Diffuse intrinsic pontine gliomas (DIPG) carry a particularly poor prognosis, with median survival shorter than one year. Recent efforts aimed at traversing the blood-brain barrier have explored the capability of convection-enhanced delivery (CED) as a possible alternative to systemic delivery. Accurate pharmacokinetic information (distribution and clearance) is problematic since most agents have no intrinsic imaging capacity. This information however is critical in designing optimal infusion parameters and monitoring response. The mainstay of current practice is to rely on imaging surrogates to estimate molecular kinetics. These imaging tracers, however, have no homologous bioactive profile with the therapeutic molecule. Our objective of the current work was to perform direct labeling using a positron-emitting [ 18 F]F 2 B-moiety that could be imaged by PET/CT. In the initial phase of this project, we first coupled the kinase-inhibitor dasatinib, a therapeutic chosen for its ability to tolerate the alteration of its molecularstructure. In vitro cell viability assays were performed to confirm that our modifications did not affect drug bioactivity. Labelled therapeutics were then delivered via CED to the frontal lobe in mice. We observed that the clearance properties vary greatly depending on the functional group added to the dasatinib backbone, with both distribution and clearance following injection being group-specific. We subsequently repeated these modifications with panobinostat. We observed that panobinostat distributes very differently from dasatinib, despite their similar molecular weight, both spatially (i.e. brain regions involved) and temporally (different clearance following infusion). This data suggests that surrogate tracers may not adequately estimate pharmacokinetics of locally delivered therapeutic compounds. If chemically possible, PET-imaging affords a more representative assessment of drug kinetics which would be more beneficial in defining dosing and scheduling. Our findings demonstrate the feasibility of designing theranostic compounds that are suitable for accurate pharmacokinetic monitoring with CED.

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Introduction: Convection enhanced delivery (CED) has been recently explored as an advantageous therapeutic strategy for central nervous system (CNS) tumors. One current limitation is the inability to quantitatively monitor distribution of chemotherapeutic agents. The use of surrogate tracers probably underestimates differences in distribution and clearance owing to discordant features between contrast molecules and therapeutic agents, including bioactivity, degradation, conductivity, and diffusivity. Ideally, direct labelling of a therapeutic compound would eliminate these concerns and afford a noninvasive method to monitor critical pharmacokinetic information. This ability would pave the way for designing infusion parameters and drug schedules that are expected to be unique for CED-based therapy. Methods: The small molecule kinase inhibitor dasatinib was modified with a dual-probe technology that utilizes a boronate trap to conjugate 18[F] with a near-infrared fluorophore into a single molecule, 1, allowing for visualization by positron emission tomography (PET) and near-infrared fluorescence (NIRF). The novel boronate trap allows for direct conjugation of 18[F] with minimal disruption of dasatinib's mechanism of action, resulting in a small, versatile probe with potential for other clinically relevant targets. Results: The modified drug was first tested in vitro in a PDGF-B driven p53 deficient DIPG tumor line from Nestin tv-a; p53 floxed mouse. 1 was shown to enter cells on fluorescence microscopy and inhibit cell proliferation. Antagonist drug potency of 1 as evaluated on pontine glioma in ATP-dependent luminescent cell viability, cell-permeant calcein AM, and an MTS cell proliferation assays show that the IC50, of 1 is ∼10nM. In addition, infusions of 1 were performed via CED and intravenous systemic delivery in a RCAS/tv-a PDGF-B driven with p53 deficiency Ntv-a mouse model of high-grade glioma. Compared to systemic delivery, CED was shown to be roughly 230 times more effective in delivery of the infusion to the tumor site. Maximal glioma delivery occurred at 115 min post a 20 min infusion, with clearance occurring with a half-life of 45 min after maximum delivery. Conclusion: Dasatinib was modified to give 1, an agent that can be imaged non-invasively by fluorescence and positron emission tomography (PET). The modified dasatinib showed little modification in biologic activity when compared to unmodified dasatinib and exhibited cytotoxic effects in vitro in glioma cell culture. CED shows a clear benefit to intravenous delivery when the target site is in the CNS. The dual-label probe technology's versatility and minimal biologic profile lends itself to various clinical uses, including the study of different therapeutic agents and delivery routes without the need to rely on surrogate tracers. Citation Format: Melinda Wang, Zhiping Zhou, Hari Krishna Kommidi, Melanie Schweitzer, Mark Chan, Yue Linda Wu, Ranjodh Singh, Richard Ting, Mark M. Souweidane. Intra-cerebral pharmacokinetic monitoring of a tyrosine kinase inhibitor (theranostic 18[F]-PET/NIRF labeled dasatinib) delivered via convection-enhanced delivery. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1367.