Highly tumorigenic lung cancer CD133+ cells display stem-like features and are spared by cisplatin treatment.

The identification of lung tumor-initiating cells and associated markers may be useful for optimization of therapeutic approaches and for predictive and prognostic information in lung cancer patients. CD133, a surface glycoprotein linked to organ-specific stem cells, was described as a marker of cancer-initiating cells in different tumor types. Here, we report that a CD133+, epithelial-specific antigen-positive (CD133+ESA+) population is increased in primary nonsmall cell lung cancer (NSCLC) compared with normal lung tissue and has higher tumorigenic potential in SCID mice and expression of genes involved in stemness, adhesion, motility, and drug efflux than the CD133(-) counterpart. Cisplatin treatment of lung cancer cells in vitro resulted in enrichment of CD133+ fraction both after acute cytotoxic exposure and in cells with stable cisplatin-resistant phenotype. Subpopulations of CD133+ABCG2+ and CD133+CXCR4+ cells were spared by in vivo cisplatin treatment of lung tumor xenografts established from primary tumors. A tendency toward shorter progression-free survival was observed in CD133+ NSCLC patients treated with platinum-containing regimens. Our results indicate that chemoresistant populations with highly tumorigenic and stem-like features are present in lung tumors. The molecular features of these cells may provide the rationale for more specific therapeutic targeting and the definition of predictive factors in clinical management of this lethal disease.

Synthesis, structural, and biological evaluation of bis-heteroarylmaleimides and bis-heterofused imides.

Bis-2,3-heteroarylmaleimides and polyheterocondensed imides joined through nitrogen atoms of the N,N'-bis(ethyl)-1,3-propanediamine linker were prepared from substituted maleic anhydrides and symmetrical diamines in good to satisfactory yields and short reaction times using microwave heating. The novel molecules were shown to inhibit proliferation of human tumor cells (NCI-H460 lung carcinoma) and rat aortic smooth muscle cells (SMCs) with variable potencies. Compound 11a, the most potent one of the series, showed IC(50) values comparable to those observed for the leading molecule elinafide in both cell lines, but with a higher selectivity toward human tumor cells. Compound 11a affected G1/S phase transition of the cell cycle, showed in vitro DNA intercalating activity and in vivo antitumor activity. A thorough structural analysis of the 11a-DNA complex was also made by mean of NMR and computational techniques.

Pharmacogenomics and analogues of the antitumour agent N6-isopentenyladenosine.

N(6)-isopentenyladenosine (i(6)A), a member of the cytokinin family of plant hormones, has potent in vitro antitumour activity in different types of human epithelial cancer cell lines. Gene expression profile analysis of i(6)A-treated cells revealed induction of genes (e.g., PPP1R15A, DNAJB9, DDIT3, and HBP1) involved in the negative regulation of cell cycle progression and reportedly up-regulated during cell cycle arrest in stress conditions. Of 6 i(6)A analogues synthesized, only the 1 with a saturated double bond of the isopentenyl side chain had in vitro antitumour activity, although weaker than that of i(6)A, suggesting that i(6)A biological activity is highly linked to its structure. In vivo analysis of i(6)A and the active analogue revealed no significant inhibition of cancer cell growth in mice by either reagent. Thus, although i(6)A may inhibit cell proliferation by regulating the cell cycle, further studies are needed to identify active analogues potentially useful in vivo.

Eradication of ovarian tumor xenografts by locoregional administration of targeted immunotherapy.

PURPOSE: Oligodeoxynucleotides containing unmethylated CpG motifs (CpG-ODN) are potent activators of innate and adaptive immunity. Recognition of CpG-ODN is mediated by Toll-like receptor 9 expressed by immune cells, endothelial and epithelial cells, and fibroblasts. We examined the antitumor effect of CpG-ODN and the role of administration route on human ovarian cancers growing in the peritoneal cavity of nude mice. EXPERIMENTAL DESIGN: Mice implanted i.p. with human ovarian carcinoma cells were treated i.p., s.c., or i.v. and assessed for survival and tumor-free incidence. Peritoneal washings were analyzed for keratinocyte chemokine production and for functional and phenotypic profiles as indicators of the cell types involved in mediating the antitumor effects. RESULTS: IGROV-1-bearing mice treated i.p. survived significantly longer than those treated i.v. or s.c. (P=0.0005), and nearly half of them (8 of 17) were tumor-free by the end of the experiment, a rate never achieved using a variety of chemotherapeutic drugs. High rates of tumor-free mice were observed in three other ovarian tumor xenografts treated i.p. Compared with peritoneal washings of mice treated s.c. or i.v., those from mice treated i.p. showed the highest level of serum and tissue keratinocyte chemokine, the highest number of natural killer cells and neutrophils, and the highest antiproliferative activity in vitro. CONCLUSIONS: The superior antitumor effect obtained by locoregional administration of CpG-ODN in i.p. tumor-bearing mice with a limited adaptive immune response points to the importance of innate effector cells amplification at the site of tumor growth and suggests the promise of i.p. CpG-ODN in clinical trials for ovarian cancer.

Preclinical profile of antitumor activity of a novel hydrophilic camptothecin, ST1968.

ST1968 is a novel hydrophilic camptothecin (CPT) derivative of the 7-oxyiminomethyl series. Because ST1968 retained ability to form remarkably stable cleavable complexes, this study was done to investigate its preclinical profile of antitumor activity in a large panel of human tumor models, including irinotecan-resistant tumors. Although less potent than SN38 in vitro, i.v. administered ST1968 caused a marked tumor inhibition, superior to that of irinotecan, in most tested models. ST1968 exhibited an impressive activity against several tumors including models of ovarian and colon carcinoma in which a high rate of cures was observed. In the most responsive tumors, complete and persistent tumor regressions were achieved even with low suboptimal doses. Even tumors derived from intrinsically resistant cells exhibited a significant responsiveness. Histologic analysis of treated tumors supports a contribution of both proapoptotic and antiangiogenic effects to ST1968 antitumor efficacy. A study done in yeast cells transformed with CPT-resistant mutant forms of topoisomerase I documented that, in contrast to other tested CPT, ST1968 was active against yeasts expressing the mutant K720E enzyme. Based on its outstanding efficacy superior to that of irinotecan and of its good therapeutic index, ST1968 has been selected for clinical development.

Antimetastatic effect of a small-molecule vacuolar H+-ATPase inhibitor in in vitro and in vivo preclinical studies.

On the basis of the evidence that vacuolar H(+)-ATPase is implicated in the development of the metastatic phenotype, we have explored the possibility to target the enzyme function in an attempt to control the metastatic behavior of tumor cells. In this study, we used an indole derivative, NiK-12192 [4-(5,6-dichloro-1H-indol-2-yl)-3-ethoxy-N-(2,2,6,6-tetramethyl-piperidin-4-yl)-benzamide], recently identified as an effective inhibitor of vacuolar H(+)-ATPase, as a potential antimetastatic agent in the treatment of NSCLC H460 xenograft, which is able to induce lung metastases in mice. Oral administration of NiK-12192 caused a significant inhibition of formation of spontaneous metastases. In contrast, the drug exhibited a negligible effect on the development of artificial metastases (i.e., after i.v. injection of tumor cells), thus supporting that the drug affects the early events of the metastatic process (e.g., migration and invasion). Cellular effects are consistent with this interpretation. In conclusion, the available results show for the first time that a vacuolar H(+)-ATPase inhibitor is effective in modulation of the metastatic behavior of a lung carcinoma, supporting its potential therapeutic interest as a novel treatment approach.

Synthesis and biological evaluation of pyrroloiminoquinone derivatives.

Synthesis of 10 pyrroloiminoquinone derivatives is presented. The strategy is based around the elaboration of a common intermediate by reaction with primary amines. All the compounds obtained have been subjected to antiproliferative activity with three different cell lines (NCI-H460, HeLa, and HL-60). The capacity of 4 selected compounds to affect the enzymatic activity of the nuclear enzyme DNA topoisomerase II and to form the typical DNA fragmentation which occurs in the apoptotic process is discussed here.

Antiproliferative effects on human tumor cells and rat aortic smooth muscular cells of 2,3-heteroarylmaleimides and heterofused imides.

A series of 2,3-heteroarylmaleimides 9 and polyheterocondensed imides 12 were prepared in good yields and short reaction time using a very efficient procedure consisting in the condensation of the corresponding anhydrides and N,N-diethylethylenediamine and microwave heating. The antiproliferative activity of the novel molecules was tested against human tumor cells (NCI-H460 lung carcinoma) and rat aortic smooth muscle cells (SMCs). The IC50 values for the novel molecules ranged from 0.08 to 13.9 microM in SMCs, and from 0.84 to 9 microM in the tumor cell line. The activity profile for compounds 9 and 12 is comparable to that obtained for amonafide in NCI-H460, except for fused imides 12b,i which proved to be about 10-fold more potent. Whereas, in rat SMCs, only the compound 12b was shown to be 10-fold more potent than amonafide. Instead 12c is equipotent to amonafide. These results suggest that the extended pi-system and the kind of heteroatom are essential in the binding with the molecular target.

Biological properties of IDN5174, a new synthetic camptothecin with the open lactone ring.

A series of water-soluble camptothecins obtained by linking a spermidine moiety to the 21-position of the open form through an amidic bond have been tested for their biochemical and biological activities. Growth inhibition assay on the human non-small cell lung cancer carcinoma NCI-H460 cell line revealed that the camptothecin analogues were less potent than topotecan and SN38 after 1 hour of treatment. The potency increased after 72 hours of exposure, being similar to that of reference camptothecins. The analysis of topoisomerase I-mediated DNA cleavage using the purified enzyme indicated that the novel camptothecin analogues retained ability to poison topoisomerase I and displayed the same cleavage pattern of SN38. Persistence of the DNA cleavage was comparable with that of SN38. Stabilization of the cleavable complex was not the result of hydrolysis of the N-C bond between polyamine and the drug because no free camptothecin was recovered at the end of DNA cleavage in presence of IDN5174, the analogue selected for detailed studies. IDN5174 exhibited an antitumor activity comparable with that of topotecan and irinotecan against NCI-H460 tumor xenograft. The pharmacokinetics in mice showed a favorable disposition in tumor tissue with low amount of camptothecin detectable in plasma and tumor (around 5-10%), thus supporting the efficacy of intact IDN5174. In conclusion, we found that IDN5174 maintained the biological and antitumor properties, in spite of lack of the closed E ring. The available results support the interpretation that the polyamine linked at the 21-position may allow a favorable drug interaction in the ternary complex.

Preclinical efficacy of ST1976, a novel camptothecin analog of the 7-oxyiminomethyl series.

In previous studies, we have documented the potential therapeutic advantages of camptothecin analogs modified at the 7-position, i.e., 7-oxyiminomethyl derivatives. The present study was performed to explore the therapeutic potential of novel hydrophilic derivatives of this series. With one exception (ST1976), the tested camptothecins exhibited a reduced antiproliferative activity and all compounds retained ability to stabilize the topoisomerase I-mediated cleavable complex. The two analogs (ST1976 and ST1968) characterized by the presence of a free amino group in the side chain also exhibited the formation of persistent cleavable complexes. The most potent compound, ST1976 (7-(4-aminobenzyl)oxyiminomethylcamptothecin), was selected for evaluation of its preclinical profile of antitumor activity in a large panel of human tumor xenografts. As expected on the basis of the introduction of a hydrophilic substituent, the novel camptothecin was a substrate for BCRP. However, in spite of an apparent recognition by BCRP, ST1976 was effective following oral administration. The antitumor activity was evaluated using various schedules and routes of administration (i.v. and p.o.). ST1976 exhibited a remarkable activity in all tested tumors and was effective in a number of tumors which are resistant to irinotecan. The biological and pharmacological profile of ST1976 supports the therapeutic potential of camptothecins containing hydrophilic substituents at the 7-position. On the basis of its excellent activity in preclinical models, ST1976 is a promising candidate for clinical development.

Isolation and in vitro propagation of tumorigenic breast cancer cells with stem/progenitor cell properties.

Breast cancer-initiating cells have been recently identified in breast carcinoma as CD44+/CD24(-/low) cells, which exclusively retain tumorigenic activity and display stem cell-like properties. However, at present, direct evidence that breast cancer-initiating cells can be propagated in vitro is still lacking. We report here the isolation and in vitro propagation of breast cancer-initiating cells from three breast cancer lesions and from an established breast carcinoma cell line. Our breast carcinoma-derived cultures encompassed undifferentiated cells capable of self-renewal, extensive proliferation as clonal nonadherent spherical clusters, and differentiation along different mammary epithelial lineages (ductal and myoepithelial). Interestingly, cultured cells were CD44+/CD24- and Cx43-, overexpressed neoangiogenic and cytoprotective factors, expressed the putative stem cell marker Oct-4, and gave rise to new tumors when as few as 10(3) cells were injected into the mammary fat pad of SCID mice. Long-term cultures of breast tumorigenic cells with stem/progenitor cell properties represent a suitable in vitro model to study breast cancer-initiating cells and to develop therapeutic strategies aimed at eradicating the tumorigenic subpopulation within breast cancer.

Therapeutic synergism of gemcitabine and CpG-oligodeoxynucleotides in an orthotopic human pancreatic carcinoma xenograft.

CpG-oligodeoxynucleotides (CpG-ODN) exhibit potent immunostimulatory activity by binding with Toll-like receptor 9 (TLR9). Based on the finding that TLR9 is highly expressed and functional in pancreatic tissue, we evaluated the antitumor effects of chemotherapy combined with CpG-ODNs in the orthotopic mouse model of a human pancreatic tumor xenograft. Chemotherapy consisted of the maximum tolerated dose of gemcitabine (i.v., 100 mg/kg, q3dx4). CpG-ODNs were delivered (i.p., 20 microg/mouse), weekly, after the end of chemotherapy. CpG-ODNs alone had little effect on tumor growth, whereas gemcitabine alone significantly delayed the median time of disease onset (palpable i.p. tumor) and of bulky disease development (extensive peritoneal tumor burden), but did not enhance survival time. When the gemcitabine regimen was followed by administration of the immunostimulator, development of bulky disease was delayed, survival time was significantly improved (median survival time, 106 days; P < 0.02 versus gemcitabine-treated mice). Autoptic examination showed that tumor spread in the peritoneal cavity was reduced to a greater extent than with gemcitabine alone. All treatment regimens were well-tolerated. The use of nude mice excluded a T cell-mediated immune response, whereas the high pancreatic expression of TLR9 might have contributed to the tumor response. The clear improvement of survival observed in an orthotopic murine model of human pancreatic cancer by the combined use of CpG-ODNs with chemotherapy suggests the promise of this therapeutic regimen in the clinical setting.

Inhibition of c-Met and prevention of spontaneous metastatic spreading by the 2-indolinone RPI-1.

Hepatocyte growth factor (HGF) and its tyrosine kinase receptor Met play a pivotal role in the tumor metastatic phenotype and represent attractive therapeutic targets. We investigated the biochemical and biological effects of the tyrosine kinase inhibitor RPI-1 on the human lung cancer cell lines H460 and N592, which express constitutively active Met. RPI-1-treated cells showed down-regulation of Met activation and expression, inhibition of HGF/Met-dependent downstream signaling involving AKT, signal transducers and activators of transcription 3 and paxillin, as well as a reduced expression of the proangiogenic factors vascular endothelial growth factor and basic fibroblast growth factor. Cell growth in soft agar of H460 cells was strongly reduced in the presence of the drug. Furthermore, RPI-1 inhibited both spontaneous and HGF-induced motility/invasiveness of both H460 and human endothelial cells. Targeting of Met signaling by alternative methods (Met small interfering RNA and anti-phosphorylated Met antibody intracellular transfer) produced comparable biochemical and biological effects. Using the spontaneously metastasizing lung carcinoma xenograft H460, daily oral treatment with well-tolerated doses of RPI-1 produced a significant reduction of spontaneous lung metastases (-75%; P < 0.001, compared with control mice). In addition, a significant inhibition of angiogenesis in primary s.c. tumors of treated mice was observed, possibly contributing to limit the development of metastases. The results provide preclinical evidence in support of Met targeting pharmacologic approach as a new option for the control of tumor metastatic dissemination.

Apoptotic cell death induction and angiogenesis inhibition in large established medullary thyroid carcinoma xenografts by Ret inhibitor RPI-1.

Recent evidence indicates that the success of molecular targeted therapies may depend on the identification of drug targets which are essential for the survival of subsets of tumors. RET oncogenes that have been implicated in the development of thyroid carcinomas are emerging as potential therapeutic targets. In the present study, we investigated the efficacy and the cellular bases of antitumor activity of the indolinone Ret tyrosine kinase inhibitor RPI-1 against large established s.c. TT tumor xenograft, a human medullary thyroid carcinoma (MTC) harboring oncogenic MEN-2A-type RET mutation. Oral treatment with RPI-1 caused growth arrest or regression in 81% treated tumors. Following treatment suspension, tumor inhibition was maintained (51%, P<0.05, 100 days) and cures were achieved in 2/11 mice. In treated tumors, Ret was tyrosine dephosphorylated. Moreover, compared to control tumors, a significant increase in apoptotic cells (210%, P<0.0001), loss of cellularity (47%, P<0.0001) and reduction of microvessel density (36%, P<0.0005) were detected. In vivo effects of RPI-1 were reflected in activation of BAD, cleavage of caspases, apoptotic DNA fragmentation and inhibition of VEGF production observed in in vitro RPI-1-treated TT cells. These findings thus indicate that RPI-1 antitumor effect on the MTC was characterized by apoptosis induction and angiogenesis inhibition. The results, consistent with a dependence on RET oncogene activation for maintenance and survival of MEN2A-type MTC, provide further preclinical rationale for a pharmacological RET-targeted intervention in thyroid cancer.

Ribozyme-mediated inhibition of survivin expression increases spontaneous and drug-induced apoptosis and decreases the tumorigenic potential of human prostate cancer cells.

Survivin is a member of the inhibitor of apoptosis protein (IAP) family, which has been implicated in inhibition of apoptosis and control of mitotic progression. The finding that survivin is overexpressed in most human tumors but absent in normal adult tissues has led to the proposal of survivin as a promising therapeutic target for anticancer therapies. We decided to evaluate the effects of a ribozyme-based strategy for survivin inhibition in androgen-independent human prostate cancer cells. We constructed a Moloney-based retroviral vector expressing a ribozyme targeting the 3' end of the CUA(110) triplet in survivin mRNA, encoded as a chimeric RNA within adenoviral VA1 RNA. Polyclonal cell populations obtained by infection with the retroviral vector of two androgen-independent human prostate cancer cell lines (DU145 and PC-3) were selected for the study. Ribozyme-expressing prostate cancer cells were characterized by a significant reduction of survivin expression compared to parental cells transduced with a control ribozyme; the cells became polyploid, underwent caspase-9-dependent apoptosis and showed an altered pattern of gene expression, as detected by oligonucleotide array analysis. Survivin inhibition also increased the susceptibility of prostate cancer cells to cisplatin-induced apoptosis and prevented tumor formation when cells were xenografted in athymic nude mice. These findings suggest that manipulation of the antiapoptotic survivin pathway may provide a novel approach for the treatment of androgen-independent prostate cancer.

Antiangiogenic effects of the novel camptothecin ST1481 (gimatecan) in human tumor xenografts.

ST1481 (gimatecan) is a novel lipophilic camptothecin with a promising preclinical pharmacological profile. On the basis of its high antitumor efficacy when delivered by the oral route, the compound is suitable for prolonged administration. This schedule of treatment has been reported as the most appropriate to exploit the antiangiogenic effects of cytotoxic drugs. The aim of the study was to investigate the antiangiogenic and antitumor effects of oral ST1481 in human tumor xenografts. In spite of a marginal drug effect against the s.c. growing A549 lung carcinoma following administration with an intermittent schedule (q4dx4 times, maximum tolerated dose: 2 mg/kg), tumor growth was strongly inhibited by a daily low-dose (0.5 mg/kg) prolonged administration. Immunohistochemical analysis showed a reduced number of microvessels in tumors of both treated groups versus controls and a significantly higher reduction in the daily versus the q4dx4-treated tumors (P < 0.0001, by Student's t test). In our experimental model, the relation between microvessel density and tumor size (r = 0.738, by the Spearman rank test) suggests a role of inhibition of tumor vasculature in tumor response. Significant inhibition of tumor angiogenesis (P < 0.0001 versus control tumors) was observed even with a very low drug dose (0.06 mg/kg) in the orthotopically implanted (i.d.) MeWo melanoma, under conditions causing minimal tumor growth inhibition. Additional evidences of the antiangiogenic activity of ST1481 were provided by antimotility effects on endothelial cells, in vivo inhibition of vascularization in the Matrigel assay, and down-regulation of the expression of the proangiogenic basic fibroblast growth factor in A549 tumor cells associated with inhibition of the pathway involving Akt. In conclusion, the available results support the possibility that the antiangiogenic properties of ST1481 contribute to its antitumor potential and that this effect might be enhanced by the continuous low-dose treatment.

Enhanced antitumour efficacy of gimatecan in combination with Bcl-2 antisense oligonucleotide in human melanoma xenografts.

The anti-apoptotic protein Bcl-2 has been implicated in the intrinsic resistance of melanoma to chemotherapy. The aim of this study was to investigate the effects of anti-Bcl-2 oligonucleotide oblimersen on the antitumour activity of gimatecan, a novel lipophilic camptothecin currently undergoing clinical phase II studies. Results showed a reduced sensitivity of melanoma cells to gimatecan following Bcl-2 transfection and inversely, increased cell sensitivity to gimatecan in combination with oblimersen. In in vivo studies performed in two melanoma xenografts expressing different Bcl-2 levels, the antitumour activity of oblimersen itself was modest, but the combination with gimatecan produced a significant therapeutic advantage. The combination therapy inhibited tumour growth and delayed regrowth of the two tumours tested. The enhancement of antitumour activity was observed at doses that were tolerated well. The effects of oblimersen on antitumour activity and toxicity of gimatecan were dose-dependent. The capability of oblimersen to improve the efficacy of gimatecan supports the therapeutic potential of the drug combination in the treatment of human melanoma.

Efficacy of the novel camptothecin gimatecan against orthotopic and metastatic human tumor xenograft models.

PURPOSE: Gimatecan, a novel oral lipophilic camptothecin characterized by favorable features at molecular/cellular level and by a promising profile of preclinical activity, is currently in clinical phase I/II. The aim of the study was to additionally investigate the therapeutic potential of the drug in human tumor xenografts growing in different organs as models representative of tumor growth in the clinical setting. EXPERIMENTAL DESIGN: The models include two orthotopic central nervous system tumors, two melanomas growing intracranially, and an ovarian carcinoma growing i.p. In addition, gimatecan was tested against experimental lung metastases of two tumor types (lung and ovarian carcinomas). Gimatecan was delivered by oral gavage according to various schedules (daily or intermittent). The time (in days) mice required to show evident signs of disease was used as end point for drug efficacy. RESULTS: Gimatecan was highly effective in delaying disease manifestations in all tumor systems investigated. In the intracranially growing tumors, a significant time increase (versus control mice) was achieved by the drug administered according to all of the schedules. In addition, almost all treated mice were alive and tumor-free at the end of the experiment in the metastatic models and in the ascitic ovarian tumor. The daily prolonged treatment schedule was the best one. CONCLUSIONS: In all tumor systems investigated, including orthotopic tumor growth models and lung metastases, the oral administration of gimatecan showed a therapeutic benefit in terms of survival increase. The good oral availability allowed a prolonged daily treatment regimen, which seems the most promising to exploit the therapeutic potential of the drug.

Cellular bases of the antitumor activity of the novel taxane IDN 5109 (BAY59-8862) on hormone-refractory prostate cancer.

Taxane-based therapies appear to have a significant efficacy in clinical trials on hormone-refractory prostate carcinoma. In the present study, we investigated the cellular response of androgen-independent prostate carcinoma cell lines to the novel taxane IDN 5109 (BAY 59-8862) and evaluated its antitumor activity. In previous preclinical studies, this new paclitaxel (PTX) analogue was characterized by high tolerability and antitumor efficacy, ability to overcome multidrug resistance, and activity by oral administration. Upon treatment, DU145 and PC3 prostate carcinoma cell lines underwent a transient mitotic arrest. This was followed by G1 arrest and rapid occurrence of apoptosis in DU145 cells, whereas in PC3 cells, which are defective for the postmitotic checkpoint, a slow cell death was preceded by DNA endoreduplication. At the biochemical level, such events were associated with tubulin polymerization, activation of the mitosis-promoting factor, and phosphorylation of Bcl-X(L)/Bcl-2/Raf-1. In addition, IDN 5109 shared with PTX the ability to down-regulate the expression of the two potent angiogenic factors vascular endothelial growth factor and basic fibroblast growth factor. These findings indicated that IDN 5109 affected the same pathways involved in the cellular response to PTX and suggested that an antiangiogenic effect mediated by inhibition of paracrine stimulation of endothelial cells might contribute to the antitumor effect of both drugs. In in vivo experiments, the new taxane displayed a superior and more persistent effect compared with PTX against DU145 tumor xenografts. Such an effect was associated with pronounced reduction of the tumor microvessel density, superior to that achieved by PTX. These results support a potential therapeutic advantage of IDN 5109 over PTX against hormone-refractory prostate carcinoma.

Pattern of antitumor activity of a novel camptothecin, ST1481, in a large panel of human tumor xenografts.

PURPOSE: ST1481 is the lead compound of a novel series of 7-modified camptothecins, the 7-oxyimino methyl derivatives, characterized by potent topoisomerase I inhibition and cytotoxic activity. Based on its therapeutic efficacy in a human non-small cell lung carcinoma model and its favorable pharmacological profile, the novel analogue was selected for further preclinical development. EXPERIMENTAL DESIGN: We investigated the growth-inhibitory effects of ST1481 and topotecan, used as a reference compound, in a panel of human tumor cell lines of various tumor types (ovarian carcinoma, glioblastoma, osteosarcoma, and melanoma), including sublines with acquired resistance to cisplatin. We explored the antitumor efficacy in a large panel of human tumor xenografts, with particular reference to intrinsically resistant tumor types, using oral administration and an intermittent treatment schedule. RESULTS: ST1481 showed a potent antiproliferative activity with comparable effects in all tested cell lines. Only U-87-MG glioma cells were less sensitive, presumably as a consequence of the efficiency of the S-phase checkpoint. ST1481 produced a remarkable antitumor effect (tumor volume inhibition > 85%) in 16 of 18 examined models, with an appreciable rate of complete tumor regressions in 11 of 18 models (despite the nonoptimal intermittent treatment schedule). The most impressive antitumor effects were observed against lung carcinoma, melanoma, and osteosarcoma models, as documented by the high rate of complete responses (up to 100%). The efficacy of ST1481 was significantly superior to that of topotecan in 9 of 17 tumors. The novel drug was also markedly effective against slowly growing tumors (A549 lung carcinoma and HT29 colon carcinoma) when a daily protracted treatment was used to fully exploit the therapeutic potential of camptothecins. CONCLUSIONS: The unusual potency of ST1481 in a variety of tumor cell lines suggests the ability of the drug to overcome several resistance factors. The profile of antitumor efficacy further supports the therapeutic interest in the novel analogue and provides a rational basis for clinical evaluation in selected tumor types.