Ph Hernigou (Créteil)
The parenteral administration of antimitotic drugs is widely used for primary bone tumours such as osteosarcoma and sometimes for secondary tumours. But even parenteral chemotherapy and wide surgical excision does not always prevent local recurrence or metastasis from bone sarcomas. For these reasons, it is now recommended that chemotherapy starts pre-operatively and is continued as soon as possible postoperatively.
Since cement is often used to fill bony defects or to implant replacement arthroplasties it was thought that the efficacy of treatment might be increased by local chemotherapy from an antimitotic drug added to the acrylic cement. Diffusion into the surrounding tissues is well established for numerous antibiotics.
We performed a number of experiments to assess acrylic cement as a vehicle for local chemotherapy:
1) Diffusion ofantimitotic drugs from acrylic cement was studied in vitro to determine that these drugs were released and were still biologically active after exposure to highly reactive monomer and the exothermic curing reaction.
2) Experiments in vivo were performed on two groups of animals. We tested the effect of such local chemotherapy on experimental osteosarcoma of the rat and on dogs with spontaneous osteosarcoma. General and local tolerance of the antimitotic-loaded cement was assessed. Finally, we report our preliminary clinical investigations with pharmacological data from patients.
In vitro experiments
These experiments were designed to measure the elution of the antimitotic drug from cement in vitro.
I . Kinetics of elution. Small methylpolymethacrylate implants containing MTX were made from the cement. For each, 200 mg of MTX were mixed with 4 g of polymer powder containing benzoyl peroxide and 2 ml of monomer was added. The mixture was poured into moulds before polymerisation giving casts 8.5 mm by 7.5 mm diameter. Each cast weighed 357 mg and had an
MTX content of3.9 mg±0.l%.
The implants were then suspended in one litre of phosphate buffer (pH 7.4, 37#176Cco) ntained in a covered, round-bottomed flask. This medium was stirred at 70 turns per minute and 1.5 ml aliquots were periodically removed and analysed for MTX content using a plasma emission spectrophotometer (Perkin Elmer, 560, Bois d’Arcy, France). The medium was maintained at a constant volume by adding to the flask the volume of antidote (citrovorum rescue) for adverse effects
In vitro experiments
These experiments were designed to measure the elution of the antimitotic drug from cement in vitro.
I . Kinetics of elution. Small methylpolymethacrylate implants containing MTX were made from the cement. For each, 200 mg of MTX were mixed with 4 g of polymer powder containing benzoyl peroxide and 2 ml of monomer was added. The mixture was poured into moulds before polymerisation giving casts 8.5 mm by 7.5 mm diameter. Each cast weighed 357 mg and had an MTX content of3.9 mg±0.l%. The implants were then suspended in one litre of phosphate buffer (pH 7.4, 37#176Cco) ntained in a covered, round-bottomed flask.
2. Longer-term liberation of methotrexate. To investigate the release of MTX from a block of acrylic cement implanted into the tissues, cubic test pieces were placed in 32 ml ofphysiological saline, which was changed every day. The concentration of MTX in the elution fluid was
measured before each change.
3. Relationship between the quantity ofantimitotic drug and the level of release. As in experiment 2, cubic 13 g specimens were prepared, but containing 20 mg and 40 mg of MTX. These had surface areas and weights equal to those of that experiment ; elution was evaluated daily for 1 5 days.
4. To assess the effect of polymerisation of the cement. Diffusion of antimitotic drug from pellets of plaster was studied and compared with that from cement. The plaster pellets were prepared from a mixture of 1 5 g of plaster, 1 g of MTX and 400 ml of water, ground in a mortar and sieved before 4 g dicalcium phosphate and 0.2 g magnesium stearate were added
5. Stability of MTX during polymerisation of the cement. Solutions of methotrexate extracted from cement and plaster were compared with control specimens by analysis using high pressure liquid chromatography (column Nova Parck, water Milford, Massachusetts, USA).
In vivo experiments
Experimental osteosarcoma in rats. The cytostatic activity of the eluted MTX was assessed against an experimental osteosarcoma , induced in the rat by injection of colloidal radioactive Cerium hydroxide (‘44Ce).
After operation, the animals were checked daily, and weighed, and the size of the tumour was measured in two perpendicular directions using calipers. The control animals were studied until they died or became moribund. The animals with active implants were followed as long as possible, except that 20 rats were killed between days 10 and 30 for histological study of the early action of the drug.
Spontaneous osteosarcoma in dogs. Experiments were conducted to establish the plasma diffusion of MTX, its general tolerance and the local action ofcement containing antimitotic drug in conditions similar to those of the management of human malignant bone tumours. We therefore chose an animal with a weight close to that of man, and a spontaneous tumour with an evolution like that of human osteosarcoma, similarly hypervascular because this may influence the diffusion of MTX. In experiments at the National Veterinary School of Maisons-Alfort, we used dogs with spontaneous osteosarcoma. This is a malignant tumour with the same aggressive properties as the human type. The total quantity of MTX received by each dog was about 100 mg in 14, 200 mg in two cases and 500 mg in one. Since the weight of the dogs varied from 30 to 80 kg, the dose per dog ranged from 1 .6 mg to 16 mg/kg.
We were able to confirm the high local concentration of MTX in vacuum drainage (10 000 times the blood concentration), the general chemotherapeutic effect during the first few days and the urinary excretion of MTX for at least 3 weeks (Fig. 10). The release and diffusion of MTX from cement was about the same (Fig. 11) whatever the site or the shape of the cement implant (4 in the pelvis, 5 in metastatic fractures of the intertrochanteric region, 3 for metastases of the thoracic spine).
Local chemotherapy was well tolerated, no patient showed general toxicity, MTX-related anaemia, depressed white cell or platelet counts and there was no change in creatinine clearance. There were wound healing problems in two patients with tumours of the pelvis ; one patient needed removal of the cement block. The clinical application of antimitotic-impregnated acrylic cement constitutes the use of an approved drug for unapproved indications. The use of such local chemotherapy in preventing local recurrence or as adjuvant therapy has not previously been reported and 0.01 administered in a continuous manner by diffusion from cement, with conventional chemotherapy given sequentially by an intravenous route.
Simple local administration of MTX seems to reduce the risk oflocal recurrence in the dog. The results appear to be significant although each tumour was spontaneous and therefore different and, for understandable reasons, there were no true controls. This result in dogs may be related to the very high local concentrations of the drug, which were observed in the vacuum drainage from the human patients. Such concentrations cannot be obtained by parenteral administration without general toxic effects.
Our experiments show that, as for antibiotics, MTX can be released from cement, and that the released MTX is still biologically active. This is proven by the general toxic effects leading to death in some rats and dogs, and the local effect on experimental osteosarcoma in the rat.
It was surprising to discover the mortality produced by the local administration of 200 mg of MTX in dogs weighing under 50 kg, in relation to the known effect of conventional sequential chemotherapy in man. However, it is difficult to compare the effects of a single dose is important. Experimental studies have shown that chemotherapy impairs wound healing, but this has not been significant in clinical trials. Our local chemotherapy caused no such problems in the rat model but skin necrosis was seen four times in 17 dogs and twice in the clinical trials on 14 patients. It is not possible to be certain if these delays in healing were directly related to a local reaction to MTX or to the extensive nature of the operations performed, but they may well be related to side effects of MTX. The systemic blood concentration only two hours after cement implantation gives an early general level ofchemotherapy ; this may be an advantage in treating primary bone tumours since there is good reason to suspect that micrometastases begin to grow
faster immediately after the primary focus has been eliminated.
We conclude that it is possible to use acrylic cement as a supporting vehicle for the diffusion of MTX for local chemotherapy. Peroperative regional chemotherapy has previously been limited to an anatomical region using intra-arterial perfusion, perfusion after tourniquet, or extra-corporeal circulation. Although these methods have given encouraging results, they have complications which can be serious enough to require amputation. If further studies confirm our initial results, the method of local chemotherapy we have described could complement other therapeutic measures for the treatment of bone tumours.