Nanoscale Metal-Organic Framework with an X-ray Triggerable Prodrug for Synergistic Radiotherapy and Chemotherapy

Abstract

As heavy-metal-based nanoscale metal-organic frameworks (nMOFs) are excellent radiosensitizers for radiotherapy via enhanced energy deposition and reactive oxygen species (ROS) generation, we hypothesize that nMOFs with covalently conjugated and X-ray triggerable prodrugs can harness the ROS for on-demand release of chemotherapeutics for chemoradiotherapy. Herein, we report the design of a novel nMOF, Hf-TP-SN, with an X-ray-triggerable 7-ethyl-10-hydroxycamptothecin (SN38) prodrug for synergistic radiotherapy and chemotherapy. Upon X-ray irradiation, electron-dense Hf₁₂ secondary building units serve as radiosensitizers to enhance hydroxyl radical generation for the triggered release of SN38 via hydroxylation of the 3,5-dimethoxylbenzyl carbonate followed by 1,4-elimination, leading to 5-fold higher release of SN38 from Hf-TP-SN than its molecular counterpart. As a result, Hf-TP-SN plus radiation induces significant cytotoxicity to cancer cells and efficiently inhibits tumor growth in colon and breast cancer mouse models.

Figure 1

Synthesis of Hf-TP-OH nMOF and its postsynthetic modification with SN38 to afford Hf-TP-SN nMOF along with the proposed mechanism for X-ray triggered release of SN38 from Hf-TP-SN.

Figure 2

(a) TEM image and (b) HRTEM image and FFT pattern (inset) of Hf-TP-OH. (c) TEM image of Hf-TP-SN. Scale bar: 50 nm. (d) Number-averaged sizes of Hf-TP-OH and Hf-TP-SN. (e) PXRD patterns of Hf-TP-OH, Hf-TP-SN and simulated pattern for Hf₁₂-TP MOF. (f) UV–vis spectra of SN38, H₂TP-OH, and digested Hf-TP-SN in dimethyl sulfoxide.

Figure 3

Relative fluorescence intensity (RFI) of (a) DCF and (b) APF indicating total ROS signals and hydroxyl radical signals, respectively, from PBS, Hf-TP-OH, and Hf-TP-SN with different X-ray doses, n = 6. Hf concentration was 40 μM. SN38 released from MeO-SN or Hf-TP-SN after 10 Gy X-ray irradiation (c) or reacting with ·OH generated by the Fenton reaction (d). Starting MeO-SN or Hf-TP-SN concentration was 100 μM.

Figure 4

Survival fractions of (a) CT26, (b) 4T1, and (c) MC38 cells after incubation with PBS, Hf-TP-OH, or Hf-TP-SN under different X-ray doses. (d) Time-dependent cellular uptake of Hf-TP-SN quantified by ICP-MS (n = 3). (e) CLSM images of CT26 cells stained by DCFH-DA (green) and Hoechst 33342 (blue, cell nucleus) for ROS detection (scale bar: 50 μm). (f) Relative intracellular ROS signals (n = 3). (g) CLSM images of CT26 cells stained by γ-H2AX (scale bar: 10 μm). (h) Relative γ-H2AX⁺ cells (n = 3). (i) Representative flow cytometry dot plots showing cell apoptosis/death stained with FITC-annexin-V and PI in different treatment groups. The X-ray dose is 3 Gy in (e)–(i).

Figure 5

(a) Growth curves, (b) end point weights (day 19), and (c) photos of CT26 tumors in BALB/c mice after treatment with PBS, irinotecan, Hf-TP-OH, or Hf-TP-SN followed by X-ray irradiation. (d) Growth curves, (e) end point weights (day 21), and (f) photos of 4T1 tumors in BALB/c mice after different treatments. n = 5. Black arrows indicate nMOF injection whereas red arrows indicate irradiation. (g) γ-H2AX, (h) Ki67, (i) TUNEL and (j) H&E staining of excised CT26 tumors (scale bar: 50 μm).