Decreased blood flow to rat bone marrow, bone, spleen, and liver in acute leukemia

Vinblastine pharmacokinetics in mouse, dog, and human in the context of a physiologically based model incorporating tissue-specific drug binding, transport, and metabolism

Vinblastine (VBL) is a vinca alkaloid-class cytotoxic chemotherapeutic that causes microtubule disruption and is typically used to treat hematologic malignancies. VBL is characterized by a narrow therapeutic index, with key dose-limiting toxicities being myelosuppression and neurotoxicity. Pharmacokinetics (PK) of VBL is primarily driven by ABCB1-mediated efflux and CYP3A4 metabolism, creating potential for drug-drug interaction. To characterize sources of variability in VBL PK, we developed a physiologically based pharmacokinetic (PBPK) model in Mdr1a/b(-/-) knockout and wild-type mice by incorporating key drivers of PK, including ABCB1 efflux, CYP3A4 metabolism, and tissue-specific tubulin binding, and scaled this model to accurately simulate VBL PK in humans and pet dogs. To investigate the capability of the model to capture interindividual variability in clinical data, virtual populations of humans and pet dogs were generated through Monte Carlo simulation of physiologic and biochemical parameters and compared to the clinical PK data. This model provides a foundation for predictive modeling of VBL PK. The base PBPK model can be further improved with supplemental experimental data identifying drug-drug interactions, ABCB1 polymorphisms and expression, and other sources of physiologic or metabolic variability.

Hyaluronan in the healthy and malignant hematopoietic microenvironment

The fate of both endogenous and transplanted stem cells is dependent on the functional status of the regulatory local microenvironment, which is compromised by disease and therapeutic intervention. The glycosaminoglycan hyaluronan (HA) is a critical component of the hematopoietic microenvironment. We summarize recent advances in our understanding of the role of HA in regulating mesenchymal stem cells, osteoblasts, fibroblasts, macrophages, and endothelium in bone marrow (BM) and their crosstalk within the hematopoietic microenvironment. HA not only determines the volume, hydration, and microfluidics of the BM interstitial space, but also, via interactions with specific receptors, regulates multiple cell functions including differentiation, migration, and production of regulatory factors. The effects of HA are dependent on the polymer size and are influenced by the formation of complexes with other molecules. In healthy BM, HA synthases and hyaluronidases form a molecular network that maintains extracellular HA levels within a discrete physiological window, but HA homeostasis is often perturbed in pathological conditions, including hematological malignancies. Recent studies have suggested that HA synthases may have functions beyond HA production and contribute to the intracellular regulatory machinery. We discuss a possible role for HA synthases, intracellular and extracellular HA in the malignant BM microenvironment, and resistance to therapy.

Activity of the hypoxia-activated prodrug, TH-302, in preclinical human acute myeloid leukemia models

PURPOSE

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm. Recent evidence has shown the bone marrow microenvironment in patients with AML to be intrinsically hypoxic. Adaptive cellular responses by leukemia cells to survive under low oxygenation also confer chemoresistance. We therefore asked whether therapeutic exploitation of marrow hypoxia via the hypoxia-activated nitrogen mustard prodrug, TH-302, could effectively inhibit AML growth.

EXPERIMENTAL DESIGN

We assessed the effects of hypoxia and TH-302 on human AML cells, primary samples, and systemic xenograft models.

RESULTS

We observed that human AML cells and primary AML colonies cultured under chronic hypoxia (1% O2, 72 hours) exhibited reduced sensitivity to cytarabine-induced apoptosis as compared with normoxic controls. TH-302 treatment resulted in dose- and hypoxia-dependent apoptosis and cell death in diverse AML cells. TH-302 preferentially decreased proliferation, reduced HIF-1α expression, induced cell-cycle arrest, and enhanced double-stranded DNA breaks in hypoxic AML cells. Hypoxia-induced reactive oxygen species by AML cells were also diminished. In systemic human AML xenografts (HEL, HL60), TH-302 [50 mg/kg intraperitoneally (i.p.) 5 times per week] inhibited disease progression and prolonged overall survival. TH-302 treatment reduced the number of hypoxic cells within leukemic bone marrows and was not associated with hematologic toxicities in nonleukemic or leukemic mice. Later initiation of TH-302 treatment in advanced AML disease was as effective as earlier TH-302 treatment in xenograft models.

CONCLUSIONS

Our results establish the preclinical activity of TH-302 in AML and provide the rationale for further clinical studies of this and other hypoxia-activated agents for leukemia therapy.

Development of a preclinical PK/PD model to assess antitumor response of a sequential aflibercept and doxorubicin-dosing strategy in acute myeloid leukemia

Timing of the anti-angiogenic agent with respect to the chemotherapeutic agent may be crucial in determining the success of combination therapy in cancer. We investigated the effects of sequential therapy with the potent VEGF inhibitor, aflibercept, and doxorubicin (DOX) in preclinical acute myeloid leukemia (AML) models. Mice were engrafted with human HL-60 and HEL-luciferase leukemia cells via S.C. and/or I.V. injection and treated with two to three doses of aflibercept (5-25 mg/kg) up to 3-7 days prior to doxorubicin (30 mg/kg) administration. Leukemia growth was determined by local tumor measurements (days 0-16) and systemic bioluminescent imaging (days 0-28) in animals receiving DOX (3 mg/kg) with or without aflibercept. A PK/PD model was developed to characterize how prior administration of aflibercept altered intratumoral DOX uptake. DOX concentration-time profiles were described using a four-compartment PK model with linear elimination. We determined that intratumoral DOX concentrations were 6-fold higher in the aflibercept plus DOX treatment group versus DOX alone in association with increased drug uptake rates (from 0.125 to 0.471 ml/h/kg) into tumor without affecting drug efflux. PD modeling demonstrated that the observed growth retardation was mainly due to the combination of DOX plus TRAP group; 0.00794 vs. 0.0043 h(-1). This PK/PD modeling approach in leukemia enabled us to predict the effects of dosing frequency and sequence for the combination of anti-VEGF and cytotoxic agents on AML growth in both xenograft and marrow, and may be useful in the design of future rational combinatorial dosing regimens in hematological malignancies.

Radioimmunotherapy with anti-CD66 antibody: improving the biodistribution using a physiologically based pharmacokinetic model

To improve radioimmunotherapy with anti-CD66 antibody, a physiologically based pharmacokinetic (PBPK) model was developed that was capable of describing the biodistribution and extrapolating between different doses of anti-CD66 antibody.

METHODS

The biodistribution of the (111)In-labeled anti-CD66 antibody of 8 patients with acute leukemia was measured. The data were fitted to 2 PBPK models. Model A incorporated effective values for antibody binding, and model B explicitly described mono- and bivalent binding. The best model was selected using the corrected Akaike information criterion. The predictive power of the model was validated comparing simulations and (90)Y-anti-CD66 serum measurements. The amount of antibody (range, 0.1-4 mg) leading to the most favorable therapeutic distribution was determined using simulations.

RESULTS

Model B was better supported by the data. The fits of the selected model were good (adjusted R(2) > 0.91), and the estimated parameters were in a physiologically reasonable range. The median deviation of the predicted and measured (90)Y-anti-CD66 serum concentration values and the residence times were 24% (range, 17%-31%) and 9% (range, 1%-64%), respectively. The validated model predicted considerably different biodistributions for dosimetry and therapeutic settings. The smallest (0.1 mg) simulated amount of antibody resulted in the most favorable therapeutic biodistribution.

CONCLUSION

The developed model is capable of adequately describing the anti-CD66 antibody biodistribution and accurately predicting the time-activity serum curve of (90)Y-anti-CD66 antibody and the therapeutic serum residence time. Simulations indicate that an improvement of radioimmunotherapy with anti-CD66 antibody is achievable by reducing the amount of administered antibody; for example, the residence time of the red marrow could be increased by a factor of 1.9 +/- 0.3 using 0.27 mg of anti-CD66 antibody.

Increased cellular hypoxia and reduced proliferation of both normal and leukaemic cells during progression of acute myeloid leukaemia in rats

The microenvironmental changes in the bone marrow, spleen and liver during progression of the transplantable promyelocytic leukaemia in the Brown Norwegian rat (BNML) have been studied. We used flow cytometry to estimate cellular hypoxia and proliferation based on in vivo pulse-labelling with a mixture of 2-nitroimidazole linked to theophylline (NITP) and bromodeoxyuridine (BrdUrd). The leukaemic cells were identified with the RM124 antibody. In rats inoculated with leukaemic cells the fraction of RM124+ cells was significantly increased from day 20 onwards in the spleen and from day 27 in the bone marrow and liver, reaching a level of 65-87% in these organs at day 32. At day 32, the NITP+ fraction of RM124+ cells had increased significantly in the bone marrow and spleen to 88% and 90%, respectively. The corresponding fractions of NITP+ normal cells reached 63% and 65%, respectively. From day 13 to day 32, the DNA-synthesizing (BrdUrd+) fraction of RM124+ cells in the bone marrow decreased significantly from 52% to 25%, and of normal cells from about 20% to 6%. In the bone marrow and spleen at day 27 and 32, the S-phase and G2/M-phase fractions according to DNA content were higher for the NITP+ than for the NITP- cells. This could partly be explained by an impaired cell cycle progression due to hypoxia. Nevertheless, we found indications of leukaemic cells that were simultaneously labelled with NITP and BrdUrd, in the bone marrow and spleen. These latter findings suggest that in contrast to normal cells some of the leukaemic cells can proliferate even during hypoxia, and this subpopulation may consequently renew and expand the leukaemic cell load.

A bioactively modified fatty acid improves survival and impairs metastasis in preclinical models of acute leukemia

PURPOSE

Polyunsaturated fatty acids (PUFA) and the sulfur-substituted fatty acid tetradecylthioacetic acid (TTA) inhibit proliferation and induce apoptosis in lymphoma and leukemic cell lines, but it is unknown if they can modify leukemogenesis in the intact organism.

EXPERIMENTAL DESIGN

We now examined the effects of PUFA and TTA in rats transplanted with either acute promyelocytic leukemia or acute T-cell leukemia. The rats were randomized to isoenergetic diets containing either lard (control), omega3 (n-3) PUFA, or TTA.

RESULTS

Whereas TTA prolonged survival (P < 0.05) in both types of rat leukemia, n-3 PUFA had no significant effect compared with controls. Only TTA inhibited (P < 0.05) leukemic infiltration in the bone marrow and spleen, probably due to apoptosis of the leukemic cells. Plasma metalloproteinase activity, a marker of metastatic activity, was significantly reduced in TTA-fed rats only.

CONCLUSIONS

Dietary intake of TTA, but not of n-3 PUFA, in rats with acute leukemia, prolonged their survival. TTA intake was also associated with reduced leukemic cell burden as well as diminished extramedullar dissemination. TTA represents a modified fatty acid that exerts unique effects on malignant hematopoietic cells, and the present study indicates that TTA may have a therapeutic potential in patients with acute leukemias.

Tumor necrosis factor alpha and adiponectin in bone marrow interstitial fluid from patients with acute myeloid leukemia inhibit normal hematopoiesis

PURPOSE

Locally residing cytokines may inhibit bone marrow hematopoiesis in acute myeloid leukemia (AML). Using a novel method to isolate bone marrow interstitial fluid, we examined if this fluid from 10 adult AML patients could affect normal bone marrow hematopoiesis.

EXPERIMENTAL DESIGN

Bone marrow interstitial fluid was isolated by centrifugation of bone marrow biopsies obtained at time of diagnosis and 2 to 4 weeks after start of induction therapy. The isolated fluid was added to normal bone marrow CD34 hematopoietic progenitor cells sampled from five healthy subjects.

RESULTS

Unlike plasma, AML-derived bone marrow interstitial fluid clearly repressed hematopoietic progenitor cell growth as determined by an in vitro colony assay, an effect that was lost after successful induction treatment. Antibodies against tumor necrosis factor alpha (TNFalpha) and adiponectin abolished growth inhibition by bone marrow interstitial fluid, suggesting a mechanistic role of these cytokines in impairing normal hematopoiesis in AML. The plasma levels of adiponectin and TNFalpha were unaffected by therapy whereas bone marrow interstitial fluid levels of both cytokines fell significantly in patients entering remission. Transcripts for TNFalpha, but not for adiponectin, were found in AML blast cells. Neither the plasma levels nor the bone marrow interstitial fluid levels of the proangiogenic factors vascular endothelial growth factor or basic fibroblast growth factor were appreciably elevated in the patients nor did they change with treatment.

CONCLUSIONS

Specific analyses of bone marrow interstitial fluid may give novel information on normal and malignant hematopoietic activity and thus form the basis for mechanism-based therapy.

Central autonomic control of the bone marrow: multisynaptic tract tracing by recombinant pseudorabies virus

Bone marrow is the primary place of hematopoiesis, where the development, survival and release of multipotent stem cells, progenitors, precursors and mature cells are under continuous humoral and neural control. Dense network of nerve fibers, containing various neurotransmitters is found in the bone marrow, however, the central neuronal circuit that regulates the activities of the bone marrow through these fibers remained unexplored. Transsynaptically connected neurons were mapped by virus-based transneuronal tracing technique using two isogenic, genetically engineered pseudorabies viruses, Bartha-DupGreen and Ba-DupLac expressing green fluorescent protein and beta-galactosidase, respectively. Bartha-DupGreen was injected into the femoral bone marrow of male rats and the progression of infection was followed 4-7 days post-inoculation. Virus-labeled cells were revealed in ganglia of the paravertebral chain and in the intermediolateral cell column of the lower thoracic spinal cord. Neurons were retrogradely labeled in the C1, A5, A7 catecholaminergic cell groups and several other nuclei of the ventrolateral and ventromedial medulla, the periaqueductal gray matter, the paraventricular and other hypothalamic nuclei, and in the insular and piriform cortex. Nerve transections and double-virus tracing from the bone marrow and the surrounding muscles were used to confirm the specific spreading of the virus. These results provide anatomical evidence for the CNS control of the bone marrow and identify putative brain areas, which are involved in autonomic regulation of the hematopoiesis, the release of progenitor cells, the blood supply and the immune cell function in the bone marrow.

Animal models of acute myelogenous leukaemia - development, application and future perspectives

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

Prevention of leptin binding to its receptor suppresses rat leukemic cell growth by inhibiting angiogenesis

Leptin promotes the growth and viability of hematopoietic cells, and it also stimulates microvessel formation, indicating a role for leptin in angiogenesis. Acute myelocytic leukemia (AML) remains a disease with poor prognosis. Similar to solid tumors, it probably requires angiogenesis to ensure adequate supplies of nutrients. We studied rats with transplanted AML to test if a neutralizing anti-leptin receptor monoclonal antibody (mAb) (anti-OB-R) could inhibit leukemogenesis. At 4 weeks after transplantation, the bone marrow contained about 80% leukemic cells as assayed with a specific mAb and flow cytometry. Microscopic examination of bone marrow sections stained with an anti-von Willebrand mAb revealed a marked increase in microvessel density in the leukemic rats compared with controls. Treatment with anti-OB-R for 3 weeks more than halved the content of bone marrow leukemic cells with a concomitant, substantial decrease in angiogenesis. A parallel experiment using an irrelevant anticasein mAb showed no effect on either leukemic cell growth or angiogenesis. We could not detect surface expression of the leptin receptor on the leukemic cells, but on mononuclear cells from healthy rats. The anti-OB-R did not affect in vitro proliferation of leukemic cells whereas proliferation of the mononuclear cells was markedly impaired. The anti-OB-R had no effect on either leukemic cell growth or angiogenesis in leukemic fa/fa rats with a mutated leptin receptor. We conclude that leptin stimulates leukemic cell growth in vivo by promoting angiogenesis. Inhibition of binding of leptin to its receptor might be a new adjunct therapy in AML.

Human bone marrow angiogenesis: in vitro modulation by substance P and neurokinin A

We have previously described a culture system for human bone marrow endothelial cells that organize into capillary tubes associated to pericytes. In the present work, we used this model to assess the angiogenic properties of tachykinins, which have been demonstrated to be involved in neuro-immuno-haematopoietic interactions. The substance P (SP) and neurokinin A (NKA) were similarly potent at increasing in vitro angiogenesis, via NK1 and NK2 receptors respectively. These mediators were not produced by cells in culture, suggesting that in vivo they may be released by nerve fibres in the bone marrow. Therefore, we looked for in situ innervation of the human bone marrow, unknown to date, using immunohistochemistry techniques. As in rodents, arterioles were largely innervated, associated with between one and 10 nerve fibres. Capillary innervation was more restrictive as a unique thin nerve fibre was found in the vicinity of only 6% of these vessels. Finally, no nerve fibres were observed in the vicinity of sinus walls. In conclusion, both in vitro results and the anatomical display of nerve fibres suggest a role in human bone marrow for the vasoactive neuropeptides SP and NKA, which were secreted into a perivascular location. These neural mediators might modulate blood flow in the bone marrow both in the short term by adjusting vascular tone and in the long term by inducing angiogenesis.

Doxorubicin pharmacokinetics: Macromolecule binding, metabolism, and excretion in the context of a physiologic model

The studies described herein were designed to determine whether doxorubicin (DOX) pharmacokinetics (PKs) could be described by a physiologically based PK model that incorporated macromolecule-specific binding and organ-specific metabolism and excretion. Model parameters were determined experimentally, or were gathered from the literature, in a species-specific manner, and were incorporated into a physiologically based description of DOX blood and tissue distribution for mice, dogs, and humans. The resulting model simulation data were compared with experimentally determined data using PK parameters calculated using compartmental or noncompartmental analysis to assess the predictability of the models. The resulting physiologically based PK model that was developed could accurately predict blood and tissue PKs of DOX in mice. When this model was interspecies extrapolated to predict DOX levels in dogs and humans undergoing treatment for cancer, predictions in dog plasma or human serum were also consistent with the actual clinical data. This model has potential utility for predicting the magnitude of PK interactions of DOX with other drugs, and for predicting changes in DOX PKs in any number of clinical situations.

Regulation of extracellular volume and interstitial fluid pressure in rat bone marrow

The volume and fluid pressure characteristics of the intact bone marrow is incompletely understood. We used microspheres and lipoproteins for measurements of intravascular volume (IVV) and EDTA for interstitial fluid volume (IFV) within the rat bone marrow. Interstitial fluid pressure (IFP) was determined with micropipettes connected to a servo-controlled counter-pressure system. Both the microspheres and the lipoproteins yielded estimates of IVV of approximately 1 ml/100 g. After a brief reactive hyperemia, IVV increased to 2.5 ml/100 g, whereas IFV decreased with approximately 1.5 ml/100 g, so that total extracellular volume did not change. Baseline bone marrow IFP was 9.7 mmHg. The hyperemia led to a transient twofold increase in IFP, whereas a marked blood loss decreased IFP by almost one-half. These novel data suggest that extracellular volume and IFP within the bone marrow can be measured with tracer methods and the micropuncture technique. The responses of IVV, IFV, and IFP during changes in blood flow to the bone marrow suggest a tight regulation and are thus compatible with those for a low-compliant tissue.

Changing bone marrow micro-environment during development of acute myeloid leukaemia in rats

The Brown Norwegian rat transplanted with promyelocytic leukaemic cells (BNML) has been used as a model for human acute myeloid leukaemia. We have previously shown that both the blood supply to the bone marrow and the metabolic rate decrease in relation to the leukaemic development in these rats. Here we have investigated how the development and progression of this leukaemia affect oxygenation, pH and proliferation of normal and leukaemic cells in vivo. Bone marrow pH was measured by a needle electrode. Nitroimidazol-theophylline (NITP) was used to identify hypoxic cells, and we applied bromodeoxyuridine (BrdUrd) to identify DNA replicating cells. The leukaemia progressed slowly until day 27 after which a rapid deterioration could be observed leading to severe changes over the following 5 d. In whole blood there was evidence of progressing metabolic acidosis. In bone marrow the fraction of leukaemic cells increased to > 90% and the pH dropped to about 6.5. The fraction of NITP+ cells increased to > 80% in bone marrow and to about 40% in blood. The fraction of BrdUrd+ cells was unchanged in blood, but decreased in bone marrow both for normal cells (from about 20% to 5%), and for leukaemic cells (from about 45% to 25%), evidently as a result of the severely changed microenvironment. In this study we have demonstrated in vivo the development of an acidic and hypoxic bone marrow hampering normal haemopoiesis during leukaemic growth. Our data support the notion of BNML as a valuable tool for studying leukaemogenesis.

Inhibition of Granulocyte-Macrophage Colony-Stimulating Factor Prevents Dissemination and Induces Remission of Juvenile Myelomonocytic Leukemia in Engrafted Immunodeficient Mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor α (TNFα) have been implicated in the pathogenesis of the fatal childhood disease termed juvenile myelomonocytic leukemia (JMML). We used a severe combined immunodeficient/nonobese diabetic (SCID/NOD) mouse model of JMML and examined the effect of inhibiting these cytokines in vivo with the human GM-CSF antagonist and apoptotic agent E21R and the anti-TNFα monoclonal antibody (MoAb) cA2 on JMML cell growth and dissemination in vivo. We show here that JMML cells repopulated to high levels in the absence of exogeneous growth factors. Administration of E21R at the time of transplantation or 4 weeks after profoundly reduced JMML cell load in the mouse bone marrow. In contrast, MoAb cA2 had no effect on its own, but synergized with E21R in virtually eliminating JMML cells from the mouse bone marrow. In the spleen and peripheral blood, E21R eliminated JMML cells, while MoAb cA2 had no effect. Importantly, studies of mice engrafted simultaneously with cells from both normal donors and from JMML patients showed that E21R preferentially eliminated leukemic cells. This is the first time a specific GM-CSF inhibitor has been used in vivo, and the results suggest that GM-CSF plays a major role in the pathogenesis of JMML. E21R might offer a novel and specific approach for the treatment of this aggressive leukemia in man.

Inhibition of Granulocyte-Macrophage Colony-Stimulating Factor Prevents Dissemination and Induces Remission of Juvenile Myelomonocytic Leukemia in Engrafted Immunodeficient Mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor α (TNFα) have been implicated in the pathogenesis of the fatal childhood disease termed juvenile myelomonocytic leukemia (JMML). We used a severe combined immunodeficient/nonobese diabetic (SCID/NOD) mouse model of JMML and examined the effect of inhibiting these cytokines in vivo with the human GM-CSF antagonist and apoptotic agent E21R and the anti-TNFα monoclonal antibody (MoAb) cA2 on JMML cell growth and dissemination in vivo. We show here that JMML cells repopulated to high levels in the absence of exogeneous growth factors. Administration of E21R at the time of transplantation or 4 weeks after profoundly reduced JMML cell load in the mouse bone marrow. In contrast, MoAb cA2 had no effect on its own, but synergized with E21R in virtually eliminating JMML cells from the mouse bone marrow. In the spleen and peripheral blood, E21R eliminated JMML cells, while MoAb cA2 had no effect. Importantly, studies of mice engrafted simultaneously with cells from both normal donors and from JMML patients showed that E21R preferentially eliminated leukemic cells. This is the first time a specific GM-CSF inhibitor has been used in vivo, and the results suggest that GM-CSF plays a major role in the pathogenesis of JMML. E21R might offer a novel and specific approach for the treatment of this aggressive leukemia in man.

Characterization of an animal model of hepatic metastasis

The experimental study of possible therapies for control of the growth of liver metastases requires the availability of a model which is technically feasible and appears to exhibit growth characteristics similar to human tumours. We report on the development of an intrasplenic injection model of liver metastases, and describe the histology, growth pattern and blood flow demonstrated by light microscopy, stereology and laser Doppler flowmetry. The hepatic metastases were induced in mice by intrasplenic injection of dimethylhydrazine (DMH) induced primary colonic carcinoma cells (10(6) cells in 1 mL). The growth and development of metastases was studied over a period of 3 weeks at predetermined time points. Tumour cells were visible in the hepatic sinusoids by day 7 by light microscopy. Macroscopically visible tumours with a diameter of 0.18 +/- 0.02 cm (mean +/- s.d.) were seen by day 10. By this time the tumours had derived a blood supply from the hepatic sinusoids adjacent to the tumour periphery. With further vascularization the tumours reached a diameter of 0.96 +/- 0.50 cm by day 22. Metastatic growth was quantitated by stereological analysis of tumour volume in relation to non-diseased hepatic tissue. Normal mouse liver had a mean volume of 1.13 +/- 0.14 cm3. Tumour growth occurred in three phases. During the initial slow phase the volume of metastases increased from 0.03 +/- 0.02 cm3 at day 10 to 0.22 +/- 0.24 cm3 by day 16. Rapid tumour growth, occurring over the next 3 days, constituted the intermediate phase with metastatic volume reaching 1.21 +/- 0.74 cm3 by day 19 (P = 0.0003 compared with day 16). This growth was followed by a plateau phase when the metastatic volume was 1.40 +/- 0.55 cm3 at day 22. The volume of total liver and of tumour necrosis followed a similar growth pattern. A necrotic tumour volume of 0.004 +/- 0.006 cm3 first seen on day 10 increased to 0.05 +/- 0.06 cm3 by day 16, and to 0.25 +/- 0.20 cm3 by day 22 (P = 0.0022 compared with day 16). The blood flow in metastases measured by laser Doppler flowmetry was lower compared to the non-diseased liver. Tumour blood flow, expressed as a percentage of normal liver blood flow, was 63.31 +/- 26.28% at day 10 and diminished to 27.91 +/- 8.99% by day 22, with an increase in tumour size and age. The decrease in flow was significant between days 13 and 16 (P = 0.0015). This intrasplenic mouse model of metastases is reproducible and should prove useful in the study of treatment of hepatic metastases.

Enhanced oxygen consumption and fatty acid metabolism in rat bone marrow with acute promyelocytic leukaemia

The metabolism of bone marrow cells during the development of acute promyelocytic leukaemia has only been scarcely characterized, even though such knowledge might improve our understanding of the mechanisms of leukemogenesis as well as of drug treatment failure. We have investigated the in vitro oxygen consumption and the metabolism of palmitate in rat bone marrow cells during development of acute promyelocytic leukaemia. As the leukaemia progressed, the cellular oxygen consumption, the beta-oxidation of palmitate and the incorporation of palmitate into phospholipids all increased markedly. Cyclophosphamide supplement led to a temporary reduction of the palmitate metabolism, but did not lower the increased oxygen consumption. We conclude that the cellular metabolic rate is elevated during the progression of acute promyelocytic leukaemia, and that this might reflect an enhanced proliferative rate of the malignant cells.