Tumor Drug Levels Research Articles

Doxorubicin encapsulated in sterically stabilized liposomes for the treatment of a brain tumor model: biodistribution and therapeutic efficacy.

Anthracyclines entrapped in small-sized, sterically stabilized liposomes have the advantage of long circulation time, reduced systemic toxicity, increased uptake into systemic tumors, and gradual release of their payload. To date, there is no information on the behavior of these liposomes in brain tumors. The objective of this study was to compare the biodistribution and clinical efficacy of free doxorubicin (F-DOX) and stealth liposome-encapsulated DOX (SL-DOX) in a secondary brain tumor model. Nine days after tumor inoculation Fischer rats with a right parietal malignant sarcoma received an intravenous dose of 6 mg/kg of either F-DOX or SL-DOX for evaluation of drug biodistribution. For therapeutic trials a single dose of 8 mg/kg was given 6 or 11 days after tumor induction, or alternatively, weekly doses (5 mg/kg) were given on Days 6, 13, and 20. Liposome-encapsulated DOX was slowly cleared from plasma with a t1/2 of 35 hours. Free-DOX maximum tumor drug levels reached a mean value of 0.8 microgram/g and were identical in the adjacent brain and contralateral hemisphere. In contrast, SL-DOX tumor levels were 14-fold higher at their peak levels at 48 hours, declining to ninefold increased levels at 120 hours. A gradual increase in drug levels in the brain adjacent to tumor was noted between 72 and 120 hours (up to 4 micrograms/g). High-performance liquid chromatography analysis identified a small amount of aglycone metabolites within the tumor mass from 96 hours and beyond, after SL-DOX injection. Cerebrospinal fluid levels were barely detectable in tumor-bearing rats treated with F-DOX up to 120 hours after drug injection (< or = 0.05 microgram/ml), whereas the levels found after SL-DOX were 10- to 30-fold higher. An F-DOX single-dose treatment given 6 days after tumor inoculation increased the rats' life span (ILS) by 135% over controls (p < 0.05) but was not effective if given on Day 11. In contrast, SL-DOX treatment resulted in an ILS of 168% (p < 0.0003) with no difference when given after 6 or 11 days. Treatment with three weekly doses of SL-DOX produced an ILS of 189% compared to 126% by F-DOX (p < 0.0002). The authors conclude that the use of long-circulating liposomes as cytotoxic drug carriers in brain tumor results in enhanced drug exposure and improved therapeutic activity, with equal effectiveness against early small- and large-sized brain tumors.

Antitumor effect of intratumoral administration of fluorouracil/epinephrine injectable gel in C3H mice

Fluorouracil/epinephrine injectable gel (5-FU/epi gel) was evaluated in vitro for its drug-release profile characteristics and in a mouse tumor model for its antitumor effectiveness. In vitro chemosensitivity studies with 5-FU in RIF-1 fibrosarcoma cells showed less than 1 log of cell kill at 1 mM after 2 h of exposure. Increasing the exposure time to 24 h resulted in greater cell killing (approximately 2.5 log cell kill at 0.5 mM), suggesting that sustained drug levels in tumors would result in an increased efficacy outcome in vivo. A 5-FU/epi injectable gel was designed, providing drug release in vitro of 50% by approximately 4 h and of 80% by 24 h. The retention of 5-FU in RIF-1 mouse tumors was determined after intratumoral administration of 5-FU/epi gel or various combinations of the formulation components. Area-under-the-curve (AUC0-24 h) calculations resulted in an AUC value of 146.4% h for the 5-FU/epi gel formulation as compared with 45.7% h for 5-FU solution. Tumor growth was significantly delayed (P < 0.05) with the 5-FU/epi gel (60 mg/kg) as compared with 5-FU solution given intratumorally or systemically. A fluorouracil dose of 150 mg/kg in the 5-FU/epi gel given weekly for 13 weeks was not lethally toxic, whereas the same dose given as drug solution was 100% lethal, suggesting that the therapeutic index for 5-FU in the gel formulation may be much greater than that for aqueous drug solution delivered intratumorally.

Improvement of combined modality therapy with cisplatin and radiation using intratumoral drug administration in murine tumors

The aim of these studies was to increase the therapeutic ratio by achieving higher tumor concentrations of cisplatin during the course of a fractionated irradiation treatment. Specific goals were to test, firstly, whether multiple drug injections could be replaced by a single slow release implant of cisplatin, and secondly, whether the therapeutic potential of the combined treatment could be increased by administering the drug intratumorally. Drug administration routes tested were intraperitoneal (i.p.) of drug in solution, intratumoral (i.t.) of drug in solution, and intratumoral of drug in a slow release formulation. The latter consisted of a hydrogel polymer formulated into rods which were implanted into the center of subcutaneous tumors. For drug alone, both i.t. routes (solution or polymer) produced higher therapeutic gains than i.p. administration, as judged by tumor growth delay for a given weight loss. When combined with radiation, dose response curves were always shifted to lower doses and were steeper than for radiation or drug alone, although isobologram analysis indicated additivity. In a first series, drug enhancement ratios ranged from 1.6 to 2.6, and were highest for the i.t. groups. In a second series, X-ray enhancement ratios ranged from 1.1 to 1.7, with overlap between results from the different routes. Therapeutic ratios, however, were highest for the i.t. groups in both series. Slow release rods produced the highest therapeutic gains in the first series, while i.t. administration of drug in solution was approximately as effective in the second series. It is concluded that i.t. administration of cisplatin in a slow release vehicle is a relatively simple and effective way of providing high tumor drug levels during a fractionated radiation scheme which can lead to significant therapeutic improvements compared with administering the drug systemically.

Dose-Related Doxorubicin Effect in an Orthotopic Secondary Lung Cancer Screen

Lung cancer is the leading cause of cancer-related death of both sexes in the United States and promises to be a major problem in the world community for decades. We are developing an orthotopic (organ specific) secondary screening system to measure the uptake and efficacy of new lung cancer agents. The elements of the system are: (1) orthotopic growth of a model human lung cancer (NCI-H460 large cell carcinoma) in the right caudal lobe of the nude rat; (2) 1-hr ex vivo pulmonary perfusion treatment of the tumor-bearing lungs; and (3) soft agar clonogenic assay of the enzymatically disaggregated tumor cells. This study characterizes dose-response aspects of the system. Perfusion of tumor-bearing lungs with 0, 1, 10, and 100 μg/ml doxorubicin resulted in a dose-related reduction in surviving fraction from 1.01 ± 0.41 to 0.019 ± 0.006 ( P < 0.05) without significant treatment-related increases in lung weight or perfusion pressure. Tumor and lung drug levels were also dose-related, with lung levels exceeding tumor levels at all doses. The tumor drug level at the 100 μg/ml dose was 62 ± 16 ng/mg. There was a strong negative correlation between the measured tumor drug level and surviving fraction in the clonogenic assay ( R 2 = 0.47, P = 0.0005). This new screening system is capable of demonstrating dose-related uptake and tumoricidal activity of doxorubicin on an orthotopic, model human large cell lung carcinoma. It may be useful for the secondary screening of agents active against human lung cancer.

Heat-induced drug release rate and maximal targeting index of thermosensitive liposome in tumor-bearing mice.

To evaluate the rate of drug release at the tumor and maximal drug targeting after administration of thermosensitive liposomes with hyperthermia, a theoretical and experimental method was derived assessing the fraction of drug released from liposomes in a single pass through the heated tumor, F, and the drug targeting index when drug release occurs completely in response to heat (F = 1), DTImax. The F and DTImax were evaluated for four types of liposomes (LUV-1 and LUV-2, thermosensitive large unilamellar liposomes; LUV-3, a nonthermosensitive large unilamellar liposome; and SUV-1, a thermosensitive small unilamellar liposome) using reported data on blood liposome levels and tumor drug levels after the liposomes were administered to tumor bearing mice. DTImax values for LUV-1 and SUV-1 were approximately 6, while the value for LUV-2 with a relatively large systemic clearance was only 2.3. The F values for LUV-1, LUV-2, and SUV-1 with hyperthermia were 0.71, 1.17, and 0.34, respectively, whereas the values for these liposomes without hyperthermia and for LUV-3 with or without hyperthermia were nearly zero. These results confirm earlier findings that LUV-1 and LUV-2 release CDDP almost completely at the heated tumor and that the large DTI value obtained in LUV-1 (DTI = 4.6) was due to its high heat sensitivity and its small systemic clearance.

Modulation of doxorubicin uptake by epinephrine in the VX-2 carcinoma

The purpose of regional chemotherapy is to deliver maximal drug concentrations to localized unresectable tumors, to minimize systemic toxicity, and to improve tumor response to treatment. Manipulation of regional blood flow by vasoactive agents could further increase tumor drug levels. This study evaluates the effect of hepatic artery infusion of epinephrine on tumor and liver doxorubicin uptake. New Zealand White rabbits ( n = 17) were implanted with hepatic VX-2 carcinomas which were allowed to grow to 2–3 cm in diameter. Doxorubicin (3 mg/kg) ± [ 14C]doxorubicin (2.5 μCi) was given alone (controls) or following low- (5 μg) or high- (15–50 μg) dose epinephrine infusion into the hepatic artery. Heart, liver, and tumor were obtained 30 min after infusion for determination of doxorubicin concentration. The doxorubicin liver concentrations were similar in all three groups but tumor levels decreased from 26.6 ± 16.3 to 6.7 ± 2.8 and 6.6 ± 4.3 nmole/g in the epinephrine groups. Myocardial levels were reduced by the high-dose epinephrine (6.8 ± 2.2 nmole/g) when compared to controls (11.3 ± 2.1 nmole/g) or low-dose epinephrine (11.5 ± 1.8 nmole/g). The liver concentration of doxorubicin was not significantly affected by intraarterial epinephrine. The myocardial doxorubicin concentration was affected only by epinephrine doses sufficient to cause severe systemic vasoconstriction. The decrease in tumor doxorubicin concentration to low-dose (5 μg) and high-dose (15–50 μg) epinephrine suggests that intraarterial epinephrine limits doxorubicin uptake by tumor.

Intra-arterial infusion of doxorubicin with degradable starch microspheres. Improvement of hepatic tumor drug uptake.

Regional infusion chemotherapy delivers higher drug concentrations to the tumor than other methods and may decrease systemic drug levels. We evaluated the efficacy of degradable starch microspheres (DSMs) to further increase drug delivery to hepatic tumors. Rabbits implanted with hepatic Vx-2 tumors were treated with hepatic arterial infusion of doxorubicin hydrochloride labeled with carbon 14 with and without DSMs. Tissue levels of doxorubicin were measured in the heart, liver, and tumor 30 minutes after drug infusion. Blood drug levels, as well as biliary and renal excretion rates of doxorubicin, were determined. In rabbits receiving the drug alone, doxorubicin uptake by the tumor and liver were 17.1 +/- 12.8 and 55.3 +/- 9.5 nmol/g of wet weight tissue (mean +/- SD), respectively. In rabbits receiving doxorubicin mixed with DSMs, the tumor and hepatic drug levels were 59.7 +/- 24.9 and 50.7 +/- 4.8 nmol/g, respectively. The tumor drug level was significantly higher in the group that received DSMs compared with the group that received only the drug; the hepatic drug uptake was unchanged. Peak blood and cardiac drug levels were decreased by the coinfusion of drug and DSMs, suggesting that tumor response rates may be improved and systemic toxicity diminished by the use of DSMs in regional infusion chemotherapy.

Intra-arterial Infusion of Doxorubicin With Degradable Starch Microspheres

• Regional infusion chemotherapy delivers higher drug concentrations to the tumor than other methods and may decrease systemic drug levels. We evaluated the efficacy of degradable starch microspheres (DSMs) to further increase drug delivery to hepatic tumors. Rabbits implanted with hepatic Vx-2 tumors were treated with hepatic arterial infusion of doxorubicin hydrochloride labeled with carbon 14 with and without DSMs. Tissue levels of doxorubicin were measured in the heart, liver, and tumor 30 minutes after drug infusion. Blood drug levels, as well as biliary and renal excretion rates of doxorubicin, were determined. In rabbits receiving the drug alone, doxorubicin uptake by the tumor and liver were 17.1±12.8 and 55.3±9.5 nmol/g of wet weight tissue (mean±SD), respectively. In rabbits receiving doxorubicin mixed with DSMs, the tumor and hepatic drug levels were 59.7±24.9 and 50.7±4.8 nmol/g, respectively. The tumor drug level was significantly higher in the group that received DSMs compared with the group that received only the drug; the hepatic drug uptake was unchanged. Peak blood and cardiac drug levels were decreased by the coinfusion of drug and DSMs, suggesting that tumor response rates may be improved and systemic toxicity diminished by the use of DSMs in regional infusion chemotherapy. (<i>Arch Surg</i>1986;121:1277-1281)

Chemotherapeutic Agent Permeability to Normal Brain and Delivery to Avian Sarcoma Virus-induced Brain Tumors in the Rodent: Observations on Problems of Drug Delivery

Four chemotherapeutic agents (cyclophosphamide, 5-fluorouracil (5-FU), methotrexate (MTX), and bleomycin) were given intravenously to rats harboring the avian sarcoma virus-induced glioma. Drug content in brain, tumor, and systemic tissue was measured. The uptake of drug and the consistency of drug levels in normal brain and tumor varied widely among these agents. [14C]Cyclophosphamide and its metabolites penetrated normal brain and, to a greater extent, brain tumor. [14C]5-FU and its metabolites also entered normal brain and brain tumor, but to lesser extent than [14C] cyclophosphamide and its metabolites. Immunoreactive MTX entry into tumor was variable, ranging from 30 to 1080 ng/g of tissue, with only minimal concentrations in normal brain. After conventional doses, immunoreactive bleomycin levels in tumor were also variable, ranging from 24 to 164 mu units/g of tissue, and little if any drug entered surrounding brain. In addition, the cerebrovascular permeability of 5-FU and MTX in normal rats was measured. Utilizing the method of Rapoport, the PA (product of permeability and capillary surface area) of 5-FU was found to be 6- to 12-fold greater than that of MTX. The PA of both drugs was increased 4- to 7-fold after osmotic blood-brain barrier opening. The variable "leakiness" of glial tumors, both experimentally and clinically, as well as the varied permeabilities of different water-soluble chemotherapeutic agents, makes the drug delivery problem in brain tumors a very complex issue.

Radiosensitization of the RIF-1 murine flank tumor by desmethylmisonidazole (Ro 05 9963) during interstitial brachytherapy

We have investigated the interaction of the nitroimidazole radiosensitizer desmethylmisonidazole (Ro 05 9963) with interstitial radiation using a clonogenic cell assay as the endpoint. Removable I-125 sources were implanted at right angles to the outer surface of globular RIF-1 tumors grown in the flanks of C3 H He mice. Desmethylmisonidazole was administered by continuous intraperitoneal infusion at a rate of 2.7 mg/gm body weight/24 hr. Tumor and serum drug levels were measured by high performance liquid chromatography. Tumor drug levels of 40–100 μm/gm tumor tissue were achieved consistently. No appreciable cytotoxicity was produced by desmethylmisonidazole alone, but a radiosensitization effect with a dose modifying factor of 1.6 was found.

Drug or radiation changes to the host which could affect the outcome of combined modality therapy

In this review, the various ways are examined by which combined modality regimens can affect the host in such a manner as to modify the outcome of the therapy. These host changes are considered under the general headings of effects on (1) drug pharmacokinetics, (2) vasculature, (3) the specific immune response, (4) non-specific host defenses, particularly those mediated by macrophages, (5) general host condition, and (6) a miscellaneous category including local infection and drug-stimulated recovery of surviving cells. Where appropriate, the relative influence is examined of each of these host effects on the commonly used endpoints for assay of tumor response. In general, the assays most likely to be affected are those in which the tumor remains in situ after treatment (tumor cure, regrowth delay, and, the most limited endpoint, increase in lifespan). However, assays for cell survival by removal of the tumor soon after treatment are not entirely free from possible host effects. A possible outcome of several different host effects is a change in the metastatic frequency of the tumor. This may have little or no effect on the “therapeutic ratio” judged in terms of local effect, but could have a large influence of the overall efficacy of a particular regimen. Since host effects are likely to be rather specific to the particular model system employed, they usually represent an unwanted side-effect of the treatment which may interfere with, or alter, interpretations of the experimental data. For this reason a list of precautions in the selection and use of experimental systems is given in the results. These include measurement of tumor drug levels, use of non-immunogenic tumor/host models, and the avoidance of stress, excessive weight loss, local infection, and the use of anesthetics for animal immobilization.