Activity of flavone acetic acid (NSC-347512) against solid tumors of mice

Flavone acetic acid (FAA) is a new antitumor agent that has recently entered Phase I clinical trials. In preclinical studies, we have found that FAA was broadly active against a variety of transplantable solid tumors of mice (colon #51, #07, #10, #26; pancreatic ductal adenocarcinomas #02 and #03; mammary adenocarcinoma #16/C/Adr; M5076 reticulum cell sarcoma and Glasgow's osteosarcoma). FAA was curative for colon adenocarcinoma # 10 and pancreatic ductal adenocarcinoma # 03. Thus, for the first time an agent has been identified with very broad, perhaps nearly universal solid tumor activity. FAA was also found to be orally active and stable in solution at 37 °C for 48 h. FAA was selectively cytotoxic in vitro for solid tumors over leukemias L1210 and P388 (in a soft-agar colony formation assay), thus correlating cellular selectivity in vitro with in vivo antitumor activity. The finding that FAA was active in vitro, established that the agent did not need metabolism (activation) outside the tumor cell. The main drawback of FAA was an unusual threshold behavior in which only a narrow range of doses were active and splitting the dose markedly decreased activity.     

Amelioration of thrombocytopenia with concomitant ornithine in sarcomabearing rats receiving high dose difluoromethylornithine

Summary The dose limiting toxicity of difluoromethylornithine (DFMO), when administered by continuous infusion, is thrombocytopenia. DFMO-induced antitumor activity and thrombocytopenia were time- and dosedependent up to 1700 mg/kg/d when administered continuously for 12 days. Concomitant ornithine administration (at selected molar ratios to DFMO) ameliorated thrombocytopenia induced by DFMO at a dose of 2000 mg/kg/day without adversely affecting its antitumor activity. The purpose of this study was to determine if ornithine could ameliorate the thrombocytopenia of higher DFMO doses and increase the efficacy of DFMO. Fischer 344 male rats with a transplantable sarcoma in the right flank were given 2000 and 3500 mg/kg/d DFMO alone or with ornithine at a molar ratio of 0.4 for 8 days by continuous infusion. Concomitant ornithine infusion overcame the thrombocytopenia that was induced by either dose of DFMO without reducing the antitumor activity against the sarcoma. The antitumor activity, tumor polyamine levels, and tumor S-adenosylmethionine decarboxylase activity did not consistently change with increasing doses of DFMO or with the addition of ornithine to the infusion regimen. These results demonstrate that the thrombocytopenia induced by doses of DFMO greater than 2000 mg/kg/d can be ameliorated without compromising the antitumor activity. Address for offrints: V.B. Grossie, Jr. Department of General Surgery, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe, Houston, TX, 77030, USA     

Preclinical antitumor activity of XK469 (NSC 656889)

XK469 (NSC 656889) is a water-soluble member of the novel quinoxaline family of antitumor agents. In vitro, XK469 demonstrated selective cytotoxicity for several murine solid tumors including colorectal and mammary adenocarcinoma cell lines, when compared to both leukemia and normal epithelial cells. In vivo, XK469 was active against 7/7 murine tumors tested, including pancreatic ductal carcinomas #02 and #03, colon adenocarcinomas #38 and #51/A, mammary adenocarcinoma #16/C and the Adriamycin resistant mammary adenocarcinomas #16/C/ADR and #17/ADR. XK469 was efficacious both intravenously and orally. Regardless of dosing schedule, conventional mice tolerated higher total doses than SCID or nu/nu mice did. Despite these reduced doses, XK469 was active against xenografts of 4/6 human tumor lines including mammary adenocarcinoma MX-1, the small cell lung cancer DMS 273, the prostate model LNCaP and the CNS tumor SF295. The lower doses in the xenograft studies were below curative levels. The dose-limiting toxicity appeared to be myelosuppression with rapid host recovery (5-8 days), and in vitro assays of XK469 toxicity to murine bone marrow neutrophil progenitors CFU-GM (colony forming unit-granulocyte/macrophage) demonstrated concentration-dependent toxicity from 0.5-30 microg/mL. The difference in drug tolerance between BDF1 and SCID mice was detected in vitro as a 3-fold difference in the IC90 for CFU-GM, despite similar IC50 values. Comparative in vitro hematotoxicology studies revealed that human bone marrow CFU-GM tolerated XK469 as well as their SCID counterparts (IC90 values 5.7 vs. 7.4 microg/mL). Based on comparison with previously tested anti-cancer agents, these data suggest that humans will be able to tolerate XK469 doses that are efficacious against human tumor xenografts.     

Phase I study of combined alpha Interferon,alpha difluoromethylornithine (DFMO), and doxorubicin in advanced malignancy

Interferon (IFN) and conventional cytotoxic chemotherapeutic agents have been successfully combined in various studies. Alpha difluoromethylornithine (DFMO) is a novel antitumor agent which is an inhibitor of polyamine metabolism. A phase I study of IFN 24 × 10⁶ U/m²/day IM (days 3–7), DFMO 9 gm/m² p.o. daily (days 1–7), and a variable dose of doxorubicin starting at 20 mg/m² (day 6), of each 28 day cycle was performed. The aim of the study was to determine the maximally tolerable dose of doxorubicin in this combination. Three patients were treated with doxorubicin at 20 mg/m² and six patients at 40 mg/m². The dose limiting toxicities were neutropenia, fatigue and fever. All other toxicities were mild and there was no grade IV toxicity. A doxorubicin dose of 40 mg/m² produced tolerable toxicity and is recommended for phase II studies. No major antitumor effects were seen.     

Modulation by melatonin of the cardiotoxic and antitumor activities of adriamycin

In this study, we investigated the effects of melatonin on adriamycin-induced cardiotoxicity both in vivo in rats and in vitro, and on the antitumor activities of adriamycin on MDA-231 and NCI breast cancer cells. Rats that received a single intraperitoneal injection of 25 mg/kg adriamycin showed a mortality rate of 86%, which was reduced to 20% by melatonin treatment (10 mg/kg, SC for 6 days). Melatonin attenuated adriamycin-induced body-weight loss, hemodynamic dysfunction, and the morphologic and biochemical alterations caused by adriamycin. Melatonin also reduced adriamycin-induced nuclear DNA fragmentation, as assessed by the comet assay. In addition, the antitumor activity of adriamycin could be maintained using lower doses of this drug in combination with melatonin. Melatonin treatment in the concentration range of 0.1-2.5 mM inhibited the growth of human breast cancer cells. In terms of oncolytic activity, the combination of adriamycin and melatonin improved the antitumor activity of adriamycin, as indicated by an increase in the number of long-term survivors as well as decreases in body-weight losses resulting from adriamycin treatment. These results indicate that melatonin not only protects against adriamycin-induced cardiotoxicity but also enhances its antitumor activity. This combination of melatonin and adriamycin represents a potentially useful regimen for the treatment of human neoplasms because it allows the use of lower doses of adriamycin, thereby avoiding the toxic side effects associated with this drug.     

新抗肿瘤药铂(Ⅱ),(Ⅳ)配合物的合成

The synthesis of sixteen new analogs of cis-platinum (CDDP) and seven known Pt analogs, as well as the antitumor activity of seven Pt analogs against solid sarcoma 180 are reported. The new congeners consist of Pt (Ⅱ) and Pt (Ⅳ) complexes containing primary amine ligands (eg· NH3, en, pren) with variable anionic ligands such as malonate and 2-substituted malonates. In the experimental antitumor activity tests, 7 new platinum complexes were given on days 1～7, 24 hours after implanted with 10⁶ cells of solid sarcoma 180 tumor and producedT/C (treated/control) value between 15～35% with less toxicity than the parent cisplatinum. The experimental data indicate that it is favorable to introduce certain hydrophilic groups into the platinum complexes, in the view of increasing their aqueous solubility and lowering their toxicity while retaining their effectiveness.     

Preclinical antitumor activity of XK469 (NSC 656889)

XK469 (NSC 656889) is a water-soluble member of the novel quinoxaline family of antitumor agents. In vitro, XK469 demonstrated selective cytotoxicity for several murine solid tumors including colorectal and mammary adenocarcinoma cell lines, when compared to both leukemia and normal epithelial cells. In vivo, XK469 was active against 7/7 murine tumors tested, including pancreatic ductal carcinomas #02 and #03, colon adenocarcinomas #38 and #51/A, mammary adenocarcinoma #16/C and the Adriamycin resistant mammary adenocarcinomas #16/C/ADR and #17/ADR. XK469 was efficacious both intravenously and orally. Regardless of dosing schedule, conventional mice tolerated higher total doses than SCID or nu/nu mice did. Despite these reduced doses, XK469 was active against xenografts of 4/6 human tumor lines including mammary adenocarcinoma MX-1, the small cell lung cancer DMS 273, the prostate model LNCaP and the CNS tumor SF295. The lower doses in the xenograft studies were below curative levels. The dose-limiting toxicity appeared to be myelosuppression with rapid host recovery (5–8 days), and in vitro assays of XK469 toxicity to murine bone marrow neutrophil progenitors CFU-GM (colony forming unit-granulocyte/macrophage) demonstrated concentration-dependent toxicity from 0.5–30 g/mL. The difference in drug tolerance between BDF₁ and SCID mice was detected in vitro as a 3-fold difference in the IC₉₀ for CFU-GM, despite similar IC₅₀ values. Comparative in vitro hematotoxicology studies revealed that human bone marrow CFU-GM tolerated XK469 as well as their SCID counterparts (IC₉₀ values 5.7 vs. 7.4 g/mL). Based on comparison with previously tested anti-cancer agents, these data suggest that humans will be able to tolerate XK469 doses that are efficacious against human tumor xenografts.     

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.     

Effect of cis-platinum on heme, drug, and steroid metabolism pathways: possible involvement in nephrotoxicity and infertility

cis-Platinum, a coordination complex of platinum, is highly effective against a number of human tumors, including steroid-dependent tumors such as testicular and prostatic cancers. It is generally assumed that DNA is the cellular target responsible for the antitumor activity of the drug. Much evidence, however, has been gathered in recent years suggesting that cis-platinum has major effects on the endocrine system, particularly the hypothalamic-pituitary-testis steroidogenesis axis, and severely disrupts the normal production of testosterone. In the axis, testis is the prime target, where the LH receptor-binding capacity of Leydig cells is decreased by nearly 80%. Within the testis, the mitochondrial cytochrome P-450scc and side-chain cleavage activity are markedly depressed and the microsomal 17 alpha-hydroxylase activity and cytochrome P-450 concentration are decreased; side-chain cleavage activity is rate-limiting in testosterone production. The effects are not limited to the testis cytochrome P-450, but extend to other organs including the liver and the kidney cytochromes. In the liver, a feminization of the cytochromes P-450 profile is produced, and hence the biotransformation of endogenous steroids as well as that of exogenous chemicals is affected. In the kidney, cis-platinum appears to be the most effective inducer of cytochrome P-450, whereby the biotransformation of the prostaglandins and fatty acids could be altered. The spectrum of the effects of cis-platinum on cytochrome P-450-dependent drug metabolism and steroid hydroxylation activity mimic those produced by hypophysectomy and are for the most part reversed by the anterior pituitary hormones. These findings suggest the possibility that general feminization of steroidogenesis caused by cis-platinum may significantly contribute to the activity of cis-platinum against hormone-dependent tumors.     

Cytotoxic effects of glutathione synthesis inhibition by L-buthionine-(SR)-sulfoximine on human and murine tumor cells

The glutathione (GSH) synthesis inhibitor, buthionine sulfoximine (BSO) was tested for cytotoxicity and thiol depletion in murine and human tumor cells in vitro, and for its antitumor activity and toxicity in vivo. The cell lines used in these studies included murine L-1210 leukemia, human RPMI 8226 myeloma, MCF-7 breast cancer and WiDr colon carcinoma. Soft agar colony forming assays showed that BSO was most effective at reducing tumor colony formation when exposed continuously to cells in vitro. Drug concentrations which inhibited colony formation to 50% of control levels ranged from 2.0–6.2 mM (for 1 hour exposures), 2–100 mM for 24 hour exposures and 0.4–1.40 M (for continuous BSO exposures). Human myeloma cells proved most sensitive to BSO. In vitro cytotoxicity correlated with depletion of intracellular nonprotein sulfhydryls to 10% of control values in both L-1210 and 8226 cells. This was routinely achieved with prolonged exposures to mM BSO concentrations for > 24 hours. Normal mice tolerated high BSO doses (up to 5.0 g/kg) without evidence of acute toxicity. BSO was not active against L-1210 leukemia-bearing DBA/2 mice. When tested in vivo against MOPC-315 plasmacytoma-bearing BALB/c mice, BSO was not active at doses up to 4.0 g/kg. In contrast, the bifunctional alkylating agent melphalan (L-PAM) was active against MOPC-315 and this activity was enhanced by a 24 hour pretreatment of mice with 50 mg/kg of L-BSO. This BSO dose was shown to significantly reduce sulfhydryl levels in the liver (50% of control) and kidney (20% of control) but not in the bone marrow (100% of control). The enhancement by BSO was most significant only for the lower doses of L-PAM tested. These results suggest that BSO may not have direct antitumor activity, but that it can enhance cytotoxicity from a classic alkylating agent in vivo. Due to its low toxicity, BSO should be tested in combination with either anticancer agents which are dependent on (GSH) for detoxification and potential drug resistance.     

Cell cycle kinetics responses of human stomach cancer cells to reduction in polyamine levels by treatment with αDifluoromethylornithine in vitro

Treatment of human gastric cancer clones in vitro with low doses of DFMO (5 mM) produced elongation of the cell population doubling times and lowering of the saturation densities. By contrast, DFMO treatment of normal human skin fibroblasts altered only the saturation density. The lack of an effect of 5 mM DFMO on the doubling time of normal fibroblasts may be directly related to baseline intracellular putrescine levels, which were about 2.5 times higher than in the cancer cells. The same dose of DFMO caused a rapid decrease in intracellular polyamine levels in the tumor clones. The effects on the doubling time and saturation density were almost totally abolished by the addition of 50 M putrescine to the growth medium during the first 24 h of treatment with DFMO. Exposure to 5 mM DFMO for 24 h caused the human gastric cancer cells to become blocked in G₁ phase only, and this led to a reduction in the fraction of cells in S phase. The G₁ block was reversible and this cohort of cells eventually passed through S phase and then through G₂ and M.A higher 100 mM dose of DFMO and longer exposure times for both doses produced cell cycle changes and death of more than 90% of the cell population. These data suggest that cell kinetics changes observed under these experimental conditions may reflect polyamine-related alterations in the biochemical events of cell cycle progression kinetics; but may also be the result of DFMO-induced loss of cell viability.Abbreviations DFMO -Difluoromethylornithine - ODC ornithine decarboxylase - ARA C cytosine arabinosidede - MGBG methylglyoxal bis(guanylhydrazone)     

Activity of 4′-0-tetrahydropyranyladriamycin hydrochloride (THP-ADM) in a human tumor cloning system

4'-0-tetrahydropyranyladriamycin hydrochloride (THP-ADM) is a new anthracycline derivative. The antitumor activity of THP-ADM was tested on 51 human tumor samples representing ten different tumor types in in vitro colony assay method. Tested tumors were: 26 cases of ovarian cancer, 8 cases of breast cancer, 6 cases of colorectal cancer, 3 cases of endometrial cancer, 2 cases each with gastric cancer and sarcoma, and another 4 cases. An in vitro colony assay was done in soft agar as described by Hamburger & Salmon. The criteria for in vitro sensitivity was defined as a 70 percent or greater reduction in the number of colonies after a 1-h exposure to drugs. The selected concentrations of THP-ADM for assay were 0.05, 0.5, and 1.0 micrograms/ml. The sensitivity rates for THP-ADM in each dose were: 0.05 micrograms/ml (7/19, 37%), 0.5 micrograms/ml (10/51, 20%), and 1.0 micrograms/ml (12/19, 63%). In vitro sensitivity of adriamycin (0.04 micrograms/ml) was simultaneously tested in 49 cancer patients. Five out of 25 ovarian cancer patients (20%) showed responses to adriamycin and an overall response rate was 12% (6/49). These data indicate that THP-ADM has an antitumor activity against various cancers and it is comparable to that of adriamycin.     

Taxol: a review of its preclinical in vivo antitumor activity.

Taxol has been demonstrated in numerous laboratories worldwide to have broad-spectrum antitumor activity against many tumor models. The susceptible tumors include murine leukemias and solid tumors, and human solid tumor xenografts. The initial findings of taxol's ineffectiveness against most distal site tumor models was probably a consequence of the insolubility of taxol in nearly all the vehicles used in those early studies. On the occasions when an ethanol-based vehicle was used to dissolve taxol, substantial distal site antitumor activity was observed. Although no definitive schedule dependency data have evolved, once-a-day or every-other-day i.v. injections for several treatments have proved to be reproducibly effective in stringent s.c. tumor models. Attempts to discern a therapeutically synergistic cytotoxic drug combination was made on two occasions without success. In the manner evaluated, taxol plus either adriamycin, cisplatin, cyclophosphamide or etoposide (VP-16) were not meaningfully more efficacious than the more effective drug in each of those combination settings.     

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.     

Comparison of the antitumor activity of gemcitabine and ara-C in a panel of human breast, colon, lung and pancreatic xenograft models

Summary Gemcitabine is a new deoxycytidine analog that exhibits significant cytotoxicity against a variety of cultured murine and human tumor cells. The cytotoxic action of gemcitabine appears to be due to the inhibition of DNA synthesis by inhibition of ribonucleotide reductase and by competition with dCTP for incorporation into DNA. We have previously shown that gemcitabine, but not cytosine arabinoside (ara-C), has a broad spectrum of antitumor activity against 7 different types of murine solid tumors. The activity of gemcitabine was schedule dependent. To further characterize its activity, gemcitabine was tested against 12 human carcinoma xenografts. When given on an every 3 day × 4 schedule, the following percent inhibitions (at maximally tolerated doses [MTD]; MTD/2) in tumor growth were seen: MX-1 mammary (93%; 80%), CX-1 colon (92%; 82%), HC-1 colon (96%; 92%), GC3 colon (98%; 94%), VRC5 colon (99%; 100%), LX-1 lung (76%; 61%), CALU-6 lung (75%; 38%), NCI-H460 lung (45%; 46%), HS766T pancreatic (73%; not tested), PaCa-2 pancreatic (69%; 40%), PANC-1 pancreatic (70%; 60%), and BxPC-3 pancreatic (9%; 19%). In contrast, only the LX-1 lung carcinoma xenograft was responsive to ara-C treatment, which inhibited tumor growth by a marginal 62 percent. Thus, like its activity against murine solid tumors, gemcitabine has excellent antitumor activity against a broad spectrum of human solid tumors.     

Protection by sodium thiosulfate and thiourea against lethal toxicity of cis-diamminedichloroplatinum (II) in bacteria and mice

The protective effect of sodium thiosulfate and thiourea on the lethal toxicity of the antitumor drug, cis-diamminedichloroplatinum (II) (cis-DDP), was investigated in bacteria and mice. Initially, the agents capable of antagonizing bactericidal activity of cis-DDP were screened using WP2 uvra, a strain of E. coli sensitive to this drug. Of the ten sulfur-containing compounds tested, thiourea and sodium thiosulfate exhibited potent protecting effects against cis-DDP cytotoxicity in bacteria. Propylthiouracil and methimazole showed intermediate levels of such protection, but the other 6 compounds had little or no protective effects. Thiourea and sodium thiosulfate were then subjected to the acute lethal toxicity test in mice to assess their protective activity in vivo. We found that cis-DDP i.v. lethality against mice can be blocked almost completely by excess amounts of thiourea or sodium thiosulfate. Thiourea protected against cis-DDP toxicity with a narrow range among the effective doses, while sodium thiosulfate was protective with a remarkably wide range of effective doses. The effectiveness of sodium thiosulfate was also indicated in experiments in which the LD50 dose of cis-DDP (16 mg/kg) i.p. increased over the level of greater than 200 mg/kg with concomitant administration of sodium thiosulfate i.p.     

Comparative nephrotoxicity of 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea (MeCCNU) and chlorozotocin: functional-structural correlations in the Fischer 344 rat

1-(2-Chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea (MeCCNU) and chlorozotocin (CZ; 2-[3-(2-chloroethyl)-3-nitrosoureido]-D-glucopyranose) are structurally related anticancer agents which differ by virtue of the increased water solubility, and comparatively low carbamylating activity, of CZ relative to MeCCNU. In the present study, a single sc injection of either of these chloroethylnitrosoureas was nephrotoxic to male Fischer 344 rats. However, at equimolar doses, CZ was shown to be a much more potent nephrotoxicant. A lethal 40-mg/kg dose of CZ (127 microM) initially resulted in acute tubular necrosis of the proximal tubules of the cortex, followed later by a necrosis of papillary collecting ducts. In contrast, lethal doses of MeCCNU (100-180 mg/kg; 400-730 microM) produced only minimal proximal tubule injury. A 250-mg/kg (1 mM) dose of MeCCNU resulted in massive papillary necrosis within 7 days, with only limited necrosis to the proximal tubules. Sublethal doses of either drug, resulted in a similar, chronic, progressive nephropathy which was delayed in onset and was characterized by polyuria, enzymuria, a decrease in urine concentrating ability, and in renal slice organic ion accumulation. Alterations in less sensitive indicators of renal toxicity (i.e., proteinuria, glucosuria, and elevated blood urea nitrogen) were observed no earlier than 3 to 7 days after administration of only the highest tested doses of CZ (40 mg/kg) or MeCCNU (250 mg/kg). At sublethal doses, administration of either drug resulted in karyomegaly to the collecting ducts in the renal medulla within 2 to 4 weeks. These studies demonstrate that carbamylation-mediated reactions may not be necessary for nephrotoxicity to develop following administration of this class of antitumor agent.     

Diarylsulfonylureas--a new class of antitumor agents

Diarylsulfonylureas (DSU) represent a new class of antitumor agents. DSU exhibit an exceptionally broad spectrum of activity against solid tumors. They show different toxicity to conventional anticancer agents and exhibit no cross-resistance with existing anticancer agents. In particular they have an unknown, but unique, potentially novel mechanism of action. Sulofenur is the first DSU to progress to clinical evaluation. The dose-limiting toxicity in humans is anemia and methemoglobinemia. Recently, DSU with novel structural features have also been reported to exhibit potent antitumor activity, demonstrating structural diversity of DSU antitumor agents.     

Activity of rapamycin (AY-22,989) against transplanted tumors

Rapamycin exhibits activity against several ascites and solid transplantable tumors; it is slightly active to inactive against leukemias. On a weight basis, rapamycin was less active than 5-fluorouracil, cyclophosphamide and adriamycin, but rapamycin's maximal activity against Colon 38 tumor was similar to that of 5-fluorouracil and cyclophosphamide. Its activity was such that it significantly inhibited tumor growth at any stage of development. In the active dose range, rapamycin appeared less toxic than the other drugs. In the Colon 38 tumor model, rapamycin at a given dose exhibited the same activity when administered ip, iv, im and sc; upon oral administration, its activity was reduced but not abolished. Rapamycin was compatible with 5-fluorouracil and cyclophosphamide. The sequential treatment 5-fluorouracil-rapamycin-cyclophosphamide was superior to the sequence 5-fluorouracil-adriamycin-cyclophosphamide in protecting Colon 38 tumor-bearing mice. 29-Demethoxyrapamycin exerted only marginal activity against P388 lymphocytic leukemia; it was inactive against B16 melanocarcinoma and Colon 38 solid tumor.     

Antitumor activity of 7-[2-(N-isopropylamino)ethyl]-(20S)-camptothecin, CKD602, as a potent DNA topoisomerase I inhibitor

We developed a novel water-soluble camptothecin analogue, CKD602, and evaluated the inhibition of topoisomerase I and the antitumor activities against mammalian tumor cells and human tumor xenografts. CKD602 was a nanomolar inhibitor of the topoisomerase I enzyme in the cleavable complex assay. CKD602 was found to be 3 times and slightly more potent than topotecan and camptothecin as inhibitors of topoisomerase, respectively. In tumor cell cytotoxicity, CKD602 was more potent than topotecan in 14 out of 26 human cancer cell lines tested, while it was comparable to camptothecin. CKD602 was tested for thein vivo antitumor activity against the human tumor xenograft models. CKD602 was able to induce regression of established HT-29, WIDR and CX-1 colon tumors, LX-1 lung tumor, MX-1 breast tumor and SKOV-3 ovarian tumor as much as 80, 94, 76, 67, 87% and 88%, respectively, with comparable body weight changes to those of topotecan. Also the therapeutic margin (R/Emax: maximum tolerance dose/ED₅₈) of CKD602 was significantly higher than that of topotecan by 4 times. Efficacy was determined at the maximal tolerated dose levels using schedule dependent i.p. administration in mice bearing L1210 leukemia. On a Q4d×4 (every 4 day for 4 doses) schedule, the maximum tolerated dose (MTD) was 25 mg/kg per administration, which caused great weight loss and lethality in <5% tumor bearing mouse. This schedule brought significant increase in life span (ILS), 212%, with 33% of long-term survivals. The ex vivo antitumor activity of CKD602 was compared with that of topotecan and the mean antitumor index (ATI) values recorded for CKD602 were significantly higher than that noted for topotecan. From these results, CKD602 warrants further clinical investigations as a potent inhibitor of topoisomerase I.