A randomized, multicenter study to determine the safety and efficacy of the immunoconjugate SGN-15 plus docetaxel for the treatment of non-small cell lung carcinoma

Exploration of the antibody-drug conjugate clinical landscape

The antibody-drug conjugate (ADC) field has undergone a renaissance, with substantial recent developmental investment and subsequent drug approvals over the past 6 y. In November 2022, ElahereTM became the latest ADC to be approved by the US Food and Drug Administration (FDA). To date, over 260 ADCs have been tested in the clinic against various oncology indications. Here, we review the clinical landscape of ADCs that are currently FDA approved (11), agents currently in clinical trials but not yet approved (164), and candidates discontinued following clinical testing (92). These clinically tested ADCs are further analyzed by their targeting tumor antigen(s), linker, payload choices, and highest clinical stage achieved, highlighting limitations associated with the discontinued drug candidates. Lastly, we discuss biologic engineering modifications preclinically demonstrated to improve the therapeutic index that if incorporated may increase the proportion of molecules that successfully transition to regulatory approval.

[DNA Damage Repair System and Antineoplastic Agents in Lung Cancer]

DNA damage repair (DDR) system plays an important role in maintaining of genomic stability. Accumulation of DNA lesions or deficiency of DDR system could drive tumorigenesis as well as promote tumor progression; meanwhile, they could also provide therapeutic opportunities and targets. Of all the antineoplastic agents of lung cancers, many of them targeted or were associated with DNA damage and repair pathways, such as chemotherapies and antibody-drug conjugates which were designed directly causing DNA damages, targeted drugs inhibiting DNA repair pathways, and immune-checkpoint inhibitors. In this review, we described the role of DNA damage and repair pathways in antitumor activity of the above agents, as well as summarized the application and clinical investigations of these antineoplastic agents in lung cancers, in order to provide more information for exploring precision and effective strategies for the treatment of lung cancer based on the mechanism of DNA damage and repair.
.

Targeting Tumor Glycans for Cancer Therapy: Successes, Limitations, and Perspectives

Simple Summary

Aberrant glycosylation is a common feature of many cancers, and it plays crucial roles in tumor development and biology. Cancer progression can be regulated by several physiopathological processes controlled by glycosylation, such as cell–cell adhesion, cell–matrix interaction, epithelial-to-mesenchymal transition, tumor proliferation, invasion, and metastasis. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs), which are suitable for selective cancer targeting, as well as novel antitumor immunotherapy approaches. This review summarizes the strategies developed in cancer immunotherapy targeting TACAs, analyzing molecular and cellular mechanisms and state-of-the-art methods in clinical oncology.

Abstract

Aberrant glycosylation is a hallmark of cancer and can lead to changes that influence tumor behavior. Glycans can serve as a source of novel clinical biomarker developments, providing a set of specific targets for therapeutic intervention. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs) suitable for selective cancer-targeting therapy. The best characterized TACAs are truncated O-glycans (Tn, TF, and sialyl-Tn antigens), gangliosides (GD2, GD3, GM2, GM3, fucosyl-GM1), globo-serie glycans (Globo-H, SSEA-3, SSEA-4), Lewis antigens, and polysialic acid. In this review, we analyze strategies for cancer immunotherapy targeting TACAs, including different antibody developments, the production of vaccines, and the generation of CAR-T cells. Some approaches have been approved for clinical use, such as anti-GD2 antibodies. Moreover, in terms of the antitumor mechanisms against different TACAs, we show results of selected clinical trials, considering the horizons that have opened up as a result of recent developments in technologies used for cancer control.

Tumor-Associated Glycans as Targets for Immunotherapy: The Wistar Institute Experience/Legacy

Tumor cells are characterized by the expression of tumor-specific carbohydrate structures that differ from their normal counterparts. Carbohydrates on tumor cells have phenotypical as well as functional implications, impacting the tumor progression process, from malignant transformation to metastasis formation. Importantly, carbohydrates are structures that play a role in receptor-ligand interaction and elicit the activity of growth factor receptors, integrins, lectins, and other type 1 transmembrane proteins. They have been recognized as biomarkers for cancer diagnosis, and evidence demonstrating their relevance as targets for anticancer therapeutic strategies, including immunotherapy, continues to accumulate. Different approaches targeting carbohydrates include monoclonal antibodies (mAbs), antibody (Ab)-drug conjugates, vaccines, and adhesion antagonists. Development of bispecific antibodies and chimeric antigen receptor (CAR)-modified T cells against tumor-associated carbohydrate antigens (TACAs) as promising cancer immunotherapeutic agents is rapidly evolving. As reviewed here, there are several cancer-associated glycan features that can be leveraged to design rational drug or immune system targets, applying multiple TACA structural and functional features to be targeted as the standard treatment paradigm. Many of the underlying targets were defined by researchers at the Wistar Institute in Philadelphia, Pennsylvania, which provide basis for different immunotherapy approaches.

Preclinical Studies of OBI-999: A Novel Globo H-Targeting Antibody-Drug Conjugate

Globo H (GH), a hexasaccharide, is expressed at low levels in normal tissues but is highly expressed in multiple cancer types, rendering it a promising target for cancer immunotherapy. OBI-999, a novel antibody-drug conjugate, is derived from a conjugation of a GH-specific mAb with a monomethyl auristatin E (MMAE) payload through a site-specific ThioBridge and a cleavable linker. OBI-999 high homogeneity with a drug-to-antibody ratio of 4 (>95%) was achieved using ThioBridge. OBI-999 displayed GH-dependent cellular internalization and trafficked to endosome and lysosome within 1 and 5 hours, respectively. Furthermore, OBI-999 showed low nanomolar cytotoxicity in the assay with high GH expression on tumor cells and exhibited a bystander killing effect on tumor cells with minimal GH expression. Tissue distribution indicated that OBI-999 and free MMAE gradually accumulated in the tumor, reaching maximum level at 168 hours after treatment, whereas OBI-999 and free MMAE decreased quickly at 4 hours after treatment in normal organs. Maximum MMAE level in the tumor was 16-fold higher than in serum, suggesting that OBI-999 is stable during circulation and MMAE is selectively released in the tumor. Excellent tumor growth inhibition of OBI-999 was demonstrated in breast, gastric, and pancreatic cancer xenograft or lung patient-derived xenograft models in a dose-dependent manner. The highest nonseverely toxic dose in cynomolgus monkeys is 10 mg/kg determined by a 3-week repeated-dose toxicology study demonstrating an acceptable safety margin. Taken together, these results support further clinical development of OBI-999, which is currently in a phase I/II clinical study in multiple solid tumors (NCT04084366). OBI-999, the first GH-targeting ADC, displayed excellent tumor inhibition in animal models across multiple cancer types, including breast, gastric, pancreatic, and lung cancers, warranting further investigation in the treatment of solid tumors.

Tumor-associated carbohydrates and immunomodulatory lectins as targets for cancer immunotherapy

During oncogenesis, tumor cells present specific carbohydrate chains that are new targets for cancer immunotherapy. Whereas these tumor-associated carbohydrates (TACA) can be targeted with antibodies and vaccination approaches, TACA including sialic acid-containing glycans are able to inhibit anticancer immune responses by engagement of immune receptors on leukocytes. A family of immune-modulating receptors are sialic acid-binding Siglec receptors that have been recently described to inhibit antitumor activity mediated by myeloid cells, natural killer cells and T cells. Other TACA-binding receptors including selectins have been linked to cancer progression. Recent studies have shown that glycan-lectin interactions can be targeted to improve cancer immunotherapy. For example, interactions between the immune checkpoint T cell immunoglobulin and mucin-domain containing-3 and the lectin galectin-9 are targeted in clinical trials. In addition, an antibody against the lectin Siglec-15 is being tested in an early clinical trial. In this review, we summarize the previous and current efforts to target TACA and to inhibit inhibitory immune receptors binding to TACA including the Siglec-sialoglycan axis.

Antibody-Drug Conjugates in Thoracic Malignancies: Clinical Trials Reveal Both Promise and Challenges

Thoracic malignancies are the main cause of cancer-related deaths worldwide. The need to develop new therapies is therefore urgent. The recognition of new potential therapeutic targets in thoracic malignancies has prompted the development of a number of antibody-drug conjugates. This new class of potent anticancer agents is supposed to more specifically and directly target the tumor while limiting toxicity for healthy tissues by delivering a toxic payload to tumor cells that are recognized by the presence of specific cell surface antigens. Progress in the development of antibody-drug conjugates over the last decade has been significant, with several promising advances. Unfortunately, many failures have also been encountered, often because of unexpectedly severe toxicities that contradicted the assumed mechanism of action, and major challenges remain. Various techniques to reduce the toxicities associated with antibody-drug conjugates are being studied, and the panorama of antibody-drug conjugates in clinical stages continues to increase and evolve. Current efforts in the conjugation and linker chemistries could result in the successful construction of clinically effective compounds. The future clinical development of antibody-drug conjugates could benefit from the identification of such payloads that can provide more safe and effective derivatives. Highly potent compounds with reasonable aqueous solubility, non-immunogenic profile, and stability in storage and the bloodstream should be important aspects of research into cytotoxic payloads.

The Therapeutic Potential of DNA Damage Repair Pathways and Genomic Stability in Lung Cancer

Despite advances in our understanding of the molecular biology of the disease and improved therapeutics, lung cancer remains the most common cause of cancer-related deaths worldwide. Therefore, an unmet need remains for improved treatments, especially in advanced stage disease. Genomic instability is a universal hallmark of all cancers. Many of the most commonly prescribed chemotherapeutics, including platinum-based compounds such as cisplatin, target the characteristic genomic instability of tumors by directly damaging the DNA. Chemotherapies are designed to selectively target rapidly dividing cells, where they cause critical DNA damage and subsequent cell death (1, 2). Despite the initial efficacy of these drugs, the development of chemotherapy resistant tumors remains the primary concern for treatment of all lung cancer patients. The correct functioning of the DNA damage repair machinery is essential to ensure the maintenance of normal cycling cells. Dysregulation of these pathways promotes the accumulation of mutations which increase the potential of malignancy. Following the development of the initial malignancy, the continued disruption of the DNA repair machinery may result in the further progression of metastatic disease. Lung cancer is recognized as one of the most genomically unstable cancers (3). In this review, we present an overview of the DNA damage repair pathways and their contributions to lung cancer disease occurrence and progression. We conclude with an overview of current targeted lung cancer treatments and their evolution toward combination therapies, including chemotherapy with immunotherapies and antibody-drug conjugates and the mechanisms by which they target DNA damage repair pathways.

Antibody drug conjugates in thoracic malignancies

Antibody drug conjugates (ADCs) have the potential to alter the efficacy: toxicity ratio of cytotoxic therapy utilizing surface markers on cancer cells as antibody targets to preferentially deliver toxic payloads to tumor cells while limiting systemic toxicity. Multiple ADCs, differing in their antibody targets, cytotoxic payloads and linker molecules are currently being evaluated in non-small-cell lung cancer, small-cell lung cancer and malignant pleural mesothelioma. Here we review the available data in thoracic malignancies and the potential issues influencing the efficacy and toxicity of these approaches.

Strategies and challenges for the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are one of the fastest growing classes of oncology therapeutics. After half a century of research, the approvals of brentuximab vedotin (in 2011) and trastuzumab emtansine (in 2013) have paved the way for ongoing clinical trials that are evaluating more than 60 further ADC candidates. The limited success of first-generation ADCs (developed in the early 2000s) informed strategies to bring second-generation ADCs to the market, which have higher levels of cytotoxic drug conjugation, lower levels of naked antibodies and more-stable linkers between the drug and the antibody. Furthermore, lessons learned during the past decade are now being used in the development of third-generation ADCs. In this Review, we discuss strategies to select the best target antigens as well as suitable cytotoxic drugs; the design of optimized linkers; the discovery of bioorthogonal conjugation chemistries; and toxicity issues. The selection and engineering of antibodies for site-specific drug conjugation, which will result in higher homogeneity and increased stability, as well as the quest for new conjugation chemistries and mechanisms of action, are priorities in ADC research.

Perspectives on Anti-Glycan Antibodies Gleaned from Development of a Community Resource Database

Antibodies are used extensively for a wide range of basic research and clinical applications. While an abundant and diverse collection of antibodies to protein antigens have been developed, good monoclonal antibodies to carbohydrates are much less common. Moreover, it can be difficult to determine if a particular antibody has the appropriate specificity, which antibody is best suited for a given application, and where to obtain that antibody. Herein, we provide an overview of the current state of the field, discuss challenges for selecting and using antiglycan antibodies, and summarize deficiencies in the existing repertoire of antiglycan antibodies. This perspective was enabled by collecting information from publications, databases, and commercial entities and assembling it into a single database, referred to as the Database of Anti-Glycan Reagents (DAGR). DAGR is a publicly available, comprehensive resource for anticarbohydrate antibodies, their applications, availability, and quality.

Structural biology of antibody recognition of carbohydrate epitopes and potential uses for targeted cancer immunotherapies

Monoclonal antibodies represent the most successful class of biopharmaceuticals for the treatment of cancer. Mechanisms of action of therapeutic antibodies are very diverse and reflect their ability to engage in antibody-dependent effector mechanisms, internalize to deliver cytotoxic payloads, and display direct effects on cells by lysis or by modulating the biological pathways of their target antigens. Importantly, one of the universal changes in cancer is glycosylation and carbohydrate-binding antibodies can be produced to selectively recognize tumor cells over normal tissues. A promising group of cell surface antibody targets consists of carbohydrates presented as glycolipids or glycoproteins. In this review, we outline the basic principles of antibody-based targeting of carbohydrate antigens in cancer. We also present a detailed structural view of antibody recognition and the conformational properties of a series of related tissue-blood group (Lewis) carbohydrates that are being pursued as potential targets of cancer immunotherapy.

A human anti-c-Met Fab fragment conjugated with doxorubicin as targeted chemotherapy for hepatocellular carcinoma

c-Met is over-expressed in hepatocellular carcinoma(HCC) but is absent or expressed at low levels in normal tissues. Therefore we generated a novel conjugate of a human anti-c-Met Fab fragment (MetFab) with doxorubicin (DOX) and assessed whether it had targeted antitumor activity against HCC and reduced the side-effects of DOX. The MetFab was screened from human phage library, conjugated with DOX via chemical synthesis, and the conjugation MetFab-DOX was confirmed by HPLC. The drug release patterns, the binding efficacy, and cellular distribution of MetFab-DOX were assessed. MetFab-DOX was stable at pH7.2 PBS while release doxorubicin quickly at pH4.0, the binding efficacy of MetFab-DOX was similarly as MetFab, and the cellular distribution of the MetFab-DOX is distinct from free DOX. The cytotoxicity of MetFab-DOX was analyzed by the MTT method and the nude mouse HCC model. The MetFab-DOX demonstrated cytotoxic effects on c-Met expressing-tumor cells, but not on the cells without c-Met expression. MetFab-DOX exerted anti-tumor effect and significantly reduced the side effect of free DOX in mice model. Furthermore, the localization of conjugate was confirmed by immunofluorescence staining of tumor tissue sections and optical tumor imaging, respectively, and the tissue-distribution of drug was compared between free DOX and MetFab-DOX treatment by spectrofluorometer. MetFab-DOX can localize to the tumor tissue, and the concentration of doxorubicin in the tumor was higher after MetFab-DOX administration than after DOX administration. In summary, MetFab-DOX can target c-Met expressing HCC cells effectively and have obvious antitumor activity with decreased side-effects in preclinical models of HCC.

Biological agents alone or in combination as second-line therapy in advanced non-small-cell lung cancer: systematic review of randomized studies

The only approved agents for second-line therapy in unselected non-small-cell lung cancer are docetaxel and pemetrexed (chemotherapies) and erlotinib (targeted therapies). Several new molecular drugs have now entered clinical trials and are being compared with approved agents (e.g., vandetanib). Alternative pathways are also being explored to overcome resistance to established agents (c-MET and ALK inhibitors), and predictive factors are now crucial for the selection of drug and of patients (e.g., EGFR mutations). Better patient selection permits second-line treatment to be tailored according to disease identity, which confers a particular benefit in certain subgroups of patients. In this review, the authors examine existing trials comparing targeted therapies with the standard of care as second-line therapy for advanced non-small-cell lung cancer.

Glycans as targets for therapeutic antitumor antibodies

Glycans represent a vast class of molecules that modify either proteins or lipids. They exert and regulate important and complex functions in both normal and cancer cell metabolism. As such, the most immunogenic glycans have been targeted in passive and active immunotherapy in human cancer for the past 25 years but it is only recently that techniques have become available to uncover novel glycan targets. The main focus of this review article is to highlight why and how monoclonal antibodies (mAbs) recognizing glycans, and in particular the glycans expressed on glycolipids, are being used in various strategies to target and kill cancer cells. The article reports on the historical use of mAbs and on very recent progress made in antitumor therapy using the anti-GD2 mAb and the antiganglioside mAbs, anti-N-glycolylneuraminic acid mAb and anti-Lewis mAb. Anti-GD2 is showing great promise in Phase III clinical trials in adjuvant treatment of neuroblastoma. Racotumomab, an anti-idiotypic mAb mimicking N-glycolylneuraminic acid-containing gangliosides, is currently being tested in a randomized, controlled Phase II/III clinical trial. This article also presents various strategies used by different groups to develop mAbs against these naturally poorly immunogenic glycans.

Different toxicity profiles for drug- versus radionuclide-conjugated BR96 monoclonal antibodies in a syngeneic rat colon carcinoma model

BACKGROUND

One of many approaches being evaluated in experimental models and in the clinic for the treatment of cancer is the use of antibodies conjugated to various drugs or radionuclides. The aim of the present study was to compare the toxicity profiles of radioimmunoconjugates and drug-immunoconjugates based on the same monoclonal antibody, evaluated in the same experimental model, that much resembles human studies. The pattern of dose-limiting toxicity of a monomethylauristatin-conjugated monoclonal antibody (BR96) was compared to that of the same antibody conjugated with lutetium-177, and to the same non-conjugated antibody.

MATERIAL AND METHODS

Rats with established colon carcinoma were injected with monomethylauristatin-conjugated mAb-BR96, (177)Lu-BR96, or non-conjugated BR96. Liver, kidney, and myelotoxicity were assessed for 100 days by analysis of blood parameters. Body weight and therapeutic effects was also monitored.

RESULTS

Myelotoxicity was found to be dose limiting for the radionuclide BR96 conjugate. The dose-limiting factor was prolonged suppression of leukocytes (>28 days) with increased risk of infections. For monomethylauristatin-conjugated BR96, liver toxicity was dose limiting, whereas no dose-limiting toxicity was observed with non-conjugated BR96. Both the drug-immunoconjugate and the radioimmunoconjugate resulted in decreased platelet counts, but the time to nadir and duration differed.

CONCLUSION

The two conjugates resulted in different patterns of toxicity. By using the two conjugates of BR96 in a sequential therapeutic design it could be possible to increase the therapeutic window and hence probably the efficacy without significantly increasing the toxicity. This concept is regarded as valid regardless of conjugate or model chosen.

A population-based clinical trial of irinotecan and Carboplatin

Purpose. Phase I trials of anticancer drugs are commonly conducted using the method of modified Fibonacci. We have developed a population-based design for phase I trials of combining anticancer drugs such as irinotecan and carboplatin. Patients and Methods. Intrapatient dose escalation of irinotecan and carboplatin was performed according to a predetermined schema to reach individual dose-limiting toxicity (DLT) in 50 patients with solid tumors refractory to previous chemotherapy. The individual toxicity-limiting dose levels were analyzed for normal distribution using the method of Ryan-Joiner and subsequently used to determine a population-based maximum tolerated dose (pMTD). For comparison, a simulation study was performed using the method of modified Fibonacci. Results. The most common dose-limiting toxicities (DLTs) included neutropenia (58%), thrombocytopenia (16%), and diarrhea (8%). The frequency of individual toxicity-limiting dose levels of 50 patients approximated a normal distribution. The dose levels associated with individual limiting toxicities ranged from level 1 (irinotecan 100 mg/m² and carboplatin AUC = 4 mg/mL x min) to level 8 (irinotecan 350 mg/m² and carboplatin AUC = 6). The pMTD was determined to be dose level 3 (150 mg/m² for irinotecan and AUC = 5 for carboplatin). In contrast, the MTD was determined to be dose level 4 (200 mg/m² for irinotecan and AUC 5 for carboplatin) by modified-Fibonacci simulation. Conclusions. The population-based design of phase I trial allows optimization of dose intensity and derivation of a pMTD. The pMTD has been applied in phase II trial of irinotecan and carboplatin in patients with small-cell lung cancer.

Will targeted therapy hold its promise? An evidence-based review

(1) Many of the significant advances in cancer management in recent years have centered on the development and introduction of molecularly targeted therapies, such as monoclonal antibodies and tyrosine kinase inhibitors.(2) Despite targeted therapy that has clearly benefited and even cured certain patients (eg, imatinib, trastuzumab), the ultimate goal of curing cancer, and the more immediate goal of replacing non-targeted chemotherapies with less toxic, targeted agents has yet to be achieved for most cancer patients.(3) Based on a systematic review of randomized controlled trials, examples of significant benefits in selected cancers are provided:(a) Non-Hodgkin's lymphoma (NHL) - A large meta-analysis and several individual randomised, controlled trials (RCTs) report that rituximab plus chemotherapy has a major survival advantage over chemotherapy alone in patients with NHL; an overview of six clinical trials supports the survival benefit of rituximab plus chemotherapy.(b) Renal cell carcinoma (RCC) - Temsirolimus or sunitinib has a significant survival benefit relative to interferon-alpha, and sorafenib carries such a benefit in patients resistant to standard therapy.(c) Colorectal cancer (CRC) - An overview of three RCTs in metastatic CRC revealed that bevacizumab plus 5-fluorouracil/leucovorin possesses a significant survival advantage over 5-fluorouracil/leucovorin and irinotecan/5-fluorouracil/leucovorin.(d) Non-small-cell lung cancer (NSCLC) - In refractory NSCLC, erlotinib significantly prolongs survival, particularly in nonsmokers, and gefitinib may have some utility in patients of Asian ethnicity.(e) Head and neck squamous-cell carcinoma (HNSCC) - Cetuximab plus radiotherapy (versus radiotherapy alone) significantly improves locoregional control and survival (hazard ratio [HR] 0.68; p = 0.005) without worsening radiotherapy-related toxicity.

Targeting Lewis Y (Ley) in Small Cell Lung Cancer with a Humanized Monoclonal Antibody, hu3S193: A Pilot Trial Testing Two Dose Levels

INTRODUCTION

Lewis Y (Le(y)) is a blood group antigen with robust expression on the surface of epithelial tumors, including small cell lung cancer (SCLC), making it a potential target for antibody-based immunotherapy. 3S193, an immunoglobulin G3 monoclonal antibody, has demonstrated superior specificity, affinity, and cytotoxicity over other anti-Le(y) antibodies. A phase I trial of humanized 3S193 (hu3S193) with dosing up to 40 mg/m2 demonstrated tumor targeting without serious toxicities or the development of human anti-human antibodies.

METHODS

We tested the targeting and pharmacokinetics of hu3S193 in patients with SCLC. Eligibility required progressive SCLC treated with up to three previous chemotherapy regimens, measurable disease not previously irradiated, and tumor samples positive for 3S193 by immunohistochemistry. Patients received four weekly injections of hu3S193, five patients at 10 mg/m2 and five patients at 20 mg/m2. The first and fourth injections were radiolabeled with indium-111 for gamma camera imaging.

RESULTS

Of 40 patients screened, 25 of 34 (74%) assessable SCLC tumor samples were 3S193 positive by immunohistochemistry. Ten patients were treated with hu3S193; nine completed all four injections. All fluorodeoxyglucose (FDG)-avid lesions >2 cm were visualized on antibody single-photon emission computed tomography. Some lesions overlying vascular structures could not be visualized. No difference was noted in imaging or pharmacokinetics between the first and fourth injections. Toxicities included grade 2 urticaria (n = 1), grade 1 vomiting (n = 2), and grade 2 hypertension (n = 1) transiently after infusion at the higher dose.

CONCLUSIONS

Given the strong tumor targeting, particularly at the higher dose, the favorable toxicity profile, and the potential for immunomodulatory effects, hu3S193 warrants further investigation in SCLC.

Anticancer carrier-linked prodrugs in clinical trials

Coupling of low molecular weight anticancer drugs to antibodies, serum proteins or polymers through a cleavable linker has been an effective method for improving the therapeutic index of cytotoxic established agents. Modern drug-antibody conjugates that have recently entered clinical trials have primarily used highly potent drugs such as calicheamicin or maytansins. Gemtuzumab ozogamicin, a conjugate of calicheamicin and an anti-CD33 humanized antibody, is the first drug-antibody conjugate to receive market approval. Drug conjugates that have undergone clinical assessment include N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates with doxorubicin, camptothecin, paclitaxel and Pt(II) complexes, poly(ethylene glycol) conjugates with camptothecin and paclitaxel, polyglutamate conjugates with paclitaxel and camptothecin, a methotrexate-albumin conjugate and an albumin-binding doxorubicin prodrug. This review summarizes the Phase I-III studies that have been performed with these macromolecular prodrugs.

Preclinical evaluation of EC145, a folate-vinca alkaloid conjugate

We recently developed a new group of folate-conjugated Vinca alkaloids, one of which, EC145, emerged as a candidate for clinical development. Brief treatment of nude mice bearing approximately 100 mm(3) folate receptor-positive human xenografts led to complete response (CR) in 5/5 mice and cures (i.e., remission without a relapse for >90 days post-tumor implantation) in 4/5 mice. Multiple CRs and cures were also noted when EC145 was used to treat mice initially bearing tumors as large as 750 mm(3). Likewise, complete cures (5/5) resulted following the treatment of an aggressive folate receptor-positive J6456 lymphoma model. The activity of EC145 was not accompanied by noticeable weight loss or major organ tissue degeneration. Furthermore, no significant antitumor activity (0/5 CR) was observed in EC145-treated animals that were co-dosed with an excess of a benign folate ligand, thus demonstrating the target-specific activity of EC145. The enhanced therapeutic index due to folate conjugation was also evidenced by the fact that the unconjugated drug (desacetylvinblastine monohydrazide) was found to be completely inactive when administered at nontoxic dose levels and only marginally active when given at highly toxic dose levels. Subsequent dose regimen studies confirmed that EC145 given on a more frequent, qdx5 schedule resulted in the most effective antitumor response as compared with an equivalent total dose given on thrice- or single-injection-per-week schedule. Taken together, these studies show that EC145 has significant antiproliferative activity and tolerability, thus lending support to an ongoing phase 1 trial for the treatment of advanced malignancies.