Example 14
Eight NH2—PEGn-RGD peptides containing spacers of various PEG lengths (n=2, 4, 6, 8, 10, 12, 14, 16) will be prepared by adding the corresponding Boc-PEGn-NHS to RGD in a PBS buffer (pH=8.2), followed by Boc deprotection. Photo-ODIBO-NHS, prepared using previously reported procedures, will then be mixed with the prepared NH2—PEGn-RGD in a PBS buffer (pH=8.2) to produce photo-OIDBO-PEGn-RGD. N3-PEG4-cetuximab will be prepared using previously reported procedures. N3—PEG4-cetuximab and the eight photo-ODIBO-PEGn-RGD peptides (n=2, 4, 6, 8, 10, 12, 14, 16) will be used for in vitro screening (at 4° C. to minimize the internalization of targeting probes). As shown in FIG. 11: 1): eight mixed-ligands stock solutions will be prepared by mixing N3-PEG4-cetuximab with one of the eight photo-OIDBO-PEGn-RGD peptides; 2) U87MG cells will be cultured in a 96-well plate; 3) one of the above eight mixed-ligands stock solution will be added into each well (eight wells in total) pre-seeded with U87MG; 2) after the ligands bind to the targeted receptors, the excess (unbound) targeting ligands will be washed off using a PBS buffer (repeated 5 times to ensure complete removal); 3) a UV lamp (365 nm) will be applied to deprotect the azide-inactive photo-ODIBO and generate azide-active “ODIBO”, subsequently triggering ligation between the N3-PEG4-cetuximab and ODIBO-PEGn-RGD; 4) after being incubated for an additional 2 h, 64Cu-labeled N3—NOTA will be added to click with the “excess” ODIBO-PEGn-RGD (that binds to cells, but does not click to N3-PEG4-cetuximab); and 5) the excess N3-(64Cu)NOTA will be removed, and the N3-(64Cu)NOTA clicked to “excess” ODIBO-PEGn-RGD will be measured on MicroBeta2 Plate Counter. One group without UV irradiation will be used as a negative control to get counts from the non-specific binding of N3-(64Cu)NOTA. After subtracting the non-specific binding, the specific binding of N3-(64Cu)NOTA obtained from the eight ODIBO-PEGn-RGD (n=2, 4, 6, 8, 10, 12, 14, 16) will be compared. The well with the lowest specific binding will contain the highest amount of clicking product (between cetuximab-PEG4-N3 and ODIBO-PEGn-RGD), thus the corresponding spacer will be the most potent.
The ODIBO-PEGn-RGD containing the most potent PEG spacer will click with Tz-NOTA-N3 and then be radiolabeled with 64Cu, and the resulting Tz-(64Cu)NOTA-PEGn-RGD will be used for the in vitro avidity studies on U87MG cells. Tz-(64Cu)NOTA-RGD (without a PEG spacer) will be used as a negative control because the distance between RGD and cetuximab in the resulting heterodimer is too short to achieve avidity effect (proved in preliminary study, FIG. 5B). Briefly, Tz-(64Cu)NOTA-PEGn-RGD/TCO-PEG4-cetuximab ligation product (cetuximab-PEG4-(64Cu)NOTA-PEGn-RGD) will be used for cell uptake/efflux, binding affinity and Bmax measurements on U87MG cells. After high avidity effect is confirmed on the above ligation product, in vivo evaluation will be performed then. Mice bearing U87MG xenografts will be pre-injected with 100 μg of TCOPEG4-cetuximab, and 24 h later, ˜250-350 pCi of Tz-(64Cu)NOTA-PEGn-RGD (or Tz-(64Cu)NOTA-RGD in the negative control group) will be injected. Then 1 h dynamic PET scans will be performed at multiple time points (p.i., 4, 18, and/or 28 h). As cetuximab is cleared through the liver, kinetics on tumor and liver at mid and late time points can be evaluated. At mid/late time points (4, 18, 28 h) when most of the un-ligated Tz-(64Cu)NOTAPEGn-RGD has been washed off, observation of relatively slower tumor washing out and faster liver clearing (compared to that from Tz-(64Cu)NOTA-RGD) can indicate the much stronger binding with tumor cells, and thus an avidity effect of in vivo ligation product (cetuximab-PEG2-(64Cu)NOTA-PEGn-RGD) is being achieved.
Various references are cited in this document, which are hereby incorporated by reference in their entireties herein.
