Design of extended bisphosphonate-based coordination polymers as bone-targeted drug delivery systems for breast cancer-induced osteolytic metastases and other bone therapies.

Abstract

Extended bisphosphonate-based coordination complexes (BPCCs) were produced when benzene-1,4-bis(bisphosphonic acid); BBPA, 1,1' -biphenyl-4,4' -bisphosphonic acid; BPBPA, and 2,2' -bipyridine-5,5' -bisphosphonic acid; 2,2' -BPBPA, the bisphosphonates (BPs) analogues of benzene 1,4-dicarboxylic acid (BDC), 1,1' -biphenyl-4,4' -dicarboxylic acid (BPDC), and 2,2' -bipyridine-5,5' -dicarboxylic acid (2,2' -BPDCA), respectively, reacted with bioactive metals (Ca²⁺, Zn²⁺, and Mg²⁺). Different distinct BBPA, BPBPA, and 2,2' BPBPA-based BPCCs crystalline phases were obtained, namely, BBPA-Ca forms I and II, BBPA-Zn form I, BBPA-Mg form I, BPBPA-Ca, BPBPA-Zn, BPBPA-Mg, 2,2' -BPBPA-Ca, 2,2' -BPBPA-Zn, and 2,2' -BPBPA-Mg. Among these, BBPA-Ca forms I (7 x 9 Å) and II (8 x 12 Å), BPBPA-Ca (11 x 12 Å), BPBPA-Zn (10 x 13 Å), and BPBPA-Mg (8 x 11 Å), and 2,2' -BPBPA-Ca (9 x 11 Å) possessed channels adequate for the encapsulation of 5-fluorouracil(5-FU) and letrozole (LET), antineoplastic drugs that combined with BPs threats breast cancer-induced osteolytic metastases (OM). Dissolution curves in phosphate-buffered saline (PBS, pH = 7.4) and fasted-state simulated gastric fluid (FaSSGF, pH = 1.6) demonstrate the pH-dependent degradation of BBPA-Ca form II, BPBPA-Ca, 2,2' -BPBPA-Ca. These results show that the structure of BBPA-Ca form II, BPBPA-Ca, and 2,2' -BPBPA are preserved in PBS, with ~10% release of BBPA, BPBPA, and 2,2' -BPBPA from these <em>3D</em> frameworks, while in FaSSGF, BBPA-Ca form II, BPBPA-Ca, and 2,2' -BPBPA can collapse almost entirely (90-100% release of the BPs). The PIT-nano-emulsion method enabled the particle size reduction of BBPA-Ca form II, BPBPA-Ca, and 2,2' -BPBPA-Ca, leading to nano-Ca@BBPA (~134 d.nm), nano-Ca@BPBPA (~160 d. nm), and nano-Ca@2,2' -BPBPA (~288 d. nm), respectively. Binding assays showed a significantly higher affinity (>1.4x) of these materials to hydroxyapatite (HA) when compared to commercial BPs such as alendronic (ALEN), zoledronic (ZOLE), and risedronic (RISE) acids. Furthermore, both BBPA-Ca form II and nano-Ca@BBPA presented comparable drug-loading and release (~ 30 wt. % 5-FU) relative to BDC-based CCs (UiO-66, MIL-53, and BDC-Zr) under similar conditions. It was found that the amount of LET encapsulated and released (~20 wt. %) and BPBPA-Ca and nano-Ca@BPBPA were comparable to BPDC-based CCs (e.i. UiO-67-(NH₂)₂, BPDC-Zr, bio-MOF-1), where antineoplastic drugs (pemetrexed and Ru-90) were loaded and release in simulated aqueous media. The 2,2' -BPBPA-Ca and nano-Ca@2,2' BPBPA demonstrate similar loading and release of LET (~20 wt. %) than BPBPA-Ca and nano-Ca@BPBPA, which might be due to the similitudes in their crystal habits. Cell viability assays show that at a 100 μM, the drug-loaded nano-Ca@BBPA demonstrates higher cytotoxicity in the breast cancer cell line MDA-MB-231 when compared to 5-FU (%RCV = 8 ± 5 % vs. 75 ± 1 %) after 72h. The drug-loaded nano-Ca@BPBPA exhibits higher cytotoxicity against breast cancer MCF-7 and MDA-MB-231 cells (%RCV = 20 ± 1 and 45 ± 4 %) compared with LET (%RCV = 70 ± 1 and 99 ± 1 %) at 12.5 μM after 72 h. At this same concentration of 12.5 μM, the drug-loaded nano-Ca@2,2' -BPBPA show higher cytotoxicity against breast cancer cells such as MCF-7 and MDA-MB-231 cells (%RCV = 37 ± 2 % and 56 ± 2 %) contrasted with LET in (% RCV = 68 ± 2 %) and 100 ± 1%) μM after 72 h. At these concentrations, no significant cytotoxicity was found for the hFOB 1.19 cells treated with the drug-loaded materials (%RCV = 100 ± 1 %). Collectively, these results demonstrate the potential of nano-Ca@BPCCs as promising DDSs to treat OM or other bone-related diseases, as these present measurably higher affinities allowing bone-targeted drug delivery under acidic environments and affecting cytotoxicity on estrogen receptor-positive and triple-negative breast cancer cell lines, without significantly affecting normal osteoblast at the bone marrow.