Doxorubicin chemomyectomy in orbicularis oculi: increasing drug infiltration at the injection site

Chemotherapy-induced weakness and fatigue in skeletal muscle: the role of oxidative stress

SIGNIFICANCE

Fatigue is one of the most common symptoms of cancer and its treatment, manifested in the clinic through weakness and exercise intolerance. These side effects not only compromise patient's quality of life (QOL), but also diminish physical activity, resulting in limited treatment and increased morbidity.

RECENT ADVANCES

Oxidative stress, mediated by cancer or chemotherapeutic agents, is an underlying mechanism of the drug-induced toxicity. Nontargeted tissues, such as striated muscle, are severely affected by oxidative stress during chemotherapy, leading to toxicity and dysfunction.

CRITICAL ISSUES

These findings highlight the importance of investigating clinically applicable interventions to alleviate the debilitating side effects. This article discusses the clinically available chemotherapy drugs that cause fatigue and oxidative stress in cancer patients, with an in-depth focus on the anthracycline doxorubicin. Doxorubicin, an effective anticancer drug, is a primary example of how chemotherapeutic agents disrupt striated muscle function through oxidative stress.

FUTURE DIRECTIONS

Further research investigating antioxidants could provide relief for cancer patients from debilitating muscle weakness, leading to improved quality of life.

Myotoxic effects of the skeletal muscle-specific immunotoxin, ricin-mAb35, on orbicularis oculi muscle after eyelid injections in rabbits

PURPOSE

The authors recently demonstrated that a single injection of the immunotoxin ricin-mAb35 has potent and long-lasting myotoxic effects in extraocular muscles. The myotoxicity of injected ricin-mAb35 was tested in the eyelids of rabbits to determine its potential for use in the treatment of benign essential blepharospasm and other dystonias.

METHODS

The immunotoxin ricin-mAb35 was injected in one eyelid of adult rabbits. After 1 week, 1 month, or 6 months, the rabbits were euthanized, and the eyelids were prepared for histologic examination of inflammatory cell infiltrate with immunohistochemical localization of cd11b and myosin heavy chain isoform expression. Muscle loss was quantified by analysis of muscle fiber cross-sectional area and total myofiber number.

RESULTS

Within the first week after a single injection of ricin-mAb35, some edema developed, which resolved by the second week. Otherwise, the eyelids were normal in appearance. A short-lived inflammatory response was seen at 1 week, but this resolved 1 month after treatment. One week after injection, there was a significant decrease in the total number of orbicularis oculi myofibers in the ricin-mAb35-treated eyelids. This myofiber loss remained significant 1 month later and was maintained 6 months after the initial injection.

CONCLUSIONS

Direct injection of the immunotoxin ricin-mAb35 resulted in significant, acute muscle loss in the orbicularis oculi of rabbits that was maintained for up to 6 months. Physiologic studies are needed to demonstrate concomitant loss of muscle strength, but these results suggest that ricin-mAb35 injection holds promise as a muscle-weakening agent in the eyelid.

Selective lesions of rabbit extraocular muscles injected with the anti-AChR immunotoxin saporin-mAb 73

PURPOSE

To evaluate the effects on extraocular muscles of a skeletal muscle-specific immunotoxin, saporin-mAb 73, as an alternative to botulinum toxin to induce a permanent correction of oculo-facial dystonias or some forms of ocular motility disorders.

METHODS

An immunotoxin was prepared with a monoclonal antibody (mAb 73) against acetylcholine receptors of skeletal muscle, linked to saporin, a type 1 ribosome-inactivating protein (RIP) from Saponaria officinalis. Sixteen New Zealand white rabbits were treated with a single injection of immunotoxin directly into the medial rectus muscle of one eye. Four different dosages of 2, 5, 20, or 50 ng saporin-mAb 73 were used. The rabbits were sacrificed at two, 7 and 14 days post-injection. The medial rectus muscle and the retractor bulbi muscle of both the injected and the fellow eyes were taken and serial sections were examined by light microscopy in a blinded manner.

RESULTS

Saporin-mAb 73, even at the dosage of 2 ng, brought about focal damage in the extraocular muscles of rabbits without histological changes in adjacent muscles. The histological examination revealed necrotic/apoptotic lesions restricted to the sites of inoculation and largely infiltrated by macrophages. No evident inflammatory reaction was detected at any time and neutrophils were substantially absent. At 14 days after injection, necrosis/apoptosis was still evident and the sclerotic reaction was minimal.

CONCLUSIONS

The immunotoxin saporin-mAb 73 injections into the extraocular muscles of rabbits caused focal damage to the muscles. There was no significant inflammatory reaction and muscle fiber loss was present even at the lower doses. Although the lesions were followed for only 14 days, our results suggest that saporin-mAb 73 has potential to cause safe focal muscle damage but longer-term follow-up are needed to investigate the persistence of muscle weakness.