A peptide nucleic acid derivative represented by Formula I, or a pharmaceutically acceptable salt thereof: wherein, n is an integer between 10 and 21; the compound of Formula I possesses at least a 10-mer complementary overlap with the 14-mer RNA sequence of [(5' → 3') UUUUUGCGUAAGUA] within the human SCN9A pre-mRNA; the compound of Formula I is fully complementary to the target pre-mRNA sequence, or partially complementary to the target pre-mRNA sequence with one or two mismatches; S 1, S 2,..., S n-1, S n, T 1, T 2,..., T n-1, and T n independently represent deuterido, hydrido, substituted or non-substituted alkyl, or substituted or non-substituted aryl radical; X and Y independently represent hydrido, formyl [H-C(=O)-], aminocarbonyl [NH 2 -C(=O)-], substituted or non-substituted alkyl, substituted or non-substituted aryl, substituted or non-substituted alkylacyl, substituted or non-substituted arylacyl, substituted or non-substituted alkyloxycarbonyl, substituted or non-substituted aryloxycarbonyl, substituted or non-substituted alkylaminocarbonyl, substituted or non-substituted arylaminocarbonyl, substituted or non-substituted alkylsulfonyl, or substituted or non-substituted arylsulfonyl radical; Z represents hydroxy, substituted or non-substituted alkyloxy, substituted or non-substituted aryloxy, substituted or non-substituted amino, substituted or non-substituted alkyl, or substituted or non-substituted aryl radical; B 1, B 2,..., B n-1, and B n are independently selected from natural nucleobases including adenine, thymine, guanine, cytosine and uracil, and unnatural nucleobases; and, at least four of B 1, B 2,..., B n-1, and B n are independently selected from unnatural nucleobases with a substituted or non-substituted amino radical covalently linked to the nucleobase moiety. n is an integer between 10 and 21; the compound of Formula I possesses at least a 10-mer complementary overlap with the 14-mer RNA sequence of [(5' → 3') UUUUUGCGUAAGUA] within the human SCN9A pre-mRNA; the compound of Formula I is fully complementary to the target pre-mRNA sequence, or partially complementary to the target pre-mRNA sequence with one or two mismatches; S 1, S 2,..., S n-1, S n, T 1, T 2,..., T n-1, and T n independently represent deuterido, hydrido, substituted or non-substituted alkyl, or substituted or non-substituted aryl radical; X and Y independently represent hydrido, formyl [H-C(=O)-], aminocarbonyl [NH 2 -C(=O)-], substituted or non-substituted alkyl, substituted or non-substituted aryl, substituted or non-substituted alkylacyl, substituted or non-substituted arylacyl, substituted or non-substituted alkyloxycarbonyl, substituted or non-substituted aryloxycarbonyl, substituted or non-substituted alkylaminocarbonyl, substituted or non-substituted arylaminocarbonyl, substituted or non-substituted alkylsulfonyl, or substituted or non-substituted arylsulfonyl radical; Z represents hydroxy, substituted or non-substituted alkyloxy, substituted or non-substituted aryloxy, substituted or non-substituted amino, substituted or non-substituted alkyl, or substituted or non-substituted aryl radical; B 1, B 2,..., B n-1, and B n are independently selected from natural nucleobases including adenine, thymine, guanine, cytosine and uracil, and unnatural nucleobases; and, at least four of B 1, B 2,..., B n-1, and B n are independently selected from unnatural nucleobases with a substituted or non-substituted amino radical covalently linked to the nucleobase moiety.