You will be shown a paragraph from a biomedical research article. Your task is to extract all drug combinations appearing in a specific sentence within in the paragraph. Each drug combination should be assigned to one of the following three categories:

- POS: Indicates a positive interaction between the drugs in the combination; for instance, drugs that have an additive or synergistic effect.
- NEG: Indicates a negative interaction between the drugs in the combination; for instance, combining these drugs might result in adverse side effects, or might reduce their efficacy.
- COMB: Indicates that the drugs are given in combination, but the type of interaction between the drugs cannot be determined based on the provided context.

Please format your answer as a json array. Each entry in the array should itself be an array formatted as [<drug_1>, <drug_2>, ..., <drug_n>, <category>] where <category> is one of the three categories listed above and <drug_1>, ..., <drug_n> are drug names copied verbatim from the input sentence. Different combinations may involve different numbers of drugs; in other words, the `n` in <drug_n> may vary.

As an example, the following output describes two extracted drug combinations; one between two drugs, and one between three drugs:

[["artesunate", "artemether", "COMB"], ["Nifedipine", "Labetalol", "Prazosin", "POS"]]

The paragraph and specific sentence are below. You should only extract relationships expressed in the specific sentence; the paragraph is provided for context.

In your output, return only the json array and no other text. If no drug combinations appear, return an empty array `[]`.

paragraph: Modulation of ara-CTP levels by fludarabine and hydroxyurea in leukemic cells. The rate of ara-cytosine triphosphate (ara-CTP) accumulation and its retention has been correlated with 1-beta-D-arabinofuranosylcytosine (ara-C)-mediated toxicity and clinical outcome in childhood and adult leukemia. We tested to what extent preincubation with the ribonucleotide reductase inhibitors fludarabine ( F-ara-A ) and hydroxyurea ( HU ) enhanced ara-CTP levels in two human myeloid ( HL-60 , CMK ) and two lymphoblastic leukemia cell lines ( MOLT-4 , BLIN-1 ) and also in blasts from 28 children with acute leukemia ( AML : 14 , ALL : 14 ) . Incubation experiments carried out with cell lines showed F-ara-A and HU to be equipotent in increasing ara-CTP levels. The highest increase was observed in HL-60 cells whereas preincubation had no modulatory effect in MOLT-4 cells. Accordingly, modulation of intracellular ara-CTP levels differed between the subtypes of childhood acute leukemia: whereas in T-ALL (five) preincubation with F-ara-A and HU had no effect on intracellular ara-C metabolism, increased ara-CTP levels were seen in some cases of pre-B-ALL (seven). In myelogenous blasts (12) clinically relevant enhancement of ara-C toxification was regularly obtained with both, F-ara-A (1.9-fold) and HU (1.5-fold). In conclusion, our data suggest that combinations of ara-C and ribonucleotide reductase inhibitors are apt to increase ara-CTP levels depending on the individual cell type and its sensitivity towards ara-C modulators.

sentence: We tested to what extent preincubation with the ribonucleotide reductase inhibitors fludarabine ( F-ara-A ) and hydroxyurea ( HU ) enhanced ara-CTP levels in two human myeloid ( HL-60 , CMK ) and two lymphoblastic leukemia cell lines ( MOLT-4 , BLIN-1 ) and also in blasts from 28 children with acute leukemia ( AML : 14 , ALL : 14 ) .
[]