The vascular pattern of the spontaneous C3H mouse mammary carcinoma and its significance in radiation response and in hyperthermia

Rationale for and measurement of liposomal drug delivery with hyperthermia using non-invasive imaging techniques

The purpose of this review is to present an overview of the state-of-the-art imaging modalities used to track drug delivery from liposomal formulations into tumors during or after hyperthermia treatment. Liposomes are a drug delivery system comprised of a phospholipid bilayer surrounding an aqueous core and have been shown to accumulate following hyperthermia therapy. Use of contrast-containing liposomes in conjunction with hyperthermia therapy holds great promise to be able to directly measure drug dose concentrations as well as to non-invasively describe patterns of drug distribution with MR and PET/SPECT imaging modalities. We will review the rationale for using this approach and the potential advantages of having such information available during and after treatment.

The C-neu mammary carcinoma in Oncomice; characterization and monitoring response to treatment with herceptin by magnetic resonance methods

To characterize spontaneously occurring c-neu/HER2 overexpressing tumours in oncomice and their response to herceptin by non-invasive magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). Oncomice were monitored by localized 31P MRS during unperturbed growth and before and after treatment with 10 mg/kg herceptin (Hoffman La Roche) intraperitoneally for up to 21 days post-treatment. Vascular morphology and function was assessed by quantitation of tumour magnetic resonance (MR) relaxation rates R2* and R2 prior to and either during carbogen (95% O2/5% CO2) breathing or following administration of the blood-pool contrast agent NC100150 (Clariscan, Amersham Health). Immunohistochemistry showed strong membrane staining for HER2 protein overexpression. The 31P MRS showed only a significant (p<0.01) increase of phosphomonoester / total phosphate ratio over 21 days of growth. Herceptin increased the tumour volume doubling time compared to untreated tumours and significantly increased the phosphomonoester / beta-nucleoside triphosphate ratio 2 days after treatment (p=0.01). Tumours showed a highly heterogeneous yet significant (p<0.01) decrease or increase in R2* in response to carbogen or NC100150 respectively. The absence of a decline in tumour bioenergetics with growth, commonly seen in 31P MRS studies of transplanted rodent tumour models, coupled with the heterogeneous blood volume revealed by 1H MRI, suggest a metabolic and vascular phenotype similar to that found in human tumours.

Intravascular HBO(2) saturations, perfusion and hypoxia in spontaneous and transplanted tumor models

Clinical trials utilizing strategies to manipulate tumor oxygenation, blood flow and angiogenesis are under way, although limited quantitative information exists regarding basic tumor pathophysiology. The current study utilized murine KHT fibrosarcomas, spontaneous mammary carcinomas and first-generation spontaneous transplants to examine heterogeneity in vascular structure and function, to relate these changes to the distribution of tumor hypoxia and to determine whether fundamental relationships among the different pathophysiological parameters exist. Three methods were included: (i) immunohistochemical staining of anatomical and perfused blood vessels, (ii) cryospectrophotometric measurement of intravascular oxyhemoglobin saturations and (iii) fluorescent detection of the EF5 hypoxic marker. While a distinct pattern of decreasing oxygenation with increasing distance from the tumor surface was observed for KHT tumors, striking intertumor variability was found in both spontaneous and first-generation transplants, with a reduced dependence on tumor volume. EF5 hypoxic marker uptake was also much more heterogeneous among individual spontaneous and first-generation tumors compared to KHT. Although mammary carcinomas demonstrated fewer anatomical blood vessels than fibrosarcomas, the proportion of perfused vessels was substantially reduced in KHT tumors, especially at larger tumor volumes. Vascular morphology, tissue histological appearance and pathophysiological parameters differed substantially between KHT tumors and both spontaneous and first-generation tumors. Such differences in vascular structure and function are also likely to correlate with altered response to therapies targeted to the vascular system. Finally, spontaneous differentiation status, tumor morphology, vascular configuration and function were well preserved in first-generation transplanted tumors, suggesting a close relationship between vascular development and function in early-generation transplants and spontaneous tumor models.

Quantification of longitudinal tissue pO2 gradients in window chamber tumours: impact on tumour hypoxia

We previously reported that the arteriolar input in window chamber tumours is limited in number and is constrained to enter the tumour from one surface, and that the pO2 of tumour arterioles is lower than in comparable arterioles of normal tissues. On average, the vascular pO2 in vessels of the upper surface of these tumours is lower than the pO2 of vessels on the fascial side, suggesting that there may be steep vascular longitudinal gradients (defined as the decline in vascular pO2 along the afferent path of blood flow) that contribute to vascular hypoxia on the upper surface of the tumours. However, we have not previously measured tissue pO2 on both surfaces of these chambers in the same tumour. In this report, we investigated the hypothesis that the anatomical constraint of arteriolar supply from one side of the tumour results in longitudinal gradients in pO2 sufficient in magnitude to create vascular hypoxia in tumours grown in dorsal flap window chambers. Fischer-344 rats had dorsal flap window chambers implanted in the skin fold with simultaneous transplantation of the R3230AC tumour. Tumours were studied at 9-11 days after transplantation, at a diameter of 3-4 mm; the tissue thickness was 200 microm. For magnetic resonance microscopic imaging, gadolinium DTPA bovine serum albumin (BSA-DTPA-Gd) complex was injected i.v., followed by fixation in 10% formalin and removal from the animal. The sample was imaged at 9.4 T, yielding voxel sizes of 40 microm. Intravital microscopy was used to visualize the position and number of arterioles entering window chamber tumour preparations. Phosphorescence life time imaging (PLI) was used to measure vascular pO2. Blue and green light excitations of the upper and lower surfaces of window chambers were made (penetration depth of light approximately 50 vs >200 microm respectively). Arteriolar input into window chamber tumours was limited to 1 or 2 vessels, and appeared to be constrained to the fascial surface upon which the tumour grows. PLI of the tumour surface indicated greater hypoxia with blue compared with green light excitation (P < 0.03 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). In contrast, illumination of the fascial surface with blue light indicated less hypoxia compared with illumination of the tumour surface (P < 0.05 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). There was no significant difference in pO2 distributions for blue and green light excitation from the fascial surface nor for green light excitation when viewed from either surface. The PLI data demonstrates that the upper surface of the tumour is more hypoxic because blue light excitation yields lower pO2 values than green light excitation. This is further verified in the subset of chambers in which blue light excitation of the fascial surface showed higher pO2 distributions compared with the tumour surface. These results suggest that there are steep longitudinal gradients in vascular pO2 in this tumour model that are created by the limited number and orientation of the arterioles. This contributes to tumour hypoxia. Arteriolar supply is often limited in other tumours as well, suggesting that this may represent another cause for tumour hypoxia. This report is the first direct demonstration that longitudinal oxygen gradients actually lead to hypoxia in tumours.

The relationship between elevated interstitial fluid pressure and blood flow in tumors: a bioengineering analysis

PURPOSE

To examine the hypothesis that elevated interstitial fluid pressure (IFP) is a cause of reduced blood flow in tumors.

MATERIALS AND METHODS

A physiologic model of tumor blood flow was developed based on a semipermeable, compliant capillary in the center of a spherical tumor. The model incorporates the interaction between the tumor vasculature and the interstitium, as mediated by IFP. It also incorporates the dynamic behavior of the capillary wall in response to changes in transmural pressure, and the effect of viscosity on blood flow.

RESULTS

The model predicted elevated tumor IFP in the range of 0 to 56 mmHg. The capillary diameter in the setting of elevated IFP was greatest at the arterial end, and constricted to between 3.2 and 4.4 microm at the venous end. This corresponded to a 2.4- to 3.5-fold reduction in diameter along the length of the capillary. The IFP exceeded the intravascular pressure distally in the capillary, but vascular collapse did not occur. Capillary diameter constriction resulted in a 2.3- to 9.1-fold steady-state reduction in tumor blood flow relative to a state of near-zero IFP.

CONCLUSION

The results suggest that steady-state vascular constriction occurs in the setting of elevated IFP, and leads to reduced tumor blood flow. This may in turn contribute to the development of hypoxia, which is an important cause of radiation treatment failure in many tumors.

Interstitial fluid pressure in cervical carcinoma: within tumor heterogeneity, and relation to oxygen tension

BACKGROUND

Interstitial fluid pressure (IFP) is elevated in many animal and human tumors. The authors assessed tumor IFP and its relation to tumor oxygenation in a prospective clinical study of patients with cervical carcinoma.

METHODS

Measurements were made in 77 patients with cervical carcinoma prior to treatment. IFP was measured in normal paravaginal submucosal tissue and at one to five positions in the visible tumor with the patients anesthetized and in the lithotomy position. Tumor oxygen tension was measured immediately prior to IFP using a polarographic needle electrode. Patients were treated with radiotherapy only. Response was evaluated 3 months after the completion of radiotherapy.

RESULTS

There was substantial variation in IFP from region to region in some tumors. The mean IFP in individual tumors ranged from 3 to 48 millimeters of mercury (mmHg). The overall mean and median values for the entire patient group were 19 mmHg and 17 mmHg, respectively. IFP was significantly higher in tumor tissue than in normal tissue (P < 0.0001). Tumors with high IFP were more likely to be hypoxic (P < 0.007) and less likely to regress completely with radiotherapy (P < 0.04).

CONCLUSIONS

IFP in cervical carcinoma is elevated above normal tissue values. Multiple measurements are needed to evaluate IFP in these tumors. High IFP is associated with hypoxia and may provide information about the mechanism of hypoxia on which treatment can be based.

Solid stress inhibits the growth of multicellular tumor spheroids

In normal tissues, the processes of growth, remodeling, and morphogenesis are tightly regulated by the stress field; conversely, stress may be generated by these processes. We demonstrate that solid stress inhibits tumor growth in vitro, regardless of host species, tissue of origin, or differentiation state. The inhibiting stress for multicellular tumor spheroid growth in agarose matrices was 45 to 120 mm Hg. This stress, which greatly exceeds blood pressure in tumor vessels, is sufficient to induce the collapse of vascular or lymphatic vessels in tumors in vivo and can explain impaired blood flow, poor lymphatic drainage, and suboptimal drug delivery previously reported in solid tumors. The stress-induced growth inhibition of plateau-phase spheroids was accompanied, at the cellular level, by decreased apoptosis with no significant changes in proliferation. A concomitant increase in the cellular packing density was observed, which may prevent cells from undergoing apoptosis via a cell-volume or cell-shape transduction mechanism. These results suggest that solid stress controls tumor growth at both the macroscopic and cellular levels, and thus influences tumor progression and delivery of therapeutic agents.

Detection of tumor response to radiation therapy by in vivo proton MR spectroscopy

PURPOSE

These studies were performed to investigate the effects of radiation on levels of metabolites such as lactate and choline compounds detected by 1H magnetic resonance spectroscopy (MRS). The purpose was to determine the ability of spatially localized 1H MRS to detect tumor response to radiation therapy.

METHODS AND MATERIALS

Proton spectroscopic images were obtained from RIF-1 tumors with voxel spatial resolutions of 8-16 mm3 before and at 24 and 48 h following 2, 4, and 20 Gy of gamma-radiation.

RESULTS

Lactate levels decreased significantly for all doses by 48 h. Tumors irradiated with 2 and 4 Gy showed a significant decrease by 48 h, but not at 24 h. A group of sham-irradiated control animals demonstrated no significant changes in lactate over the period of observation.

CONCLUSIONS

Changes in lactate observed in this study are consistent with an increased blood flow observed in previous studies (15) in the same tumor model following 20 Gy X-irradiation. These studies point to the feasibility of detecting response to clinical doses of fractionated radiation therapy by 1H MRS.

Characterisation of tumour blood flow using a 'tissue-isolated' preparation

Tumour blood flow was characterised in a 'tissue-isolated' rat tumour model, in which the vascular supply is derived from a single artery and vein. Tumours were perfused in situ and blood flow was calculated from simultaneous measurement of (1) venous outflow from the tumour and (2) uptake into the tumour of radiolabelled iodo-antipyrine (IAP). Comparison of results from the two measurements enabled assessment of the amount of blood 'shunted' through the tumours with minimal exchange between blood and tissue. Kinetics of IAP uptake were also used to determine the apparent volume of distribution (VDapp) for the tracer and the equilibrium tissue-blood partition coefficient (lambda). lambda was also measured by in vitro techniques and checks were made for binding and metabolism of IAP using high-pressure liquid chromatography. VDapp and lambda were used to calculate the perfused fraction (alpha) of the tumours. Tumour blood flow, as measured by IAP (TBFIAP), was 94.8 +/- 4.4% of the blood flow as measured by venous outflow, indicating only a small amount of non-exchanging flow. This level of shunting is lower than some previous estimates in which the percentage tumour entrapment of microspheres was used. The unperfused fraction ranged from 0 to 20% of the tumour volume in the majority of tumours. This could be due to tumour necrosis and/or acutely ischaemic tumour regions. For practical purposes, measurement of the total venous outflow of tumours is a reasonable measure of exchangeable tumour blood flow in this system and allows for on-line measurements. Tracer methods can be used to obtain additional information on the distribution of blood flow within tumours.

Effects of clonidine-induced hypotension and dopamine-induced hypertension on blood flows in prostatic adenocarcinoma (Dunning R3327) and normal tissues

In the present study it was investigated whether hypertension induced by dopamine or hypotension induced by clonidine could influence the relative blood distribution in a s.c. transplanted prostatic adenocarcinoma in relation to blood flow in normal tissues in rats. The blood flow was measured by using a radioactive microspheres technique. A bolus injection of 5 micrograms clonidine caused a decrease in the systemic blood pressure with 15-45 mm Hg, and blood flow to the central parts of the tumor, decreased with more than 50%. In the prostate, testes and ileo-psoas muscle a similar reaction was seen. During an infusion of 95-120 micrograms/kg/min dopamine, the blood pressure increased with 15-30 mm Hg, but the blood flow to the tumor was unchanged. However, in the testes and kidneys a decreased blood flow was observed. Moreover, mean blood flow to the central parts of the tumor decreased with increase in tumor size. The results further indicated that hyper- or hypotension or concomitantly given vasoactive drugs with the specific cancer treatment can have unwarranted effects on the distribution of cytotoxic drugs and oxygenation of the tumor.

Differences in vascular response between primary and transplanted tumours

The vast majority of studies on tumour vasculature are performed on transplanted tumours in rodents. However, it is known that there may be differences between primary and transplanted lesions. The purpose of this study is to test whether a specific vascular response is similar in primary tumours and in transplanted tumours derived from them. The technique used was to give an intraperitoneal injection of 5 mg kg-1 hydralazine, which is known to result in hypoxia in transplanted tumours. Changes in perfusion were indicated by changes in metabolism, monitored using 31P Magnetic Resonance Spectroscopy. The primary tumours were induced by local irradiation many months previously and only 4/11 (36%) of these responded to hydralazine. One of the non responders was subsequently transplanted into isogeneic mice to produce a tumour line which was histologically very similar to the primary. Of these 16/17 (94%) responded. The difference is statistically significant (P = 0.001). The reasons for this difference are not known. A number of possibilities are discussed and in the authors' opinion, the most likely cause is that it results from an artefact of transplantation.

Hydralazine-induced changes in tissue perfusion and radiation response in a C3H mammary carcinoma and mouse normal tissues

Hydralazine has been reported to reduce blood perfusion in tumours, thereby increasing hypoxia and subsequently enhancing tumour sensitivity to certain drugs and hyperthermia. We have investigated the ability of hydralazine to induce such changes in a C3H mouse mammary carcinoma and various normal tissues. In tumours, hydralazine (5 mg/kg; i.v.) modified the radiation response, measured by a local tumour control assay, producing an effect equivalent to that seen in tumours made fully hypoxic by clamping. This effect was time-dependent and correlated with the decrease in tissue perfusion estimated by the 86-RbCl extraction procedure. Similar effects were seen in normal skin, although the changes were less dramatic and of a shorter duration. Hydralazine also reduced 86-RbCl uptake in liver, kidney, gut and spleen, but not in bladder, muscle and lung, suggesting that it may have the potential to increase the sensitivity of some normal tissues to hypoxic cell cytotoxins.

The relationship between regional variations in blood flow and histology in a transplanted rat fibrosarcoma

The regional distribution of blood flow to the LBDS1 fibrosarcoma, transplanted into the subcutaneous site in rats, was investigated using the readily diffusible compound 14C-iodo-antipyrine (14C-IAP). Quantitative autoradiography was used to establish absolute values of specific blood flow F for 100 X 100 X 20 microns adjacent tissue volumes of the unperturbed tumour. Mean blood flow to whole tumours was found to decrease with increase in tumour size. This relationship was abolished if blood flow was only measured in sections cut from the periphery of the tumours. Detailed analysis of a sub-group of tumours showed that blood flow to individual tumours was heterogeneous. The range of blood flow was large, indicating that mean blood flow to a whole tumour is a poor reflection of the blood perfusion pattern of that tumour. Necrotic tumour regions were usually very poorly perfused. With the exception of the smallest tumours studied, blood flow was lower in the centre of tumours than in the periphery. Necrosis also tended to develop centrally. However, the peripheral to central gradient of blood flow was apparent even when densely cellular, viable tumour regions and necrotic regions were analysed separately. The decrease in blood flow with tumour size was also apparent in densely cellular, viable tumour regions when analysed separately. Qualitative comparison of tumour histology and regional blood flow showed that there were areas of very low blood flow associated with viable tumour regions. Less common were areas of rather high blood flow associated with necrotic tumour regions. A complicated relationship exists between tumour histology and blood flow. The quantitative autoradiography technique is suitable for investigating the most poorly perfused and the most well perfused viable fractions of animal tumours which may limit the efficacy of different types of therapy.

Radiosensitizing effect of camphor on transplantable mammary adenocarcinoma in mice

The comparative radiosensitizing effects of camphor and metronidazole on murine transplantable mammary adenocarcinoma are reported. Male C3H/Jax mice bearing transplanted mammary tumours were treated with camphor (0.5 microM/body wt) or metronidazole (0.5 microM/g body wt) 45 min before subjecting to local X-irradiation at the dose levels of 30, 80, 100 or 120 Gy. Sequential in situ measurement of the tumour volumes during the follow-up period of 45 days revealed that the maximum enhancement ratios of tumour growth delay for camphor and metronidazole were 4.8 and 2.5, respectively. This suggests that camphor can be a potential radiosensitizing agent in cancer radiotherapy.

Microangiographic and histologic analysis of the effects of hyperthermia on murine tumor vasculature

The effects of hyperthermia on murine tumor vasculature were studied by microangiography and histological examination. The tumors used were SCC VII carcinoma and mammary adenocarcinoma of syngeneic C3H/He mice. For the quantitative analysis of microangiographic changes, the percent (%) vascular area, which was defined as the percentage of opacified tumor vessel area to the entire tumor area, was determined in each microangiogram. The % vascular area after heating in a water bath at 44 degrees C for 30 min was minimized 24 hr after heating in both types of tumors. The histologic study revealed that the initial decrease of the % vascular area was due to congestion, thrombosis, and rupture of tumor vessels, and its subsequent increase was due to angiogenesis. SCC VII was more heat sensitive than mammary adenocarcinoma in terms of tumor growth delay, and tumor vessels of SCC VII were more vulnerable to heat than those of mammary adenocarcinoma. Histological examinations showed a marked difference in the architecture of vessels between the two types of tumors. Tumor vessels of mammary adenocarcinoma were supported by a connective tissue band, whereas those of SCC VII consisted of a single endothelial cell layer. Our findings suggest that the tumor vessels supported by a connective tissue band are less sensitive to heat than those without such support. The vascular damage of SCC VII was temperature dependent, and the critical temperature at which dramatic vascular damage appeared was between 42.7 degrees C and 43.7 degrees C.

The lymphnodal clonogenicity and kinetics of metastatic cells disseminated by a transplanted rat carcinoma

We report data on the transplantation of primary tumour cells and of lymph nodes containing metastatic cells disseminated by a mammary carcinoma (LMC1) implanted s.c. in the Johns' Strain Wistar rat. A new method is described for deriving the TD50 of metastatic cells and for comparing their lymphnodal clonogenicity in the transplanted and the original, i.e. 'primary' tumour host. The TD50 for transplanted primary LMC1 cells was approximately 12 (fiducial limits 8-20 cells), and the latency of the 8-10mm tumours formed (T8-10) after inocula of 10(2) to 10(5) cells decreased linearly with the logarithmic increase in the number of cells injected. From the T8-10 and tumour incidence data for transplanted inguinal, axillary and para-aortic nodes, the TD50 for metastatic cells was calculated to be 1120 cells (fiducial limits 790-1603 cells) indicating that the clonogenicity of naturally disseminated metastatic cells was about a 100 fold lower than that determined for transplanted primary tumour cells. The incidence and T8-10 data for axillary, inguinal and para-aortic lymph node metastases in primary-tumour-excised hosts suggests that, although metastatic cells may continue translymphnodal dissemination in situ, their TD50 is still consistent with that determined by node transplantation.

Vascularization of experimental tumours

At first sight, experimental tumours in observation chambers seem to contain areas with wide vessels showing a sluggish circulation as well as ischaemic areas. Only by careful analysis on cleared specimens can neovascularization be discerned. This process probably occurs primarily in the perimeter of the tumour. It is quite possible that areas of intense vascularization and ischaemic areas in tumours may both result from differences in intensity between the angiogenic stimulus and local tissue pressure.

Differential effect of hyperthermia and x-irradiation on regrowth rate and tumour-bed effect for a rat sarcoma

The regrowth rate of the rat sarcoma SSB1a was assessed, following treatment with either X-rays or hyperthermia. The growth rate of untreated tumours implanted in pre-irradiated or pre-heated normal tissue was also measured. For treatments giving similar levels of tumour regrowth delay, the regrowth of irradiated tumours was markedly slower than that of untreated tumours, whilst the regrowth rate of tumours subjected to hyperthermia did not differ from that of untreated tumours. The growth rate of untreated tumours implanted in pre-irradiated skin was also slower than that of control tumours, though the growth-rate reduction was less dramatic than for regrowth following tumour irradiation in situ. Tumours implanted in pre-heated skin grew at the same rate as control tumours. Slower regrowth in situ after X-rays than after hyperthermia would produce a larger growth delay for X-rays than for hyperthermia, for equal levels of tumour-cell kill or probability of tumour sterilization. This effect could lead to a systematic underestimation of the efficacy of hyperthermia relative to X-rays, when efficacy is assessed by growth delay.

Differences in vascular pattern between the spontaneous and the transplanted C3H mouse mammary carcinoma

The transplanted C3H tumor differs from the spontaneous in its multi-focal origin and in its increasing loss of differentiation. Loss of differentiation is principally important in that even the partial branching into lobes, which occurs in the spontaneous tumour, is lost and that the parenchyma no longer consists of single-layered and multi-layered tubules, as in the spontaneous tumour, but of multi-layered only. Absence of branching removes the interlobular pressures, which in spontaneous tumours lead to infarction of the efferent vessels and sinus formation. Consequently; sinuses are absent from the transplanted tumour and the circulation is thereby improved. In contrast, since the vascular pattern of the spontaneous tumour is preserved and capillaries do not penetrate into the multi-layered tubules, although these have developed into solid cylinders, the diffusion pathway of oxygen is extended, resulting in necrosis at their cores. Accumulating necrotic fluid is at first removed by lymphatics, but subsequently invades the efferent vascular system. These changes are reflected in the pattern of tumour growth and in the radiation responses.