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

Abstract

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.

Nanoparticle conjugates of a highly potent toxin enhance safety and circumvent platinum resistance in ovarian cancer

“…Additionally, they have generally relied on drug encapsulation as opposed to chemical conjugation; as a result, these NPs have displayed continuous drug release during their intravascular circulation 10 , which has led to persistent off-target side effects with only mild increases in efficacy 13 . While there are numerous examples of NP-drug conjugates in the literature, to date these formulations have also utilized either conventional or experimental small molecules with similar antitumor activities (i.e., 10–500 nM IC 50 s) 14 , 15 . As only 1–2 wt% of the injected NP dose is typically delivered to tumors after intravenous (IV) administration 16 , large amounts of carrier material are required for therapeutic efficacy, which has, hitherto, stymied clinical translation and/or induced material toxicities.…”

Lipid and Polymer-Based Nanoparticle siRNA Delivery Systems for Cancer Therapy

“…In vitro experiments showed strong downregulation of Bcl-2 mRNA levels in MCF-7 and OVCAR-4 breast cancer cell lines. In addition, this formulation induced cell death was up to 100-fold more efficient than the free drugs in all the cancer cell lines tested [70]. However, these NPs were not tested in murine tumor models.…”

Microneedles loaded with anti-PD-1–cisplatin nanoparticles for synergistic cancer immuno-chemotherapy

“…Clinical studies demonstrated that stromal fibroblasts in the tumor microenvironment confer cis-diammineplatinum(II) (CDDP) chemo-resistance, and CD8+ T cells abolish the cancer-associated fibroblast-mediated chemo-resistance through CD8+ T-cell-derived interferon (IFN)-γ (a major effector cytokine of CD8+ T-cell), which reveals the interplay between chemotherapy and immunotherapy. [10][11][12] The clonal expansion of T-cells in the tumor microenvironment correlates with a better response to chemotherapy; 13 therefore, the effectiveness of chemotherapy relies on the induction of a durable anticancer immune response. 14,15 Pre-existing CD8+ T-cells in the tumor microenvironment also predict the efficacy of aPD-1 therapy.…”