Past, Present, and Future: Development of Theranostic Agents Targeting Carbonic Anhydrase IX

Abstract

Theranostics is the integration of diagnostic information with pharmaceuticals to increase effectiveness and safety of cancer treatments. Nuclear medicine provides a non-invasive means to visualize drug target expression across primary and metastatic sites, and assess pharmacokinetics and efficacy of companion therapeutic agents. This is significant given the increasing recognition of the importance of clonal heterogeneity in treatment response and resistance. Carbonic anhydrase IX (CA-IX) has been advocated as an attractive diagnostic and therapeutic biomarker for targeting hypoxia in solid malignancies. CA-IX confers cancer cell survival under low oxygen tension, and is associated with increased propensity for metastasis. As such, CA-IX is overexpressed in a broad spectrum of cancers. Different classes of antigen recognition molecules targeting CA-IX including monoclonal antibodies, peptides, small molecule inhibitors, and antibody mimetics have been radiolabeled for imaging and therapeutic applications. cG250, a chimeric monoclonal antibody, has been labeled with an assortment of radionuclides (¹²⁴I, ¹¹¹In, ⁸⁹Zr, ¹³¹I, ⁹⁰Y, and ¹⁷⁷Lu) and is the most extensively investigated CA-IX radiopharmaceutical. In recent years, there have been tremendous advancements made by the research community in developing alternatives to cG250. Although still in preclinical settings, several small molecule inhibitors and antibody mimetics hold great promise in improving the management of aggressive and resistant cancers.

Keywords: Nuclear medicine; cancer.; carbonic anhydrase IX; hypoxia; theranostics.

Figure 1

¹³¹I-cG250 scintigraphy in two patients with RCC metastases after a RIT infusion. ¹³¹I-cG250 enabled good visualization of (sub)cutaneous and muscle metastatic lesions (A) and less clear visualization of lung metastases (B). Uptake in thyroid glands in both patients was observed despite thyroid blocking. Figure reproduced with permissions from Brouwers et al.

Figure 2

Patient with a 1.0 cm ccRCC of the right kidney. (A) The mass is visible in the noncontrast CT component of the PET/CT scan, (B) is positive on ¹²⁴I-cG250 PET, and (C) is clearly evident on the fused image. The mass was deemed to be positive on the CECT scan of the (D) parenchymal component and (E) excretory component by Hounsfield criteria and qualitatively. Figure reproduced with permissions from Divgi et al..

Figure 3

Preclinical imaging with ¹¹¹In-DTPA-G250-IRDye800CW in SK-RC-52 bearing nude mice. (A) Preoperative SPECT/CT, and (B) fluorescence images 48 h p.i. showed accumulation in tumour (arrow). Tumour was removed using fluorescence image-guided surgery. (C) After resection, no residual tumour was detected macroscopically or by optical imaging. Figure reproduced with permissions from Muselaers et al..

Figure 4

Chemical structures of radiolabeled small molecule inhibitors of CA-IX. With the notable exceptions of compounds 1, 3, 4, and 5, these low molecular weight imaging agents attain CA-IX selectivity through cell impermeability.

Figure 5

A 78 y-old male with left-sided ccRCC, indicated by an arrow, (A) detected on contrast-enhanced CT. (B) Axial ¹⁸F-VM4-037 PET and (C) PET/CT show uptake in left kidney lesion with a SUVmean of 1.86. (D) Coronal ¹⁸F-VM4-037 PET shows uptake within the lesion as well as the high uptake of the tracer in normal kidney parenchyma and liver. Figure reproduced with permissions from Turkbey et al.

Figure 6

PET/CT images of trimeric ¹⁸F-sulfonamides at 1 h after injection of (A) ¹⁸F-AmBF₃-(AEBS)₃, (B) ¹⁸F-AmBF₃-(ABS)₃, and (C) ¹⁸F-AmBF₃-(ABS)₃ preinjected with 10 mg/kg acetazolamide, a pan CA inhibitor. Tumours are indicated by arrows. Scale bar unit is %ID/g. Preinjection of acetazolamide significantly reduced tumour uptake to near-background levels for ¹⁸F-AmBF₃-(ABS)₃, demonstrating target specificity. Figure reproduced with permissions from Lau et al.

Figure 7

Maximal intensity projection images of PET/CT and PET with ⁶⁸Ga tracers at 1 h p.i. (A) ⁶⁸Ga-DOTA-AEBSA; (B) ⁶⁸Ga-DOTA-AEBSA preblocked with 10 mg/kg of acetazolamide; (C) ⁶⁸Ga-DOTA-(AEBSA)₂; (D) ⁶⁸Ga-NOTGA-(AEBSA)₃. Tumour uptake was observed for all three compounds with ⁶⁸Ga-DOTA-AEBSA displaying highest contrast. t = tumour; l = liver; k = kidney; bl = bladder. Adapted with permissions from Lau et al. Copyright 2016 American Chemistry Society.

Figure 8

Longitudinal study: uptake of ⁶⁸Ga-DOTA-AEBSA in HT-29 cancer xenograft increases as tumour grows. This tumour-bearing mouse was imaged 17 d, 24 d and 33 d post-cell inoculation with ⁶⁸Ga-DOTA-AEBSA. Adapted with permissions from Lau et al. Copyright 2016 American Chemistry Society.

Figure 9

PET/CT images of ⁶⁴Cu-XYIMSR-06 enabled the detection of CA-IX-expressing SK-RC-52 tumour in vivo. Images were obtained at 1 h, 4 h, 8 h, and 24 h p.i. Arrows indicate location of tumours. Scales were adjusted to percent injected dose per volume (%ID/cc). Figure reproduced with permissions from Minn et al., in accordance with the Creative Commons Attribution 3.0 Unported license (https://creativecommons.org/licenses/by/3.0/legalcode).

Figure 10

Maximum intensity projections of microSPECT/CT using CA-IX targeting affibodies at 4 h p.i. (A) Imaging using ^99mTc-(HE)₃-ZCAIX:2. The linear color scale was adjusted to provide clear visualization of a tumour. (B) Imaging using ¹²⁵I-(HE)₃-ZCAIX:4. Full linear colour scale was applied. Adapted with permissions from Garousi et al. Copyright 2016 American Chemistry Society.