An investigation into the formation of N- [2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 6-[2-(dimethylamino)ethylamino]- 3-hydroxy-7H-indeno[2, 1-C]quinolin-7-one dihydrochloride (TAS-103) stabilised DNA topoisomerase I and II cleavable complexes in human leukaemia cells

The antitumour agents DACA (XR5000; N-[2-(dimethylamino)ethyl]acridine-4-carboxamide) and TAS-103 (6-[2-(dimethylamino)ethylamino]-3-hydroxy-7H-indeno[2, 1-c]quinolin-7-one dihydrochloride) have been shown to inhibit two essential nuclear enzymes in vitro, DNA topoisomerase I and DNA topoisomerase (topo) II. To examine whether DACA or TAS-103 stabilise topo I, topo IIalpha, and topo IIbeta cleavable complexes in human leukaemia CCRF-CEM cells, the TARDIS assay (trapped in agarose DNA immunostaining) was used. This assay can reveal drug-stabilised topo-DNA complexes formed in situ in individual cells. The results showed that both DACA and TAS-103 can stabilise topo IIalpha cleavable complexes in these cells. Topo IIbeta cleavable complexes were also formed, but only at high concentrations of DACA and TAS-103. The effect on topo I was less clear, with TAS-103 showing only low levels of cleavable complex formation and DACA having no detectable effect under these assay conditions. This is in contrast to the purified enzyme cleavable complex assay, where both DACA and TAS-103 poisoned topo I. Although both DACA and TAS-103 show a preference for topo IIalpha in whole cells using the TARDIS assay, the formation of low levels of topo I or topo IIbeta cleavable complexes may still play a role in cell death.     

Efficacy of MGI 114 (HMAF) against the MRP+ metastatic MV522 lung carcinoma xenograft

This study is part of an effort to evaluate efficacy of the novel agent MGI 114 (HMAF) against tumors resistant to conventional chemotherapeutic agents. MGI 114 is a novel semisynthetic anticancer agent currently in chemotherapeutic phase II trials to evaluate activity against various solid tumors. Previous studies indicate MGI 114 was active against human MDR1/gp170+ solid tumor xenografts. Recent evidence suggests overexpression of the MRP protein may also be clinically relevant to development of drug resistance in solid tumors. We evaluated the efficacy of MGI 114 against a human MRP+ lung carcinoma xenograft. Parent MV522 lung carcinoma cells were transfected with a MRP cDNA expression vector and resistant cells selected by exposure to vinblastine (30-fold resistance). Analysis of resistant clones indicated 20- to 40-fold increases in expression of both MRP mRNA and MRP protein. Administration of MGI 114 at the maximum tolerated dose (7 mg/kg, 5 x/week for 3 weeks) to MRP tumor-bearing mice demonstrated this novel agent was active against MRP+ tumors and significantly extended their lifespan (p<0.001). In contrast, other cytotoxic agents had minimal activity against this MRP+ xenograft. These results indicate MGI 114 should retain activity in vivo against MRP+ tumor types. The development of this MRP+ xenograft model, in conjunction with the parent MV522 and MDR1/gp170+ xenograft models, will be useful for screening new classes of agents for activity against multidrug-resistant tumors.     

A new mechanism of 6-((2-(dimethylamino)ethyl)amino)-3-hydroxy-7H-indeno(2,1-c)quinolin-7-one dihydrochloride (TAS-103) action discovered by target screening with drug-immobilized affinity beads

6-((2-(Dimethylamino)ethyl)amino)-3-hydroxy-7H-indeno(2,1-c)-quinolin-7-one dihydrochloride (TAS-103) is a quinoline derivative that displays antitumor activity in murine and human tumor models. TAS-103 has been reported to be a potent topoisomerase II poison. However, other studies have indicated that cellular susceptibility to TAS-103 is not correlated with topoisomerase II expression. Because the direct target of TAS-103 remained unclear, we searched for a TAS-103 binding protein using high-performance affinity latex beads. We obtained a component of the signal recognition particle (SRP) as a TAS-103 binding protein. This component is a 54-kDa subunit (SRP54) of SRP, which mediates the proper delivery of secretory proteins in cells. We fractioned 293T cell lysates using gel-filtration chromatography and performed a coimmunoprecipitation assay using 293T cells expressing FLAG-tagged SRP54. The results revealed that TAS-103 disrupts SRP complex formation and reduces the amount of SRP14 and SRP19. TAS-103 treatment and RNAi-mediated knockdown of SRP54 or SRP14 promoted accumulation of the exogenously expressed chimeric protein interleukin-6-FLAG inside cells. In conclusion, we identified signal recognition particle as a target of TAS-103 by using affinity latex beads. This provides new insights into the mechanism underlying the effects of chemotherapies comprising TAS-103 and demonstrates the usefulness of the affinity beads.     

雄黄注射液体内外抗肿瘤作用研究

目的:初步探讨雄黄注射液的体内外抗肿瘤作用。方法:采用噻唑蓝(MTT)方法观察雄黄注射液对培养的人白血病细胞株K562,人肝癌细胞株HepG-2,人胃癌细胞株MGC-803,和小鼠Lewis肺癌细胞的增殖抑制作用;建立小鼠S180腹水型肉瘤模型,采用1、2、3mg/kg剂量雄黄注射液作用于小鼠模型,观察雄黄注射液体内抗肿瘤作用。结果:MTT法显示雄黄注射液对人白血病细胞株K562,人肝癌细胞株HepG-2,人胃癌细胞株MGC-803,和小鼠Lewis肺癌细胞增殖有一定的抑制作用;灌胃给予雄黄注射液对小鼠S180腹水型肉瘤生长有一定抑制作用。结论:雄黄注射液能够抑制培养的肿瘤细胞生长,灌胃给药对S180腹水型肉瘤细胞移植的模型小鼠肿瘤增殖有明显的抑制作用。     

Effects of the Ru(III) complexes [mer-RuCl3(DMSO)2Im]degrees and Na[trans-RuCl4(DMSO)Im] on solid mouse tumors.

The effects of two new Ru(III) complexes, [mer-RuCl3(DMSO)2Im] degrees and Na[trans-RuCl4(DMSO)Im], were investigated on primary tumor growth and on the survival time using three solid metastasizing tumors of the mouse: Lewis lung carcinoma, B16 melanoma and MCa mammary carcinoma. Na[trans-RuCl4(DMSO)Im] appears to be the most promising compound, in that: (1) it is soluble in water and therefore easy to handle in comparison with the neutral species [mer-RuCl3(DMSO)2Im]degrees or to the already described BBR2382; (2) similarly to cisplatin, though at a lower level, it reduces tumor growth in its primary site in each tumor model employed; (3) unlike cisplatin, it increases the life span of tumor-bearing hosts in all tumors used, independently of the effects on primary tumor growth; and (4) it is also effective in reducing spontaneous metastasis formation when the effects on primary tumor growth are completely absent. Dimethylsulfoxide (DMSO), used for solubilizing poorly water-soluble compounds (i.e. [mer-RuCl3(DMSO)2Im]degrees) or for stabilizing the compound in the solution before injection (i.e. Na[trans-RuCl4(DMSO)Im]), reduces the anti-tumor potency. Conversely, the antitumor effects of Na[trans-RuCl4(DMSO)Im] are more pronounced in mice hydrated with isotonic saline. We conclude that Na[trans-RuCl4(DMSO)Im] is a good candidate for further investigations aimed at ascertaining the mechanism of the anti-metastatic activity and of the positive effects on survival time of mice bearing solid metastasizing tumors.     

Promising antitumor activity of a novel quinoline derivative, TAS-103, against fresh clinical specimens of eight types of tumors measured by flow cytometric DNA analysis

TAS-103, 6-[[2-(dimethylamino)ethyl]amino]-3-hydroxy-7H-indeno-[2,1-c]quinolin-7-one dihydrochloride, is a dual topoisomerases I and II inhibitor. Antitumor activities of TAS-103 against fresh surgical specimens resected from 525 patients (32 types of tumors) were examined by flow cytometric (FCM) analysis of DNA integrity of tumor cells, and compared with those of five other investigational new drugs and 31 clinically available anticancer agents. Concentrations of clinically available anticancer agents were set at one-tenth of the peak plasma concentration (PPC) of the clinically recommended doses. On the other hand, since PPCs of investigational new drugs in humans were frequently unknown, these were estimated by a method that determines the theoretically achievable concentration in body fluid (TAC method). Correlations between TAC and PPC were examined for 16 clinically available anticancer agents, and it was found that TAC at 7n (the modified Fibonacci's dose-escalation scheme) of 14 drugs corresponded well with each one-tenth of PPC. By defining a 30% or more reduction in the integrated diploid peak as effective and a 60% or more reduction as definitely effective, TAS-103 at 5 microg/ml (7n) showed significantly higher effective rates and definitely effective rates than those of all other investigational new drugs, as well as almost all clinically available anticancer agents, against various malignancies, including non-small cell lung cancer, brain tumor and renal cancer. These results strongly suggest that TAS-103 will be expected to show excellent antitumor activities against a wide range of human tumors.     

鸦胆子油亚纳米乳注射液对小鼠移植性肿瘤的抑制作用

目的观察鸦胆子油亚纳米乳注射液对3种小鼠移植性肿瘤的抑制作用。方法应用移植性s180腹水瘤、Heps肝癌细胞、Lewis肺癌细胞荷瘤小鼠,设鸦胆子油亚纳米乳注射液0．45、0．9、1．8g·kg^-13个剂量组,尾静脉给药,计算肿瘤生长抑制率。结果鸦胆子油亚纳米乳注射液低、中、高剂量对小鼠S180腹水瘤的抑制率分别为11．1％、19．5％、33．5％;对小鼠Heps肝癌细胞抑制率分别为12．6％、21．1％、33．0％;对小鼠Lewis肺癌细胞抑制率分别为14．0％、24．9％、42．2％。与模型对照组比较,低剂量组差异无统计学意义（P〉0．05）,中、高剂量组差异有统计学意义（P〈0．05,P〈0．01）,呈现一定的剂量相关性。结论鸦胆子油亚纳米乳注射液对ICR小鼠S180腹水瘤、Heps肝癌、Lewis肺癌有明显的抑制作用。     

Preparation and in vivo evaluation of liposomal everolimus for lung carcinoma and thyroid carcinoma

Everolimus has demonstrated antitumor efficacy for various cancers as a result of its inhibition of the mammalian target of rapamycin (mTOR) signaling cascade, which activates cell growth and cell proliferation. However, the low water solubility and low bioavailability of everolimus have prevented its clinical development as an anticancer drug. Therefore, to address the unsuitable characteristic of everolimus, we attempted to prepare liposomal everolimus as a viable drug delivery system, and then evaluated the anticancer efficacy of this system against a medullary thyroid carcinoma cell line (TT cells), a breast cancer cell line (MCF-7 cells) and a small lung carcinoma cell line (NCI-H446 cells). The particle size and entrapment efficacy of liposomal everolimus was ca. 80 nm and more than 90%, respectively. Liposomal everolimus showed higher cytotoxicity against NCI-H446 cells compared with TT cells. Against NCI-H446 tumors, significant suppression of the tumor volume was observed in liposomal everolimus-treated mice by intravenous injection, compared with free everolimus-treated mice by intraperitoneal injection, at a dose of 5 mg/kg without body weight loss. This study showed that liposomal everolimus could be a powerful formulation with anticancer efficacy for some cancers.     

Potential antitumor agents. 49. 5-substituted derivatives of N-[2-(dimethylamino)ethyl]-9-aminoacridine-4-carboxamide with in vivo solid-tumor activity

Derivatives of N-[2-(dimethylamino)ethyl]-9-aminoacridine-4-carboxamide bearing a wide variety of different groups at the 5-position (and for comparative purposes at the 7-position) have been prepared, and their physicochemical properties and biological activities have been determined. Although both 5- and 7-substituted compounds bind equally well to DNA by intercalation, only the 5-substituted compounds have in vivo antitumor activity. All the 5-substituted compounds showed in vivo antileukemic activity, but only those bearing electron-withdrawing substituents sufficiently powerful to ensure the acridine chromophore was uncharged at physiological pH showed activity in vivo against the Lewis lung solid tumor. The weakly basic derivatives do not show greater intrinsic cytotoxicity or selectivity toward solid tumor cells, and their broader spectrum of in vivo antitumor activity is attributed to the fact that they exist predominantly as monocations, which can distribute more efficiently.     

USP apparatus 4 method for in vitro release testing of protein loaded microspheres

In this study, we investigated whether the therapeutic efficacy of liposomal doxorubicin (DXR-SL) could be enhanced by angiotensin II (AT)-induced hypertension. AT-induced hypertension increased the volume of tumor blood flow in mice bearing a poorly vascularized Lewis lung carcinoma (LLC) tumor, but only slightly in mice bearing a well-vascularized colon carcinoma Colon 26 (C26) tumor. In therapeutic efficacy, AT-induced hypertension enhanced the antitumor activity of DXR-SL in mice bearing LLC and C26 tumors. Localization of DXR-SL after injection by AT-induced hypertension was observed outside tumor blood vessels in LLC and C26 tumors, but within them under the normotension. From these findings, AT-induced hypertension had potential to improve the delivery of DXR-SL to both well- and poorly vascularized solid tumors.     

Potential usage of liposomal 4beta-aminoalkyl-4'-O-demethyl-4-desoxypodophyllotoxin (TOP-53) for cancer chemotherapy

To enhance the therapeutic efficacy as well as to reduce the side effect, we attempted to liposomalize 4beta-aminoalkyl-4'-O-demethyl-4-desoxypodophyllotoxin (TOP-53), a novel and effective topoisomerase II inhibitor. More than 90% of TOP-53 was efficiently incorporated into the liposomes composed of dipalmitoylphosphatidylcholine and cholesterol by remote-loading method. Anti-tumor activity of liposomal TOP-53 against solid tumor was examined in vivo using colon26 NL-17 carcinoma model mice. Three doses of liposomal TOP-53 (12 mg/kg/dose) showed significant tumor growth suppression (97.5% reduction determined at day 25) and the increase in life span (33%) of tumor-bearing mice. Furthermore, one mouse out of 5 was completely cured after treatment. Since similar efficacy was observed in the free TOP-53 treated group, liposomalization does not contribute much to the enhancement of therapeutic efficacy. However, a slight but measurable damage at the injection site was observed when free TOP-53 was injected, and the damage was diminished by the liposomalization. Taken together, liposomalization reduces the side effect rather than enhancing the therapeutic efficacy when TOP-53 is used.     

Mutagenicity studies on catena-(S)-[mu-[N alpha-(3-aminopropionyl)histidinato(2-)-N1,N2,O:N tau]-zinc]

Z-103 (catena-(S)-[mu-[N alpha-(3-aminopropionyl)histidinato (2-)-N1,N2,O:N tau]-zinc], CAS 107667-60-7) was examined in the bacterial mutation test, a chromosomal aberration test with mammalian cells in culture and the micronucleus test using male mice. 1. Z-103 did not increase the number of revertants in Escherichia coli WP2 uvrA when tested at up to 5000 micrograms/plate in the presence or absence of metabolic activation. And Z-103 did not increase mutants in Salmonella typhimurium SD 100 (streptomycin dependent strain) or in Salmonella typhimurium TM677 (8-azaguanine sensitive strain) when tested at up to 5000 micrograms/ml in the presence or absence of metabolic activation. 2. The chromosomal aberration test was carried out with cultured Chinese hamster lung cells (CHL). For the direct assay procedure, the cells were treated with 3.3 x 10(-4)-3.3 x 10(-6) mol/l Z-103 for 24 or 48 h, after which time chromosome preparations were made. For the metabolic activation assay procedure, the cells were treated with 1.0 x 10(-3)-3.3 x 10(-6) mol/l of Z-103 for 6 h in the presence or absence of metabolic activation, and the chromosome preparations were made after a further 18-h incubation in the absence of Z-103 and metabolic activation. Z-103 did not cause chromosome aberrations either in the presence or in the absence of metabolic activation. 3. The micronucleus test was performed in ddY male mice. Z-103 was administered orally to mice at a dose of 400, 200 or 100 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)     

4-[4”-(2”,2”,6”,6”-四甲基哌啶氮氧自由基)氨基]-4’-去甲表鬼臼毒抗肿瘤作用

新合成的鬼臼毒素氮氧自由基衍生物4-[4”-(2”,2”,6”,6”-四甲基哌啶氮氧自由基)氨基]-4’-去甲表鬼臼毒(GP-7)显著抑制小鼠移植性肿瘤S180、实体型HePS和Lewis肺癌生长;7.5～20mg/kg,给药10d,抑瘤率分别为36.0％～58.4%、29.6%～60.0%和27.2%～46.5%;抑制作用和鬼臼乙叉甙(VP-16)相似。GP-7小鼠一次ip,LD_(50)为231.2mg/kg,是VP-16的3.3倍;连续给药10d,对小鼠脾和胸腺指数的影响较VP-16小,对小鼠WBC的影响和VP-16相同。GP-7和VP-165mg/L处理L1210细胞24h,抑瘤率分别为75.5%和73.6%;处理SGC-7901细胞72h,抑瘤率分别为81.4%和84.2%。     

Comparative antitumor activities of 7-N-(p-hydroxyphenyl)mitomycin C (M-83) and mitomycin C

The antitumor activity of 7-N-(p-hydroxyphenyl)mitomycin C (M-83) against 7 kinds of ascitic tumors and 4 kinds of solid tumors was compared with that of mitomycin C (MMC). M-83 showed more potent activities than MMC against ascites sarcoma 180, fibrosarcoma Meth 1, sarcoma Meth A, melanoma B-16, leukemia P388 and lymphoma EL4, by a single intraperitoneal injection. Furthermore, M-83 gave markedly higher chemotherapeutic ratio than MMC in these tumor systems. M-83 was also markedly effective against solid tumors of sarcoma 180, Meth 1, Meth A and Lewis lung carcinoma, by a single intravenous injection. M-83 gave lower myelo-suppression than MMC at the doses which gave almost equal inhibition on the tumor growth of solid Meth 1. M-83 and MMC significantly inhibited the growth of HeLa S3 cells. Cell growth was observed at 24 hours after addition of 3 X 10(-3) mM of drugs, but no growth was shown thereafter. M-83 inhibited more strongly the incorporation of the radioactive precursor into DNA than that into RNA or protein at the concentration of 3 X 10(-3) mM.     

The effect of a newly synthesized indazole compound, TAS-3-124, on experimental autoimmune disease

The effects of a newly synthesized compound, 6-acetoamido-1-acetyl-1-indazole (TAS-3-124), on autoimmune diseases were studied. We used animal models of collagen-induced arthritis (CIA) in mice and experimental autoimmune encephalomyelitis (EAE) in rats to evaluate the efficacy of TAS-3-124. TAS-3-124 at doses of 100 and 300 mg/kg p.o. inhibited the development of CIA, decreasing the swelling of fore- and hind-limbs and bone destruction in knee joints. This agent also suppressed the delayed type hypersensitivity reaction (DTH) against type II collagen. These effects were confirmed by histopathological examination and measurement of the expression of mRNA of proinflammatory cytokines in the knee joint. In addition, TAS-3-124 at a dose of 300 mg/kg inhibited the development of EAE and the DTH to myelin basic protein (MBP) in rats. Moreover, TAS-3-124 inhibited the production of proinflammatory cytokines including interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha and IL-6 but not T cell derived cytokines in mice. These demonstrate the efficacy of TAS-3-124 against experimental autoimmune disease, probably due to the suppression of the production of proinflammatory cytokines in the pathological lesion.     

DMH1 (4-[6-(4-isopropoxyphenyl)pyrazolo[1,5-a]pyrimidin-3-yl]quinoline) inhibits chemotherapeutic drug-induced autophagy

Our previous work found that DMH1 (4-[6-(4-isopropoxyphenyl)pyrazolo [1,5-a]pyrimidin-3-yl]quinoline) was a novel autophagy inhibitor. Here, we aimed to investigate the effects of DMH1 on chemotherapeutic drug-induced autophagy as well as the efficacy of chemotherapeutic drugs in different cancer cells. We found that DMH1 inhibited tamoxifen- and cispcis-diaminedichloroplatinum (II) (CDDP)-induced autophagy responses in MCF-7 and HeLa cells, and potentiated the anti-tumor activity of tamoxifen and CDDP for both cells. DMH1 inhibited 5-fluorouracil (5-FU)-induced autophagy responses in MCF-7 and HeLa cells, but did not affect the anti-tumor activity of 5-FU for these two cell lines. DMH1 itself did not induce cell death in MCF-7 and HeLa cells, but inhibited the proliferation of these cells. In conclusion, DMH1 inhibits chemotherapeutic drug-induced autophagy response and the enhancement of efficacy of chemotherapeutic drugs by DMH1 is dependent on the cell sensitivity to drugs.KEY WORDS: Autophagy, Tamoxifen, 5-Fluorouracil, Cancer cells     

小分子靶向肽（RGD）2C与力达霉素的偶联物抗肿瘤作用研究

目的：考察小分子靶向肽（RGD）：C与力达霉素的偶联物的抗肿瘤作用。方法：MTr法观察偶联物和力达霉素在体外对人口腔鳞癌KB细胞、人乳腺癌MCF-7细胞以及人肝癌Bel7402细胞的细胞毒性。克隆形成法观察其对人肝癌Bel7402细胞克隆形成的抑制作用。采用C57BIM6小鼠Lewis肺癌移植瘤模型观察其实验治疗作用。结果：MrlT法结果表明,偶联物对人口腔鳞癌KB细胞、人肝癌Bel7402细胞和人乳腺癌MCF-7细胞的细胞毒性比力达霉素分别下降13倍、46倍和186倍。克隆形成法表明．偶联物对人肝癌Bel7402细胞的克隆形成抑制率比力达霉素下降10倍。0．2,0．1,O．05mg·kg-1偶联物对C57BL／6小鼠Lewis癌皮下原发瘤的生长抑制率分别为35．8％,25．6％和10．3％;0．05mg·kg-1素对肿瘤生长的抑制率为32．4％。0．2,0．1,0．05mg·kg-1偶联物对小鼠Lewis癌肺转移的抑制率分别为69．6％,50．5％和34．2％,0．05mg·kg-1达霉素、0．05mg·kg-1力达霉素＋1mg·kg-1（RGD）：C肽的抑制率分别为53．3％和54．9％。结论：按等细胞毒性剂量来计算,偶联物体内抗肿瘤活性和抗肿瘤转移活性比力达霉素强,提示小分子靶向肽RGD与力达霉素偶联后发挥了一定的导向作用。     

Optimizing the dosing schedule of l-asparaginase improves its anti-tumor activity in breast tumor-bearing mice

Proliferation of acute lymphoblastic leukemic cells is nutritionally dependent on the external supply of asparagine. l-asparaginase, an enzyme hydrolyzing l-asparagine in blood, is used for treatment of acute lymphoblastic leukemic and other related blood cancers. Although previous studies demonstrated that l-asparaginase suppresses the proliferation of cultured solid tumor cells, it remains unclear whether this enzyme prevents the growth of solid tumors in vivo. In this study, we demonstrated the importance of optimizing dosing schedules for the anti-tumor activity of l-asparaginase in 4T1 breast tumor-bearing mice. Cultures of several types of murine solid tumor cells were dependent on the external supply of asparagine. Among them, we selected murine 4T1 breast cancer cells and implanted them into BALB/c female mice kept under standardized light/dark cycle conditions. The growth of 4T1 tumor cells implanted in mice was significantly suppressed by intravenous administration of l-asparaginase during the light phase, whereas its administration during the dark phase failed to show significant anti-tumor activity. Decreases in plasma asparagine levels due to the administration of l-asparaginase were closely related to the dosing time-dependency of its anti-tumor effects. These results suggest that the anti-tumor efficacy of l-asparaginase in breast tumor-bearing mice is improved by optimizing the dosing schedule.     

Antitumor activity of XR5944, a novel and potent topoisomerase poison

Inhibitors of topoisomerases are widely used in the treatment of cancer, including inhibitors of topoisomerase I (camptothecin analogs such as irinotecan and topotecan) and topoisomerase II (etoposide and doxorubicin). The novel bis-phenazine, XR5944, is a joint inhibitor of topoisomerase I and II as shown by the stabilization of topoisomerase-dependent cleavable complexes. XR5944 demonstrated exceptional activity against human and murine tumor cells in vitro and in vivo. In a range of cell lines XR5944 (IC50 0.04-0.4 nM) was significantly more potent than TAS-103, originally proposed as a joint topoisomerase I and II inhibitor, as well as agents specific for topoisomerase I or II (topotecan, doxorubicin and etoposide). In addition, XR5944 was unaffected by atypical drug resistance and retained significant activity in cells overexpressing P-glycoprotein or multidrug resistance-associated protein. Antitumor efficacy of XR5944 was demonstrated in human carcinoma xenograft models (H69 small cell lung cancer and HT29 colon). In the HT29 model, which is relatively unresponsive to chemotherapy, XR5944 (15 mg/kg i.v., q4dx3) induced tumor regression in the majority of animals (six of eight), whereas TAS-103, dosed at its maximum tolerated dose (45 mg/kg i.v., q7dx3), only induced a delay in tumor growth compared with control animals. In the H69 model, low doses of XR5944 (5 mg/kg i.v., qdx5/week for 2 weeks or 10-15 mg/kg i.v., q4dx3), induced complete tumor regression in the majority of animals. In contrast, topotecan (20 mg/kg i.v., q4dx3) or etoposide (30 mg/kg i.v., q5dx5) only slowed the tumor growth rate. These studies show that XR5944 is a highly active novel anticancer agent that is well tolerated at efficacious doses.