Chemoresistance is a major factor driving cancer recurrence. This study investigated the potential of zebularine, a dual cytidine deaminase (CDA)/epigenetic inhibitor, to circumvent gemcitabine-resistance in pancreatic cancer using a nanomedicine co-delivery approach. The mRNA expression of key metabolic enzymes, including CDA for gemcitabine deactivation in a gemcitabine-resistant cell line Gr2000 and its parental MIA PaCa-2 was compared using quantitative reverse transcription polymerase chain reaction. A highly gemcitabine-resistant population (HRP) in Gr2000 were characterised for their growth pattern, β-galactosidase activity (a hallmark of senescence) and chemosensitivity to zebularine after isolation. The CDA inhibition effects of zebularine on the intracellular gemcitabine accumulation and pharmacokinetics in rats when co-delivered with pH-sensitive liposomes (pSL) were investigated. Gr2000 had a 3-time upregulated mRNA expression and enzyme activity for CDA. The HRP (28% of bulk Gr2000) were predominately senescent cells which re-proliferated following a growth arrest for a week. Zebularine suppressed the regrowth of senescent cells, meanwhile enhanced cellular gemcitabine concentration by 2-fold. When co-delivered with pSL, zebularine increased cellular gemcitabine concentration by 4-fold, and extended the half-life of gemcitabine in plasma by 22-fold in rats. In conclusion, multiple mechanisms including therapy-induced senescence were identified with gemcitabine-resistance. Co-delivery of zebularine using liposomes could provide multifaceted benefits in gemcitabine therapy for pancreatic cancer treatment.

化学抗性是驱动癌症复发的主要因素。这项研究使用纳米药物共同给药方法研究了双胞苷脱氨酶（CDA）/表观遗传抑制剂zebularine在胰腺癌中规避吉西他滨耐药的潜力。使用定量逆转录聚合酶链反应比较了吉西他滨耐药细胞系Gr2000和其亲本MIA PaCa-2中关键代谢酶（包括用于吉西他滨失活的CDA）的mRNA表达。分离后，Gr2000中具有高度吉西他滨耐药性的种群（HRP）的特征在于它们的生长方式，β-半乳糖苷酶活性（衰老的标志）和对zebularine的化学敏感性。研究了zebularine与pH敏感脂质体（pSL）共同递送时对大鼠胞内吉西他滨积累和药代动力学的CDA抑制作用。Gr2000对CDA具有3倍上调的mRNA表达和酶活性。HRP（占Gr2000总量的28％）主要是衰老细胞，在生长停滞一周后会重新增殖。Zebularine抑制衰老细胞的再生，同时将细胞吉西他滨浓度提高2倍。当与pSL共同给药时，zebularine使大鼠吉西他滨的细胞浓度增加4倍，而吉西他滨在血浆中的半衰期延长22倍。总之，吉西他滨耐药可鉴定多种机制，包括治疗引起的衰老。