Abstract
在过去的十年中,免疫治疗已被证实在黑色素瘤、肾细胞癌、非小细胞肺癌等多种实体肿瘤中具有抗肿瘤活性,开启了肿瘤免疫治疗的新时代。具有微卫星高度不稳定性(microsatellite instability-high,MSI-H)或错配修复缺陷(mismatch repair deficient,dMMR)的结直肠癌(colorectal cancer,CRC)对免疫检查点抑制剂(immune checkpoint inhibitors,ICIs)敏感,ICIs单药治疗及ICIs联合治疗在MSI-H/dMMR型CRC治疗中取得突破性进展,目前已有多种ICIs被批准用于CRC患者的一线及后线治疗。然而,MSI-H/dMMR型肿瘤仅占转移性CRC的5%,大部分CRC为微卫星稳定(microsatellite stable,MSS)型或者错配修复完整(mismatch repair proficient,pMMR)型。许多临床试验正在探索MSS/pMMR型CRC患者的有效治疗方法,ICIs和不同机制药物的联合治疗有望提高MSS/pMMR型CRC患者的疗效。未来应更加注重寻找ICIs的潜在疗效标志物和ICIs的耐药机制,突破MSS/pMMR型CRC患者的免疫耐受。
Keywords: 结直肠癌, 免疫检查点抑制剂, 程序性细胞死亡蛋白-1, 程序性细胞死亡蛋白配体-1, 细胞毒T淋巴细胞相关抗原4
Abstract
Over the past decade, immunotherapy has been shown to have antitumor activity in a variety of solid tumors, such as melanoma, renal cell carcinoma, and non-small cell lung cancer, keeping a lead in a new era of tumor immunotherapy. Colorectal cancer with high microsatellite instability (MSI-H) or mismatch repair deficient (dMMR) is sensitive to immune checkpoint inhibitors (ICIs). ICIs monotherapy and ICIs combination therapy have made breakthroughs in the treatment of MSI-H/dMMR CRC. At present, a variety of ICIs have been approved for first- and post-line treatment in patients with CRC. However, MSI-H/dMMR type tumors only account for 5% of metastatic CRC, and the most CRCs were microsatellite stable (MSS) or mismatch repair proficient (pMMR). Many clinical trials are exploring effective treatments for patients with MSS/pMMR CRC, and the combination of ICIs and drugs with different mechanisms is expected to improve the efficacy of MSS/pMMR CRC patients. In the future, attention should be paid to finding the potential therapeutic markers of ICIs and the drug resistance mechanism of ICIs, so as to break through the immune tolerance of MSS/pMMR CRC patients.
Keywords: colorectal cancer, immune checkpoint inhibitors, programmed death-1, programmed death ligand-1, cytotoxic T lymphocyte antigen 4
结直肠癌(colorectal cancer,CRC)的发病率在恶性肿瘤中位列全球第三,病死率位列全球第二[1]。尽管早期疾病预后良好,但是转移性结直肠癌(metastatic colorectal cancer,mCRC)的5年生存率仍然很低。随着肿瘤分子生物学的不断发展,人们对CRC的生物学特点有了更深的了解,CRC的治疗策略发生了巨大的改变。针对免疫检查点抑制剂(immune checkpoint inhibitors,ICIs)在CRC免疫治疗领域中的研究不断取得进展。免疫检查点是人体免疫系统中起保护作用的分子,在正常情况下通过抑制T细胞分化增殖来调控免疫平衡。肿瘤组织过度表达免疫检查点分子,抑制T细胞活化增殖或诱导T细胞凋亡,导致免疫抑制性肿瘤微环境形成,使肿瘤细胞逃避机体的免疫监控和杀伤。免疫检查点疗法可以阻断抑制性检查点,从而恢复有效的T细胞功能[2-3]。现阶段用于临床的ICIs主要有程序性细胞死亡蛋白-1(programmed death-1,PD-1)抗体、程序性细胞死亡蛋白配体-1(programmed death ligand-1,PD-L1)抗体及细胞毒T淋巴细胞相关抗原4(cytotoxic T lymphocyte antigen 4,CTLA-4)抗体。笔者主要对ICIs在CRC中的使用现状及进展进行综述。
1. ICIs在新辅助治疗中的运用
在肺癌和黑色素瘤的治疗中,新辅助免疫治疗能诱导广泛的肿瘤特异性T细胞反应,从而增强局部和全身性抗肿瘤免疫反应[4-5]。但免疫治疗在CRC新辅助治疗中的作用仍不清楚。NICHE研究[6]对免疫治疗在结肠癌新辅助治疗中的效果进行了探索。该研究共招募40例早期结肠癌患者,其中21例为错配修复缺陷(mismatch repair deficient,dMMR)型,20例为错配修复完整(mismatch repair proficient,pMMR)型。81%的dMMR患者和40%的pMMR患者为III期结肠癌,所有患者在术前第1天使用1 mg/kg伊匹木单抗(ipilimumab),第1天和第15天使用3 mg/kg纳武利尤单抗(nivolumab)治疗。研究结果显示:治疗耐受性良好,所有患者在入组6周内接受了根治性切除术,仅有5例患者出现3~4级治疗相关毒性反应;仅接受2次新辅助免疫治疗的dMMR型结肠癌患者缓解率达到100%,而pMMR型结肠癌患者缓解率仅为27%。NICHE研究为CRC的新辅助免疫治疗提供了新的选择,但是ICIs在CRC新辅助治疗中的效果及安全性需要更多的临床研究进一步验证。
2. ICIs在局部晚期CRC治疗中的应用
放射治疗(以下简称放疗)、化学药物治疗(以下简称化疗)联合根治性手术虽是局部进展期直肠癌的标准治疗方法[7],但是局部晚期直肠癌的最佳治疗方法仍在探索之中。Yuki等[8]在2020年欧洲肿瘤内科学会(European Society for Medical Oncology,ESMO)上汇报了VOLTAGE研究的结果。该研究将37例微卫星稳定(microsatellite stable,MSS)型T3-4NanyM0的局部晚期直肠癌患者纳入A1队列;5例微卫星高度不稳定性(microsatellite instability-high,MSI-H)型局部晚期直肠癌患者纳入A2队列。所有患者行新辅助放化疗后,接受5个疗程纳武利尤单抗治疗,最后行全直肠系膜切除术(total mesorectal excision,TME)。研究显示:MSS型和MSI-H型局部晚期直肠癌患者接受新辅助放化疗联合免疫治疗后再行根治术的病理完全缓解(pathological complete response,pCR)率分别可达30%和60%。仅有3例患者发生免疫相关的严重不良事件,但均接受了根治性手术并痊愈。后续的分子标志物分析结果提示PD-L1表达和CD8/T受体比值升高可能是纳武利尤单抗治疗获益的预测因子[8]。正在进行的POLEM研究[9]招募完全切除的Ⅲ期dMMR/MSI-H型CRC患者,评估5-氟尿嘧啶联合阿维鲁单抗(avelumab)免疫治疗的效果。另一项正在进行的ATOMIC研究[10]旨在探索FOLFOX化疗联合阿特珠单抗(atezolizumab)治疗III期MSI-H/dMMR型CRC患者的效果和安全性。ICIs在CRC中的应用已由后线治疗逐渐拓展至一线治疗,甚至早期CRC的新辅助治疗。许多相关临床研究正在开展中,期待ICIs在CRC的治疗中能够取得更大的突破。
3. ICIs在晚期转移性CRC患者中的应用
3.1. ICIs单药治疗
dMMR的多种肿瘤均可从帕博利珠单抗(pembrolizumab)免疫治疗中获益[11-12]。Le等[12]首次报道了在KEYNOTE-016研究中帕博利珠单抗用于MSI-H/dMMR型mCRC后线治疗并获得良好的客观缓解率(objective response rate,ORR)。结果显示dMMR型mCRC患者中的ORR和无进展生存(progression-free survival,PFS)率分别为40%和78%,远高于pMMR型mCRC患者的0和11%。2017年该数据被更新[13]:CRC患者队列的ORR为52%,完全缓解率(complete response,CR)为12%。2016年7月,美国食品药品监督管理局(Food and Drug Administration,FDA)对MSI-H/dMMR型肿瘤患者的数据进行了汇总分析。汇总数据包含KEYNOTE-016、KEYNOTE-164、KEYNOTE-158、KEYNOTE-012和KEYNOTE-28 5项临床试验,共149例dMMR癌症患者,其中mCRC患者90例。结果显示:总ORR为39.6%,CR率为7%,部分缓解(partial response,PR)率为32%。KEYNOTE-164研究[14]显示:经过二线以上治疗(61例)和一线以上治疗(63例)的MSI-H型CRC患者接受帕博利珠单抗(200 mg)免疫单药治疗的ORR均为33%,中位PFS时间分别为2.3和4.1个月。最近Diaz等[15]更新了KEYNOTE-164研究第2阶段的长期随访结果。二线以上治疗和一线以上治疗患者的ORR分别为32.8%和34.9%。该研究显示帕博利珠单抗具有持久的抗肿瘤活性,对于接受一线及以上治疗后进展的MSI-H型CRC患者,其安全性可控。KEYNOTE-177[16]研究在MSI-H型mCRC患者的一线治疗中比较了帕博利珠单抗和标准治疗(mFOLFOX6或FOLFIRI±贝伐珠单抗或西妥昔单抗)的效果和安全性,结果显示:帕博利珠单抗组的PFS时间优于标准治疗组(中位PFS时间为16.5个月vs 8.2个月),两组的ORR分别为43.8%和33.1%。基于这一研究结果,2020年6月29日美国FDA批准了帕博利珠单抗用于MSI-H/dMMR型无法切除肿瘤或mCRC患者的一线治疗。CheckMate142研究[17]是一项多中心、开放、非随机、多个队列的Ⅱ期临床研究,74例使用纳武利尤单抗的dMMR/MSI-H型mCRC患者中有23例(31.1%)达到研究者评估的客观反应,有51例(69%)患者的疾病控制了12周或更长时间。最常见的3级或4级治疗相关的不良反应事件(treatment-related adverse events,TRAEs)是脂肪酶和淀粉酶浓度升高。纳武利尤单抗在mCRC中显示出了持久的抗肿瘤活性。由此可见,ICIs单药方案可用于dMMR/MSI-H型mCRC患者的一线或后线治疗,且安全性良好。
3.2. 双ICIs治疗
Overman等[18]向2018年美国临床肿瘤协会(American Society of Clinical Oncology,ASCO)汇报了CheckMate142研究中纳武利尤单抗+伊匹木单抗双免疫治疗在dMMR/MSI-H型mCRC二线及后线治疗中的效果。研究纳入119例患者,ORR达55%,12周的疾病控制率(disease control rate,DCR)为80%,9个月和12个月的总生存(overall survival,OS)率分别为87%和85%。2018年的ESMO大会首次公布了CheckMate142研究[19]双免疫联合方案的一线治疗数据。纳武利尤单抗联合伊匹木单抗一线治疗的ORR为60%,CR率为7%,DCR为84%,PFS率和OS率分别为77%和83%。2020年ASCO会议更新了CheckMate142研究[20]双免疫联合方案一线治疗的结果。研究者评估的ORR从60%提高到69%,CR率从7%提高到13%,84%患者的肿瘤负荷较基线时降低。对于dMMR/MSI-H型mCRC患者而言,单独使用PD-1抑制剂或联合使用抗CTLA-4抑制剂的治疗均能够实现持久响应[16-17, 20]。CCTG CO.26研究[21]结果显示:替西木单抗(tremelimumab)联合度伐利尤单抗(durvalumab)治疗mCRC患者的OS时间较最佳支持治疗组延长2个月(6.6个月vs 4.1个月),但未改善PFS时间和ORR。替西木单抗联合度伐利尤单抗组DCR为22.6%,支持治疗组为6.6%。治疗组3~4级TRAEs发生率明显更高。以上研究结果提示:与ICIs单药相比,免疫双药联合方案不仅可改善dMMR/MSI-H型mCRC患者的疗效,也为MSS型mCRC患者的治疗带来一种新的选择。在选择双免疫治疗方案的同时应重视免疫治疗相关不良反应的管理。
3.3. ICIs联合靶向治疗
一项III期随机临床试验IMblaze370[22]评估了阿特珠单抗(atezolizumab)联合考比替尼对比瑞戈非尼三线治疗mCRC的效果和安全性,遗憾的是IMblaze370研究没有达到其主要终点。但是近期MSS型CRC免疫治疗相关研究取得了突破。一项Ib期研究显示:在阿特珠单抗联合考比替尼治疗的mCRC患者中有7例达到了PR,其中4例是非MSI-H型mCRC,中位OS时间为10个月[23]。这表明mCRC患者可从免疫联合靶向治疗中受益。2020年在ESMO会议上阿维鲁单抗(avelumab)联合西妥昔单抗在RAS/BRAF野生型mCRC患者中的疗效被报道[24]。研究结果显示中位OS时间为13.1个月,中位PFS时间为3.6个月。REGONIVO研究[25]是一项探索瑞戈非尼联合纳武利尤单抗治疗胃癌和mCRC效果和安全性的Ib期试验。该研究纳入25例进展期胃癌和25例mCRC患者,结果显示:ORR为40%,mCRC患者的总体治疗反应率为36%,其中MSS型CRC患者治疗反应率为33%,mCRC患者的中位PFS为7.9个月。REGONIVO研究在MSS型进展期胃癌和mCRC患者中采用80~120 mg的瑞戈非尼与纳武利尤单抗的联合治疗,观察到较好的抗肿瘤活性,其安全性可控。REGOMUNE研究[26]结果显示:瑞戈非尼联合阿维鲁单抗治疗MSS型mCRC的中位PFS时间为3.6个月,中位OS时间为10.8个月。Lieu等[27]在2020年ASCO会议上报告了帕博利珠单抗+比美替尼+贝伐珠单抗治疗既往多线治疗失败的mCRC患者的Ⅱ期研究结果,在免疫治疗难治的患者人群中有82%的患者达到疾病稳定(stable disease,SD),临床获益率为94%,中位PFS时间为6.4个月。Gou等[28]回顾性分析了呋喹替尼联合信迪利单抗在三线及三线以后的mCRC治疗中的有效性,结果显示ORR为15.38%,DCR为57.69%。血管内皮生长因子(vascular endothelial growth factor,VEGF)和表皮生长因子受体(epidermal growth factor receptor,EGFR)是CRC中常见的治疗靶点。已有研究[29-30]显示EGFR拮抗剂、VEGF拮抗剂及丝裂原激活的蛋白激酶激酶(mitogen-activated protein kinase kinase,MEK)拮抗剂均与免疫治疗存在协同抗肿瘤作用。目前CRC的治疗进入了分子靶向治疗及免疫治疗的新时代,免疫治疗联合靶向治疗为MSS/pMMR型mCRC患者带来新的选择和希望。
3.4. ICIs联合化疗
正在进行的一项II期临床研究[31]报道了帕博利珠单抗联合FOLFOX方案在MSS型CRC治疗中的效果和安全性。初步结果显示:24周的ORR为53%,8周DCR为100%。Kim等[32]在2020年ESMO大会更新了KEYNOTE-651研究队列B和D的结果。他们将未接受系统化疗的MSS/pMMR型mCRC患者纳入队列B,予以帕博利珠单抗联合mFOLFOX7方案化疗;将接受过化疗的MSS/pMMR型mCRC患者纳入队列D,予以帕博利珠单抗联合FOLFIRI方案化疗。该研究共纳入63例mCRC患者,结果显示:B组和D组的DCR分别为94%和63%,ORR分别为58%和16%;B组和D组3级TRAEs发生率分别为58%和53%。结果提示帕博利珠单抗联合mFOLFOX7或FOLFIRI治疗MSS/pMMR型mCRC是安全、可耐受的。已有研究[33]表明细胞毒性化学药物可诱导免疫原性肿瘤细胞死亡并抑制免疫耐受,从而增强对免疫疗法的反应。化疗可能与ICIs有潜在协同作用,但在MSS/pMMR型mCRC患者中ICIs联合化疗能否提高疗效、改善预后仍有待进一步验证。
3.5. ICIs联合放疗
一项II期临床研究[34]评估了伊匹木单抗+纳武利尤单抗联合放疗在MSS型mCRC中的效果和安全性。研究纳入40例MSS型mCRC患者,所有患者在至少接受了2线及以上的治疗后进展。纳入的患者予以伊匹木单抗(1 mg/kg,每6周1次)、纳武利尤单抗(240 mg,每2周1次),在第2周期每隔1 d接受1次8 Gy的放疗,共3次。结果显示意向治疗分析人群DCR为17.5%(7/40),ORR为7.5%(3/40),中位疾病控制时间为77 d。TRAEs发生率为55%。该研究表明伊匹木单抗+纳武利尤单抗联合放疗在MSS型mCRC患者中可行且具有持久的疗效,但仍然需要更多的研究去探索ICIs联合放疗的具体治疗方案。
3.6. 多种不同机制药物联合治疗方案
MPDL3280A是一种人源抗PD-L1单抗。一项Ib期研究将14例难治性mCRC患者纳入A组并予以MPDL3280A+贝伐珠单抗治疗,将未经奥沙利铂治疗的30例mCRC患者纳入B组中,予以MPDL3280A+贝伐珠单抗+FOLFOX治疗。结果显示A组的ORR为8%,B组为36%[35]。该研究表明患者对MPDL3280A+贝伐珠单抗±FOLFOX的耐受性良好,没有出现意外的不良反应事件。AVETUX研究[36]显示阿维鲁单抗+西妥昔单抗+mFOLFOX6一线治疗KRAS野生型CRC患者的早期肿瘤退缩(early tumor shrinkage,ETS)率为81%,CR率为11%,PR率为70%。2020年在ASCO大会上报道的FOLFOX+度伐利尤单抗+替西木单抗一线治疗RAS突变的MSS型mCRC患者的结果显示:DCR为87.5%,ORR为62.5%,CR率为25%,6个月和12个月的PFS率分别为62.5%和50%[37]。这个数据已经超越了单纯FOLFOX治疗的缓解率和PFS率。此外,COMMIT试验[38]正在探索FOLFOX+阿特珠单抗的基础上加用贝伐珠单抗在MSI-H/dMMR型mCRC一线治疗中的作用。CheckMate 8HW研究[39]是一项探索纳武利尤单抗、纳武利尤单抗联合伊匹木单抗或化疗在复发性或mCRC患者中的效果和安全性的前瞻性III期临床研究。单一治疗方案在MSS/pMMR型mCRC患者中疗效有限,ICIs用于MSS/pMMR型mCRC患者的研究未显示明显获益,但多种不同机制药物联合治疗初显成效。
3.7. ICIs维持治疗
ICIs作为诱导化疗后的维持治疗在mCRC中的作用正在研究中。MODUL研究[40]是一项II期临床研究,其中队列2评估了阿特珠单抗在BRAF野生型mCRC中维持治疗的疗效。445例BRAF野生型mCRC患者被随机分配进行维持治疗(297例5-氟尿嘧啶+贝伐珠单抗+阿特珠单抗,148例5-氟尿嘧啶+贝伐珠单抗),中位随访18.7个月,尚未获得中位PFS时间和OS时间。在5-氟尿嘧啶+贝伐珠单抗诱导化疗后予以阿特珠单抗作为BRAF野生型mCRC患者的一线维持治疗并未改善患者的预后。ICIs和不同机制药物联合治疗的模式在mCRC一线维持治疗中的数据暂时是失败的。
4. 结 语
ICIs治疗对于dMMR/MSI-H型CRC患者效果显著,在晚期CRC的一线及后线治疗、早期CRC的新辅助治疗中均显示出非常好的效果。但是大部分的CRC为pMMR/MSS型,对ICIs治疗不敏感。免疫治疗联合其他治疗策略在MSS型CRC中初步显示出抗肿瘤活性。进一步了解免疫治疗的肿瘤微环境、生物标志物、ICIs耐药机制对ICIs治疗CRC,特别是MSS/pMMR型CRC至关重要。虽然ICIs在CRC中的治疗仍处于初级阶段,但是随着研究的深入,ICIs的治疗将取得更大的突破。
利益冲突声明
作者声称无任何利益冲突。
原文网址
http://xbyxb.csu.edu.cn/xbwk/fileup/PDF/202108894.pdf
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