NOVELTY - Method-I for selecting one or more nucleic acids from a library of nucleic acids that encode one or more stable and bioavailable peptide(s), comprises selecting one or more nucleic acids encoding one or more stable and bioavailable peptide(s) from the nucleic acid library, where the members of the nucleic acid library contain one or more unnatural amino acids and/or codon lacking natural cognate transfer (t)RNAs.    USE - The non-naturally occurring peptide or the conjugate is useful: for inhibiting the growth of a breast cancer cell, detecting a breast cancer cell in a subject and treating breast cancer. The compositions are useful for regulating blood sugar, treating diabetes and prediabetes and associated condition or disorder in a subject (preferably human) (all claimed). The ability of the peptide to treat breast cancer was tested in human epidermal growth factor receptor-2 using 5-bromo-2'-deoxyuridine assay. The result showed that flavin adenine mononucleotide-Asp-Gln-Leu-Tyr-Trp-Trp-Glu-Tyr-Leu-(CH2CH2NH)-Arg exhibited IC50 value of 520 nM.    ADVANTAGE - The non-naturally occurring peptide exhibits improved bioavailability and in vivo half life, is free of toxicity, efficiently delivers cargo across a lipid bilayer to target intracellular drug targets, and can be simply prepared in an economical manner.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method-II for selecting one or more peptides that possess secondary structure;    (2) a method-III for preparing one or more nucleic acids that encode peptide(s);    (3) an isolated RNA library prepared by the method-III;    (4) an isolated peptide library prepared by the method-III;    (5) an isolated peptide prepared by the method-III;    (6) a composition-A comprising one or more of the isolated RNA library, the isolated peptide library, the isolated peptide, the peptide conjugate and a carrier;    (7) a non-naturally occurring peptide comprising a specific amino acid sequence of formula (M1-A1-V1-Y1-V1-H1-Y2-H2-K1) (I), (M1-F1-V1-Q1-V1-Y1-Y2-H1-K1) (II), (M1-L1-H1-Y1-V1-Y2-V1-R1-K1) (III), (M1-V2-Cys-V1-V1-L1-Y1-D1-D2-K1) (IV), (M1-E1-V1-Y1-E2-Y2-V1-S1-L1-K1) (V) or (M1-N1-E1-Y1-V1-L1-Y2-V1-L2-K1) (VI);    (8) a peptide conjugate comprising either the non-naturally occurring peptide, where the peptide is conjugated to polyethylene glycol or a lipid molecule, a peptide linked to biotin on the side chain of lysine of the peptide or a peptide linked to biotin through an amide linkage or an ester linkage, or a peptide linked at the N- and/or C- terminal to a molecule of the group of a biotin molecule, a biotin analog or unsaturated fatty acid such as palmitoleic acid, each linked optionally through a disulfide linkage;    (9) a composition-B comprising the non-naturally occurring peptide or the peptide conjugate and a carrier;    (10) a method-IV for detecting a breast cancer cell in a subject;    (11) a vector comprising the isolated nucleic acid;    (12) an isolated host cell comprising the isolated nucleic acid or isolated peptide;    (13) a method-IV for producing the non-naturally occurring peptide;    (14) a method-V for determining if a candidate agent is a potential therapeutic to inhibit the growth of a breast cancer cell;    (15) a kit for one or more of inhibiting the growth of a breast cancer cell or for treating breast cancer, or for determining if a candidate agent is a potential therapeutic to inhibit the growth of a cancer cell, comprising the non-naturally occurring peptide, the conjugate or the composition, and instructions for use;    (16) a method-VI for determining if a candidate agent is a potential therapeutic suitable for oral administration; and    (17) a kit for determining if a candidate agent is a potential therapeutic suitable for oral administration, comprising the peptide conjugate and instructions for use.    In formula (I):    M1 = Met or norvaline, norleucine, alanine;    A1 = Ala or V1, Met, Ser, Thr, His, Lys, Arg, Gln, Asp, Leu, Val, Iso;    V1 (in position 2) = N-methyl norvaline or Ser, Thr, Gln, Asn, His, Pro, Ile, Val, Leu, Tyr, Phe, Pro;    Y1 = Tyr or V1, Tyr, Phe, Gln, Asn, Ser, Thr, His;    V1 (in position 5) = N-methyl norvaline or Tyr, Phe, Ser, Thr, Glu, Asp, Met, Ala, Pro;    H1 = His or V1, Tyr, Phe, Gln, Asn;    Y2 = His or V1, Phe, Tyr, Val, Ile or Leu;    H2 = His or any amino acid; and    K1 = Lys or lysine derivatives (e.g. ornithine).    In formula (II):    M1 = Met or norvaline, norleucine, alanine;    F1 = Phe or any amino acid;    V1 (in position 3) = N-methyl norvaline or Gln, Asn, Ser, Thr, His, Tyr, Phe, Pro;    Q1 = Gln o Phe, V1, Pro, Ser, Thr;    V1 (in position 5) = N-methyl norvaline or Tyr, Phe, Ser, Thr, Asp, Glu, Ala, Met;    Y1 = Tyr or Phe, His;    Y2 = Tyr or Phe, Lys, Ile, Val, Ser, Thr, V1;    H1 = His or Thr, Ser; and    K1 = Lys or lysine derivatives (e.g. ornithine).    In formula (III):    M1 = Met or norvaline, norleucine, alanine;    L1 = Leu or Ile, Val;    H1 = His or Tyr, Phe;    Y1 = Tyr or Phe;    V1 (in position 5) = N-methyl norvaline or Ser, Thr, Asp, Glu, Ala, Met, Pro;    Y2 = Tyr or His, Gln, Asp, Leu, Ile, Val, V1;    V1 (in position 7) = N-methyl norvaline or Phe, Tyr, Leu, Ile, Val, His, Pro; and    R1 = Arg or any amino acid.    In formula (IV):    M1 = Met or norvaline, norleucine, alanine;    V2 = Val or Ile, Leu;    V1 (in position 4) = N-methyl norvaline or Tyr, Phe, Pro, Asp, Glu, Met;    V1 (in position 5) = N-methyl norvaline or Tyr, Phe, Asp, Glu, Trp, Cys, Gly, Pro;    L1 = Leu or Tyr, Phe, V1, Val, Ile, Pro, Cys;    Y1 = Tyr or V1, Gln, Asp;    D1 = Asp or Ser, Thr, Glu, Tyr, Phe, Ala, Pro, V1; and    D2 = Asp or Glu, G, Leu, Ile, Val.    In formula (V):    M1 = Met or norvaline, norleucine, alanine;    E1 = Glu or any amino acid;    V1 (in position 3) = N-methyl norvaline or Pro, Asp, Glu, Phe, Tyr, Ser, Thr, Glu, Asn;    Y1 = Tyr or Asp, Glu, Phe, V1, Pro;    E2 = Glu or Asp, Tyr, Phe, Pro, V1;    Y2 = Tyr or Phe, Leu, Val, Ile, Pro, V1;    V1 (in position 7) = N-methyl norvaline or Phe, Leu, Val, Ile, Pro, V1;    S1 = Ser or any other amino acid; and    L1 = Leu or any other amino acid.    In formula (VI):    M1 = Met or norvaline, norleucine, alanine;    N1 = Asn or any amino acid;    E1 = Glu or Asp, Ile, Val, Leu, Phe, Tyr, Pro, V1;    Y1 = Tyr or Asp, Glu, Pro, V1;    V1 (in position 5) = N-methyl norvaline or Asp, Glu, Phe, Tyr, Gly, Cys, Pro;    L1 = Leu or Tyr, Phe, Pro, V1;    Y2 = Tyr or Phe, Val, Ile, Leu;    V1 (in position 8) = N- methyl norvaline or Ser, Thr, Tyr, Phe, Glu, Asp, Ala, Pro;    L2 = Leu or Lys, Arg, Ile, Leu, Val, Asp, Glu, Gly, Ser, Thr; and    V1 = N-methyl amino acid or any modified amino acid that confers stabilization to the peptide.