine to abrogate PMX-induced cytotoxicity was demonstrated in vitro with an MTT assay using KB and MA104 cells. Cell viability was reduced to 50% (KB cells) and 70% (MA104 cells) of untreated controls if PMX (5 μM and 15 μM, respectively) was coincubated. Addition of thymidine (10 μM or 100 μM) compensated PMX's toxic effects in a dose-dependent manner. The effect of thymidine was also investigated in non-tumor bearing mice treated with high-dosed PMX. Rescue of mice with side effects after the third and fourth cycles of PMX application (1 mg/mouse) was achieved by application of thymidine (20 mg/mouse) at five consecutive days starting the day of PMX injection. Application of PMX together with thymidine as a cocktail is effective to improve the tissue distribution of radiofolates while preventing pharmacological and potentially toxic side effects of the chemotherapeutic agent PMX. These findings open new perspectives for folate-based nuclear imaging in preclinical research potentially allowing longitudinal investigations and monitoring therapies in animal models of cancer and inflammatory diseases.
    Molecular Pharmaceutics 02/2013; · 4.57 Impact Factor
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    Christopher P Leamon, Chandra D Lovejoy, Binh Nguyen
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    ABSTRACT: Ovarian cancer (OC) has the highest mortality rate of any gynecologic cancer, and patients generally have a poor prognosis due to high chemotherapy resistance and late stage disease diagnosis. Platinum-resistant OC can be treated with cytotoxic chemotherapy such as paclitaxel, topotecan, pegylated liposomal doxorubicin, and gemcitabine, but many patients eventually relapse upon treatment. Fortunately, there are currently a number of targeted therapies in development for these patients who have shown promising results in recent clinical trials. These treatments often target the vascular endothelial growth factor pathway (eg, bevacizumab and aflibercept), DNA repair mechanisms (eg, iniparib and olaparib), or they are directed against folate related pathways (eg, pemetrexed, farletuzumab, and vintafolide). As many targeted therapies are only effective in a subset of patients, there is an increasing need for the identification of response predictive biomarkers. Selecting the right patients through biomarker screening will help tailor therapy to patients and decrease superfluous treatment to those who are biomarker negative; this approach should lead to improved clinical results and decreased toxicities. In this review the current targeted therapies used for treating platinum-resistant OC are discussed. Furthermore, use of prognostic and response predictive biomarkers to define OC patient populations that may benefit from specific targeted therapies is also highlighted.
    Pharmacogenomics and Personalized Medicine 01/2013; 6:113-125.
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    ABSTRACT: Folate receptors (FRs) may have utility for targeted cytotoxic drugs in invasive urothelial carcinoma (iUC) where improved therapy is needed. We explored FR expression and function in iUC and evaluated the antitumor activity and toxicity of a folate-targeted vinblastine conjugate in dogs with naturally-occurring iUC, an excellent model for human iUC. FR immunohistochemistry was performed on iUC and normal human and dog bladder tissues along with nuclear scintigraphy in dogs to monitor iUC folate uptake. Dose escalation of folate-targeted vinblastine compound EC0905 was conducted in dogs with biopsy-confirmed, FR-positive iUC. FRs were detected by immunohistochemistry (PU17) in most primary iUC and many nodal and lung metastases from dogs, and scintigraphy confirmed folate uptake in both primary and metastatic lesions. The maximum tolerated dose of EC0905 in dogs was 0.25 mg/kg IV weekly with neutropenia at higher doses. Tumor responses included partial remission ≥ 50% reduction in tumor volume) in 5 dogs and stable disease (<50% change in tumor volume) in 4 dogs. Immunoreactivity to PU17 was similar in humans (78% of primary iUC, 80% of nodal metastases). Less immunoreactivity to mab343 (22% of cases) occurred. FR-β was noted in 21% of human iUC cases. Our findings suggest folate-targeted therapy holds considerable promise for treating iUC, where FR-β may be important in addition to FR-α.
    Cancer Research 11/2012; · 9.28 Impact Factor
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    ABSTRACT: PURPOSEEC145 (vintafolide), a conjugate of folic acid and the vinca alkaloid desacetylvinblastine hydrazide (DAVLBH), is a ligand for the folate receptor (FR), with activity against FR-positive tumor xenografts in vivo. This phase I study determined the maximum-tolerated dose (MTD) of EC145 administered as a bolus intravenous injection or 1-hour infusion in patients with refractory solid tumors. PATIENTS AND METHODSEC145 was administered as a bolus injection or 1-hour infusion on days 1, 3, and 5 and days 15, 17, and 19 of each 28-day cycle with dose escalation in cohorts of three to six patients until the MTD was identified. Plasma pharmacokinetics were determined on days 1 and 3 of the first cycle.ResultsThe MTD of EC145 was 2.5 mg when administered as either a bolus injection or 1-hour infusion. Constipation was the dose-limiting toxicity with both routes. Constipation, nausea, fatigue, and vomiting were the most commonly reported adverse events. One partial response to therapy was observed in a patient with metastatic ovarian cancer. CONCLUSIONEC145 administered by bolus injection or as a 1-hour infusion at a dose of 2.5 mg on days 1, 3, and 5 and days 15, 17, and 19 of a 28-day cycle has an acceptable safety profile in patients with advanced cancer. On the basis of these findings, phase II studies of EC145 have been initiated in patients with advanced epithelial ovarian cancer and non-small-cell lung cancer.
    Journal of Clinical Oncology 10/2012; · 17.88 Impact Factor
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    ABSTRACT: Activation of the mammalian target of rapamycin (mTOR) signaling pathway is aberrant in autosomal-dominant polycystic kidney disease (ADPKD). The mTOR inhibitors, such as rapamycin, ameliorate PKD in rodent models, but clinical trials have not shown benefit, possibly as a result of low tissue concentrations of rapamycin at clinically tolerable doses. To overcome this limitation, we synthesized a folate-conjugated form of rapamycin (FC-rapa) that is taken up by folate receptor-mediated endocytosis and cleaved intracellularly to reconstitute the active drug. We found that renal cyst-lining cells highly express the folate receptor in ADPKD and mouse models. In vitro, FC-rapa inhibited mTOR activity in a dose- and folate receptor-dependent manner. Treatment of a PKD mouse model with FC-rapa inhibited mTOR in the target tissue, strongly attenuated proliferation and growth of renal cysts and preserved renal function. Furthermore, FC-rapa inhibited mTOR activity in the kidney but not in other organs. In summary, these results suggest that targeting the kidney using FC-rapa may overcome the significant side effects and lack of renal efficacy observed in clinical trials with mTOR inhibitors in ADPKD.
    Journal of the American Society of Nephrology 08/2012; 23(10):1674-81. · 9.47 Impact Factor
  • Iontcho R Vlahov, Christopher P Leamon
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    ABSTRACT: The folate receptor (FR) is a potentially useful biological target for the management of many human cancers. This membrane protein binds extracellular folates with very high affinity and, through an endocytic process, physically delivers them inside the cell for biological consumption. There are now many examples of how this physiological system can be exploited for the targeted delivery of biologically active molecules to cancer. In fact, strong preclinical as well as emerging clinical evidence exists showing how FR-positive cancers can be (i) anatomically identified using folate conjugates of radiodiagnostic imaging agents and (ii) effectively treated with companion folate-targeted chemotherapies. While the biological results are compelling, it is of equal importance to understand the conjugation chemistries that were developed to produce these active molecules. Therefore, this review will focus on the methods utilized to construct folate-based small-molecule drug conjugates (SMDCs), with particular attention focused on modular design, hydrophilic spacers, and self-immolative linkers.
    Bioconjugate Chemistry 06/2012; 23(7):1357-69. · 4.82 Impact Factor
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    ABSTRACT: Tubuylsins are extremely potent cytotoxic agents which inhibit tubulin polymerization and lead to cell cycle arrest and apoptosis. Tubulysins have been isolated from fermentation mixtures and have been chemically synthesized; however, these efforts have been hampered by poor yields and arduous purifications. In contrast, treatment of a mixture of natural tubulysins A, B, C, G, and I, obtained from a fermentation batch with trifluoroacetic acid results in the formation of a single N-acyliminium ion. Subsequent addition of butyric, isopentyl, or acetic acid results in the formation of tubulysin B, A, or I, respectively, as a single species. New tubulysin analogs can be formed upon treatment of the acyliminium ion with other nucleophiles such as alcohols, thiols, and nitriles, resulting in corresponding N-acyl-N,O-acetals, N-acyl-N,S-thioacetals, and N,N'-diacyl-aminals. Carbon-carbon bond formation is also possible with a modification of this protocol. The cytotoxicies of the natural tubulysins and tubulysin analogs synthesized by this method were evaluated on KB cells.
    Bioorganic & medicinal chemistry letters 11/2011; 21(22):6778-81. · 2.65 Impact Factor
  • Cancer Research 07/2011; 71(8 Supplement):3259-3259. · 9.28 Impact Factor
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    ABSTRACT: Use of folic acid radioconjugates for folate receptor (FR) targeting is a promising strategy for imaging purposes as well as for potential therapy of cancer and inflammatory diseases due to the frequent FR overexpression found on cancer cells and activated macrophages. Herein, we report on preclinical results using a novel DOTA-Bz-EDA-folate conjugate radiolabeled with [(67)Ga]-gallium. DOTA-Bz-EDA-folate was prepared by conjugation of ethylenediamine-(γ)-folate with 2-(p-isothiocyanobenzyl)-DOTA. Radiolabeling was carried out with (67)GaCl(3) according to standard procedures. Biodistribution studies of the tracer were performed in mice bearing FR-positive KB tumor xenografts. The effects on radiofolate biodistribution with coadministered renal uptake-blocking amino acids, diuretic agents, antifolates as well as different routes of administration were likewise investigated. Supportive imaging studies were performed using a small-animal single photon emission computed tomography (SPECT)/CT scanner. (67)Ga-DOTA-Bz-EDA-folate showed a high and specific accumulation in tumors (6.30%±0.75% ID/g, 1 h pi and 6.08%±0.89% ID/g, 4 h pi). Nonspecific radioactivity uptake in nontargeted tissues was negligible, but significant accumulation was found in FR-positive kidneys, which resulted in unfavorably low tumor-to-kidney ratios (<0.1). Coadministered amino acids or diuretics did not effectively reduce renal accumulation; in contrast, predosed pemetrexed did significantly reduce kidney uptake (<29% of control values). The SPECT/CT studies confirmed the excellent tumor-to-background contrast of (67)Ga-radiofolate and the favorable reduction in kidney uptake (with improved imaging quality) resulting from pemetrexed administration. Conventional methods to reduce kidney uptake of radiofolates fail. However, the novel (67)Ga-radiolabeled DOTA-Bz-EDA-folate can effectively be used to image FR-positive cancer and potentially inflammatory diseases. Due to its rapid blood clearance properties, this tracer is also a promising candidate for positron emission tomography imaging if radiolabeled with the short-lived [(68)Ga]-gallium radionuclide.
    Nuclear Medicine and Biology 07/2011; 38(5):715-23. · 2.41 Impact Factor

Publication Stats

3k Citations
369.77 Total Impact Points


  • 2010–2013
    • Paul Scherrer Institut
      • Center for Radiopharmaceutical Sciences (CRS)
      Villigen, AG, Switzerland
  • 1999–2013
    • Endocyte
      West Lafayette, Indiana, United States
  • 2012
    • University of California, Santa Barbara
      • Department of Molecular, Cellular, and Developmental Biology
      Santa Barbara, CA, United States
  • 1991–2005
    • Purdue University
      • Department of Chemistry
      West Lafayette, IN, United States