Predictive value of the fluorescent cytoprint assay (FCA): a retrospective correlation study of in vitro chemosensitivity and individual responses to chemotherapy

Benefits of functional assays in personalized cancer medicine: more than just a proof-of-concept

As complex and heterogeneous diseases, cancers require a more tailored therapeutic management than most pathologies. Recent advances in anticancer drug development, including the immuno-oncology revolution, have been too often plagued by unsatisfying patient response rates and survivals. In reaction to this, cancer care has fully transitioned to the “personalized medicine” concept. Numerous tools are now available tools to better adapt treatments to the profile of each patient. They encompass a large array of diagnostic assays, based on biomarkers relevant to targetable molecular pathways. As a subfamily of such so-called companion diagnostics, chemosensitivity and resistance assays represent an attractive, yet insufficiently understood, approach to individualize treatments. They rely on the assessment of a composite biomarker, the ex vivo functional response of cancer cells to drugs, to predict a patient's outcome. Systemic treatments, such as chemotherapies, as well as targeted treatments, whose efficacy cannot be fully predicted yet by other diagnostic tests, may be assessed through these means. The results can provide helpful information to assist clinicians in their decision-making process. We explore here the most advanced functional assays across oncology indications, with an emphasis on tests already displaying a convincing clinical demonstration. We then recapitulate the main technical obstacles faced by researchers and clinicians to produce more accurate, and thus more predictive, models and the recent advances that have been developed to circumvent them. Finally, we summarize the regulatory and quality frameworks surrounding functional assays to ensure their safe and performant clinical implementation. Functional assays are valuable in vitro diagnostic tools that already stand beyond the “proof-of-concept” stage. Clinical studies show they have a major role to play by themselves but also in conjunction with molecular diagnostics. They now need a final lift to fully integrate the common armament used against cancers, and thus make their way into the clinical routine.

Tumor Chemosensitivity Assays Are Helpful for Personalized Cytotoxic Treatments in Cancer Patients

Tumor chemosensitivity assays (TCAs), also known as drug response assays or individualized tumor response tests, have been gaining attention over the past few decades. Although there have been strong positive correlations between the results of these assays and clinical outcomes, they are still not considered routine tests in the care of cancer patients. The correlations between the assays' results (drug sensitivity or resistance) and the clinical evaluations (e.g., response to treatment, progression-free survival) are highly promising. However, there is still a need to design randomized controlled prospective studies to secure the place of these assays in routine use. One of the best ideas to increase the value of these assays could be the combination of the assay results with the omics technologies (e.g., pharmacogenetics that gives an idea of the possible side effects of the drugs). In the near future, the importance of personalized chemotherapy is expected to dictate the use of these omics technologies. The omics relies on the macromolecules (Deoxyribonucleic acid -DNA-, ribonucleic acid -RNA-) and proteins (meaning the structure) while TCAs operate on living cell populations (meaning the function). Therefore, wise combinations of TCAs and omics could be a highly promising novel landscape in the modern care of cancer patients.

Clinical Correlation of the Histoculture Drug Response Assay in Gastrointestinal Cancer

The histoculture drug response assay (HDRA) with tumors histocultured on Gelfoam^® was tested for clinical correlation for advanced gastric and colorectal cancer patients. In one study, 29 patients were treated with drugs shown to be ineffective in the HDRA, and all 29 cases showed clinical chemoresistance. In nine patients treated with drugs shown to be effective in the HDRA, six showed clinical chemoresponse and three showed arrest of disease progression. In a study of 32 patients with stage III and IV gastric cancer treated with mitomycin C and 5-fluorouracil (5-FU), the survival rate of 10 patients whose tumors were sensitive to either mitomycin C and/or 5-fluorouracil in the HDRA was significantly better than that of 22 patients whose tumors were insensitive to both drugs in the HDRA. Twenty-nine patients with stage III and IV colorectal cancer without remaining measurable tumor lesions after surgery were treated with fluoropyrimidines adjuvantly. The recurrence-free survival rate of 7 patients whose tumors were sensitive to 5-fluorouracil in the HDRA was significantly better than that of 22 patients whose tumors were insensitive in the HDRA. In a companion study of 128 gastric cancer patients whose tumors were evaluated in the HDRA, the overall and disease-free survival rates of the HDRA-sensitive group were found to be significantly higher than those of the HDRA-resistant group, treated with the same drugs.

Predictive Value of Ex Vivo Chemosensitivity Assays for Individualized Cancer Chemotherapy: A Meta-Analysis

Current treatment strategies for chemotherapy of cancer patients were developed to benefit groups of patients with similar clinical characteristics. In practice, response is very heterogeneous between individual patients within these groups. Precision medicine can be viewed as the development toward a more fine-grained treatment stratification than what is currently in use. Cell-based drug sensitivity testing is one of several options for individualized cancer treatment available today, although it has not yet reached widespread clinical use. We present an up-to-date literature meta-analysis on the predictive value of ex vivo chemosensitivity assays for individualized cancer chemotherapy and discuss their current clinical value and possible future developments.

A technology platform to assess multiple cancer agents simultaneously within a patient's tumor

A fundamental problem in cancer drug development is that antitumor efficacy in preclinical cancer models does not translate faithfully to patient outcomes. Much of early cancer drug discovery is performed under in vitro conditions in cell-based models that poorly represent actual malignancies. To address this inconsistency, we have developed a technology platform called CIVO, which enables simultaneous assessment of up to eight drugs or drug combinations within a single solid tumor in vivo. The platform is currently designed for use in animal models of cancer and patients with superficial tumors but can be modified for investigation of deeper-seated malignancies. In xenograft lymphoma models, CIVO microinjection of well-characterized anticancer agents (vincristine, doxorubicin, mafosfamide, and prednisolone) induced spatially defined cellular changes around sites of drug exposure, specific to the known mechanisms of action of each drug. The observed localized responses predicted responses to systemically delivered drugs in animals. In pair-matched lymphoma models, CIVO correctly demonstrated tumor resistance to doxorubicin and vincristine and an unexpected enhanced sensitivity to mafosfamide in multidrug-resistant lymphomas compared with chemotherapy-naïve lymphomas. A CIVO-enabled in vivo screen of 97 approved oncology agents revealed a novel mTOR (mammalian target of rapamycin) pathway inhibitor that exhibits significantly increased tumor-killing activity in the drug-resistant setting compared with chemotherapy-naïve tumors. Finally, feasibility studies to assess the use of CIVO in human and canine patients demonstrated that microinjection of drugs is toxicity-sparing while inducing robust, easily tracked, drug-specific responses in autochthonous tumors, setting the stage for further application of this technology in clinical trials.

Prediction of individual response to anticancer therapy: historical and future perspectives

Since the introduction of chemotherapy for cancer treatment in the early 20th century considerable efforts have been made to maximize drug efficiency and at the same time minimize side effects. As there is a great interpatient variability in response to chemotherapy, the development of predictive biomarkers is an ambitious aim for the rapidly growing research area of personalized molecular medicine. The individual prediction of response will improve treatment and thus increase survival and life quality of patients. In the past, cell cultures were used as in vitro models to predict in vivo response to chemotherapy. Several in vitro chemosensitivity assays served as tools to measure miscellaneous endpoints such as DNA damage, apoptosis and cytotoxicity or growth inhibition. Twenty years ago, the development of high-throughput technologies, e.g. cDNA microarrays enabled a more detailed analysis of drug responses. Thousands of genes were screened and expression levels were correlated to drug responses. In addition, mutation analysis became more and more important for the prediction of therapeutic success. Today, as research enters the area of -omics technologies, identification of signaling pathways is a tool to understand molecular mechanism underlying drug resistance. Combining new tissue models, e.g. 3D organoid cultures with modern technologies for biomarker discovery will offer new opportunities to identify new drug targets and in parallel predict individual responses to anticancer therapy. In this review, we present different currently used chemosensitivity assays including 2D and 3D cell culture models and several -omics approaches for the discovery of predictive biomarkers. Furthermore, we discuss the potential of these assays and biomarkers to predict the clinical outcome of individual patients and future perspectives.

Cytotoxicity of unsaturated fatty acids in fresh human tumor explants: concentration thresholds and implications for clinical efficacy

Background

Unsaturated fatty acids (UFAs) exhibit in vitro cytotoxicity against many malignant cell lines and yield decreased cancer incidence and reduced tumor growth in animal models. But clinical and animal studies to date have achieved response using only localized delivery methods such as intratumoral infusion. To explore possibilities for enhanced clinical efficacy, fresh surgical explants of tumors from 22 patients with five malignancies were exposed to γ-linolenic acid (GLA) and α-linolenic acid (ALA) and analyzed with an in vitro chemosensitivity testing system, the Fluorescent Cytoprint Assay (FCA). A total of 282 micro-organ cultures derived from these malignant tumors were exposed to GLA and ALA at different concentrations.

Results

GLA and ALA exhibited greater than 90% cytotoxicity at a sharp concentration threshold between 500 μM and 1 mM against all but two malignant micro-organ cultures tested in 5-10% serum. In tests using 30-40% serum, GLA and ALA killed tumor at concentrations of 2 mM and above.

Conclusions

The concentration threshold of 500 μM to 2 mM exhibited for antitumor activity by GLA and ALA is much higher than that observed in most previously reported cell culture studies but consistent with physiological concentrations found to kill tumor clinically and in animals. A mechanism of antitumor activity by unsaturated fatty acids through selective destabilization of the malignant plasma membrane is considered. An oral regimen is proposed for phase I clinical testing that could push the area under the curve for serum concentration of unbound unsaturated fatty acids over time to much higher levels than previously achieved for systemic administration and into the range that could yield antitumor response.

Ex vivo programmed cell death and the prediction of response to chemotherapy

Since the earliest introduction of cytotoxic chemotherapy, investigators have pursued laboratory techniques designed to match patients to available drugs. Most of the work, published through the 1980s, reflected the prevailing view of cancer as a disease of dysregulated cell proliferation. Noteworthy, the description of apoptosis and programmed cell death, fundamental to our modern understanding of human tumor biology, did not occur until well after the heyday of in vitro chemosensitivity testing. By incorporating the modern tenets of carcinogenesis associated with perturbations in cell survival we can now re-examine laboratory assays of drug response in the context of drug-induced programmed cell death. Although there is interest in the use of genomic analyses for the prediction of chemotherapy response, the painful recognition that genotype does not equal phenotype will continue to limit broad application of these platforms. Biosystematics instructs that biological pathways rarely follow predicted routes. Efforts to force human biology to behave according to preconceived scientific dictates have proven costly and unsuccessful. Whole-cell experimental models with the capacity to evaluate all the operative mechanisms of cellular response to injury, acting in concert, provide valid tools for the study of human cancer. Educated by cellular behavior, we can expeditiously examine molecular processes of interest. This article briefly reviews the history of whole-cell experimental models of in vitro chemosensitivity testing then focuses on cell-death measures as the most robust predictors of clinical outcome in human cancer.

Assay-assisted treatment selection for women with breast or ovarian cancer

Although women suffering from advanced cancer of the breast or ovary are unlikely to be cured, several active agents are available that can prolong their lives. The use of these agents is based on demonstrated benefit in large randomized clinical trials, and the clinical activity of these chemotherapy regimens is initially high, with 60%-70% of patients responding. Unfortunately, their benefit in the second-line setting is often limited, with less than 30% of patients showing significant disease response. Thus some 70% of patients may undergo ineffective treatment during the course of their disease, while still suffering from significant chemotherapy-related toxicity. Having some foreknowledge of a given agent's expected result before its administration would therefore benefit the individual patient. In vitro drug response testing, first developed to assist in the selection of antibiotics for patients with bacterial infections, has recently been demonstrated to accurately predict how cancer patients will respond to chemotherapy. This review discusses the historical development of in vitro testing for cancer patients, some of the pitfalls encountered, and offers an assessment of their current utility. Results of various clinical trials that evaluated correlations between in vitro tumor response and clinical outcomes are described. These data suggest that in vitro drug response assays can accurately predict drug resistance and can identify patients who are more or less likely to benefit from a given agent.

Predictive value of the ATP chemosensitivity assay in epithelial ovarian cancer

OBJECTIVE

The aims of this study were to define the specific parameters of the ATP chemosensitivity assay which most accurately predict a patient's clinical response to chemotherapeutic agents in epithelial ovarian cancer and to assess the clinical utility of the ATP assay.

METHODS

In our laboratory from 1992 to 1994, fresh tumor specimens from patients with epithelial ovarian carcinomas were assayed with the ATP chemosensitivity assay (ATP-CSA) for their in vitro responses to several chemotherapeutic agents including cisplatin, paclitaxel, and cyclophosphamide. Clinical data on 161 of those patients including all follow-up assessments were then collected, and an investigator blinded to the in vitro assay results determined the patients' responses to chemotherapy. In order to determine which parameter of the assay was the best predictor of clinical response for each drug, receiver-operator characteristic (ROC) curves were constructed for several parameters, including the amount of cell kill at particular dosage levels of drug, the slope of the dose-response curve, and the IC50, or the average concentration of drug at which 50% of the cells were nonviable.

RESULTS

The specific parameter of the ATP-CSA which was most predictive of clinical response differed for each drug tested. The resulting positive predictive values for cisplatin, cyclophosphamide, and paclitaxel ranged from 70.0 to 78.3% and negative predictive values from 46.2 to 60.9%, with overall ATP-CSA positive and negative predictive values of 83.0 and 56.5%. Overall, patients whose tumors tested sensitive to an agent in vitro were almost twice as likely (83% versus 43%) to show a clinical response (RR 1.91, 95% CI 1.34-2.71).

CONCLUSION

Analysis of the ROC curves in this study shows that different parameters of the ATP-CSA need to be utilized for each drug tested in order to give the best prediction of clinical chemosensitivity. Although the ATP-CSA shows predictive ability, routine use of the ATP-CSA for clinical selection of drug therapy in patients with epithelial ovarian cancer would not be warranted without a prospective study comparing chemotherapy treatment based on assay results versus clinician selection of drug.

Multidrug resistance-1 and p-glycoprotein in human chondrosarcoma cell lines: expression correlates with decreased intracellular doxorubicin and in vitro chemoresistance

We report on two chondrosarcoma cell lines, FS and AQ, that may be used as models of multidrug resistance in chondrosarcoma. Multidrug resistance-1 expression was assayed with reverse transcription-polymerase chain reaction. Immunostaining for the multidrug resistance-1 product, P-glycoprotein, was performed with the monoclonal antibody C494. Intracellular levels of doxorubicin were measured by fluorescent emission at 590 nm after 1 hour of incubation with the agent and again after 1, 2, and 4-hour washout periods. Chemosensitivity was assayed by staining micropellet cultures of AQ and FS cells with fluorescein acetate before and after the cells were exposed to varying doses of doxorubicin for 48 hours. Cytotoxicity was assessed by comparison of computer-processed images before and after treatment. The FS cell line was positive for multidrug resistance-1 expression, stained heavily for P-glycoprotein, and had significantly lower intracellular levels of doxorubicin than the AQ cell line, which was negative for multidrug resistance-1 and P-glycoprotein. Chemosensitivity testing showed that the FS cell line was significantly more resistant to doxorubicin than was the AQ cell line at all doses tested. Our results show that multidrug resistance-1 expression in a human chondrosarcoma cell line results in resistance to doxorubicin in vitro.

Determination of in vitro drug sensitivity to a panel of cystostatic drugs and interferon alpha-2b in patients with renal cell carcinoma

Fresh operative cells from 27 renal cell carcinomas (RCC) were cultured in vitro for the determination of in vitro drug sensitivity. Two samples were not culturable. Incubation was carried out in triplicate in the presence and absence of various concentrations of chemotherapeutic agents. Sensitivity of the tumour cells to interferon-alpha (IFN-alpha), cisplatin (CDDP), mitomycin C (MMC), vinblastine (VBL), doxorubicin (DOX), etoposide (ETOP), bleomycin (BLM), vincristine (VCR) were tested by a colorimetric assay using MTT. A preexposure viability over 75% was essential for in vitro drug sensitivity assay (IVDSA). Sensitivity was determined by a more than 50 +/- 2 SD% reduction from the control absorbance. All eight drugs in their low concentrations exhibited cell proliferation inhibition in 0-12% of RCCs. On the other hand, IFN-alpha in its higher concentration (60 IU/ml) was effective in 88% of RCCs. After IFN, CDDP was found to be the second most effective drug in its higher concentration (36% efficacy). The results indicate that IFN appears to be the most effective in vitro agent in our 25 RCCs and the clinical trials either as a monotherapy or multiple combinations of various agents should include IFNs for the treatment of RCC.

In vitro drug sensitivity testing of human testicular germ cell tumours with cytostatic drugs and interferon alpha-2b

In spite of the significant advances in the chemotherapy of germ cell neoplasms, some patients do not achieve disease-free status and ultimately die from their diseases. Therefore, it is reasonable to select the best chemotherapeutic agents in these patients by in vitro drug sensitivity assay (IVDSA) in order to apply the most effective agent in case of resistance to primary chemotherapy. Fresh operative cells from 12 testicular germ cell tumours (TGCT) were cultured in vitro. Sensitivity of the tumour cells to interferon-alpha (IFN-alpha), cisplatin, mitomycin C, vinblastine, doxorubicin, etoposide, bleomycin, vincristine (VCR) were tested by a colorimetric assay using MTT. A preexposure viability over 75% was essential for IVDSA. Sensitivity was determined by a more than 50 +/- 2 SD% reduction from the control absorbance. All eight drugs in their high concentrations exhibited cell proliferation inhibition in 83.3 +/- 100% of TGCT. But in low concentrations efficacy of IFN and VCR were found to be lower than the others (33.3% and 58.3%, respectively). The results indicated that although TGCT are highly sensitive to various agents IVDSA may help to identify the effective agents which might be necessary for second line chemotherapy in a small percentage of patients.

Prediction of response to drug therapy of cancer. A review of in vitro assays

Cancer chemotherapy has witnessed a great deal of progress since the introduction of the nitrogen mustards in the 1940s. Unfortunately, individual patients with apparently identical tumour histologies do not always respond identically to the same drug regimen. Determining the sensitivity and resistance of an organism before treatment has been the standard of care in infectious diseases for many years, while in oncology treatment has been initiated according to tumour histology rather than the tumour's sensitivity to a given agent. Attempts to individualise therapy have been the goal of oncologists since the 1950s. Since that time a number of in vitro assays have been developed to predict therapeutic outcome prior to the start of therapy. In the 1970s, with the introduction of the human tumour stem cell assay, it was generally believed that oncology was on the threshold of entering an era of predictive in vitro chemosensitivity testing. Unfortunately, this assay was shown to have a number of technical drawbacks including the low plating efficiencies of many primary tumour samples which thus limits the percentage which can be evaluated, leaving us still at this threshold today. Several recent developments, such as the Kern assay, which measures inhibition of radioactive precursors into tumour cells in the presence of antineoplastic agents, ATP bioluminescence assays, and the fluorescent cytoprint assay offer the promise of rapid and sensitive results. Other assays, such as the tetrazolium-based MTT and the sulphorhodamine blue assay appear to hold more promise in the screening and evaluation of potential new agents in established tumour cell lines than for evaluating chemosensitivity of clinical specimens. However, before a particular assay can be considered as an in vitro test of chemosensitivity or resistance, controlled prospective studies must be carried out to validate the assay in a number of different tumour types.

The hybrid spheroid clonogenic assay for the intrinsic radio- and chemo-sensitivities of human tumors

The Hybrid Spheroid assay is based on packaging tumor cells into agglomerates of non-proliferating, but metabolically active, HeLa cells. These agglomerates provide an in vivo-like environment for entrapped test cells. Clonogenicity is determined by varying the number of test cells per hybrid spheroid so that some, but not all, spheroids give rise to macrocolonies. From the fraction of noncolony forming spheroids and the Poisson distribution, the average number of clonogens per spheroid can be calculated. The clonogenicity and radiation survival curves of cells derived from human tumors (of the maxilla, tongue, larynx, mouth floor, lung, breast, ovary, and colon) were so determined. Plating efficiency was increased in these normally poorly plating tumor cells, thus enabling survival measurements which are not practical using conventional methods. The Hybrid Spheroid assay has also been applied to determine the chemosensitivity of colon cancer cells.