Direct measurement of reoxygenation in malignant mammary tumors after a single large dose of irradiation

First-In-Human Study in Cancer Patients Establishing the Feasibility of Oxygen Measurements in Tumors Using Electron Paramagnetic Resonance With the OxyChip

OBJECTIVE

The overall objective of this clinical study was to validate an implantable oxygen sensor, called the 'OxyChip', as a clinically feasible technology that would allow individualized tumor-oxygen assessments in cancer patients prior to and during hypoxia-modification interventions such as hyperoxygen breathing.

METHODS

Patients with any solid tumor at ≤3-cm depth from the skin-surface scheduled to undergo surgical resection (with or without neoadjuvant therapy) were considered eligible for the study. The OxyChip was implanted in the tumor and subsequently removed during standard-of-care surgery. Partial pressure of oxygen (pO2) at the implant location was assessed using electron paramagnetic resonance (EPR) oximetry.

RESULTS

Twenty-three cancer patients underwent OxyChip implantation in their tumors. Six patients received neoadjuvant therapy while the OxyChip was implanted. Median implant duration was 30 days (range 4-128 days). Forty-five successful oxygen measurements were made in 15 patients. Baseline pO2 values were variable with overall median 15.7 mmHg (range 0.6-73.1 mmHg); 33% of the values were below 10 mmHg. After hyperoxygenation, the overall median pO2 was 31.8 mmHg (range 1.5-144.6 mmHg). In 83% of the measurements, there was a statistically significant (p ≤ 0.05) response to hyperoxygenation.

CONCLUSIONS

Measurement of baseline pO2 and response to hyperoxygenation using EPR oximetry with the OxyChip is clinically feasible in a variety of tumor types. Tumor oxygen at baseline differed significantly among patients. Although most tumors responded to a hyperoxygenation intervention, some were non-responders. These data demonstrated the need for individualized assessment of tumor oxygenation in the context of planned hyperoxygenation interventions to optimize clinical outcomes.

Assessment of the changes in 9L and C6 glioma pO2 by EPR oximetry as a prognostic indicator of differential response to radiotherapy

Tumor hypoxia impedes the outcome of radiotherapy. As the extent of hypoxia in solid tumors varies during the course of radiotherapy, methods that can provide repeated assessment of tumor pO2 such as EPR oximetry may enhance the efficacy of radiotherapy by scheduling irradiations when the tumors are oxygenated. The repeated measurements of tumor pO2 may also identify responders, and thereby facilitate the design of better treatment plans for nonresponding tumors. We have investigated the temporal changes in the ectopic 9L and C6 glioma pO2 irradiated with single radiation doses less than 10 Gy by EPR oximetry. The 9L and C6 tumors were hypoxic with pO2 of approximately 5-9 mmHg. The pO2 of C6 tumors increased significantly with irradiation of 4.8-9.3 Gy. However, no change in the 9L tumor pO2 was observed. The irradiation of the oxygenated C6 tumors with a second dose of 4.8 Gy resulted in a significant delay in growth compared to hypoxic and 2 Gy × 5 treatment groups. The C6 tumors with an increase in pO2 of greater than 50% from the baseline of irradiation with 4.8 Gy (responders) had a significant tumor growth delay compared to nonresponders. These results indicate that the ectopic 9L and C6 tumors responded differently to radiotherapy. We propose that the repeated measurement of the oxygen levels in the tumors during radiotherapy can be used to identify responders and to design tumor oxygen guided treatment plans to improve the outcome.

Tumor oxygenation: an appraisal of past and present concepts and a look into the future : Arisztid G. B. Kovách Lecture

Since 1970, the multifactorial pathogenesis of the deficient and heterogeneous oxygenation of transplanted murine tumors and of human cancers (including parameters determining oxygen delivery, e.g., blood flow, diffusion geometry, oxygen transport capacity of the blood) has been investigated in vivo. Hypoxia and/or anoxia was quantitatively assessed and characterized using microtechniques and special preclinical tumor models. Hypoxia subtypes were identified, and critical supply conditions were theoretically analyzed. In the 1980s, first experiments on humans were carried out in cancers of the rectum and of the oral cavity. In the 1990s, the clinical investigations were carried out on cancers of the breast and of the uterine cervix, clearly showing that hypoxia is a hallmark of locally advanced human tumors. In multivariate analysis, hypoxia was found to be an independent, adverse prognostic factor for patient survival due to hypoxia-driven malignant progression and hypoxia-associated resistance to anticancer therapy.

Radiation-induced changes in microcirculation and interstitial fluid pressure affecting the delivery of macromolecules and nanotherapeutics to tumors

The immature, chaotic microvasculature of most solid tumors can present a significant impediment to blood-borne delivery, uneven distribution, and compromised penetration of macromolecular anticancer drugs and diagnostic agents from tumor microvessels across the interstitial space to cancer cells. To reach viable tumor cells in relevant concentrations, macromolecular agents are confronted with several barriers to vascular, transvascular, and interstitial transport. Amongst those (1) heterogeneous and poor blood supply, (2) distinctly reduced or even abolished hydrostatic and oncotic pressure gradients across the microvessel wall abrogating the convective transport from the vessel lumen into the interstitial space (impairment of transvascular transport), and (3) impediment of convective transport within the interstitial compartment due to elevated interstitial fluid pressure (IFP) (resulting from hyperpermeable blood vessels coupled with non-functional lymphatics) and a dense structure of the interstitial matrix are the major mechanisms hindering drug delivery. Upon irradiation, changes in these barrier functions are inconclusive so far. Alterations in vascular transport properties following fractionated radiation up to 40 Gy are quite inconsistent in terms of direction, extent, and time course. Total doses above 45 Gy can damage tumor microvessels, additionally impeding vascular delivery. Vascular permeability for macromolecules might be enhanced up to a total dose of 45 Gy. However, this effect is counteracted/abolished by the elevated IFP in solid tumors. When assessing IFP during fractionated radiotherapy in patient tumors, inconsistent alterations have been observed, both in direction and extent. From these data it is concluded that modulations in vascular, transvascular, and interstitial transport by irradiation of solid tumors are rather unclear so far. Translation of experimental data into the clinical setting thus needs to be undertaken with especial care.

Radiation-induced vascular damage in tumors: implications of vascular damage in ablative hypofractionated radiotherapy (SBRT and SRS)

We have reviewed the studies on radiation-induced vascular changes in human and experimental tumors reported in the last several decades. Although the reported results are inconsistent, they can be generalized as follows. In the human tumors treated with conventional fractionated radiotherapy, the morphological and functional status of the vasculature is preserved, if not improved, during the early part of a treatment course and then decreases toward the end of treatment. Irradiation of human tumor xenografts or rodent tumors with 5-10 Gy in a single dose causes relatively mild vascular damages, but increasing the radiation dose to higher than 10 Gy/fraction induces severe vascular damage resulting in reduced blood perfusion. Little is known about the vascular changes in human tumors treated with high-dose hypofractionated radiation such as stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS). However, the results for experimental tumors strongly indicate that SBRT or SRS of human tumors with doses higher than about 10 Gy/fraction is likely to induce considerable vascular damages and thereby damages the intratumor microenvironment, leading to indirect tumor cell death. Vascular damage may play an important role in the response of human tumors to high-dose hypofractionated SBRT or SRS.

Repeated tumor pO(2) measurements by multi-site EPR oximetry as a prognostic marker for enhanced therapeutic efficacy of fractionated radiotherapy

PURPOSE

To investigate the temporal effects of single or fractionated radiotherapy on subcutaneous RIF-1 tumor pO(2) and to determine the therapeutic outcomes when the timing of fractionations is guided by tumor pO(2).

METHODS

The time-course of the tumor pO(2) changes was followed by multi-site electron paramagnetic resonance (EPR) oximetry. The tumors were treated with single 10, 20, and 10 Gy x 2 doses, and the tumor pO(2) was measured repeatedly for six consecutive days. In the 10 Gy x 2 group, the second dose of 10 Gy was delivered at a time when the tumors were either relatively oxygenated or hypoxic. The changes in tumor volumes were followed for nine days to determine the therapeutic outcomes.

RESULTS

A significant increase in tumor pO(2) was observed at 24h post 10 Gy, while 20 Gy resulted in a significant increase in tumor pO(2) at 72-120 h post irradiation. The tumors irradiated with a second dose of 10 Gy at 24h, when the tumors were oxygenated, had a significant increase in tumor doubling times (DTs), as compared to tumors treated at 48 h when they were hypoxic (p<0.01).

CONCLUSION

Results indicate that the time of tumor oxygenation depends on the irradiation doses, and radiotherapeutic efficacy could be optimized if irradiations are scheduled at times of increased tumor oxygenation. In vivo multi-site EPR oximetry could be potentially used to monitor tumor pO(2) repeatedly during fractionated schemes to optimize radiotherapeutic outcome. This technique could also be used to identify responsive and non-responsive tumors, which will facilitate the design of other therapeutic approaches for non-responsive tumors at early time points during the course of therapy.

Changes in the tumor microenvironment during low-dose-rate permanent seed implantation iodine-125 brachytherapy

PURPOSE

There is a lack of data regarding how the tumor microenvironment (e.g., perfusion and oxygen partial pressure [pO2]) changes in response to low-dose-rate (LDR) brachytherapy. This may be why some clinical issues remain unresolved, such as the appropriate use of adjuvant external beam radiation therapy (EBRT). The purpose of this work was to obtain some basic preclinical data on how the tumor microenvironment evolves in response to LDR brachytherapy.

METHODS AND MATERIALS

In an experimental mouse tumor, pO2 (measured by electron paramagnetic resonance) and perfusion (measured by dynamic contrast-enhanced magnetic resonance imaging) were monitored as a function of time (0-6 days) and distance (0-2 mm and 2-4 mm) from an implanted 0.5 mCi iodine-125 brachytherapy seed.

RESULTS

For most of the experiments, including controls, tumors remained hypoxic at all times. At distances of 2-4 mm from radioactive seeds ( approximately 1.5 Gy/day), however, there was an early, significant increase in pO2 within 24 h. The pO2 in that region remained elevated through Day 3. Additionally, the perfusion in that region was significantly higher than for controls starting at Day 3.

CONCLUSION

It may be advantageous to give adjuvant EBRT shortly (approximately 1 to 2 days) after commencement of clinical LDR brachytherapy, when the pO2 in the spatial regions between seeds should be elevated. If chemotherapy is given adjuvantly, it may best be administered just a little later (approximately 3 or 4 days) after the start of LDR brachytherapy, when perfusion should be elevated.

Early reoxygenation in tumors after irradiation: determining factors and consequences for radiotherapy regimens using daily multiple fractions

PURPOSE

To characterize changes in the tumor microenvironment early after irradiation and determine the factors responsible for early reoxygenation.

METHODS AND MATERIALS

Fibrosarcoma type II (FSaII) and hepatocarcinoma transplantable liver tumor tumor oxygenation were determined using electron paramagnetic resonance oximetry and a fiberoptic device. Perfusion was assessed by laser Doppler, dynamic contrast-enhanced MRI, and dye penetration. Oxygen consumption was determined by electron paramagnetic resonance. The interstitial fluid pressure was evaluated by the wick-in-needle technique.

RESULTS

An increase in oxygen partial pressure was observed 3-4 h after irradiation. This increase resulted from a decrease in global oxygen consumption and an increase in oxygen delivery. The increase in oxygen delivery was due to radiation-induced acute inflammation (that was partially inhibited by the antiinflammatory agent diclofenac) and to a decrease in interstitial fluid pressure. The endothelial nitric oxide synthase pathway, identified as a contributing factor at 24 h after irradiation, did not play a role in the early stage after irradiation. We also observed that splitting a treatment of 18 Gy into two fractions separated by 4 h (time of maximal reoxygenation) had a greater effect on tumor regrowth delay than when applied as a single dose.

CONCLUSION

Although the cell cycle redistribution effect is important for treatment protocols using multiple daily radiation fractions, the results of this work emphasize that the oxygen effect must be also considered to optimize the treatment strategy.

Differences in pO2 peaks of a murine fibrosarcoma between carbon-ion and X-ray irradiation

We measured and compared the oxygen partial pressure (pO(2)) profiles in experimental tumors after irradiation with carbon ions and with X-rays. The NFSa fibrosarcomas grown in the hind legs of C3H male mice received isoeffect single doses of carbon ions or X-rays. Coaxial oxygen microelectrodes of high spatial resolution were inserted into the tumor with 20 microm steps by a computerized micromanipulator. The number of pO(2) peaks that reached 15 mmHg were at least 0.45 per 3,000 microm in unirradiated tumors and significantly increased to 1.55 per 3,000 microm as early as day 1 of carbon-ion irradiation (p < 0.001). The tumors that received X-ray irradiation also significantly increased pO(2) peaks, but as late as day 3. The time course of pO(2) peak appearance in the present study coincides with a previous report where reoxygenation was measured by paired growth delay assay. The pO(2) peaks appeared selectively in peripheral regions of X-ray irradiated tumors, but they appeared rather homogeneously in the tumor after carbon-ion irradiation. It is concluded that carbon-ion irradiation reoxygenated the NFSa fibrosarcomas earlier in time and deeper in space than the X-ray irradiation did.

Preservation of tumour oxygen after hyperbaric oxygenation monitored by magnetic resonance imaging

Hyperbaric oxygen (HBO) has been proposed to reduce tumour hypoxia by increasing the dissolved molecular oxygen in tissue. Using a non-invasive magnetic resonance imaging (MRI) technique, we monitored the changes in MRI signal intensity after HBO exposure because dissolved paramagnetic molecular oxygen itself shortens the T1 relation time. SCCVII tumour cells transplanted in mice were used. The molecular oxygen-enhanced MR images were acquired using an inversion recovery-preparation fast low angle shot (IR-FLASH) sequence sensitizing the paramagnetic effects of molecular oxygen using a 4.7 tesla MR system. MR signal of muscles decreased rapidly and returned to the control level within 40 min after decompression, whereas that of tumours decreased gradually and remained at a high level 60 min after HBO exposure. In contrast, the signal from the tumours in the normobaric oxygen group showed no significant change. Our data suggested that MR signal changes of tumours and muscles represent an alternation of extravascular oxygenation. The preserving tumour oxygen concentration after HBO exposure may be important regarding adjuvant therapy for cancer patients.

Oxygen tension in transplanted mouse osteosarcomas during fractionated high-LET- and low-LET radiotherapy--predictive aspects for choosing beam quality?

PURPOSE

The lower OER of high-LET radiations, compared to conventional (low-LET) radiations, has often been put forward as an argument for using high-LET radiotherapy in the management of hypoxic tumours. Among the different neutron beams used in therapy, the reactor fission neutrons have the lowest OER. The aim of the present study is to follow the variations of tumour oxygenation status during fractionated irradiation with different radiation qualities. Little information is available so far after fractionated high-LET irradiation. In addition, the RBE of reactor fission neutrons for effects on tumours and on normal tissues are compared.

MATERIAL AND METHODS

Murine OTS 64-osteosarcomas were transplanted in 102 balb-C mice and irradiated by 36 Gy of photons in fractions of 3 Gy five times a week (group P-36/3) or by 12 Gy of reactor fission neutrons in fractions of 2 Gy two times a week (group N-12/2). Irradiations started at a tumor volume of 500 to 600 mm3. A third group received no radiotherapy, but all investigations (group CG). Tumor volume and tumor oxygenation were measured once a week under therapy and during three weeks after therapy. For in vivo-evaluation of oxygen status a computerized polarographic needle electrode system (KIMOC pO2 histograph, Eppendorf) was used. The median pO2 and the hypoxic fraction (pO2 values < 5 mm Hg) of single tumors and of total groups were calculated from pooled histograms and from row data as well.

RESULTS

In correlation with the increase of tumor volume, from day 1 to day 42 of follow-up the median pO2 decreased from 20 mm to 8 mm Hg and the hypoxic fraction increased from 7% to 31%. After fractionated photon therapy a growth delay of three weeks was observed. Six weeks after beginning of the irradiation the median tumor volume had been doubled again. After fission neutron therapy growth delay continued until the end of the follow-up period. In both of the irradiated groups a significant decrease of median pO2 values and an increase of the hypoxic fraction were observed under radiotherapy. Hypoxia was more intensive after neutrons with a decrease of the median pO2 from 20 mm Hg to 1 mm Hg vs. 10 mm Hg after photon therapy and with an increase of the hypoxic fraction from 7% to 78% vs. 36% respectively. Two weeks after the end of therapy the median pO2 and the hypoxic fraction of both treated groups reached the levels prior to irradiation indicating a complete reoxygenation.

CONCLUSION

During fractionated irradiation of murine osteosarcomas with photons and reactor fission neutrons, a marked hypoxia was observed for both radiation qualities, but hypoxia was more intense during fractionated neutron irradiation. After irradiation, a complete reoxygenation occurred in both groups independently of the degree of hypoxia observed during the treatment. The RBE of reactor fission neutrons, after fractionated irradiation, was much higher for effects on murine osteosarcomas compared to their RBE observed for normal tissues in previous experiments. Present data are in agreement with our clinical observations on more than 300 patients treated with reactor fission neutrons for advanced and hypoxic tumours with various histologies.

Combined castration and fractionated radiotherapy in an experimental prostatic adenocarcinoma

PURPOSE

The present study using the Dunning R3327-PAP rat prostatic adenocarcinoma model was designed to study the effect on tumor growth of castration prior to or after irradiation with 20-25 Gy as compared with either irradiation or castration alone.

METHODS AND MATERIALS

Rats were bilaterally orchidectomized. During the irradiation procedure the nonanesthetized animals were held in a metallic frame with a strong cotton net and they were observed by means of a video camera. The suboptimal irradiation dose was given once daily with a 4-MeV linear accelerator, 4-5 Gy/fraction, during 5 consecutive days. Tumor volumes and rat weights were followed. At the end point of the study the animals were sacrificed and the tumors were morphometrically analyzed.

RESULTS

The combination of irradiation and castration delayed tumor regrowth better than irradiation alone with the same suboptimal dose. Castration before irradiation delayed tumor regrowth more efficiently than castration after irradiation. However, castration alone delayed tumor regrowth even more effectively than suboptimal irradiation doses combined with castration.

CONCLUSIONS

In combination with suboptimal irradiation neoadjuvant androgen deprivation was more inhibitory to rat prostatic adenocarcinoma regrowth than adjuvant androgen deprivation. Irradiation with suboptimal doses combined with castration may cause an earlier relapse to androgen-independent tumor growth than castration alone.

Tumor oxygenation in a transplanted rat rhabdomyosarcoma during fractionated irradiation

PURPOSE

To quantify the changes in tumor oxygenation in the course of a fractionated radiation treatment extending over 4 weeks.

METHODS AND MATERIALS

Rhabdomyosarcomas R1H of the rat were irradiated with 60Co-gamma-rays with a total dose of 60 Gy, given in 20 fractions over 4 weeks. Oxygen partial pressure (pO2) in tumors was measured at weekly intervals using polarographic needle probes in combination with a microprocessor-controlled device (pO2-Histograph/KIMOC). The pO2 measurements were carried out in anesthetized animals under mechanical ventilation and in respiratory and hemodynamic steady state. Tumor pO2 values were correlated to the arterial oxygen pressure paO2, arterial pCO2, and pH determined with a blood gas analyzer.

RESULTS

Tumor oxygenation did not change significantly during the 3 weeks of irradiation (up to 45 Gy), from a median pO2 of 23 +/- 2 mmHg in untreated controls to 19 +/- 4 mmHg after the third week. The decrease of the number of pO2 values between 0 and 5 mmHg indicated that an improved oxygenation in the tumors occurred. However, with increasing radiation dose (fourth week, 60 Gy) a significant decrease in tumor oxygenation to a median pO2 of 8 +/- 2 mmHg and a rapid increase in the frequency of pO2 values (35 +/- 4%) between 0 and 5 mmHg was found.

CONCLUSION

Improved oxygenation in rhabdomyosarcomas R1H was only present in the early phase of the fractionated irradiation. Radiation does above 45 Gy led to a considerable decrease of tumor oxygenation in the later phase of irradiation.

PO2 in irradiated versus nonirradiated tumors of mice breathing oxygen at normal and elevated pressure

PURPOSE

To determine if prior tumor irradiation influences tumor pO2 changes in mice breathing oxygen (100%) at normal and elevated pressure.

METHODS AND MATERIALS

Single-point pO2 measurements were performed in nonirradiated and previously irradiated (72 h) isotransplanted MCaIV tumors in C3H/Sed mice. Continuous recordings were performed at the same tumor locus under air breathing, followed by 100% oxygen and oxygen at three atmospheres pressure. Following decompression and induction of pentobarbital anesthesia, the procedure was repeated at the same locus. Six nonirradiated and five irradiated tumors were evaluated under the three gas breathing conditions +/- anesthesia.

RESULTS

The mean, median, and range of pO2 values did not differ under air-breathing conditions in the nonirradiated vs. previously irradiated tumors. However, prior irradiation substantially enhanced the tumor pO2 increase when the inspired gas phase was switched from air to 100% oxygen at 1 or 3 atmospheres pressure. In four of six nonirradiated tumors, 100% oxygen breathing resulted in a pO2 increase of < 4 mmHg; in the irradiated tumors, the minimum increase was 16 mmHg. Pentobarbital anesthesia did not significantly influence the results obtained.

CONCLUSION

These data indicate that the efficacy of oxygen breathing increases during tumor treatment, and suggests that oxygen breathing is a simple nontoxic method for reducing or eliminating radiobiologic hypoxia during therapy.

Heterogeneity in tumor microvascular response to radiation

Viable hypoxic cells have reduced radiosensitivity and could be a potential cause for treatment failure with radiotherapy. The process of reoxygenation, which may occur after radiation exposure, could increase the probability for control. However, incomplete or insufficient reoxygenation may still be a potential cause for local treatment failure. One mechanism that has been thought to be responsible for reoxygenation is an increase in vascular prominence after radiation. However, the effect is known to be heterogeneous. In this study, tumor microvascular hemodynamics and morphologies were studied using the R3230 Ac mammary adenocarcinoma transplanted in a dorsal flap window chamber of the Fischer-344 rat. Measurements were made before and after (at 24 and 72 hr) 5-Gy radiation exposure to assess microvascular changes and to explore possible explanations for the heterogeneity of the effect. There was considerable heterogeneity between tumors prior to radiation. Vascular densities ranged from 67 to 3000 vessels/mm3 and median vessel diameters from 22 to 85 microns. Pretreatment perfusion values varied by a factor of six. In irradiated tumors, conjoint increases in both vascular density and perfusion occurred in most tumors, although the degree of change was variable from one individual to the next. The degree of change in density was inversely related to median pretreatment diameter. Relative change in flow, as predicted by morphometric measurements, overestimated observed changes in flow measured hemodynamically. These results support that heterogeneity in tumor vascular effects from radiation are somewhat dependent on pretreatment morphology as well as relative change in morphology. Since changes in flow could not be completely explained by morphometric measurements, however, it is likely that radiation induced changes in pressure and/or viscosity contribute to the overall effect. Further work in this laboratory will investigate these hypotheses.

Phosphorus-31 magnetic resonance spectroscopy and blood perfusion of the RIF-1 tumor following X-irradiation

Phosphorus-31 magnetic resonance spectra were obtained from the RIF-1 tumor in C3H mice before and up to 2 days after various doses of X rays. Parallel studies were performed to measure relative changes in tumor blood perfusion using [14C]iodo-antipyrine and changes in % tumor necrosis using Chalkley's method. Tumor ratios of phosphocreatine to inorganic phosphate (PCr/Pi) and nucleotide triphosphates to inorganic phosphate (NTP/Pi) as well as pH as measured by 31P-MRS increased significantly at most time points after irradiation with doses of 5, 10, and 20 Gy. Tumor blood perfusion was found to significantly improve after a dose of 20 Gy but not after a dose of 2 Gy. Percent tumor necrosis increased to about 3 times its control level at 1 day after a dose of 20 Gy and then declined to about twice its control value at 2 days. The magnitude of the changes in the 31P-MRS parameters makes it unlikely that any of them are entirely due to radiation-induced changes in the radiobiologically hypoxic fraction of these tumors. Changes in the necrotic fraction did not appear to influence the tumor spectra. However, the observed improvement in tumor blood perfusion may have resulted in an increase in oxidative phosphorylation of the whole tumor population as well as a clearance of inorganic phosphate and acid metabolites, so that 31P-MRS changes may indirectly reflect changes in tumor blood perfusion.