Possible antitumor activity of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106) against an established gemcitabine (dFdCyd)-resistant human pancreatic cancer cell line

We established a variant of MIAPaCa-2 human pancreatic cancer cells that is resistant to 2',2'-difluorodeoxycytidine (gemcitabine, dFdCyd), MIAPaCa-2/dFdCyd, and elucidated the biochemical characteristics and mechanism of dFdCyd-resistance in these cells. We also evaluated 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106, RNA polymerase inhibitor), a new anticancer ribonucleoside, for antitumor activity against the resistant cells in vitro and in vivo. MIAPaCa-2/dFdCyd cells were 2541-fold more resistant to dFdCyd than parental MIAPaCa-2 cells, and the major mechanism of the dFdCyd-resistance was found to be a decrease in the intracellular pool of dFdCyd and its active metabolites, which would result in a decrease in incorporation of dFdCyd triphosphate into DNA. This finding was confirmed by the discovery of decreased deoxycytidine kinase activity, increased cytidine deaminase and ribonucleotide reductase activity, and increased 5'-nucleotidase mRNA expression in the MIAPaCa-2/dFdCyd cells. The cytotoxicity of TAS-106 as an antitumor nucleoside analog was similar in both parental and dFdCyd-resistant cells, with IC(50) values of 6.25 and 6.27 nM, respectively, and this finding was supported by similar intracellular uptake and metabolism of TAS-106 in both cell lines. We also evaluated the in vivo antitumor activity of TAS-106 against MIAPaCa-2 and dFdCyd-resistant MIAPaCa-2/dFdCyd tumors implanted into nude mice. The tumor growth inhibition rate of weekly additions of TAS-106 (7 mg/kg, iv) against parental and dFdCyd-resistant tumors was 73% and 76%, respectively, while that of dFdCyd administered twice a week (240 mg/kg, iv) was 84% and 34%, respectively. These results suggest that TAS-106 would contribute to the treatment of patients with advanced pancreatic carcinomas in whom dFdCyd-based chemotherapy has failed.     

Preclinical in vivo activity of 2',2'-difluorodeoxycytidine (Gemcitabine) against human head and neck cancer

2',2'-Difluorodeoxycytidine (dFdCyd, Gemcitabine) is a new deoxycytidine analogue with striking preclinical antitumor activity in solid tumors from murine and human origin. In this study, dFdCyd was tested for its antitumor effect in human tumor xenografts derived from squamous cell carcinoma of the head and neck (SCCHN). NMRI nude mice bearing s.c. growing tumors with a volume of 50 to 150 mm3 were given i.p. injections of a maximum tolerated dose of 120 mg/kg dFdCyd, every 3 days for four injections. A significant antitumor effect was observed in all five tested SCCHN tumor lines; in four of these lines the median tumor volume doubling time increased more than a 3-fold upon dFdCyd treatment. In two lines dFdCyd was curative (no tumor regrowth 90 days after treatment) in one of six and two of eight xenografts, respectively. Schedule dependency was investigated in three SCCHN lines, showing, in the two most sensitive lines, that treatment with a 3-day interval was superior to the schedules with daily or weekly injections. At equitoxic doses, dFdCyd was more active in this model than the drugs that are clinically used in SCCHN, i.e., cisplatin, methotrexate, 5-fluorouracil, and cyclophosphamide. dFdCyd is a good candidate for clinical trials with SCCHN patients.     

Antitumor activity of 2'-deoxy-2'-methylidenecytidine, a new 2'-deoxycytidine derivative

The antitumor activity of 2'-deoxy-2'-methylidenecytidine (DMDC), an inhibitor of DNA synthesis, was examined and compared with that of 1-beta-D-arabinofuranosylcytosine (ara-C) against various murine tumors and human tumor xenografts. Against P388 murine leukemia, repeated treatments of DMDC were more effective than its single administration. Interestingly, DMDC was effective against colon 26 murine carcinoma, M5076 murine reticulum cell sarcoma, LX-1 human lung cancer xenograft, and SK-Mel-28 human melanoma xenograft, which are less sensitive or refractory to ara-C, while DMDC was not more potent against murine leukemias P388 and L1210 than ara-C. The in vitro cytotoxic effects of DMDC and ara-C against L1210 leukemia cells were prevented dose dependently by deoxycytidine, suggesting that DMDC, like ara-C, may require phosphorylation by deoxycytidine kinase for antitumor activity. DMDC was effective against human and murine experimental tumor models, especially nonleukemic tumors refractory to ara-C, suggesting that DMDC will be a promising agent for the treatment of cancer.     

Antitumor activity of a derivative of mitomycin, 7-N-[2-[[2-(γ-l-glutamylamino)ethyl]dithio]ethyl]mitomycin C (KW-2149), against murine and human tumors and a mitomycin C-resistant tumor in vitro and in vivo

Summary The antitumor activity of a mitomycin derivative, 7-N-[2-[[2-(-glutamylamino)ethyl]dithio]ethyl]mitomycin C (KW-2149), was evaluated in murine and human tumor models, including a mitomycin C (MMC)-resistant tumor in vitro and in vivo. KW-2149 showed a profound effect against i.p. inoculated P388 leukemia on both a single and an intermittent administration schedule. Against s.c. implanted colon adenocarcinoma 38 (colon 38), KW-2149 was as effective as MMC in ILS% and in tumor growth inhibition on a single-administration schedule. Both compounds were similarly effective when an intermittent schedule was used. KW-2149 showed activity against human tumor xenografts and was effective in two of four non-small-cell lung carcinomas but was not effective against three gastric adenocarcinomas on the singleadministration regimen. The activity of KW-2149 against gastric adenocarcinoma was inferior to that of MMC on a single-administration schedule. However, the antitumor activity of KW-2149 was higher on an intermittent schedule than on a single-administration regimen. The antitumor activity of KW-2149 against human tumor xenografts was similar to that of MMC on an intermittent schedule, and the former drug was effective against both gastric adenocarcinomas and both non-small-cell lung carcinomas. KW-2149 was more effective than MMC against a subline of P388 leukemia that is resistant to MMC in vitro as well as in vivo.     

Radiosensitization produced in vivo by once- vs. twice-weekly 2'2'-difluoro-2'-deoxycytidine (gemcitabine)

PURPOSE: Gemcitabine (2'2'-difluoro-2'-deoxycytidine, dFdCyd) is a potent radiosensitizer of rodent and human tumor cells. Our Phase I clinical trial using once-weekly dFdCyd as a radiosensitizer in the treatment of patients with Stage IV squamous cell head and neck cancer has produced a high rate of tumor response and significant normal mucosal toxicity. These findings raised the question of whether we are using dFdCyd in the optimal dose and schedule. In vitro studies suggest that twice-weekly dFdCyd has the potential to be more effective than once-weekly dFdCyd when administered in combination with radiation (RT) given 5 days per week. Therefore, we have used a mouse model to assess whether the therapeutic ratio of combined modality therapy may be improved by using a twice-weekly drug regimen. We asked two questions: 1) Does a once-weekly or twice-weekly dFdCyd regimen cause more normal tissue radiosensitization? 2) Does a once-weekly or twice-weekly dFdCyd + RT regimen produce a better therapeutic index? METHODS AND MATERIALS: To assess normal tissue toxicity, C3H mice underwent mouth (60)Co RT (27.5 Gy in 5 daily fractions) +/- dFdCyd delivered intraperitoneally (IP) either once or twice weekly 6 hours prior to irradiation. Acute lip reactions were quantified according to a standard scoring system, and weight loss was measured. We measured tumor control using squamous cell carcinoma (SCC) VII murine squamous cell flank tumors (50-125 mm(3)) treated with the same regimens used in the mouth irradiation model. RESULTS: We found that dFdCyd delivered 800 mg/kg once weekly or 150 mg/kg twice weekly caused similar (and maximal tolerable) weight loss; therefore these regimens were chosen to test which schedule produced more acute lip radiosensitization. Twice-weekly dFdCyd + RT was somewhat more toxic by weight loss (800 mg/kg once weekly: 11.9%; 150 mg/kg twice weekly: 17.7%; p = 0.09). To assess therapeutic index, we treated SCC VII flank tumors with RT combined with isotoxic drug/RT regimens (dFdCyd 800 mg/kg once weekly or 100 mg/kg twice weekly). Tumors treated with twice-weekly dFdCyd + RT were significantly smaller than tumors treated with once-weekly drug + RT at 28 days from the start of treatment (p < 0.03). CONCLUSIONS: These findings demonstrate that equitoxic once- versus twice-weekly dFdCyd regimens cause differing levels of oral mucosal radiosensitization. This would suggest that each radiation-dFdCyd schedule will require its own dFdCyd dose escalation trial (which cannot be determined by the maximum tolerated dose (MTD) for dFdCyd alone using that schedule). In addition, our findings suggest that for head and neck cancers twice-weekly dFdCyd may have a higher therapeutic index compared with once-weekly dFdCyd when combined with daily RT.     

Preclinical antitumor activity of a new Vinca alkaloid derivative, S 12363

S 12363 is a new Vinca alkaloid derivative obtained by appending an optically active alpha-aminophosphonate at the C23 position of O4-deacetyl vinblastine. S 12363 was evaluated for cytotoxic and antitumor activity against a spectrum of murine and human tumors. This compound was, respectively, on average, 72- and 36-fold more cytotoxic than were vincristine and vinblastine, when tested on a panel of 2 murine and 37 human tumor cell lines using the microculture tetrazolium assay. S 12363 exhibited significant antitumor activity against murine transplantable tumors (i.p. and s.c. P388 leukemia, i.p. L1210 leukemia, i.p. and i.v. B16 melanoma, i.p. M5076 sarcoma, and s.c. colon adenocarcinoma 38), while no activity was observed on s.c. Lewis lung carcinoma. S 12363, when administered i.p., showed moderate activity on human NCI-H460 lung and PANC-1 pancreas tumor xenografts in nude mice. However, when it was administered i.v., it exerted a significant activity against human HT-29 colon, NCI-H460 lung, NCI-H125 lung, PANC-1 pancreas, and A-431 vulvar tumor xenografts. S 12363 was also active in vivo against a P388 leukemia subline resistant to vincristine. On the in vivo panel of tumors used in this study, S 12363 was at least as active as reference compounds, while its optimal dosage was 10- to 40-fold lower than that of vinblastine, depending on the models studied. The effects of schedule and route of administration on the antitumor activity of S 12363 were studied in both i.p. inoculated P388 leukemia and B16 melanoma, in which the activity was improved by single and intermittent treatment (Days 1, 8, and 15) and i.p. route. S 12363, which differs only by the configuration of the asymmetric carbon atom of the side chain, was 300-fold less cytotoxic and 1000-fold less potent in vivo than was S 12363. These results suggest that S 12363 could present a therapeutic advantage over its congeners and deserves further pharmacological evaluations.     

Tumor uptake and elimination of 2',2'-difluoro-2'-deoxycytidine (gemcitabine) after deoxycytidine kinase gene transfer: correlation with in vivo tumor response.

PURPOSE: We hypothesized that tumor uptake and elimination of 2',2'-difluoro-2'-deoxycytidine/2',2'-difluoro-2'-deoxycytidine 5'-triphosphate (dFdCyd/dFdCTP) would be altered after dCK gene transfer and that this change would result in an enhanced cytotoxic effect. To test this hypothesis, we examined dFdCyd/dFdCTP uptake and clearance in HT-29 human colon carcinoma xenografts in nude mice by high-performance liquid chromatography (HPLC) and fluorine-19 magnetic resonance spectroscopy (F-19 MRS). EXPERIMENTAL DESIGN: HT-29 tumors were grown from cells infected with either the retroviral vector alone (LNPO-LacZ) or vector containing the dCK gene (LNPO-dCK). HPLC and F-19 MRS analyses were performed after a single 160 mg/kg i.p. injection of dFdCyd. Tumor response was determined in animals receiving a similar dosing schedule of dFdCyd. RESULTS: HPLC experiments revealed an increased tumor accumulation of dFdCTP in xenografts overexpressing dCK compared with wild-type controls (P < or = 0.05). dFdCTP in the dCK-infected tumors was easily identified at 24 h postinjection. Conversely, no dFdCTP could be detected in the control xenografts 14 h postinjection. Subsequent F-19 MRS experiments confirmed an altered uptake, revealing a 2.5-fold greater accumulation of dFdCyd/dFdCTP in the dCK xenografts. Whereas a modest tumor growth delay was observed in the wild-type tumors receiving dFdCyd, dCK xenografts demonstrated a marked tumor growth delay following treatment (P < or = 0.05). CONCLUSIONS: These data support the hypothesis that increased expression of dCK cDNA in HT-29 xenografts results in an enhanced dFdCTP accumulation and prolonged elimination kinetics, and ultimately a potentiated in vivo tumor response to dFdCyd. Related to these effects, changes in the overall tumor metabolism of dFdCyd/dFdCTP was detectable by noninvasive F-19 MRS. These data are relevant to future preclinical and clinical studies evaluating dCK gene transfer and dFdCyd therapy.     

The role of cell cycle progression in radiosensitization by 2',2'-difluoro-2'-deoxycytidine

Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdCyd) has been shown to be a potent radiosensitizer in tumor cells both in vitro and in vivo. We evaluated the ability of dFdCyd to enhance the radiosensitivity of two human glioblastoma cell lines. The results demonstrated that U251 cells were more sensitive to the cytotoxicity of dFdCyd, and that dFdCyd was able to radiosensitize these cells. In contrast, D54 cells were more resistant to the cytotoxic effect of dFdCyd, and no radiosensitization occurred at any concentration of dFdCyd tested. Because radiosensitization by dFdCyd has been correlated with its ability to deplete dATP pools through inhibition of ribonucleotide reductase by dFdCyd diphosphate, we evaluated the metabolism of dFdCyd in both cell lines. At equitoxic concentrations of dFdCyd, both cell lines accumulated similar levels of the cytotoxic metabolite, dFdCyd triphosphate, as well as similar levels of dFdCyd monophosphate in DNA. In U251 cells, radiosensitizing concentrations of dFdCyd (10 or 25 nM; IC10 or IC50) depleted dATP by approximately 80% within 4 h. In contrast, 80 nM (IC50) was unable to deplete dATP by >30% within 4 h in D54 cells. Higher concentrations of dFdCyd or hydroxyurea, an inhibitor of ribonucleotide reductase that depleted dATP >90%, also did not produce radiosensitization in D54 cells. D54 cells were not resistant to radiosensitization because bromodeoxyuridine was able to induce radiosensitization. Because D54 cells express wild-type p53, whereas U251 cells express a mutant p53, the effect of dFdCyd and ionizing radiation on cell cycle progression was evaluated. Radiation alone produced a G1 block in D54 cells and a transient G2-M block in U251 cells. After a 24 h incubation with dFdCyd alone or in combination with ionizing radiation, U251 cells readily accumulated in S-phase, which remained elevated for at least 72 h, consistent with previous results in other mutant p53 cell lines. In addition, radiation enhanced the ability of dFdCyd to induce S-phase-specific cell death in U251 cells. In contrast, D54 cells showed a G1 block after dFdCyd and radiation exposure, with fewer cells in S-phase for at least 48 h after drug washout/irradiation. Furthermore, treatment with dFdCyd and/or radiation did not increase the amount of S-phase-specific cell death in D54 cells compared with control cells. These results suggest that the G1 block in D54 cells resulting from wild-type p53 induction prevented radiosensitization by dFdCyd.     

Antitumor activity of ethyl 5-amino-1,2-dihydro-2-methyl-3-phenyl-pyrido [3,4-b]pyrazin-7-ylcarbamate, 2-hydroxyethanesulfonate, hydrate (NSC 370147) against selected tumor systems in culture and in mice

Ethyl 5-amino-1,2-dihydro-2-methyl-3-phenylpyrido[3,4-b]pyrazin- 7-ylcarbamate, 2-hydroxyethanesulfonate, hydrate (NSC 370147) was evaluated for antitumor activity against a spectrum of tumor systems in culture and in mice. NSC 370147 was cytotoxic to a variety of mouse and human cell lines at nanomolar concentrations. The compound exhibited good in vivo antitumor activity against several murine tumors (P388 and L1210 leukemia, colon 11/A and 36, mammary 16/C, and M5076 sarcoma). Activity was largely independent of route of administration but favored a prolonged treatment schedule. NSC 370147 was as active against murine leukemia sublines resistant to Adriamycin, amsacrine, vincristine, melphalan, cisplatin, methotrexate, and CI-920 (a topoisomerase II inhibitor) as against the corresponding parental lines. Only the 1-beta-D-arabinofuranosylcytosine-resistant P388 subline exhibited any cross-resistance to NSC 370147. NSC 370147 has a spectrum of activity similar to that of vincristine and, unlike vincristine, is active against multidrug-resistant cell lines. Therefore, NSC 370147 is a candidate for clinical trial because of its favorable activity compared to vincristine, its effectiveness against multidrug-resistant cells, and its retention of activity for p.o. administration.     

Antitumor efficacy of PD115934 (NSC 366140) against solid tumors of mice

PD115934 (NSC 366140) is a soluble pyrazoloacridine derivative presently undergoing preclinical toxicology evaluation with the anticipation of Phase I human investigation. The agent displayed both human and murine solid tumor selectivity in vitro in a soft agar disk diffusion assay, relative to its activity against murine L1210 leukemia. In vivo it was highly active against solid tumors colon adenocarcinoma 38 and pancreas ductal carcinoma 03, which was consistent with the cellular cytotoxicity seen in the disk diffusion assay. A log cell kill of greater than 4.0 was demonstrated in vivo against both models. PD115934 was administered by both bolus and infusional therapy. After completion of these trials, it was determined that this compound was a schedule category III agent, i.e., a schedule-independent agent with peak plasma level toxicity. The main toxicity encountered with infusional therapy was myelosuppression. With bolus therapy, central nervous system toxicities were dose limiting. On the basis of our preclinical infusion studies, we recommend a 2-h infusion twice weekly in humans in order to obtain a total dose of 360 mg/m2 over 8 weeks.     

Cancer gene therapy mediated by CTS1, a p53 derivative: advantage over wild-type p53 in growth inhibition of human tumors overexpressing MDM2

Recently, a new p53 derivative has been designed, namely chimeric tumor suppressor 1 (CTS1), in which the p53 domains that are known to mediate p53 inactivation have been replaced. In this study, the antitumoral activity of CTS1 mediated by adenovirus vector has been evaluated in comparison with a p53 adenovirus vector in various human tumor cell lines. In vitro, in terms of cell growth inhibition, the CTS1 vector was significantly (P < .01) more efficient (2- to 7-fold) than the p53 vector in tumor models overexpressing an inhibitor of p53, murine double minute-2. This result was confirmed in vivo in a pre-established tumor developed in nude mice. In an osteosarcoma model overexpressing murine double minute-2, we have shown a significantly (P < .05) higher tumor growth delay with the CTS1 vector compared with the p53 vector (25.6 days compared with 12.4 days). Furthermore, both in vitro and in vivo, we have shown that this higher inhibition of tumor growth with the CTS1 vector was correlated with a higher induction of apoptosis. Therefore, CTS1 is a potentially improved tumor suppressor gene for the treatment of human tumors resistant to wild-type p53 gene therapy.     

A fluorine-containing anthracycline (ME2303) as a new antitumor agent against murine and human tumors and their multidrug-resistant sublines

A new fluorine-containing anthracycline derivative, ME2303, showed excellent antitumor activity against various experimental tumor models. The i.p. or i.v. administrations of ME2303 on Day 1 or on Days 1, 5, and 9 against i.p.-implanted L1210 leukemia cells rendered more than 50% of mice tumor free at wide ranges of nontoxic doses, whereas the incidence of cure obtained with Adriamycin (ADM) was less than that obtained with ME2303. ME2303 given i.p. or i.v. on Day 1 or Days 1, 5, and 9 was also effective against i.p.-implanted P388 leukemia cells, and higher incidences of cure were obtained than with ADM. ME2303 administered i.v. on Days 1, 8, 15, and 22 showed prominent antitumor activity against s.c.-implanted colon adenocarcinomas 26 and 38, Lewis lung carcinoma, B16 melanoma, and M5076 sarcoma. Against colon adenocarcinoma 26, ME2303 induced cure in 16 of 20 mice at doses of 35 to 71 mumol/kg, whereas no cure was observed with ADM. Significant growth inhibition of colon adenocarcinoma 38, Lewis lung carcinoma, B16 melanoma, and M5076 sarcoma cell lines was also observed at a dose of 18 to 106 mumol/kg. ME2303 was effective against human and murine multidrug-resistant cells in vitro. For example, human myelogenous leukemia K562 resistant to ADM (K562/ADM) was only 2.8-fold more resistant to ME2303, while the cells were 200-fold more resistant to ADM when the values for the concentration of drug required for 50% inhibition of cell growth were compared. ME2303 was also more effective than ADM against human leukemia CCRF-CEM resistant to vinblastine, human ovarian carcinoma A2780 resistant to ADM, human epidermoid carcinoma KB cells resistant to colchicine, and mouse leukemia P388 resistant to ADM and vincristine. Therapeutic effects were obtained in vivo against ADM- and, especially, vincristine-resistant P388 leukemia. ME2303 is one of the most interesting potential antitumor agents to be studied further.     

Anti-tumor efficacy of Cloretazine (VNP40101M) alone and in combination with fludarabine in murine tumor and human xenograft tumor models

Cloretazine (VNP40101M), a new sulfonylhydrazine alkylating agent, has demonstrated broad-spectrum anti-tumor activity in preclinical studies. In this study, Cloretazine was evaluated both as a monotherapy and in combination with fludarabine in murine tumor and human tumor xenograft models. Cloretazine significantly inhibited the growth of subcutaneously implanted tumors, including B16F10 murine melanoma in C57BL/6 mice, and H460 human lung carcinoma and WiDr human colon carcinoma in athymic nude CD1 mice. The inhibition of tumor growth by Cloretazine was dose dependent, increasing from 42.2 to 87% as the dose escalated from 100 to 150 mg/kg. Cloretazine showed equivalent efficacy but lower toxicity compared to cyclophosphamide in these models. The combination therapy, consisting of a single dose of 10 mg/kg Cloretazine plus five doses of 70 mg/kg fludarabine, given every other day intraperitoneally, significantly increased the long-term survival of BDF1 mice bearing the L1210 murine leukemia. On Day 65 post-tumor implantation, the combination therapy yielded a 90% survival rate compared to 40% for Cloretazine alone and 0% for fludarabine alone.     

Epigenetic regulation by decitabine of melanoma differentiation in vitro and in vivo

Apoptosis genes, such as TP53 and p16/CDKN2A, that mediate responses to cytotoxic chemotherapy, are frequently nonfunctional in melanoma. Differentiation may be an alternative to apoptosis for inducing melanoma cell cycle exit. Epigenetic mechanisms regulate differentiation, and DNA methylation alterations are associated with the abnormal differentiation of melanoma cells. The effects of the deoxycytidine analogue decitabine (5-aza-2'-deoxycytidine), which depletes DNA methyl transferase 1 (DNMT1), on melanoma differentiation were examined. Treatment of human and murine melanoma cells in vitro with concentrations of decitabine that did not cause apoptosis inhibited proliferation accompanied by cellular differentiation. A decrease in promoter methylation, and increase in expression of the melanocyte late-differentiation driver SOX9, was followed by increases in cyclin-dependent kinase inhibitors (CDKN) p27/CDKN1B and p21/CDKN1A that mediate cell cycle exit with differentiation. Effects were independent of the TP53, p16/CDKN2A and also the BRAF status of the melanoma cells. Resistance, when observed, was pharmacologic, characterized by diminished ability of decitabine to deplete DNMT1. Treatment of murine melanoma models in vivo with intermittent, low-dose decitabine, administered sub-cutaneously to limit high peak drug levels that cause cytotoxicity and increase exposure time for DNMT1 depletion, and with tetrahydrouridine to decrease decitabine metabolism and further increase exposure time, inhibited tumor growth and increased molecular and tumor stromal factors implicated in melanocyte differentiation. Modification of decitabine dose, schedule and formulation for differentiation rather than cytotoxic objectives inhibits the growth of melanoma cells in vitro and in vivo.     

Preclinical antitumor activity of penclomedine in mice: cross-resistance, schedule dependence, and oral activity against tumor xenografts in brain

Penclomedine is 3,5-dichloro-2,4-dimethoxy-6-(trichloromethyl)pyridine (NSC 338720), an alpha-picoline derivative with p.o. antitumor activity in preclinical leukemia and solid tumor models. Described here are an in vivo cross-resistance profile of penclomedine, treatment schedule dependence studies, and studies exploring the effects of p.o. drug on human tumors xenografted into mouse brain. The latter studies exploited the apparent facile distribution of penclomedine to the central nervous system. Tumor models used included murine leukemia lines selected in vivo for acquired resistance to various antitumor drugs and the human mammary and lung tumor xenografts MX-1 and H82, respectively. The therapeutic effects of p.o. penclomedine against s.c. MX-1 and H82 xenografts were shown to be independent of treatment schedule. Therapeutic activity was comparable when p.o. and parenteral treatments were compared. Lines of P388 leukemia resistant to melphalan, cyclophosphamide, and carmustine were cross-resistant to penclomedine in vivo. Leukemia lines resistant to antimetabolites, DNA binders/intercalators, and vincristine were not cross-resistant to penclomedine. Intracerebrally implanted MX-1 xenografts retained their sensitivity to p.o. penclomedine, and therapeutic activity was at least comparable to that of carmustine, a drug known for its ability to cross the blood-brain barrier. These results demonstrate attributes of penclomedine that are relatively uncommon among currently available antitumor drugs and that are of interest for the anticipated clinical development of this drug.     

Direct evidence for a role of cyclooxygenase 2-derived prostaglandin E2 in human head and neck xenograft tumors

Both nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX) 2-selective inhibitors such as celecoxib are being reported as having potent anticancer activity in laboratory models. Several reports have suggested that the mechanism of action of these agents in reducing tumor volume/burden is unrelated to their inhibition of prostaglandin synthesis. Many in vitro reports use supraphysiological concentrations of these drugs to demonstrate COX-independent activities on apoptosis or proliferation. In vivo, most murine tumor models express COX-2 only in the vasculature and stroma, unlike human tumors that also express COX-2 in the tumor cells. In general, these models have the limitation of having no measurable, COX-2-derived, prostaglandins, the inhibition of which correlates with antitumor efficacy. We report here that 1483 human head and neck xenograft tumors express COX-2 similar to the pattern observed in human solid tumors and that COX-2 activity produces high levels of prostaglandin E2 (PGE2). Inhibition of COX-2 by celecoxib resulted in loss of intratumor PGE2 levels and reduced tumor growth in a dose-dependent manner. In contrast, a selective COX-1 inhibitor, SC-560, did not measurably reduce tumor prostaglandin levels or tumor growth despite the presence of COX-1 in the host and tumor cells. Celecoxib-treated tumors showed reduced proliferation and increased apoptosis of both tumor and stromal cells compared with vehicle controls. Specific inhibition of PGE2 activity by a neutralizing antibody mimicked the reduced tumor growth observed after celecoxib treatment, suggesting growth is PGE2 mediated. These data indicate that a major antitumor mechanism of action of celecoxib is inhibition of COX-2-derived prostaglandins, particularly PGE2, and suggest celecoxib as a novel therapeutic agent for human head and neck cancer.     

Dimethyl sulfoxide-induced differentiation does not alter tumorigenicity of neuroblastoma cells

It has been shown that agents that are known to be scavengers of hydroxyl radicals may induce differentiation and inhibit growth of murine neuroblastoma cells in tissue culture. The present study tests dimethyl sulfoxide as a differentiation agent of the human neuroblastoma cell lines LA-N-1 and murine neuroblastoma NIE-115.Results indicate that DMSO induces morphologic and biochemical differentiation of neuroblastoma cells coupled to growth inhibition and inhibition of collony formation in semi liquid tissue culture systems.DMSO treatment in vitro had no effect on tumorgenicity of NIE-115 cells. In vivo DMSO treatment of athymic nude mice with transplanted LA-N-1 human neuroblastoma tumors has not affected tumor size or animal survival. No diminishing effect of natural killer cell activity could be attributed to DMSO treatment.     

Synergistic activity of recombinant human endostatin in combination with adriamycin: analysis of in vitro activity on endothelial cells and in vivo tumor progression in an orthotopic murine mammary carcinoma model.

PURPOSE: Current combination treatment strategies in malignancy are designed to evaluate the use of cytotoxic drugs and antiangiogenic agents. Endostatin, a fragment of collagen XVIII, specifically inhibits proliferation, migration, and differentiation of endothelial cells in vitro as well as angiogenesis and tumor progression in in vivo models. In this study, we determine the antitumor effect of rhEndostatin administered alone or in combination with Adriamycin against established orthotopic murine mammary carcinoma. EXPERIMENTAL DESIGN: Mice bearing orthotopically established DA-3 mammary adenocarcinoma tumors received varying doses of rhEndostatin alone and in combination with Adriamycin to assess tumor growth inhibition. Additional studies of this in vivo combination included a determination of Adriamycin-induced cardiotoxicity and in vitro effects on human umbilical vein endothelial cell proliferation and cord formation. RESULTS: For single-agent activity, optimal tumor growth inhibition was observed after s.c. administration of 50 mg/kg/day rhEndostatin or 5 mg/kg Adriamycin injected i.v. every 4 days. Combination of Adriamycin with optimal or suboptimal doses of rhEndostatin resulted in synergistic inhibition of DA-3 tumor growth. Importantly, unlike other antiangiogenic agents, rhEndostatin did not exacerbate the cardiotoxicity of Adriamycin. The synergistic interaction between rhEndostatin and Adriamycin was also observed in vitro for inhibition of human umbilical vein endothelial cell proliferation and inhibition of cord formation. CONCLUSIONS: These data suggest that the synergy observed with rhEndostatin in combination with Adriamycin is exerted at the level of the endothelial cell and can result in enhanced tumor growth inhibition. The potential benefit of Adriamycin used in combination with rhEndostatin is being considered for clinical evaluation.     

Growth inhibitory activity of succinylacetone: studies with Walker 256 carcinosarcoma, Novikoff hepatoma and L1210 leukemia

Succinylacetone (SA, 4,6-dioxoheptanoic acid) inhibits d-aminolevulinic acid dehydrase, the second enzyme of the heme biosynthetic pathway and thereby inhibits heme biosynthesis. In the present study SA is shown to inhibit the growth of the Walker carcinosarcoma (W256) in vitro and in vivo, the Novikoff hepatoma in vivo, and L1210 leukemia in vitro, but only slightly in vivo. Rats can tolerate significantly larger doses of SA for at least twice as long as were administered in the present study without gross evidence of toxicity. In contrast to findings in previously published studies with murine erythroleukemia cells, the inhibition of growth of L1210 and W256 cells by SA in vitro is not accompanied by a decrease in cellular heme and is not reversed by addition of hematin to the medium. This suggests a second mechanism of growth inhibition of tumor cells unrelated to heme biosynthesis. Although the growth of both W256 and L1210 cells was markedly inhibited by the same concentration of SA in culture, there was a great difference in responsiveness in vivo, in that much greater inhibition of the growth of the Walker tumor was produced by SA.     

Antitumor Activity of TZT-1027, a Novel Doiastatin 10 Derivative

Dolastatin 10, a pentapeptide isolated from the marine mollusk Dolabella auricularia , has antitumor activity. TZT-1027, a dolastatin 10 derivative, is a newly synthesized antitumor compound. We evaluated its antitumor activity against a variety of transplantable tumors in mice. Intermittent injections of TZT-1027 were more effective than single or repeated injections in rake with P388 leukemia and B16 melanoma. Consequently, TZT-1027 shows schedule dependency. TZT-1027 was effective against P388 leukemia not only when administered i.p., but also when given i.v. However, although TZT-1027 given i.v. was active against murine solid tumors, TZT-1027 administered i.p. was ineffective against all the tumors tested with the exception of colon 26 adenocarcinoma. The i.v. injection of TZT-1027 at a dose of 2.0 mg/Ag remarkably inhibited the growth of three murine solid tumors; colon 26 adenocarcinoma, B16 melanoma and M5076 sarcoma, with T/C values of less than 6%. The antitumor activities of TZT-1027 against these tumors were superior or comparable to those of the reference agents; dolastatin 10, cisplatin, vincristine, 5-fluorouracil (5-FU) and E7010. In experiments with drug-resistant P388 leukemia, TZT-1027 showed good activity against cisplatin-resistant P388 and moderate activity against vincristine- and 5-fluorouracil-resistant P388, but no activity against adriamycin-resistant P388. TZT-1027 was also effective against human xenografts, that is, tumor regression was observed in mice bearing MX-1 breast and LX-1 lμng carcinomas. TZT-1027 at 10 μM almost completely inhibited the assembly of porcine brain microtubules. Therefore, its mechanism of antitumor action seems to he, at least in part, ascrihable to the inhibition of microtubule assembly. Because of its good preclinical activity, TZT-1027 has been entered into phase I clinical trials.