ABSTRACT
Aggregation represents a significant challenge for the long-term formulation stability of insulin therapeutics. The supramolecular PEGylation of insulin with conjugates of cucurbit[7]uril and polyethylene glycol (CB[7]‒PEG) has been shown to stabilize insulin formulations by reducing aggregation propensity. Yet prolonged in vivo duration of action, arising from sustained complex formation in the subcutaneous depot, limits the application scope for meal-time insulin uses and could increase hypoglycemic risk several hours after a meal. Supramolecular affinity of CB[7] in binding the B1-Phe residue on insulin is central to supramolecular PEGylation using this approach. Accordingly, here we synthesized N-terminal acid-modified insulin analogs to reduce CB[7] interaction affinity at physiological pH and reduce the duration of action by decreasing the subcutaneous depot effect of the formulation. These insulin analogs show weak to no interaction with CB[7]‒PEG at physiological pH but demonstrate high formulation stability at reduced pH. Accordingly, N-terminal modified analogs have in vitro and in vivo bioactivity comparable to native insulin. Furthermore, in a rat model of diabetes, the acid-modified insulin formulated with CB[7]‒PEG offers a reduced duration of action compared to native insulin formulated with CB[7]‒PEG. This work extends the application of supramolecular PEGylation of insulin to achieve enhanced stability while reducing the risks arising from a subcutaneous depot effect prolonging in vivo duration of action.
ABSTRACT
Objective: To assess the clinical features, diagnosis and treatment of gastrointestinal stromal tumor in the rectum.Methods: Records of 18 patients diagnosed as GIST in the rectum between January 2002 and April 2009 were re-viewed and the major clinical features, treatment modalities and outcomes were analyzed.Results: The clinical features of GIST in the rectum were nonspecific.Most patients manifested with bloody stool or changes in bowel habits.CT scan or MRI findings showed necrosis and/or hemorrhage in the tumor and well defined tumor margins.Even in the case of large GIST, no lymphadenopathy was not found, which could be a factor for the differential diagnosis of GIST from other rectal neoplasms.All of the resected tumor specimens showed positive expression of CD117 and CD34 in immunohistochemical staining.Low and very low risk patients accounted for 44.4% (8/18).All patients received surgery.Twelve patients were treated with local excision with different approaches.Anterior resection of the rectum (Dixon) was undertaken in three pa-tients and abdominoperineal resection (Miles) in three patients.Neoadjuvant therapy with imatinib was applied for three pa-tients with partial response.After a median follow-up of 34 months (1～84 months), recurrence and/or metastasis occurred in five patients, and three of them were treated with imatinib.One patient received Miles surgery after repeated local exci-sions.Only one patient died of bone metastasis.Recurrence-free survival (RFS) of the local excision group was longer than that of abdominoperineal resection (APR) group (75.0±8.4 months vs 26.0±11.1 months, P=0.023).Conclusion: The treatment for rectal GIST should be individualized and be different from that of rectal cancer.Treatment decision and choice of procedures should be based on careful preoperative evaluation of tumor size, location, extent and risk level.Most of the anorectal GIST were rated as low-risk in this cohort and could be excised locally by different approaches with satisfactory outcome.Neoadjuvant therapy with imatinib may benefit some patients to obtain the opportunity of sphincter-saving.