Samuel G. Awuah

Singlet Oxygen Generation by Novel NIR BODIPY Dyes

Five novel near-infrared BODIPY dyes were prepared for improved singlet oxygen generation using thiophene and bromine. Theoretical, optical, photostable, and singlet oxygen generation characteristics of these dyes were assessed. Predicted excitation energies by TDDFT calculations were in good agreement (ΔE ≈ 0.06 eV) with experimental data. All five dyes showed both excitation and emission in the NIR range. In particular, two dyes having sulfur and bromine atoms showed efficient singlet oxygen generation with high photostability.

Tobacco Mosaic Virus Delivery of Phenanthriplatin for Cancer therapy

Phenanthriplatin, cis-[Pt(NH3)2Cl(phenanthridine)](NO3), is a cationic monofunctional DNA-binding platinum(II) anticancer drug candidate with unusual potency and cellular response profiles. Its in vivo efficacy has not yet been demonstrated, highlighting the need for a delivery system. Here we report tobacco mosaic virus (TMV) as a delivery system for phenanthriplatin. TMV forms hollow nanotubes with a polyanionic interior surface; capitalizing on this native structure, we developed a one-step phenanthriplatin loading protocol. Phenanthriplatin release from the carrier is induced in acidic environments. This delivery system, designated PhenPt-TMV, exhibits matched efficacy in a cancer cell panel compared to free phenanthriplatin. In vivo tumor delivery and efficacy were confirmed by using a mouse model of triple negative breast cancer. Tumors treated with PhenPt-TMV were 4× smaller than tumors treated with free phenanthriplatin or cisplatin, owing to increased accumulation of phenanthriplatin within the tumor tissue. The biology-derived TMV delivery system may facilitate translation of phenanthriplatin into the clinic.

Visible Light Controlled Release of Anticancer Drug through Double Activation of Prodrug.

We designed and synthesized a novel double activatable prodrug system (drug-linker-deactivated photosensitizer), containing a photocleavable aminoacrylate-linker and a deactivated photosensitizer, to achieve the spatiotemporally controlled release of parent drugs using visible light. Three prodrugs of CA-4, SN-38, and coumarin were prepared to demonstrate the activation of deactivated photosensitizer by cellular esterase and the release of parent drugs by visible light (540 nm) via photounclick chemistry. Among these prodrugs, nontoxic coumarin prodrug was used to quantify the release of parent drug in live cells. About 99% coumarin was released from the coumarin prodrug after 24 h of incubation with MCF-7 cells followed by irradiation with low intensity visible light (8 mW/cm(2)) for 30 min. Less toxic prodrugs of CA-4 and SN-38 killed cancer cells as effectively as free drugs after the double activation.

Necroptosis-inducing rhenium(V) oxo complexes.

Rhenium(V) oxo complexes of general formula [ReO(OMe)(N^N)Cl2], where N^N = 4,7-diphenyl-1,10-phenanthroline, 1, or 3,4,7,8-tetramethyl-1,10-phenanthroline, 2, effectively kill cancer cells by triggering necroptosis, a non-apoptotic form of cell death. Both complexes evoke necrosome (RIP1-RIP3)-dependent intracellular reactive oxygen species (ROS) production and propidium iodide uptake. The complexes also induce mitochondrial membrane potential depletion, a possible downstream effect of ROS production. Apparently, 1 and 2 are the first rhenium complexes to evoke cellular events consistent with programmed necrosis in cancer cells. Furthermore, 1 and 2 display low acute toxicity in C57BL/6 mice and reasonable stability in fresh human blood.

Thieno-Pyrrole-Fused 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene–Fullerene Dyads: Utilization of Near-Infrared Sensitizers for Ultrafast Charge Separation in Donor–Acceptor Systems

Donor-acceptor dyads featuring near-IR sensitizers derived from thieno-pyrrole-fused BODIPY (abbreviated as SBDPiR) and fullerene, C60 have been newly synthesized and characterized. Occurrence of ultrafast photoinduced electron transfer (PET) leading to the formation of charge-separated state in these dyads, capable of harvesting light energy from the near-IR region, is established from femtosecond transient absorption studies.

Chemical Approach to Positional Isomers of Glucose–Platinum Conjugates Reveals Specific Cancer Targeting through Glucose-Transporter-Mediated Uptake in Vitro and in Vivo

Glycoconjugation is a promising strategy for specific targeting of cancer. In this study, we investigated the effect of d-glucose substitution position on the biological activity of glucose-platinum conjugates (Glc-Pts). We synthesized and characterized all possible positional isomers (C1α, C1β, C2, C3, C4, and C6) of a Glc-Pt. The synthetic routes presented here could, in principle, be extended to prepare glucose conjugates with different active ingredients, other than platinum. The biological activities of the compounds were evaluated both in vitro and in vivo. We discovered that varying the position of substitution of d-glucose alters not only the cellular uptake and cytotoxicity profile but also the GLUT1 specificity of resulting glycoconjugates, where GLUT1 is glucose transporter 1. The C1α- and C2-substituted Glc-Pts (1α and 2) accumulate in cancer cells most efficiently compared to the others, whereas the C3-Glc-Pt (3) is taken up least efficiently. Compounds 1α and 2 are more potent compared to 3 in DU145 cells. The α- and β-anomers of the C1-Glc-Pt also differ significantly in their cellular uptake and activity profiles. No significant differences in uptake of the Glc-Pts were observed in non-cancerous RWPE2 cells. The GLUT1 specificity of the Glc-Pts was evaluated by determining the cellular uptake in the absence and in the presence of the GLUT1 inhibitor cytochalasin B, and by comparing their anticancer activity in DU145 cells and a GLUT1 knockdown cell line. The results reveal that C2-substituted Glc-Pt 2 has the highest GLUT1-specific internalization, which also reflects the best cancer-targeting ability. In a syngeneic breast cancer mouse model overexpressing GLUT1, compound 2 showed antitumor efficacy and selective uptake in tumors with no observable toxicity. This study thus reveals the synthesis of all positional isomers of d-glucose substitution for platinum warheads with detailed glycotargeting characterization in cancer.

Maximizing Synergistic Activity When Combining RNAi and Platinum-Based Anticancer Agents

RNAi approaches have been widely combined with platinum-based anticancer agents to elucidate cellular responses and to target gene products that mediate acquired resistance. Recent work has demonstrated that platination of siRNA prior to transfection may negatively influence RNAi efficiency based on the position and sequence of its guanosine nucleosides. Here, we used detailed spectroscopic characterization to demonstrate rapid formation of Pt-guanosine adducts within 30 min after coincubation of oxaliplatin [OxaPt(II)] or cisplatin [CisPt(II)] with either guanosine monophosphate or B-cell lymphoma 2 (BCL-2) siRNA. After 3 h of exposure to these platinum(II) agents, >50% of BCL-2 siRNA transcripts were platinated and unable to effectively suppress mRNA levels. Platinum(IV) analogues [OxaPt(IV) or CisPt(IV)] did not form Pt-siRNA adducts but did display decreased in vitro uptake and reduced potency. To overcome these challenges, we utilized biodegradable methoxyl-poly(ethylene glycol)-block-poly(ε-caprolactone)-block-poly(l-lysine) (mPEG-b-PCL-b-PLL) to generate self-assembled micelles that covalently conjugated OxaPt(IV) and/or electrostatically complexed siRNA. We then compared multiple strategies by which to combine BCL-2 siRNA with either OxaPt(II) or OxaPt(IV). Overall, we determined that the concentrations of siRNA (nM) and platinum(II)-based anticancer agents (μM) that are typically used for in vitro experiments led to rapid Pt-siRNA adduct formation and ineffective RNAi. Coincorporation of BCL-2 siRNA and platinum(IV) analogues in a single micelle enabled maximal suppression of BCL-2 mRNA levels (to <10% of baseline), augmented the intracellular levels of platinum (by ∼4×) and the numbers of resultant Pt-DNA adducts (by >5×), increased the cellular fractions that underwent apoptosis (by ∼4×), and enhanced the in vitro antiproliferative activity of the corresponding platinum(II) agent (by 10-100×, depending on the cancer cell line). When combining RNAi and platinum-based anticancer agents, this generalizable strategy may be adopted to maximize synergy during screening or for therapeutic delivery.

Repair shielding of platinum-DNA lesions in testicular germ cell tumors by high-mobility group box protein 4 imparts cisplatin hypersensitivity

Significance High-mobility group box protein 4 (HMGB4) is a transcription repressor preferentially expressed in the testes and binds cisplatin-damaged DNA. Investigating the DNA-damage recognition potential of HMGB4 and its relevance to cancer is of clinical importance. In this study, we found that HMGB4 regulates the sensitivity of testicular germ cell tumors (TGCTs) to cisplatin treatment. HMGB4 imparts repair shielding of platinum-DNA lesions in human TGCTs, rendering lesions inaccessible to the nucleotide excision repair (NER) machinery. Our results show that cisplatin-resistant breast cancer cells complemented with HMGB4 become sensitive to cisplatin. Furthermore, the ability of HMGB4 to modulate the cell cycle response, NER, apoptosis, and MAPK suggests a critical role for this protein in conveying cisplatin hypersensitivity in TGCTs. Cisplatin is the most commonly used anticancer drug for the treatment of testicular germ cell tumors (TGCTs). The hypersensitivity of TGCTs to cisplatin is a subject of widespread interest. Here, we show that high-mobility group box protein 4 (HMGB4), a protein preferentially expressed in testes, uniquely blocks excision repair of cisplatin-DNA adducts, 1,2-intrastrand cross-links, to potentiate the sensitivity of TGCTs to cisplatin therapy. We used CRISPR/Cas9-mediated gene editing to knockout the HMGB4 gene in a testicular human embryonic carcinoma and examined cellular responses. We find that loss of HMGB4 elicits resistance to cisplatin as evidenced by cell proliferation and apoptosis assays. We demonstrate that HMGB4 specifically inhibits repair of the major cisplatin-DNA adducts in TGCT cells by using the human TGCT excision repair system. Our findings also reveal characteristic HMGB4-dependent differences in cell cycle progression following cisplatin treatment. Collectively, these data provide convincing evidence that HMGB4 plays a major role in sensitizing TGCTs to cisplatin, consistent with shielding of platinum-DNA adducts from excision repair.