Dana M. Clausen

In Vitro Cytotoxicity and In Vivo Efficacy, Pharmacokinetics, and Metabolism of 10074-G5, a Novel Small-Molecule Inhibitor of c-Myc/Max Dimerization

The c-Myc oncoprotein is overexpressed in many tumors and is essential for maintaining the proliferation of transformed cells. To function as a transcription factor, c-Myc must dimerize with Max via the basic helix-loop-helix leucine zipper protein (bHLH-ZIP) domains in each protein. The small molecule 7-nitro-N-(2-phenylphenyl)-2,1,3-benzoxadiazol-4-amine (10074-G5) binds to and distorts the bHLH-ZIP domain of c-Myc, thereby inhibiting c-Myc/Max heterodimer formation and inhibiting its transcriptional activity. We report in vitro cytotoxicity and in vivo efficacy, pharmacodynamics, pharmacokinetics, and metabolism of 10074-G5 in human xenograft-bearing mice. In vitro, 10074-G5 inhibited the growth of Daudi Burkitts lymphoma cells and disrupted c-Myc/Max dimerization. 10074-G5 had no effect on the growth of Daudi xenografts in C.B-17 SCID mice that were treated with 20 mg/kg 10074-G5 intravenously for 5 consecutive days. Inhibition of c-Myc/Max dimerization in Daudi xenografts was not seen 2 or 24 h after treatment. Concentrations of 10074-G5 in various matrices were determined by high-performance liquid chromatography-UV, and metabolites of 10074-G5 were identified by liquid chromatography/tandem mass spectrometry. The plasma half-life of 10074-G5 in mice treated with 20 mg/kg i.v. was 37 min, and peak plasma concentration was 58 μM, which was 10-fold higher than peak tumor concentration. The lack of antitumor activity probably was caused by the rapid metabolism of 10074-G5 to inactive metabolites, resulting in tumor concentrations of 10074-G5 insufficient to inhibit c-Myc/Max dimerization. Our identification of 10074-G5 metabolites in mice will help design new, more metabolically stable small-molecule inhibitors of c-Myc.

A Cell-Targeted Photodynamic Nanomedicine Strategy for Head and Neck Cancers

Photodynamic therapy (PDT) holds great promise for the treatment of head and neck (H&N) carcinomas where repeated loco-regional therapy often becomes necessary due to the highly aggressive and recurrent nature of the cancers. While interstitial light delivery technologies are being refined for PDT of H&N and other cancers, a parallel clinically relevant research area is the formulation of photosensitizers in nanovehicles that allow systemic administration yet preferential enhanced uptake in the tumor. This approach can render dual-selectivity of PDT, by harnessing both the drug and the light delivery within the tumor. To this end, we report on a cell-targeted nanomedicine approach for the photosensitizer silicon phthalocyanine-4 (Pc 4), by packaging it within polymeric micelles that are surface-decorated with GE11-peptides to promote enhanced cell-selective binding and receptor-mediated internalization in EGFR-overexpressing H&N cancer cells. Using fluorescence spectroscopy and confocal microscopy, we demonstrate in vitro that the EGFR-targeted Pc 4-nanoformulation undergoes faster and higher uptake in EGFR-overexpressing H&N SCC-15 cells. We further demonstrate that this enhanced Pc 4 uptake results in significant cell-killing and drastically reduced post-PDT clonogenicity. Building on this in vitro data, we demonstrate that the EGFR-targeted Pc 4-nanoformulation results in significant intratumoral drug uptake and subsequent enhanced PDT response, in vivo, in SCC-15 xenografts in mice. Altogether our results show significant promise toward a cell-targeted photodynamic nanomedicine for effective treatment of H&N carcinomas.

Abstract 1019: Cytotoxicity in vitro, pharmacokinetics and tissue distribution of Link-N3 and Link-F3, two bivalent small molecules inhibitors of c-Myc/Max interactions in C.B-17 SCID mice bearing Daudi Burkitt's lymphoma xenografts.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: c-Myc plays an important role in cellular proliferation, differentiation, apoptosis and cell cycle progression and its overexpression is associated with aggressiveness and poor prognosis in many cancers. In order to be transcriptionally active, c-Myc must heterodimerize via its bHLH-ZIP domain with its obligatory partner Max. Two small molecules that prevent c-Myc/Max heterodimerization and inhibit c-Myc function are 10074-G5 and 10058-F4. Analogues of these small molecule c-Myc inhibitors have been linked together by a flexible bridge to form Link-N3 and Link-F3. We have characterized the ability of these Link analogues to inhibit the in vitro growth of a c-Myc-overexpressing human cell line, Daudi Burkitts lymphoma. We evaluated their pharmacokinetics, metabolism and efficacy in mice bearing Daudi xenografts. Methods: Inhibition of Daudi cell growth by Link-N3 and Link-F3 was assessed by MTT assay after 72 h of incubation. Accumulation of Link-N3 and Link-F3 by Daudi cells incubated with 10 μM of Link-N3 and Link-F3 was measured by HPLC. For pharmacokinetic and metabolic studies, C.B-17 SCID mice bearing Daudi xenografts were treated with 10 mg/kg Link-N3 or 5mg/kg Link-F3 IV. Plasma and tissues were collected between 5 and 1440 min. Urine was collected at 360 and 1440 min. Concentrations of Link-N3 and Link-F3 were determined by HPLC-UV, and metabolites were identified by LC-MS/MS. For efficacy compounds were administered qdx4 at the same doses. Results: The IC50’s for Link-N3 and Link-F3 against Daudi cells could not be determined because compounds precipitated at concentrations above 30 μM. Daudi cells accumulated Link-N3 and Link-F3 ∼19-fold and ∼17-fold, respectively, with peak intracellular concentrations between 3 and 6 h of incubation. Neither compound resulted in tumor growth inhibition following IV dosing. Following a single IV dose of 10 mg/kg Link-N3 or 5 mg/kg Link-F3, peak plasma concentrations at 5 min were 27.3 μg/ml and 5.3 μg/ml, respectively. Plasma Auc0-t for Link-N3 and Link-F3 were 1759.6 μg·min/ml and 137.9 μg·min/ml, respectively. Plasma T1/2 of Link-N3 and Link-F3 were 394 and 7 min, respectively. The volume of distribution was approximately 3204 ml/kg and 35 ml/kg for Link-N3 and Link-F3, respectively. Clearances for Link-N3 and Link-F3 were 5.6 ml/min/kg and 3.6 ml/min/kg, respectively. Peak tumor concentration of Link-N3 at 30 min was 0.77 μg/g and Link-F3 at 5 min was 0.49 μg/g, both much lower than peak plasma concentrations. Conclusion: The lack of significant antitumor activity of Link-N3 or Link-F3 in tumor-bearing mice is related to the low concentrations that reached the xenografts. Modification will be required in these bivalent compounds to make them more drug-like. Support: 1R01CA142580 and P30-CA47904 Citation Format: Jianxia Guo, Dana M. Clausen, Edward V. Prochownik, Steven J. Metallo, Robert A. Parise, Jan H. Beumer, Julie L. Eiseman. Cytotoxicity in vitro , pharmacokinetics and tissue distribution of Link-N3 and Link-F3, two bivalent small molecules inhibitors of c-Myc/Max interactions in C.B-17 SCID mice bearing Daudi Burkitts lymphoma xenografts. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1019. doi:10.1158/1538-7445.AM2013-1019

Novel small molecule inhibitors of MDM2/4-p53 interaction, YH264 and its ethyl ester YH263: Preclinical evaluation

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Introduction: In p53+/+ cells, expression of MDM2/4 leads to turnover of p53 and inhibition of downstream gene transcription decreasing cell cycle arrest or apoptosis. Prevention of MDM2/4-p53 interaction is a promising therapeutic strategy. Two in-house developed small molecule inhibitors of MDM2/4-p53 binding, YH264 and YH263, had nM activity in protein binding assays, were characterized by co-crystal structures, and had low µM activity in the NCI 60 cell screen. We evaluated in vitro cytotoxicity in HCT 116, human p53+/+ colon cancer cells as well as efficacy, pharmacokinetics, and metabolism in mice bearing HCT 116 xenografts. Methods: Cytotoxicity against HCT 116 cells was assessed by 72 h MTT assay. C.B-17 SCID mice bearing HCT 116 xenografts (5 mice/group) were dosed with either YH264 or YH263 (150 mg/kg IV or PO), or vehicle QDx5 and tumors were measured twice weekly for at least 1 week post dosing. For pharmacokinetic studies, mice bearing HCT 116 xenografts were treated with 150 mg/kg YH264 or YH263 IV and PO. Plasma and tumor were collected between 5 min and 24 h. Urine was collected between 0-6 h and 6-24 h. YH264 and YH263 in cells from the in vitro study and tissues were quantitated with an LC-MS/MS assay. Pharmacokinetic parameters were calculated non-compartmentally. Results: IC50 values of YH264 and YH263 were 18.6 (9 µg/ml) and 8.9 µM (4 µg/ml), respectively. When mice were dosed IV or PO for QDx5 with YH264 or YH263, no decrease in body weights or significant decrease in xenograft volume was observed when compared to vehicle treated mice. Plasma elimination of IV YH264 was biphasic. Plasma and tumor parameters were respectively: Cmax 1,451 µg/ml and 44 µg/g; AUC0-t 125,000 µg·min/ml and 38,000 µg·min/g. Tumor concentrations remained above 17 µg/g out to 24 h. Plasma t1/2 was 147 min and clearance was 1.2 ml/min/kg. Metabolites included hydroxylated and glucuronidated products. After PO dosing, bioavailability was 18% and YH264 was undetectable in tumor. IV plasma elimination of the ethyl-ester YH263 was biphasic as well. Plasma and tumor parameters were respectively: Cmax 995 µg/ml and 21 µg/g; AUC0-t 45,477 µg·min/ml and 18,950 µg·min/g. Tumor concentrations remained above 7 µg/g for 24 h. Plasma t1/2 was 263 min and clearance was 3.3 ml/min/kg. 2% of the YH263 dose was converted to YH264 and there were multiple hydroxylated and glucuronidated metabolites. After PO dosing, bioavailability was 4.8%. In culture YH264 and YH263 cellular concentrations were ∼60- and 200-fold higher than medium concentrations. Conclusions: At the IC50 medium concentration, the cells accumulated 200-fold higher concentrations: of YH263 than medium. Despite dosing the mice at the maximum soluble dose, we could not achieve tumor concentrations (∼800 µg/g) equivalent to those required to inhibit cells in vitro. This may explain the absence of efficacy on the current schedule. P30-CA47904, Dept. of Pharm.Sci. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4726. doi:1538-7445.AM2012-4726

Abstract 5465: Modulation of DMS612 (BEN) pharmacokinetics and metabolism in mice by disulfiram, and aldehyde dehydrogenase inhibitor

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Introduction: DMS612 (NSC 281612, BEN) is an alkylating agent in clinical trials based on its in vitro and in vivo activity against renal cell carcinoma. We previously reported that BEN is rapidly metabolized into its carboxylic acid (BA), and that BEN and BA undergo chemical degradation both in vitro and in vivo. In addition, we demonstrated that BEN is rapidly metabolized into at least 13 different analytes in vivo. We hypothesized that BEN is metabolized to BA by aldehyde dehydrogenase (ALDH). In an attempt to increase the exposure to BEN, we explored the effect of the ALDH inhibitor disulfiram on the pharmacokinetics of BEN in mice. Materials & Methods: Female CD2F1 mice were dosed with either 20 mg/kg BEN i.v. alone or 24 h after the i.p. administration of 300 mg/kg disulfiram. Plasma and urine concentrations of BEN and its metabolites were quantitated by LC-MS/MS. Plasma pharmacokinetic parameters were calculated non-compartmentally. Urinary excretion of BEN and metabolites was calculated as percentage of the dose. Results: BEN was metabolized to at least 13 different products as previously reported. In the BEN alone study, BEN was metabolized quickly with a half-life <5 min. The half-lives of the metabolites were < 2 h. Pretreatment with disulfiram resulted in a 300-fold increase in exposure to BEN, from AUC0-inf 143 ng/mL*min to 40,515 ng/mL*min, while BA exposure remained similar, at AUC0-inf 254,280 ng/mL*min after BEN alone to AUC0-inf 274,947 ng/mL*min after disulfiram. In addition, the half-lives and AUCs of some of the metabolites in the BEN + disulfiram study appeared to be longer than when BEN was administered alone. Urinary excretion of BEN was increased 50% after disulfiram (from 1% to 1.5 % of the dose), BA excretion accounted for 5.8% of the dose after BEN alone and this was not markedly affected by disulfiram pretreatment. Conclusions: BEN is rapidly metabolized into many metabolites, which could affect the efficacy of BEN as an anti-neoplastic agent. We have demonstrated that by administering the ALDH inhibitor disulfiram the exposure to BEN is greatly increased, suggesting that ALDH is at least partly responsible for the rapid metabolism of BEN. However, the plasma exposure to BA increased only 8%. Our results will aid in the interpretation of ongoing clinical studies with BEN, which include genotyping for ALDH. Support: N01-CM07106, N01-CM52202, P30-CA47904. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5465. doi:10.1158/1538-7445.AM2011-5465

Abstract 2532: In vitro cytotoxicity, and pharmacokinetics, tissue distribution, and metabolism of the protein kinase D inhibitors, kb-NB142-70 and kb-NB184-43, in mice bearing human cancer xenografts

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Introduction: Protein kinase D (PKD) contributes to prostate and pancreatic cancer cell growth and survival. Therefore, PKD inhibitors are potential anticancer agents. kb-NB142-70 (NB142) and its methoxy-analogue, kb-NB184-43 (NB184), inhibit PKD in vitro. Methods: The in vitro inhibition of growth of Pc 3 prostate cells and Panc-1 pancreatic cells by NB142 and NB184 was evaluated by MTT assay. We evaluated the pharmacokinetics of NB142 in SCID mice bearing Pc 3 human prostate cancer xenografts and of NB184 in SCID mice bearing Panc-1 cancer xenografts. NB142 or NB184 was administered i.v. at 25 mg/kg. Three mice per time point were euthanized at 5, 15, 30, 60, 120, 240, 360, 960 and 1440 min after dosing. Plasma, tissues and urine were collected, and concentrations of NB142 and NB184 were quantitated by HPLC-UV. Metabolites in plasma and urine were characterized by LC-MS/MS. Results: The IC50s of NB142 and NB184 were 21.0 µM and 24.3 µM, respectively, against Pc 3; and 33.7 µM and 27.4 µM, respectively, against Panc-1. After dosing NB142, the plasma NB142 Cmax (at 5 min) was 36.9 µM, and the NB142 Pc 3 tumor Cmax was 11.8 µM. NB142 was not detected in plasma, liver, kidney, spleen, or heart beyond 30 min. After dosing NB184, the plasma, liver, and kidney NB184 Cmax, (at 5 min) were 61.9 µM, 42.6 µM, and 94.8 µM, respectively. The NB184 Cmax in Panc-1 tumors (at 15 min) was 8.0 µM. Areas under the concentration vs time curves of NB142 and NB184 in plasma were 409 and 782 nmol·min/ml, respectively. The plasma half-lives of NB142 and NB184 were 6 and 14 min, respectively. The major metabolite of NB142 was a glucuronide. Between 0-6 h, urinary excretion of NB142 and metabolites accounted for 2.5 % and 7.6%, respectively, of the administered dose. NB184 underwent oxidation and glucuronidation, and more than 10 metabolites were observed. NB142 was not detected in plasma after administration of NB184. Between 0-16 h, urinary excretion of NB184 and metabolites accounted for 2.1 % and 5.3%, respectively, of the administered dose. Conclusions: Although the inclusion of a methoxy group in NB184 increased its plasma half-life approximately 3-fold compared to NB142, metabolic and urinary elimination of both compounds was relatively rapid. Peak tumor concentrations of NB142 and NB184 were of the same order of magnitude as the concentrations required in vitro for cytotoxicity. (Support: P30-CA47904 and P01-[CA078039][1]) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2532. [1]: /lookup/external-ref?link_type=GEN&access_num=CA078039&atom=%2Fcanres%2F70%2F8_Supplement%2F2532.atom

Abstract 3524: Plasma pharmacokinetics and metabolism of benzaldehyde dimethane sulfonate (NSC281612, DMS612, BEN) in mice

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Introduction: BEN is an alkylating agent in early clinical trials based on its in vitro and in vivo activity against renal cell carcinoma. We have previously reported that BEN is rapidly metabolized into its carboxylic acid (BA) and that BEN and BA undergo chemical conversion in vitro. In support of current clinical trials, we characterized the pharmacokinetics of BEN, BA, and their products in mice. Materials & Methods: Female CD2F1 mice were dosed with 20 mg/kg BEN i.v. Twelve blood samples were obtained between 0 and 24 hrs and urine was collected at 0-6 hrs and 6-24 hrs. Formic acid was added to all samples (5%, v/v) and the sample processing was performed on ice to stop ex vivo chemical conversions. Plasma and urine concentrations of BEN, and its metabolites and conversion products were quantitated with LC-MS/MS. Plasma and urine pharmacokinetic parameters were calculated non-compartmentally. Results: BEN was rapidly converted to at least 13 different metabolites or products. The half-life (T1/2) of BEN was approximately 60 min. Half-lives of metabolites were all >2 h. The analytes that could be quantitated in urine represented approximately 30% of the dose administered. View this table: ND, not detectable; NQ, not quantifiable. Conclusions: BEN is rapidly metabolized to BA and chemically converted to many subsequent products, some of which are glucuronidated. Several metabolites and conversion products contain chloroethyl or methanesulphonate moieties, which would allow them to alkylate cellular targets and exhibit anti-neoplastic properties or cause toxicity. The enzymes responsible for the metabolism of BEN and BA need to be identified. Support: N01-CM07106, N01-CM52202, P30-CA47904 from the NCI. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3524.

Abstract 2540: Cytotoxicity, pharmacokinetics and metabolism of 10074-G5, a novel small-molecule inhibitor of c-Myc

Introduction The transcription factor c-Myc plays an important role in cellular proliferation, differentiation, apoptosis and cell cycle progression; is overexpressed in numerous cancer types; and is associated with cancer aggressiveness and poor prognosis. In order to be transcriptionally active, c-Myc must heterodimerize via its bHLH-ZIP domain with its obligatory partner Max. 10074-G5 is a small molecule that prevents c-Myc/Max heterodimerization, thereby inhibiting c-Myc function. We have characterized the ability of 10074-G5 to inhibit the in vitro growth of 2 c-Myc-overexpressing human cell lines: Daudi, a Burkitt9s lymphoma; and HL-60, a myelocytic leukemia. We also analyzed the effect of 10074-G5 on c-Myc/Max heterodimer formation and total c-Myc protein expression in Daudi cells and evaluated the pharmacokinetics and metabolism of 10074-G5 in mice bearing Daudi xenografts. Methods Inhibition of Daudi and HL-60 cell growth by 10074-G5 was assessed by MTT assay after 72 h of incubation. Accumulation of 10074-G5 by Daudi cells incubated with 10 μM 10074-G5 was measured by HPLC. c-Myc/Max co-immunoprecipitations and Western blots were performed on whole cell lysate from control and 10 μM 10074-G5-treated Daudi cells. For pharmacokinetic and metabolic studies, C.B-17 SCID mice bearing Daudi xenografts were treated with 20 mg/kg 10074-G5 iv. Plasma and tissues were collected at 12 specified time points between 5 and 1440 min. Urine was collected at 360 and 1440 min. Concentrations of 10074-G5 were determined by HPLC-UV, and metabolites were identified by LC-MS/MS. Results 10074-G5 inhibited in vitro growth of Daudi cells (IC50 15.6 µM) and HL-60 cells (IC50 13.5 µM). Daudi cells accumulated 10074-G5 approximately 50-fold, and peak intracellular concentrations of >20 nmoles/108 cells were observed between 4 and 8 h of incubation. After exposure to 10 µM 10074-G5, c-Myc/Max heterodimer formation was inhibited at 4 h, and c-Myc total protein expression was decreased by 70% after 24 h. In mice, 10074-G5 was non-toxic at the highest soluble dose of 20 mg/kg iv. 10074-G5 had a peak plasma concentration of 58 µM, a plasma half-life of 37 min, and concentrations in plasma were below the limit of detection beyond 240 min. Structural elucidation of 19 metabolites by LC-MS/MS indicated that hydroxylation and glucuronidation were the major metabolic pathways of 10074-G5. Concentrations of 10074-G5 in the tumor peaked at 5 min and were 5.6 µM, which was 10-fold lower than concomitant plasma concentrations. After 120 min, tumor concentrations of 10074-G5 were below the limit of detection. Conclusion 10074-G5 is rapidly metabolized in mice, and, based on in-vitro data, tumor concentrations of 10074-G5 at the currently administered dose are too low to inhibit c-Myc/Max dimerization. Evaluation of more metabolically stable and soluble analogues is warranted. (Support: P01-CA078039 and P30-CA47904) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2540.

Abstract 4549: Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice

Introduction Cytidine drugs, such as gemcitabine, undergo rapid, inactivating catabolism by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine drug metabolism. However, p.o. THU is at most 20% bioavailable (Beumer et al.), which limits its preclinical evaluation and clinical use. Therefore, the more lipophilic prodrug triacetyl THU (taTHU) was developed. We characterized THU pharmacokinetics after administration of taTHU to mice. Methods Mice were dosed 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters and p.o. bioavailability were calculated non-compartmentally and compartmentally. We assessed taTHU inhibition of metabolism of gemcitabine by recombinant CD. Results THU, after 150 mg/kg taTHU i.v., had a 235 min terminal half-life and produced plasma THU concentrations >1 µg/mL, the concentration shown to inhibit CD, for 10 h. A multi-compartment model fit the data best. 150 mg/kg p.o. taTHU produced a concentration versus time profile with a plateau of approximately 10 µg/mL from 0.5-2 h, followed by a decline with a 122 min half-life. Approximately 68% of i.v. taTHU was converted to THU. Approximately 30% of p.o. taTHU reached the systemic circulation as THU. After i.v dosing, renal excretion accounted for 40-55% of the taTHU dose, 26-35% as THU and an additional 14-19% as acetylated forms of THU. After p.o. dosing, the renal excretion percentages were 6-12%, 5.2-11%, and 0.42-0.71%, respectively. taTHU did not inhibit recombinant CD. Conclusion The availability of THU after p.o. taTHU in mice is 30%, as compared to the 20% achieved after p.o. THU. Clinical studies are warranted to evaluate availability of THU from taTHU in humans. Support: N01-CM07106, N01-CM52202, P30-CA47904 from the NCI and P41-EB001978. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4549.

Noninvasive assessment of tissue distribution and tumor pharmacokinetics of Pc 181, a silicon phthalocyanine analogue, in mice

Objective: In in vitro photodynamic therapy, the LD50 of Pc 181 has been reported to be 7 to 8 times less than that of silicon phthalocyanine 4 (Pc 4). The Optical Pharmacokinetic System (OPS) can measure photosensitizer concentrations in accessible tissues non-invasively. We used OPS to evaluate the tumor pharmacokinetics of Pc 181 and Pc 4 and the tissue drug distribution in SCID mice bearing either human breast cancer MDA-MB-231 or human head and neck squamous cell carcinoma SCC-15 xenografts. Methods: Following iv administration of 2.5 mg/kg Pc 181 or 2 mg/kg Pc 4 to SCID mice, OPS measurements were taken on tumor and normal tissues between 5 and 4320 min in vivo or in situ. Results: Large variations in tumor Pc 181 concentrations were observed among mice. In MDA-MB-231 tumors, the Pc 181 concentration peaked at 240 min, and was retained in the tumor. Tumor Pc 181 concentrations were much less than the tumor Pc 4 concentrations at an equimolar dose. Pc 181 concentrations were the highest in liver, followed by spleen, and kidney. In mice bearing SCC-15 xenografts, skin and underlying tissue Pc 181 concentrations were higher than tumor concentrations at all time points examined. Conclusions: This first Pc 181 pharmacokinetics study described a tissue Pc 181 distribution similar to that of Pc 4. However, tumor Pc 181 concentrations were lower than those of Pc 4 at equimolar doses.