(556g) Filomicelles Self-Assembled from Degradable Di-Block Copolymers Deliver Retinoids and Chemotherapeutics in Durable Control of Carcinoma Cell Fate

Introduction: Conventional injection of semi-soluble drugs hit both healthy and tumor cells, causing side effects that limit dose. While this approach might be broadened with nanocarriers (such as flexible cylindrical micelles or filomicelles that have been previously shown to circulate longer and accumulate better in vivo [1]), the lack of aromatic groups in the core of the nanoparticles may hamper it from reaching peak loading of common aromatic chemotherapeutics.

Results 1: In order to improve the delivery of aromatic drugs in filomicelles, aromatic groups were integrated into the hydrophobic block of a degradable di-block copolymer. Aromatic filomicelles were formed by self-assembly of biodegradable amphiphilic di-block copolymer polyethylene glycol- poly-α-benzyl caprolactone (PEG-PBCL) with suitable block ratios. and loaded with a common chemotherapeutic, Paclitaxel. Aromatic filomicelles loaded more Paclitaxel than analogous aliphatic systems. Cell death and the aneuploidy in surviving cells (which indicates toxicity) were higher in both liver and lung carcinoma lines in vitro compared to aliphatic filomicelles. Importantly, the filomicelles themselves were bio-compatible and led to minimal cell death. Initial tests in vivo also suggested more potent tumor shrinkage, with minimal effects on thrombocrit and hematocrit.

Thus, aromatic filomicelles demonstrated a marked an improvement over the corresponding aliphatic nano-carriers [2]. However, despite inducing higher levels of aneuploidy in surviving cancer cells, the cells reverted back to the original proliferative state over several periods of the normal cell cycle. This is consistent with relapse commonly seen clinic. Retinoic acid (RA) and other retinoids regulate RA receptor transcription factors that induce differentiation and arrest proliferation of many cell types, including cancer cells [3]. Combining RA with select chemotherapeutics has produced durable cures of select cancers, notably pro-myeloblastic leukemia (PML) where RA differentiates cells while chemotherapeutic kills the cancer stem cell [4].

Results 2: The above mentioned filomicelles were loaded with Paclitaxel, as well as RA, for testing effects on cancer cell lines in vitro and in vivo. Across multiple liver and lung carcinoma lines, we find dual treatment with RA plus Paclitaxel increases, aneuploidy, Lamin-A (a marker of differentiation) levels and cell death beyond those achieved by either drug single-handedly, with effects being durable. A month after treatment, relapse rates are low for RA-Paclitaxel treated cells (15%), compared to almost all (92%) for cells treated with Paclitaxel alone. Decreases in levels of key cell cycle factor Cyclin-D1 and particularly proliferation marker Ki-67 help clarify the basis for drug synergy. These effects are greatly enhanced by loading the drugs into filomicelles. Co-loading the drugs into filomicelles lead to a more potent system compared to separate loading, with no loss in the integration efficiency of drugs. Notably, relapse rates were ~2% three months after treatment, highlighting the improvement offered by nano-carriers. Ki-67 was the key affected protein, with levels half of those in free RA-Paclitaxel treated cells. Preliminary tests in vivo demonstrate sustained delivery for days as well as efficacy in shrinking tumors. Injections of RA-Paclitaxel combination are able to shrink tumors and arrest growth for over 15 days, a feat not achieved by Paclitaxel alone [2].

Conclusion: The above results highlight the irreversible synergy of killing cancerous cells while driving differentiation. Filomicelles accumulate better in tumors, thus increasing the efficacy of delivery and hence the treatment. The overall result is a system that efficiently delivers drugs to the tumor that leads to higher cell death, while arresting proliferation in surviving ones.

References:

1. Geng Y, Dalhaimer P, Cai S, Tsai R, Tewari M, Minko T, Discher DE. Shape effects of filaments versus spherical particles in flow and drug delivery. Nature Nanotechnology. 2(4), 249-255 (2007).
2. D. Christian, S. Cai, O. Garbuzenko, T. Harada, A. Zajac, T. Minko, and D. Discher Mol. Pharmaceutics, 2009 (6) 1343-1352
3. R. Connolly, N. Nguyen, and S. Sukumar. Clinical Cancer Research 2013 (19) 1651-1659.
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