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Objective: Development of companion diagnostics for targeted radionuclide therapy is critical, especially for full-size antibodies with prolonged circulation times. Engineering antibodies to modify their in-vivo pharmacokinetics, such as incorporating neonatal Fc receptor (FcRn)-binding mutations, can potentially enable earlier imaging timing and improved patient stratification. This study aimed to evaluate the impact of FcRn-binding mutations on the in-vitro binding characteristics and in-vivo biodistribution and imaging performance of a CD44v6-targeting full-size antibody, UU-40, labeled with different radionuclides, and to assess its potential as a companion diagnostic.

Methods: The study involved engineering UU-40 with LALA and IAHA mutations, evaluating specific binding, internalization, and affinity using in-vitro cell assays. Biodistribution and imaging studies [PET and single-photon emission computed tomography (SPECT)] were conducted in mice carrying human tumor xenografts in a dual-nuclide setting.

Results: The FcRn mutations (LALA/IAHA) did not affect antibody specificity or affinity, which was target-specific and affinity remained in the subnanomolar range. Biodistribution studies demonstrated that the residualizing radiometal label (¹⁷⁷Lu) resulted in higher liver and spleen uptake compared with the nonresidualizing ¹²⁵I-label, leading to reduced tumor-to-organ ratios. Tumor uptake was higher in A431 xenografts, with peak accumulation at 24 h postinjection. SPECT and PET imaging confirmed superior contrast at later time points (∼24 h) with ¹²⁵I-UU-40_LALA/IAHA, while earlier imaging with ⁶⁸Ga was hindered by increased nonspecific accumulation.

Conclusion: FcRn-binding mutations in full-size antibodies significantly alter their in-vivo pharmacokinetics without affecting binding affinity or specificity. Introducing these mutations enables earlier imaging time points, enhancing the potential for companion diagnostics in clinical settings. 

Targeted radionuclide therapy is an emerging potent therapeutic strategy in oncology. The cell surface antigen CD44v6 is a potential pan-cancer target for radionuclide therapy. This study aimed to evaluate the therapeutic efficacy, biodistribution, dosimetry, and safety profile of AKIR001, an antibody targeting CD44v6 labeled with ¹⁷⁷Lu.

Methods: The biodistribution and preclinical dosimetry of [¹⁷⁷Lu]Lu-AKIR001 were calculated in the highly CD44v6-expressing A431 murine xenograft model, with subsequent extrapolation to predict human dosimetry. Therapeutic efficacy was evaluated across 3 xenograft models, 2 with high and 1 with moderate levels of CD44v6, using multiple dosing levels, fractionation regimens, and combinations with cisplatin. Preclinical toxicology was evaluated in a cross-reactive rabbit model and complemented by a PET imaging study using ⁶⁸Ga-labeled AKIR001 in a cynomolgus macaque.

Results: Biodistribution studies confirmed the high and selective tumor uptake of [¹⁷⁷Lu]Lu-AKIR001, resulting in favorable dosimetry predictions for clinical application. Therapeutic evaluations demonstrated significant dose-dependent efficacy in all tested xenograft models, with fractionated dosing (2 doses) resulting in complete tumor regression in 80% of the animals in a radioresistant xenograft model. Biodistribution in rabbits demonstrated low uptake in normal tissues, and a good-laboratory-practice study using an excessive dose of AKIR001 was well tolerated, with no signs of adverse effects. PET imaging in a cynomolgus macaque corroborated these findings.

Conclusion: Collectively, these data strongly support the therapeutic efficacy, safety, and dosimetry of [¹⁷⁷Lu]Lu-AKIR001, justifying its advancement into clinical trials. A phase 1 clinical trial of [¹⁷⁷Lu]Lu-AKIR001for CD44v6-positive solid cancers (NCT06639191) is currently recruiting patients.

Aim:

This study aimed to improve the efficacy of the CD44v6-targeting antibody UU-40 for molecular radiotherapy through affinity maturation and IgG subclass optimization.

M&M:

A panel of affinity-matured antibody candidates was generated and characterized as both human IgG4 and IgG1 with LALA mutations. Surface plasmon resonance and LigandTracer analyses identified several candidates with superior affinity and off-rates compared to the parental UU-40. Biodistribution studies in xenograft models using Lutetium-177 (177Lu)-labeled antibodies showed improved tumor retention for selected candidates, particularly UU-A-155. Species cross-reactivity assays confirmed binding to cynomolgus and rabbit v6-peptides, supporting future toxicity studies.

Results:

The IgG1 LALA format demonstrated reduced binding to Fc gamma receptors, potentially improving the safety profile. UU-A-155 emerged as the lead candidate for clinical translation, showing superior performance in both affinity and tumor retention. Our findings highlight the importance of comprehensive in vitro and in vivo assessments in antibody development, and provides valuable insights into optimizing antibody-based molecular radiotherapy.

Anaplastic thyroid cancer (ATC) is a rare but severe form of thyroid cancer responsible for approximately 50% of thyroid cancer deaths. Consequently, the identification of innovative therapies remains crucial for the effective treatment of ATC. Molecular radiotherapy is a rapidly growing field within oncology, and the cell surface antigen CD44v6, which is overexpressed in several cancers, is a plausible target for molecular radiotherapy of ATC. IHC of 39 patient samples with ATC was evaluated for CD44v6 expression. Biodistribution and dosimetry of iodine-125 (¹²⁵I)–/lutetium-177 (¹⁷⁷Lu)–labeled UU-40, a CD44v6-specific antibody, followed by in vivo efficacy in two ATC xenograft models with varying target expression levels (ACT-1 and BHT-101), accompanied by single-photon emission computed tomography (SPECT) imaging, evaluated radiolabeled UU-40 for therapeutic efficiency in ATC xenografts. The IHC revealed CD44v6 immunoreactivity in 46% of patient samples with ATC. The biodistribution favored ¹⁷⁷Lu-labeled UU-40 over the ¹²⁵I-labeled antibody and confirmed the in vivo specificity of both radioconjugates. The in vivo efficacy and accompanied SPECT imaging of a moderate CD44v6-expressing xenograft model (BHT-101) verified the tumor specificity, as well as the target-specific effect of ¹⁷⁷Lu-labeled UU-40 on tumor growth and survival. A 100% complete response rate was demonstrated as a result of therapy using a single dose of 16 MBq ¹⁷⁷Lu-labeled UU-40 in a high CD44v6-expressing xenograft model (ACT-1), and SPECT imaging revealed excellent tumor uptake of the radioconjugate at 14 days after injection. This study verifies the expression of CD44v6 in ATC and strengthens the superiority and promise of ¹⁷⁷Lu-labeled UU-40 over ¹³¹I-labeled UU-40 for antibody-based molecular radiotherapy of CD44v6-positive ATC.

Objective. The cell surface antigen CD44v6 is a promising target for several cancers, with favorable in vivo characteristics such as high affinity and suitable biodistribution. In normal tissues, expressions are restricted to basal epithelial cells in skin and mucosa. Consequently, previous clinical studies have reported varying degrees of toxicity in these tissues. To support new radioimmunotherapies (RIT), we developed small-scale internal dosimetry models for abdominal skin and esophageal mucosa. Using published biodistribution data, we compared absorbed doses to epithelial tissues and bone marrow from four clinically relevant radionuclides: rhenium-186, lutetium-177, terbium-161, and actinium-225. Approach. From the Genotype-Tissue Expression database, 288 H&E-stained sections of abdominal skin and esophageal mucosa were obtained from donors aged 21-70 and segmented to generate voxelized models. Monte Carlo simulations were conducted for the radionuclides across multiple source/target combinations. A compartment model generated serum, skin, and bone marrow biodistributions to estimate AD to the epithelium and bone marrow. Main results. Absorbed dose estimates to the basal layer of the skin were highest for 161Tb at 23.7 Gy GBq-1, followed by 177Lu and 186Re, with values of 9.5 and 5.3 Gy GBq-1, respectively, whereas the alpha emitter 225Ac delivered a dose of 4.9 Gy MBq-1. For the beta-emitters, three methods produced absorbed-dose estimates for the red marrow (RM) consistent within 5% of each other, with the highest values in the hip bone: 0.36, 0.25, and 0.39 Gy GBq-1 for 186Re, 177Lu, and 161Tb, respectively, compared to 0.66 Gy MBq-1 for 225Ac. Significance. This study presents a dosimetry framework for CD44v6-targeted RIT, demonstrating that, at clinically relevant administered activities, short-ranged emitters like 161Tb and 225Ac deliver substantially higher doses to basal epithelial layers compared to 186Re. RM doses were comparable for 161Tb and 186Re, lower for 177Lu, and highly uncertain for 225Ac due to daughter redistribution. Overall, these results support the use of 177Lu for initial clinical trials.

Thyroid cancer is the most common endocrine malignancy, affecting nearly 600,000 new patients worldwide. Treatment with the BRAF inhibitor sorafenib partially prolongs progression-free survival in thyroid cancer patients, but fails to improve overall survival. This study examines enhancing sorafenib efficacy by combination therapy with the novel HSP90 inhibitor onalespib. In vitro efficacy of sorafenib and onalespib monotherapy as well as in combination was assessed in papillary (PTC) and anaplastic (ATC) thyroid cancer cells using cell viability and colony formation assays. Migration potential was studied in wound healing assays. The in vivo efficacy of sorafenib and onalespib therapy was evaluated in mice bearing BHT-101 xenografts. Sorafenib in combination with onalespib significantly inhibited PTC and ATC cell proliferation, decreased metabolic activity and cancer cell migration. In addition, the drug combination approach significantly inhibited tumor growth in the xenograft model and prolonged the median survival. Our results suggest that combination therapy with sorafenib and onalespib could be used as a new therapeutic approach in the treatment of thyroid cancer, significantly improving the results obtained with sorafenib as monotherapy. This approach has the potential to reduce treatment adaptation while at the same time providing therapeutic anti-cancer benefits such as reducing tumor growth and metastatic potential.

Molecular radiotherapy combines the advantages of systemic administration of highly specific antibodies or peptides and the localized potency of ionizing radiation. A potential target for molecular radiotherapy is the cell surface antigen CD44v6, which is overexpressed in numerous cancers, with limited expression in normal tissues. The aim of the present study was to generate and characterize a panel of human anti-CD44v6 antibodies and identify a suitable candidate for future use in molecular radiotherapy of CD44v6-expressing cancers. Binders were first isolated from large synthetic phage display libraries containing human scFv and Fab antibody fragments. The antibodies were extensively analyzed through in vitro investigations of binding kinetics, affinity, off-target binding, and cell binding. Lead candidates were further subjected to in vivo biodistribution studies in mice bearing anaplastic thyroid cancer xenografts that express high levels of CD44v6. Additionally, antigen-dependent tumor uptake of the lead candidate was verified in additional xenograft models with varying levels of target expression. Interestingly, although only small differences were observed among the top antibody candidates in vitro, significant differences in tumor uptake and retention were uncovered in in vivo experiments. A high-affinity anti-CD44v6 lead drug candidate was identified, mAb UU-40, which exhibited favorable target binding properties and in vivo distribution. In conclusion, a panel of human anti-CD44v6 antibodies was successfully generated and characterized in this study. Through comprehensive evaluation, mAb UU-40 was identified as a promising lead candidate for future molecular radiotherapy of CD44v6-expressing cancers due to its high affinity, excellent target binding properties, and desirable in vivo distribution characteristics.

Aim: The aim of this study was to assess the feasibility of targeted therapy of thyroid carcinoma, first exploring potential targets BRAF, EGFR and CD44v6 in patient material through immunohistochemistry and mutation analysis.

Materials and methods: A patient cohort (n = 22) consisting of seven papillary (PTC), eight anaplastic (ATC) and seven follicular (FTC) thyroid carcinomas were evaluated. Additionally, eight thyroid carcinoma cells lines were analyzed for CD44v6-expression and sensitivity to the multi-kinase inhibitor sorafenib (Nexavar (R)), which targets numerous serine/threonine and tyrosine kinases, including the Raf family kinases. Targeted therapy using 131I-AbN44v6, a novel anti-CD44v6 antibody, and/or sorafenib was evaluated in 3D multicellular tumor spheroids.

Results: Of the two cell surface proteins, EGFR and CD44v6, the latter was overexpressed in >80 % of samples, while EGFR-expression levels were moderate at best in only a few samples. BRAF mutations were more common in PTC patient samples than in ATC samples, while FTC samples did not harbor BRAF mutations. CD44v6-expression levels in the thyroid carcinoma cell lines were more heterogenous compared to patient samples, while BRAF mutational status was in line with the original tumor type. Monotherapy in 3D multicellular ATC tumor spheroids with either 131I-AbN44v6 or sorafenib resulted in delayed spheroid growth. The combination of 131I-AbN44v6 and sorafenib was the most potent and resulted in significantly impaired spheroid growth.

Conclusion: This "proof of concept" targeted therapy study in the in vitro ATC 3D multicellular tumor spheroids indicated applicability of utilizing CD44v6 for molecular radiotherapy both as a monotherapy and in combination with sorafenib.

Background: Precision therapeutics continuously make advances in cancer therapy, and a field of growing interest is the combination of targeted radionuclide therapy (TRNT) with potential radiosensitizing agents. This study evaluated whether the effects of in vitro TRNT, using the Lu-177-labeled anti-CD44v6 antibody AbN44v6, were potentiated by the novel stapled MDM2/X-p53 antagonist PM2.

Materials and methods: Two wt p53 cell lines, HCT116 (colorectal carcinoma) and UM-SCC-74B (head and neck squamous cell carcinoma), expressing different levels of the target antigen, CD44v6, were used. Antigen-specific binding of Lu-177-AbN44v6 was initially verified in a 2D cell assay, after which the potential effects of unlabeled AbN44v6 on downstream phosphorylation of Erk1/2 were evaluated by western blotting. Further, the therapeutic effects of unlabeled AbN44v6, Lu-177-AbN44v6, PM2, or a combination (labeled/unlabeled AbN44v6 +/- PM2) were assessed in 3D multicellular tumor spheroid assays.

Results: Radiolabeled antibody bound specifically to CD44v6 on both cell lines. Unlabeled AbN44v6 binding did not induce downstream phosphorylation of Erk1/2 at any of the concentrations tested, and repeated treatments with the unlabeled antibody did not result in any spheroid growth inhibition. Lu-177-AbN44v6 impaired spheroid growth in a dose-dependent and antigen-dependent manner. A single modality treatment with 20 mu M of PM2 significantly impaired spheroid growth in both spheroid models. Furthermore, the combination of TRNT and PM2-based therapy proved significantly more potent than either monotherapy. In HCT116 spheroids, this resulted in a two- and threefold spheroid growth rate decrease for the combination of PM2 and 100 kBq Lu-177-AbN44v6 compared to monotherapies 14-day post treatment. In UM-SCC-74B spheroids, the combination therapy resulted in a reduction in spheroid size compared to the initial spheroid size 10-day post treatment.

Conclusion: TRNT using Lu-177-AbN44v6 proved efficient in stalling spheroid growth in a dose-dependent and antigen-dependent manner, and PM2 treatment demonstrated a growth inhibitory effect as a monotherapy. Moreover, by combining TRNT with PM2-based therapy, therapeutic effects of TRNT were potentiated in a 3D multicellular tumor spheroid model. This proof-of-concept study exemplifies the strength and possibility of combining TRNT targeting CD44v6 with PM2-based therapy.

Rational Cisplatin based cancer therapy is an affordable and effective standard therapy for several solid cancers, including lung, ovarian and head and neck cancers. However, the clinical use of cisplatin is routinely limited by the development of drug resistance and subsequent therapeutic failure. Therefore, methods of circumventing cisplatin resistance have the potential to increase therapeutic efficiency and dramatically increase overall survival. Cisplatin resistance can be mediated by alterations to the DNA damage response, where multiple components of the repair machinery have been described to be client proteins of HSP90. In the present study, we have investigated whether therapy with the novel HSP90 inhibitor onalespib can potentiate the efficacy of cisplatin and potentially reverse cisplatin resistance in ovarian and head and neck cancer cells. Methods Cell viability, cancer cell proliferation and migration capacity were evaluatedin vitroon models of ovarian and head and neck cancer cells. Western blotting was used to assess the downregulation of HSP90 client proteins and alterations in downstream signaling proteins after exposure to cisplatin and/or onalespib. Induction of apoptosis and DNA damage response were evaluated in both monotherapy and combination therapy groups. Results Results demonstrate that onalespib enhances the efficiency of cisplatin in a dose-dependent manner. Tumor cells treated with both drugs displayed lower viability and a decreased migration rate compared to vehicle-control cells and cells treated with individual compounds. An increase of DNA double strand breaks was observed in both cisplatin and onalespib treated cells. The damage was highest and most persistent in the combination group, delaying the DNA repair machinery. Further, the cisplatin and onalespib co-treated cells had greater apoptotic activity compared to controls. Conclusion The results of this study demonstrate that the reduced therapeutic efficacy of cisplatin due to drug-resistance could be overcome by combination treatment with onalespib. We speculate that the increased apoptotic signaling, DNA damage as well as the downregulation of HSP90 client proteins are important mechanisms promoting increased sensitivity to cisplatin treatment.