Growth hormone receptor antagonists therapy for acromegaly

Treatment of pituitary gigantism with the growth hormone receptor antagonist pegvisomant

CONTEXT

Treatment of pituitary gigantism is complex and the results are usually unsatisfactory.

OBJECTIVE

The objective of the study was to describe the results of therapy of three children with pituitary gigantism by a GH receptor antagonist, pegvisomant.

DESIGN

This was a descriptive case series of up to 3.5 yr duration.

SETTING

The study was conducted at a university hospital.

PATIENTS

Patients included three children (one female, two males) with pituitary gigantism whose GH hypersecretion was incompletely controlled by surgery, somatostatin analog, and dopamine agonist.

INTERVENTION

The intervention was administration of pegvisomant.

MAIN OUTCOME MEASURES

Plasma IGF-I and growth velocity were measured.

RESULTS

In all three children, pegvisomant rapidly decreased plasma IGF-I concentrations. Growth velocity declined to subnormal or normal values. Statural growth fell into lower growth percentiles and acromegalic features resolved. Pituitary tumor size did not change in two children but increased in one boy despite concomitant therapy with a somatostatin analog.

CONCLUSIONS

Pegvisomant may be an effective modality for the therapy of pituitary gigantism in children. Titration of the dose is necessary for optimal efficacy, and regular surveillance of tumor size is mandatory.

The effect of atorvastatin on serum lipoproteins in acromegaly

OBJECTIVE

Acromegaly is associated with long-term adverse effects on cardiovascular mortality and morbidity. Reducing growth hormone secretion improves well-being and symptoms, but may not significantly improve the lipoprotein profile. An additional approach to cardiovascular risk reduction in acromegaly may therefore be to target lipoprotein metabolism directly. In this study we investigated the effect of statin treatment.

DESIGN

Double blind, placebo-controlled, crossover study of the effects on circulating lipoproteins of atorvastatin 10 mg daily vs. placebo. Each treatment was given for 3 months in random order.

SUBJECTS

Eleven patients with acromegaly.

MEASUREMENTS

Lipids, lipoproteins, apolipoproteins, enzyme activity and calculated cardiovascular risk.

RESULTS

Atorvastatin treatment compared to placebo resulted in a significant decrease in serum cholesterol (5.85 +/- 1.04 mmol/l vs. 4.22 +/- 0.69 mmol/l; mean +/- SD; P < 0.001), low-density lipoprotein (LDL) cholesterol (2.95 +/- 1.07 mmol/l vs. 1.82 +/- 0.92 mmol/l; P < 0.001), very low-density lipoprotein (VLDL) cholesterol (0.31 (0.21-0.47) mmol vs. 0.23 (0.13-0.30) mmol/l median (interquartile range); P < 0.05), apolipoprotein B (111 +/- 28 mg/dl vs. 80 +/- 18 mg/dl; P < 0.001), and calculated coronary heart disease risk (6.8 (3.3-17.9) vs. 2.8 (1.5-5.7)% over next 10 years; P < 0.01). Serum triglyceride was 1.34 (1.06-1.71) mmol/l on placebo and 1.14 (0.88-1.48) mmol/l on atorvastatin (ns). HDL cholesterol, apolipoprotein A1 and Lp(a) concentrations and cholesteryl ester transfer protein and lecithin: cholesterol acyl transferase activities were also not significantly altered.

CONCLUSION

Atorvastatin treatment was safe, well tolerated and effective in improving the atherogenic lipoprotein profile in acromegaly.

Somatostatin analogs in medical treatment of acromegaly

Although acromegaly remains a disease primarily addressed by pituitary microsurgery, most patients require secondary treatment for persistent growth hormone (GH) hypersecretion and elevated serum insulin-like growth factor-1 (IGF-1) concentrations following adenomectomy. Persistently abnormal serum GH and IGF-1 can be reduced to normal concentrations in better than half of post-surgery acromegalics using the pharmacologic treatments available at present, the dopamine agonists (DA) and somatostatin (SST) analogs. The long-acting SST analogs octreotide LAR and lanreotide SR have become the mainstay of medical treatment for acromegaly, having largely supplanted DA agents since the introduction of bromocriptine for the suppression of GH secretion in the 1970s. The DA cabergoline may be effective in up to half of patients, however, in particular those patients whose tumors cosecrete prolactin. On the horizon is the GH-receptor antagonist pegvisomant, which is expected to enable the reduction of serum IGF-1 to the normal range in the vast majority of postoperative acromegaly patients, representing a revolutionary development in the medical treatment of this disease. We here review the choices available to the endocrinologist in the pharmacologic treatment of acromegaly, focusing upon the SST analogs.

Medical management of growth hormone-secreting pituitary adenomas

The primary treatment of acromegaly remains transsphenoidal adenomectomy, yet the tissue overgrowth of acromegaly often progresses following surgery, and responds to radiotherapy only after significant delay. Persistently elevated serum growth hormone (GH) and insulin-like growth factor-I (IGF-I) concentrations can be normalized in about half of post-surgery acromegalics using the pharmacologic alternatives presently available, the dopamine agonists (DA) and somatostatin (SST) analogs. Cabergoline, the most efficacious DA, normalizes IGF-I in approximately 37% of patients, whereas the long-acting SST analogs, Octreotide LAR and Lanreotide SR, do so in 66%. Significant tumor shrinkage may be attained with SST analogs in particular, and when necessary, the primary medical treatment of acromegaly may be successfully addressed with this class of drugs. Greatly enhanced efficacy is expected from the GH receptor antagonist pegvisomant, which is nearing market availability and will enable the normalization of serum IGF-I in virtually all patients treated. We review here the pharmacologic treatments of excessive GH secretion.

Acromegaly: historical perspectives and current therapy

Soon after the initial description of acromegaly in the late 19th century, neurosurgeons performed the first operative procedures for the disease. Transcranial procedures eventually yielded to the transsphenoidal approach. Reasonably effective medical therapy was introduced in the 1970s and pharmacological progress continues to be realized. It is now recognized that excess growth hormone is associated with significant morbidity and mortality and that biochemical remission improves outcome. Although medical and radiation treatments offer useful adjuncts, surgery provides optimal results.