Contributed Talk

Androgen receptor signaling inhibition enables biophysical changes in prostate cancer associated with increased metastatic potential

Clayton Molter, Taisei Fu, Dongyue Xie, Ke Du, Samina Vafi, Allen Ehrlicher

Department of Bioengineering, McGill University, Montreal, Canada

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Prostate cancer (PCa) is a common health hazard for men that displays androgen-dependent growth at early stages through signaling mediated by the Androgen Receptor (AR). This has inspired androgen deprivation therapy (ADT) - a technique which interferes with the AR signaling axis - to be the gold standard treatment. However, in later stages, PCa displays a transition to androgen-independence and loss of AR, accompanied by a drastic increase in invasiveness and metastasis. Critically, both the loss of AR and ADT have been shown to induce PCa invasiveness by promoting the epithelial-to-mesenchymal transition (EMT) which has been associated with biophysical changes in other cell models. Indeed, during metastasis, cancers cells change their biophysical properties to facilitate migration through crowded microenvironments, namely in the form of reduced cell stiffness and increased contractility. Given AR’s essential role in mediating PCa progression, we suspect that AR signaling may also regulate mechanical transitions required for PCa metastasis and directed cell migration over the course of long-term ADT.

In this study, we quantify changes in PCa biophysics under long-term ADT in terms of cell contractility, motility, and nuclear stiffness. We model the progression of PCa and therapy resistance under ADT pressure from two directions by: (i) using lowly-metastatic AR-positive/androgen-dependent PCa cells (LNCaP), and (ii) using a highly metastatic, AR-negative PCa cells (PC3) stably re-expressing GFP-labelled AR. First, we applied traction force microscopy to quantify changes in cell contractility and monitored cell motility under androgen-supplemented conditions, and androgen-deprived conditions by treating with AR inhibitor enzalutamide. We find that AR expression suppresses androgen-induced contractile and migratory effects in AR-positive cell lines, whereas androgen-deprivation uniquely induces contractility in AR-positive cells. These findings support previous demonstrations that ADT induces EMT only in AR-positive cell lines.

Next, we quantified nuclear stiffness conditions using osmotic compression. As the stiffest organelle, the nucleus is a key determinant mediating invasiveness. Interestingly, although nuclear softening is seen in a variety of metastatic cancer types, some studies have suggested androgen-sensitive PCa deviates from this trend. One significant factor determining nuclear stiffness is chromatin condensation, which we can also conveniently use as a proxy for transcriptional activity. We find that chromatin condensation tends to increase in cells undergoing enzalutamide treatment where AR nuclear localization is restricted. Notably, we also identify a clear increase in nuclear stiffness in enzalutamide-treated AR-positive cells. These results are consistent with previous studies suggesting nuclear stiffening during metastatic PCa progression, and we show this deviation may in part be due to AR- or ADT-driven changes in chromatin state. Altogether, this study suggests contractility, motility, and nuclear stiffness are sensitive to both androgen availability and AR expression.