Tumor treatment by sustained intratumoral release of 5-fluorouracil: effects of drug alone and in combined treatments

: To evaluate an intratumoral polymer implant for sustained delivery of 5-fluorouracil (5-FU) in a mouse tumor model.

: 5-FU was incorporated into a polyanhydride-based polymer, bis(p-carboxyphenoxy)propane sebacic acid (CPP:SA) and implanted in RIF-1 mouse fibrosarcoma growing s.c. The effectiveness of treatment was evaluated by tumor growth delay. External beam radiation was ⁶⁰Co gamma rays, and the source of interstitial radiation was implanted ¹²⁵I seeds. A second drug, cis-diamminedichloroplatinum (cis-DDP), was administered by intraperitoneal injection or by osmotic pump.

: For drug/polymer implant alone, the tumor growth delay was proportional to the amount of drug in the implant. The 5-FU polymer implant was most effective when combined with cis-DDP or with acute or fractionated radiation, and in some cases, the effects of combined treatments were greater than additive. The most effective combination was intratumoral 5-FU and low-dose-rate radiation delivered from an interstitial radiation source.

: Results indicate that 5-FU can be effectively delivered by polymer implant and that this mode of delivery is particularly appropriate for combined treatments.     

Intra-arterial bromodeoxyuridine radiosensitization of malignant gliomas

In the 1950's it was first observed that mammalian cells exposed to the halogenated deoxyuridines were more sensitive to ultraviolet light and radiation than untreated cells. This prompted early clinical trials with bromodeoxyuridine (BUdR) which showed mixed results. More recently, several Phase I studies, while establishing the feasibility of continuous intravenous (IV) infusion of BUdR, have reported significant dose limiting skin and bone marrow toxicities and have questioned the optimal method of BUdR delivery. To exploit the high mitotic activity of malignant gliomas relative to surrounding normal brain tissue, we have developed a permanently implantable infusion pump system for safe, continuous intraarterial (IA) internal carotid BUdR delivery. Since July 1985, 23 patients with malignant brain tumors (18 grade 4, 5 grade 3) have been treated in a Phase I clinical trial using IA BUdR (400-600 mg/m2/day X 8 1/2 weeks) and focal external beam radiotherapy (59.4 Gy at 1.8 Gy/day in 6 1/2 weeks). Following initial biopsy/surgery the infusion pump system was implanted; BUdR infusion began 2 weeks prior to and continued throughout the 6 1/2 week course of radiotherapy. There have been no vascular complications. Side-effects in all patients have included varying degrees of anorexia, fatigue, ipsilateral forehead dermatitis, blepharitis, and conjunctivitis. Myelosuppression requiring dose reduction occurred in one patient. An overall Kaplan-Meier estimated median survival of 20 months has been achieved. As in larger controlled series, histologic grade and age are prognostically significant. We have shown in a Phase I study that IA BUdR radiosensitization is safe, tolerable, may lead to improved survival, and appears to be an efficacious primary treatment of malignant gliomas.     

Auger electron contribution to bromodeoxyuridine cellular radiosensitization

Halogenated thymidine analogs become incorporated into the DNA of proliferating cells during S-phase and may be used clinically to radiosensitize tumors that are otherwise poorly responsive to radiation. Although radiosensitization has been studied for years, mechanisms of radiosensitization are poorly understood. One possible mechanism involves the release of short range, high-LET, Auger electrons following photoelectric absorption of an X ray by the K-shell of the incorporated halogen. Such absorption occurs only with X ray energies slightly greater than the K-shell binding energy. We report the results of an experiment designed to measure this effect, in which cultured monolayers of Chinese hamster V79 cells, with 32% replacement of thymidine by bromodeoxyuridine (BUdR), were exposed to monoenergetic X rays just below (13.450 KeV) or above (13.490 KeV) the K-edge (13.475 KeV) of bromine. Enhancement ratios calculated in five different ways were slightly increased (3-12%) above the K-edge compared to below. However, only a calculation using a linear-quadratic fit to the data and a surviving fraction of 0.01 demonstrated a statistically significant increased enhancement ratio (12%) above the K-edge. We conclude that Auger electrons produced following photoelectric absorption of X rays by the K-shell of bromine contribute minimally to observed BUdR cellular radiosensitization.     

Tumor radiosensitization through reductions in hemoglobin affinity

Alterations in the oxygen (O2) distribution in a tumor due to changes in the quantity of O2 carried in the blood can affect the response of a tumor to radiation. For example, the blood hemoglobin (Hb) level has been shown to be an important prognostic and therapeutic factor in radiation therapy. Another factor affecting the delivery of O2 to tissues is the Hb affinity for O2. Changes in Hb affinity for O2 result in shifts of the Hb-O2 dissociation curve which increase or decrease tissue oxygenation. The aim of the present studies was to determine whether reductions in Hb affinity prior to irradiation could improve the resultant tumor response. KHT sarcomas were irradiated in female C3H/HeJ mice, possessing either normal or reduced Hb affinities for O2 at the time of treatment. Changes in Hb affinity for O2 were induced by keeping tumor-bearing mice in a 12% O2 environment for various periods of time. Erythrocyte 2,3-diphosphoglycerate (2,3 DPG) was measured as an indicator of Hb affinity for O2. After 36 hr of low O2 exposure, 2,3 DPG levels increased 20-30%. This change in 2,3 DPG reflected a proportional decrease in Hb affinity for O2. Following the exposure of 12% O2, the animals were removed from the low O2 chamber and their tumors locally irradiated while the mice breathed air. After irradiation, tumor cell survival was determined using an in vivo to in vitro excision assay. The results indicate that the fraction of hypoxic cells in tumors of mice whose Hb affinity had been reduced prior to irradiation was approximately 3%. By comparison, the hypoxic fraction in tumors irradiated in mice with normal Hb affinities was approximately 15%. Thus, reductions in Hb affinity prior to irradiation can yield significant radiation sensitization in tumors. These findings form the basis for future investigations of the use of pharmacologic methods for the in vivo alteration of the Hb-O2 dissociation curve to improve tumor oxygenation.     

Tumor oxygenation and radiosensitization by pentoxifylline and a perflubron emulsion carbogen breathing

Oxygen tension measurements were made in three tumors: (i) the murine FSaII fibrosarcoma, (ii) the rat 9L gliosarcoma and (iii) the rat 13672 mammary adenocarcinoma using a pO2 histograph. Tumor oxygenation measurements were made while the animals breathed air or breathed carbogen (95% oxygen/5% carbon dioxide). Pentoxifylline or a perflubron emulsion was administered to the animals and tumor oxygen measurements were repeated under both breathing conditions. Both pentoxifylline and the perflubron emulsion improved the oxygenation of the FSaII fibrosarcoma under air breathing conditions but did not alter the oxygen profiles of either rat tumor compared with air breathing alone. Carbogen breathing increased the oxygenation of all tumors. Pentoxifylline administration did not change the oxygen profiles of the tumors under carbogen breathing conditions but administration of the perflubron emulsion increased the oxygenation of all three tumors under carbogen breathing conditions compared with carbogen breathing alone. Co-administration of pentoxifylline and the perflubron emulsion enhanced the radiation response of the Lewis lung tumor to daily fractionated radiation under air breathing conditions with a dose modifying factor of 1.65 and under carbogen breathing conditions with a dose modifying factor of 2.25. Over a range of perflubron emulsion doses, pentoxifylline increased the growth delay of the Lewis lung tumor in a constant manner. These results indicate that pentoxifylline and the perflubron emulsion have the largest impact on the oxygenation of more hypoxic tumors and that administration of the perflubron emulsion/carbogen breathing is the most effective means of increasing tumor oxygenation and radiation response.     

Tumor irradiation followed by intratumoral cytokine gene therapy for murine renal adenocarcinoma

To circumvent the toxicity caused by systemic injection of cytokines, cytokine cDNA genes encoding the human interleukin IL-2 cDNA (Ad-IL-2) and murine interferon IFN-gamma gene (Ad- IFN-gamma) were inserted into adenoviral vectors. These constructs were used for intratumoral gene therapy of murine renal adenocarcinoma Renca tumors. Treatment with three doses of Ad-IL-2 or Ad- IFN-gamma, given a day apart, was more effective than single-dose gene therapy. We found that tumor irradiation enhanced the therapeutic efficacy of Ad-IL-2 and Ad-IFN-gamma intratumoral gene therapy. Tumor irradiation, administered 1 day prior to three doses of Ad-IL-2 treatment, was more effective than radiation or Ad-IL-2 alone, resulting in tumor growth arrest in all mice, increased survival and a consistent increase in complete tumor regression response rate. Complete responders rejected Renca tumor challenge and demonstrated specific cytotoxic T-cell activity, indicative of specific tumor immunity. The effect of radiation combined with three doses of Ad-IFN-gamma was less pronounced and did not lead to tumor immunity. Histological observations showed that irradiation of the tumor prior to gene therapy increased tumor destruction and inflammatory infiltrates in the tumor nodules. These findings demonstrate that tumor irradiation improves the efficacy of Ad-IL-2 gene therapy for induction of antitumor immune response.     

Lack of prostate cancer radiosensitization by androgen deprivation.

PURPOSE: The majority of clinical trials have shown that high-grade prostate cancer patients treated with androgen deprivation (AD) plus radiation (RT) have a survival advantage over those treated with RT alone. One possible mechanism for such a favorable interaction is that AD sensitizes cells to radiation. Animal model studies have provided suggestive evidence that AD sensitizes cells to radiation, but this mechanism is difficult to confirm conclusively in vivo. This question was investigated in LNCaP cells grown in vitro. METHODS AND MATERIALS: LNCaP cells were cultured in vitro in Dulbecco's modified Eagle's medium (DMEM)-F12 medium, containing 10% fetal bovine serum (complete medium [CM]). AD was achieved by culture in charcoal-stripped serum (SS)-containing medium. Replacement of androgen was done by adding the synthetic androgen R1881 at 1 x 10(-10) M to SS. Apoptosis was measured with a terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. Clonogenic survival was used to determine overall cell death, and the results were corrected for differences in plating efficiency from the various growth conditions. RESULTS: LNCaP cells were grown in CM, SS, or SS + R1881 medium, and cell counts obtained at 3, 4, and 5 days. Cell number increased exponentially in CM, whereas no increase in cell number was observed in SS medium. Cell counts from growth in SS + R1881 were intermediate between these extremes. Apoptosis was measured to determine if the combination of AD + RT in vitro resulted in supra-additive cell death, as has been previously described in an in vivo model system. The cells were cultured for 3 days before RT and apoptosis quantified 24 h after RT. There was a consistent supra-additive increase in apoptosis in cells exposed to AD + RT (2 or 8 Gy), as compared to either treatment given individually. In contrast, significant radiosensitization by AD was not observed by clonogenic survival even when the conditions of AD were varied. No radiosensitization was observed upon incubation in SS medium for 3, 4, or 5 days before RT, or extending AD after RT for 6 h before plating or 24 h after plating. CONCLUSION: The results show that in LNCaP prostate tumor cells supra-additive apoptosis does not translate into radiosensitization by clonogenic survival. Because clonogenic survival is a measure of overall cell death, either the level of apoptosis is too small a component of overall cell death or the increases in apoptosis occurred in a subpopulation that would have been killed by other mechanisms. Although the findings indicate that AD does not act by sensitizing prostate cancer cells to RT, the additive cell death and growth inhibitory effects of AD + RT are clinically meaningful.     

Tumor radiosensitization by antiinflammatory drugs: evidence for a new mechanism involving the oxygen effect

We hypothesized that nonsteroidal antiinflammatory drugs (NSAIDs) might enhance tumor radiosensitivity by increasing tumor oxygenation (pO2), via either a decrease in the recruitment of macrophages or from inhibition of mitochondrial respiration. The effect of four NSAIDs (diclofenac, indomethacin, piroxicam, and NS-398) on pO2 was studied in murine TLT liver tumors and FSaII fibrosarcomas. At the time of maximum pO2 (t(max), 30 minutes after administration), perfusion, oxygen consumption, and radiation sensitivity were studied. Local pO2 measurements were done using electron paramagnetic resonance. Tumor perfusion and permeability measurements were assessed by dynamic contrast-enhanced magnetic resonance imaging. The oxygen consumption rate of tumor cells after in vivo NSAID administration was measured using high-frequency electron paramagnetic resonance. Tumor-infiltrating macrophage localization was done with immunohistochemistry using CD11b antibody. All the NSAIDs tested caused a rapid increase in pO2. At t(max), tumor perfusion decreased, indicating that the increase in pO2 was not caused by an increase in oxygen supply. Also at t(max), global oxygen consumption decreased but the amount of tumor-infiltrating macrophages remained unchanged. Our study strongly indicates that the oxygen effect caused by NSAIDs is primarily mediated by an effect on mitochondrial respiration. When irradiation (18 Gy) was applied at t(max), the tumor radiosensitivity was enhanced (regrowth delay increased by a factor of 1.7). These results show the potential utility of an acute administration of NSAIDs for radiosensitizing tumors, and shed new light on the mechanisms of NSAID radiosensitization. These results also provide a new rationale for the treatment schedule when combining NSAIDs and radiotherapy.     

Tumor suppressive efficacy through augmentation of tumor-infiltrating immune cells by intratumoral injection of chemokine-expressing adenoviral vector

Our goal in the present study was to evaluate antitumor effects and frequency of tumor-infiltrating immune cells upon intratumoral injection of RGD fiber-mutant adenoviral vector (AdRGD) encoding the chemokines CCL17, CCL19, CCL20, CCL21, CCL22, CCL27, XCL1, and CX3CL1. Among eight kinds of chemokine-expressing AdRGDs, AdRGD-CCL19 injection most efficiently induced infiltration of T cells into established B16BL6 tumor parenchyma, whereas most of these T cells were perforin-negative in immunohistochemical analysis. Additionally, the growth of AdRGD-CCL19-injected tumors decreased only slightly as well as that of other tumors treated with each chemokine-expressing AdRGD, which indicated that accumulation of naive T cells in tumor tissue does not effectively damage the tumor cells. Tumor-bearing mice, in which B16BL6-specific T cells were elicited by dendritic cell-based immunization, demonstrated that intratumoral injection of AdRGD-CCL17, -CCL22, or -CCL27 could considerably suppress tumor growth and attract activated T cells. On the other hand, AdRGD-CCL19-injection in the immunized mice showed slight increase of tumor-infiltrating T cells compared to treatment using control vector. Collectively, although AdRGD-mediated chemokine gene transduction into established tumors would be very useful for augmentation of tumor-infiltrating immune cells, a combinational treatment that can systemically induce tumor-specific effector T cells is necessary for satisfactory antitumor efficacy.     

瘤内注射紫杉醇脂质体对小鼠H22移植瘤抑制作用的研究

目的比较瘤内注射和静脉注射紫杉醇脂质体对小鼠H22肝细胞癌皮下移植瘤的抑瘤作用,探讨瘤内注射微球化疗药物应用的可行性。方法采用ICR小鼠建立H22皮下移植瘤模型,随机分为瘤内注射紫杉醇脂质体组（IT-PL）、静脉注射紫杉醇脂质体组（IV-PL）和瘤内注射5％葡萄糖溶液组（IT-GS）。10天后待瘤体生长至直径10mm左右,分别予经超声引导瘤内注药及尾静脉给药处理。紫杉醇脂质体的给药浓度为3mg／ml,剂量为75mg／kg,每周1次,共2周。采用近红外荧光活体显像法观察注药24h内药物在小鼠体内的分布情况。隔日记录瘤体积变化并观察小鼠的不良反应,计算各组的抑瘤率。瘤体组织石蜡包埋后行HE染色。结果超声引导下瘤内注射紫杉醇脂质体时,针头附近区域见回声增高有助于确认药物分布于瘤体内。近红外荧光活体显像示瘤内注射24h药物持续集中在瘤体内,无明显全身分布;静脉注射药物则逐渐集中至瘤体,但瘤体内的药物浓度低于瘤内注射组。IT-PL组与IV-PL组的抑瘤率分别为95.0％和56.1％,差异有统计学意义（P＜0.05）。病理组织学检查示IT GS组的肿瘤细胞生长旺盛,而IT-PL组的瘤体内及周边有脂质沉积,仅边缘少量残存肿瘤细胞。瘤内注射部位皮下组织未见溃破、糜烂;未观察到明显全身不良反应。结论紫杉醇脂质体瘤内注射有可能成为针对局部实体肿瘤安全、有效的给药模式。     

Local and sustained delivery of 5-fluorouracil from biodegradable microspheres for the radiosensitization of glioblastoma: a pilot study.

BACKGROUND: The authors have developed a new method of drug delivery into the brain using implantable biodegradable microspheres. In this study, this method was used to provide localized and sustained delivery of 5-fluorouracil (5-FU) after the surgical resection of glioblastoma. This antimetabolite and radiosensitizing drug was selected in an attempt to decrease the rate of local recurrence of the tumor. METHODS: Eight patients with newly diagnosed glioblastoma were included in the study and 2 increasing amounts of 5-FU were studied (70 mg and 132 mg). After surgical resection of the tumor, poly(D-L lactide-co-glycolide) 5-FU-loaded microspheres with an average dimension of 45 microm were implanted in the wall of the surgical bed. External beam radiation (59.4 grays) was initiated before the seventh postsurgical day. Patients were followed by clinical examination, magnetic resonance imaging, and 5-FU assays in the blood and cerebrospinal fluid (CSF). RESULTS: 5-FU assays confirmed sustained concentrations in the CSF for at least 1 month. Concentrations of 5-FU in the blood were lower and transitory. Systemic tolerance to the treatment was good; one case of recurrent brain swelling was observed at the higher dose studied. At the time of last follow-up the overall median survival time was 98 weeks from the time of implantation and 2 patients had achieved disease remission at 139 and 153 weeks, respectively. CONCLUSIONS: This study demonstrates that biodegradable microspheres are efficient systems for drug delivery into the brain and may have future application in the treatment of brain tumors. Further studies are needed to confirm the potential of 5-FU-loaded microspheres for the radiosensitization of glioblastoma. [Please see editorial on pages 197-9, this issue].     

Cytokinetic analysis of lung cancer by in vivo bromodeoxyuridine labelling.

Cytokinetic parameters of various types of lung cancer were determined in bronchoscopy specimens after in vivo labelling with the thymidine analogue bromodeoxyuridine (BrdU). The S-phase fraction and BrdU labelling index were measured flow cytometrically, allowing calculation of the S-phase transit time and potential tumour doubling time. The methodology used was found to be feasible for obtaining cytokinetic data from 76% of the bronchial biopsy samples. Despite the difference in clinical behaviour and growth pattern between small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC), no significant differences were observed between the mean values of the cytokinetic parameters of SCLC and NSCLC. The estimated cell loss factor was higher in NSCLC than in SCLC. It appears that the growth of a tumour, as clinically observed, is to a considerable extent influenced by cell loss. In accord with this assumption is the fact that we have observed non-BrdU labelled S-phase cells, both in tumour biopsies and in apparently normal tissue. The presence of these so-called unlabelled S-phase cells in relation to cell loss is discussed.     

Injectable drug carriers with sustained release of cis-platinum

The authors devised injectable drug carriers with sustained release of cis-platinum (CDDP). We formed the carriers using biodegradable medical materials applied clinically: namely, fibrin hydrogel clot (FC) made from tissue adhesive, and gelatin powder (Gp) for hemostasis. Two different types of carriers were prepared: plain fibrin hydrogel clots (FCs) and Gp-containing FCs. Each carrier was dehydrated and crushed into granules, then irradiated with ultraviolet (UV) rays. These modified materials were saturated with a CDDP solution to prepare CDDP-loaded injectable sol, which were incubated at 37 degrees C in our experimental fibrinolytic systems. We examined the in vitro release profile of the CDDP and antineoplastic activities with the drug delivered from the sol. The UV-treated materials gradually released the CDDP over more than 20-30 days. Non-UV-treated carriers released the drug within 3-5 days. More than 90% of the released CDDP was revealed to be a protein-binding type, which favorably inhibited the growth of cultured cancer cells. Conversely, the CDDP incubated with human plasma showed no inhibiting functions against the growth of cancer cells. Our newly devised material appears to have great potential for loco-regional cancer chemotherapy based on the principle of local drug delivery.     

Multi-layer polymeric implants for sustained release of chemopreventives

The polycomb group (PcG) protein BMI1 plays a critical role in regulating self renewal capacity of both normal and leukemic stem cells. BMI1 is frequently overexpressed in several types of cancer, which is associated with poor prognosis. However, there are few researches on BMI1 in myelodysplastic syndromes (MDS). In this study, we reported that overexpression of BMI1 protein was detected in MDS patients, and inversely correlated with the apoptosis of CD34+ cells. In vitro overexpression of BMI1 facilitated proliferation and inhibited apoptosis of MDS-L cells. The overexpression of BMI1 could downregulate apoptosis sensitivity to cytotoxic agents in MDS-L cells; on the contrary, MDS-L cells could be rendered apoptosis-sensitive by BMI1 knockdown. Overexpression of BMI1 antagonised apoptosis by downregulating several apoptosis-related proteins, such as p16^INK4a, phospho-p53 (Ser46) and caspase 3/9. In addition, overexpression of BMI1 was correlated with an elevated IPSS score and a shorter survival. Collectively, overexpression of BMI1 induces resistance to apoptosis and contributes to adverse prognosis in MDS. BMI1 could serve as a therapeutic target for patients with MDS.     

Immunotherapy of a mouse mammary carcinoma by sustained peritumor release of IL-2

The purpose of this study was to compare the local and systemic therapeutic effects of Interleukin-2 (IL-2) used in 3 different preparations: suspended in PBS, suspended in 2% agar, and entrapped in multi-lamellar liposomes suspended in 2% agar. The liposomes were composed of phosphatidylglycerol and phosphatidylcholine in a 1:4 molar ratio. The net release of IL-2 in vitro (by ELISA assay) at 37 degrees C, measured at 4 hr, 2 days, and 10 days, was 50%, 75%, and 100% from agar, and 8%, 22%, and 33% from liposomes in agar. In the therapeutic tests, the IL-2 preparations were injected close to s.c. implants of the MC2 mouse mammary carcinoma. Four injections at weekly intervals of IL-2 in agar had as much local and systemic (against uninjected contralateral tumor implants in treated mice) therapeutic effect as the same total amount of IL-2 in PBS given in 20 daily injections over 4 weeks. The IL-2 liposome-gel preparation was most effective (p less than 0.05), probably due to the more sustained release of IL-2. Three injections of this preparation gave a fixed and sustained peritumor release of IL-2 which, at sub-toxic levels, resulted in both local and systemic therapeutic effects.     

Immunotherapy of primary methylcholanthrene-induced mouse tumours by intratumoral BCG.

Tumours were induced s.c. in C3H/uip, SJL/uip, DBA/2 uip, C57BL/6 uip and BDF1 mice by different doses of methylcholanthrene (MCA) diluted in oil: 1 mg, 0.1 mg and 0.01 mg. In each mouse strain, tumour frequency showed a different decreasing pattern in relation to the decreasing dose of MCA. Tumour latent period (LP) increased between the 1mg and 0.1mg doses of MCA, but the 0.01mg dose induced tumours with a similar or shorter LP than those tumours induced by 1 mg. Half of the tumours were treated with two injections of intratumoral (IT) BCG. The strains of mice differed in their sensitivity to this treatment, but only tumours induced by 0.01 mg MCA were sensitive to IT BCG. The induction of tumours by MCA pellets gave similar results. After transplantation of the untreated tumours, very few were cured by BCG treatment. Analysis of the role of tumour LP, growth rate and immunogenicity favours a slow growth rate as the most important characteristic for BCG sensitivity of the primary tumour. The tumours induced by 0.01 mg MCA were less immunogenic than those induced by 1 mg MCA, but the difference was not significant. This finding permits us to exclude an important role for tumour immunogenicity in the sensitivity of the primary tumour to BCB.     

Multi-layer polymeric implants for sustained release of chemopreventives

Poor oral bioavailability limits the use of many chemopreventives in the prevention and treatment of cancer. To overcome this limitation, we report an improvised implant formulation (“coated” implants) using curcumin, individual curcuminoids, withaferin A and oltipraz. This method involves the coating of blank polycaprolactone implants with 20–30 layers of 10–20% polycaprolactone solution in dichloromethane containing 0.5–2% of the test agent. The in vitro release showed that while oltipraz was released with almost zero-order kinetics over 8 weeks, curcumin, individual curcuminoids and withaferin A were released with some initial burst. The in vivo release was determined by grafting implants subcutaneously in A/J mice. When delivered by coated implants, oltipraz significantly diminished lung DNA adducts in mice treated with dibenzo[a,l]pyrene compared with sham treatment (28 ± 7 versus 54 ± 17 adducts/10⁹ nucleotides). Withaferin A also diminished DNA adducts, but it was insignificant. Curcumin and individual curcuminoids were ineffective. Analysis of lung, liver and brain by UPLC-fluorescence showed the presence of the three test curcuminoids indicating effectiveness of the implant delivery system. Further, based on its known antitumor activity in vivo, withaferin A given via the implants significantly inhibited human lung cancer A549 xenograft in athymic nude mice, while it was ineffective when the same total dose was administered i.p. and required over 2-fold higher dose to elicit effectiveness. Together, our data suggest that coated polymeric implants can accommodate heat-labile compounds, can furnish sustained release for long duration, and elicit DNA damage-inhibiting and anti-tumor activities.     

Stealth liposomes: an improved sustained release system for 1-beta-D-arabinofuranosylcytosine.

Newly developed liposomes with prolonged circulation half-lives and dose-independent pharmacokinetics (Stealth liposomes) have been tested for their efficacy as a slow release system for the rapidly degraded, schedule-dependent, antineoplastic drug 1-beta-D-arabinofuranosylcytosine (ara-C) in the treatment of murine L1210/C2 leukemia. Mice were given injections of either 10(5) cells or 10(6) cells by either the i.v. or the i.p. routes. Leukemia-bearing mice were treated with either i.v. or i.p. injections of free drug, i.v. or i.p. injections of liposome-entrapped drug, or 24-h i.v. infusions of free drug. Long-circulating liposomes contained, as the stealth component, either monosialoganglioside or polyethylene glycol-distearoylphosphatidylethanolamine. Liposomes lacking the stealth components (non-stealth liposomes) were also injected for comparison. At lower dose ranges, stealth liposomes were superior to non-stealth liposomes in prolonging mean survival times of the mice, and all liposome preparations were superior to injections of the free drug. Drug entrapped in stealth liposomes, when administered at or near the maximum tolerated dose of 100 mg/kg ara-C were considerably superior to 24-h free drug infusions given at the same total drug dose. Therapeutic effect was related to the half-life of leakage of ara-C from the liposome formulations, as well as to circulation half-life, with maximum therapeutic effect achieved with long circulation half-lives and more rapid leakage rates. The therapeutic efficacy of non-stealth liposomes increased with increasing liposome (and drug) dose as a result of saturation of liposome uptake by the mononuclear phagocyte system, which resulted in longer circulation half-lives for these liposomes at higher doses (Michaelis-Menten pharmacokinetics). Liposome entrapment can protect rapidly degraded drugs from breakdown in vivo, with release of the drugs in a therapeutically active form over periods of up to several days. The dose-independent pharmacokinetics and reduced mononuclear phagocyte system uptake of stealth liposomes gives them distinct advantages over non-stealth liposomes.