Dermatology-related quality-of-life outcomes in patients with RAS wild-type metastatic colorectal cancer treated with fluorouracil and folinic acid with or without panitumumab (Pmab) maintenance after FOLFOX + Pmab induction: a prespecified secondary analysis of the phase II randomized PanaMa (AIO KRK 0212) trial.

BACKGROUND: The key endpoints for the assessment of the effect of maintenance therapy for metastatic colorectal cancer (mCRC) are survival and quality-of-life outcomes. We aimed to compare dermatology-related quality of life (DRQOL) in patients with RAS wild-type (wt) mCRC treated with fluorouracil and folinic acid (FU/FA) + panitumumab (Pmab) versus FU/FA alone as maintenance therapy after folinic acid, fluorouracil and oxaliplatin + Pmab induction. PATIENTS AND METHODS: The phase II randomized PanaMa (AIO KRK 0212; NCT01991873) trial included 387 patients at 70 community/academic sites in Germany. For this prespecified secondary analysis, DRQOL outcomes were assessed using the Functional Assessment of Cancer Therapy-epidermal growth factor receptor inhibitor (FACT-EGFRI), Dermatology Life Quality Index (DLQI), and Skindex-16 questionnaires at every second cycle of therapy until disease progression/death. RESULTS: At least one DRQOL questionnaire was completed by a total of 310/377 (82%) patients who received induction therapy, and by 216/248 (87%) patients who were randomized and received maintenance therapy. Patients who experienced skin toxicity according to the National Cancer Institute (NCI)-Common Terminology Criteria for Adverse Events (CTCAE) during induction therapy had significantly worse DRQOL according to all three measures, compared to those who did not [i.e. Skindex-16, mean difference at cycle 2 -12.87; 95% confidence interval (CI) -20.01 to -5.73; P < 0.001]. During maintenance therapy, significantly improved recovery was observed in all DRQOL measures for patients receiving FU/FA, compared to those receiving additional Pmab (i.e. Skindex-16, mean difference at cycle 6 -16.53; 95% CI -22.68 to -10.38; P < 0.001). CONCLUSIONS: In this secondary analysis of a phase II randomized clinical trial, patient-reported DRQOL outcomes correlated with skin toxicity according to NCI-CTCAE during induction therapy. Maintenance therapy with FU/FA + Pmab was associated with deteriorated DRQOL versus FU/FA alone in patients with RAS wt mCRC.

Influence of FPGS, ABCC4, SLC29A1, and MTHFR genes on the pharmacogenomics of fluoropyrimidines in patients with gastrointestinal cancer from the Brazilian Amazon.

PURPOSE: Fluoropyrimidines are one of the most used drug class to treat cancer patients, although they show high levels of associated toxicity. This study analyzed 33 polymorphisms in 17 pharmacogenes involved with the pharmacogenomics of fluoropyrimidines, in gastrointestinal cancer patients undergoing fluoropyrimidine-based treatment in the Brazilian Amazon. METHODS: The study population was composed of 216 patients, 92 of whom have an anatomopathological diagnosis of gastric cancer and 124 of colorectal cancer. The single nucleotide polymorphisms (SNP) were genotyped by allelic discrimination using the TaqMan OpenArray Genotyping technology, with a panel of 32 customized assays, run in a QuantStudio ™ 12K Flex Real-Time PCR System (Applied Biosystems, Life Technologies, Carlsbad USA). Ancestry analysis was performed using 61 autosomal ancestry informative markers (AIMs). RESULTS: The study population show mean values of 48.1% European, 31.1% Amerindian, and 20.8% African ancestries. A significant risk association for general and severe toxicity was found in the rs4451422 of FPGS (p = 0.001; OR 3.40; CI 95% 1.65-7.00 and p = 0.006; OR 4.63; CI 95% 1.56-13.72, respectively) and the rs9524885 of ABCC4 (p = 0.023; OR 2.74; CI 95% 1.14-6.65 and p = 0.024; OR 5.36; IC 95% 1.24-23.11, respectively) genes. The rs760370 in the SLC29A1 gene (p = 0.009; OR 6.71; CI 95% 1.16-8.21) and the rs1801133 in the MTHFR toxicity (p = 0.023; OR 3.09; CI 95% 1.16-8.21) gene also demonstrated to be significant, although only for severe toxicity. The results found in this study did not have statistics analysis correction. CONCLUSION: Four polymorphisms of the ABCC4, FPGS, SLC29A1, and MTHFR genes are likely to be potential predictive biomarkers for precision medicine in fluoropyrimidine-based treatments in the population of the Brazilian Amazon, which is constituted by a unique genetic background.

Conversion Chemotherapy With a Modified FLOX Regimen for Borderline or Unresectable Liver Metastases From Colorectal Cancer: An Alternative for Limited-Resources Settings.

PURPOSE: Conversion chemotherapy is often used for borderline or unresectable (B/U) liver metastases from colorectal cancer (CRC) with the aim of achieving resectability. Although intensive and costly regimens are often used, the best regimen in this scenario remains unclear. We aimed to evaluate the outcomes of patients with B/U liver metastases from CRC treated with conversion chemotherapy with the modified fluorouracil, leucovorin, and oxaliplatin (mFLOX) regimen followed by metastasectomy. METHODS: We performed a single-center retrospective analysis of patients with B/U liver metastases from CRC treated with chemotherapy with the mFLOX regimen followed by surgery. B/U disease was defined as at least one of the following: more than four lesions, involvement of hepatic artery or portal vein, or involvement of biliary structure. RESULTS: Fifty-four consecutive patients who met our criteria for B/U liver metastases were evaluated. Thirty-five patients (64%) had more than four liver lesions, 16 (29%) had key vascular structure involvement, and 16 (29%) had biliary involvement. After chemotherapy, all patients had surgery and 42 (77%) had R0 resection. After a median follow-up of 37.2 months, median progression-free survival (PFS) was 16.9 months and median overall survival (OS) was 68.3 months. R1-R2 resections were associated with worse PFS and OS compared with R0 resection (PFS: hazard ratio, 2.65; P = .007; OS: hazard ratio, 2.90; P = .014). CONCLUSION: Treatment of B/U liver metastases from CRC with conversion chemotherapy using mFLOX regimen followed by surgical resection was associated with a high R0 resection rate and favorable survival outcomes. On the basis of our results, we consider mFLOX a low-cost option for conversion chemotherapy among other options that have been proposed.

Second-Line Treatment for Advanced Pancreatic Adenocarcinoma: Is There a Role for Gemcitabine?

PURPOSE: Advanced pancreatic adenocarcinoma (PA) is an aggressive disease that has poor prognosis and frequently interferes with patient's quality of life. There has been progress in first-line regimens; however, there is no standard second-line regimen. The aim of this study is to analyze second-line gemcitabine after first-line fluorouracil (FU) + leucovorin (LV) + irinotecan + oxaliplatin (FOLFIRINOX) regimen. METHODS: This study included consecutive patients with advanced PA treated at Hospital Sirio-Libanês from 2011 to 2016. The patients received FOLFIRINOX as first-line treatment and upon progression, received gemcitabine alone. Survival analysis was performed using the Kaplan-Meier method. RESULTS: A total of 54 patients were evaluated. Most patients were male (61.1%) and most had an ECOG performance status of 0 or 1 prior to the beginning of second-line treatment (66.6%). The mean number of gemcitabine cycles was 3.4. Most patients had disease progression as the best response to treatment (75.9%), 11.1% had stable disease, and 9.3% experienced a partial response. The median progression-free survival was 1.7 months, and the median overall survival was 6.8 months. CONCLUSIONS: Gemcitabine alone did not show meaningful clinical benefit as second-line treatment after FOLFIRINOX.

Combination of Irinotecan, Oxaliplatin and 5-Fluorouracil as a Rechallenge Regimen for Heavily Pretreated Metastatic Colorectal Cancer Patients.

PURPOSE: Our objective was to evaluate the benefit of re-exposing patients with refractory metastatic colorectal cancer (mCRC) to a combination of oxaliplatin, irinotecan and 5-fluorouracil treatment. METHODS: We retrospectively analysed patients with mCRC who received a combination of oxaliplatin, irinotecan and fluorouracil as a rechallenge regimen after progressing on the same drugs. Both FOLFOXIRI and FOLFIRINOX were used. Toxicity was evaluated for each treatment cycle, and survival analysis was performed using the Kaplan-Meier method. RESULTS: A total of 21 patients who were treated between January 2011 and December 2013 were selected for this study. Most of the patients (95.2%) had an ECOG status of 0-1. The median age at diagnosis was 52.1 years (range 36-77 years), and 14 (66.6%) patients had wild-type KRAS. Thirteen patients received FOLFIRINOX, and eight received FOLFOXIRI. Most patients had previously received at least three regimens, with 80% receiving anti-VEGF and 66% anti-EGFR antibodies. The response rate was 38%, and 24% patients had stable disease. The median time to disease progression was 4.0 months (range 1.0-9.1 months), and the median overall survival duration was 8.6 months (range 6.3-11.5 months). Most patients required dose adjustment and treatment delays. One patient experienced grade 5 neutropenic sepsis. CONCLUSIONS: Both FOLFIRINOX and FOLFOXIRI are active and potentially feasible rechallenge treatment options for heavily pretreated patients with good performance status. With dose reduction and close monitoring for toxicity, the risk of serious adverse events can be minimised.

Functional impairment in submandibular gland of rats induced by 5-fluorouracil and calcium leucovorin.

One of the main clinical problems during chemotherapy is the occurrence of severe systemic toxicities, including those related to the stomatognathic system, which contribute to reducing the patient's quality of life. The most frequent oral complications are mucositis, dysgeusia, inflammation, gingival bleeding and decreased salivary flow or hyposalivation, a factor that predisposes to xerostomia, and other local complications that alter the homeostasis of the system. The purpose of this study was to evaluate the functional activity of salivary glands in Wistar rats subject to chemotherapy by measuring salivary flow, glycogen levels and glandular tissue response to autonomic nervous system agonists. Five experimental groups were used: 1) Control group fed "ad libitum"; 2) 5-fluorouracil (20 mg/kg body weight); 3) Calcium leucovorin (10 mg/kg body weight); 4) 5-fluorouracil + calcium leucovorin (20 and 10 mg/kg, respectively) by intraperitoneal injection for five consecutive days and 5) control with paired diet. Groups 1 and 5 did not receive drugs. Treatment with fluorouracil + leucovorin produced an increase in stimulated salivary flow and a higher response to increasing doses of beta agonists compared to other experimental groups. In both groups treated with cytostatic drugs, blocking of glycogen consumption at the end of the experimental period was observed. Our work suggests that salivary secretion may be affected by a dual mechanism: the first would be toxicity induced by 5-FU, which would cause depression of the process of glucose utilization. The second mechanism would affect the sympathetic autonomic reflex arc. In this instance, the synergistic action of 5-FU + LV would have a negative effect on the nerve activity with a reduction of salivary secretion. This would explain the hyposalivation, cited by several authors in patients undergoing the 5-FU + LV scheme in the treatment of colon carcinoma.

Functional impairment in submandibular gland of rats induced by 5-fluorouracil and calcium leucovorin

One of the main clinical problems during chemotherapy is the occurrence of severe systemic toxicities, including those related to the stomatognathic system, which contribute to reducing the patient's quality of life. The most frequent oral complications are mucositis, dysgeusia, inflammation, gingival bleeding and decreased salivary flow or hyposalivation, a factor that predisposes to xerostomia, and other local complications that alter the homeostasis of the system. The purpose of this study was to evaluate the functional activity of salivary glands in Wistar rats subject to chemotherapy by measuring salivary flow, glycogen levels and glandular tissue response to autonomic nervous system agonists. Five experimental groups were used: 1) Control group fed "ad libitum"; 2) 5-fluorouracil (20mg/ kg body weight); 3) Calcium leucovorin (10 mg/kg body weight); 4) 5-fluorouracil + calcium leucovorin (20 and 10 mg / kg, respectively) by intraperitoneal injection for five consecutive days and 5) control with paired diet. Groups 1 and 5 did not receive drugs. Treatment with fluorouracil + leucovorin produced an increase in stimulated salivary flow and a higher response to increasing doses of beta agonists compared to other experimental groups. In both groups treated with cytostatic drugs, blocking of glycogen consumption at the end of the experimental period was observed. Our work suggests that salivary secretion may be affected by a dual mechanism: the first would be toxicity induced by 5-FU, which would cause depression of the process of glucose utilization. The second mechanism would affect the sympathetic autonomic reflex arc. In this instance, the synergistic action of 5-FU + LV would have a negative effect on the nerve activity with a reduction of salivary secretion. This would explain the hyposalivation, cited by several authors in patients undergoing the 5-FU+LV scheme in the treatment of colon carcinoma.

Uno de los principales problemas clinicos durante la quimioterapia es la aparicion de graves efectos toxicos sistemicos, incluidos los relacionados con el sistema estomatognatico, que contribuyen a la reduccion de la calidad de vida del paciente. Las complicaciones orales mas frecuentes son la mucositis, disgeusia, inflamacion, sangrado gingival y la disminucion del flujo salival o hiposalivacion, un factor que predispone a la xerostomia, y otras complicaciones locales que alteran la homeostasis del sistema. El objetivo de este estudio fue evaluar la actividad funcional de las glandulas salivales de ratas Wistar sometidas a quimioterapia, a traves de la medicion del flujo salival, los niveles de glucogeno y la respuesta del tejido glandular a agonistas del sistema nervioso autonomo. Se utilizaron cinco grupos experimentales: 1) Control con alimentacion "ad libitum"; 2) 5 - fluorouracilo (20 mg / kg de peso corporal); 3) Leucovorina calcica (10 mg/ kg de peso corporal); 4) 5 - fluorouracilo + leucovorina calcica (20 y 10 mg / kg, respectivamente) por via intraperitoneal durante cinco dias consecutivos, y 5) control con dieta apareada. Grupos 1 y 5 no recibieron drogas. El tratamiento con 5 - fluorouracilo + leucovorina produjo un aumento de flujo salival estimulado y una mayor respuesta a dosis crecientes de agonistas beta en comparacion con otros grupos experimentales. En ambos grupos tratados con citostaticos, se observo bloqueo del consumo de glucogeno al final del periodo. Nuestro trabajo sugiere que la secrecion salival puede estar afectada por un doble mecanismo: el primero seria la toxicidad inducida por 5-FU que causaria depresion del proceso de utilizacion de la glucosa. El segundo mecanismo afectaria el arco reflejo autonomo simpatico. En este caso, la accion sinergica de ambos farmacos de 5-FU + LV repercutiria negativamente sobre la actividad nerviosa con una reduccion de la secrecion salival. Esto explicaria la hiposalivacion citada por varios autores en pacientes sometidos al esquema 5-FU + LV en el tratamiento del carcinoma colorrectal.

Azithromycin inhibits vertical transmission of Toxoplasma gondii in Calomys callosus (Rodentia: Cricetidae).

Toxoplasma gondii infection during pregnancy may cause severe consequences to the embryo. Current toxoplasmosis treatment for pregnant women is based on the administration of spiramycin or a drug combination as sulphadiazine-pyrimethamine-folinic acid (SPFA) in cases of confirmed fetal infection. However, these drugs are few tolerated and present many disadvantages due to their toxic effects to the host. The aim of this study was to evaluate the effectiveness of different treatments on the vertical transmission of T. gondii, including azithromycin, Artemisia annua infusion, spiramycin and SPFA in Calomys callosus as model of congenital toxoplasmosis. C. callosus females were perorally infected with 20 cysts of T. gondii ME49 strain at the day that a vaginal plug was observed (1st day of pregnancy - dop). Treatment with azithromycin, A. annua infusion, and spiramycin started at the 4th dop, while the treatment with SPFA started at the 14th dop. Placenta and embryonic tissues were collected for morphological and immunohistochemical analyses, mouse bioassay and PCR from the 15th to 20th dop. No morphological changes were seen in the placenta and embryonic tissues from females treated with azithromycin, spiramycin and SPFA, but embryonic atrophy was observed in animals treated with A. annua infusion. Parasites were found in the placenta and fetal (brain and liver) tissues of animals treated with SPFA, A. annua infusion and spiramycin, although the number of parasites was lower than in non-treated animals. Parasites were also observed in the placenta of animals treated with azithromycin, but not in their embryos. Bioassay and PCR results confirmed the immunohistochemical data. Also, bradyzoite immunostaining was observed only in placental and fetal tissues of animals treated with SPFA. In conclusion, the treatment with azithromycin showed to be more effective, since it was capable to inhibit the vertical transmission of T. gondii in this model of congenital toxoplasmosis.

Neoadjuvant radiochemotherapy in the treatment of fixed and semi-fixed rectal tumors. Analysis of results and prognostic factors.

PURPOSE: To report the retrospective analysis of patients with locally advanced rectal cancer treated with neodjuvant radiochemotherapy. METHODS AND MATERIALS: From January 1994 to December 2003, 101 patients with fixed (25%) or semi-fixed (75%) rectal adenocarcinoma were treated by preoperative radiotherapy with a dose of 45 Gy at the whole pelvis and 50.4 Gy at primary tumor, concomitant to four weekly chemotherapies with 5-Fluorouracil (425 mg/m2) and Leucovorin (20 mg/m2). In 71 patients (70.3%) the primary tumor was located up to 6 cm from the anal verge and in 30 (29.7%) from 6.5 cm to 10 cm. Age, gender, tumor fixation, tumor distance from the anal verge, clinical response, surgical technique, and postoperative TNM stage were the prognostic factors analyzed for overall survival (OS), disease-free survival (DFS), and local control (LC) at five years. RESULTS: Median follow-up time was 38 months (range, 2-141). Complete response was observed in eight patients (7.9%), partial in 54 (53.4%) and absence in 39 (38.7%). OS, DFS and LC were 52.6%, 53.8%, and 75.9%, respectively. Distant metastasis occurred in 40 (39.6%) patients, local recurrence in 20 (19.8%) and both in 16 (15.8%). Patients with fixed tumors had lower OS (17% Vs 65.6%; p < 0.001), DFS (31.2% Vs 60.9%; p = 0.005), and LC (58% Vs 82%; p = 0.004). Patients with tumors more than 6 cm above the anal verge had better LC (93% Vs 69%; p = 0.04). The postoperative TNM stage was a significant factor for DFS (I:64.1%, II:69.6%, III:35.2%, IV:11.1%; p < 0.001) and for LC (I:75.7%, II: 92.9%, III:54.1%, IV:100%; p = 0.005). Patients with positive lymph nodes had worse OS (37.9% Vs 70.4%, p = 0.006), DFS (32% Vs 72.7%, p < 0.001) and LC (56.2% Vs 93.4%; p < 0.001). CONCLUSION: This study suggests that the neoadjuvant treatment employed was effective for local control. Fixation of the lesion and lymph nodes metastasis were the main adverse prognostic factors. Distant failures were frequent, supporting the need of new drugs for adjuvant chemotherapy.

Methotrexate inhibition of bone mineral density increase in growing rabbits: prevention by folinic acid.

OBJECTIVE: Methotrexate (MTX) action on bone metabolism is as yet not completely understood. The results of clinical studies are controversial, since it is difficult to distinguish the side effects of MTX from those of the primary disease. This study assessed the effect of MTX, with and without folinic acid supplementation, on bone mineral density in growing normal rabbits. METHODS: Three groups of young NZW growing female rabbits were treated with: saline (n = 6) or MTX (0.25 mg/kg/week, n = 5) or MTX (same dose as above) plus folinic acid (0.25 mg/kg/week, n = 6) for a period of 3 months. The dose, duration and frequency of MTX administration were similar to the treatment of RA patients. The animals were submitted to dual-energy absorptiometry densitometry (HologicQDR 2000) before and after treatment; total body and L4-L5 BMD were evaluated. Histomorphometric analysis (L4 vertebrae) was also performed. RESULTS: Growing control rabbits showed increased total body BMD from a baseline of 0.180 +/- 0.006 to 0.198 +/- 0.007 gm/cm2 (mean +/- S.E.M, p < 0.006). In contrast, no increase in BMD (0.182 +/- 0.006 versus a baseline of 0.184 +/- 0.004, ns) was observed in the group treated with MTX, while the addition of folinic acid resulted in an increase in BMD values similar to controls, from a baseline of 0.181 +/- 0.004 to 0.198 +/- 0.003, p < 0.02), thus preventing adverse MTX bone effects. Average percent variations in BMD were +7.7%, -1% and +8.4% respectively. Spine (L4-L5) BMD showed analogous results, in line with the histomorphometric data. CONCLUSION: These results strongly support a deleterious action of MTX on bone metabolism, which is prevented by folinic acid supplementation. The potential clinical implications of our data are particularly significant for paediatric therapy.

Irinotecan and oxaliplatin: an overview of the novel chemotherapeutic options for the treatment of advanced colorectal cancer

Colorectal cancer is one of the most frequent malignancies in humans and an important cause of cancer death. Metastatic colorectal cancer remains incurable with available systemic therapeutic options. The most active cytotoxic drug against this malignancy, the antimetabolite 5-fluorouracil, was developed more than forty years ago, and as a single agent produces responses in only 10 to 15 percent of patients which in general last less than one year. Efforts to ameliorate these poor results resulted in the 5-fluorouracil/leucovorin combination, which enhances response rates about two-fold, without, however, significantly improving survival rates. The recent emergence of a handful of new 5-fluorouracil analogues and folate antagonists, as well as the topoisomerase I inhibitor irinotecan, and the third-generation platinum compound oxaliplatin, is likely to alter this gloomy scenario. These agents are at least as effective as 5-fluorouracil in patients with advanced colorectal carcinoma, both untreated and previously treated with 5-fluorouracil-based regimens. This has led to the approval of irinotecan as second-line treatment for 5-fluorouracil-refractory disease, while the use of oxaliplatin has been suggested for patients having a defective 5-fluorouracil catabolism. Recently, FDA approved the combination of irinotecan with 5-fluorouracil and leucovorin for first-line treatment of advanced colon cancer. Based on the synergistic preclinical antitumor effects of some of these agents, their meaningful single-agent activity, distinct mechanisms of cytotoxicity and resistance, and only partially overlapping toxicity profiles, effective combination regimens are now being developed, which are likely to lead to a new, more hopeful era for patients suffering from advanced colorectal carcinoma

Irinotecan and oxaliplatin: an overview of the novel chemotherapeutic options for the treatment of advanced colorectal cancer.

Colorectal cancer is one of the most frequent malignancies in humans and an important cause of cancer death. Metastatic colorectal cancer remains incurable with available systemic therapeutic options. The most active cytotoxic drug against this malignancy, the antimetabolite 5-fluorouracil, was developed more than forty years ago, and as a single agent produces responses in only 10 to 15% of patients which in general last less than one year. Efforts to ameliorate these poor results resulted in the 5-fluorouracil/leucovorin combination, which enhances response rates about two-fold, without, however, significantly improving survival rates. The recent emergence of a handful of new 5-fluorouracil analogues and folate antagonists, as well as the topoisomerase I inhibitor irinotecan, and the third-generation platinum compound oxaliplatin, is likely to alter this gloomy scenario. These agents are at least as effective as 5-fluorouracil in patients with advanced colorectal carcinoma, both untreated and previously treated with 5-fluorouracil-based regimens. This has led to the approval of irinotecan as second-line treatment for 5-fluorouracil-refractory disease, while the use of oxaliplatin has been suggested for patients having a defective 5-fluorouracil catabolism. Recently, FDA approved the combination of irinotecan with 5-fluorouracil and leucovorin for first-line treatment of advanced colon cancer. Based on the synergistic preclinical antitumor effects of some of these agents, their meaningful single-agent activity, distinct mechanisms of cytotoxicity and resistance, and only partially overlapping toxicity profiles, effective combination regimens are now being developed, which are likely to lead to a new, more hopeful era for patients suffering from advanced colorectal carcinoma.

Methotrexate: pentose cycle and oxidative stress.

The effect of methotrexate (MTX) and leucovorin (LCV) on pentose cycle enzymes and the activity of enzymes involved in enzyme defence mechanisms against ROS in HeLa cells, were studied. The effect of MTX was also investigated on the cellular levels of glutathione. MTX inhibited the activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenases. The activities of glutathione reductase and gamma-glutamylcysteine synthetase were also inhibited by the drug. No effect was observed on the activities of catalase, superoxide dismutase or transketolase. LCV had no effect on any of the enzymes studied. MTX decreased the cellular levels of glutathione (70 per cent), while the presence of LCV and glutamine did not interfere with the effect of MTX. The net results appear to show that the biological situation resulting from treatment with MTX leads to a reduction of effectiveness of the antioxidant enzyme defence system.

The pattern of myeloid suppression and recovery after the addition of methotrexate to murine long-term bone marrow culture.

Treating long-term bone marrow culture with 10(-7)-10(-5) M methotrexate caused a 95% reduction in myelopoiesis as assessed by supernatant cell count and granulocyte/macrophage colony forming unit number. The suppression was irreversible with 10(-5) M methotrexate. Complete recovery of myeloid cell production occurred four and five weeks after cultures were treated with either 10(-7) M or 10(-6) M methotrexate, respectively. The suppression of myelopoiesis was completely prevented if 10(-3) M leucovorin was added to culture within 6 h of 10(-6) M methotrexate. The addition to culture of lung conditioned medium containing high concentrations of granulocyte/macrophage colony-stimulating factor shortened the time of myelopoietic suppression by one week. The addition of WEHI-3B medium containing both interleukin 3 and GM-CSF shortened the suppression by two weeks. This in vitro model provides unique opportunities to examine mechanisms involved in the myelopoietic and chemotherapy-induced suppression. A close analysis of approaches to modify the recovery process will also be possible.