Abstract

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.

Results from nanoScan® SPECT/CT and MultiScan™ PET/CT

• Biodistribution studies were performed in BALB/c nu/nu mice carrying A431 xenografts (high CD44v6 expression). Increasing tumor uptake was observed, peaking at 65 %ID/g at 96 h after injection. Blocking with an excess of unlabeled AKIR001 reduced uptake to 19 %ID/g (P < 0.0001), confirming specificity.

Figure 1.: Biodistribution and small-animal SPECT imaging at 3 dose levels of 177Lu-AKIR001 in A431 xenografts. (A) Biodistribution of 177Lu-AKIR001 (15 µg) in BALB/c nu/nu mice carrying A431 xenografts, terminated at 4, 24, 48, 96, 168, and 240 h after injection. In vivo block using 30-fold molar excess of nonradiolabeled AKIR001 was evaluated at 96 h after injection.

• Dose-Dependent and Target-Specific Effect of ¹⁷⁷Lu-AKIR001

Figure 3.: Efficacy studies on ACT-1. (A) Kaplan–Meier survival of animals carrying ACT-1 xenografts (high CD44v6) treated with phosphate-buffered saline, nonradiolabeled AKIR001, [¹⁷⁷Lu]Lu-iso control (AK-MO176-156, hIgG1 LALA isotype control, 17 MBq), or high dose (17 MBq) or low dose (8 MBq) of [¹⁷⁷Lu]Lu-AKIR001. (B) Small-animal SPECT of mouse injected with 17 MBq of [¹⁷⁷Lu]Lu-AKIR001 at 4 d after injection. (C) Individual tumor growth by treatment group.

• To evaluate [¹⁷⁷Lu]Lu-AKIR001 against lower-expressing tumors, efficacy was evaluated in BHT-101 xenografts with moderate CD44v6 expression levels.

Figure 4.: Efficacy studies on BHT-101. (A) Kaplan–Meier survival plot of mice carrying BHT-101 xenografts treated with either placebo (phosphate-buffered saline, n = 10) or 10 MBq of [¹⁷⁷Lu]Lu-AKIR001 (n = 9, N = 19). (B) Individual tumor growth by treatment group. (C) Small-animal SPECT/CT of mouse carrying BHT-101 xenograft injected with 10 MBq of [¹⁷⁷Lu]Lu-AKIR001 at 4 d after injection.

• AKIR001’s cross-reactivity with rabbit CD44v6 enabled biodistribution studies on New Zealand white rabbits using [¹¹¹In]In-AKIR001 (>90% labeling yield), and to assess potential off-target binding in normal tissues, a [⁶⁸Ga]Ga-labeled UU-40 imaging study was conducted on a cynomolgus monkey.

Figure 5.: Biodistribution of [¹¹¹In]In-AKIR001 in male (A) and female (B) New Zealand white rabbits (presented as percentage injected dose [%ID] per gram) at 4, 24, 72, and 168 h after injection (N = 9; n = 5 males and n = 4 females). (C) Whole-body ⁶⁸Ga PET images of cynomolgus macaque showing biodistribution of [⁶⁸Ga]Ga-UU-40_IAHA at different time points.

Conclusion

[¹⁷⁷Lu]Lu-AKIR001 is a CD44v6-targeted RPT with strong preclinical efficacy, specificity, and safety. Its broad tumor applicability and its potential for use in combination support clinical evaluation, and it is currently being assessed in a phase 1 trial (NCT06639191) for safety and therapeutic potential in CD44v6-expressing cancers.

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