Novel Pathways in the Control of Lineage Plasticity in Neuroendocrine Prostate Cancer

总结 对癌症靶向治疗的获得性耐药性是一个日益增长的未满足的临床需求。在前列腺癌（PCa）中， 下一代雄激素受体（AR）通路抑制剂的成功受到以下因素的阻碍： 抗药性的证据。在许多情况下，这种获得性抵抗涉及AR轴的重新激活， 几种不同的机制。然而，很明显，另一种耐药机制是 由前列腺癌细胞的重编程驱动，以经历谱系可塑性，从而采用AR非依赖性 状态并获得神经内分泌表型，这允许它们生长和存活并逃避AR治疗。 更有效和持续的AR靶向导致神经内分泌前列腺癌的发病率增加 （NEPC），其是一种极具侵袭性、高度增殖性和转移性的PCa变体。因此，我们认为， 了解控制NEPC分化的分子机制是一个迫切的未满足的临床需求。 我们的初步数据已确定蛋白激酶C（PKC）I/I作为一种新的肿瘤抑制剂在NEPC。我们 最近发表的数据表明，激酶PKCl/i在人类NEPC患者中下调， 损失促进代谢重编程，维持增加的增殖，以及表观遗传变化 所需的PCa细胞经历癌细胞可塑性向NEPC分化。PKCl/i结果的丢失 丝氨酸和一碳途径代谢的上调，导致S- 腺苷甲硫氨酸（SAM），其是DNA和组蛋白甲基化的甲基供体。我们新的未出版的 数据表明，PKCl/i除了对SAM的产生至关重要外，还直接调节DNMT 1， EZH 2是利用SAM的关键甲基转移酶，是最终的染色质修饰剂。所以我们的 总体假设是PKCl/i不仅通过调节SAM的产生，还通过调节表观遗传修饰剂， 在NEPC分化过程中PCa基因组的突变产生了新的脆弱性，可以在治疗上加以利用。 本文将探讨三个关键问题：（目的1）PKCl/i介导的磷酸化是如何在细胞内发生的？ 控制NEPC分化过程中EZH 2和DNMT 1的功能？(Aim 2）DNMT 1和EZH 2如何- PKCl/i下游的依赖性表观遗传重编程有助于获得不同的NEPC 特质(Aim 3）PHGDH（丝氨酸生物合成中的限制酶）抑制是单独的还是与 表观遗传抑制剂是治疗NEPC肿瘤的有效方法吗？圆满完成 这一建议将使我们能够进一步了解控制谱系的分子机制。 在NEPC分化过程中的可塑性，并帮助识别新的脆弱性，可能导致新的 治疗这种致命的前列腺癌。

SUMMARY Acquired resistance to targeted therapies in cancer is a rising unmet clinical need. In prostate cancer (PCa), the success of next-generation androgen receptor (AR) pathway inhibitors have been hampered by the development of drug resistance. This acquired resistance involves, in many cases, the reactivation of the AR axis through several different mechanisms. However, it has become apparent that an alternative mechanism of resistance is driven by the reprogramming of prostate cancer cells to undergo lineage plasticity to adopt an AR-independent state and to acquire a neuroendocrine phenotype, that allow them to grow and survive and escape AR-therapy. More potent and sustained AR targeting has driven an increased incidence of neuroendocrine prostate cancer (NEPC), which is an extremely aggressive, highly proliferative and metastatic PCa variant. Therefore, understanding the molecular mechanisms that govern NEPC differentiation is a pressing unmet clinical need. Our preliminary data have identified protein kinase C (PKC)l/i as a novel tumor suppressor in NEPC. Our recently published data demonstrate that the kinase PKCl/i is downregulated in human NEPC patients, and its loss promotes a metabolic reprogramming that sustains increased proliferation, as well as epigenetic changes needed by PCa cells to undergo cancer cell plasticity towards NEPC differentiation. The loss of PKCl/i results in the upregulation of the serine and one-carbon pathway metabolism that leads to increased production of S- adenosine methionine (SAM), which is the methyl donor for DNA and histone methylation. Our new unpublished data demonstrate that PKCl/i, in addition to be critical to produce SAM, also directly regulates DNMT1 and EZH2, key methyltransferases that utilize SAM, and are the ultimate chromatin modifiers. Therefore, our overarching hypothesis is that PKCl/i by regulating not only SAM generation but also the epigenetic modifiers of the PCa genome during NEPC differentiation creates new vulnerabilities that can be exploited therapeutically. Three key questions will be addressed in this proposal: (Aim 1) How does PKCl/i-mediated phosphorylation control EZH2 and DNMT1 functions during NEPC differentiation? (Aim 2) How does DNMT1 and EZH2- dependent epigenetic reprogramming downstream of PKCl/i contribute to the acquisition of the different NEPC traits? (Aim 3) Is PHGDH (the limiting enzyme in serine biosynthesis) inhibition alone or in combination with epigenetic inhibitors an effective therapeutic approach for treating NEPC tumors? The successful completion of this proposal will allow us to advance our understanding of the molecular mechanisms governing lineage plasticity during NEPC differentiation and help in the identification of new vulnerabilities that could lead to novel therapies in this lethal PCa.