Anti-epidermal Growth Factor Receptor Drugs Research Articles

Head and neck cancer: pathogenesis and targeted therapy.

Head and neck cancer (HNC) is a highly aggressive type of tumor characterized by delayed diagnosis, recurrence, metastasis, relapse, and drug resistance. The occurrence of HNC were associated with smoking, alcohol abuse (or both), human papillomavirus infection, and complex genetic and epigenetic predisposition. Currently, surgery and radiotherapy are the standard treatments for most patients with early-stage HNC. For recurrent or metastatic (R/M) HNC, the first-line treatment is platinum-based chemotherapy combined with the antiepidermal growth factor receptor drug cetuximab, when resurgery and radiation therapy are not an option. However, curing HNC remains challenging, especially in cases with metastasis. In this review, we summarize the pathogenesis of HNC, including genetic and epigenetic changes, abnormal signaling pathways, and immune regulation mechanisms, along with all potential therapeutic strategies such as molecular targeted therapy, immunotherapy, gene therapy, epigenetic modifications, and combination therapies. Recent preclinical and clinical studies that may offer therapeutic strategies for future research on HNC are also discussed. Additionally, new targets and treatment methods, including antibody-drug conjugates, photodynamic therapy, radionuclide therapy, and mRNA vaccines, have shown promising results in clinical trials, offering new prospects for the treatment of HNC.

Angiogenesis inhibition in metastatic colorectal cancer continuum of care

Current treatment for most patients with metastatic colorectal cancer consists of sequential lines of different systemic therapies, including chemotherapy combinations (5-fluorouracil plus irinotecan or oxaliplatin) with the addition of molecular-targeted drugs, such as anti-angiogenic drugs (independently of the molecular characterisation of the tumour) or anti-epidermal growth factor receptor drugs (for patients whose tumours are wild type for KRAS and NRAS genes). More recently, for the subgroup of patients with high microsatellite instable or mismatch repair deficient tumours (approximately 5% of patients), immune checkpoint inhibitors (pembrolizumab or nivolumab plus ipilimumab) have been shown to be highly effective as first-line or second-line therapies. 1 Ciardiello F Ciardiello D Martini G Napolitano S Tabernero J Cervantes A Clinical management of metastatic colorectal cancer in the era of precision medicine. CA Cancer J Clin. 2022; 72: 372-401 Crossref PubMed Scopus (49) Google Scholar , 2 Cervantes A Adam R Roselló S et al. Metastatic colorectal cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Ann Oncol. 2023; 34: 10-32 Summary Full Text Full Text PDF PubMed Scopus (70) Google Scholar Furthermore, in patients whose tumours show HER2 gene amplification, BRAFV600E mutation, or KRASG12C mutation, current treatment options also incorporate the corresponding appropriate molecular-targeted drugs. 1 Ciardiello F Ciardiello D Martini G Napolitano S Tabernero J Cervantes A Clinical management of metastatic colorectal cancer in the era of precision medicine. CA Cancer J Clin. 2022; 72: 372-401 Crossref PubMed Scopus (49) Google Scholar , 2 Cervantes A Adam R Roselló S et al. Metastatic colorectal cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Ann Oncol. 2023; 34: 10-32 Summary Full Text Full Text PDF PubMed Scopus (70) Google Scholar Fruquintinib versus placebo in patients with refractory metastatic colorectal cancer (FRESCO-2): an international, multicentre, randomised, double-blind, phase 3 studyFruquintinib treatment resulted in a significant and clinically meaningful benefit in overall survival compared with placebo in patients with refractory metastatic colorectal cancer. These data support the use of fruquintinib as a global treatment option for patients with refractory metastatic colorectal cancer. Ongoing analysis of the quality of life data will further establish the clinical benefit of fruquintinib in this patient population. Full-Text PDF

Third-line treatment patterns and clinical outcomes for metastatic colorectal cancer: a retrospective real-world study.

There are multiple recommendations on the third-line therapy of metastatic colorectal cancer (mCRC); however, no consensus has been reached. This study aimed to explore the patient demographics and the real-world third-line treatment landscape of mCRC. A retrospective real-world cohort study. Electronic medical records of mCRC patients from Tianjin Medical University Cancer Institute and Hospital between 2013 and 2020 were collected. Upon descriptive, comparative, and survival analyses, a retrospective study was conducted to describe demographics and clinical outcomes of mCRC patients receiving third-line treatment. Among 218 mCRC patients receiving third-line therapy, 65.5% received chemotherapy combined with or without targeted drugs, followed by anti-angiogenic monotherapy (18.4%), anti-epidermal growth factor receptor drugs (6.9%) and immunotherapy (6.4%). The overall response rate and disease control rate reached 10.2% and 59.2%, respectively; and median progression-free survival (PFS) and overall survival were 4.0 m and 10.7 m, respectively. After Cox multivariate analysis, we found that therapeutic regime was an independent prognostic factor. Compared to patients receiving anti-angiogenic monotherapy, those receiving chemotherapy combined with or without targeted drugs exhibited better prognosis. For patients whose PFS were longer in the front-line treatment, the PFS of third-line therapy was also relatively longer (p = 0.023). Multiple types of therapies (>3, p = 0.002) or multiple drugs (>5, p = 0.024) in the whole-course management of mCRC are indicators of longer survival. Chemotherapy combined with or without targeted therapy remained dominated third-line choice and showed favorable efficacy compared with anti-angiogenic monotherapy. With the application of more types and quantities of effective drugs, patients would achieve better survival.

P-68 Regorafenib monotherapy as second-line treatment of patients with RAS-mutant advanced colorectal cancer (STREAM): An academic, multicenter, single-arm, two-stage, phase 2 study

Therapeutic options after first-line treatment in patients with RAS mutant metastatic colorectal cancer (mCRC) are limited by poor clinical outcomes and lack of activity of anti-epidermal growth factor receptor drugs. Maintaining angiogenesis inhibition and switching the chemotherapy backbone represents the current therapeutic strategy of second-line mCRC therapy. Regorafenib, an oral broad-spectrum multikinase inhibitor targeting angiogenesis, has been shown to prolong overall survival (OS) and is approved after progression on chemotherapy. STREAM trial was an academic, multicentric, phase 2, single-arm, Simon’s two-stage design, aimed to establish the activity of regorafenib, defined as the rate of patients alive and progression free after 6months from study entry (6mo-PFS) in patients with RAS mutant mCRC, after progression on fluoropyrimidine, oxaliplatin and bevacizumab.Setting α and β errors at 0.10, defining a 6mo-PFS rate of 30% as p0 and 50% as p1, to consider the study positive ≧8 patients without progression at 6mo, were needed in the first stage (N=22) and ≧18 in the overall population (N=46). Regorafenib was administered orally at the approved schedule of 160mg day1-21 q28. Secondary endpoints were the evaluation of toxicity, objective response rate (ORR), progression-free survival (PFS), OS. Early metabolic response assessed by PET-CT scan after 2 weeks of treatment was an exploratory endpoint. Translational analyses are ongoing and will be presented at a later stage. Between November 2015, and December 2020, 46 patients were enrolled. median age was 67ys; 80.4% had ECOG performance status 0, 32.6% single organ involvement, 26% lung-limited disease. The study did not meet its predefined primary endpoint. Eight of the first 22 patients and 14 in the overall population were 6mo-PFS, as compared to the 18 required by the study protocol. At a median follow-up of 50.2 months (95%CI=24.2-56.3), ORR was 10.9%, Disease Control Rate (DCR) was 54.6%, median (m)PFS was 3.6mo (95%CI=1.9-6.7).Despite the short mPFS, regorafenib did not preclude a subsequent treatment: mPFS2 (from study entry to progression to subsequent treatment line) was 13.3mo (95%CI=8.4-19.7) and mOS was 18.9mo (95%CI=10.3-35.3). No unexpected toxicity was reported. Grade≥3 AEs occurred in 18 patients(39.1%), mostly hand foot syndrome(13%), fatigue and bilirubin increase(6.5%). Early metabolic response with PET/CT was not associated with ORR, mPFS and mOS. Baseline metabolic assessment, not predictive of ORR and mPFS, was significantly associated with mOS. A subgroup of patients, with single organ involvement, mostly lung-limited disease, low baseline PET-CT parameters, a low rate of early progression in first line (<6months=21.4%) and a long mPFS2 (23.3mo 95%CI=13.3-39.9), reported a long disease control with regorafenib: ORR=35.7%; mPFS=10.2mo (95%CI =8.6-13.5), mOS=38.8mo (95%CI=23.9-NR). Conversely, patients with higher radiological and metabolic burden of disease, higher rate of early progression in first-line (<6months=56.3%) and a shorter mPFS2 (8.4mo CI95%=6.1-13.3), reported unfavorable outcomes. Despite the study did not meet its primary endpoint, treatment with regorafenib had no unexpected toxicity and did not preclude efficacy of subsequent treatments. A subgroup of patients characterized by good prognostic features (limited disease, lung metastasis and low metabolic burden) had clinical benefit with regorafenib. Appropriate patients selection might guide the clinical development of regorafenib in an earlier setting, ensuring a chemotherapy-free interval in the treatment sequence.

Optimizing treatment with anti-epidermal growth factor receptor drugs for patients with metastatic colorectal cancer: novel mechanisms of resistance beyond RAS

Optimizing treatment with anti-epidermal growth factor receptor drugs for patients with metastatic colorectal cancer: novel mechanisms of resistance beyond RAS

Molecular targeted treatment of metastatic colorectal cancer: the cardiovascular adverse effects of Bevacizumab and Cetuximab.

Novel emerging therapies have changed paradigms in metastatic colorectal cancer. The advantages of molecular targeted treatments, either the anti-angiogenic or the anti-epidermal growth factor receptor drugs, reside in the fact that while their specificity for the cancer cell is higher, their toxicity on normal tissues is significantly lower when compared to chemotherapy. But when it comes to their safety, especially from a cardiovascular point of view, they still need to pass the test of time and further prospective studies are needed. Clinical trial patients are very well selected with regards to comorbidities and therefore, they often differ from real-life patients. In order to maximize the benefits from these drugs, we need to better identify the population at risk, understand and early diagnose their on- and off-target adverse effects and to adequately choose the diagnostic tools; with a better prevention and early treatment, the quality and quantity of our patients’ lives can be significantly improved.

SMO Gene Amplification and Activation of the Hedgehog Pathway as Novel Mechanisms of Resistance to Anti-Epidermal Growth Factor Receptor Drugs in Human Lung Cancer.

Resistance to tyrosine kinase inhibitors (TKI) of EGF receptor (EGFR) is often related to activation of other signaling pathways and evolution through a mesenchymal phenotype. Because the Hedgehog (Hh) pathway has emerged as an important mediator of epithelial-to-mesenchymal transition (EMT), we studied the activation of Hh signaling in models of EGFR-TKIs intrinsic or acquired resistance from both EGFR-mutated and wild-type (WT) non-small cell lung cancer (NSCLC) cell lines. Activation of the Hh pathway was found in both models of EGFR-mutated and EGFR-WT NSCLC cell line resistant to EGFR-TKIs. In EGFR-mutated HCC827-GR cells, we found SMO (the Hh receptor) gene amplification, MET activation, and the functional interaction of these two signaling pathways. In HCC827-GR cells, inhibition of SMO or downregulation of GLI1 (the most important Hh-induced transcription factor) expression in combination with MET inhibition exerted significant antitumor activity.In EGFR-WT NSCLC cell lines resistant to EGFR inhibitors, the combined inhibition of SMO and EGFR exerted a strong antiproliferative activity with a complete inhibition of PI3K/Akt and MAPK phosphorylation. In addition, the inhibition of SMO by the use of LDE225 sensitizes EGFR-WT NSCLC cells to standard chemotherapy. This result supports the role of the Hh pathway in mediating resistance to anti-EGFR-TKIs through the induction of EMT and suggests new opportunities to design new treatment strategies in lung cancer.

Celecoxib increases EGF signaling in colon tumor associated fibroblasts, modulating EGFR expression and degradation.

We previously demonstrated that non-toxic doses of Celecoxib induced the immediate phosphorylation of Erk1-2 in colon tumor associated fibroblasts (TAFs), increasing their responsiveness to epidermal growth factor (EGF). We have now identified two concomitant mechanisms explaining the EGF-Celecoxib cooperation. We found that a 24-48h Celecoxib priming increased EGF receptor (EGFR) mRNA and protein levels in colon TAFs, promoting EGF binding and internalization. Celecoxib-primed TAFs showed a reduced EGFR degradation after EGF challenge. This delay corresponded to a deferred dissociation of EEA1 from EGFR positive endosomes and the accumulation of Rab7, pro Cathepsin-D and SQSTM1/p62, suggesting a shared bottleneck in the pathways of late-endosomes/autophagosomes maturation. Celecoxib modulated the levels of target proteins similarly to the inhibitors of endosome/lysosome acidification Bafilomycin-A1 and NH(4)Cl. Cytoplasmic vesicles fractionation showed a reduced maturation of Cathepsin-D in late endosomes and an increased content of EGFR and Rab7 in lysosomes of Celecoxib-treated TAFs.Our data indicate a double mechanism mediating the increased response to EGF of colon TAFs treated with Celecoxib. While EGFR overexpression could be targeted using anti EGFR drugs, the effects on endosome trafficking and protein turnover represents a more elusive target and should be taken into account for any long-term therapy with Celecoxib.

Chemotherapy combined with target drugs in the treatment of advanced colorectal cancer: a meta-analysis based on Chinese patients.

Colorectal carcinoma is one of most diagnosed solid malignant carcinoma. The chemotherapy combined with target drugs in the treatment of advanced colorectal cancer in not conclusive. The clinical studies reporting the activity and adverse events between chemotherapy alone versus chemotherapy combined with anti-epidermal growth factor receptor drugs were screened in the databases of Medline, the Cochrane Library, Wanfang and CNKI and included in this meta-analysis. The risk ratio (RR) and its 95% confidence interval (CI) for treatment response and adverse events were pooled by random or fixed effect model. A total of 10 clinical studies reporting chemotherapy combined with the target in the treatment of advanced colorectal cancer were included in this study. The pooled RR was 3.26 (95% CI: 1.74-6.11, P < 0.05), 1.49 (95% CI: 1.23-1.80) and 1.65 (95% CI: 1.37-1.98) for complete response (CR), partial response and objective response rate, respectively. For nausea and vomiting events, the RR was 1.62 (95% CI: 1.33-1.97, P < 0.05) indicating higher incidence of nausea and vomiting was observed in the combined group compared with chemotherapy alone. However, the diarrhea (RR = 1.10, 95% CI: 0.86-1.42, P > 0.05), liver function damage (RR = 1.03, 95% CI: 0.74-1.42), myelosuppression (RR = 1.04, 95% CI: 0.83-1.31) and neurotoxicity (RR = 1.12, 95% CI: 0.93-1.35) were not different between the two groups. For Chinese patients with advanced colorectal cancer, chemotherapy combined with target drug can improve the response rate, but also increase the risk of nausea and vomiting.

Primary Colectomy in Patients With Stage IV Colon Cancer and Unresectable Distant Metastases Improves Overall Survival: Results of a Multicentric Study

Whether patients with stage IV colon cancer and unresectable distant metastases should be managed by primary colectomy followed by chemotherapy or immediate chemotherapy without resection of the primary tumor is still controversial. This study aimed to evaluate predictive factors associated with survival in patients with stage IV colon cancer and unresectable distant metastases. This large retrospective multicentric study included 6 academic hospitals. This study was conducted at 6 Paris University Hospitals (Assistance Publique-Hôpitaux de Paris; Saint Antoine, Henri Mondor, Ambroise Paré, Hôpital Europeen Gorges Pompidou, Bichat, and Avicenne). Between 1998 and 2007, 208 patients with good performance status and stage IV colon cancer with unresectable distant metastases received chemotherapy, either as initial management or after primary tumor resection. Survival was estimated by use of the Kaplan-Meier method. Factors associated with survival were tested by means of a log-rank test. Results were expressed as median values with 95% confidence intervals. Factors independently related to survival were tested using a Cox regression model adjusted for a propensity score. Of the 208 patients, 85 underwent colectomy before chemotherapy, whereas 123 were treated with use of primary chemotherapy with or without biotherapy. At univariate analysis, the following factors were significantly associated with survival: primary colectomy (P = .031), secondary curative surgery (P < .001), well-differentiated primary tumor (P < .001), exclusive liver metastases (P < .027), absence of need for colonic stent (P = .009), and addition of antiangiogenic (P = .001) or anti-epidermal growth factor receptor (P = .013) drugs to chemotherapy. After Cox multivariate analysis and after adjusting for the propensity score, all of these factors, with the exception of two, colonic stent and anti-epidermal growth factor receptor drug, were found to be independently associated with overall survival. This study was limited by its retrospective nature. In a selected population of patients with colon cancer and unresectable synchronous distant metastases, immediate colectomy followed by chemotherapy in association with targeted therapy was associated with longer overall survival. This strategy appears to be the most appropriate, especially for those with good performance status, well-differentiated tumors, and synchronous liver metastases only.

Infusional 5-Fluorouracil and ZD1839 (Gefitinib–Iressa) in Combination With Preoperative Radiotherapy in Patients With Locally Advanced Rectal Cancer: A Phase I and II Trial (1839IL/0092)

To report the final data of a Phase I and II study (1839IL/0092) on the combination of an anti-epidermal growth factor receptor drug (gefitinib), infusional 5-fluorouracil, and preoperative radiotherapy in locally advanced, resectable rectal cancer. Patients received 45 Gy in the posterior pelvis plus a boost of 5.4 Gy on the tumor and corresponding mesorectum. Infusional 5-fluorouracil (5-FU) and gefitinib (250 and 500 mg/day) were delivered during all radiotherapy course. An IORT boost of 10 Gy was allowed. The main endpoints of the study were to establish dose-limiting toxicity (DLT) and to evaluate the rate of pathologic response according to the tumor regression grade (TRG) Mandard score. A total of 41 patients were enrolled. The DLT was not reached in the 6 patients enrolled in the dose-escalation part of the study. Of the 33 patients in the Phase II, TRG 1 was recorded in 10 patients (30.3%) and TRG 2 in 7 patients (21.2 %); overall 17 of 33 patients (51.5%) had a favorable endpoint. Overall, Grade 3+ toxicity was recorded in 16 patients (41%); these included Grade 3+ gastrointestinal toxicity in 8 patients (20.5%), Grade 3+ skin toxicity in 6 (15.3%), and Grade 3+ genitourinary toxicity in 4 (10.2%). A dose reduction of gefitinib was necessary in 24 patients (61.5%). Gefitinib can be associated with 5-FU-based preoperative chemoradiation at the dose of 500 mg without any life-threatening toxicity and with a high pCR (30.3%). The relevant rate of Grade 3 gastrointestinal toxicity suggests that 250 mg would be more tolerable dose in a neaoadjuvant approach with radiotherapy and infusional 5-FU.

Computational design of antibody-affinity improvement beyond in vivo maturation

Antibodies are used extensively in diagnostics and as therapeutic agents. Achieving high-affinity binding is important for expanding detection limits, extending dissociation half-times, decreasing drug dosages and increasing drug efficacy. However, antibody-affinity maturation in vivo often fails to produce antibody drugs of the targeted potency, making further affinity maturation in vitro by directed evolution or computational design necessary. Here we present an iterative computational design procedure that focuses on electrostatic binding contributions and single mutants. By combining multiple designed mutations, a tenfold affinity improvement to 52 pM was engineered into the anti-epidermal growth factor receptor drug cetuximab (Erbitux), and a 140-fold improvement in affinity to 30 pM was obtained for the anti-lysozyme model antibody D44.1. The generality of the methods was further demonstrated through identification of known affinity-enhancing mutations in the therapeutic antibody bevacizumab (Avastin) and the model anti-fluorescein antibody 4-4-20. These results demonstrate computational capabilities for enhancing and accelerating the development of protein reagents and therapeutics.

Synergistic cytotoxic interaction in hormone-refractory prostate cancer with the triple combination docetaxel–erlotinib and 5-fluoro-5′-deoxyuridine

The current reference treatment of hormone-refractory prostate cancer consists mainly of chemotherapy with docetaxel. To improve the management of advanced prostate cancer, one should examine the benefits of adding other agents to docetaxel. We examined the growth inhibitory effects of a triple combination, including the anti-epidermal growth factor receptor drug erlotinib, docetaxel and 5-fluoro-5'-deoxyuridine (the main intermediary metabolite of capecitabine), on the human prostate cancer cell lines PC3 and DU145, which are both devoid of androgen receptors. Marked synergistic cytotoxic effects were observed with the application of the double combination of erlotinib-5-fluoro-5'-deoxyuridine for both cell lines and to a lesser magnitude with the triple combination. For PC3 cells, all conditions resulted in synergistic interactions. The combination between erlotinib and docetaxel resulted in an approximately 50% reduction in thymidylate synthase activity (the molecular target of 5-fluorodeoxyuridine monophosphate, the active capecitabine anabolite) with an higher impact observed with DU145 cells than with PC3 cells. Neither erlotinib nor docetaxel alone displayed marked effects on thymidine phosphorylase activity (the enzyme that governs at the cellular level the final and crucial step in the activation cascade of capecitabine), in contrast to their combination that resulted in a strong increase in thymidine phosphorylase activity in PC3 cells. These data may serve as a rational basis for setting up clinical trials in advanced prostate cancer combining epidermal growth factor receptor-targeting agents like erlotinib together with docetaxel and capecitabine.

Epidermal growth factor receptor/angiogenesis dual targeting: preclinical experience

This review aims to critically examine the preclinical background regarding the combination of drugs targeting the epidermal growth factor receptor and anti-angiogenic compounds. There are studies exploring the anti-tumor efficacy of dual inhibitors, such as the compound ZD6474, which combines in the same molecule an anti-tyrosine kinase activity against the epidermal growth factor receptor and the vascular endothelial growth factor receptor. In addition, several studies have investigated the anti-tumor effects of combinations of an anti-epidermal growth factor receptor agent and a vascular endothelial growth factor receptor inhibitor. In general, in these studies, supra-additive anti-tumor efficacy was apparent when combining anti-epidermal growth factor receptor and anti-angiogenic treatments. Beneficial effects were also observed when combining this dual targeted therapy with either conventional chemotherapy or irradiation. Early clinical trials combining the anti-epidermal growth factor receptor drug erlotinib (Tarceva) and the anti-angiogenic agent bevacizumab (Avastin) show acceptable toxicity and promising anti-tumor activity (lung cancer), which need to be confirmed in randomized trials.

Epidermal growth factor receptor expression and gene amplification in colorectal carcinoma: an immunohistochemical and chromogenic in situ hybridization study

Recent data suggest that detection of epidermal growth factor receptor protein by immunohistochemistry (IHC) does not predict response to the antiepidermal growth factor receptor drug, cetuximab, in patients with colorectal carcinoma. In searching for foundation for further investigation to optimize patient selection for cetuximab therapy, this study sought to exploit the tissue microarray and chromogenic in situ hybridization techniques to evaluate the status of epidermal growth factor receptor gene amplification in colorectal cancer and its relationship with protein expression by IHC. The study included 158 primary or metastatic colorectal adenocarcinomas. Immunohistochemical results were scored as 0–3+ based on the intensity of membrane staining. The in situ hybridization signals were counted in 30 nuclei per tissue core. Overall, the rate of tissue loss was 7%, yielding 147 analyzable cases: 123 primary, 24 metastatic. Positive immunohistochemical staining of any intensity was detected in 85% (105/123) of primary and 79% (19/24) of metastatic tumors, whereas gene amplification (>5 gene copies/nucleus) was only seen in 12% (15/123) of primary and 8% (2/24) of metastatic tumors. Only 2/15 primary and 1/2 metastatic tumors that showed gene amplification were amplified at a high level (>10 gene copies/nucleus). Although a positive correlation was detected between the intensity of protein expression and the likelihood of gene amplification in both the primary (P=0.01) and the metastatic (P=0.05) tumors, IHC had a low specificity (17% in primary, 23% in metastatic) in predicting gene amplification. Conversely, all tumors that did not express the protein by IHC lacked gene amplification. Thus, this study shows that only a small fraction of epidermal growth factor receptor- positive colorectal carcinomas detected by IHC are associated with gene amplification. Additional studies are needed to determine whether epidermal growth factor receptor gene amplification bears any informative value in predicting response to cetuximab-based therapy.

Inhibition of human tumor growth in nude mice by a conjugate of doxorubicin with monoclonal antibodies to epidermal growth factor receptor.

Monoclonal antibodies that recognize the extracellular domain of the epidermal growth factor receptor (mAb108) were conjugated with doxorubicin through a dextran bridge. Several antibody-drug conjugates, containing different amounts of doxorubicin, retained binding capacity to human epidermoid carcinoma (KB) cells overexpressing epidermal growth factor receptors. Slight decrease in drug cytotoxicity was seen in in vitro tests, as determined either by inhibition of thymidine incorporation into cells or by reduction in number and size of KB-cell colonies. Yet, when tested in vivo against KB tumor xenografted into nude mice, the anti-epidermal growth factor-receptor drug conjugates with high drug-substitution levels were significantly more effective than free doxorubicin, antibody alone, mixture of dextran-doxorubicin and antibody, or drug conjugated with irrelevant antibody. When the labile covalent bonds linking antibody to dextran bridge were stabilized by reduction, the therapeutic efficacy of the conjugate was markedly decreased. These results show that antibodies against the extracellular domain of the epidermal growth factor can deliver doxorubicin specifically and efficiently to tumor sites that express high receptor levels exerting a specific antitumor effect.