Primary resistance to cetuximab in a panel of patient-derived tumour xenograft models: activation of MET as one mechanism for drug resistance

Cetuximab (Erbitux®) targets the epidermal growth factor receptor (EGFR) and is approved for treatment of colorectal and head and neck cancer. Despite wide expression of EGFR, only a subgroup of cancer patients responds to cetuximab therapy. In the present study we assessed the cetuximab response in vivo of 79 human patient-derived xenografts originating from five tumour histotypes. We analysed basic tumour characteristics including EGFR expression and activation, mutational status of KRAS, BRAF and NRAS, the expression of EGFR ligands and the activation of HER3 (ErbB3) and the hepatocyte growth factor receptor MET. Based on these results, a cetuximab response score including positive and negative factors affecting therapeutic response is proposed. Positive factors are high expression and activation of EGFR and its ligands epiregulin or amphiregulin, negative factors are markers for downstream pathway activation independent of EGFR. In cetuximab resistant NSCL adenocarcinoma LXFA 526 and LXFA 1647, overexpression due to gene amplification and strong activation of MET was identified. Knock-down of MET by siRNA in the corresponding cell lines showed that anchorage-independent growth and migration are dependent on MET. MET knock down sensitized LXFA 526L and LXFA 1647L to EGF. Combined treatments of a MET inhibitor and cetuximab were additive. Therefore, combination therapy of cetuximab and a MET inhibitor in selected lung cancer patients could be of high clinical significance.     

Gene polymorphisms predict toxicity to neoadjuvant therapy in patients with rectal cancer

BACKGROUND

Toxicity from neoadjuvant chemoradiation therapy (NT) increases morbidity and limits therapeutic efficacy in patients with rectal cancer. The objective of this study was to determine whether specific polymorphisms in genes associated with rectal cancer response to NT were correlated with NT‐related toxicity.

METHODS

One hundred thirty‐two patients with locally advanced rectal cancer received NT followed by surgery. All patients received 5‐fluorouracil (5‐FU) and radiation (RT), and 80 patients also received modified infusional 5‐FU, folinic acid, and oxaliplatin chemotherapy (mFOLFOX‐6). Grade ≥3 adverse events (AEs) that occurred during 5‐FU/RT and during combined 5‐FU/RT + mFOLFOX‐6 were recorded. Pretreatment biopsy specimens and normal rectal tissues were collected from all patients. DNA was extracted and screened for 22 polymorphisms in 17 genes that have been associated with response to NT. Polymorphisms were correlated with treatment‐related grade ≥3 AEs.

RESULTS

Overall, 27 of 132 patients (20%) had grade ≥3 AEs; 18 patients had a complication associated only with 5‐FU/RT, 3 patients experienced toxicity only during mFOLFOX‐6, and 6 patients had grade ≥3 AEs associated with both treatments before surgery. Polymorphisms in the genes x‐ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1), xeroderma pigmentosum group D (XPD), and tumor protein 53 (TP53) were associated with grade ≥3 AEs during NT (P < .05). Specifically, 2 polymorphisms—an arginine‐to‐glutamine substitution at codon 399 (Q399R) in XRCC1 and a lysine‐to‐glutamine substitution at codon 751 (K751Q) in XPD—were associated with increased toxicity to 5‐FU/RT (P < .05), and an arginine‐to‐proline substitution at codon 72 (R72P) in TP53 was associated with increased toxicity to mFOLFOX‐6 (P = .008).

CONCLUSIONS

Specific polymorphisms in XRCC1, XPD, and TP53 were associated with increased toxicity to NT in patients with rectal cancer. The current results indicated that polymorphism screening may help tailor treatment for patients by selecting therapies with the lowest risk of toxicity, thus increasing patient compliance. Cancer 2013. © 2012 American Cancer Society.     

KRAS mutational status assessment in patients with metastatic colorectal cancer: are the clinical implications so clear?

HEBBAR M., FOURNIER P. & ROMANO O. (2010) European Journal of Cancer Care 19 , 145–166
KRAS mutational status assessment in patients with metastatic colorectal cancer: are the clinical implications so clear? The CRYSTAL study demonstrated an advantage in terms of objective response and progression‐free survival for the FOLFIRI–cetuximab combination compared with first‐line FOLFIRI for patients with metastatic colorectal cancer. The results of an ancillary biological study with screening for a KRAS gene mutation in 540 patients were reported at the 2008 American Society of Clinical Oncology congress. The analysis confirmed the value of adding cetuximab only in the absence of KRAS mutation. These results led to recommend restriction of the use of cetuximab in Europe to patients with a tumour bearing wild‐type KRAS. How should this apparent simplification be integrated into clinical practice? The FOLFIRI–cetuximab combination is certainly a useful supplementary first‐line option although its place in relation to other high‐dose regimens (high‐dose FOLFIRI, FOLFOXIRI or FOLFOX‐7), conventional chemotherapy plus bevacizumab, or even a fluoropyrimidine alone in the case of unresectable metastases, has yet to be specified. For subsequent lines, no study has prospectively assessed the value of the chemotherapy–anti‐epidermal growth factor receptor combination as a function of KRAS status. Should the absence of objective response constantly observed in retrospective analyses in patients with a tumour presenting a KRAS mutation definitively exclude these patients while stable disease (and potentially a slight gain in survival) may be obtained?     

Which is false: Oxaliplatin or fluoropyrimidine? An analysis of patients with KRAS wild‐type metastatic colorectal cancer treated with first‐line epidermal growth factor receptor monoclonal antibody

This meta‐analysis was performed to determine whether the addition of monoclonal antibodies (mAbs) of epidermal growth factor receptor (EGFR) to oxaliplatin‐based chemotherapy treatment improves efficacy in KRAS wild‐type metastatic colorectal cancer (mCRC), and whether infusional 5‐fluorouracil (5‐FU) and oxaliplatin is a preferred combination for EGFR mAbs. Oxaliplatin (including treatment), EGFR mAbs, first‐line treatment, KRAS wild‐type, and mCRC were used as key words. The PRIME, OPUS, COIN, and NORDIC VII trials were identified by two independent authors. Time‐to‐event outcomes of overall survival (OS) and progression‐free survival (PFS) were analyzed using HRs (hazard ratios) with fixed effect, and response rate (RR) using odd ratios (OR) with fixed effect. A total of 1767 patients who were KRAS wild‐type were included in this meta‐analysis, with 866 patients in the mAbs and chemotherapy combination group and 901 patients in the chemotherapy alone group. The addition of mAbs to oxaliplatin‐based chemotherapy in patients with KRAS wild‐type mCRC as first‐line treatment resulted in significant improvements in PFS (HR = 0.88; 95% confidence interval (CI), 0.79–0.99; P = 0.03) and response rate (RR) (OR = 1.38; 95% CI, 1.14–1.66; P = 0.009) compared with chemotherapy alone, but the difference in OS was not significant (HR = 0.96; 95% CI, 0.85–1.08; P = 0.48). However, the differences in OS and PFS were not significant when mAbs were added to bolus 5‐FU or capecitabine‐based regimens compared with chemotherapy alone, whereas PFS improved with an infusional 5‐FU and oxaliplatin combination (P = 0.06; PFS, HR = 0.76; 95% CI, 0.65–0.86; P = 0.0002), and even OS was marginally significant, which was consistent with the subgroup analysis of cetuximab and panitumumab. EGFR mAbs combined with oxaliplatin and an infusional 5‐FU regimen was associated with significantly improved RR, PFS and OS as first‐line treatment in KRAS wild‐type mCRC.     

Phase I study of cetuximab in combination with 5-fluorouracil,mitomycin C and radiotherapy in patients with locally advanced anal cancer

Background5-fluorouracil (5FU) and mitomycin C (MMC)-based chemoradiotherapy (CRT) is standard treatment for anal squamous cell carcinoma. In this phase I study cetuximab was added and the primary aim was to determine the maximum tolerated dose (MTD) of 5FU and MMC in this combination.Methods and materialsPatients with locally advanced anal cancer, T2 (≥4 cm)–4N0–3M0, received weekly standard doses of cetuximab starting 1 week before CRT. Intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) with simultaneous integrated boost (SIB) was given to 57.5/54.0/48.6 Gy in 27 fractions to primary tumour/lymph node metastases/adjuvant lymph node regions. 5FU/MMC was given concomitantly on RT weeks 1 and 5 according to a predefined dose escalation schedule.ResultsThirteen patients were enrolled. Two patients discontinued cetuximab due to hypersensitivity reaction. The median age was 65 years (range 46–70), nine were females, and 85% had stage IIIB disease. Dose-limiting toxicity events (diarrheoa, febrile neutropenia and thrombocytopenia) occurred in 3 of 11 patients. The most common grade 3–4 side-effects were radiation dermatitis (63%), haematologic toxicity (54%), and diarrheoa (36%). No treatment-related deaths occurred. Three months following completion of treatment, ten patients (91%) had a local complete remission (CR), but two patients had developed liver metastases, yielding a total CR rate of 73%.ConclusionThe MTDs were determined as 5FU 800 mg/m² on RT days 1–4 and 29–32 and MMC 8 mg/m² on days 1 and 29 when combined with IMRT/VMAT with SIB and cetuximab in locally advanced anal cancer.     

Postoperative radiation and concomitant bolus fluorouracil with or without additional chemotherapy with fluorouracil and high-dose leucovorin in patients with high-risk rectal cancer: A randomized phase III study conducted by the Hellenic Cooperative Oncology Group

Background: Randomized studies have shown that postoperative chemotherapy with or without radiation therapy (RT) improved local control and survival of patients with stages II or III rectal cancer. However, the optimal sequence of treatments and the optimal chemotherapeutic regimen have not been defined. Modulation of fluorouracil (FU) by leucovorin (LV) has yielded a highly significant difference in response rate from that of FU monotherapy, as suggested by an overview of randomized trials in patients with advanced colorectal cancer. However, this difference in response rate did not translate into a survival benefit.Purpose: To evaluate the impact on the disease-free survival (DFS) and overall survival (OS) of patients with stages II or III rectal cancer of postoperative RT and concomitant bolus FU administration alone or with additional chemotherapy using FU and high-dose LV.Patients and methods: From October 1989 until February 1997, 220 patients were randomized postoperatively to receive either one cycle of chemotherapy with FU (600 mg/m²/week × 6 followed by a two-week rest) and leucovorin (LV, 500 mg/m²/week × 6 as a two-hour infusion) followed by pelvic RT with concomitant FU (400 mg/m²) as a rapid intravenous injection during the first three and last three days of RT, and three more cycles of the same chemotherapy with FU and LV (standard, group A, 111 patients) or pelvic RT with concomitant FU only (experimental, group B, 109 patients).Results: As of August 1998, after a median follow-up of 4.9 years, there was no significant difference in either three-year DFS (Group A, 70.3%; group B, 68.2%, P = 0.53) or OS (group A, 77%; group B, 73.3%, P = 0.75). Cox multivariate analysis revealed stage of disease, number of infiltrated nodes, tumor grade, presence of regional implants and perforation to be significant prognostic factors. The incidence of severe side effects was significantly higher in the patients in group A than in those in group B (32.4% vs. 4.6%, P < 0.0001).Conclusions: The incorporation of additional chemotherapy with FU and LV into postoperative concomitant RT and bolus infusion of FU does not offer a 10% three-year survival benefit over that of concomitant RT and bolus infusion of FU, and significantly increases toxicity in patients with stages II or III rectal cancer.     

KRAS mutation status is predictive of response to cetuximab therapy in colorectal cancer

The anti-epidermal growth factor receptor (anti-EGFR) cetuximab has been proven to be efficient in metastatic colorectal cancer. The molecular mechanisms underlying the clinical response to this drug remain unknown. Genetic alterations of the intracellular effectors involved in EGFR-related signaling pathways may have an effect on response to this targeted therapy. In this study, tumors from 30 metastatic colorectal cancer patients treated by cetuximab were screened for KRAS, BRAF, and PIK3CA mutation by direct sequencing and for EGFR copy number by chromogenic in situ hybridization. Eleven of the 30 patients (37%) responded to cetuximab. A KRAS mutation was found in 13 tumors (43%) and was significantly associated with the absence of response to cetuximab (KRAS mutation in 0% of the 11 responder patients versus 68.4% of the 19 nonresponder patients; P = 0.0003). The overall survival of patients without KRAS mutation in their tumor was significantly higher compared with those patients with a mutated tumor (P = 0.016; median, 16.3 versus 6.9 months). An increased EGFR copy number was found in 3 patients (10%) and was significantly associated with an objective tumor response to cetuximab (P = 0.04). In conclusion, in this study, KRAS mutations are a predictor of resistance to cetuximab therapy and are associated with a worse prognosis. The EGFR amplification, which is not as frequent as initially reported, is also associated with response to this treatment.     

A comprehensively characterized large panel of head and neck cancer patient‐derived xenografts identifies the mTOR inhibitor everolimus as potential new treatment option

Patient‐derived xenograft (PDX) models have shown to reflect original patient tumors better than any other preclinical model. We embarked in a study establishing a large panel of head and neck squamous cell carcinomas PDX for biomarker analysis and evaluation of established and novel compounds. Out of 115 transplanted specimens 52 models were established of which 29 were characterized for response to docetaxel, cetuximab, methotrexate, carboplatin, 5‐fluorouracil and everolimus. Further, tumors were subjected to sequencing analysis and gene expression profiling of selected mTOR pathway members. Most frequent response was observed for docetaxel and cetuximab. Responses to carboplatin, 5‐fluorouracil and methotrexate were moderate. Everolimus revealed activity in the majority of PDX. Mutational profiling and gene expression analysis did not reveal a predictive biomarker for everolimus even though by trend RPS6KB1 mRNA expression was associated with response. In conclusion we demonstrate a comprehensively characterized panel of head and neck cancer PDX models, which represent a valuable and renewable tissue resource for evaluation of novel compounds and associated biomarkers.     

KRT-232 and navitoclax enhance trametinib’s anti-Cancer activity in non-small cell lung cancer patient-derived xenografts with KRAS mutations

Activating mutations of the KRAS gene are one of the major genomic alterations associated with tumorigenesis of non-small cell lung cancer (NSCLC). Thus far, treatment of KRAS-mutant NSCLC remains an unmet medical need. We determined the in vivo treatment responses of 13 KRAS mutant and 14 KRAS wild type NSCLC patient-derived xenografts (PDXs) to agents that target known NSCLC vulnerabilities: the MEK inhibitor trametinib, the MDM2 inhibitor KRT-232, and the BCL-X_L/BCL-2 inhibitor navitoclax. The results showed that the tumor regression rate after single agent therapy with KRT-232, trametinib and navitoclax was 11%, 10% and 0%, respectively. Combination therapies of trametinib plus KRT-232 and trametinib plus navitoclax led to improved partial response rates over single-agent activity in a subset of PDX models. Tumor regression was observed in 23% and 50% of PDXs after treatment with trametinib plus KRT-232 and trametinib plus navitoclax, respectively. The disease control rates in KRAS-mutant PDXs tested were 90%-100% after treatment with trametinib plus KRT-232 or plus navitoclax. A correlation analysis of treatment responses and genomic and proteomic biomarkers revealed that sensitivity to KRT-232 was significantly associated with TP53 wild-type or STK11 mutant genotypes (P<0.05). The levels of several proteins, including GSK3b, Nrf2, LKB1/pS334, and SMYD3, were significantly associated with sensitivity to trametinib plus navitoclax. Thus, the combination of trametinib plus KRT-232 or navitoclax resulted in improved efficacy compared with the agents alone in a subgroup of NSCLC PDX model with KRAS mutations. Expanded clinical trials of these targeted drug combinations in NSCLC are warranted.     

An overview of approaches to adjuvant therapy for colorectal cancer in the United States

Adjuvant chemotherapy for colon cancer and combined chemotherapy and radiation therapy (RT) for rectal cancer increases the proportion of patients cured of their disease. Adjuvant chemotherapy is indicated for stage III colon cancer, and although controversial for stage II disease, there is evidence to suggest that these patients may benefit as well. Adjuvant chemotherapy and RT is recommended for patients with stage II/III rectal cancer. Studies incorporating oral fluoropyrimidines as well as combination chemotherapy have been completed, with results demonstrating the value of these approaches. A new generation of studies will evaluate the biologic agents bevacizumab and cetuximab in the adjuvant therapy of colorectal cancer. For rectal cancer, optimal outcomes are dependent not only on the systemic therapy, but also on the expertise of the surgeon and the timing of RT, with improved local control and toxicity seen with preoperative therapy.     

西妥昔单抗联合伊立替康为主方案治疗转移性结直肠癌

目的：观察西妥昔单抗联合伊立替康治疗晚期结直肠癌的疗效、安全性及KRAS基因突变与疗效的相关性。方法：对经西妥昔单抗联合伊立替康为主方案治疗且可评价疗效的15例晚期结直肠癌患者进行疗效分析,并对其中12例患者进行KRAS基因测定,分析KRAS基因突变与疗效的相关性。结果：（1）疗效分析：15例患者治疗后取得部分缓解4例,病情稳定7例,疾病进展4例,客观有效率26.7％,疾病控制率73.3％,中位疾病进展时间16周。主要的不良反应是痤疮样皮疹、腹泻和骨髓抑制。痤疮样皮疹发生率为80％（12 /15）,腹泻发生率为46.7％（7/15）,骨髓抑制发生率为60％（9/15）。在出现痤疮样皮疹的12例患者中,客观有效率为33.3％,疾病控制率为83.3％。（2）KRAS基因突变与疗效的相关性：12例患者进行KRAS基因检测中,KRAS基因野生型的患者7例,客观有效率为28.6％,疾病控制率为85.7％,中位疾病进展时间18周;KRAS基因突变的患者5例,疗效为部分缓解1例,客观有效率为20％,疾病控制率为60％,中位疾病进展时间为12周。因纳入病例数较少,两者比较差异无统计学意义。结论：西妥昔单抗联合CPT-11为主方案对晚期结直肠癌患者有效。除痤疮样皮疹外,不良反应无明显增加。对于出现痤疮样皮疹患者提示获益可能。对于KRAS基因野生型的患者,预示西妥昔单抗联合CPT-11能获得良好的疗效,对于KRAS基因突变型的患者,预示西妥昔单抗联合CPT-11未能增加疗效。     

Afatinib treatment for her-2 amplified metastatic colorectal cancer based on patient-derived xenograft models and next generation sequencing

Background: Substantial progress has been made in metastatic colorectal cancer (mCRC) treatment, but there is still a fraction of patients cannot find any effective therapeutic strategy after guideline-recommended standard chemotherapy and molecular targeted therapy.

Case presentation: Here we present a KRAS/NRAS/BRAF wild-type mCRC patient who has been previously treated with FOLFIRI (fluorouracil, leucovorin, and irinotecan), XELOX (capecitabine and oxaliplatin), cetuximab and bevacizumab, and then received the next generation sequencing (NGS) and whose metastatic subcutaneous nodule was resected to generate patient-derived xenograft (PDX) models. The NGS revealed HER-2 amplification as well as an activating mutation S310F and PDX models tested several drugs finding that afatinib was the optimal agent with notable efficacy and well tolerance among 6 regimens. Therefore, this patient started to take afatinib orally and achieved 3 months progression-free survival (PFS) and relief of clinical symptoms without severe adverse effects.

Conclusions: NGS and PDX models have great significance for precision and individualized medicine in the mCRC treatment, especially for patients whose diseases have been progressed after multiline standard therapies.     

Progress in metastatic colorectal cancer: growing role of cetuximab to optimize clinical outcome

The prognosis of metastatic colorectal cancer remains poor despite advances made in recent years, particularly with new treatments directed towards molecular targets. Cetuximab, a chimeric immunoglobulin (Ig)G1 monoclonal antibody that targets the ligand-binding domain of the epidermal growth factor receptor (EGFR), is active in metastatic colorectal cancer. As an IgG1 antibody, cetuximab may exert its antitumour efficacy through both EGFR antagonism and antibody-dependent cell-mediated cytotoxicity. The benefits of cetuximab in metastatic colorectal cancer are well documented in clinical trials and are acknowledged in the approval and licensing of this agent. There is evidence of the role of cetuximab not only in irinotecan-refractory or heavily pretreated patients, but also of the efficacy and safety of the addition of this agent to FOLFIRI (irinotecan/5-fluorouracil/leucovorin) in first-line metastatic colorectal cancer, with an enhanced effect in 5-fluorouracil patients with Kirsten rat sarcoma (KRAS) wild-type tumours. In these patients, a recent meta-analysis of the pooled Cetuximab Combined with Irinotecan in First-Line Therapy for Metastatic Colorectal Cancer (CRYSTAL) and Oxaliplatin and Cetuximab in First-Line Treatment of mCRC (OPUS) patient populations confirms that the addition of cetuximab to first-line chemotherapy achieves a statistically significant improvement in the best overall response, overall survival time, and progression-free survival (PSF) compared with chemotherapy alone. In nonresectable colorectal liver metastases, cetuximab plus FOLFOX-6 (oxaliplatin/5-fluorouracil/leucovorin) or cetuximab plus FOLFIRI increased significantly resectability of liver metastases, including R0 resections. Also, preliminary data indicate that cetuximab can be administered in a more convenient 2-week schedule in combination with standard chemotherapy. Cetuximab is generally well tolerated. Acne-form rash is the most frequent toxicity. Up to the present time, the results obtained with targeted therapy combinations are not as encouraging as initially expected. The identification of biomarkers associated with disease control, including KRAS and BRAF mutation status in patients treated with cetuximab, is changing the current management of metastatic colorectal cancer. Clinical and molecular predictive markers of response are under active evaluation in order to better select patients who could benefit from cetuximab treatment, with the aim of both optimising patient outcomes and avoiding unnecessary toxicities.     

5‐Fluorouracil preferentially sensitizes mutant KRAS non‐small cell lung carcinoma cells to TRAIL‐induced apoptosis

Mutations in the KRAS gene are very common in non–small cell lung cancer (NSCLC), but effective therapies targeting KRAS have yet to be developed. Interest in tumor necrosis factor–related apoptosis‐inducing ligand (TRAIL), a potent inducer of cell death, has increased following the observation that TRAIL can selectively kill a wide variety of human cancer cells without killing normal cells both in vitro and in xenograft models. However, results from clinical trials of TRAIL‐based therapy are disappointingly modest at best and many have demonstrated a lack of therapeutic benefit. Current research has focused on selecting a subpopulation of cancer patients who may benefit from TRAIL‐based therapy and identifying best drugs to work with TRAIL. In the current study, we found that NSCLC cells with a KRAS mutation were highly sensitive to treatment with TRAIL and 5‐fluorouracil (5FU). Compared with other chemotherapeutic agents, 5FU displayed the highest synergy with TRAIL in inducing apoptosis in mutant KRAS NSCLC cells. We also found that, on a mechanistic level, 5FU preferentially repressed survivin expression and induced expression of TRAIL death receptor 5 to sensitize NSCLC cells to TRAIL. The combination of low‐dose 5FU and TRAIL strongly inhibited xenograft tumor growth in mice. Our results suggest that the combination of TRAIL and 5FU may be beneficial for patients with mutant KRAS NSCLC.     

Using heterogeneity of the patient-derived xenograft model to identify the chemoresistant population in ovarian cancer

A cornerstone of preclinical cancer research has been the use of clonal cell lines. However, this resource has underperformed in its ability to effectively identify novel therapeutics and evaluate the heterogeneity in a patient''s tumor. The patient-derived xenograft (PDX) model retains the heterogeneity of patient tumors, allowing a means to not only examine efficacy of a therapy, but also basic tenets of cancer biology in response to treatment. Herein we describe the development and characterization of an ovarian-PDX model in order to study the development of chemoresistance. We demonstrate that PDX tumors are not simply composed of tumor-initiating cells, but recapitulate the original tumor''s heterogeneity, oncogene expression profiles, and clinical response to chemotherapy. Combined carboplatin/paclitaxel treatment of PDX tumors enriches the cancer stem cell populations, but persistent tumors are not entirely composed of these populations. RNA-Seq analysis of six pair of treated PDX tumors compared to untreated tumors demonstrates a consistently contrasting genetic profile after therapy, suggesting similar, but few, pathways are mediating chemoresistance. Pathways and genes identified by this methodology represent novel approaches to targeting the chemoresistant population in ovarian cancer     

Primary resistance to cetuximab therapy in EGFR FISH-positive colorectal cancer patients

The impact of KRAS mutations on cetuximab sensitivity in epidermal growth factor receptor fluorescence in situ hybridisation-positive (EGFR FISH+) metastatic colorectal cancer patients (mCRC) has not been previously investigated. In the present study, we analysed KRAS, BRAF, PI3KCA, MET, and IGF1R in 85 mCRC treated with cetuximab-based therapy in whom EGFR status was known. KRAS mutations (52.5%) negatively affected response only in EGFR FISH+ patients. EGFR FISH+/KRAS mutated had a significantly lower response rate (P=0.04) than EGFR FISH+/KRAS wild type patients. Four EGFR FISH+ patients with KRAS mutations responded to cetuximab therapy. BRAF was mutated in 5.0% of patients and none responded to the therapy. PI3KCA mutations (17.7%) were not associated to cetuximab sensitivity. Patients overexpressing IGF1R (74.3%) had significantly longer survival than patients with low IGF1R expression (P=0.006), with no difference in response rate. IGF1R gene amplification was not detected, and only two (2.6%) patients, both responders, had MET gene amplification. In conclusion, KRAS mutations are associated with cetuximab failure in EGFR FISH+ mCRC, even if it does not preclude response. The rarity of MET and IGF1R gene amplification suggests a marginal role in primary resistance. The potential prognostic implication of IGF1R expression merits further evaluation.     

Evaluation of azacitidine and entinostat as sensitization agents to cytotoxic chemotherapy in preclinical models of non-small cell lung cancer

Recent clinical data in lung cancer suggests that epigenetically targeted therapy may selectively enhance chemotherapeutic sensitivity. There have been few if any studies rigorously evaluating this hypothesized priming effect. Here we describe a series of investigations testing whether epigenetic priming with azacitidine and entinostat increases sensitivity of NSCLC to cytotoxic agents.We noted no differences in chemosensitivity following treatment with epigenetic therapy in in vitro assays of viability and colony growth. Using cell line and patient-derived xenograft (PDX) models, we also observed no change in responsiveness to cisplatin in vivo. In select models, we noted differential responses to irinotecan treatment in vivo. In vitro epigenetic therapy prior to tumor implantation abrogated response of H460 xenografts to irinotecan. Conversely, in vitro epigenetic therapy appeared to sensitize A549 xenografts (tumor growth inhibition 51%, vs. 22% in mock-pretreated control). In vivo epigenetic therapy enhanced the response of adenocarcinoma PDX to irinotecan.Taken together, these data do not support broadly applicable epigenetic priming in NSCLC. Priming effects may be context-specific, dependent on both tumor and host factors. Further preclinical study is necessary to determine whether, and in which contexts, priming with epigenetic therapy has potential to enhance chemotherapeutic efficacy in NSCLC patients.     

Radioresistance of KRAS/TP53-mutated lung cancer can be overcome by radiation dose escalation or EGFR tyrosine kinase inhibition in vivo

Recent clinical data have linked KRAS/TP53 comutation (mut) to resistance to radiotherapy (RT), but supporting laboratory in vivo evidence is lacking. In addition, the ability of different radiation doses, with/without epidermal growth factor receptor (EGFR)-directed treatment, to achieve local tumor control as a function of KRAS status is unknown. Here, we assessed clonogenic radiation survival of a panel of annotated lung cancer cell lines. KRASmut/TP53mut was associated with the highest radioresistance in nonisogenic and isogenic comparisons. To validate these findings, isogenic TP53mut NCI-H1703 models, KRASmut or wild-type (wt), were grown as heterotopic xenografts in nude mice. A clinical RT schedule of 30 fractions over 6 weeks was employed. The dose that controlled 50% of tumors (TCD₅₀) was calculated. The TCD₅₀ for KRASwt/TP53mut xenografts was 43.1 Gy whereas KRASmut/TP53mut tumors required a 1.9-fold higher TCD₅₀ of 81.4 Gy. The EGFR inhibitor erlotinib radiosensitized KRASmut but not KRASwt cells and xenografts. The TCD₅₀ associated with adding erlotinib to RT was 58.8 Gy for KRASmut, that is, a ~1.4-fold dose enhancement. However, the EGFR antibody cetuximab did not have a radiosensitizing effect. In conclusion, we demonstrate for the first time that KRASmut in a TP53mut background confers radioresistance when studying a clinical RT schedule and local control rather than tumor growth delay. Despite the known unresponsiveness of KRASmut tumors to EGFR inhibitors, erlotinib radiosensitized KRASmut tumors. Our data highlight KRAS/TP53 comutation as a candidate biomarker of radioresistance that can be at least partially reversed by dose escalation or the addition of a targeted agent.     

A molecularly annotated platform of patient-derived xenografts ("xenopatients") identifies HER2 as an effective therapeutic target in cetuximab-resistant colorectal cancer

Only a fraction of patients with metastatic colorectal cancer receive clinical benefit from therapy with anti-epidermal growth factor receptor (EGFR) antibodies, which calls for the identification of novel biomarkers for better personalized medicine. We produced large xenograft cohorts from 85 patient-derived, genetically characterized metastatic colorectal cancer samples ("xenopatients") to discover novel determinants of therapeutic response and new oncoprotein targets. Serially passaged tumors retained the morphologic and genomic features of their original counterparts. A validation trial confirmed the robustness of this approach: xenopatients responded to the anti-EGFR antibody cetuximab with rates and extents analogous to those observed in the clinic and could be prospectively stratified as responders or nonresponders on the basis of several predictive biomarkers. Genotype-response correlations indicated HER2 amplification specifically in a subset of cetuximab-resistant, KRAS/NRAS/BRAF/PIK3CA wild-type cases. Importantly, HER2 amplification was also enriched in clinically nonresponsive KRAS wild-type patients. A proof-of-concept, multiarm study in HER2-amplified xenopatients revealed that the combined inhibition of HER2 and EGFR induced overt, long-lasting tumor regression. Our results suggest promising therapeutic opportunities in cetuximab-resistant patients with metastatic colorectal cancer, whose medical treatment in the chemorefractory setting remains an unmet clinical need. SIGNIFICANCE: Direct transfer xenografts of tumor surgical specimens conserve the interindividual diversity and the genetic heterogeneity typical of the tumors of origin, combining the flexibility of preclinical analysis with the informative value of population-based studies. Our suite of patient-derived xenografts from metastatic colorectal carcinomas reliably mimicked disease response in humans, prospectively recapitulated biomarker-based case stratification, and identified HER2 as a predictor of resistance to anti-epidermal growth factor receptor antibodies and of response to combination therapies against HER2 and epidermal growth factor receptor in this tumor setting.