Explore efflux transporter-associated chemoresistance using a chemical biology approach and develop efflux resistant TOPO I inhibitors as ADC payloads

抗体-药物缀合物（ADC）是一类新兴的癌症治疗剂，其由经由接头连接至细胞毒性药物的单克隆抗体（mAb）组成。抗体组分通过与特定细胞表面抗原结合来确定ADC的特异性，从而允许选择性靶向某些细胞类型1。相对于常规化疗药物，ADC的主要优势是治疗窗口增加，因为抗体的细胞靶向特性降低了脱靶毒性2。迄今为止，FDA已经批准了11种ADC，其中大多数被批准用于治疗液体肿瘤，只有3种ADC被批准用于实体肿瘤。适当选择有效载荷对于开发用于临床开发的成功ADC至关重要3。可开发性问题，如外排倾向、非选择性毒性、耐药性、现有有效载荷的不良药代动力学和药效学特征，导致临床开发失败。目前临床评价中的大多数ADC使用微管抑制剂或DNA损伤剂作为有效载荷，但最近由于Trodelvy R和Enhertu R分别使用拓扑异构酶抑制剂SN-38和Dxd作为有效载荷（图1），大量具有拓扑异构酶I（TOPO I）抑制剂的ADC已进入临床开发4。喜树碱及其衍生物与TOPO 1/DNA复合物结合以防止再退火，再退火可由于部分切割的DNA 5的积累而导致细胞死亡。SN-38和Dxd都是喜树碱类似物，由于与微管抑制剂和DNA结合剂相比尺寸相对较小且毒性较低，因此被视为下一代ADC有效载荷。然而，SN-38和Dxd都是P-gp和BCRP外排泵的外排底物，这降低了它们的有效性，导致非选择性毒性，通常导致化疗耐药性，特别是在癌症干细胞中6，7。伦敦国王学院的Rahman实验室开发了一种专有的外排阻力阻断剂（ERB）技术，该技术允许对化学支架进行修饰，以降低其外排敏感性，同时保持靶向活性（图2）8，9。这增加了细胞内药物的浓度，可以克服耐药性，降低耐药性出现的可能性。这个博士项目的目的是探索使用化学生物学方法的外排转运蛋白相关的耐药现象，并产生ERB修饰的TOPO I抑制剂，可以进一步开发为ADC有效载荷。

Antibody-drug conjugates (ADCs) are an emerging class of cancer therapeutics that consist of a monoclonal antibody (mAb) connected to a cytotoxic drug via a linker. The antibody component determines the specificity of the ADC by binding to specific cell surface antigens, allowing selective targeting of certain cell types1. The main advantage of ADCs relative to conventional chemotherapeutics is an increased therapeutic window since the cell-targeting properties of antibodies decrease off-target toxicity2. The FDA has approved 11 ADCs to date with majority of them approved for the treatment of liquid tumours and only 3 ADCs have been approved for solid tumours. An appropriate choice of payload is critical to developing a successful ADC for clinical development3. Developability problems such as efflux liability, non-selective toxicity, chemoresistance, poor pharmacokinetic and pharmacodynamic profiles of existing payloads are leading to failures in clinical development. The majority of ADCs currently in clinical evaluation use microtubule inhibitors or DNA damaging agents as the payload, but more recently a significant number of ADCs with Topoisomerase I (TOPO I) inhibitors have entered clinical development due to the approval of Trodelvy R and Enhertu R which utilise Topoisomerase inhibitors SN-38 and Dxd as payloads (Figure 1), respectively4. Camptothecin and its derivatives bind to the TOPO 1/DNA complex to prevent reannealing, which can cause cell death due to the accumulation of partially cleaved DNA5. Both SN-38 and Dxd are Camptothecin analogues and are considered as next generation ADC payloads due to their relatively small-size and lower toxicity compared to microtubule inhibitors and DNA binding agents. However, both SN-38 and Dxd are efflux substrates of P-gp and BCRP efflux pumps which reduces their effectiveness, causing non-selective toxicity and often leading to chemoresistance particularly in cancer stem cells6,7. The Rahman lab at King's College London has developed a proprietary Efflux Resistance Breaker (ERB) Technology that allows modification of chemical scaffolds to reduce their efflux susceptibility while maintaining the on-target activity (Figure 2)8,9. This increases the intracellular concentration of the drugs which can overcome chemoresistance and reduce the likelihood of resistance emergence.The aim of this PhD project is to explore the phenomenon of efflux transporter-associated resistance using a chemical biology approach and produce ERB-modified TOPO I inhibitors that can be further developed as ADC payloads.