Modified Desmopressin (mDesmo) Using Cold-Kit for PET/CT

Cushing's syndrome (CS) is one of the most enigmatic endocrine disorders. It is important to confirm the adrenocorticotropic Hormone (ACTH) dependent hypercortisolism and distinguishing Cushing's disease from ectopic CS. Most of the ACTH dependent CS are caused by Cushing's disease, of which majority are due to microadenoma being less than 6 mm. Visualizing tumors within 10 mm pituitary and confirming its functional status is challenging. Long-term remission/cure is determined by the correct functional and anatomical delineation of corticotropinoma (pituitary-tumor). The treatment of choice in Cushing's disease is pituitary microsurgery also known as transsphenoidal surgery (TSS). However, pituitary-tumor is not well delineated within the sella in 30-40% using currently available investigations especially MRI and inferior petrosal sinus sampling, which affects intra-operative navigation for selective adenectomy and influence remission rate. The modified Desmopressin (mDesmo) was synthesized to be conjugated with 1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid (DOTA) and radiolabelled with Gallium-68 (Ga-68), a positron emitter, for Positron Emission Tomography/Computed Tomography (PET/CT) imaging to delineate pituitary-tumor. It provides surgeon with the requisite information for intra-operative tumor navigation. Objectives of the Project 1. Preparation of freeze-dried DOTA conjugated mDesmo cold-kit for radiolabelling with Ga-68 and PET/CT imaging. 2. Bioevaluation of radiotracer prepared with mDesmo cold-kit for the molecular imaging of ACTH-releasing pituitary adenoma (Cushing's disease). 3. Evaluate the application of Ga-68 mDesmo PET/CT in intra-operative tumor navigation, residual disease and recurrence. 4. Study the self-life of mDesmo cold-kit. Deliverables: Cushing's syndrome may be due to a) extra pituitary tumors (also known as EAS or ECS) that can be easily detected by Gallium-68-1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid Tyr3-octreotate/Nal3-octreotide (68GaDOTATATE/NOC) and resected, b) tumors within the pituitary (known as pituitary corticotropinoma). Many a times these tumors are very small (\<6mm, microadenoma). The treatment of choice is pituitary microsurgery (trans-sphenoidal surgery). However, the correct delineation of these microadenomas within small pituitary (10 mm) before microsurgery is challenging but crucial to preserve normal functioning pituitary. None of the currently available diagnostic modalities can delineate the tumor from normal functional pituitary. Often MRI and BIPSS, an invasive and overly expensive, is used to guide surgery. Therefore * The mDesmo cold-kit has been developed for PET/CT imaging as single modality to correctly delineate microadenomas noninvasively. * Provides surgeon with the requisite information for intra-operative tumor navigation * Cost-effective * Facile procedure of radiolabelling * Developed first time globally * International market Significance of the Project 1. Major applications of the proposed technology Cushing's syndrome (CS) is a rare endocrine disorder. The diagnosis can be challenging due to the non-specific nature of many symptoms. On suspicion of the disease, it is important to confirm the presence of ACTH dependent hypercortisolism. Seventy to 80% cases of ACTH dependent Cushing's syndrome are caused by Cushing's disease (pituitary tumor), of which 90% are due to microadenoma of less than 6 mm. Visualizing these small tumors within 10 mm pituitary and confirming its functional status is a challenge. In patients with clinically and biochemically confirmed endogenous Cushing's syndrome, the long-term remission/cure is determined by the correct functional and anatomical delineation of corticotropinoma (pituitary tumor) i.e. to distinguish between Cushing's disease (access ACTH production within pituitary due to tumor) and ectopic ACTH production (Corticotrophin-releasing hormone (CRH) producing tumors outside pituitary) and most importantly, correct visualization of tumour, preoperative. The ectopic ACTH syndrome require resection of the primary tumour while the treatment of choice in Cushing's disease is pituitary microsurgery. Corticotropinoma is not well delineated within the sella in 30 to 40% cases of Cushing's disease using currently available investigations especially MRI and bilateral inferior petrosal sinus sampling (BIPSS), which affects intra-operative navigation for selective adenomectomy and thus may influence remission rates after trans-sphenoidal surgery (TSS). Anatomical imaging (Computed Tomography (CT), Magnetic Resonance Imaging (MRI) can delineate the tumor while cannot confirm its functionality, while vice versa is true for functional test/imaging. None of the currently available diagnostic modality can achieve these goals simultaneously. Several tests are used to serve this purpose. However, none of the tests are diagnostic. Pituitary tumor i.e corticotropinoma continues to express receptors for Corticotropin releasing hormone (CRH) and Arginine vasopressin (AVP) as that of normal corticotrophs and rather corticotropinoma hyper responds to these stimuli due to upregulation of the respective receptors. Desmopressin, a small peptide consist of 9 amino acids, is more potent and specific for tumorous corticotrophs, therefore we explored this molecule for PET/CT imaging. The native Desmopressin could not be conjugated to bifunctional chelator for radionuclide binding, some modifications were done in amino acid sequence of Desmopressin to conjugate with bifunctional chelator (DOTA in this case) without affecting it binding property with receptor. The modified and DOTA conjugated desmopressin (mDesmo) when radiolabelled with Gallium-68 (Ga-68 mDesmo), the PET/CT hybrid imaging is able to delineate cortitropinoma i.e. integrated functional imaging of tumor with anatomical localization and provides surgeon with the requisite information for intra-operative tumor navigation. 2. Clinical Need (Include significance and estimated patient population/year if known). Cushing's syndrome is a clinical state resulting from inappropriate and excess production of cortisol. This syndrome may arise due to excessive adrenocorticotrophic hormone (ACTH) production from the pituitary gland or ACTH/ corticotropin releasing hormone (CRH) secretion from an extra-pituitary source or autonomous cortisol secretion from adrenal glands. The incidence of Cushing's syndrome is 1·2-2·4 cases per million per year, of which 80% is due to excess ACTH production (1). Amongst the ACTH dependent causes, Cushing's disease is the most common cause seen in 90% of cases, the rest being due to ectopic ACTH/CRH production (ECS). In most of the cases, Cushing's disease is caused by micro-corticotropinoma of less than 6 mm (2). The localization the source of ACTH is crucial for management. This begins with Contrast enhanced Magnetic resonance imaging (CEMRI) of sella as Cushing's disease constitutes 90% of ACTH dependent Cushing's syndrome (3). However, CEMRI has a sensitivity of 50 to 60% with a positive predictive value of 86% (2). Furthermore, it is an anatomical imaging and do not indicate the functional status of the tumor. It may reveal innocent pituitary incidentaloma in up to 10% of the general population including patients with ectopic Cushing's syndrome (ECS) (4). Thereby, meaning that these pituitary tumor picked up on MRI may just be an incidental finding and not the actual culprit behind the symptomatology. While the presence of macroadenoma favours pituitary source of ACTH, the presence of microadenoma warrants further corroboration with the functional/dynamic tests for the confirmation of corticotropinoma which include high dose dexamethasone suppression test (HDDST), CRH stimulation test and bilateral inferior petrosal sinus sampling (BIPSS). The pre- test probability of having pituitary disease in ACTH dependent CS is between 85 to 90%, which makes it mandatory for any additional dynamic test to be of any clinical use to have a high specificity. Patients with concordant response to CRH stimulation and HDDST indicating pituitary source are almost certain to harbour corticotropinoma. However, in case of discordant results and/or non-yielding MRI, BIPSS is required (5). Importantly, BIPSS is an invasive procedure which is limited by its availability, need for high degree of technical skill and cost. Even though it is a good modality for differentiating ectopic from pituitary source of ACTH production, its positive predictive value for corticotropinoma lateralization within pituitary as indicated by inter sinus ACTH ratio is only 60-70% (5). Furthermore, it does not provide sufficient information for planning surgical navigation, due to which surgeries solely based on lateralization as indicated by inter-sinus ACTH gradient on BIPSS leads to only 45% cure rates (6). Thus, with the current modalities, corticotropinoma is not well delineated within the sella in 30 to 40% cases of Cushing's disease. This affects intra-operative navigation for selective adenomectomy which may influence remission rates after trans-sphenoidal surgery (TSS). Currently there is no imaging modality available globally that can give functional and anatomical details of ACTH dependent pituitary adenoma. Earlier we have developed Ga-68 CRH for this purpose and evaluated clinically in patients with ACTH dependent Cushing's Syndrome (8). However, being a large peptide of 41 amino acid there was high uptake of Ga-68 CRH in liver. it also demonstrated diffuse physiological uptake in normal pituitary and other organs (9). Desmopressin is deamino D-arginine vasopressin (DDAVP) is found more potent and specific than arginine vasopressin (AVP) and CRH for tumorous corticotrophs. Therefore, we explored this molecule for PET/CT imaging of ACTH dependent pituitary adenoma. Desmopressin was modified to enable radiolabelling with PET radion…