The headword phrase is presumably extracted from the quotation given. The verb form here is the present active participle, neuter nominative singular, of me/lw, I am of interest. See LSJ s.v. (and cf. generally omicron 918).
[1] The gloss employs an adjectival verbal noun form denoting necessity (cf. Smyth, 358), in the neuter nominative/accusative singular, from frontiste/os (one must take heed), ultimately derived from the verb fronti/zw, I take heed; see generally LSJ s.v.
[2] A city in northeast Mesopotamia, present-day Nusaybin, Turkey (Barrington Atlas map 89 grid D3); cf. nu 426 and see generally OCD(4) s.v. Nisibis.
[3] Menander Protector fr. 16.2 Blockley (36a FHG, 4.240); see Blockley, pp. 154-5. This fragment is generally associated with the preemptive siege of Nisibis by the Roman general Marcian (PLRE IIIb s.v. Marcianus 7) in early 573 CE (Blockley, p. 271).