IT-141

试想，一款具有颠覆性功效的ADC诞生，会由怎样的技术革新所推定，究竟是更高毒性的有效载荷，还是更新型、适用范围更广、更多类型的靶向载体，抑或是更具创新意义的连接子技术？ 这对于不同专注领域的企业而言，答案或许有所不同。 但可以确认的是，尽管根据癌细胞类型选择最佳目标特异性抗体和有效载荷非常重要，但合适的Linker才是成功ADC的重要支柱。 而设计一款合适的linker，在蛋白质工程和药物传递系统中是一个复杂的过程，不仅需要考虑多个因素以确保linker的功能性和稳定性，并且在工艺生产方面同样需要考虑多种要素。 Linker 在偶联药物中的重要性 所谓linker，是ADC设计中必不可少的组件，是连接抗体和有效载荷的化学桥梁，其核心作用归根到底只有一点，即“确保偶联药物在血液循环中保持稳定，并在肿瘤细胞内化时有效地释放有效载荷”。 也正是因为有了linker，使得原有“靶向载体”效力较低与“有效载荷”高毒性副作用的缺点得以被补偿，使两者可以协同一起，显著扩大了其狭窄的治疗窗口。 简单来讲就是，linker的特性直接影响着偶联药物的治疗指数、疗效、安全性与药代动力学。 一般而言，越是稳定的linker其偶联药物在血液循环过程中就越不容易被释放，脱靶毒性也就越低，安全性也就越高。但同时，过于稳定的结构，也很可能直接影响靶向部位的释放程度，导致偶联药物的有效性不足。 因此，理想的linker就是偶联药物兼顾有效性与安全性的关键，其往往需要具备以下三个关键特征： 最佳稳定性：在保证血液循环过程中保持足够稳定，却又能在肿瘤细胞内或附近时能快速释放活性payloads。 高释放性：偶联药物到达靶肿瘤组织时，linker需要具有被快速裂解并释放毒性分子的能力。 高水溶性：疏水性连接基团和疏水性payloads通常会促进ADC小分子的聚集，从而引起免疫原性。 这种无法量化，需要根据不同设计需求，当稳则稳，当断则断才是linker发展的困难所在。 可裂解linker 与不可裂解linker 以目前linker的发展现状而言，其大致可以分为两种类型：可裂解型Linker和不可裂解型Liner。 就不可裂解Linker而言，其主要由抗蛋白酶降解的稳定键构成，特点是在血液中非常稳定，严格依赖ADC抗体成分被胞质和溶酶体蛋白酶完全降解，最终释放出与降解抗体衍生的氨基酸残基相连的payloa来杀伤癌细胞，然而带电荷的氨基酸复合物往往缺乏细胞渗透性，无法顺利穿过靶细胞膜的疏水性脂质双层，因此其原则上无法发挥旁观者效应。 而缺少了旁观者效应的加持，靶抗原阳性细胞周围低表达或阴性的癌细胞将难以得到有效的杀伤，使得治疗始终受限于肿瘤的异质性。因此该类型Linker的ADC适用范围相对有限，目前主要用于对高抗原表达肿瘤或血液肿瘤的治疗。 不过，在某些情况和有效载荷下，不可裂解的linker也同样会成为理想之选。比如免疫刺激剂和免疫调节剂等非细胞毒性药物作为有效载荷时，其主要附着在肿瘤或组织靶向抗体上，通过非可分解连接体。使用不可裂解连接体可将免疫反应定位在肿瘤或组织部位，防止有效载荷散失并引发大范围炎症或免疫抑制。 而针对可裂解Linker，其与不可裂解linker最大的区别在于，其在特定条件下能有效将药物释放到靶细胞处，而不需要依靠内吞环节。一般而言，可裂解linker的稳定性相对较差，更容易产生脱靶毒性，但其却能和更多类型的有效载荷一起使用，因此整体用途相对更广。 设计可裂解linker的核心条件在于利用其在血液系统与肿瘤细胞之间的环境差异，根据其适用范围又可细分为化学可裂解型linker、酶可裂解型linker与其他裂解型linker三大类。 第一代可裂解型linker： 化学可裂解型 化学可裂解型linker作为早期ADC疗法广泛使用的技术类型，推动了偶联药物领域的快速发展，根据其不同类型，可以分为酸裂解型linker、还原条件下裂解型linker与外源刺激裂解型linker三类。 1. 酸裂解型linker 酸可裂解型linker是利用肿瘤环境与血液循环之间的PH差异，在pH 7.4的生理条件下保持循环稳定性，却能在PH（4.0-5.0）的肿瘤微环境下有效释放，历史上第一款 ADC药物 Mylotarg（麦罗塔）采用的就是该项技术，由卡奇霉素通过一个包含腙键的酸可裂解Linker与Gemtuzumab偶联而成，虽然该类型ADC其最终平均药物抗体比（DAR）只有1.5，但也成功于2000年被FDA批准用于治疗急性髓系白血病（AML)。 之后，陆续还有Besponsa与Trodelvy等多款新药获批上市，但随着对该技术的研究与应用的广泛，酸裂解linker稳定性不足的局限性逐渐体现，最终导致其在ADC中应用中逐渐没落。 2. 还原条件下裂解型linker 虽然多款ADC疗法利用酸可裂解技术取得了成功，但理论上，严格区分pH 5和pH 7.4环境的要求过于苛刻，因此后续绝大多数ADC连接技术已不再选用酸裂解Linker。 后续，研究者发现，血浆和细胞质的还原条件似乎也可以为ADC选择性释放Payload提供机会，以二硫键为首的可还原linker开始出现，以二硫键为例，其具有还原型谷胱甘肽依赖性，与血浆（∼5μmol/L）中相比，细胞质中谷胱甘肽的水平较高（1–10 mmol/L），因此还原型二硫键连接子在血液循环中相对稳定，在细胞内谷胱甘肽还原裂解二硫键连接子以释放有效载荷。 3. 外源刺激可裂解型linker 与上述两款内源性裂解linker不同，外界刺激释放Payload虽然没有前者那么逻辑简单，但却能有效避免患者生物学差异所导致的裂解率不一，同时外源性可裂解linker也可以作为内源性裂解linker的补充措施，在内源性裂解不足以有效释放Payload时，使ADC也可以继续发挥作用。 该项技术中最显著的代表即已在日本上市的Akalux，其采用近红外光敏感的Linker，通过690 nm红光照射后释放毒性IRDye700发挥治疗作用，属于近红外光免疫疗法。除此之外，目前研究较多的有金属离子（Pt、Pd、Fe、Lu）催化裂解、UV/Vis和NIR光敏感的Linker。 第二代可裂解linker： 酶裂解型linker 与化学裂解型连接子不同，酶裂解的连接子在作用机制上是利用细胞中独特的高浓度水解酶来切割并释放药物，在控制药物释放方面较前面几种裂解linker优势更加明显。 而在临床应用方面，过去十年linker的研究重点多围绕着开发更稳定的酶可裂解型Linker，已上市的15款ADC中，有8款疗法均是酶可裂解型Linker。 表1. 上市ADC linker分类详情 linker类型 批准年份 商标名 原研公司 靶标 有效载荷 适应症 - 2020 Akalux Rakuten Medica EGFR IRDye700DX 头颈癌 不可裂型 2013 Kadcyla Genentech,Roche HER2 DM1 转移性乳腺癌 2020 Blenrep GlaxoSmithKline  (GSK) BCMA MMAF 多发性骨髓瘤 化学可裂型 2000(2017) Mylotarg Pfizer/Wyeth CD33 N-乙酰卡奇霉素 急性髓性白血病 2017 Besponsa Pfizer/Wyeth CD22 N-乙酰卡奇霉素 急性淋巴母细胞性、白血病 2020 Trodelvy ImmunoMedics TROP2 SN-38 转移性膀胱癌、转移性乳腺癌 2022 Elahere ImmunoGen FRa DM4 卵巢癌 酶可裂解型 2018 Lumoxit AstraZeneca CD22 PE38 毛细胞白血病 2019 Poivy Genentech,Roche CD79-b MMAE 弥漫大B细胞淋巴瘤 2019 Padcev Astellas/Seatte Genetics Nectin-4 MMAE 转移性尿路上皮癌 2021 Zynlonta ADC Therapeutics CD19 PBD B细胞淋巴瘤 2021 Aidix RemeGen(荣昌生物) HER2 MMAE 尿路上皮癌、转移性胃癌 2021 Tivdak Genmab/Seagen TF MMAE 转移性膀胱癌 2011 Adcetris Seattle GeneticsMilennium/Takeda CD30 MMAE 细胞淋巴瘤、霍奇金病、蕈样真菌病 2019 Enhertu AstraZeneca/DaiichSankyo HER2 喜树碱衍生物 转移性乳腺癌、转移性胃癌 数据来源：公开数据整理‌ 目前，酶裂解linker主要分类可有多肽类连接子与葡萄糖苷酶类连接子两大类，其中组织蛋白酶B的应用最为成功，目前上市的药物Adcetris、Polivy、Padcev、Tivdak、Aidixi、Lumoxiti、Zynlonta、Enhertu均是使用组织蛋白酶B裂解的多肽Linker。 其中，最具代表意义的应用疗法主要有Adcetris与Enhertu两者，前者作为领域开拓者，引领了后续技术研究，而Enhertu则是目前应用最成功的代表疗法。 Adcetris作为酶裂解型linker最显著的代表，是由抗CD30单克隆抗体通过蛋白酶可裂解linker（mc-VC-PABC）与微管破坏剂MMAE连接。Adcetris在肿瘤细胞内化后，可切割连接子降解，释放出的MMAE能破坏靶细胞并扩散到细胞膜上，到达并杀死邻近的癌细胞，有效发挥“旁观者效应”，允许释放的MMAE杀死CD30阳性和CD30阴性的肿瘤细胞。 目前，该药已在美国获得了七项适应症批准，自2011年在美国首次获批以来，已有超过55,000名患者接受了治疗，而在全球范围内则有超过140,000名患者接受了治疗。 图注：Adcetris结构示意图 图片来源： 爱医时空 Enhertu在连接子上，选择了更稳定与有效的四肽Gly-Gly-Phe-Gly连接子，在不含增溶剂的情况下，也能达到7.7DAR值，实属罕见，毕竟这与之前广泛确立的原理相矛盾，即高DAR结合物可能具有较差的药代动力学特征。 DS-8201a能够在体内有效地将DXd输送到异质性肿瘤中，并显示出很高的治疗效果。在转移性HER2阳性乳腺癌的III期临床研究中，DS-8201a成功地与T-DM1进行了比较，并最终于2019年12月底获得FDA批准。 图注：Enhertu结构示意图 图片来源： 爱医时空 而国内领域，恒瑞医药的SHR-A1811连接子的结构与Enhertu连接子结构基本相同，但却又在Enhertu的基础上做了创新设计即在有效载荷与连接子临近处引入了一个环丙基，这不仅形成了有效载荷的空间位阻，还增强了酶切后的穿膜性和杀伤性。这种设计使得SHR-A1811的半衰期降低、清除效率提高，以实现更安全有效的治疗效果。 图注：SHR-A1811的结构 图片来源：爱医肺时空 综合来看，不同类型的linker对比之下，可裂解型linker因其更广阔的应用场景占据了目前欧联药物的主流，而在可裂解型linker范围内，酶可裂解型linker因其旁观者效应可进一步提高对肿瘤细胞杀伤力的重要性，已经成为了目前大多数偶联药物的首选技术类型，这一点在以上市ADC产品的酶裂解linker占比情况中也得到充分验证。 至于未来，以酶裂解linker为主，辅以如光响应可裂解linker和生物正交可裂解linker等各种外源性化学触发器，或许会对linker的行业发展起到推动作用。 小结 很明显，Linker作为抗体与细胞毒性药物之间的桥梁，其设计直接影响到ADC的有效性和安全性。 纵观linker设计的历史发展，虽然不可裂解型Linker的成功案例亦有不少，但由于游离态Payload的细胞毒性以及旁观者效应的重要性，使其临床使用受到了限制，可裂解型Linke成为了大多数ADC药物的首选。 至此，酸裂解与还原条件裂解等第一代可裂解型linker出现，并在某些创新疗法中得到充分利用，多款药品随之上市，不过，随着ADC产业的发展，越来越多高毒性Payload的逐渐出现，间接使得其对linker的稳定要求越来越高，应用价值随之也大幅下降。 之后，酶可裂解等第二代可裂解型linker出现，其利用细胞中独特的高浓度水解酶来切割并释放药物，在控制药物释放方面优势明显。并在多项基础研究的推动下，逐渐衍生出越来越多如外源性裂解型linker、非多肽裂解型linker等成员。 但是，对于ADC产业而言，无论是不可裂解型linker，还是可裂解型linker抑或或是酸裂解型linker与酶裂解型linker都没有严格意义上的最优技术，一切linker设计的要求，都在强调“可控性”三个字，只有严格遵循最初设计的理念，并根据不同应用场景，不同的有效载荷与靶向载体组合形式而灵活变化，才是linker的最佳使用方式。 未来，随着我们对不同Payload的深入了解以及最佳Linker-spacer连接的临床验证，新型可裂解Linker的研发任重道远，但要相信，在越来越多创新linker技术的加入下，开发出具有颠覆功效的理想ADC，或许也只是时间问题，我们拭目以待。 来源 | 博药（药智网获取授权转载） 撰稿 | 头孢 责任编辑 | 八角 声明：本文系药智网转载内容，图片、文字版权归原作者所有，转载目的在于传递更多信息，并不代表本平台观点。如涉及作品内容、版权和其它问题，请在本平台留言，我们将在第一时间删除。 商务合作 | 王存星 19922864877（同微信）  阅读原文，是受欢迎的文章哦

First patient dosed in Phase 2 clinical trial with NGC-Cap for metastatic breast cancer Positive data from preclinical studies support NGC-Iri’s ability to deliver more SN-38 to tumors compared with either irinotecan or Onivyde® HANOVER, Md., Oct. 30, 2024 (GLOBE NEWSWIRE) -- Processa Pharmaceuticals, Inc. (Nasdaq: PCSA) (Processa or the Company), a clinical-stage pharmaceutical company focused on developing the next generation of chemotherapeutic drugs with improved efficacy and safety, provides updates on its product pipeline, upcoming milestones and business activities, and reports financial results for the three and nine months ended September 30, 2024. “We continued to make progress with our programs as we further demonstrate the potential benefits of our oncology therapeutics,” said George Ng, Chief Executive Officer of Processa Pharmaceuticals. “Our NGC-Cap Phase 2 clinical trial in metastatic breast cancer is underway with the first patient dosed. As this is an open-label trial, we anticipate sharing initial data in the second half of 2025. Additionally, we reported positive findings from preclinical studies that support NGC-Iri’s potential for improved efficacy and a superior side effect profile compared with the commonly used FDA-approved chemotherapy drugs irinotecan and Onivyde®. We are pleased with our progress and remain committed to improving the lives of people with cancer.” Key Program UpdatesProcessa is focused on developing next-generation chemotherapies (NGC) by improving widely used U.S. Food and Drug Administration (FDA)-approved drugs to extend cancer patients’ survival and/or improve their quality of life. This is achieved by altering how drugs are metabolized and/or distributed in the body, including how they reach cancer cells. In addition, Processa utilizes its Regulatory Science Approach, including the principles associated with FDA’s Project Optimus Oncology initiative, in the development of its NGC drug products to achieve a more favorable benefit-risk profile. PCS6422: Next-Generation Capecitabine (NGC-Cap) NGC-Cap is a combination of PCS6422 and capecitabine, which is the oral prodrug of the cancer drug 5-fluorouracil (5-FU). PCS6422 alters the metabolism of 5-FU, resulting in more 5-FU distributed to cancer cells.Earlier this month, the first patient was dosed in a Phase 2 clinical trial (NCT06568692) evaluating NGC-Cap for the treatment of advanced or metastatic breast cancer. The Phase 2 study is a global, multicenter, open-label, adaptive-design trial comparing two different doses of NGC-Cap to FDA-approved monotherapy capecitabine in approximately 60 to 90 patients. The trial is designed to evaluate the safety-efficacy profile of NGC-Cap versus monotherapy capecitabine, to determine the potential optimal dosage regimens of NGC-Cap as required by the FDA Project Optimus Initiative and to evaluate the possibility of personalizing NGC-Cap therapy. The Company expects to announce interim data from this trial in the second half of 2025. PCS3117: Next-Generation Gemcitabine (NGC-Gem) NGC-Gem is an oral analog of gemcitabine (Gemzar®) that is converted to its active metabolite by a different enzyme system, with potential for a positive response in gemcitabine patients including those inherently resistant to or who acquire resistance to gemcitabine.Processa is evaluating the potential of NGC-Gem in patients with pancreatic and other cancers, as well as ways to identify patients who are more likely to respond to NGC-Gem than gemcitabine alone. The Company is requesting a meeting with the FDA to discuss potential trial designs, including implementation of the Project Optimus initiative. PCS11T: Next-Generation Irinotecan (NGC-Iri) NGC-Iri is an analog of SN-38, the active metabolite of irinotecan, that is expected to have an improved safety-efficacy profile in every type of cancer where irinotecan is currently used.As announced in August, two studies in a human melanoma xenograft mouse model measured SN-38 in tumors, plasma and other tissues following administration of NGC-Iri, irinotecan and Onivyde®, the liposomal formulation of irinotecan. One study compared NGC-Iri with irinotecan, and the other compared irinotecan with Onivyde®. The results found that mice administered NGC-Iri had greater accumulation of SN-38 in the tumor compared with other tissues and that less SN-38 accumulated in non-cancer tissues, which could lead to improved efficacy with a more favorable adverse event profile compared with irinotecan and Onivyde®.The Company is currently evaluating the manufacturing process and potential sites for NGC-Iri. In addition, Processa is defining the potential paths to approval, which includes defining the target patient population and the type of cancer, and expects to conduct IND-enabling toxicology studies in 2025. Third Quarter Financial Results Research and development expenses for the third quarter of 2024 were $2.3 million, compared with $1.2 million for the third quarter of 2023. General and administrative expenses for the third quarter of 2024 were $1.1 million, compared with $1.0 million for the third quarter of 2023. The net loss for the third quarter of 2024 was $3.4 million, or $1.03 per share, compared with the net loss for the third quarter of 2023 of $2.1 million, or $1.54 per share. All per-share figures reflect a 1-for-20 reverse stock split that was effective as of January 22, 2024. Cash and cash equivalents were $2.9 million as of September 30, 2024. About Processa Pharmaceuticals, Inc. Processa is a clinical-stage pharmaceutical company focused on developing the Next Generation Chemotherapy (NGC) drugs with improved safety and efficacy. Processa’s NGC drugs are modifications of existing FDA-approved oncology therapies resulting in an alteration of the metabolism and/or distribution of these drugs while maintaining the existing mechanisms of killing the cancer cells. By combining its novel oncology pipeline with proven cancer-killing active molecules and its Regulatory Science Approach, Processa’s strategy is to develop more effective therapy options with improved tolerability for cancer patients through an efficient regulatory path. For more information, visit our website at www.processapharma.com. Forward-Looking Statements This release contains forward-looking statements. The statements in this press release that are not purely historical are forward-looking statements which involve risks and uncertainties. Actual future performance outcomes and results may differ materially from those expressed in forward-looking statements. Please refer to the documents filed by Processa Pharmaceuticals with the SEC, specifically the most recent reports on Forms 10-K and 10-Q, which identify important risk factors which could cause actual results to differ from those contained in the forward-looking statements. Company Contact:Patrick Lin(925) 683-3218plin@processapharma.com Investor Relations Contact:Yvonne BriggsAlliance Advisors Investor Relations(310) 691-7100ybriggs@allianceadvisorsir.com [Financial Tables to follow]PROCESSA PHARMACEUTICALS, INC. CONDENSED CONSOLIDATED BALANCE SHEETS(in thousands, except share information) (unaudited) September 30, 2024 December 31, 2023 ASSETS Current Assets Cash and cash equivalents $2,891 $4,706 Prepaid expenses and other 1,947 926 Total Current Assets 4,838 5,632 Property and Equipment, net 5 3 Other Assets Lease right-of-use assets, net of accumulated amortization 93 146 Security deposit 6 6 Total Other Assets 99 152 Total Assets $4,942 $5,787 LIABILITIES AND STOCKHOLDERS’ EQUITY Current Liabilities Current maturities of lease liabilities $94 $84 Accounts payable 712 312 Due to licensor - 189 Due to related parties - - Accrued expenses 413 146 Total Current Liabilities 1,219 731 Non-current Liabilities Non-current lease liabilities 2 67 Total Liabilities 1,221 798 Commitments and Contingencies - - Stockholders’ Equity Common stock, par value $0.0001, 100,000,000 shares authorized: 3,271,944 issued and 3,266,944 outstanding at September 30, 2024; and 1,291,000 issued and 1,286,000 outstanding at December 31, 2023 - - Additional paid-in capital 88,511 80,658 Treasury stock at cost — 5,000 shares at September 30, 2024 and December 31, 2023 (300) (300)Accumulated deficit (84,490) (75,369)Total Stockholders’ Equity 3,721 4,989 Total Liabilities and Stockholders’ Equity $4,942 $5,787 PROCESSA PHARMACEUTICALS, INC. CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS(in thousands, except per share data)(unaudited) Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Operating Expenses Research and development $2,288 $1,152 $5,557 $4,479 General and administrative 1,137 1,016 3,760 4,509 Operating Loss (3,425) (2,168) (9,317) (8,988) Other Income (Expense) Interest income, net 40 86 195 271 Net Loss $(3,385) $(2,082) $(9,122) $(8,717) Net Loss per Common Share - Basic and Diluted $(1.03) $(1.54) $(3.13) $(6.81) Weighted Average Common Shares Used to Compute Net Loss Applicable to Common Shares - Basic and Diluted 3,275,998 1,350,188 2,909,941 1,279,298 # # #